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potential schemes for handling pulp and paper waste as developed in the research organizations within the industry, and discusses the situation understandingly with the mill executives, its purpose will be accomplished most effectively. Industry, on the other hand, must appreciate that the tide of public opinion is rising against industrial pollution. The good neighbor policy will pay off in many ways. It is a mistake to postpone installing save-all equipment for reducing fiber losses t o a minimum. There is also little excuse for not removing gross suspended matter, such as pigments, bark, and even raw sewage, from plant wastes. T h e commissions know t h a t necessary equipment for correcting these nuisances exists and is practical. Deinking waste treatment has not reached technical or practical status sufficient t o adequately correct stream pollution in most localities. Kraft and sulfite mills that find it difficult t o install modern devices which have been proved feasible in the newer, larger modern mills should explain their economical situation to the pollution commission in a manner which creates confidence t h a t they really intend t o solve the problem. Competent engineers on industrial waste disposal will be helpful in projecting the best means for solving these local problems. I n another decade, modern methods and well-designed equipment will have reduced stream pollution from the pulp and paper industry to a matter of little importance. Ne+ mills have already demonstrated this trend. When supply and demand for pulp and paper products becomes more in balance, competition will force older mills t o modernize their operations or close down. It is this potentially obsolete equipment in these older mills which contributes most t o the waste disposal situation of today. Spent sulfite liquors will eventually become a profitable by-product. Utilization processes for converting the soluble lignin and sugars into chemicals and other products will offer a number of opportunities. The unused spent sulfite liquor together with the residual liquors from one or more utilization operations will then be evaporated and burned in a manner already proved feasible commercially. Confidence in the future of theindustryis well justified,
Literrrture C i t e d (1) Baker, R. E., and Hutton, F., P u l p & Paper M a g . C a n . , 51, 82
(May 1950). Baker, R. E., and Wilooxson, L. S., T A P P I , 33, 187 (April 1950). (3) Ekholm, E., P u l p & Papel I n d . , 25, 54 (July 1951). (4) Elgee, H., Craig, D., and Russell, J. K., P u l p & Paper Mag. Can., 51, Convention Issue, 178 (1950). ( 5 ) Gehm, H. W., Sewage and I n d . Wastes, 23,765 (June 1951). (6) Gehm, H. W., TAPPI, 34,120A (May 1951). (7) Hazelquist, S., and Rogers, C. E., I b i d . , 33, 77A (August 1950). (8) Holderby, J. M., and Wiley, A. J., Sewage and I n d . Wastes, 22, 61 (January 1950). (9) Joseph, H. G., Sewage Works J., 19,60 (January 1947). (10) Lawrence, W. A., Sewage and I n d . Wastes, 22,820 (June 1950). (11) Murdock, H. R., IND. ENG.CHEM.,42,71A (June 1950). (12) Ibid., p. 73A (October 1950). (13) Ibid., 43, 79A (January 1951). (14) Murdock, H. R., private correspondence. (15) National Council for Stream Improvement, Int., Ann. Rept., 1950. (16) PLarl,A. I., Chem. E n g . News, 26,2950 (Oct. 4, 1948). (17) P u l p & Paper Ind., 24, 28 (February 1950). (18) Ibid., p. 23 (April 1950). (19) Ibid., p. 31 (August 1950). (20) Ibid., 25, 66 (January 1951). (21) Ibid., p. 29 (February 1951). (22) Ibid., p. 55. (2)
(23) Ibid..
D. 56.
(24j Ibid.; i. 64 (June 1951). (25) Rogers, C. E., and Jolley, R. S., Paper Trade J . (Nov. 16, 1950). (26) Rosenblad, Curt, P u l p & Paper M a g . Can., 51, 85 (May 1950). (27) T A P P I , 34, 52A (February 1951). (28) Ibid., p. 99A (March 1951). (29) Ibid., p. 100A. (30) Ibid., p. 22A (June 1951). (31) Tyler, R. G., Sewage W o r k s J., 14, 734 (April 1942). (32) Tyler, R. G., et al., Ibid., 18, 1155 (November 1946). (33) Van Horn, W. M., Anderson, J. B., and Katz, M., T A P P I , 33. 209 (May 1950). (34) Waddell, R. D., P u l p & Paper Ind., 25, 56 (July 1951). (35) Wiley, A. J., etal., Paper TTadeJ., 124, No. 12, 123 (1947). RECEIVIOD for review September 6, 1951.
ACCEPTED January 21, 1952.
STEEL INDUSTRY RICHARD D. HOAH, Mellon Institute, Pittsburgh 13,Pa. During the past 75 years steelmaking has grown from a relatively minor enterprise into an industrial giant that has been a major factor in the development of modern civilization. In common with all basic industries, steel cannot be manufactured without producing a variety of wastes. Some of these can be reworked directly, while
others must be processed for re-use. But some wastes cannot be converted to useful products economicaIly, and these pose difficult disposal problems. This paper reviews current waste treatment practice in the industry. Special emphasis has been placed on spent pickle liquor because it is a particularly vexatious problem.
HEN t h e AMERICAN CHEMICAL SOCIETY was founded in
The manufacture of steel in the United States may be mid to date from 1744, because about '/2 ton was made t h a t year. I n 1750 there were five steel furnaces in commercial production, but by 1876 the annual output of steel was only 541,900 gross tons (18). The total production of steel ingots in 1950 was 96,836,075 net tons, with equipment operating a t a n average rate of 96.9% of capacity. The production of alloy and stainless steel ingots i n t h a t year was 8,436,872 net tons (1). No early statistics on coke production are available. Some coke had been used in blast furnaces before 1850, but it had not been generally accepted as a substitute for charcoal. Four establishments, employing 14 men, made coke worth $15,250 in 1850. I n 1876, somewhat more than a million tons of coke were manufactured (18). Although, by 1860, considerable progress had been made abroad i n operating closed retort ovens t o permit
1876, no one could have predicted the tremendous size and importance the iron and steel industry would attain in the next 75 years. No other manufactured product contributed more t o the development of our civilization than steel, and this versatile metal continues to play a significant role in practically every human undertaking. Indeed, without steel, the nations of the world could never have evolved beyond agricultural societies. The first commercial pig iron in this country came from a furnace near Lynn, Mass., in 1645. By 1876 there were 714 furnaces, and the 236 t h a t were on blast t h a t year produced iron a t a n average annual rate of 7919 gross tons (18). Many of today's furnaces yield t h a t amount in less than a week. In 1950, 229 furnaces made 64,586,907 net tons of pXg iron (19)for a n average annual production of 282,039 tons per furnace.
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recopery of by-products from the coking process, beehive coke \vas preferred for blast furnace use in this country. The first byproduct ovens erected here were built in 1893 a t Syracuse, K.Y., €or the Solvay Process Co., according to designs made by Louis Semet. These were installed principally t o supply ammonia for the Solvay ammonia-soda process (2.4). The first tabulation of by-product recoveries appeared in 1907, when $7,500,000 was realized from the sale of gas, tar, and ammonia (19). Coke produced by the iron and steel industry in 1950 totaled 57,940,078 tons, of which 55,987,350 tons were made in by-product oven? and 1,952,728 tons in beehive ovens ( 1 ) . The insatiable demand for metallurgical coke was responsible for restoring 635 beehive ovens to service in 1948, making a total of 14,078 of these ovens available in t h a t year. The value of all by-products of the coking process (except coke) t h a t were sold in 1948 was $267,126,556. T h e principal products were gas, tar, creosote oil, t a r acid oil, phenol, pitch, ammonia, ammonium sulfate, crude light oil, benzene, toluene, xylene, solvent naphtha, naphthalene, pyridine, eodium phenolate, and sulfur ( 2 3 ) . Steel cannot be manufactured without producing a variety of wastes. Some of these can be reworked directly-for example, scrap from blooms, billets, sheets, and other rolled products. Some are converted t o other materials used in steel manufacture, as in sintering blast furnace dust t o agglomerates suitable for smelting. Others are processed t o recover by-products, of which the coke ovens yield the greatest variety. But many wastes cannot be economically converted t o useful products, and others must be treated t o avoid disposal problems.
Slag The amount of slag produced by the blast furnace varies with the type of ore being smelted. For example, 1100 t o 1300 pounds of slag will be made per ton of pig iron by furnaces operating on Mesabi ores (4). Blast furnace slags consist primarily of the oxides of silicon, aluminum, calcium and magnesium, but small amounts of other compounds will also be present, depending on the impurities in the ore and the method of operating the furnace. The 68 slag processing plants operating in the United States in 1948 sold 21,131,000 short tons of various sizes ( 2 3 ) . More than 90% of this product was used for railroad ballast, cement, concrete blocks, highway construction, and land-fill material. A substantial tonnage was used t o manufacture mineral wool, and a small amount was used in fertilizers for its high phosphorus content. Whereas the ratio of basic (CaO MgO) to acidic (Si02 4A1203) oxides in blast furnace slags usually falls in the range 1 to 1.2, final open hearth slags are more basic and always contain a t least twice as much lime and magnesia as silica, alumina, and phosphorus. Although basic open hearth slags do not find as many commercial uses as blast furnace slag, they are valuable as soil conditioners. The excess lime and magnesia in this kind of slag are loosely combined with silica, phosphorus, iron, and manganese, forming a stable, almost neutral substance t h a t yields its basic components gradually to the soil as needed, without danger of plant damage. I n addition, it contains many trace elements essential to plant health. Not properly a fertilizer, because i t lacks nitrogen and potassium and is often lean in phosphorus, it iinproves the physical condition of heavy clay soils and is an ideal corrective for acid soils. It is effective in promoting the growth of winter legumes, clover, citrus fruits, and pecans ( 5 ) . Although used t o a considerable extent in the south, where the local high phosphorus iron ores produce a slag relatively rich in phosphorus, it has not yet found favor in areas whereits phosphorus content is too Bow t o justify the expense of grinding and merchandising. The world manganese situation has directed considerable research attention t o open hearth slag as a source of this metal. Modern steel cannot be made without manganese, except a t greatly increased cost, because it is the most practical deoxidizer and convenient desulfurizer known. I n addition, it iniparts de-
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sirable physical properties to a wide range of coinnrercial steels. From 12 to 14 pounds of manganese are used in the manufacture of a ton of steel, and about half this quantity is found in the final slag. Practically all the manganese in open hearth slag can be extracted with dilute sulfuric acid, but this is not an economically feasible recovery method, especially in view of the current shortage of acid. The U. s. Bureau of Mines is developing a pyrometallurgical recovery method, but these studies have not yet been completed. Sylvester & Co. have reported a process t h a t has been carried through a substantial pilot investigation, whereby the slag is roasted and separated into high manganese and high phosphorus fractions; the former is suitable for smelting to fwromanganese and the latter is valuable as a fertilizer component ( 2 ) . These studies suggest that open hearth slag may eventually be processed t o yield useful by-products in substantid quantities.
Blast Furnace Dust People outside the steel industry are always surpiised to learn that the air blown into a blast furnace to support combustion of the coke weighs more than the total weight of iron ore, limestone, :ind coke required to produce pig iron. As this large volume of gas passes through the furnace its velocity through the voids in the charge is very high, and it carries with it a considerable amount of fine ore, limestone dust, and coke breeze. Although some of the particles in this dust are quite large, much of it is fine enough to pass a ZOO-mesh screen. As the gas leaves the furnace, it passes first through a cyclone system where part of the dust is removed, and then through a wat>er scrubber where moat of the remainder is washed out. Part of the gas is burned in stoves containing refractory checkerwork, where the furnace air is preheated. Part of the gas may be used t o provide fuel for the blowing engines that compress the air delivered to the stoves; this gas must be thoroughly scrubbed in a special water-spray washer, or passed through an electrostatic precipitator, t o remove substantially all the residual dust. Any remaining gas is generally used as a boiler fuel. It was formerly common practice to discharge the water from t h e wet washers to streams or lakes where, as the solid matter settled, i t filled navigation channels and built sludge banks. For more than 20 years, however, pollution from this source has been increasingly reduced by construction of subsidence basins or thickeners. Dust recovered by these methods can be converted to blast furnace charging material by sintering. When blast furnace dust is mixed with suitable amounts of iron ore and fine coke, ignited, and subjected t o a strong dcwndraft of air, i t fuses into a mass of agglomeratee that has sufficient strength t o be charged t o blast furnaces and smelted to pig iron. Sintering, which was originally begun t o dispose of dust, is the major process in use today for agglomeration of fine iron ore. The annual capacity of sintering plants in the United States in 1948 was 18,000,000 gross tons, as compared with 82,000,000 gross tons of lake ores shipped t h a t year. Only the iron content of sinter is recoverable, and there have been many complaints from furnace operators-for example, too many fines, lack of porosity, too much fusion, wide size range, small average size, low reducibility ( 8 1 ) . The American Iron and S.teel Institute recently (1949) established a fellowship a t Mellon Institute to investigate sint,ering techniques with a view to overcoming the objections of operat,orsand to encourage a n increased m e of sinter.
Coal Chemicals from C e k e Ovens In the early days of coke manufacture, n-hen iweliive o ~ e n n-ere s the only source of coke, waste disposal !vas an insignificant prohlem because the volatile products of the process were partly consumed in the ovens amd partly discharged to the atmosphere. With the development of by-product ovens, lioil-ever, difficult disposal problems appeared which were gradual1:- solved as improved methods were evolved for recovering :I great v a ~
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Storage Lagoon for Neutralized Waste Pickle Liquor Lagoon is in center of very large slag dump; sludge is hauled from neutralization plant to lagoon in tank cars 0
compounds from the gaseous, liquid, and solid products of the distillation of coal. Indeed, these recovery processes constitute a n industry that is the source of such a wide range of valuable materials that i t would be appropriate to discard the term “byproducts” and speak instead of the manufacture of coal chemicals. At the high temperature of the coke oven, substantially all the volatile matter in the coal is evolved as a dense, brownish yellow gas. As this gas passes to a collecting main it is scrubbed by sprays of flushing liquor which cool it to 75” t o 90’ C., condense most of the high boiling constituents, and dissolve a large proportion of the water-soluble compounds. The flushing liquor flows t o a decanter where the heavy tar is separated; part of the supernatant liquor is returned to the flushing system and part is sent t o the ammonia still. The weak ammonia liquor enters the top of a bubble-plate column where the free-ammonium salts are decomposed by steam. The liberated ammonia, hydrogen sulfide, carbon dioxide, and hydrogen cyanide are returned to the coke oven gas main, and the liquor which collects in the bottom of the column is pumped to a dephenolizer. The dephenolized liquor is returned t o the lime leg of the ammonia still where the fixed-ammonium salts are decomposed. The ammonia passes to the free leg of the still, and the liquor from the lime leg flows to the fixed leg where its ammonia content is volatilized by steam, which carries i t to the free leg. The bottoms from the fixed leg have been a frequent source of steam pollution. There are two dephenolization processes in use in this country. The vapor recirculation method continuously passes a current of steam through the liquor t o volatilize the phenols, which are then absorbed in a caustic soda solution. Any desired degree of phenol removal can be effected by this process, and installations commonly remove 90 to 95%. The solvent extraction processes operate similarly, except that the phenol is stripped from the liquor with benzene which is subsequently scrubbed with caustic soda solution t o rerover the phenol as sodium phenolate. Up to 99% of the phenol has been removed commercially by solvent extraction. Phenol and its homologs give a pronounced taste to water, even in very low concentrations, and the taste is increased where the water is chlorinated. The medicinal taste caused by 5 parts March 1952
per billion of chlorophenol has been detected by some observers and a concentration of 100 parts per billion will cause most users of water t o complain. Phenols are quite toxic t o the biota In streams, and, even below the toxic level, they impart an unpleasant flavor to fish, making them inedible. Discharge of ammonia still waste to sewage that is not treated before passage to bodies of water is no longer practiced unless the waste has becn almost completely dephenolized or there is adequate dilution t o reduce the phenol concentration below an unobjectionable level (about 5 p.p.b.). Pollution from still waFte can be avoided by adding the waste to the coke quenching water and operating a closed system. The phenolsare vaporized by the incandescent coke, but this method of disposal causes difficulty in controlling the moisture content of the coke, and the calcium chloride in the waste results in serious corrosion of the quenching equipment. The waste can be combined with domestic sewage and treated successfully by biochemical oxidation if the waste is discharged a t a uniform rate and its proportion to the sewage does not exceed about 0.2 to 0.5%, depending on its tar content. A cooperative study (do), sponsored by the Ohio River Vallev Water Sanitation Commission, resulted in valuable but as yet incomplete information on still waste disposal. This investigation, which employed a pilot plant erected a t a steel mi11 coke plarit, showed that phenols can be completely oxidized by chlorine, ozone, or chlorine dioxide; that a substantial reduction in phenol concentration can be attained with a small amount of oxidant, but that increasingly larger quantities are required as the oxidation is carried further; that oxygen consumed and B.O.D. values can be reduced more than 60% by each of the oxidants; and that partial treatment is possible with ozone or chlorine dioxide; but complete treatment is necessary with chlorine to prevent formation of chlorophenols. When applied t o still waste, the required chemical dosage could not be correlated with the phenol content. Accordingly, further research is indicated t o determine just what other factors exist in the still waste before this process can be generally adopted.
Waste Pickle Liquor One of the most vexatious wastes produced by the steel industry is the spent liquor discharged from pickling operations. I t is
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Liquid Industdal W a s t e s essential to remove the oxide film from certain steel products prior to further processing, and this can be accomplished most satisfactorily by immersing the steel in a dilute acid bath for a brief time. As part of the scale and some of the base metal dissolve, iron salts accumulate in the bath, which gradually loses its effectiveness and must be discarded. The tonnage of steel requiring this treatment is steadily increasing; in 1950, 19,549,671 net tons of full finished sheets, tin plate, strip, and flat galvanized products were made (1). Pickle liquor disposal is a troublesome problem because of the large quantity involved, the uneconomic nature of the processes proposed t o utilize it, and the fact that steel mills often have several pickling shops in widely separated locations. The pickle liquor problem has been discussed in detail by Hodge (16) and Hoak (8). Only the newer developments and the most significant aspects of the problem are dealt with in this paper. Disposal without Treatment. A variety of methods has been used in the past for disposing of pickle liquor without treatment, idcluding discharge of the liquor into limestone caves, deep wells, exhausted oil and gas sands, evaporation ponds, sand or gravel sumps near large bodies of water, and sewers terminating in streams, lakes, or tidewater, but all these expedients proved to be geneially unsatisfactory. As a result, little strong liquor is now discharged without treatment except in regions where streams are heavily polluted with acid mine water or other wastes. One steel company disposes of pickle liquor by pouring it on hot blast furnace slag. When the molten slag is hauled to the dump, one or more tank cars of spent liquor are attached to the end of the train. After the slag ladles are emptied, the train is pulled ahead and the liquor is discharged on the slag. Less than a n hour is required to vaporize 20,000 gallons of liquor completely. Succeeding taps of slag are deposited a t the same place, and any iron salt that might have escaped decomposition is covered with molten slag. I t might be supposed that aerial pollution would result from this procedure, but this is not the case. Standing directly in the dense vapor a slight prickling sensation in the nostrils is the only noticeable effect; a t a distance of 10 feet from the steam there is only a faint, unobjectionable odor. It is of interest that the liquor comprises the combined waste from sulfuric acia and stainless steel (HXOS-HF) pickling operations. A thorough investigation of this disposal method was made before it was put into practice, and it has been approved by the Pennsylvania Department of Health. Pickle liquor is being treated successfully with domestic sewage a t some municipal sewage plants. This disposal method requires discharge of the liquor a t a uniform rate, preferably proportioned t o the sewage flow, and neutralization of its free acid. It is a practicable method only a t primary treatment, chemical precipitation, and Imhoff tank-trickling filter plants; it cannot be used where the activated sludge process is installed because iron in sewage clogs the air-diffusion plates in the activation tanks. Ferrous sulfate is a good coagulant in an alkaline medium, and this property improves clarification in primary sedimentation tanks, I t increases sewage sludge volume, however, and this might present a problem if sludge-drying beds are taxed to capacity. Where an agreement can be made with a municipality to treat pickle liquor a t the local sewage plant, advantages often accrue to both parties. Neutralization. Treatment of waste pickle liquor with an alkaline agent, usually lime, to neutralize the free acid and precipitate the iron is practiced aidely in the steel industry. Some of the more likely processes that have been proposed for pickle liquor utilization are described later in this paper, but the majority of these are so unsuited to a complex steel mill economy that a majority of plants have no alternative but to employ neutralization. It is for this reason that the Mellon Institute Fellowship of the American Iron and Steel Institute has devoted a great deal of .research attention to the development of improved neutralization
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techniques whereby this costly operation can be performed with maximum efficiency. The first necessity for optimum neutralization economy is an accurate method for determining the proper amount of alkaline agent to provide the required degree of treatment. Chemical analysis of complex alkaline substances is time-consuming and generally will reverll little about their reactivity or available basicity. Basicity factors (11), determined under conditions simulating the actual neutralization, provide both an accurate measure of available basicity and considerable information about reaction rate. They are expressed as grams of equivalent calcium oxide per gram of substance, regard1e;s of the composition of the alkaline material. When lime slurry is mixed with pickle liquor, hydroxyl ions combine rapidly with hydrogen and/or iron ions, permitting more lime to dissolve. For every hydrogen ion that reacts, an equivalent amount of calcium sulfate is foimed; this compound largely precipitates because of its limited solubility. Complete treatment of pickle liquor by neutralization can therefore be considered to be a union of calcium and sulfate ions to form calcium sulfate. To compute the amount of alkaline agent required to neutralize a given quantity liquor, it is thus necessary to know only the basicity factor of the agent and the total sulfate equivalent of the liquor. The acid value of a liquor, expressed as grams of equivalent sulfate ion per liter, can be determined accurately in 15 to 20 minutes by a procedure that involves boiling a sample briefly ~ i t han excess of standard alkali, filtering off the precipitate, and titrating the excess alkali (11). The basicity factoracid value relation provides a simple method for controlling the proportions of pickle liquor and neutralizing agent. Among the variety of alkaline substances that can be used to neutralize pickle liquor, lime is by far the most popular. Its mide availability and relatively 101%cost promote its general use for the purpose, Lime may be either high calcium or dolomitic, unslaked or hydrated. For large installations, high calcium quicklime will usually prove t o be the most economical agent; high calcium hydrate is often used at small plants because handling problems are simpler, but it is more costly than quicklime. Dolomitic lime has a higher basicity than high calcium, though selling for approximately the same price, but a special procedure (use of an excess, aeration, heat) is required to utilize its basicity fully; however, the basicity advantage of dolomitic lime may result in an over-all operating economy. The economic and technical factors in neutralization of pickle liquor with lime have been discussed in detail by Hoak et al. (12-1.4). Pulverized high calcium limestone can be used successfully for pickle liquor treatment vihere adequate reaction time and effective aeration can be provided. Limestones vary widely in reactivity, and 4 or more hours may be required for complete precipitation of iron, but the low cost of this material on a basicity basis is an advantage where operating costs must be held to a minimum (12). Dolomitic limestones are usually wholly unsatisfactory for this use. An aeration-oxidation technique (15) has been developed for neutralizing pickle liquor with lime and other alkaline agents; this yields the minimum sludge volume attainable with a given substance. Controlled aeration of the lime-pickle liquor mixture converts the precipitated iron to magnetic iron oxide which settles very rapidly. The coprecipitated calcium sulfate acts as a filter aid and results in remarkably high filtration rates on a vacuum filter (400 pounds of m t cake per square foot per hour; wet cake 60y0dry solidsj. This process was developed primarily for mills in areas where no space is available to lagoon the sludge from conventional neutralization plants. A process has recently been worked up on a commercial scale by Wunderley (26) in which pickle liquor is treated with granulated blast furnace slag. The liquor and slag, in a 1: 1 ratio by weight, are fed to a rotary mixing drum where the free acid is neutralized and part of the iron precipitated. The mixture is placed on a
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Liquid Industrial Wastes dump where the remainder of the iron gradually precipitates; after several days no iron can be leached from the mass. The method uses a very cheap neutralizing agent, and the product can be used as fill t o provide for building construction because it sets to a hard mass. Heide has proposed a different method (7) for using blast furnace slag t o treat pickle liquor. He pours molten slag into such a . volume of liquor that most of the water is vaporized, leaving a granular mass containing 10 t o 12% moisture. This product could be used advantageously as a filler for fertilizers because of its content of trace elements. Practical development of this process would reduce the cost of pickle liquor treatment in some areas. Many other alkaline materials can be used to treat pickle liquor successfully, but commercial compounds are too costly, even where a by-product could be recovered. The most practical methods for reducing neutralization costs lie in keeping the volume requiring treatment to a minimum (especially rinse waters), and using waste products of other operations as neutralizing agents-for example, acetylene sludge, cement dust, calcium carbonate waste. By-product Recovery. A large number of processes have been proposed for utilizing pickle liquor, and some have been operated on a commercial scale, but none has yet shown the profit potential claimed by its advocates. Actually, this might have been anticipated because the low cost of sulfuric acid and ferrous sulfate automatirally limits the allowable investment in equipment for their economical recovery. Many other factors introduce serious difficulties, and no process would be practical that could be operated profitably by substituting scrap iron and dilute acid for pickle liquor. The possibility that pickle liquor processes will be developed t h a t can break even, or show a small profit, must not be discounted. Research is going forward in many places, and no one can predict the outcome, but the vast amount of investigational work that has already been done by the steel industry itself suggests that the prospects are not particularly good. Although copperas can be made easily from pickle liquor by a variety of processes, the market demand for this compound is very small in relation to the amount potentially recoverable. The same argument holds for conversion of ferrous sulfate to iron oxide pigments. Processes for recovering the free acid in pickle liquor have a more practical promise in the light of the worldwide shortage of sulfur. As the manufacture of sulfuric acid from other materials, such as pyrites, expands, the price of acid will necessarily increase and this will improve the economics of acid recovery. A situation of this kind, however, is not likely to occur for quite a few years. Two processes have recently been proposed for recovering free acid and ferrous sulfate monohydrate from pickle liquor. The Martin process ( 1 7 ) was designed to operate continuously as an integral part of the pickling process. It had been assumed that a high concentration of ferrous sulfate in the bath inhibited pickling, but Martin's work disclosed that the pickling rate is unaffected by ferrous sulfate, even a t the saturation level, if the free acid is maintained at 18 to 22y0 by volume and the temperature is held at 190" to 210" F. Based on this finding, spent liquor, at 18.5% free acid and 66 grams F e + + p e r liter, is continuously withdrawn from the last tank of a continuous strip pickler and pumped to an evaporator where i t is combined with approximately five times its volume of recycle liquor from the crystallizer. The mixed liquor is sprayed into a stream of hot gases at 2000" F. from a PetroChem furnace. This combustion gas effects evaporation of water from the solution and is cooled to 215" F. The concentrated liquor is removed from the gas b y a centrifugal separator and drains t o a crystallizer. The gas from the separator is washed with rinse water from the pickler t o scrub out any entrained acid, The liquor in the crystallizer is heated to 220 O F. by superheated steam generated in the Petro-Chem furnace. Fresh acid is added
March 1952
to the crystallizer to supply the acid consumed in pickling; this raises the acid concentration to about 32% by volume. Under these conditions ferrous sulfate monohydrate crystallizes, and the suspended crystals increase in size by being held in the crystallizer for about 2 hours. Clear acid solution is drawn off; part-of this is recycled t o the evaporator and part goes t o a dilution tank. The crystal slurry is drawn from the crystallizer and separated from the acid solution in a centrifuge. The crystals are washed and dried. The strong acid and the wash waters are discharged to the dilution tank where the composition of the solution is adjusted 60'23.5% acid and 14 grams of Fe++per liter before being pumped to the first tank in the pickle line. T h e flow of solution in the pickler is concurrent with the strip. The temperature in the first tank is held a t 205' F., but it is decreased in the remaining three tanks to 190" F. in the last one, to increase successively the solubility of the monohydrate. Properly balanced, this process provides continuous separation of ferrous sulfate from spent pickle liquor and maintains constant pickling conditions. I t s disadvantage lies in high capital and operating costs, but development of a market for the superior quality monohydrate i t produces would act as a partial offset. The Chemical Construction Corp. has developed a process (3) which uses a submerged combustion burner to concentrate waste pickle liquor and precipitate ferrous sulfate monohydrate. In the pilot plant study, pickle liquor containing about 12y0 free acid and 20% ferrous sulfate was fed continuously to a cone-bottomed, lead- and brick-lined steel tank equipped with a combustion dip pipe fired with light fuel oil. Evaporation maintained the acid concentration at 60 t o 70% to cause precipitation of practically all the ferrous sulfate as the monohydrate. The slurry was continuously withdrawn t o a rotary vacuum filter constructed of lead and covered with a plastic filter.cloth. The pilot plant was designed t o process 50 tons of pickle liquor per day. This process utilizes the efficiency of high temperature, direct-flame evaporation and provides a method that is reported t o be economical for recovering about 85% of the free acid in pickle liquor. The process has been extended t o the production of fresh sulfuric acid and iron oxide, as follows: The monohydrate is mixed in a pug mill with 12% of crushed coal by weight, plus some fine, sintered oxide. The mixture is extruded through a perforated plate to yield short l/r-inch cylinders which are dried on a moving grate. The pellets are distributed on a layer of coarse oxide sinter on a Dwight-Lloyd machine and sintered. This produces large chunks of semifused oxide suitable for blast furnace burden. The wind-box of the sintering machine is divided into two parts; one supplies a gas containing 7.5y0 sulfur dioxide t h a t is suitable for a vanadium contact acid plant after being scrubbed, the other contains less than 0.1% sulfur dioxide and is used t o dry the monohydrate pellets. Manufacture of sulfuric acid from waste pickle liquor, by one means or another, is feasible, but such a method for utilizing the spent liquor has serious disadvantages. Sulfuric acid plants must be operated continuously and on a large scale (not less than 50 to 75 tons of acid per day) for reasons of economy. The installations are costly and maintenance charges are high. Possibly no single steel mill produces enough pickle liquor t o operate a plant of its own on a sound basis unless the cost of sulfuric acid increases markedly. Operation of a cooperative plant t o serve a single steel-producing area has been discussed, but transportation and physical problems have interposed obstacles that appear to be insoluble. Alternatively, it has been suggested that monohydrate be produced a t the mills and this compound be processed in existing acid plants for a conversion charge, but similar difficulties have prevented a workable plan, From the viewpoint of over-all economy, manufacture of sulfuric acid from pickle liquor is not especially attractive, despite its apparent reasonableness, but exhaustion of supplies of natural sulfur may eventually alter the economics of acid manufacture.
INDUSTRIAL AND ENGINEERING CHEMISTRY
51 7
Liquid Industrial Wastes
COURTESY U.
s. STEEL ca.
Neutralizing Tatiks Showing Air Distribution Headers Lime slurry and waste pickle liquor enter from far side of tanks j air is used principally for agitation. Tanks at right are being agitated te ensure complete neutralization: tanks a t left are completely neutral and are awaiting shipment to dump
The autoxidation principle, which was patented in 1894, has attracted attention in recent years as a ineans for preparing ferric sulfate or sulfuric acid from waste pickle liquor. The Mellon Institute group studied this process in a reactor they designed to improve oxidation efficiency.
A stream of sulfur dioxide and oxygen is dispersed in pickle liquor a t 60" C. by a special impeller that causes a pronounced shearing action and thus distributes the gases as thin films. The rocess yields ferric sulfate in concentrations up t o 600 grams per h e r (42% solution) with a low free acid content. The oxidation rate is primarily a function of total iron concentration and temperature. It can be expressed by the equation dFe+++/dQ = -0.0609Fe
+ 1.92t0.413
over the temperature range 47" to 80" C. dFe++"/d8 represents the rate of formation of ferric iron in grains per minute; Fe IJ total iron in grams per liter; and t is degrees centrigrade. A plot of this equation shows that oxidation increases with temperature a t a decreasing rate and that little would be gained by operating above SO" C. This type of process has been operated in conjunction with a sewage treatment plant to provide ferric sulfate solution for use as a coagulant. The British Iron and Steel Research Association is investigating a process on a pilot scale that involves flash roasting of copperas n i t h coal, direct absorption of the sulfur oxides in vater, and catalytic oxidation to sulfuric acid, but full details are not yet available. The treatment of coke oven ammonia with waste pickle liqucr to produce ammonium sulfate and iron oxide continues to encourage research, despite the great practical difficulties involved in such processes. Several recent developments deserve description. The Elzi process ( 6 ) neutralizes the free acid in waste pickle liquor with scrap iron; passes this liquor through a packed toxl-er where it is scrubbed countercurrently n i t h coke oven gas to raise the p H of the liquor to 7.0 t o 7.5 by absorption of ammonia; raises the pH of the liquor to 8 0 to 8.5 in another packed ton er m-ith pure ammonia from the ammonia still; aerates the 518
liquor in a third tower to oxidize the iron to ferric oxide; and filters off the oxide, which may be calcincd to rouge or sintered for blast furnace burden. The filtrate may be evaporated t o recover ammonium sulfate or sent to the conventional ammonium sulfate saturators of the coke plant. A process patented by Tiddy ( 2 2 ) scrubs ammonia and hydrogen sulfide from coke oven gas with pickle liquor in two stages. The gas passes successively through a first and second chamber countercurrent to the flow of a feed liquor comprising piclrle liquor and recycle liquor. The pickle liquor and recycle liquor enter the top of the second chamber and the liquor is pumped from the bottom of the second chamber to the top of the first chamber. The flow of coke oven gas is so regulated t'hat t,he liquor leaving the first chamber will contain not less than 2.0 grams per liter of ferrous sulfate. The precipit,at,e of ferrous oxide and sulfide is separated by decantation from the slurry flowing from the bottom of t'he first chamber, and part of the clear liquor is recycled t,o the stream of pickle liquor entering the second chamber. The animonia content of the remainder of the clear liquor is increased to atleast 0.5 gram per liter. This liquor is pumped to an aeration tower where its iron content is oxidized with air and precipitated. The precipitate is separated, and the liquor passes t,o an evapoi'ator for recovery of ammonium sulfate. The oxide-sulfide sludge is sintered to a material suitable for charging t'o blast furnaces. Development of sound processes for combining coke oven animonia and waste pickle liquor has been beset by a variety of practical difficulties, but the advantages of a feasible method could be very great. After a lengthy study of the factors involved, two processes were developed by the lIellon Institute group which appear to have overcome the chief t,echnical difficulties t,hat were encountered by prior workers. In the first process ( I O ) , purified ammonia and pickle liquor are fed continuously to a. reactor of special design in which the precipitated ferrous hydrate is oxidized under controlled conditions to ferroso-ferric oxide; by thin means t,he iron ia precipitated completely. The nisgnetia
INDUSTRIAL AND ENGINEERING CHEMISTRY
Yoi. 44, No. 3
Liquid Industrial Wastes iron oxide produced in this manner settles rapidly (95% in 5 minutes), and i t can be separated from the ammonium sulfate liquor by continuous decantation. Efficient separation of the iron oxide was the operation that defeated many of the previous processes. Pure ammonium sulfate is recovered by evaporation of the final liquor. It is instructive t o examine the mechanism of the reaction involved in this process. Successful operation requires maintenance of the ratio of ferric to ferrous iron in the precipitate in the approximate range 2.5 t o 3.5. It had been observed that a n ironfree supernatant could never be obtained until the ferric-ferrous ratio had been raised to 2.0 or higher, but that such a ratio did not necessarily ensure a n iron-free supernatant. This observation led to a hypothesis which explained experimental data that previously had seemed to be inconsistent. At the beginning of the feed period, when the process is operated by the cyclic continuous method, ammonia and pickle liquor are fed t o a slurry consisting of magnetic iron oxide suspended in an iron-free solution of ammonium sulfate. X-ray diffraction analysis has shown that the principal component of the slurry is ferroso-ferric oxide (FeaOJ, and it may be assumed t h a t the solid phase is substantially this compound. This oxide may be represented by the formula Fe0.Fe20a and it contains two atoms of ferric iron for each atom of ferrous iron or a ferric-ferrous ratio of 2.0. As the pickle liquor and ammonia react, and the reaction product is oxidized by air dispersed in the slurry, molecules of ferric and ferrous oxide deposit simultaneously in a 1:1 ratio on existing crystal lattices or else form new nuclei in the same ratio. The fact t h a t the ferric-ferrous ratio of the desired compound is 2.0 may be interpreted t o mean that the crystal lattice will accept only one molecule of ferric oxide for each molecule of ferrous oxide. On the other hand, the observation that iron-free supernatants occur where the ratio is greater than 2.0 does not prove that the lattice will accept a larger number of ferric than of ferrous oxide molecules. Any excess ferric ions would precipitate at the p H of the slurry, b u t the reddish color of the hydrated ferric oxide would be completely masked by the black color of the preponderant ferroso-ferric oxide. This hypothesis indicates t h a t two distinct reactions are involved in the formation of magnetic iron oxide. The first is the oxidation of a fraction of the ferrous oxide precipitated by the ammonia, and the second the deposition of equal numbers of molecules of ferric and ferrous oxide on existing ferroso-ferric lattices or the formation of new nuclei. The experimental data show not only t h a t both of these reactions occur but that they proceed at such rates t h a t either may be the controlling factor, depending on the conditions of the operation. Similar reasoning can readily be applied t o continuous operation of the process. I n actual practice the operation is easy to control. The ferricferrous ratio can be determined analytically by a simple procedure, or the progress of the reaction can be followed by observing the settling rates of the slurry and determining the presence or absence of soluble iron in the supernatant. Pilot plant studies have demonstrated the technical practicability of the process and have indicated that it is economically sound. Its obvious advantage lies in the use of waste sulfate ion to produce ammonium sulfate. B u t the process would have the effect of increasing the world supply of ammonium sulfate. Although the demand for this compound as a fertilizer component is currently almost insatiable, this situation is an impermanent one resulting from a temporary world-wide condition. Normally, manufacture of ammonium sulfate at by-product coke plants is a break-even operation, and a n y marked increase in production might depress the price to a point at which all manufacturers would lose money. A process based on direct treatment of coke oven gas with pickle liquor would have several obvious advantages. Such a process was developed with coke oven ammonia liquor, fortified with additional cyanide and sulfide, to determine the maximum
March 1952
limits of these impurities for production of pure ammonium sulfate. The process was then operated with waste pickle liquor t h a t had been used to scrub coke oven gas. The process was an outgrowth of the pure ammonia-pickle liquor process described. When an attempt was made to adapt that process to a material containing sulfides, the ferrous sulfide that precipitated settled poorly and was difficult t o filter. This obstacle was overcome by carrying the oxidation of the precipitate t o ferric oxide, which settled and filtered very well. This step also caused the sulfur t h a t had been combined with the iron t o separate as elemental sulfur which could be recovered by froth flotation or solvent extraction. The cyanides were removed in combination with the iron oxide sludge. This process not only saves the sulfuric acid now used in the ammonia saturators, but i t reduces the sulfur in the coke oven gas, thereby making i t a more desirable fuel for many steel mill purposes. It has been demonstrated t h a t pure ammonium sulfate can be prepared from gas containing a much higher concentration of sulfides and cyanides than is normally present. The cyanides can be completely recovered from the sludge by extraction with caustic soda solution. The process would appear to offer an advantageous method for disposing of pickle liquor and accomplishing other desirable results. There are, however, a number of technical problems t h a t decrease its attractiveness. Pickle liquor and coke oven ammonia are rarely in stoichiometric balance; usually there is a substantial deficiency of the former. This means t h a t existing saturators would have to be retained to remove the excess ammonia. Where pickle liquor and ammonia are in balance, the liquor will usually contain only enough iron to combine with about half the hydrogen sulfide in the gas. In such cases, supplemental sulfide removal equipment would have to be operated where a low concentration in the gas is essential. Coke ovens and pickling shops are not often close enough t o each other t o avoid costly pickle liquor transport equipment. For sound economic evaluation the process would have to be operated on a pilot scale a t a steel mill; this has not yet been done. It is possible t h a t the process will eventually prove to be economically feasible, but plant scale investigation will first be necessary. This country has large deposits of low-grade manganese ores but almost none of sufficiently high grade for direct conversion to ferromanganese, an essential product required for manufacturing steel. The shortage of manganese was acute in the early days of World War 11,and an investigation was made a t Mellon Institute to determine whether the reducing property of ferrous sulfate could be used t o concentrate the manganese in pyrolusite ores of low quality (9). Low-grade ore is ground t o -60 mesh, mixed with a small excess of pickle liquor, and the gangue separated by filtration. The clear extract consists of manganous and ferric sulfates, plus a small amount of ferrous sulfate. The sulfates are converted to chlorides by treatment with calcium chloride, and the gypsum that precipitates can be recovered as a compound of high purity. The ferric iron in the filtrate is precipitated by controlled treatment with precipitated chalk. The filtrate is treated with lime slurry to precipitate the manganese, which is filtered off, washed, and dried as the main product. The filtrate from this step is substantially a solution of calcium chloride; its volume is reduced by evaporation and returned to the process. This process produces a manganese concentrate containing upwards of 60% manganese and two by-products of low value. I t s principal disadvantage is one of geography; most of the suitable manganese ores are mined at a great distance from centers of steel manufacture.
Summary This paper has presented an outline of waste disposal and utilization practices in the steel industry. The prospects for economical recovery of by-products from wastes, other than those
INDUSTRIAL AND ENGINEERING CHEMISTRY
519
Liquid Industrial Wastenow being salvaged, are not especially promising. But important research is in progress, both in the industry and in private laboratories, and there will always be the hope that these studies will result in practical developments. Meanwhile, the industry is making progress in eliminating all wastes that contribute to stream pollution and is constantly alert to adapt new processes to the solution of these difficult problems.
Acknowledgment This paper is a contribution from the fellowship the American Iron and Steel Institute has sustained a t Mellon Institute since 1938.
Literature Cited -
(1) Am. Iron & Steel Inst., N. Y . , Ann. Statistical Rept. (1951). (2) Anon., Steel, 124,33 (May 30, 1950). (3) Bartholomew, F. J., Ibid., 127,68-72 (July 31, 1950). (4) Bray, J. L., “Ferrous Production Metallurgy,” Kew York, John Wiley & Sons, 1942. ( 5 ) Camp, J. M., and Francis, C. B., “The Making, Shaping, and Treating of Steel,” 5th ed., Carnegie-Illinois Steel Corp., 1940. 66) Elzi, F. A., U. S. Patent 2,427,555 (1947).
Heide, 8.S.,unpublished data. Hoak, R. D., IND.EKG.CHEM.,39, 614-18 (1947). Hoak, R. D., U. S. Patent 2,462,499 (1949); Hoak, R. D., mil Coull, J., Chem. Eng. Progress, 46, 158-62 (1950). (10) Hoak, R. D., U. S. Patent 2,529,874 (1950). (11) Hoak, R. D., Lewis, C. J., and Hodge, IT. W., ISD. ENG.CHEY., 36. 274-8 (1944). (12) Ibid.: 37, 553-9 (1945). (13) Hoak, R. D., Lewis, C. J., Sindlinger, C. J., and Klein, B., Ibid., 39, 131-5 (1947). (14) Ibid., 40,2062-7 (1948). (15) Hoak, R. D., and Sindlinger, C. J., Ibzd., 41, 65-70 (1949). (16) Hodge, W,W., Ibid., 31, 1364-81 (1939). 117) Martin. E. D.. Blast Furnace & Steel R a n t . 36. 1089-94 (1948). (18) Mineral Ind., 1 (1892). (19) Zbid., 16 (1907). (20) Ohio River Valley Water Sanitation Comm., Cincinnati, Ohio, “Phenol Waste Treatment by Chemical Oxidation” (1951). (21) Powers, R. E., Steel, 128, 98 (Feb. 5, 1981). (22) Tiddy, TV., U. S.Patent 2,511,307 (1980). (23) C. S. Bureau of Mines, “Minerals Yearbook,” Washington, Govt. Printing Office, 1950. (24) Wilson, P. J., and Wells, J. H., “Coal, Coke, and Coal Chemicals,” New York, McGraw-Hill Book Co., 1950. (25) Wunderley, J., unpublished data. RECEIVED for review September 6, 1951.
ACCEPTED January 5 , 19.52.
TANNERIES JOHN W. HARNLY’, A. H.Roes & Sons Co., Chicago, Ill. Serious investigation of tannery waste disposal started in 1895 and the trend of treatments proposed is outlined. The Public Health Service and the American Leather Chemists’ Association have been the most active in this work, usually in cooperation with the individual tanneries.
The pattern of disposal is given for 190 tanneries that are concentrated in fourteen localities and represent a cross section of the industry. The hest method of disposal appears to be mixing with domestic sewage when a a adequate volume of domestic sewage is available ( 2 9 ) .
T
Of these 443 tanneries, 183 (417,) are concentrated in nine citiea, each of which has 10 or more:
HE tanneries of the United States turn out about, 20 billion gallons of liquid waste yearly and this, in relation to suspended solids and B.O.D., is a source of pollution approaching that of the domestic sewage from a city the size of Chicago. The following analyses of raw tannery effluent are typical : Literatiire Cited (91) (49) Ga1./100 Ih. hide .. ... Total solids, p.p.m. 5990 Suspended solids, p.p.m. 1340 1200 &day B.O.D.. p.p.m. 885 1350a PH ... a Estimated from data on components.
..
(36)
(90)
(41)
800 7200 2400 1200 11.0
1320 4870 1050 335 11.9
600-800 7000 2500 1200 11.0
The solids given in the analysis from reference (20) show the effect of the greater dilution, but the B.O.D. is lower than can be accounted for by this means, because this tannery uses no sulfides in its beamliouse operation, which is a principal source of B.O.D. in a tannery effluent. Another characteristic of tannery waste (90) is the extreme fluctuation in rate of hourly flow (in t’erms of per cent of weekly total) from 0.2% a t 6 Ax., when it begins to rapidly increase t o a peak of 1.5% ?t 11: 30 A . M . ; it then drops as rapidly back t o 0.2% at. 5 P.M. The daily flow is fairly uniform for the working days, dropping to less than one half on Sunday and the ot’her days of inactive operation. Figure 1 shows that 60% of the country’s tanneries are geographically concentrated in about 5y0 of its area (26); distribution by geographical sections is: Location
No. Tanneries
% of Total
443 398 272 82 53 24 12 1
Present address, Whitehall Leather Co., Whitehall, Mich.
520
100 90 61 19 12
5 3
30.
Tanncries Peabody, Mass. h-ewark, N. J. Salem, LIZ-s. Gloversville S . Y Chicago, Ill. Philadelphia, Pa. Milwaukee, Wis. Johnstown, K.Y. Wilmington, Del.
39 27 26 22 16 15 15 13 10
Lynn and Haverhill, Mass., have eight and seven tanneries, respectively; seven towns have three to seven tanneries each; seventeen towns have two tanneries, and 186 towns have one tannery.
American Leather Chemists’ Committee on Disposal of T a n n e r y Waste The principal contribution of this committee, formed in 1911, is a bibliography, from 1893, when the first recorded investigation of tannery sewage was made by the Massachusetts State Board of Health, to 1911. Esten, the compiler (15), had this t o say: There is no very extensive literature on the subject of tannery waste. Such as there is, consists partly of investigation of individual tanneries by boards of health and largely of references to the subject in standard works on the disposal of trade wastes in general. I n fact;the development of the disposal of tannery waste is so closely connected with that of general seTvage disposal that a bibliography, in order to be of value to those wishing to investigate the subject, must make reference to works which mark a distinct advance in the matter of trade wastes in general, even if they do not refer specifically to tannery wastes. Seven of the 35 references listed in the bibliography were issued by the Massachusetts State Board of Health and were principally experiments with filtration (28).
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 3
