Industrial Wastes
WASTE PICKLE LIQUOR RICHARD D. HOAK Mellon Institute, Pittsburgh, Pa.
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H E removal of oxide scale from certain steel products prior to further processing is a n essential operation. The film of oxide is usually removed by immersing the metal in a bath of dilute acid for arelatively brief period. Aspicklingproceeds, the dissolution of the scale and some of the base metal results in accumulation of ferrous sulfate in the bath. Eventually the pickling liquor becomes ineffective and must be wasted; disposal of this liauor has been a Droblem for manv. Years. _ T h e development of practicable processes for recovery of useful products from this waste has engaged the attention of a large number of workers, and their industry is evidenced by the eighty-odd p r w s s e s which have been proposed. Unfortunately, however, few of these processes have ever been operated succes& fully. A consideration of the nature of the problem suggests the reasons for this lack of success. A variety of acids (sulfuric, hydrochloric, nitric, bydrofluoric, phosphoric, individually and in combination) is employed, depending on the kind of product being treated; but sulfuric acid accounts for more than 90% of the tonnage pickled, and this paper is concerned primarily with sulfate liquors. Both batch and continuous picklers are wed. The spent liquor from the former normally has a composition ranging from 0.5 t o 2% free sulfuric acid and 15 to 22% ferrous sulfate; the spent liquor from the la& ter, 4 to 7% and 14 to 16%, respectively, by weight. Impressed by the logic and relative ease of recovering copperas and free acid from the waste liquor, many investigators have studied this type of process only t o encounter certain inescapable economic facts. The demand for copperas in this country can be supplied by less than 4% of the pickle liquor produced by the steel industry, and other enterprises, notably the manufacture of titanium dioxide, produce large quantities of this substance. Coppems cannot be shipped very far economically because 45% of its weight is water of crystallieation; this is an obstacle to the development of new markets. The fsct that ferrous sulfate and sulfuric acid are low cost chemicals demands that their salvage be accomplished by the simplest possible prockss and equipment. But hot, dilute sulfuric acid is very corrosive, and high equipment and maintenance costs are occasioned where it must be prooeased. The prohibitive expense of concentrating the recovered acid requires that i t be used in the plant producing it, but it is not entirely satisfactory for re-use in the picklers b e c a w of the tendency for impurities t o accumulate. Mills frequently have several picbling shops which are sometimes widely separated, and collection of the liquor for treatment in a single plant is always costly. Where production of more vduable derivatives is investigated, similar difficulties are met; furthermore no process wodd be practicable which could be operated profitably by using waste acid and scrap iron as a starting point. The tonnage of steel products which require pickling (sheets, strip, wire, tubing, tanks, small parts) has increased rapidly. From a production in the United States of less than 1000 tons of tin, terne, and black plate in 1891, the industry has grown to manufacture 4,328,000tons of these products in 19411 the latest normal year for which figures are available ( f ) . In the same year 5,746,000net tons of full finished sheets, strip, and 5at gdvaniaed products were made. An accurate estimate of the volume of
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waste. pickle liquor produced in these operations is difficult to obtain, but it is probably in excess of 6~,000,000 gallons ann& ally. The rapid growth of the industry, which is still continuing, has contributed to the dXculty of r e d i n g a satisfactory solution t o the disposal problem. Foreign producers, who have studied pickle liquor treatment intensively, are faced with au analogous situation. PICKLE LIQUOR DISPOSAL
Those concerned with stream pollntion abatement prefer to discuss waste utilization rather than waste disposal, because such a term connotes a profitable process. In the case of waste pickle liquor, however, it has alwaya seemed more appropriate to speak of its disposal because of the apparent remoteness of any possibility that a u n i v e d y feasible recovery process would be developed. As a result i t became customary to discharge the spent liquor into already polluted tidewater, streams, or lakes, eaher directly or through sanitary sewers, since this offered the most convenient and least objectionable dispossl method. Complaints against this procedure led the industry to adopt other metbods to avoid discharging the liquor into bodies of water. The expedients most frequently employed were (a) Isc gooning the liquor to permit i t to disappear through solar evapporationandseepsgeinto theearthorintoslagdumps, or (a) treating with lime. Except where streams already carry a heavy burden of other washs, especially acid mine water, very little pickle liquor reaches them directly. Wherever these disposal methods are in use, they are regarded as temporary measures which will be changed when more economical procedures are developed. Ov& a long period of years various units of the steel industry have manufactured a large tonnage of copperas from pickle liquor, but the market has been able to absorb only a limited amount of this commodity. PICKLE LIQUOR TREATME"
The various proceeaea which have been proposed for pickle liguor treatment fall into a number of classes, as follows: recovery or manufacture of (a) copperas and lower hydrates of ferrous sulfate, (b) copperas and sulfuric acid, (c) ferrous sulfate monohydrate and sulfuric acid, (d) ferric sulfate and sulfuric acid, (e) iron oxide and sulfuric wid, (f)electrolytic iron and sulfuric acid, (g) iron oxide for pigments or polishing rouge, (h) coustructiod matsial, (i) iron oxide and ammonium sulfate, and 0 misoellaneous inorganic compounds. Hodge (IS) described these claases of processes in considerable detail and included an extensive bibliography. Only the more important prmeases am outlined here. COPPERAS(7). Recovery of copperas from pickle liquor involvesnounusualprobleme. Whererecoveryof thefreeacidisnot desired, the waste liquor is heated with scrap iron to neutralize the acid, the resulting solution is settled t o remove suspended matter, and the copperas is orystallised either by evaporation or refrigeration. By carefully drying the crystals, i t is possible to produce lower hydrates, but ordinarily the drying is not carried beyond the trihydrate. Copperas-and-lime and chlorinated c o p
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1947
peras are valuable congulants for the treatment of water, sewage, and certain industrial wastes. Expansion of this market, especidly near nrw of steel production, is a possibility which has not been overlooked. COPPERASANDFREE ACID ( I ) . Where thefreeacidisrecovered for re-we, the mabeup acid is usually added to the waste liquor prior t o crystalhation. This step reduces the solubility of ferrous sulfate and increases the efficiency of copperas recovery. I n one DL'OCR~S(23)the hot liquor is spraved into the tOD of an open tower to takeadvantage oi atmosphericevaporatiDn. I n mot& the liquor is concentrated in a vacuum evaporator until the sulfuricacidreachesaconcentrationof about 28% (18); theliquor is then withdrawn, the copperas crystallized, and the mid returned to the picklers. Other improvements t o the basic procesa have been developed, bub copperas recovery offers little promise 8s a general solution of the problem because of a limited market for the compound. FEBROUS SULFATE MONOHYDRATE. The advantages of ferrous sulfate monohydrate (low water content, good storage properties, Dreferred form for sulfuric acid manufacture) have led to a numkr of p r n w w s for prepnrinu I& w m p u n d from pickJ~liquor. The Drinrinlrs uied by I C diKQrentDIWWSXJ are ( a ) evworatinn of the liquor, whose free acid bas been neutraliBed with scrap, in a direct-fired rotary dryer (22), (b) evaporation of the neutralized liquor i n a spray dryer (in, (e) vacuum evaporation until the sulfuric acid concentration approaches 78%, where ferrous sulfate is completely insoluble, and (d) autoclaving the liquor at 300' to 400'' F. And 6ltering the monohydrate without reducing temperature or pressure (23). The last two methcds provide for recovery of the free acid. Several of tbese types of process are in commercial operation. F E ~SULFATE C m n S U L ~ACID C (8). The autoxidation principle, which WBS patented in 1894, has attracted attention in recent years as a means for preparing ferric sulfate or sulfuric acid from waste pickle liquor. Althougb the proposed processes differ in some particulars, they depend upon the provision of intimate contact of air and sulfur dioxide with a solution of ferrous sulfate. It is claimed that this type of process can be controlled to produce either a strong solution of ferric sulfate or a 20% solution of sulfuric acid. Such a process has been success' fully operated in conjunction with a sewage treetment plant to provide ferric sulfate solution far use as a coagulant. If operating costs could be kept low enough, this type of procesa would find applica*ion in certajn areas.
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ACID (22). One of the first N ~ S of intelligent waste-treatment practice is to attempt to couvert a waste material into one or more other products which can be consumed in the establishment producing the waste. Conversion of waste pickle liquor into iron oxide and sulfuric acid would appear to fit this rule perfectly, and the problem of evolving a feasible P ~ O C ~ Shas S been studied extensively. One process, which has operated successfully in another field, neutralizes the FURIC
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spent liquor with iron oxide and evaprates it to dryness in a direct-fired rotary kiln. The cinder is mixed with pyrite and roasted, and the purified kiln gas iS oonverted to sulfuric acid in a vanadium contact plant. Other processes obtain sulfur dioxide by roasting a mixture of ferrous sulfate trihydrate with brown coal (20); dry copperas to the monohydrate and roast i t iu a Herreshoff furnace; spray dry the neutralized liquof and roast the monohydrate in a special furnaee (4j to which a controlled amount of excess air is added to convert tbe sulfur dioxide to the trioxide through the catalytic effect of the bot, freshly [ormed iron oxide. Manufacture of sulfuric acid from waste picble liquor, by one means or anobher, is practicable, but such a method for utilizing the spent liquor has aerious disadvantages. Sulfuric acid plants must be operated continuously and on a large scale (not lese than 50 to 75 tons of acid per day) for reasons of economy. The installations are costly and maintenance charges high. Probably no single mill produces enough pickle liquor to operate a plant of its own on a sound basis. Operation of a cooperative plant t o serve a sinale steel-producina area has been discussed. but transporration and phydiral prohim* hxvr intcrpowd obataules which a p w u tn be insoluble. Alternativelv. ic has b r a suawstcd that m o n o h y h t e be produced a t the &and this compound be processed in existing acid plants for a conversion charge, but similar difficultieshave prevented the development of a workable plan. From the viewpoint of over-all economy, manufacture of sulfuric acid from pickle liquor is not especially attractive despite its a p parent reasomhleness. ELECTROLYTIC IRON.Several processes have been proposed for therecoveryof ironfrcmpickleliquor byelectrolysis, butnone has been notably successful. Ferrous iron tends to oxidize and precipitate basic salts; frequent regulation of the acidity of tbe bath is necessary to avoid this tendency and maintain a high cell efficiency. The cwt of producing electrolytic iron requires a premium price for the product; production of silicoirons and alloys with low hysteresis losses have discouraged the develop ment o€ electrolytic iron installatiom. IRON POWDER. The increasing utility of various metsl powders for die casting has drawn the attention of several investigators t o the iron oxide obtainable from pickle liquor a8 a raw material for reduction. It has been predicted that the market for iron powder could be extended considerahly if a product of proper qudity could be produced at a price appreciably below the current $150 per ton. Preparation of the oxide in suitable form for reduction and sources of cheap hydrogen have been obstacles, but progress is being made in overcoming these prohiems. IFCON OXIDE PIQMENTS (18). Various naturd iron oxides have been used as pigments since ancient times, and similar products are mannfactured by decomposing copperas under controlled conditions. No special problems are inI volved where the pigments are produced by those skilled in the art, b u t the consumption of
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these products is relatively small in comparison with the total amount of waste pickle liquor available. CONSTRUCTIOSAL MATERIAL (18). Ferron, a constructional material with interesting possibilities, has been made from the sludge which results when pickle liquor is neutralized xith lime. The plastic material so produced is blended with fillers in a pug mill, pressed into sheets or blocks, and dried at 175" F. A plasterboard has been made whose physical performanee is reported to equal that of siniflar products on the market. Shingles have been made by incorporating an asphalt emulsion with the sludge, and performance tests indicate that they are of good quality. Development of the Ferron process was suspended during the war, but it has now been resumed and future findings are awaited with interest. A m i o x n I SULFATE (6). The obviousness of combining spent pickle liquor with coke oven ammonia to produce ammonium sulfate and iron oxide has encouraged many research workers to investigate the pract.icability of such a procedure. The obstacles to the development of a feasible process were very great-for example, difficulty of eliminating impurities in ammonia and pickle liquors to avoid contamination of the ammonium sulfate, separation of the hydrated iron oxides from the sulfate liquor, evaporation of large volumes of water, and lack of stoichiomet'ric relation between pickle liquor and ammonia. Severtheless, a number of processes were developed, some industrially; but none ever reached successful commercial operation, largely because of the costly equipment required, corrosion encountered and difficulty in producing an acceptable ammonium sulfate. A new process was report,ed recently that has been developed through the pilot plant stage. This process conibines pickle liquor n-ith raw coke oven gas in a special manner which eliminates the problem of preparing pure ammonium sulfate and precipitates the iron as an easily filterable sulfide, but complete details are not yet available. ~IISCELLASEOUS ISORGANIC COIIPOLXDS.Among the miscellaneous processes which have been proposed for utilizing waste pickle liquor, there are several that merit mention. One produces sodium natrojarosite, SatFea(OH)1?.(SO,)2, by oxidizing ferrous sulfate and hydrolyzing it in an autoclave by direct injection of steam a t 100 t,o 200 pounds per square inch. Addition of sodium sulfate and ferric oxide then results in the formation of the complcx salt, which is separated, dried, and calcined to form a soluble ferric salt for use as a coagulant (9). Attempts have been made to develop a sound process for producing sodium sulfate from pickle liquor by treatment with sodium carbonate, The cost of soda ash, the evaporation of large volumes of water, and the undesirability of iron carbonat'e as blast furnace charge have militated against the success of such a process. Similar objections have discouraged the use of caustic soda in this type of process. Ferric phosphate has been made (6)from pickle liquor by treatment with ground phosphate rock. Ferric phosphate has been claimed to be a good coagulant for water and sewage treatment. Its use in chemical treatment of sewage would have the advantage of improving the fertilizer value of digested sewage sludge. I n a process (19) based on the sulfat'e-sulfide cycle, pickle liquor is treated with barium sulfide, the hydrogen sulfide is converted t o sulfuric acid, the sludge is dewatered, reduced with coal, and leached, and the barium sulfide solution is used to treat more spent liquor, The insoluble residue is discarded. This process is open to the objections cited against the economics of sulfuric acid manufacture. Kone of these miscellaneous processes has been operated commercially. MELLON INSTITUTE RESEARCH
The steel industry has long recognized its public responsibility to abate stream pollution arising from its widespread operations.
Vol. 39, No. 5
Individual companies have conducted independent research on pickle liquor t'reatment for many years, and several costly installations were made xhich proved to be economically impracticable. The size and complexity of the pickle liquor problem convinced the American Iron and Steel Institute that the most rapid progress in solving it could be made if a separate organization were authorized to study it on an industry-wide basis. This decision was implemented in 1938 by sponsorship of a research program at Mellon Institute. The purpose of the new project was to correlate the efforts of individual companies and to conduct original research in an atmosphere free from the interruptions which frequently interfere with this type of work in steel mills. A sound foundation was laid for the research program by the first incumbent, SIr. W.Hodge, who made anexhaustive survey of the literature and held numerous conferences \vith steel mi11 officials and individuals who had studied the problem. The results of this survey n-ere published as a contribution to the Industrial ivast,e Symposium of the AMERICASCHEMICAL SOCIETY in 1939 (29). This revieff of available information disclosed that, although a large number of processes had been developed through various stages of completion, not only was there no single process that would solve the problem for the entire industry, but no practicable process existed that' could serve the needs of an individual mill, rvhether large or small. I n the face of the great effort which had been expended by many workers, the prospects for developing any radically neiv process were not encouraging. But the Mellon Institute group, while continuing its investigations of processes with potential value, considered the possibilities in hitherto untried procedureb which might he developed into processes to reduce the cost of pickle liquor disposal. This research program gradually expanded, and now practically all of the fellowship time is devoted to original studies. It has not been feasible, because of the war, to make, pilot plant evaluations of the proceases which originated a t hIellon Institute. For this reason publication of results has been withheld until complete descriptions can be presented. The processe5 wit,h the greatest potentiality are outlined here with the reservation that they are, for the most part, laboratory developments which may be no more successful than many of those which have appeared in the literature. IROSSULFATES IN CEJIEST (14). The setting time of portland cement is regulated by grinding 2 to 3 5 of gypsum, CaS04.2H0, with the cement clinker. Laboratory investigation has indicated that iron sulfate, on an SO3basis, can be substituted for gypsum. Experimental cements cont,aining iron sulfate compared favorably with commercial portland cements in setting time and in tensile and compressive strengths. Test briquets made from samples of the experimental cements which had been stored for five years showed no appreciable diminution in strength. If this use for ferrous sulfate were adopted generally, it would consume more of the compound than i,s produced as waste pickle liquor. There are, unfortunately, a number of serious drawbacks to this apparently simple method of utilizing pickle liquor. The procedure has not been studied on a commercial scale, and, until this is done, there is no assurance that, the laboratory results can be duplicated in practice. ;Ilthough the cream to light brown color of cement cont,ainingiron sulfate would be advantageous for highway construction, contractors and consumers would have to be converted to the use of the new material. Amendment of the specifications of the American Society for Testing Materials would be necessary before the substitution would be permitted. The most significant objection, however, is the improbability that sulfate in the form of copperas could be purchased a t so low a price as sulfate in the form of gypsum. DIFFERENTIAL SOLUBILITY (15 ) . Certain water-soluble organic solvents have the property of reducing the solubility of moderately soluble inorganic salts. This principle was applied to
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waste pickle liquor, and a large number of aolveuts were investigated. Acetone was h d y determined to be the moat desirahle &gent for the purpase, and a practicable p r o 6 ess was devised. The unit operations involved are rather simpIe in themselves. Equal volumes of acetone and pickle liquor are mixed thoroughly, the 5 e l y crystalline copperas is separated in a basket centrifuge, and the acetone is recovered from the mother liquor by fractionation. Practically all of the free acid is recovered in the still bottoms which, when made up to pickling strength with fresh acid, will contain less tbsn 2% of ferrous sulfate. ' An experimental CUNe of copperas precipitation against acetone volnme shows that the curve h t t e n s rapidly after the proportion of acetone exceeds 50%. The yield of copperas is increased moderately by cooling the mixture t o 0" C. The copperas recovered by this method has the property of drying more rapidly and to a lower final water content than that recovered oonventionally, and monohydrate is acetone entrsjne salvaged, and th r recovery system. A laboratory study of the free-ecovered in this process indicates that it is suitablefor &e in the Dicklem Dirkline ~~. Si* r--~-and recovery cyclea were made in which the operations of batch pickling were simulated, and there was no tendency for impurities t o sccumulate in the liquor. The ,recovered acidappeared to be the equivalent of fresh acid as a pickling agent. This proceas has the advantage of recovering 95% of the ferrous sulfate and substantially all of the free acid in waste pickle liquor. T h e recovered acid solution contains a lower proportion of ferrous sulfate than similar solutions from refrigeration processes. On the other band, the process depends upon a relatively expensive, highly iiammahle solvent of which not less than 99.5% must, be recycled. FERRIC CILIARIDEAND SODIUM SULFATE. The desirability of converting the iron in waste piCklQliquor into compounds more valuable than copperas led M the development of afeasiblr proress-for producing saturated ferric chloride solution and pure anhydrous sodium sulfate. Where the spent liquor is treated with an exceas of sodium chloride, a double salt of iron and sodium sulfate precipitates. Glauber salt, N&304.10H20, is separated from the mixture by successive crystdhations, and dunng these operations a ferrous chloride solution is produced from which a s d amount of residual sulfate is precipitated by addition of calcium chloride. The ferrous chloride solution is chlorinated and evaporated to a 60% solution of ferric chloride. At this concentration substantidy d of the excess sodium chloride precipitstes; it is filtered 05 &d returned to the process. At 60" C. Giauber salt melts in its water of c&din;ation and precipitates anhydrous sodium sulfate. The sodium sulfate is filtered off and the mother liquor recycled. This is a practicable process for producing a saturated'solutiou (60%) of ferric chloride, which could be p r w s e d to the anhydrous salt, snd anhydrous sodium sulfate containing not more than 0.05% of iron and 0.15% of,sodium chloride, The process has the disadvantage of requiring a numher of filtrations and refrigerations which must be carefully controlled for best results. The demand for pure sodium sulfate and the increasing usefulneas of ferric chloride may, in t i e , uuprove the commercial potentiality of the proceea. ~
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Continuous Strip Pickling Lines
This country has large reserves MANQANESE CONCENTRATE. of low grade mangaaese ores but practically none of sutfciently high grade for conversion to ferromanganese, an essential product required for manufacturing steel. Tbeshortage of manganese was acute in the early days of the war, and an investigation was begun €0 determine whether the reducing property of ferrous sulfate oould be employed to concentrate the manganese in low quality pyrolusite ores. This study resulted in a process of some merit. Low grade ore is bd-milled 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 which precipitates is recovered as a compound of high purity. The ferric iron in the filtrate b precipitated by controlled trenlmeut with lime slurry. T L hydrated ferric oxide recovered in this step is suitable lor sintering for blsst furnace burden. The filtrate is treated with more lime to precipitate the manganese, which is filtered o f f , washed, anddried as the main product. The filtrate from this step is substantidy a solution of calcium chloride; it is reduced by evaporation and returned to the process. This proceea produces a manganese concentrate containing upwards of 60% ma-we and two by-products of low value. Its principal d i d v a n t a g e is one of geography; most of the suit-
ablemanganeseoresllreminedatagreatdistancefromtheoenters of steel manufacture. MAGNESIA.The economical recovery of magnesia from dol* mite is a problem which has engaged the attention of many research workers. The advantage of being able touse a waste product to effect such a recovery suggested that pickle liquor might be suitable for the purpose, and a rather Simple process was evolved. The sulfates in pickle liquor are converted to chlorides by treatment with calcium chloride, and, by we of the proper technique, pure gypsumis atered 05. The iron is preoipitated.by controlled treatment with dolomitic lime slurry, and the precipitate is discarded. More dolomitic lime is then added t o the 6ltrate to precipitate the magnesia, and the calcium chloride brine remaining is evaporated and recycled.
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I n the laboratory a magnesia of 91 to 9iycpurity was prepared by this process. The chief contaminant of the magnesia was calcium oxide, and this compound could be leached nith water to improve the quality of the principal product. The hydrated iron oxide which is precipitated in the iron removal step has a high sulfur content that cannot be reduced xithout impairing the quality of the magnesia. Evaporation of the large volume of wash water required for recovery of calcium chloride is a disadvantage. It is possible that further research n-ill improi-e the economics of the process. h f h r O s I V M SULFATE. The obstacles to the development of a sound process for combining coke bven ammonia,and waste pickle liquor did not deter the Mellon Institute group from attacking this problem, because the advantages of a successful solution could be great. After a lengthy study of t,he factors involved, a process was developed which appears to have overcome the chief difficulties which viere encountered by prior workers. Purified ammonia and pickle liquor are fed continuously to a reactor of special design in which the precipitated ferrous hydroxide is oxidized under carefully controlled conditions to ferroso-ferric oxide; by this means the iron is precipitated completely. The magnetic iron oxide produced in this manner settles rapidly (95% in 5 minutes), and it can be separated from the ammonium sulfate liquor by continuous decantation. Separation of the iron oxide by filtration was the operation nhich defeated many of the previous processes. Based upon small scale pilot plant studies, the economies of the process appear to be sound. The obvious economic advantage of the process is the ability to substitute the sulfate in t,he pickle liquor for the sulfuric acid used in the amGmoniasat'urators to manufacture ammonium sulfate. SEUTRALIZATIOS PROCESSES. Regardless of the success of pickle liquor utilization processes, their economics are such that t'hey must be operated on a very large scale. This means that the smaller producers probably will allmys have t o neutralize their liquor if other means of disposal are impracticable. Extensive investigations (10, 11, 12) of neutralization processes have btcn made to provide the greatest possible economy for this type of treatment, It costs roughly a cent per gallon to treat waste pickle liquor with lime. Limestone is usually a cheaper source of alkaline agent, but treatment with this material has not been found frasible because the large aggregates used soon became coated with a layer of calcium sulfate, which reduced the reactivity to zero. Pulverized limestone, holvever, should not suffer from this disadvantage, and investigat,ion disclosed that the iron in pickle, liquor can be precipitated conipletely by pulverized limestone provided it is approximately 200 mesh in size (the so-called mine dusting grade) and the reaction mixture is aerated. Unfortunately, calcium carbonate does not proride a SUEciently high pH to precipitate ferrous iron directly, and it is necessary to depend on oxidation and hydrolysis to complete the reaction. According to the reactivity of tile limestone, from 2 t o 8 hours are required for complete precipitation of the iron, and this mixing period is too long for most mills. The pulverized stone, however, reacts with free acid quite rapidly, and, on the basis of this fact, a split limestone-lime process v a s developed n.hereb?the free acid is neutralized with limestone and the iron precipitated with lime slurry. The process ]vas proved on a commercial scale and is showing attractive economies in the one mill in which it has been installed. The process is practicable only nhere pulverized limestone of the proper grade can bc purchased a t a!on-cr cost than its calcium oxide equivalent as quicklime. This means that pulverized stone a t approximately 5S7Gof the price of quicklime is the break-even point. Only high calcium limeetone is suitable for this process; stones containing more t,lian 2Yc of magnesium carbonate are inefficient, and dolomitic stone is completely un.5atiefactory.
Vol. 39, No. 5
Th(, current shortage of high calcium lime suggmted ii study of the less desirable dolomitic lime to establish a procedure for its most effective utilization in pickle liquor treatment. This study showed that dolomitic limes could be made to approach the cffectivencsf of high calcium limes if a moderate excess were uscd, if the liquor were treated hot, and if aeration were provided. Dolomitic lime has a higher basicity per unit Tveight than high calcium, and thi- permits the use of a n excess of the agent. Usually no prohlim is involved in treating the liquor soon after it is discharged from the pickling tub8, and this conyerves its heat. Aeration can he provided by installing the proper t,ype of agit:ator iri the neutralinttion tank. Further studies are in progress on a variety of other ncutrslizing agents Tyhich are not ordinarily considered for use in piclilt, liquor. These results nil1 be combined \i.ith those already obtained in a complete economic analysis of the neutralization process. STAISLESS STEELPICKLE LIQUOR. The research program ha? been almost completely occupied wit,h investigations of sulfate, liquors, but attention is being increasingly given to treatment of !Taste liquor from stainless steel pickling. These liquors usually contain the salts of iron, chromium, and nickel in an aqueous solution of nitric and hydrofluoric acids. The relatively high value of the compounds dissolved in such liquors indicates thct economic practicability of a recovery process. Preliminary study has shown that pure calcium nitrate and a sludge of metal oxides can be obtained by treatment of the liquor with high calcium lime. The nitrate finds a good market in the fertilizer field, arid the oxides can be sintered for recharging to t,he furnaces. Separation of the sludge from the calcium nitrate liquor is rather difficult, but cooperative study has shown that continuous ccmtrifugation may be applied successfully. LITERATURE CITED
(1) .igde, G., Stahl u . Eisen, 57, 789-93 (1937) ; Droof, J., I b i d . , 57, and Cochran, R. S.,U. S. Patents, 838-9 (1937) ; Marsh, H. S., Reissue 15,119 of 1,369,451 (1921), 1,450,216 (1923), and 1,589,610 (1926); Zahn & Co., G.m.b.H., French Patents i23.484 (1931) and 808,033 (1937). (2) Ani. Iron and Steel Inst., Annual Statistical Rept., 1941. (3) Clark, L. F., private communication, 1938. (4) Clarkson, D. L., private communication, 1938. (5) Coleman, H. S., and Coleman, F. H., U. S. Patent 2,063.029 (1936). (6) Da,vies, C., Jr., U. S.Patent 1,942,060 (1934); Falding, F. J., I b i d . , 961,763-4 (1910); Falding, F. J., and Cathcart, TI-. It.. Brit. Patent 11,364 (1910); Harris, A . W., U. S. Patent 1,994,702 (1935); Sierp, F.,Stahl u . Eisen, 58, 491-7 (1938); Sperr, F. IT-., Jr., U. S. Patents 1,928,510 (1930), 1,983,320 (1934), and 1,986,900 (1936). ( 7 ) Diescher, S.E., I b i d . , 1,023,458 (1912). (S) Emmens, 9. H., I b i d . , 513,490 (1894) and 543,002 (1595); Iieyes, H. E., U. S.Bur. Mines, Bull. 321 (1930); Lyles, J. E., J . Am. r a t e r Works Assoc., 26, 1214-18 (1938). (9) Hoak, R. D., Science, 101, 940-45 (1945). (10) Hoak, R. D., Lewis, C. J., and Hodge, JT. IT., IXD.C S G . CHmf. 36, 274-8 (1944). (111 Ibid.. 37. 553-9 11945). (12) Iloak, R . D., Lewis: C. J., Sindlinger, C. J., and Klein, B., ISD. ESG.CHEM.,39, 131-35 (1947). (13) Hodge, W.IT.,I b i d . , 31, 1364-81 (1939). 114) Hodge, IT. IT., 6. S.Patent 2,307,270 (1043). (15) I b i d . , 2,322,134 (1943). (16) Mantius, Otto, F i r e arid T i r e Products, 13,585-9 (1938). (17) Rearell, J. A,, J . SOC.Chem. Ind., 47, 347-61T (1928). (18) Rentschler, AI, J., Iron Steel Engr., 16, 52-62 (1939). (19) Robenstein, L., C. S.Patent 2,055,419 (1936). (20) Sierp, F., Stahl u . Eisen, 58, 491-7 (1938). (21) Spmgler, S. F., Blast Furnace Steel Plant, 23, 319-21 (1W5); Chem. d. M e t . Eng., 42, 13941 (1935); Spangler, S . F., and Titlestad, K.,Wire a n d Wire Products, 13,591-4 (1938). (22) Stevenson, E. P., Zi.9 . Patent 1,515,799 (1924). (23) SThetzel, J. C., and Zimmerman, R. E., I b i d . , 2,005,120 (1935). I ~
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PREBEHTED before the Industrial Waste Symposium a t the 111th Meeting of the .IIIERICAS CHELIICAL SOCIETY, Atlantic City, ii. 3.
