Wastes Problems of the Iron and Steel Industries - Industrial

Wastes Problems of the Iron and Steel Industries WILLARD W. HODGE' Mellon Institute of Industrial Research, Pittsburgh, Penna.

The rapid growth of the iron, steel, and associated by-product coking industries has brought problems in the utilization and disposal of waste materials; among the more important are slags, flue dust, mill scale, scrap iron, spent pickle liquor, coke breeze, ammonia liquors, coal tar, and phenolic liquors. Fairly satisfactory processes for the utilization of certain of these materials have been in operation for years, but improvements are desired. The extended researches which have resulted in methods and processes for keeping flue dust and also phenolic waste liquors out of streams and for utilizing a large portion of these materials are reviewed.

T

HE more rapid the growth of a city, or of a mining or manufacturing industry, the more acute often become the problems of proper treatment and disposal of the waste materials unavoidably arising during the course of useful activities. The iron and steel industries developed rapidly from a total world production of pig iron in 1850 of 4,400,000 gross tons to 1929 when 97,330,000 tons were manufactured (95). World production of steel in gross tons increased from 510,000 in 1870 to 118,400,000in 1929; and production in the United States from 11,838 in 1860 to 56,433,473 gross tons in 1929 (74, 75,,96). Statistics for the United States are shown graphically in Figure 1. The closely associated coal coking industry has increased coke production in the United States from 13,333,714 short tons in 1895 to 59,883,845in 1929, with a drop to 51,362,098in 1937 (127); further data are given in Table I. The more important wastes problems of these industries have related to the following materials: slags, mill scale, flue dust, spent pickle liquors, oil and grease, coke breeze, ammonia liquors, coal tar, phenolic liquors, hydrogen sulfide, and certain other gases and finely divided particles discharged into the atmosphere. Continual investigations by the research departments of iron and steel companies, the United States Bureau of Mines and other federal and state agencies, colleges and universities, chemical companies, and other private organizations have led to the development of fairly satisfactory processes for the utilization of several waste materials and methods of disposal for others. For many years mill scale has been charged back into the furnaces to make more iron and steel; the blast furnace gas has been purified and burned in the hot blast stoves t o preheat the air being blown into. the blast furnaces, and for the generation of power; the ammonia liquors have been

Developments in the utilization of slags are outlined. For more than fifty years technical men with certain steel and chemical companies and also independent investigators have been striving to develop a satisfactory process for the treatment of waste pickle liquors. Preliminary studies have been conducted on twelve methods of disposal and on forty processes proposed for treatment of waste pickle liquors. A few of the more promising processes are being accorded detailed investigation. The marketing of the by-products obtainable from spent pickle liquors presents problems ; some possible uses for the by-products are discussed. manufactured into ammonium sulfate, hydroxide, chloride, and other compounds. In comparatively more recent times processes have been developed for making useful products from slag, flue dust, coal tar, coke breeze, phenolic liquors, hydrogen sulfide, and spent pickle liquors. Despite years of research certain of the waste materials, such as the spent pickle liquors, still await the discovery of processes which are technically and economically satisfactory for their more complete utilization. Improvements are desired and are being attained even in some of the older processes for treating certain of the wastes. This fact is well illustrated in the case of hydrogen sulfide. The old method in general use for years was to remove the hydrogen sulfide from the coal gas by passing it through box purifiers containing trays filled with iron oxide mixed with wood shavings or other filler. The iron sulfide formed was

TABLE I. COKEPRODUCTION IN THE UNITEDSTATES (72) (In Short Tons) Year 1895 1900 1910 1916 1919 1920 1925 1929 1930 1932 1935 1937

Beehive Coke 13,315,193 19,457,621 34,570.076 35 464 224a 19:042:936b 20,511,092 11,364,784 6,472,019 2,776,316 651,888 917,200 3,156,300

By-Product Coke 18,521 1,075,727 7,138,734 19,069,361 25,137,621 30,833,951 39,912,159 53,411,826

Total 13,333,714 20,533,348 41,708,810 54,533,585 44,180,557 5 1,345,043 51,266,943 59,883,845=

45,195,705 21,136,842 34,224,063

47,972,021 21,788,730d 35,141,253 (94)

49,205,798

52,362,098 (94)

Maximum all-time annual production of beehive ooke. b Production of by-product coke exceeded t h a t of beehive coke for first time in 1919. Maximum all-time annual production of metallurgical coke. d Lowest annual production of coke since 1900. 5

1 American Iron and Steel Institute's Industrial Fellowship: on leave of absence from Department of Chemical Engineering, West Virginia, University, 1938-40.

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blast furnaces for pig iron and of the basic openhearth processes for steel has greatly increased --Basic Open-Hearth Furnacethe quantities of slag produced. Compara.-Blast FurnacFirst slag Final slag Electric Furnace tively small quantities of slag were made in the 2 (16) 3 (26) 4 1 (16) 2 (16) Constituent 1 (16) 2 (16) 3 (119) 1 (16) manufacture of steel by the acid Bessemer procSi02 35.02 35.55 33 1.00 8.54 10.80 20.74 17.90 19.58 Fe ... . . . . . 0.32 1.09 ess, and they could often be charged back into FeO 1.16 0.68 14- 78:24 61:05 22:01 10:84 ... ... FezOa .. 15.31 11.10 ... 5.24 ... ... the blast furnace. I n the early days of the iron .41zOa l4:09 l2:05 12 0.37 1.98 1.55 3.55 6.00 3.04 industry the slag mas frequently dumped over Mn ... . . . . . ... ... ... ... 0.35 0.62 M nO 1.08 0.81 2.31 9.0 5.86 some river bank and part of the slag would be Cao 44.03 40:i2 i S 2.70 9.13 44.00 40.90 6i:ii 60138 MgO 2.72 8.86 6 1.12 5.48 6.53 9.67 7.47 10.32 mashed downstream. However, there was a PZOS . . . 0.14 0.26 5.61 2.85 ... ... limit to this practice without closing the river S 1.35 1166 .. 0.25b 0.16b ... 0.27b 1.30 0.85 Others , .. ... 1 . . . ... ... ... ... ... channel; hence iron companies had to purchase CaCz ... . . . . . ... ... ... ... 0.51 0.23 suitable ravines or fields to which the slag was a Average of tapping slags from thirteen basic furnaces. b S f so3 hauled and dumped. These operations added considerable overhead and transportation cmts to the manufacture of the iron, but constituted the cheapest disposal method available at that time. removed irom the purifiers, and in this country was usually The quantities of slags produced annually vary with the thrown on the dump and thus produced another objectionable amounts and kinds of pig iron and steels manufactured. On waste product. I n Europe the spent iron oxide and iron sulthe average, approximately half a ton of blast furnace slag fide were and are used to manufacture sulfuric acid. As A. R. is made per ton of pig iron produced. Modern blast furnaces Powell (83)and Monkhouse (78) showed, far greater progress make from 700 to 1000 tons of pig iron per day; some now has been made in the past ten years than was made in the preceding fifty years in the development of new and satisfacunder construction are designed to make 1200 tons per day. On this basis such furnaces would produce from 350 to 600 tory processes for the rapid removal of the hydrogen sulfide tons of slag daily, and the annual United States production from fuel gases and in its utilization. Among these newer of blast-furnace slags would be approximately 6,000,000 tons liquid processes for recovery of hydrogen sulfide from coal in 1900; 18,500,000 tons in 1920; 21,000,000 tons in 1929; gases, oil refinery gases, and others, are the following: Sea4,300,000 tons in 1932; and 18,500,000 tons in 1937. I n board (lor),Ferrox (108), nickel (85),Auto (78), Houdry (83), dlkazid (78),Thylox (28, 44, 66, 82), improved ammonia (83), 1936 the European production of basic slag was 4,918,000 tons (128). magnesium hydroxide ( l o g ) , borate (14), Girbotol (78) or The composition of slag varies according to the kind of iron Girdler ( l a ) , phenolate (18, 84, 98), Espenhahn (839,and and steel being manufactured; a few typical analyses are phosphate processes. Certain processes such as the Thylox recover sulfur in a very finely divided form (mostly under 3 given in Table 11. A comparison of the composition of blast furnace slags under microns in diameter), which makes it especially suitable for former and present conditions of operation is given in Table use as a fungicide and insecticide in agricultural sprays and 111 (68). dusting powders. Some finely divided sulfur is also used in making antiseptic sulfur soaps, and some is melted and cast into brimstone sticks. Other processes, such as the phenoTABLE111. PERCENTAGE ANALYSISOF PIG IRON AND BLAST late, afford the recovered sulfur as hydrogen sulfide, which FURNACE SLAGS is largely employed in the manufacture of sulfuric acid. --Foundry IronBasic Iron --I n Germany the marked increase in recovery of sulfur from Former Present Former Present Item practice practice practice practice fuel gases, largely by-product coke-oven gas, is shown by the Pig Iron following data: 10,000 metric tons in 1927; 32,000 metric 3.25 0.55 0.60 Si 3.I tons in 1937; and estimated for 1938 about 50,000 metric 0.010 0.05 0.13 S 0.020 2.00 1.80 1.85 P 1.17 tons (83). I n Great Britain where many of the iron oxide gas 0.28 1.42 0.45 Mn 0.30 purifiers are still in operation, the sulfur recovered from fuel Corresponding Slags gases each year accounts for the manufacture of some 220,000 tons of sulfuric acid calculated as the monohydrate (78)) equivalent to 20 per cent of the annual production. There are said to be twenty-one Thylox plants in operation in America, Japan, and Germany (78). It is estimated that phenolate plants recover 26,000 tons of sulfur annually, equivalent to 75,000 tons of 66” BB. sulfuric acid. Approximate estiAs a result of many years of research several uses have been mates for the United States place the annual recovery of suldeveloped for slags. The thirty-four commercial slag comfur from fuel gases a t 8000 tons of elemental sulfur and 35,000 panies in the United States reported for 1938 the utilization tons of sulfur as hydrogen sulfide. When the plants now of about 7,900,000 tons of slag, allocated approximately as under construction are put into operation, A. R. Powell (83) follows: 50 per cent for road building; 20 per cent for railestimates that the recovery of the sulfur as hydrogen sulfide road ballast; 20 per cent in concrete construction; and 10 mill be about 50,000 tons per year. Great progress has been per cent for miscellaneous applications, including that used made in recent years in the development of new and better for trickling filters, for roofing, for sweetening acid soils, and processes for the recovery of hydrogen sulfide from fuel in the manufacture of mineral wool (8, 129). During 1935 gases; but there are many more possible applications for the some 327,000 tons of blast furnace slag mere used in the processes which recover a material that is objectionable in manufacture of portland cement; in 1936 about 35,000 tons the gases, has caused atmospheric pollution, and can be of basic open-hearth slag of high phosphate content, made in manufactured into useful products. the Birmingham, Ala., district, were sold for “soil-conditioning” purposes (128). Notwithstanding all these uses, large Slag quantities of slags are still available as a cheap raw- material The disposal of metallurgical slags has always been a if continued investigations can discover profitable fields of utilization. problem t o the industries. The development of the modern TABLE

11.

PERCENT.4GE

ANALYSISOF

SLAGS

. . I

--

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Flue Dust Recovery and Utilization

VOL. 31, NO. 11

by-product coking ovens greatly reduced the atmospheric pollution, conserved approximately $100,000,000worth of byThe flue dust (very fine iron ore and other solid particles products annually, and increased by 5 to 10 per cent the yield in the exit gases from the blast furnaces) was for many years of coke per ton of coal processed. a waste material which frequently caused atmospheric and The output in the United States of by-product coke passed stream pollution. A considerable portion of this dust would that of beehive coke in 1919 and has gradually displaced most pass a 200-mesh sieve. Some forty years ago the construction of the beehive coke, as Table I shows. The by-product cokof dust-settling chambers and later of scrubbers or gas washers ing of coal did cause new problems in the disposal of liquid greatly reduced the quantities of flue dust going into the air wastes, ammonia liquors, coal tar, and phenolic liquors. and streams. Within the past five to ten years the construcProcesses were soon developed for manufacturing from the tion a t the blast furnace plants of sedimentation basins and ammonia liquors useful compounds such as ammonium hythe installation of Dorr settlers and rotary filters have redroxide, ammonium sulfate for fertilizer, ammonium chloride for dry batteries and as a flux, ammonium carbonate and bicarbonate for baking powders, smelling salts, and other preparations. Comparatively few people realize how many of the common necessities and conveniences of modern life are obtained either directly from coal tar or indirectly by applications of the proper synthetic chemical reactions to the primary products derived from the distillation of the tar. Only a few of the thousands of commodities can be mentioned-namely, motor benzene; solvent naphthas, phenol, cresols, hexylresorcinol, trinitrophenol (picric acid), and trinitrotoluene (TNT) ; phenacetin, sulfanilamide, acetyl salicylate, sodium salicylate, and other medicinals; methyl salicylate (oil of wintergreen), saccharin, dulcin, and other flavoring and sweetening agents; artificial musk, ionone (violet), methyl anthranilate (rose), and other perfumes. Malachite green, indigo blue, and alizarin are among the hundreds of so-called FIGURE 1. TRENDS IN PRODUCTION OF IRON ORE, PIGIRON, coal-tar dyes synthesized from aniline, naphthalene, anthraAND STEELIN THE UNITEDSTATES, 1880-1937 (125) cene, and other coal-tar chemicals. Pitch is used in road and roof construction and in paints. duced still further the pollution caused by flue dust. For Notwithstanding this fact, much coal tar is utilized as a liquid many years the recovered flue dust was stored in piles around fuel. Only about half of the anthracene fraction is efficiently the steel plants; about 150 pounds of flue dust is made per used. The pitch makes up 50 to 60 per cent of the tar. Aside ton of pig iron produced. Last year an official of one large from its free carbon content of about 20 to 25 per cent, comsteel company informed the author that they had about paratively little is known regarding the other constituents 500,000 tons of flue dust stored; an engineer a t another iron present. I n fact, coal-tar pitch is a mystery awaiting the and steel works said they had nearly 1,000,000 tons of reconstructive attack of research chemist and engineers. It covered flue dust on the plant site. may be possible to crack the large multinuclear compounds Within the past decade many steel companies have installed or to hydrogenate them and thus make more valuable malarge sintering machines. Flue dust usually mixed with small terials; recent articles indicate that pitch is being subjected amounts of other iron ore and fine coke is subjected to a to further chemical research. thermal beneficiation treatment which produces small lumps Only small quantities of phenols are present in the waste of iron oxide cinder of sufficient size, strength, and purity to liquors from the by-product coking plant. However, during be charged into the blast furnace and be smelted into pig the decade 1920-30, Ellms and Lawrence (SI), Kohman (64), iron. Not only the current production of flue dust, but also, Hodge (629,Howard (64),and others found that even traces gradually, that stored in previous years is being sintered and of phenols, or the chlorophenols formed when the water was utilized. Thus another material, which for seventy years was chlorinated, imparted disagreeable taste and odor to water regarded as an objectionable waste, is not only being largely supplies. This form of stream pollution occasioned such widekept out of the atmosphere and streams, but is being manuspread discomfort that four of the states of the Ohio River factured into useful products. basin entered into an agreement in 1924 for cooperative investigations with the industries on this problem. As a result Coke Works processes were developed for the recovery of phenols and methods of disposal which kept phenols out of the streams. The fuel requirements of blast furnaces led to a rapid deSome steel and by-products coke companies installed benzene velopment in the manufacture of coke from bituminous coal. absorption processes, as outlined by Jones (67) and Hatch Forty years ago most of the coke was obtained from hundreds of beehive ovens usually located near the coal mines. n’ow (4BA); others, the Heffner-Tiddy process (46B); and several, many steel companies have large by-product oven coking the Koppers vapor recirculation process plants (46, 137) for the recovery of the phenols. Other companies constructed plants situated adjacent to their iron and steel works. Thus the coke is manufactured near the blast furnaces, and the byrecirculation systems in which the phenolic waste liquors are added to the water used in quenching the coke. Judging from product oven gas is readily available for use in heating the open-hearth and annealing furnaces in the mills. the summary by Tisdale (118) of the reports of the United States Public Health Service and sanitary engineers of several The operations of the beehive ovens gave a good metallurgistate health departments, marked progress has been made in cal coke but caused bad atmospheric pollution for miles around the ovens, burned all the valuable by-products in the the abatement of stream pollution caused by this industrial waste. There are still opportunities for improvement in some volatile matter of the coal being coked, and gave 5 to 10 per of t h e methods used, and work is being carried on toward that cent less coke per ton of coal processed than is now obtained from the by-product or retort coking plants. The change to objective.

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INDUSTRIAL AND ENGINEERING CHEMISTRY

Waste Pickle Liquor The waste pickle liquor problem is of world-wide significance. For more than fifty years scientifically trained men in the iron and steel and the chemical industries have been working to develop technically and economically satisfactory processes for the treatment of spent pickle liquors. Kirkman (61) in 1888, Bowen (13) in 1889, and Parker (80) in 1895 were granted British patents on processes for treating acid wastes from the iron works. I n the United States investigations of the acid pollution of streams were in progress as early as 1890 (61, 1.23). Stabler (111) reported in 1906 on investigations of stream pollution by acid-iron wastes and described a plant for the recovery of copperas from spent pickle liquors, constructed in Ohio in 1904. The Ruhr Association has for some years been conducting research on processes for treating waste pickle liquors from many of the large German iron and steel works so as to reduce the pollution of the Ruhr river (86). The manufacture of iron and steel products has increased in Japan and Manchukuo from 1,639,494 tons in 1928 to 4,279,464 in 1936; and in U. S. S. R. from 4,245,800 to 16,300,000 tons, respectively, in the same years. Recently a consulting engineer from Bombay, India, interviewed the author regarding processes for treating waste pickle liquors in that country. I n a resume published in 1937, Heinrich (49) refers t o many patents and articles on treating spent pickle liquors. Forty years ago the tonnage of iron and steel which was surface-cleaned by pickling operations was small compared to the present. I n 1891 the production of terne and tin plate in the United States was 999 tons; in 1929, 1,968,280 tons. Some factors contributing to this greatly increased demand for surface-cleaned iron and steel are the increased use of canned foods, beers, and lubricating oils; other commercial products packaged in cans, tubes, and drums, such as tobacco, tooth paste, shaving cream, cosmetics, chemicals, paint and varnish; electroplated and enameled products; and galvanized materials such as wire, nails, transmission towers, oil well derricks, sheets, tubs, pails, tanks, culverts, troughs, down spouts, and tubing. All these materials and many

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others require that the surfaces of the iron and steel be thoroughly cleaned, usually by pickling operations, so that the tin, terne, zinc, nickel, enamel, lacquer, or other material will form a continuous, impervious, and uniform protective coating. The developments for terne and tin plate are partially summarized in Figure 2. The greatly increased demands for surface-clean iron and steel have caused marked developments in the methods of manufacturing sheet and strip iron and steel, and has necessarily changed and enlarged the pickling operations. The old method of reducing the bar steel to sheets in the twohigh hand pull-over rolling mills has largely given way to the continuous strip mills, and this practice, in turn, has resulted in continuous strip picklers. Estimates of the total annual production of waste pickle liquors in the United States vary from 500,000,000 t o 800,000,000 gallons, which indicates the real magnitude of this problem. Most pickling is done with solutions of sulfuric acid, but hydrochloric, nitric, and hydrofluoric acids are used in some types of pickling operations, especially of alloy steels. The discussions in this paper are limited mainly to waste sulfuric acid pickle liquors. The free acid content of spent pickle liquor from batch picklers usually ranges from 0.75 to 2 per cent; of continuous strip picklers, from approximately 3 to 7 per cent. Partial percentage analyses of waste pickle liquors, contributed by certain steel companies, are as follows: r

Constituent Free acid Ferrous sulfate Water by difference

-Batch1 2 3 2 4 25 93 73

Type of Pickling Operation -Continuous-. 3 4 1 2 1.5 5 7 7 30 15 12.3 15.7 68.5 80 80.7 77.3

Disposal of Waste Pickle Liquors

I n recent years the steel industries have shown renewed interest in the waste pickle liquor problem to recover usable by-products, and, together with mblic agencies. to abate stream pollution. le combined influelee of ’ industrial economy and public health has activated this movement. For the first time in the history of pickling the desirability of summoning systematic scientific investigation became apparent t o the researchful iron and steel industry, which is now spending $10,000,000 annually in all types of investigational work. Hence, the American Iron and Steel Institute in 1938 established a fellowship a t Mellon I n s t i t u t e t o stimulate and focus the efforts being made by the industry to develop a technically and economically satisfactory process for the treatment of spent pickle liquors. During the first year of the fellowship preliminary studies have been conducted on twelve methods of disposal and forty processes proposed for the treatment of waste pickle liquors with recovery of by-products. A few of the more promising processes are now being accorded detailed investigation as rapidly as reliable technical and cost data can be Courtesy, Wheeling Steel Corporation and Standard Slag C o m p a n y secured on which to make comparaBLASTFURNACE AND OPERATIONS FOR THE PREPARATION OF BLAST FURNACE SLAGFOR tive evaluations and t o base estiINDUSTRIAL USES-EXCAVATION, HAULING, DUMPING, GRINDING, CLASSIFICATION, AND mates for large installations. LOADING

INDUSTRIAL AND ENGINEERING CHEMISTRY

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KO PRELIMINARY TREATMENT OR RECOVERY OF BYPRODUCTS.Comparatively little information is available in the literature on methods of disposal, but through personal interviews and inspection trips the author has learned of the efforts of steel companies to dispose of waste pickle liquors by several proposed methods: pumping the liquors into (1) limestone caves, (2) deep wells, (3) abandoned mines, (4) exhausted oil and gas sands, (5) evaporation ponds made on lowland areas by damming ravines or excavating lagoons, (6) sand or gravel sumps located near large bodies of water, or (7) sewers which discharge into rivers, lakes, or tidewaters. I n general, serious objections have arisen to each of these methods, although procedures 5 and 6 are known to be in operation a t four steel plants, and 7 is the only disposal method available without excessive .cost to steel companies in many localities. PRELIMINARY TREATMENT BUT S o RECOVERY OF BYPRODUCTS. I n this group the usual objective is to neutralize the free acid in the waste pickle liquor before disposing of the waste. I n some states the iron present in the waste liquor must be treated so as to form an insoluble product and thus preclude the possibility of its redissolving and hydrolyzing with resultant future stream pollution from iron sulfates. There are seven methods in this classification: (1) T h e w a s t e pickle l i q u o r is treated with lime sufficient to neutralize t h e free acid present, and the resulting suspension is pumped into settling and evaporation ponds where there is no danger of seepage into streams. (2) FIGURE 2. TRENDSIN PRODUCTIOK T o the waste OF TIE ASD TERNEPLATE IN THE pickle liquor U N I T E D STATES, 1890-1937 (18, 186) e n o u g h excess lime is added to neutralize the free acid and precipitate the iron as ferrous hydroxide, according to the reactions: FeS04

Ca(0H)Z = CaS04.2H20 ++ Ca(0H)z + 2Hz0 = Fe(0H)z + CaS04.2Hz0

Small amounts of ferric hydroxide may be formed. Disposal is accomplished by either method a or b: Pump the suspension into sedimentation basins or lagoons and allow solar evaporation and ground seepage to dissipate the water. b. AIlow the suspended materials to settle, discharge the clear, neutral to alkaline supernatant liquid into a sewer, and haul the settled sludge to a suitable dump so located that the runoff after heavy rains will not wash the iron hydroxides and calcium sulfate into any adjacent streams. a.

(3) Addition of crushed limestone to the waste pickle liquor:

CaC03

+ HzSO~= Cas04 +,HzO + COZ

The surfaces of the limestone soon coat over with a nearly impervious layer of calcium sulfate, and further reaction is practically stopped. (4)Addition of pulverized limestone to the waste pickle liquor accompanied by vigorous air agitation and recirculation of a portion of the suspension. This process (the Dorr 82) has been developed within the past two years.

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Reports of pilot-plant tests indicate that favorable results are being obtained in the operation of the process. (5) Addition of marl to the spent pickle liquors (the Travers process, 182). It is stated that the resulting sludge may be recovered and used in the treatment of ozganic wastes and sewage. (6) Treatment of the waste pickle liquors with ground basic slag. The reaction has been found to be rather slow and incomplete. Also objectionable quantities of hydrogen sulfide have been evolved in some steel plants where this method has been tried. (7) Sufficient scrap iron or iron oxide is added to neutralize the free acid in the waste pickle liquor, and the solution of iron sulfate is pumped into evaporation ponds. Each of these treatment and disposal methods adds materially to the expense of manufacturing the steel. I n fact, reports from certain companies using method 2 indicate that costs for lime plus the charges for disposal of the suspension or sludge are nearly equal to the cost of the sulfuric acid used in pickling the steel. There are possibilities of recovering usable by-products from methods 2, 4, and 5 , and development work is being done along those lines. Whether the recovered products can be marketed a t prices sufficient to meet the cost of the treatment has not yet been fully determined. At present, certain steel companies are spending thousands of dollars annually in treating their waste pickle liquors by some of these methods, with the sole objective of reducing stream pollution. For some steel plants where certain conditions of location and production prevail, one or another of these methods may prove to be the cheapest for the treatment and disposal of their waste pickle liquors.

Treatment of Waste Pickle Liquor Involving Recovery of Usable By-products The large number of processes for treating waste pickle liquor which have been proposed, patented and put into industrial operation under this grouping may be classified, with a few exceptions, into ten general types based on the byproducts recovered. There is considerable similarity also in the unit operations applied in certain of the classes. This classification is based on processes for the recovery or manufacture of (1) copperas (FeS04.7Ht0) or siderotilate (FeS04.5H20) after neutralization of the free acid in the waste pickle liquor, (2) copperas and the free sulfuric acid, (3) ferrous sulfate monohydrate and the free sulfuric acid, (4) ferric sulfate and sulfuric acid, ( 5 ) sulfuric acid and iron oxide, (6) electrolytic iron and sulfuric acid, (7) iron oxide for paint pigments and/or polishing rouge, (8) “Ferron”, (9) ammonium sulfate and iron oxide, sulfide, or carbonate, and (10) miscellaneous processes for making other inorganic compounds.

Recovery of Copperas or Siderotilate The usual sequence of unit operations in this class of processes is: neutralization of the free acid with scrap iron or iron oxidesettling to remove suspended impurities +evaporationcooling+crystallization+ centrifuging or filtrationdrying the salt +finished product storage or sale

*

The reaction may be summarized by the equation

+

+

FeSOk HzS04 nHzO (waste pickle liquor)

+ Fe +2FeS04.7H20 + Ha + ( n- 14)HzO

By careful regulation of the drying operation, siderotilate may be produced instead of copperas. Among the older processes in this class are those of Diescher (29) and Berry and Knerr (99). Most of the copperas manufactured in the United States is made by this process or slight modifications of it, including the use of modern double-effect evaporators and improved crystallizers and dryers.

NOVEMBER, 1939

INDUSTRTAL AND ENGINEERING CHEMISTRY

Recovery of Copperas and Free Sulfuric Acid An important characteristic of this type of process is that in each one of them a portion of the iron sulfate is removed as copperas from the spent pickle liquor, and the mother liquor (still containing some iron sulfate, the free acid of the spent liquor, plus the correct quantities of make-up sulfuric acid and inhibitors) is returned to the pickling vats for further use. The processes differ markedly in the operations applied and equipment used to remove the portion of ferrous sulfate from the waste pickle liquor. A general outline of the operations employed is:

-

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for further development of the process, which is designed for continuous recirculation operation. The Simonson-Mantius process A (70) involves evaporation of the clarified waste pickle liquor under vacuum in leadlined evaporators until the sulfuric acid reaches a concentration of about 28 per cent. The liquor is then withdrawn from

pickling vat + settling out impurities in the waste pickle /'cooling liquor drying +crystallizing, centrifuging, or filter\evaporating ing out the copperas --f mother liquor make-up sulfuric acid and inhibitors +pickling vats

+

Among the processes which may iiivolve some evaporation, but depend primarily on cooling to crystallize the copperas are the Agde (I), Kestner-Fakler (S), Marsh-Cochran (71), Zahn (1S9), and Drooff (SO). I n certain of the processes the make-up sulfuric acid is added to the waste pickle liquor before it is cooled; thus advantage is taken of the common ion effect to increase the quantity of copperas crystallized when the liquid is cooled. I n the Drooff double-crystallization process the k s t crop of crystals is obtained by atmospheric cooling of the waste pickle liquor. The mother liquor is drawn off into another tank, and concentrated sulfuric acid is mixed with it until 28 per cent sulfuric acid is reached. Mechanical refrigeration is applied to cool the solution to about 0" C. (32" F.) and a second crop of copperas is obtained. The second mother liquor is withdrawn from the copperas, diluted with water to a concentration of 18 per cent sulfuric acid, and returned to the pickling tank. T o accomplish the cooling and crystallizing operations in this class of processes, a number of ingenious types of equipment have been developed-heat exchangers, mechanical refrigeration applications, high-vacuum steam jet evaporators, and cold air circulation. I n the Sulfrian (114) and the Sierp and Fransemeier (fO1) processes a portion of the recovered copperas is put through a rotary dryer producing the ferrous sulfate monohydrate, which is then added to the waste pickle liquor a t an early stage of the process. The addition of the monohydrate, combined with cooling in one to three stages, is said to produce good yields of copperas. Examples of processes in which considerable vaporization or evaporation and cooling are applied to recover copperas from the waste pickle liquor without neutralizing the free acid present are the Butler-Little ( 7 , 1 1 2 ) ,Simonson-Mantius (70), and the Compagnie des Forges de Chatillon (24, 42) or the Lurgi system. I n the Butler-Little reclamation process the waste pickle liquor is sprayed into the top of a high leadlined circular tower through which an upward current of cool air is blown. The effects of this countercurrent flow system are to vaporize some of the moisture and cool the descending spray to such an extent that considerable quantities of copperas crystallize and are collected in the large cone-bottom tank constructed, under the base of the tower. The suspension of copperas and acidic mother liquor is withdrawn from the bottom of the tank and pumped to centrifugals which separate the copperas, and the mother liquor is recirculated to the pickling vats. This process has progressed through about three years of pilot-plant development a t the iron and steel works of the American Rolling Mill Company. Some two years ago the company constructed a large n e b reclamation tower and installed the necessary auxiliary equipment

Courtesy, Tennessee Coal, I r o n , and Railroad C o m p a n y

TANKS FOR NEUTRALIZING WASTEPICKLE LIQUORWITH LIME

the evaporator and cooled, copperas is separated by use of a centrifuge or rotary filter, and the acid mother liquor is returned to the pickling vats. If detrimental impurities should gradually accumulate in the mother liquors obtained from process A, then process B should be used. As soon as the impurities accumulate to a harmful extent, the mother liquor from process A is transferred for further evaporation to a lead-lined, high-vacuum superconcentrator in which a liquor of 68-78 per cent sulfuric acid is produced, and practically all solid impurities separate and can be removed from the solution. Should there be any objections to using the recovered acid in pickling steel, it may be utilized in the manufacture of ammonium sulfate, other fertilizers, and commercial sulfatea, for washing light oil or benzene from the coke works, or for other purposes. The process of the Compagnie des Forges de Chatillon (24, 42), a modern development of the early Charpy process (19), as described by Gensecke (42) utilizes a multijet vacuum evaporator and crystallizer to vaporize some of the water in the waste pickle liquor and cool it. A portion of the ferrous sulfate crystallizes as copperas and is separated in a centrifugal from the acidic mother liquor which is then recirculated to the picklers. There have been one or more installations of nearly all the processes outlined in this class, most of which are designed for continuous operation. A somewhat different method for separating the copperas from the free acid in the spent pickle liquor was proposed last year. A patent was issued to de Lattre (65) on a process for adding a fatty alcohol (methyl alcohol mas specifically mentioned) to waste pickle liquor; most of the iron in the waste liquor is thus precipitated as copperas. A centrifuge is used to separate the copperas from the waste liquor, which is then subjected to fractional distillation to recover the alcohol and the free acid present in the spent pickle liquor. The recovered acid containing small quantities of alcohol and some ferrous sulfate would be reused in the pickling operations. The copperas is dried and sold or stored.

1370

INDUSTRIAL AND ENGINEERING CHEMISTRY

The costs for installation and operation, combined with the objections of many operators to using recovered acid in pickling the steel and especially the lack of anything like adequate markets for the recovered copperas, have prevented the more general adoption of the processes by the iron and steel industries.

Recovery of Ferrous Sulfate Monohydrate and Free Sulfuric Acid Within recent years considerable research and development work have been carried out on processes to produce directly from waste pickle liquor the ferrous sulfate monohydrate (FeSOd1/2H20, approximately) and also to recover the free sulfuric acid in the spent liquor. The monohydrate is made as an intermediate material in several processes-“Chemico” sulfate conversion (105, 106), Sierp and Fransemeier ( I O l ) , Sulfrian (114),Kestner-Neil1 (89, 90), and Mantius-LeonardMonsanto (66, 69). The ferrous sulfate monohydrate is usually made by one of six methods (a)carefully regulated drying of copperas, ( b ) direct evaporation and drying of neutralized spent pickle liquor in a continuous rotary dehydrator, as in the “Chemico” processes or (c) in a spray dryer as in the Kestner-Neil1 process, (d) spray drying of the neutralized and possibly the unneutralized liquor, as in the process being developed by the Western Precipitation Corporation (79), (e) evaporation in vacuum lead-lined evaporators until the concentration of sulfuric acid becomes about 78 per cent, as in the Mantius process (GO), (f) the Whetzel-Zimmerman process (136) in which the unneutralized waste pickle liquor in an autoclave is heated with steam to a temperature above 140” F. (usually between 300” and 400” F.). The monohydrate is precipitated from the solution and is filtered under similar conditions of temperature and pressure to those existing in the autoclave. I n processes e and f most of the free sulfuric acid in the waste pickle liquor may be recovered in addition to the ferrous sulfate monohydrate. Samples of the monohydrate sent to the author have been of two kinds. One consists of small reddish brown lumps, like small pebbles; the others are light gray powders, fine but not excessively dusty, and free flowing. The samples are acid to moist litmus paper. Among the desirable properties of the monohydrate are its low weight of water of hydration per unit weight of ferrous sulfate (FeS0.J and good storage

VOL. 31, NO. 11

properties; i t flows freely and hence could probably be used in automatic feed machines, and i t is the preferred compound if sulfuric acid is to be made from the waste pickle liquor. There are industrial installations of several of the processes mentioned in this class, others are ili the pilot-plant stage of development. Comparative technical and costs evaluations of the processes should be of interest as soon as sufficient construction and operating data are available.

Ferric Sulfate and Sulfuric Acid from Waste Pickle Liquor The method for preparing ferric sulfate by treating ferrous sulfate with sulfur dioxide and oxygen has long been known. Emmens (36) in 1894-95 obtained patents on a process for ‘(autoxidation” of ferrous sulfate according to the reaction 2FeSO4 4- SO2

+ O2 = Fe2(SO&

More recently Ralston (87), Keyes (60, I%), and others have contributed to our knowledge of the reactions, ferrous sulfate

-2

ferric sulfate

sulfuric acid

Two of the processes developed along these lines within the past five years are the Lyles “sulfanation” (66) and Keyes (60). These respective processes have been developed in connection with the purification of the Tampa, Fla., water supply and the leaching of copper ores and treatment of sewage in Arizona plants. The processes differ in certain of the procedures applied and equipment used. I n each process, to manufacture the ferric sulfate, streams of air and sulfur dioxide are made to contact a ferrous sulfate solution which may be obtained by treating scrap iron with dilute sulfurous acid plus air or with sulfuric acid, dissolving copperas in water, or using waste pickle liquor. It is stated that in the Keyes process (60) the reaction may be regulated to produce (a)a strong solution of ferric sulfate or ( b ) sulfuric acid of about 20 per cent concentration containing only small amounts of ferric or ferrous sulfates. Good results have been reported in the use of the ferric sulfate solutions (either alone or, better, chlorinated) in the purification of water and treatment of sewage, with marked savings in operating costs. Further experimental and development work is being carried out on these processes.

Sulfuric Acid and Iron Oxide from Waste Pickle Liquor

a,

f

9

: >

li

w.5

IV6C/MNVISM

S L U0C.e-

10 B8DS

Courtesv, Transactions of Institution of Chemical Enoineers ( L o n d o n )

FIGURE3. FLOWSHEETSHOWING USE OF CHLORINATED COPPERAS IN SEWAGE TREATMENT (50)

The ancient method for making fuming sulfuric acid (Nordhausen oil of vitriol) was to roast ferrous sulfate, copperas, until reactions represented approximately by the following equations took place (76) :

+

FeS04.7Hz0 = FeSOl 7Hz0 6FeSOc l1/2O2= 2Fez(SO4)3 f Fez03 Fe2(SO& = 3503 Fez03

+

+

Based on somewhat similar principles and operations, a number of processes have been proposed and some of them developed industrially for making sulfuric acid and iron oxide from waste pickle liquor. Brief outlines of four of the processes in this class follom. The “Chemico” sulfate conversion process (105, 106) has been developed in the United States by the Chemical Construction Corporation and is designed for continuous operation on a comparatively large production scale. The

XOVEMBER, 1939

INDUSTRIAL AND ENGINEEllING CHEMISTRY

1371

1372

INDUSTRIAL AND ENGINEERING CHEMISTRY

wasteliquor is neutralized with iron oxide, directly evaporated, and dried in a continuous rotary dehydrator to ferrous sulfate monohydrate which is then mixed with the correct amount of pyrites and roasted in a rotary furnace to produce sulfur dioxide and iron oxide. A portion of the iron oldde is used to neutralize the free acid of the incoming waste liquor, and the balance of the oxide is sold. The furnace gases containing the sulfur dioxide are carefully purified, and the sulfur dioxide is manufactured into sulfuric acid in a standard vanadium contact plant. The first industrial-size plant to use this process was constructed in 1934 at St. Louis. A larger installation has been in operation since 1935 at the Sayreville, N. J., plant of the Titanium Pigment Company. This plant is operating on a leach liquor containing 18 to 25 per cent free sulfuric acid, 10 to 16 per cent ferrous sulfate, and traces of titanium sulfate. The original contact sulfuric acid unit installed was designed to produce 120 tons per day of 100 per cent sulfuric acid. Average production over certain months is reported to have considerably exceeded the rated capacity of the unit. Last year a second contact unit of similar capacity was installed (106). The concentrated sulfuric acid produced is used to treat more titanium ore. Recent improvements in the roasting operation produce the iron oxide as a cinder of sufficient size, strength, and purity to be used in a blast furnace (105). Hence, markets are available for both end products from tlie process. The I. G. Farhenindustrie process (100) has heen developed in Germany and is based on the experimental results obtained by this company and by the Ruhr Verband (Essen). Copperas recovered from the waste pickle liquor by one of the previously described processes is dried to approximately the trihydrate (FeS04.3H20), or the correct mixture of the monohydrate and heptahydrate may be used. About 8.5 tons of brown coal are required to dry 100 tons of FeS04.7H,0 to FeS04.3H20. The partially dehydrated ferrous sulfate is thoroughly mixed xith a calculated quantity of finely ground,

b

/.. -4,,,

I

VOL. 31, NO. 11

low-volatile, noncaking coal, and the mixture is roasted to a final temperature of 1250-1300" C. (2280' to 2370" P.) in 8 continuous rotary furnace in which the iron sulfatc1 1s completely decomposed into water vapor, sulfur dioxide, and iron oxide. After careful purification the exit gases are used to manufacture sulfuric acid. The iron oxide at the discharge end of the furnace is sintered sufficiently to produce a cinder which can be charged into a blast furnace. The Mantius-Leonard-Monsanto process (26,OS), on wliich a large amount of pilot-plant work is reported to have h e n satisfactorily complet,ed, proposes to recover the copperas from the waste pickle liquor by the previously outlined Mantius process (70). As described, the copperas wonld be dried to the monohydrate in a Louisville continnous rotary drier. The monolrydrate, with or without admixture of pyrites, would be roasted in a Herreshoff multiple-hearth furnace (97). On the last hearth the oxide could he sufficiently sintered for cliarging into a blast furnace, or a final lomer temperature could be used and an iron oxide suitable for other purposes obtained. After purification the exit gases from the furnace would be sent to a standard Monsanto contact unit (M, 69) in wliich sulfur dioxide is made into concentrated sulfuric acid. The Clarkson or Fersul process (21) is similar in its first stages to the Kestner-Neil1 process (90)hut differs markedly in the treatment applied to the ferrous sulfate monohydrate produced in the Kestner spray dryer. The monohydrate would be roasted in the presence of extra oxygen in a twocompartment rotary furnace. As a result of tho catalytic effect of the hot freshly formed iron oxide, the presence of excess oxygen, and the special design of the furiiace which gives an accnrately controlled temperature gradient, it is claimed that most of the sulfur dioxide evolved from the iron sulfate is cliunged in the furnace into sulfur trioxide which may be made directly into sulfuric acid. It is stated that the iron oxide inuy be produced in a form suitable for use as a paint pigment or i t may be briquetted and the briquets used in the blast furnace. Aich have been raised against the processes :high costs for installation and operation, and the requirements for continnous operation and large prodncadvantages are that, as a rule, sufficient marble for both end products-sulfuric acid and iron oxide-or they may be used in the steel plant itself in w k l i t,tie waste uickle liauor is made.

Electrolytic Processes for Iron and Sulfuric Acid

3

I

I

The electrolysis of waste pickle liquor to make electrolytic iron and regenerate the sulfuric acid early attracted the attention of investigators, Among the patented processes in this class are those of Kamage (88) in which thc waste pickle liquor saturated with sulfur dioxide is electrolyzed between lead anodes and iron cathodes in multiplecompartment cells. Electrolytic iron is deposited an tlie cathodes, and tlic sulfuric acid is formed a t the anodes. In the Parnham process (S6) perforakd lead plates closely covered with layers of sheet asbestos serve as the anodes and iron plates as cathodes. The electrodes are placed alternately in slots in the sides of the wooden tank and hence form the chambers of the cells, which are designed for continuous operation. When tlig cathodes become heavily coated with iron, they are removed from the cell

NOVEMBER, 1939

INDUSTRIAL AND ENGINEERING CHEMISTRY

and new iron plates are inserted in the slots. The Gaver process (W,41)is now in the pilot-plant stage of development. Zinc oxide ores or wastes may be added to the waste pickle liquor to neutralize the free acid, and the solution is then clarified and electrolyzed with alternate iron and zinc electrodes in a multiple-chamber compartment cell. The iron is thrown out of solution and zinc sulfate is formed. Further electrolysis under slightly changed conditions with zinc and lead electrodes is said to produce electrolytic zinc and sulfuric acid. Another advantage claimed for this process is that, by proper adjustment of voltage and surface density in the different chambers, fairly good separation can be made in the precipitation of the chromium, nickel, and iron present in the spent liquors from pickling stainless steel. There are several other electrolytic processes for treating spent pickle liquors. During and for a time after the World War certain processes were developed specifically for the manufacture of electrolytic iron, as described by Koehler (63). The discovery of silicoirons and other alloys having very low hysteresis losses, and also improvements in metallurgical processes for making purer iron and steel militated against the growth of any premium-price market for electrolytic iron and against the installation of electrolytic processes for treating waste pickle liquor. Recent articles on powder metallurgy indicate that there may be a renewed interest in processes for producing finely divided iron, and that some waste pickle liquor may be used in electrolytic processes.

Manufacture of Iron Oxide Pigment and/or Polishing Rouge Certain grades of iron oxide have long been used for paint pigments and for polishing purposes. The preparation of pure and especially fine-particle-size iron oxide by thermal decomposition of copperas has been practiced for years. A few of the processes designed primarily for the production of iron oxides from waste pickle liquor are outlined. In the Kestner-Neil1 process (90) the free acid in the spent liquor is neutralized with scrap iron, the impurities are settled out, and the clarified solution is fed into the atomizer of a Kestner spray-drying plant which produces ferrous sulfate monohydrate in the form of minute hollow spheres. As originally designed for the manufacture of iron oxide paint pigments (90) the monohydrate was roasted in a continuous rotary furnace. However, the largest present installation of this process is probably a t the plant of Pilkington Brothers, Ltd., glass manufacturers, in England (38). Here the monohydrate is roasted in a gas-fired muffle furnace containing a flat turntable rotated slowly on a vertical axis and equipped with radial arms supporting plows which gradually turn over the iron oxide and move it to the edge of the turntable. Accurate control of rate of feed and temperatures in the spray dryer and the muffle furnace are maintained. It is reported that a very fine and uniform size iron oxide, free from grit, is obtained which is especially valuable as a glass-polishing rouge. The gaseous products from the calcining furnace, sulfur dioxide, sulfur trioxide, and water vapor, are passed to a lime tower and neutralized. The gases can be purified and used in the manufacture of sulfuric acid. I n 1918 Fireman (37) patented a process for treating waste pickle liquor with an alkaline earth chloride, preferably calcium chloride, and calcining the resulting material so as to produce iron oxide pigments of several different colors. This process appears to be quite similar to that of Parker (80). The Kaplan-Reger process (58, 59) was developed for making paint pigments from the acid drainage of coal mines and from waste pickle liquors. In the process of the Verein fur chemische und metallurgische Produktion in Assig (132) the waste pickle liquor

1373

is treated with sodium sulfate and the double salt of sodium and iron sulfates is obtained by crystallization. The salt is roasted a t 650” to 750” C. (1200” to 1380” F.), and the resulting mass is leached. Most of the sodium sulfate is recovered from the leach liquor, and the iron oxide is calcined for use as a paint pigment. A process patented by Wespy and assigned to Padberg (136) involves subjecting zinc oxide, residues from sulfuric acid plants, or finely divided zinc to sulfuric acid or to copperas recovered from waste pickle liquor. I n the latter application the copperas- and zinc-bearing material is finely ground, and the mixture is heated a t 650” to 750” C. until the reaction is completed. The zinc sulfate is leached from the calcined mass, the suspension is filtered, and the iron oxide obtained is dried and may be used as a paint pigment. The zinc sulfate is recovered from the leach liquor and filtrates. This process is reported to have been carried only through the experimental stage (100). I n a process for the manufacture of paint pigments as developed by Stich (100) in Munich, the waste pickle is neutralized and clarified, and the diluted liquor is treated with soda ash or ammonia solutions. The resulting precipitate is oxidized with air to form the ferric compounds which are filtered and placed in an autoclave a t a pressure of 7 atmospheres, and iron oxide is produced. This precipitate is filtered, dried, and finely ground to give a pigment containing about 97.3 per cent ferric oxide. By evaporation of the filtrates obtained in the process, either sodium sulfate or ammonium sulfate may be recovered. There are several other processes for making iron oxide paint pigments and polishing rouge from spent pickle liquor or from the copperas obtained from it. Some are believed to be more or less secret. There are limited markets for these products, but the total demand would require only a small portion of the waste pickle liquor produced.

“Ferron” from Waste Pickle Liquor During the past four years a process for making “Ferron” from waste pickle liquor has been developed by Rentschler (92) and Colton (23) of the Allied Development Corporation. The waste pickle is neutralized with milk of lime under carefully controlled conditions of temperature, concentration, and pH. The resulting suspension of calcium sulfate and iron hydroxide formed by the reactions

+

.+

FeSOI HaSOl nHzO (waste pickle liquor)

+ 2Ca(OH)z+2CaS04.2Hz0+ Fe(OHL

+ (n-2)&0

is filtered, and the filter cakes are mixed in a pug mill from which the green “Ferron” is extruded in the form of long blocks, bars, or other shapes. This plastic material is dried a t about 175” E’. and the color changes to a light reddish brown,, probably caused by the oxidation of the ferrous hydroxide to ferric compounds. The “Ferron” thus produced is no longer plastic. It can be sawed and machined into bricks, blocks, slabs, and sheets, and used as an interior construction material. The granulated “Ferron” is said to be a good absorbent for removing hydrogen sulfide from gases. The first industrial-size installation of this process wm made in September, 1938, by the Sharon Steel Corporation. Considerable further development work has been carried on this year. Favorable reports have recently been made regarding improvements in certain unit operations in the process and in a method for making wallboard from “Ferron” (23). The difficulties in filtration of ferrous hydroxide and the marketing problem are involved in the operation of this process. The field for utilization of good construction materials is a large one.

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INDUSTRIAL AND ENGINEERING CHEMISTRY

FeSO4 In 1910 Falding and Cathcart obtained patents (84, 56) on “an improved process for the recovery of valuable products from iron pickle liquor and gas liquor”. A calculated quantity of the waste pickle liquor is added to the gas liquor, sufficient to purify it of sulfides, cyanides, chlorides, and tarry matters. The purified ammonia liquor is treated with a quantity of waste pickle liquor based on the sulfate equivalent to the ammonia available in the gas liquor used, but a slight excess of ammonia is maintained to keep the reaction mixture alkaline. The solutions are heated and air is blown through the mixture to oxidize the ferrous to ferric hydroxide, which is removed by filtration and sintered for use in the blast furnace. The filtrate is concentrated by evaporation and the ammonium sulfate crystallized and recovered.

+ 2NH8 + H,S

VOL. 31, NO. 11

=

FeS

+ (NH&S04

If there is not sufficient hydrogen sulfide in the fuel gas for complete removal of the ammonia, more hydrogen sulfide may be added to the gas, or most but not all of the remaining ammonia may be removed by formation of ferrous carbonate, according to the reaction: FeSO4

+ 2NH8 + COz + HzO = FeCOs + (“&SO4

For complete recovery of the ammonia the gas may be treated in the saturator with sulfuric acid or ammonium bisulfate. The iron sulfide may be used to manufacture hydrogen sulfide or sulfuric acid. The ammonium sulfate in the filtrate may be recovered by evaporation and crystallization or from the saturator by the regular method. A somewhat similar process was developed through the pilot-plant stage by Hilgenstock and Jung (100). The raw

NOVEMBER, 1939

INDUSTRIAL AND ENGINEERING CHEMISTRY

coke-oven gas containing 8 grams of ammonia and 10 t o 12 grams of hydrogen sulfide is washed with hot (158" to 176' F.) waste pickle liquor. The presence of the hydrogen sulfide is said to convert the iron hydroxides and basic iron sulfate into iron sulfide which is more easily filtered. Bag filters are used to separate the iron sulfide, and a series of five to six recycling operations are applied until all the iron is removed. Any remaining ammonia can be recovered by two-stage washing. The filtrate can be evaporated and the ammonium sulfate crystallized; or the filtrate plus the correct quantity of sulfuric acid can be fed into the saturator and the ammonium sulfate obt,ained by the regular process, a t the by-product coking plant. The iron sulfide sludge can be roasted to sulfur dioxide and iron oxide, the sulfur dioxide used to manufacture sulfuric acid, and the iron oxide sintered for use in the blast furnace. The process being developed by the Koppers Company is based largely on the Sperr patents (110). The spent pickle liquor containing about 0.9 to 1 per cent free sulfuric acid and 25 to 30 per cent ferrous sulfate is treated with an excess of ammonia vapor which precipitates from 60 to 80 per cent of the iron as ferrous hydroxide; this is filtered from the hot suspension. The filtrate is then treated with raw gaseous ammonia containing hydrogen sulfide and/or carbon dioxide to precipitate the remaining iron. If cyanides are present in the raw gas, a small amount of iron is left in the solution to form ferrocyanides and keep this impurity out of the ammonium sulfate, which is recovered by the usual methods. One of the patents includes an operation of subjecting the waste pickle liquor to alternate treatments with ammonia vapor and air, gradually oxidizing the ferrous to ferric compounds, and precipitating the iron as ferric hydroxide which is more easily filtered than ferrous hydroxide. I n the Bochmann process (100)developed in Germany, the waste pickle liquor is treated with a slight excess of lime to produce a suspension of calcium sulfate (gypsum), hydrated lime, and ferrous hydroxide, which is filtered. The filter cakes are mixed with about twice their weight of water, and carbon dioxide from waste flue gases is passed through the suspension for a time to change the lime to calcium carbonate. Then raw ammonia gas and carbon dioxide are passed through the suspension which gives as final products calcium carbonate, ammonium sulfate, ferrous hydroxide, and basic iron carbonate. The suspension is filtered, and the ammonium sulfate in the filtrate is recovered by evaporation, crystallization, centrifuging, or filtration. The precipitate is dried and sintered to yield a mixture of lime and ferric oxide, said to be suitable for use in the blast furnace. The Ruhr Verband process (100) involves drying copperas (FeSOc. 7H20) to the trihydrate (FeSOd.3H20) and exposing this material to ammonia and air, which yields a coarse, semicrystalline product of ferric hydroxide and ammonium sulfate, with small amounts of ferrous hydroxide. The material is thoroughly washed and leached with the hot mother liquor from previous crystallizations of ammonium sulfate. The iron hydroxides are separated by filtration, the ammonium sulfate is recovered from the filtrate in a crystallizing evaporator equipped with salt separator and heat exchanger, and the filtrate is returned to the process for use in leaching out more ammonium sulfate. The iron hydroxide filter cakes containing 35 to 40 per cent moisture may be used for gas purification, may be dried and roasted in an oxidizing furnace for use as paint pigment, or may be sintered into form suitable for charging into the blast furnace. The Ruhr Verband is reported to have appropriated funds for further development of this process and investigation of two other processes for treating of waste pickle liquors. Peyton (81) patented one of the early processes in this class.

1375

some objections which have been raised to the ammonium sulfate processes are as follows: They require expensive types of equipment and construction to resist the corrosive action of the acidic and ferric sulfate materials processed. Difficulties are involved in filtration of iron hydroxides, evaporation to recover the ammonium sulfate is costly, and objectionable impurities are liable to appear in the ammonium sulfate. Evident advantages of this class of processes are the good markets usually available for ammonium sulfate and iron oxide, close proximity of the raw materials with resultant low transportation costs, utilization of two waste materials to produce two useful products, and reduction of stream pollution. Considerable further research and development work is in progress. Where the by-product cokeplant gas and ammonia liquors are available close to the waste pickle liquor, the possibilities for installation of an ammonium sulfate-iron oxide process would appear to merit serious investigation. '

Other Inorganic Compounds from Waste Pickle Liquor A number of other processes for making various inorganic compounds from waste pickle liquor have been proposed; some have been patented and developed to a considerable extent. I n certain of these processes intermediate products different from any obtained in the above descriptions are made, although similar &a1 products might be manufactured. I n a process described by Clark ($0) the ferrous sulfate in the spent pickle liquor is oxidized and then hydrolyzed in an autoclave a t 100 to 200 pounds gage pressure by direct injection of steam. An alkali salt, such as sodium sulfate, and soluble ferric oxide are added in the required quantities, and physicochemical conditions are adjusted to form natrojarosite [NazFes(OH)12.(SO4)4]. The formation of this mineral is claimed to precipitate more than 95 per cent of the iron in the waste liquor. The precipitate is separated from the suspension by a filter or centrifuge, and the filtrate is discarded. The precipitate is calcined to form a soluble ferric salt which may be used as a coagulant. It is understood that investigations are in progress for other uses and markets for the final product. I n the Imhoff process (56)the free acid in the spent pickling liquor is neutralized with scrap iron, and the resulting ferrous sulfate solution is treated with zinc or a zinc compound. A suspension is formed which is run onto a series of filter beds to separate the iron as a fine black powder, soot iron. The filter beds are constructed of such materials that aluminum salts are said to be formed which may be made into valuable chemical compounds. Further developments are reported to be in progress on the process and for uses for the powder iron and the recoverable aluminum compounds. The Coleman process (22) was designed to reduce stream pollution by treating acid mine drainage, spent pickling liquor, and other acidic wastes, with phosphate rock. I n treating waste pickle liquor, preferably containing 10 per cent or more of acid equivalent, the liquor is thoroughly agitated with ground phosphate rock in a series of overflow tanks until reactions are completed approximately according to the general equation:

The calcium su1fate"is settled, the slurry is sent to a rotary filter for final dewatering, and the precipitate is then agitated with water and pumped to the gypsum dump. The supernatant solution and filtrate are treated with soda ash in a tank equipped with paddle stirrer and air agitation until the following reaction is completed :

INDUSTRIAL AND ENGINEERING CHEMISTRY

1376

+

+

++

++ 3C02 + 6Ha0

4H~P01 3FeSO4 Fea(PO& 3NazC03 30 (air oxidation) = 3NazS04 6FeP04

The iron phosphate is settled, the slurry filtered, and the filtrate sent to the sewer. The iron phosphate is dried and stored or sold, but there appears to be only a limited market for ferric phosphate. Considerable experimental work has been done by the Solvay Process Company and others (104) toward developing a process for the treatment of waste pickle liquor with soda ash and recovering from the reaction sodium sulfate and iron carbonate as indicated in the general equation:

+

+

FeSOd Hi304 nHzO (waste pickle liquor)

+ 2NazCOs +2NazS04.10H20 + (n - 19) HzO + FeCOs + COZ

Sodium sulfate is used in the glass, paper and pulp, textile, and other industries, but the markets are quite limited. Other factors which have apparently militated against the industrial development of this process are the cost of the soda ash and of the evaporation to recover the sodium sulfate. Also, iron carbonate or siderite is, in general, an expensive iron ore to process in the United States, where such an abundance of good hematite ores are still available. Some experimental work has been carried out using sodium hydroxide to treat the waste pickle liquor with the production of sodium sulfate and iron hydroxide. Objections have been raised which aresimilar to those against the use of soda ash, although the iron oxide could be more easily obtained from the iron hydroxides. As noted under the Stich process (100) the iron oxide may be ground and used for paint pigment. The neutralization of the acidic waste liquor by addition of chalk and applying the calcium sulfate e calcium sulfide cycle was reported by Weber (134) as having been tried out by the B. Laporte Company in England. The results obtained were not satisfactory, and no industrial installation of the process was made. The Rosenstein patent (93) covers a process for the “recovery of sulfuric acid from waste acid liquors from leaching of ores, pickling of metals, manufacture of alcohols, ethers, olefine polymers, etc., waste acid sludge from oil refineries, and roaster gases from metallurgical processes”. The general successive steps in the process are dilution of the acidic waste until the concentration of sulfuric acid therein does not exceed 20 per cent sulfuric acid, and addition of barium sulfide to the solution in a covered reactor tank equipped with offtake pipe to convey the evolved hydrogen sulfide to the sulfuric acid plant for oxidation into sulfuric acid. These reactions are represented by the equations :

The suspension of barium sulfate is settled in a Dorr thickener, and the slurry is filtered through an Oliver continuous rotary filter to dewater the barium sulfate further. The overflow from the thickener and the filtrate are run into the sewer. The barium sulfate plus the required make-up barytes plus the calculated quantity of finely ground coal or coke are thoroughly mixed and roasted in a reducing furnace to produce the reaction: Bas04

+ 4C

=

Bas

+ 4CO

The resulting furnace product, black ash, is leached with water and the solution of barium sulfide is pumped to the reactor tank. The insoluble residue left in the leach vats is hauled to the dump. Here is another application that employs the metal sulfate =. metal sulfide cycle and is claimed to make complete recovery of the sulfuric acid in the waste liquors, sludges, or gases.

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No attempt has been made in this brief review to include all the processes for the treatment of waste pickle liquors. Most of those dealing with hydrochloric, nitric, and mixed acids, such as the process developed by Sullivan (116), have been omitted. Sufficient information has been given to indicate the large amount of work which has been done on the technical phases of the wa’ste pickle liquor problem. Apparently the economic factors involved have not always received adequate consideration.

Uses and Marketing of By-products The adverse economic factors involved in treating waste pickle liquor are most difficult to overcome. The comparatively high costs for installation, equipment, maintenance, and operation, due largely to the corrosive nature of the materials being processed and to the lack of anything like adequate markets for most of the by-products recoverable, have undoubtedly been the more important retarding factors in the installation of recovery processes by the industry. Copperas is probably the most easily and economically recovered by-product from spent pickle liquor. If the annual production in the United States is assumed to be 500,000,000 gallons of waste pickle liquor having an average composition of 3 per cent free sulfuric acid and 15 per cent ferrous sulfate, it would be equivalent to 75,000 tons of sulfuric acid and 686,250 tons of copperas. Large additional quantities of copperas could also be readily recovered from waste liquors of other industries, such as the titanium pigment plants. In 1937 there were twenty copperas factories in operation in this country. They manufactured 43,916 tons of copperas (124), which was somewhat more than the market demand that year. However, during 1938 when many of the steel mills were on exceptionally low production schedules, a shortage of copperas was reported in some sections of the country. In the same year 6789 tons of ferric chloride were manufactured, but there is comparatively little hydrochloric waste pickle liquor produced in the United States, and most of the ferric chloride was made by synthetic processes. The production of iron-containing paint pigments and of iron oxides for polishing rouge, etc., in the United States in 1935 was about 59,000 tons (124). Since the application of inhibitors in pickling solutions has become common practice, certain pigment companies have reduced the quantities of spent pickle liquor processes because of the objectionable effects produced on the pigments by the inhibitors. Extended efforts have been made by certain steel and chemical companies, since some aspects of the problem are more chemical than metallurgical, to increase the uses for copperas and other by-products obtainable from waste pickle liquors, but these efforts have met with only moderate success. Among other possible uses for copperas are the following: alone or as iron alums in the leather industry and in dye works; in agriculture for weed control; in sprays as a fungicide or insecticide; in small amounts as fertilizers for pineapples, grapes, and certain other crops; as a wood preservative; as a coagulant in purification of water supplies and treatment of sewage and certain industrial wastes; for making iron oxide, iron oxide plus lime, and iron oxide plus calcium sulfate products for purification of fuel gases, and for building materials; in the manufacture of other sulfates, such as ammonium, sodium, or calcium sulfates, and sulfuric acid. Economic factors relating to the production and utilization of spent pickle liquor in Germany were outlined last year by Sierp (100). It was estimated that about 6,500,000 tons of steel wire, sheets, plates, pipe, and strip were surface-cleaned annually with acid solutions. About one third of the metal pickling was with hydrochloric acid. Assuming an iron to

NOVEMBER, 1939

INDUSTRIAL AND ENGINEERT” CHEMISTRY

acid ratio of 40 to 1, approximately 100,000 tons of sulfuric acid would be consumed by the pickling operations. Allowing for acid and iron sulfate lost in wash waters, he estimates that reclamation plants could recover about 225,000 tons of copperas annually from the waste liquors. The actual production of copperas is about 30,000 tons per year, of which agricultural uses consumed 6000 to 7000 tons and purification of water about 1200 tons; the remainder is sold for the other uses. “In general . the open market is about saturated and cannot absorb any large additional quantities of ferrous sulfate.” In the United States there has been a trend in recent years towards making larger uses of iron sulfates and chlorides in water purification and for treating sewage and certain industrial wastes (5, I?’, 85). The use of chlorinated copperas, alone dr in combination with lime or alum, depending on the nature of the water supply, has been adopted in several water-treating plants. A few of the papers dealing with the use of iron salts as coagulants in water and sewage treat-

..

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INDUSTRIAL AND ENGINEERING CHEMISTRY

ments are those by Hedgepeth and Olsen (47),Mohlman and Palmer (77), Decker and Menke (27), Hopkins and Whitmore (63),Billings (9),Smith (103), Hendon (60),S‘immons (102), Todd (121),and Carpenter et al. (17, 86). According to Gettrust and Hostettler (43) chlorinated waste pickle liquor plus lime, or sometimes alum, is giving satisfactory results a t the Akron, Ohio, water works, with marked savings in costs over the methods previously used; one ratio is 1 to 1.8 in favor of the pickle liquor. At the Tampa water purification plant, Lyles (66) and Black (10) report excellent results from the use of ferric sulfate and chlorine, again with decided reduction in operating costs. Other cities reported to be using iron salts obtainable from spent pickle liquors in the purification of their water supplies are St. Louis, Mo., and Chicksaw, Ala. (27), Hammond, Ind., and Richmond, Va. (103), Dallas, Texas (9),Cincinnati, Ohio, and Wheeling, W. Va. (121). According to a recent report the manufacture of ferrous sulfate for the treatment of public water supplies is being considered by the Egyptian Government. Chlorinated copperas, ferric sulfate, ferric chloride, and certain other chemicals are now being used in sewage treatment a t Shades Valley, Ala., Dearborn, Mich., Coney Island, N. Y., Perth Amboy, N. J., Milwaukee, Wis., Phoenix, Ariz., Denver, Colo., Ashland, Ohio, New Britain, Conn., and several Pearse et al. (80A). other plants, according to Hendon (&(I), Factors which have led to the changed point of view on the part which chemical treatment can successfully perform in the treatment of sewage and certain industrial wastes are improved types of mechanical equipment, mixers, Dorr thickeners and settlers, magnetite and rotary filters; an increased knowledge of colloid chemistry and the phenomena of coagulation, including the importance of pH control and the development of instruments to apply that control; better handling and proportioning equipment, such as rubber-lined or other corrosion-resistant valves, pipes, orifices, tanks, and cars; improved methods of making the chemicals and more dependable supplies; and the possibilities of recovering usable by-products from waste materials which might otherwise cause stream pollution. The greater possibilities for the use of chemical treatments as an aid in sewage disposal works was foreseen by Enslow (33) as early as 1933: “Although chemical treatment of sewage was once a closed chapter in sewage treatment, there now seems to be a greater appreciation of values and need for a process less sensitive than the activated sludge process, less space requiring and nuisance producing than sprinkling filters and less costly than either. Some form of chemical precipitation bids fair to become an established practice for filling a demand created by the gap now existing between the results procurable from plain sedimentation practice and that which necessitates biological secondary treatment.’’ Considerable research work along these lines is being carried on by several investigators. Through cooperative experimental work between municipalities located near iron and steel works and those steel industries, it may be possible for other cities to develop new or apply known methods for utilizing iron salts recoverable from waste pickle liquors, or the liquor itself, in the purification of the municipal water supplies and treatment of sewage. Such cooperation would aid the industries in their effortsto abate stream pollution and, as in the cases cited, might prove financially advantageous to the municipalities.

General Relations of Major Wastes Disposal Problems The Advisory Committee on Water Pollution (130) calls attention to the ever-increasing importance of the abatement of water pollution and classifies the deleterious wastes as

VOL. 31, NO. 11

coming from three major sources-municipal sewage, mining wastes (including oil well brines, culm, coal mine drainage, and tailings from hydraulic mining operations), and industrial wastes resulting during the manufacture of useful inorganic and organic products. It was estimated that in August, 1938, 73,000,000 people in the United States were served by sewers. Sewage from a population of approximately 19,000,000 persons received primary and, from an additional 20,700,000 persons, secondary treatment; the remainder, nearly half the total sewage, received no treatment before being discharged into streams or other waters. During the past six years, largely as a result of funds from the Federal Government, more progress has been made in the construction of sewage treatment plants and abatement of other forms of stream pollution than in the preceding twenty years. However, municipal and domestic sewage is still probably the largest and among the worst over all sources of stream pollution. Approximately 2,500,000,000 gallons of raw sewage, 1,500,000,000 gallons of sewage which has received only primary treatment, and 1,750,000,000 gallons of sewage which has been subjected to secondary treatment are daily discharged into the rivers and other water bodies of the United States. I n several sections of this country, wastes from the mining, petroleum refining, sulfite pulp, and certain chemical manufacturing and metal pickling operations add acid loads to the streams. Army engineers have been empowered by Congress, through bills introduced in 1899 and suksequently, to prevent the acid pollution of navigable waters (123). The United States Army Engineers, Public Health Service (39,40), and many others have done a great deal of investigational and regulatory work on the problem, especially in the Ohio River Basin. I n a summary by Hodge (61)of the work done on and effects of acid pollution conditions in the Ohio River watershed, the total acid load in 1933 was estimated a t approximately the equivalent of 3,000,000 tons of concentrated sulfuric acid per year. Tisdale and Lyon (120) reported on the mine sealing program to 1935. It had been estimated that about 2,700,000 tons of the acid came from coal mines, and the balance from the many manufacturing plants in this highly industrialized area. A recent report by Lyon and Chapman (67) and information by Reid (91) indicate that, as a result of the work done on the Federal Program for Sealing Abandoned Coal Mines, begun in 1933 and continued by the United States Public Health Service in cooperation with nine states and by funds from CWA, FERA, and WPA, the quantity of acid coming from the mines has been reduced about 375,000 tons per year. When all the mines sealed attain “stabilization”, the reduction according to estimates will be about 600,000 tons annually. If funds should be made available to complete the sealing of abandoned mines, it has been estimated that the acid load on the Ohio River and its tributaries could be reduced from the 1933 quantities by over 1,000,000 tons of sulfuric acid per year. The Advisory Committee on Water Pollution (130) estimates the costs for accomplishing a reasonable abatement of the remaining water pollution in the United States to be approximately by classes as follows: (1) capital costs to treat municipal sewage, $1,000,000,000with annual operating charges of $15,000,000; (2) to complete sealing abandoned coal mines $12,000,000, control of anthracite wastes $40,000,000, for minimum treatment of oil field brines $100,000,000; (3) for treating various industrial wastes in the cases where practicable processes are known, capital costs $900,000,000, with operating and fixed charges of $225,000,000 per year. The report states further: “Complete treatment of all wastes is not attainable; also, in some cases it would be cheaper to move the industrial plants than to install the necessary treatment .”

.

NOVEMBER, 1939

INDUSTRIAL AND ENGINEERING CHEMISTRY

The proper treatments of sewage, mining, and industrial wastes, are problems of vital importance to the national welfare, especially to the thickly settled and highly industrialized areas. Judging by the number of antistream pollution bills introduced in Congress in recent years, there will soon be broad federal legislation directed towards the abatement of pollution of rivers, lakes, and coastal waters, in addition to the laws of many states. In the present Congress (76th) a number of water pollution abatement bills have been introduced. According to Wolman (138) the costs for the complete job of stream purification as outlined in certain of the Congressional bills would be about $5,000,000,000. Others of the bills would appropriate some funds for cooperative federal and state investigations and procedures for abatement of the water pollution. In any event, the committee estimates that a coordinated program for the abatement of the major pollutions of the nation’s water bodies would require from ten to twenty years for accomplishment.

1379

solve in a technically and, as nearly as possible, economically satisfactory manner the waste pickle liquor problem, as well as their other waste disposal problems. There is also much helpful activity on the waste pickle liquor problem by the chemical companies, universities, and federal, state, and municipal laboratories. The Federal Government has enlarged the activities of the Cincinnati Station of the United States Public Health Service to include a three-year constructive survey of stream pollution of the Ohio River and its tributar’es (119). The passage by Congress of a bill which would set up funds for cooperative research between the states, cities, and industries on sewage and industrial wastes problems would probably be another important step in the right direction. The movement for the sensible conservation of our natural resources has met with popular approval, From the standpoint of a far-sighted national economy in the utilization of unreplaceable national resources, the abatement of all unnecessary stream pollution and the recovery of valuable by-products from waste materials are both of vital importance in the continued development of our country.

Summary While progress in the abatement of atmospheric and stream pollution often seems slow, history proves that more time is often required to develop a technically and economically sound process for the treatment of a waste material than is required to install the process which creates the waste. A glance back over the past twenty years a t the wastes problems of the iron and steel industry shows that atmospheric pollution from beehive coke ovens and blast furnace flue dust has been nearly eliminated; that stream pollution from flue dust, coal tar, ammoniacal, and phenolic liquors has been largely abated, and that useful products are being recovered or manufactured from most of these wastes, from hydrogen sulfide recovered from fuel gases, and from the slags. The greatly enlarged demand for tin and terne plate and other stock (Figure 2), especially for automobiles, furniture, office equipment, and the like, which require iron and steel surfacecleaned by pickling operations has increased the importance of the waste pickle liquor problem. Extensive experimental work on this problem is in proqress in the laboratories of several steel and chemical companies, a t Mellon Institute, and certain universities. Pilot-plant and industrial-scale developments of some of the processes, as previously mentioned, are also being carried on a t certain steel works, chemical plants, and universities. The research and development work is mainly along four lines: improvements of present known processes, possible discovery of new and better processes for treating the waste pickle liquors, development of uses for the by-products recoverable from the spent liquors, and possible developments of other methods than acid pickling for cleaning iron and steel. Several processes and methods have been proposed for the latter; among them are the Tainton process (116, 117),electrolytic cleaning of the steel in a bath of molten sodium hydroxide, the “Feracid” process (QK), the use of alkali salts and nitric acid, mechanical cleaning such as sandblasting and buffing, and the use of chlorine and ferric chloride. Industrial installations of certain of these processes are in operation. However, most of the pickling a t present is done with sulfuric acid, and only relatively small tonnages with hydrochloric, nitric, and hydrofluoric acids, alkalies, and electrolytic or other processes. During the past year marked improvements have been reported on five processes for treating waste pickle liquors, and a few new processes have been proposed A t least four comparatively new fields of usefulness for by-products recoverable from spent pickle liquor are being thoroughly investigated. The iron and steel industry is determined to

Acknowledgment The author thanks the Special Committee on Stream Pollution of the American Iron and Steel Institute (R. E. Zimmerman, chairman), Walter S. Tower, executive secretary of the institute, rind W. A. Hamor and E. Ward Tillotson, of Mellon Institute of Industrial Research, for their assistance in the preparation of and permission to present this paper. The author also acknowledges with grateful appreciation the helpful cooperation, the supplying of recent intormation, data, and photographs, and the constructive suggestions received from officids, engineers, and chemists of the iron and steel companies, and of cliemical and ot,her procem industries; from federal. state, and municipal public health departments and sanitary districts; from university professors; and from technical representatives of equipment companies.

Bibliography Agde, G.. Stahl u. Eisen, 57, 789-93 (1937); German Patent 431,581 (1925). Almy, E., private communication, 1938. Anonymous, Chem. Age (London), 38, No. 988, Met. Sect. 33 (1938). Anonymous. Chem. Met. Eng., 45, 430 (1938). Baldwin, R. T., and Faber, H. A., private communications, 1938. Barkholt, Hans, U. S. Patent 2,118,802 (1937). Barnes, H . C., private communications, 1938-9. Bartholomew, T . , (for National Slag Assoc.), Ibid., 1939. Billings, L. C., Water Works & Sewerage, 81, 73-7 (1934). Black, A. P., J. A m . Watm Works Assoc., 26, 1713-18 (1934). Bloxam, A. G., British Patent 27,353 (1908). Bottoms, R. R., IND.ENO.CHEM.,23, 501-4 (1931). Bowen, E., British Patent 3179 (1889). Bragg, G. A,, U. 9. Patent 1,920,626 (1933). Bray, J. L., “Principles of Metallurgy”, pp. 441, 480 (1929). Camp, J. M., and Francis, C. B., “The Making, Shaping and Treating of Steel”, 4th ed., pp. 146-7. 334, 399 (1925). Carpenter, L. V.. Setter, L. R., and Coates, J. J., J . Am. Water Works Assoc., 31, 1400-16 (1939). Carvlin. G. M., Natl. Petroleum News, 30, R268-74 (1928). Charpy, G., 7th Intern. Congr. Applied Chem., London, 1910, Sec. 11, 189-91. Clark, L. F., private communication, 1938. Clarkson, D. A., Ibid., 1938. Coleman, H. S., and Coleman, F. H., U. S. Patent 2,063,029 (1930) : private communication, 1939. Colton, H . 5,. private communications, 1938-9. Compagnie des Forges de Chatillon, French Patent 395,917 (1908): British Patent 27,353 (1908).

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(25) Davies, C., Jr., U. S. Patent 1,942,050 (1934). (26) Dean, C. M., private communications, 1938-9. (27) Decker, A. C., and Menke, H. G., Am. J . Pub. Health, 20, 357-64 (1930). (28) Denig, Fred, Am. Gas Assoc. Proc., 1933, 903-12. (29) Diescher, S. E., U. S. Patent 1,023,458 (1912). (30) Drooff, J., Stahl u. Eisen, 57, 838-9 (1937). (31) Ellms, J. W., and Lawrence, W. C., J . Am. Wuter Works ASSOC., 9, 463-73 (1922). (32) Emmens, S. H., U. S. Patents 513,490 (1894) and 543,002 (1895). (33) Enslow, L. H., et al., Civil Eng., 5, 234-45 (1933). (34) Falding, F. J., U. S.Patents 961,763-4 (1910). (35) Falding, F. J., and Cathcart, W. R., British Patent 11,364 (1910). (36) Farnham, F. F., U. S. Patent, 1,006,836 (1911). (37) Fireman, P., Ibid., 1,287,939 (1918). (38) Forbes, L. J. B., and Meikle, James, private communications, 1938-9. (39) Frost, W. H., U.S. Pub. Health Repts., 41, 75-85 (1926). (40) Frost, W. H., Hoskins, J. K., Tarbett, H. E., and Streeter, H. W., U.S . Pub. Health Service, Bull. 143 (1924). (41) Gaver, K. A., private communications, 1938-9. (42) Gensecke, W., Stahl u. Eisen, 57, 841-2 (1937). (43) Gettrust, J. S., and Hostettler, C. O., Rept. Ohio Conf. Water Purif., 18, 47-51 (1939); Water Works Eng., 92, 245-8 (1939). (44) Gollmer, H. R., IND. ENG.CHEM.,26, 130-2 (1934). (45) Harris, A. W., U. S.Patent 1,994,702 (1935). (46) Hatch, B. F., IND. ENG.CHEM.,21,431-3 (1929); Blast Furnace Steel Plant, 17, 1493-6, 1510 (1929). (46A) Ibid., 17, 1797-1800 (1929). (46B) Ibid., 18, 296-8 (1930). (47) Hedgepeth, L. L., and Olsen, W. 0. and N. C., J . Am. Water Works Assoc., 20, 467-72 (1928). (48) Heimberger, W., Stahl u. Eisen, 57, 839-40 (1937). (49) Heinrich, F., Ibid., 57, 757-62 (1937). (50) Hendon, H. H., Trans. Inst. Chem. Engrs. (London), 15, 55-69 (1937). (51) Hodge, W. W., IND. ENG.CHEM.,29, 1048-55 (1937). (52) Hodge, W. W., W. Va. Univ. Eng. Expt. Sta., Tech. Bull. 1, 40-54 (1927). (53) Hopkins, E. S.,and Whitmore, E. R., IND.EXG.CHEM.,22, 79-81 (1930). (54) Howard, N. J., J . Am. Water Works Assoc., 9, 766-82 (1922) ; Eng. and Contr., 58, Waterworks, 43-9 (1922). (55) Imhoff, W. G., private communication, 1938. (56) Jacobson, D. L., Gas Age-Record, 63, 597-600 (1929). (57) Jones, H. E., W. Va. Univ. Eng. Expt. Sta., Tech. Bull. 1, 31-9 (1927); Chem. Met. Eng., 35,215-18 (1928). (58) Kaplan, B. B., Proc. W . V u . Acad. Sci., 4, 90-2 (1930). (59) Kaplan, B. B., (to D. B. Reger), U. S. Patent 1,878,525 (1932). (60) Keyes, H. E., U. S. Bur. Mines, Bull. 321 (1930); private communications, 1939. (61) Kirkman, H. J., British Patent 16,247 (1888). (62) Knowles, C. L., Steel, 104, No. 20, 54-6 (1939). (63) Koehler, W. A., “Electrochemistry”, Vol. 11, pp. 129-31, 186-88, 221-2 (1935). (64) Kohman, E. F., IND.ENG.CHEM.,15, 518 (1923). (65) Lattre, P. de, British Patent 491,640 (1938). (66) Lyles, J. E., J. Am. Water Works Assoc., 26, 1214-18 (1933); private communication, 1938. (67) Lyon, E. W., and Chapman, C. L., private communication, 1939. (68) McCaffrey, R. S.,American Iron and Steel Inst. Year Book, pp. 187-202 (1938). (69) Mantius, Otto, private communication, 1938. (70) Mantius, Otto, W i r e & W i r e Products, 13, No. 10, 585-9 (1938). (71) Marsh, H. S.,and Cochran, R. S., U. 5. Patents, Reissue 15,119 of 1,369,451 (1921) ; 1,450,216 (1923) ; 1,589,610 (1926). (72) Metal Statistics, 1935, 26. (73) Ibid., 1935, 147. (74) Ibid., 1935, 165. (75) Ibid., 1935, 193. (76) Miles, F. D., “Manufacture of Sulfuric Acid (Contact Process)”, pp. 23-6 (1925). (77) Mohlman, F. W., and Palmer, J. R., Eng. News-Record, 100, 147-50 (1928). (78) Monkhouse, A. C., Chemistw & Industry, 58, 596-600 (1939). (79) O’Mara, R., private communications, 1938-9. (80) Parker, T., British Patent 24,859 (1895). (80A) Pearse, L., et al., Sewage Works J., 7, 997-1108 (1935). (81) Peyton, E., British Patent 15,250 (1901).

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(82) Powell, A. R., Gas Age-Record, 77, 711-15, 720 (1936). Powell, A. R., IND.ENQ.CHEM.,31, 789-96 (1939). Powell, A. R., Natl. Petroleum News, 29, No. 24, 50-8 (1937). Powell, S. T., Carpenter, L. V., Setter, L. R., and Coates, J. J., Chem. Met. Eng.,46,481-4 (1939). (86) Pruss. M., Stahl u. Eisen, 57, 7 6 2 4 (1937). (87) Ralston, 0. C., U. S.Bur. Mines, Bull. 260 (1927). (88) Ramage, A. S., U. S. Patents 788,064 (1905) and 984,703 (1911’1. Re‘avell: E. A., and B. N., private communications, 1938-9. Reavell, J. A,, J. SOC.Chem. Ind., 47, 347-511‘ (1928). Reid, K. A., Hearing on Water Pollution Control Bill 5-1691, pp. 18-22 (1939). (92) Rentschler, M. J., Iron Steel Engr., 16, No. 1, 52-62 (1939). (93) Rosenstein. L.. U. S.Patent 2.055.419 (1936). (94) Rousch, G.’ A.; Mineral Industry, 46, li2-13 (1937). (95) Ibid., 46, 332 (1937). (96) Ibid., 46, 339 (1937). (97) Rowan, R. W., private communication, 1939. (98) Shaw, J. A., U. S.Patents, 2,028,124-5 (1936). (99) Siebert, C. L., private communication, 1938. (100) Sierp, F., Stahl u. Eisen, 58, 491-7 (1938). (101) Sierp, F., and Friinsemeier, F., Ibid., 57, 815-17 (1937) ; German Patent 561,514 (1929). (102) Simmons, P. D., W. Va. Univ. Eng. Expt. Sta., Tech. Bull. 11, 21-3 (1938). (103) Smith, M. C., Water Works & Sewerage, 83, 229-32 (1936). (104) Solvay Process Co., private communications, 1938-9. (105) Spangler, S.F., Blast Furnace Steel PZant, 23, 319-21 (1935); Chem. Met. Eng., 42,139-41 (1935) ; private communications, 1938-9. (106) Spangler, S. F., and Tillestad, N., W i r e & W i r e Products, 13, 5 9 1 4 (1938). (107) Sperr, F. W., Jr., Am. Gas Assoc. Proc., 1921, 282-5. (108) Sperr, F. W., Jr., Gas Age-Record, 58, 73-6, 80 (1926). (109) Sperr, F. W., Jr., U. S.Patent 1,523,845 (1925). (110) Ibid., 1,928,510 (1930); 1,983,320 (1934); 1,986,900 (1935). (111) Stabler, H., U. S. Geol. Survey, Water S u p p l y & Irrigution Paper 186 (1906). (112) Stevenson, E. P., U. S. Patent 1,515,799 (1924); private communication, 1939. (113) Stoughton, B., “Metallurgy of Iron and Steel”, 4th ed., p. 102 (1934). (114) Sulfrian, A,, Stahl u. Eisen, 57, 813-15 (1937). (115) Sullivan. W. L.. Chem. Met. Eno.. 35. 483-5 (1928). (116) Tainton; U. C.,’French Patent 776,083 (1935) ; British Patent 442,859 (1936) ; German Patent 636,489 (1936). (117) Tainton, U. C., and Harris, H. W., U. S. Patent 2,063,529 (1937). (118) Tisdale, E. S., J. Am. Water Works Assoc., 18, 574-86 (1927). (119) Tisdale, E. S., private communication, 1939. (120) Tisdale, E. S.,and Lyon’, E. W., J . Am. Water Works Assoc., 27, 1186-98 (1935). (121) Todd, A. R., W. Va. Univ. Eng. Expt. Sta., Tech. Bull. 11, 18-20 (1938). (122) Travers, J. T., U. S.Patents 1,440,253-4 (1922). (123) U. S. Army Engineers, “The Ohio River”, 5th ed., 1935. (124) U. S. Bur. of Census, Census of Manufactures, 1937. (125) U. S. Bur. Mines, Minerals Yearbook, p. 480 (1938). (126) Ibid., p. 617 (1938). (127) Ibid., p. 782 (1938). (128’1 Ibid... 13. _ 1186 (1938). (1295 Ibid., p. 1178 (1939j. (130) U. S. Natl. Resources Committee, 3rd Rept. of Special Advisory Committee on Water Pollution, 76th Congr., 1st Session, House Document No. 155 (1939). (131) U. S. Senate, Committee on Commerce, Hearing on Water Pollution Control Bill 9. 1691 (1939). (132) Verein chemische metallurgische Produktion, German Patent 593,269 (1934). (133) Wartman, F. S., and Keyes, H. E., U. S. Bur. Mines, Rept. Investigations 2839 (1927). (134) Weber, I. E., private communication, 1939. (135) Wespy, C. R. C. C. (to C. Padberg), U. S.Patent 2,007,233 (1935). (136) Whetzel, J. C., and Zimmerman, R. E., Ibid., 2,005,120 (1935). (137) Wilson, P. J., Am. Gas Assoc. Proc., 1929, 934-6. (138) Wolman, A., Hearing on Water Pollution Control Bill 5. 1961, 53-6 (1939). (139) Zahn & Co., G. m. b. H., French Patents 723,484 (1931); 808,033 (1937). I

Other photographs of processes described i n this article are shown on pages 1322, 1337, 1351, and 1401.