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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Vol. 9 , No. 7
ORIGINAL PAPERS RESULTS OF RECENT INVESTIGATIONS OF THE SMELTER SMOKE PROBLEM' BY A. E. WELLS Received June 1, 1917
At many of t h e smelting plants throughout t h e United States, t h e smoke problem continues t o be one of considerable importance. I n fact, due t o t h e increased tonnages of ores being handled during t h e last two years a t many plants, some damage has been done b y smoke where formerly no serious smoke troubles were encountered, and t h e problem in those places has assumed serious proportions. Elsewhere t h e problem has become important mainly because a greater number of those people engaged in agricultural pursuits in t h e vicinity of smelters have heard through various sources t h a t t h e smelter smoke might be injurious t o crops a n d t o live stock; thus, whenever any adverse condition arises in districts contiguous t o smelters, i t has become t h e custom t o blame t h e smelter smoke first, before trying t o determine t h e true causes. Careful investigations in many cases have proved t h a t t h e causes were wholly foreign t o t h e smelter smoke. Whether actual damage has been on t h e increase, due t o increased smoke output, or whether there has been a greater tendency on t h e p a r t of t h e farmers a n d stock raisers t o lay their natural crop a n d stock troubles a t t h e door of t h e smelter smoke, t h e result has been t h a t a t many plants i t has become necessary for t h e companies t o enter upon careful investigations t o determine t h e facts. Believing t h a t a n outline of these investigations as carried out b y t h e lead and copper smelting companies would be of interest t o those who are directly concerned with t h e metallurgy of zinc, a n attempt has been made in these pages t o present this outline in as brief a form as possible. As metallurgist on t h e smoke problem for t h e United States Bureau of Mines, t h e writer has been associated directly or indirectly with nearly all these investigations, and in many cases has assisted in t h e work. Cooperation with t h e smelting companies is possible in nearly every instance, because it is evident t h a t t h e companies wish t o have t h e t r u e facts determined concerning t h e conditions in t h e zones around their plants. T h e y are ready t o face squarely a n y facts so determined which might be considered even detrimental t o their interests, a n d are showing a willingness t o go as far as practicable toward t h e ultimate solution of t h e problem b y t h e elimination of t h e substances t h a t are found t o be t h e causes for damage. I n general i t might be stated t h a t t h e companies are ready t o meet t h e situation fairly, and t h a t wherever there is a possibility of injury resulting from their present methods of operatian, they are ready t o make decided improvements. These improvements often involve expenditures of money beyond those yielding any financial return.
AS this can be b u t a brief presentation of some of t h e most important features of t h e smoke problem, i t will be necessary t o dismiss with a few words any consideration of t h e dust a n d metallic fume element of t h e smoke, as this element is of minor importance. 'DUST
AND
METALLIC
FUME
E L E M E P U ' T OF
MINOR
IMPORTANCE
The investigations t h a t have been conducted during t h e last few years, including those of t h e Selby Smelter Commission,' American Smelting and Refining Co., etc., have proven conclusively t h a t as far as damage t o vegetation is concerned, dust a n d fume particles or acid mist are practically negligible quantities. The effect of dust a n d f u m e particles upon animal life is another matter. K O doubt some injury has been done and may now be done in certain places t o animal life by t h e toxic salts in t h e smelter emanations where there have been large accumulations of these toxic salts on vegetation. Generally speaking, however, wherever t h e amount of dust and fume being emitted is so large as t o constitute a menace t o live stock in t h e community, i t is found t h a t t h e value of t h e solids being lost would p a y a reasonable return on t h e investment necessary for installations t o recover them, without a n y damage consideration being involved. I n most cases i t is a comparatively easy matter t o recover t h e greater portion of t h e solids, a n d at t h e present time there is no excuse for a smelter turning large amounts of t h e solid constituents of t h e smoke into t h e atmosphere, especially if those solids are known t o be causing injury t o live stock. SULFUR DIOXIDE
PROBLEM
MOST I M P O R T A N T
The most important problem, therefore, is t h e sulfur dioxide problem. At many plants where large quantities of sulfide ores are being handled serious efforts are being made t o utilize t h e waste sulfur dioxide through t h e manufacture of sulfuric acid, liquid sulfur dioxide and even elementary sulfur. Technical methods have been worked out for accomplishing t h e last two schemes, a n d small scale commercial plants erected. Two of t h e largest copper smelters of t h e west, namely, Anaconda a n d Garfield, have recently made heavy investments in acid plants. However, many plants are situated a t such great distances from t h e markets for these products t h a t only a comparatively small amount of t h e available sulfur dioxide can be utilized. It is recognized t h a t although t h e amount of t h e waste sulfur gases t h a t will be utilized in commercial products will be steadily increasing, yet for many years t o come t h e smelters will be obliged t o waste large quantities of sulfur dioxide into t h e atmosphere. Thus, investigations are in progress t o determine how, under different climatic a n d topographic conditions, these volumes of sulfur dioxide, whether large or small, can be discharged into t h e atmosphere without causing injury t o vegetation in t h e surrounding country. Zinc,
1 Presented e t the Symposium on the Chemistvy and Mefallurgy of 54th Meeting American Chemical Society, Kansas City, April 12, 1917. Published with the permission of the Director of the Bureau of Mines.
1 See THIS J O U R N A L , 7 (1915), 41, for abstract of Selby Smelter Commission report.
July, 1917
T H E J O U R N A L OF I N D U S T R I A L A N D EXGINEERING C H E M I S T R Y
EFFECTS O F BLEACHING ON YIELD
I n this connection i t is necessary t o determine first of all what are t h e effects, both in regard t o superficial bleaching a n d in regard t o t h e economic results on yield, of applying various concentrations of sulfur dioxide t o various forms of plant life a n d under different atmospheric conditions. If t h e time were available, i t would be interesting t o discuss t h e earlier methods t h a t were used in this country and in Germany for determining t h e effect of sulfur dioxide on vegetation, a n d t o show wherein t h e vast amount of d a t a t h a t were determined b y these investigations are of no value as furnishing d a t a upon which t o base definite conclusions. I t is necessary t o dismiss a n y consideration of these investigations with t h e brief statement t h a t in none, whether t h e tests were made in cabinets, glass jars or in smoke houses, were normal field conditions even approximated, nor was there a n y knowledge of t h e actual concentration of t h e sulfur dioxide in contact with t h e plants, nor of t h e atmospheric conditions. A knowledge of t h e attendant atmospheric conditions is of t h e greatest importance. The first research work along t h e line of making determinations under actual field conditions was t h a t done by t h e Selby Smelter Commission. In these determinations, known volumes of air containing known definite concentrations of sulfur dioxide were blown for definite periods of time under known atmospheric conditions over plants growing normally in t h e field. -4 cabinet framed with wood a n d with celluloid sheets for t h e sides was placed over t h e plants during t h e period of investigation, which varied between two minutes and eight hours. Check plots were fumigated simultaneously under t h e same conditions with air containing no sulfur dioxide. All t h e determinations of t h e Selby Commission were made on barley, as this was supposed t o be t h e most sensitive of all t h e crops. T h e department of smoke investigations for t h e American Smelting and Refining Company in Utah, under t h e direction of Mr. P. J. O’Gara a n d Mr. E. P. Fleming, has continued t h e work t h a t was started by t h e Selby Commission, and, through many elaborate series of careful a n d detailed investigations, has obtained a vast amount of reliable a n d definite d a t a on t h e smoke problem, especially t h a t phase of t h e problem concerned with sulfur dioxide. As far as t h e d a t a obtained by t h e Selby Commission went, they were checked quite closely by those obtained b y later tests, However, t h e work of t h e A. S. & R. Co. was carried out on a much larger scale, and t h e experiments covered so much greater range in t h e number of crops treated, a n d in regard t o variety of atmospheric conditions, t h a t comparison cannot be carried very far. I n conducting these investigations, t h e smoke department of t h e A. s. & R . Co. has endeavored t o determine if damage was being done in t h e vicinity of t h e smelters by t h e smoke, if so, how i t was done a n d t o what extent t h e damage was of economic importance. These investigations were carried further t o determine what steps were necessary t o prevent such damage. ils soon as i t was evident t h a t such inves-
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tigations were producing reliable and tangible data, a n d were answering in a definite manner many questions concerning t h e smoke problem, other companies followed their example, a n d at t h e present time companies in different parts of t h e country are carrying on similar studies, though on a much more modest scale. Wherever i t is evident t h a t there is no effort or desire t o conceal d a t a or twist t h e m t o suit convenient theories, i t is t h e aim of t h e Bureau of Mines t o cooperate and help in investigations as far as practicable. T h e method used by t h e A. S. & R . Co. for determining t h e effect of sulfur dioxide on plant life was practically t h e same as t h a t devised by t h e Selby Smelter Commission, improvement having been made in t h e method of introducing t h e air into t h e cabinet. In t h e experiments of t h e A . S. & R. Co., t h e experimental plots were 6 ft. by 6 ft. in area a n d cabinets were 4 ft. high. The fan delivered approximately I O cubic meters of air per minute into t h e cabinet, this volume being sufficient t o keep t h e temperature and relative humidity of t h e air in t h e cabinet similar t o those of t h e outside air. In every experiment two plots were fumigated simultaneously, one with t h e sulfur dioxide mixture, t h e other with air free from sulfur dioxide, t h e latter being t h e check plot. The determinations were made on a great number of crops, including potatoes, tomatoes, sugar beets, cereals, alfalfa, red clover a n d garden truck. In 1915 and 1916there were, in all, nearly 3000 experimental plots. Besides t h e work in t h e field, experiments were made in which t h e gases were drawn from t h e top of t h e stack, these gases diluted t o concentrations desired, and t h e mixture blown over plants t h a t were grown in boxes under conditions similar t o those in t h e field. In order t o determine t o what extent visible bleaching affected t h e yield or whether a n economic loss could be sustained b y t h e crops without visible injury, i t was necessary t o harvest t h e experimental plots very carefully. Records were kept of t h e total yield of vegetable matter, a n d in t h e case of grains, t h e weight of grain, weight of kernels, number of kernels per head and percentage of germination. The A. S. & R. Co. have made complete analyses for protein, carbohydrates, f a t , sulfur and crude fiber. T o summarize briefly, the fumigation tests have demonstrated these facts: (I) Under certain atmospheric conditions, bleaching of crops, especially grain crops, can be produced b y very small concentrations of sulfur dioxide, even as low as one part sulfur dioxide per million parts air, if t h e time of application is sufficiently long. T h e A. S. & R . Co. tests have demonstrated t h a t other crops are much more resistant t o sulfur dioxide t h a n are t h e cereals, b u t t h a t in all cases t h e concentrations required are low if t h e other factors are favorable for injury. ( 2 ) -4 visible bleaching on grain and many other crops, if endured during t h e early stages of growth, does not necessarily affect t h e ultimate yield. (3) A considerable amount of bleaching can be sustained a t all stages by t h e plants without cutting down t h e yield greatly. I n fact, in t h e Selby work, i t was found t h a t in order t o decrease the yield 30 per cent
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T H E J O U K N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Vol. 9, No. 7
ciin pass into or out of the palisade cells a n d spongelike tissue of the leaf where, under t h e action of light. plant food is manufactured. T h e opening and closing of these breathing pores or stomata are controlled b y guard cells. As t h e walls of t h e guard cells, like t h e epidermis of the plant cells, are very impervious to gases, sulfur dioxide not excepted, whenever t h e breathing pores are closed b y t h e guard cells, no gases can he absorbed by t h e plant, excepting under extremely high concentrations, far above those encountered under any imaginahle conditions. Even carbon dioxide, which is a n essential plant food and which is found normally a t 300 p. p. m. in the air, is not absorbed b y t h e plants when t h e stomata arc closed. Thus, whenever t h e guard cells are closed, this generally taking place a t night, t h e plants are much more resistant to sulfur dioxide than when t h e cells are open. Furthermore, carbon assimilation does not t a k e place at night, but only during hours of daylight, all other factors being favorable. It is believed t h a t t h e nascent oxygen given off when carbon is assimilated is effective in oxidizing any sulfur dioxide in t h e cells t o sulfuric acid, a n d this produces the injury t o t h e plants. IILC I-CUrNClnSNCii "B I,I
