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3. Cooperation with trade organizations and pollution control agencies endeavoring to solve general waste treatment problems for industry, rather than attem ting to avoid waste treatment, employing homemade rnakes&fts, or buying off lower riparian objectors. 4. Removal of waste from natural waters, not only to benefit recreational and domestic water users, but also other industrial users and ultimately all industry.
Literature Cited (1) Buswell, A. M., Alexander’s “Colloid Chemistry”, Vol. IV, p. 693, New York, D. Van Nostrand Co., 1937. (2) Fales, A. L., Sewage Works J . , 9, 970 (1937). (3) Geyer, J. C., and Perry, W. A., “Textile Waste Treatment and Recovery”, Washington, Textile Foundation, Inc., 1936. (4) Goodrich, R. B., master’s thesis, Wesleyan Univ., 1938. (5) Hoover, C. R., State Water Commission Conn., 5th Biennial Rept., 1934.
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(6) Hoover, C. R.. Aaronson. H. J., and Deitch, M . , Div. Water, Sewage, and Sanitation Chemistry, A. C. S., Rochester, 1937. (7) Hoover, C. R., Phelps, I. K., and Jones, L. G., Ibid., Milwaukee, 1938. (8) Miles, H. J., and Porges, R., Sewage Works J., 10, 323, 856 (1938). (9) ‘Raab, E. L., master’s thesis, Wesleyan Univ., 1937. (IO) Rudolfs, W., and Setter, L. R., Sewage Works J.,9, 549 (1937). (11) Snell, F. D., Am. Dyestus Reptr., 26, 730 ,1937). (12) Snell, F.D., Iwn. ENG.CHEM.,29, 1438 (1937). (13) Spoehr, H. A., J . Am. Chem. Soc., 46, 1494 (1924). (14) Theriault, E. J., Butterfield, C . J., and McNamee, P. D., Ibid., 55, 2012 (1933). (15) Trice, M. F., Industrial Waste Survey, State Board Health, Raleigh, N. C., 1931. (16) Urbain, 0, M., U. S. Patent 1,967,916 (1934). (17) Vollrath, H. B., Chern. & Met. Eng., 43, 303 (1936). (18) Weston, R.s., J. Boston Soc. civil Eng., 16, 358 (1929); IKD. ENG.CHEM.31, 1311 (1939).
Wastes Problems in the Nonferrous Smelting Industry ROBERT E. SWAIN Stanford University, Calif.
N
ONFERROUS smelting operations have traditionally been accompanied by a great waste of by-products. These have embraced many substances, both metallic and nonmetpllic, which because of their relatively small quantity or their high degree of dispersion in enormous volumes of exit gases, of slag, or of refinery slimes, were long regarded as beyond the bounds of economic recovery. But that day is passing, as even a superficial survey of the advances of recent years cannot fail to reveal.
Sulfur Here sulfur must take first place. It is not only a waste product which is stupendous in the gross amount discharged from smelting operations the world over, but it is probably the world’s greatest trouble maker for the metallurgical industry. It takes first place in smelting progress in the last ten years as a result of developments through which i t is being recovered from waste gases of high dilution and sent into useful channels. We are actually in a new era so far as the sulfur problem in the smelting industry is concerned. This remarkable attack upon the problem found its initial impulse in a recognition by the industry a t large that here was a menace to agriculture and forestry which must be put under control. In more recent years, the great economic loss being suffered and the possibility of the profitable recovery of sulfur dioxide in waste gases have spurred efforts to meet the situation. This is now a dominant motive in countries like Germany with no native sulfur, little iron pyrites, and an urge toward national sufficiency. Like every other movement it passed slowly through many initial stages. As far back as 1910 sulfuric acid was produced on a large scale from the smelters a t Ducktown, Tenn., as a remedial measure, and soon afterward a sulfuric acid plant was installed a t Anaconda, to be followed by similar installations a t other points. Yet the surface was hardly scratched by these developments, for two dominant reasons.
One was a limited market for sulfuric acid, especially in the great western smelting areas. The other was the fact that many smelting operations, especially with lead ores and to a degree with copper ores, did not yield sulfur dioxide in concentrations sufficient to permit economic recovery. The prevailing concentrations of 0.5 to 2 per cent in enormous volumes of waste gases were not regarded as recoverable, even in the wildest flights of the imagination. Thus the problem stood practically up to the threshold of this decade. Then two new ideas took shape, one the outgrowth of the other. The first was to strip the sulfur dioxide from these dilute gases by means of absorbents, then to release it and make it available in more concentrated form. The other was to produce elementary sulfur from the concentrated sulfur dioxide and thus to tap a much wider market. It is impossible here to give an adequate review of the work done in these directions during the last seven or eight years when the major developments have taken place. Many of the investigations upon which they are based are superb examples of the application of physical-chemical principles to a complicated problem. From this work three outstanding processes have emerged; all of them are today in successful operation on a large scale on waste gases from smelting operations. At the great lead and zinc smelter a t Trail, Canada, the Consolidated Mining and Smelting Company has developed and put into successful operation a process in which a solution of ammonia is the primary absorbent. The waste gases are sent through scrubbing towers, where the absorption of sulfur dioxide is continued until a strong solution of ammonium bisulfite, with some normal sulfite, results. This is then treated with sulfuric acid to form ammonium sulfate and release pure sulfur dioxide, the former being sent to the fertilizer by-product plant. The sulfur dioxide is then sent through reducing furnaces, fired with coke, to produce elementary sulfur. This plant has a production capacity of nearly 200 tons of sulfur per day. The recovery of sulfur dioxide from the gases treated is practically
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complete. It operates equally well on lead plant gases which carry only from 0.5 to 1 per cent sulfur dioxide as it does on the richer zinc plant gases. If sulfur productionis too heavy, some of the pure sulfur dioxide produced can be used t o enrich the zinc plant gases for more efficient operation of the sulfuric acid plant designed to handle them. Or if sulfuric acid production is too high, zinc plant gases may be by-passed to the ammonia absorption system and their sulfur dioxide converted to elementary sulfur. This process has another notable advantage. It is flexible to the extent that it may be interrupted at any time by dampering the waste gases or any part of them t o the exit stack, and again go into immediate operation whenever that is desired. Accordingly, wherever conditions permit its economical operation, and there is a market for the product, i t can be used effectively for smoke control purposes by reducing the emission of sulfur dioxide during periods of the day or night when wind and weather conditions are unfavorable to smoke dispersion and there is risk of injury to plant life in neighboring areas. This admirable process faces one limiting factor. It is contingent upon a favorable market for ammonium sulfate. This, however, may be met by use of a process carried through the pilot-plant stage a few years ago by the American Smelting and Refining Company a t Garfield, Utah, and later in modified form fully developed for use as a stand-by process, a t Trail, when the ammonium sulfate market is low. If a solution of ammonium bisulfite is heated, sulfur dioxide will be released and the former will revert to the normal salt. This reaction may be continued until ammonia begins to come off, but in practice it is carried only to the point where about 14 per cent of sulfur dioxide is removed, owing to the higher heat consumption in the later stages. The resulting solution is sent back in circuit to take up another load of sulfur dioxide. Upwards of 3 per cent of the sulfur dioxide is oxidized in the process, and in time the concentration of ammonium sulfate requires attention. At Trail the solution is then removed, the bisulfite decomposed by sulfuric acid, and the entire crop of ammonium sulfate recovered by evaporation. At Garfield successive small accumulations of ammonium sulfate are removed by chilling the solution, and the crystallized product is sent to a separate unit, dissolved in water, and treated with lime, and the ammonia liberated is sent back without appreciable loss into the circuit again. Another excellent process is known as the sulfidine or Lurgi process, in which a water suspension of aromatic amines, especially toluidine and xylidine, is the absorbent. This was developed by the Gesellschaft fur Chemische Industrie in Base1 in cooperation with Metallgeschellschaft in Frankfort. It has a high absorption capacity for sulfur dioxide and is applicable to gases with very low concentrations of sulfur dioxide. When the absorbent is heated to 80-100" C., pure sulfur dioxide is expelled, and the absorbent, which slowly forms a homogeneous solution with water as absorption progresses, separates again to form an insoluble layer. This process is now in successful operation and is one of high efficiency. Finally, there is the process of Imperial Chemical Industries Ltd., which is handled under joint agreement with Bolidens Gruvaktiebolag of Sweden. The former contributes particularly the absorption process, based upon the use of basic aluminum sulfate solution, and the latter a process for the reduction of pure sulfur dioxide to elementary sulfur. As in the other absorption processes the absorbed sulfur dioxide is removed by heating the solution. The reduction to elementary sulfur makes use of the reducing gases from cokefired furnaces as the chief agent in a catalytic reduction of the sulfur dioxide. This process is in operation on a large scale a t several points. It is applicable to metallurgical gases of almost any sulfur content, and in ordinary operation dis$chargesterminal gases so low in sulfur dioxide as to be wholly
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negligible as a possible nuisance. At the Ronnskar plant in Sweden about 25,000 tons of sulfur were being produced annually by the Bolidens reduction process. Some promising work has been done in an effort to find a suitable inhibitor for the troublesome oxidation of sulfur dioxide to sulfuric acid in all these processes. Methylene blue, tannic acid, pyrogallol, and other organic compounds have been found effective, but none has yet been practicable for commercial use. This is a problem which awaits solution. The relatively high price of coke is a n important factor in the present processes for the reduction of sulfur dioxide to sulfur. This may be a hazardous prediction, but it seems probable that the coming decade will see the direct reduction of sulfur dioxide when present in concentrations of 5 per cent or more in roaster gases by use of natural gas, which is now finding a place in so many industrial operations. This would permit more precise control of operating conditions since the gaseous phase prevails throughout the process; there would be no fly ash to contaminate the product; and the cost factor would be much lower. All signs point to a bright future for pure sulfur dioxide in industry. The way is now open to cheap commercial production. It submits to tank-car transportation in liquid form and has many advantages over burner gas for the pulp industry and other chemical processes where it is directly used. Although it may be transported easily, its consumption will probably be restricted to a radius of 400-500 miles from the point of production. Beyond those limits i t would hardly be able to compete with elementary sulfur. The problem of waste sulfur dioxide is not yet fully solved, but this much may now be stated, visionary as it appeared ten or fifteen years ago: These recent achievements through which enormous volumes of waste gases from smelting operations can be treated to recover sulfur dioxide economically endow industry at favorable centers throughout the world with the means for adding immensely to the supply of sulfur provided there is a market sufficient to absorb the product. As a rough indication of what this means in this country alone, the emission of sulfur as a waste product from smelting operations today probably exceeds the total annual output of elementary sulfur from the deposits of Texas and Louisiana.
Arsenic Sulfur and arsenic not only stand together a t the head of the list of objectionable waste products in smelting operations, but they are old side partners. Not all sulfide ores contain arsenic, but wherever arsenic has been a source of trouble, sulfur has been present to aggravate it. Owing to the volatility of the metal and its trioxide, arsenic is found in the flue dust and gases from all roasting operations in which it is a component of the charge. The finely divided condition, usually 1-3 microns particle size, in which it goes over to the solid phase in the cooler sections of the flue system, made settling chambers ineffective in its recovery, and a large proportion found its way out of the stack. Thereafter, however, its small particle size was a great advantage, for the rate of subsidence was extremely slow and atmospheric dispersion over an extensive area resulted. That was true a t Anaconda nearly three decades ago where many years of effort to meet a baffling situation, involving a daily emission of 25 to 30 tons of arsenic trioxide, culminated in complete recovery and a t once put this country far out in front in world production. In the last few years a similar problem has faced the splendid new Ronnskar plant on the small peninsula which juts into the Gulf of Bothnia on the northern coast of Sweden. That plant treats the auriferous copper ores from the newly discovered Boliden deposits. Here is an ore body of great extent running around 2 per cent copper, 10.8 per cent arsenic, and
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PART OF THE METALLURGICAL AND CHEMICAL PLANTSOF THE CONSOLIDATED MINING & SMELTING COVPANY OF CANADA, LTD., TRAIL,
u. c.
The lead and zinc plants are in the background and the sulfuric acid and sulfur plants in the center foreground with large blocks of stored sulfur t o the left. The sulfuric acid and sulfur are utilizing the formerly wastedsulfur dioxidegas.
30 per cent sulfur. Large-scale operations a t once brought sulfur and arsenic to the front as important problems to be solved. Reference has already been made to the recovery of sulfur. Partial roasting removes all of the arsenic as the trioxide. When the gases are cooled and subjected to electrical precipitation, the recovery is practically complete. Already this enterprise has made Sweden the world’s largest producer of arsenic, with an annual output of around 50,000 tons, and with nearly 200,000 tons in storage 2 years ago. This overproduction led to an extensive program of research designed to stimulate consumption a t home and abroad. Arsenical wood preservatives have a promising outlook, and arsenical cements, alloys, and new insecticides are among the subjects under investigation.
Cadmium and the Rarer Elements Cadmium now has an established place in the metal industry with an annual domestic production of over 4 million pounds, which is half the world’s production. The former has quadrupled in the last seven years. The only source is a by-product once thrown away from zinc smelter flue dust and electrolytic plant residues. It is now produced a t a dozen or more smelters in this country and Canada, and has a growing use in bearing metals alloys, cadmium pigments, and metal plating. Thallium is one of those elusive rarer metals which generally escaped notice in smelting and refining operations. The flue dust and electrolytic slimes studies of recent years have revealed that, although i t often occurs in small amounts, chiefly in zinc ores, its presence is almost invariably associated with cadmium. Practically all ores which contain cadmium carry thallium in varying amounts, and in smelting it goes along with cadmium in the fumes and deposits in the same areas of the dust recovery system. It is recovered by distillation with carbonaceous material from retorts and separation from cadmium by electrolytic deposition of the latter. It finds use as a rodent killer, in the glass and photographic industry, and for medicinal purposes. Similarly, other rarer elements such as bismuth, antimony, indium, vanadium, selenium, and tellurium are recovered from the flue dust or electrolytic slimes from smelting and refining operations, but no detailed reference here is possible. The
search for some of these rarer elements has been stimulated greatly in recent years owing to the research on alloys.
Slag One of the great waste products of metallurgical operations is slag. Two lines of attack upon this material have been made in recent years. One is to reduce its metal values through better control of furnace operations or by slag treatment. As an illustration of progress, a t Trail lead blast furnace slag, carrying around 4 per cent lead and 16 per cent zinc, has lately been subjected to retreatment by fuming it in specially designed furnaces. As a result of the recoveries of volatilized zinc and lead, they now turn out a waste slag practically free of lead and with only about 3 per cent of zinc. The other has been the use of slag as one of the raw materials for the production of mineral wool. This is a new industry which in ten years has risen to an annual output of around 750,000 tons. The wooly fluffy material which every visitor to Kilauea, Hawaii, sees floating in the air or clinging like moss on foliage is the result of jets of steam spouting through the molten lava. The natives had a tribal belief that when the Goddess Pele became angry she pulled out her hair in handfuls and tossed it out of the crater. It is now a product of the industry of man who has not departed very far from the method of Kilauea. But refinements are now yielding masses of interlaced fibers from 5 to 20 microns in diameter. This is a product of wide use in the advancing program of house insulation, refrigeration, and air conditioning. Time does not permit a review of important recoveries a t the other end of the line, preliminary to the smelting process. Here flotation has entered the program of conservation with an impressive showing. For example, molybdenum has been known to be present as the disulfide in the great ore body a t Bingham, Utah, to the extent of about 0.04 per cent in the crude ore. It could not be mined selectively, and in flotation i t went along with the copper and ultimately out with the slag a t the smelter. Recent investigations have shown that if the concentrates are heated to vaporize the flotation oils, new flotation reagents may then be used to depress the copper sulfide and float off the molybdenum. Under normal operation, from 25,000 to 30,000 pounds of molybdenum disulfide are now being separated daily, which takes second placein
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world production of this metal. Another valuable contribution has been the removal of iron pyrites from other sulfide ores. This is now standard practice. It reduces the load on smelting operations, often by as much as one half, and makes a similar reduction in the sulfur emission, which in many centers has gone a long way toward relieving injury by sulfur dioxide. It is also an important medium in conservation since the huge accumulations of rejected iron pyrites now being made may be of much value to succeeding generations as a source of iron and of sulfur.
Electrical Precipitation No survey would be complete without referring to the great contribution which the electrical precipitation process devised by Cottrell has made to the waste problems which have beset smelting interests and have led to enormous losses in the past. Sulfuric acid mists are no longer a menace; toxic lead and arsenic fumes have been put under practically complete control; many of the rarer metals on the way out in exit gases have been recovered; and dust losses of the common metals of around a thousand tons per day are being recovered daily by it. The treatment of several billion cubic feet of gas is involved. Its efficiency is high; i t picks up fume, which because of its small particle size of a few microns or less cannot
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be collected by settling, as well as dusts and acid mists of larger particle size; and it can be operated efficiently over a wide range of temperature. Another valuable application in waste recovery is in the clean-up of suspended particles from waste gases as one of the preliminaries to subsequent operations, such as the removal of fly ash from sulfur-reducing furnace gases before the sulfur is conderised, or the removal of fume and dust before the conversion of sulfur dioxide from roasting operations to sulfuric acid. It has thus served uniquely a purpose which has been indispensable in the recovery of smelter waste and is today a contribution of outstanding importance to the whole program of advancement in that field. One other development of the past decade or so deserves to be put among the first, instead of the last, in this review. This is the new attitude of the smelting industry toward research. It is rapidly becoming by-product conscious. One finds now throughout the larger smelting organizations research groups and equipment of high rank, and senses in the management from the highest officials down, a feeling of pride in their research program. That means much for the future of the industry, not only in relation to its own dividends and relief from much bitter litigation, but to the whole program of conservation in the world a t large.
Waste Prablems in the Petroleum
Industry J. BENNETT HILL Sun Oil Company, Philadelphia, Penna.
The petroleum industry has cooperatively studied its pollution problems. Oil in effluent waters is removed by a specially designed gravity separator making use of the principles of low-velocity uniform distribution, film rupture and coalescence, and continuous skimming of oil, and giving effluents containing only 10-15 p. p. m. of oil. Acid sludges are extensively worked for sulfuric acid recovery. Soda sludges from washing gasoline must be neutralized and freed from odoriferous compounds before discharge. Hydrogen sulfide recovered from the crude and cracked gases has become an important by-product and is largely converted to sulfuric acid. No oil fractions are wastes, since all have at least a fuel value. The trend is to remove as many of the products as possible from the common fuel class.
T
HE petroleum refining industry of forty years ago had no waste problem. Refineries were of necessity located near a water supply, and the same water supply became a convenient carrying medium for waste acid and soda, oil emulsions, and even the totally useless oil fraction which we now know as gasoline. Fortunately the disposal of gasoline, for other reasons, is still not a problem, but through the increase in the size of the industry and the awakening of public conscience, the disposal of the other wastes has presented a series of difficult problems. To cover the pollution angles the American Petroleum Institute maintains a standing Committee on Disposal of Refinery Wastes, which has done a splendid job of classifying problems and recommending solutions (1). Oil Since this paper deals with the oil industry, we will first consider problems arising from oil itself. Since any petroleum fraction, however unsalable, has a definite fuel value a t the refinery, there are no problems connected with the disposal of anything which is even mostly oil. The refinery boilers and still furnaces adequately handle this problem; the only thing to be considered is the collection of oil and prevention of pollution. This subject, however, constitutes a real problem, since refinery effluent water must be cleaned to t,he point where the oil concentration is too lorn to show
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