Occurrence of Selenium in Pyrites KENNETHT. WILLIAMSAND HORACE G. BYERS,Bureau of Chemistry and Soils, Washington, D. C.
T
HE work of Kurt W. Franke, state chemist of South
No attempt has been made to determine the sulfur content of the pyritiferous material of the samples reported in Table 11. The ores were far from pure pyrites and in no case is there any guarantee that they may be represented by any definite formula. It is probable, however, that the mean sulfur content is not more than 40 per cent, corresponding to 400,000 parts per million. The mean selenium content is 59.0 parts per million. The ratio of sulfur to selenium is, therefore, of the order of 6 X lo3. The mean ratio of sulfur to selenium in the earth's crust is, according to Clark and Washington ( I ) , about IO6. Both these quantities are of course a rough approximation, but even so, it is evident that in this series of minerals there is a very marked concentration of selenium.
Dakota, which traced the causes of a certain animal disturbance, locally known as alkali disease, to the vegetation grown upon certain definite soil areas, and the subsequent detection in the Bureau of Chemistry and Soils of selenium in the vegetation of these areas has led to a series of investigations upon selenium. I n the course of these investigations the presence of selenium has been traced from plant to soil and from soil to its parent shales. Among the shales known to contain selenium is the Pierre shale, in certain sections of which occur nodules of iron pyrites. One of these nodules, collected by one of the writers, was found to contain 205 parts per million of selenium. This is a greater concentration of selenium than has been found in any other portion of the shale, some hundreds of samples of which have been examined in this laboratory. This fact, coupled with the known occurrence of selenium in chamber sulfuric acid made by roasting pyrites, and the historical fact that selenium was discovered, in 1817, in the sulfuric acid chambers in which the sulfur dioxide used was derived from certain copper pyrites (a), made it of interest to determine how general the association of sulfur and selenium in pyrites may be. There was also the added incentive that over the area of soils known to be derived from the Pierre shale, the presence of selenium in both soil and vegetation had been determined to be of general occurrence.' These soils all occur in arid or semi-arid areas. If selenium occurs in pyrites in general, the fate of the selenium in humid areas, as contrasted with its disposition in arid areas is of striking interest in relation to the whole selenium problem. Initial data were secured through the analyses by W. 0. Robinson of the samples indicated in Table I. TABLE1. SELENIUM IN SELECTED SAMPLES OF PYRITES SAMPL~ Concretionary pyrite Massive p rites Crystals oYpyrjte Crystals of pyrite Mispickel
SOURCE Fischer's Gully, Nebr. Brigham Utah Saratoga: C O ~ O . Isle of Elba Paris, Me.
SELENIUM CONTENT P. p . m. 205 15 10 Trace Trace
With these facts in mind, T. D. Rice, of the Soil Survey, was requested to locate a number of sources of pyritiferous materials in the humid area of the eastern portion of the United States. In 1917 a survey of available pyrite sources was published by Smith (4), and through this a number of the sources of pyrite listed below were located and samples collected by Rice and Byers. Other samples were secured from a pyritiferous clay deposit near Bay Springs, Miss. A sample of concretionary pyrite was secured by S.A. Swenson from the Selma chalk of Alabama, and samples of pyrite and of limonite pseudomorphs after pyrite through the courtesy of W. H. Sage of the Alberene Company of Schuyler, Va. I n addition to the pyrite samples a number of samples of soil and of other materials presumably derived from materials of pyrite content were also secured. These samples were all examined quantitatively for their selenium content by the appropriate one of the methods outlined by Robinson, Dudley, and Williams (3). The results obtained are given in Table 11. Where only whole number values are given, the accuracy does not exceed 2 parts per million. 1
Unpublished data, Bureau of Chemistry and Soils.
TABLE11. SELENIUM CONTENT OF PYRITEAND ASSOCIATED MATERIALS
sm>€3.___ LAB. NO.
B-3179 B-3183 B-3174 B-3192 B-3196 B-3197 B-3199 B-3202 B-3203 B-3204 B-3205 B-3207 B-3169 B-3170 B-3171 B-3209 B-3210 B-3211 B-3212 B-3213 B-3215 B-3216 B-3464 B-3465
NIUM
TYPEOF MATERIAL
LOCATION
Marcasite in black clay Bay Springs Miss. Marcasite in clay Bay Springs' Miss. Concretionary pyrite in Selma chalk Liviystone,' Ala. Pyr!te Pyriton Ala. Pyrite Draketdwn Breme; Ga 'Ga. Pyrite Pyrite Villa. Rica, 'Ga. Pyrite Dallas, Ga. Pyrite Marjetta, Ga. Pyrjte Marietta Ga. Pyrite Marietta' Ga. Pvrite Ball GroLnd Ga. Pj.rite Crouse, N. d. Pyrite (partially decomposed) Crouse N. C. Pyrites Crouse' N. C. Pyrrhotite Ducktdwn, Tenn. Chalcopyrite Duoktown Tenn. Pyrite Ducktown: Tenn. Mineral Va. Pyrite Mineral: Va. Pyrite Pvrite .MadiRon, Va. Dumfriee, Va. PGrite Pyrite in serpentine Schuyler, Va. Pseudomorphs after pyrites Schuyler, Va. Av.
CONTENT
P. p . n. 0.3 0.6 8 75 8 50 45 250 110 160 180 80 10 55 50 5
10 1
IE
0 125 75 45 59
It would appear, therefore, that in the hydrolysis of pyritiferous material to produce soil, the selenium content, when conditions are not favorable for removal of both sulfur and selenium, should be higher than in soils derived from other sources. It is to be expected that the processes which convert pyrites to limonitic material accompanied by oxidation of the sulfur to sulfuric acid will cause a like transformation of selenium to soluble form. If these processes are accompanied by leaching both selenium and sulfur should be almost completely removed from the soil produced. This should be the case in humid areas. On the contrary, in arid or semi-arid areas where little percolation accompanies soil formation, pyritiferous soil parent material should result in a soil which, along with a high sulfur content, should have appreciable selenium content. This appears to be the case in the soils derived from the Pierre shale. I n this shale the selenium content varies between wide limits, a range from traces up to 103 parts per million having been observed. In soils derived from these shales, in an area of present mean annual rainfall of 15 inches, selenium has been found as high as 32 parts per million. I n sdils of humid areas selenium has been found only in traces, though it must be confessed that no extensive examinations have as yet been made. A little light is thrown upon the fate of selenium in soil formation under humid conditions: by the data given in Table 111.
296
July 15, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
CONTENT OF SECTIONS OF TABLE111. SELEXIUM NEAR BAYSPRINGS, MISS. LAB.
No.
B-3175 B-3176 B-3176a B-3177 B-3178 B-3187 B-3179 B-3183 B-3180 B-3182 B-3181 B-3185
MATERIAL Surface soil Yellow sand (0-6 f t . ) Limonite scales in sand Yellow sand (6-20 ft.) Iron stone cap of clay Yellow clay beneath cap Black clay with pyrites Pyrites scale Linht-colored scale Wiathered black clay Weathered mixed clay Concentrated extract of weathered clay
A
297
CLAYBED The presence of selenium in gypsum deposits in weathered Pierre shale has also been determined in quantities ranging SELENIUM from 5 to 15 parts per million.2 CONTENT A small number of shales were also collected and their P. p. m. 0.0 selenium content determined in Table IV. 0.0 0.4 0.1 0.3 0.4 0.3 0.6 0.15 0.15 0.20
0.01
The samples reported in Table 111 were obtained from a deposit which is being used as the source of supply of a “medicine.” The clay bank has been excavated t o a depth of about 50 feet. The over-burden is a yellow sandy clay of a maximum depth of about 25 feet. On parts of this sandy slope small pillars of clay are capped with thin scales of limonitic material. Below the sandy layer is a crust of limonitic material about 2 inches thick. This crust is apparently a partly hydrolyzed pyrite layer. Immediately below this crust is a thin layer of yellow clay. Below the yellow clay is a %foot layer of dense black clay containing large numbers of small crystals of marcasite. Below the black clay is a very thin layer of scale consisting largely of marcasite. Below this, and of a thickness not determined, is a deposit of clay somewhat lighter in color than the black clay and containing much smaller quantities of pyrites. The clay layers are used for the preparation of the above mentioned medicine by being allowed to dry and weather, under cover, for a year or more. The weathered material, which contains considerable quantities of ferrous sulfate, is leached with water.
It is unfortunate that this deposit is so low in selenium content, since otherwise it offers a very favorable set of conditions for tracing the course of the selenium in weathering. It is, however, clear that the soil proper is essentially free from selenium, that the weathering produces water-soluble selenium removable by leaching, and that the removal of selenium from the limonitic material does not keep full pace with the removal of the sulfur. This last fact is also indicated by B-3465 of Table 11. In this sample nearly all the sulfur is removed while a considerable selenium content remains, The transfer of selenium by leaching of weathered products, and its relation to sulfur translocation, are also indicated by the presence of selenium in certain shallow wells in the Pierre shale. These waters are high in sulfate content and selenium has been found in quantities as high as 0.07 part per million.
TABLEIV. SELENIUM CONTENT OF ALABAMA SHALES LAB.
No.
MATERIAL
B-3191
Dark calcareous shale
B-3188 B-3189 B-3190 B-3195
Dark shale Ferruginous shale Dark shale Light shale
LOCATION
SBLBNIUM CONTENT P . w. n.
3 miles south of Desmopolis Leeds Leeds Leeds Heflin
0.6 0.15 0.20 0.15 0.15
GENERAL REMARKS It would appear from the data above presented, supplemented by a mass of unpublished data on file in this bureau, that selenium is of much greater distribution in soils and vegetation than has heretofore been suspected. It seems probable that in arid and semi-arid areas the presence of selenium is to be expected in every case where the sulfur content of the soil parent material is high and that, where the selenium content permits, the derived soils and their vegetation may contain suqcient selenium to render them potentially dangerous. The mere presence of selenium in soil is not to be considered a n indication of an inferior soil. It also seems probable that soils produced in humid areas are not likely to have a pernicious selenium content even though the parent materials are relatively rich in this element. If the above inferences be warranted, it would appear that investigations of the selenium contamination of soils should be greatly broadened in scope, and that, in particular, they should cover soils which are to be used under irrigation. LITERATURE CITED (1) Mellor, J. W., “Treatise on Inorganic and Theoretical Chemistry,” Vol. 10, p. 693, Longmans, Green & Co., N. Y., 1930. (2) Ibid., Vol. 11, p. 1. (3) Robinson, W. O., Dudley, H., Williams, K. T., and Byers, H. G., IND.ENG.CHEY.,Anal. Ed., 6, 274 (1934). (4) Smith, P. S., U. S. Geol. Survey, MineraE Resources of U. S., 1917, Part 11, pp. 19-62. RECEIVEDMarch 24,
1934.
Unpublished data, Bureau of Chemistry and Soils.
Constant-Feed Buret and Apparatus for Catalytic Dehydration of Alcohols B. B. CORSON, Universal Oil Products Company, Chicago, Ill. MANY reactions a constant rate of liquid feed is desirable and it is impossible to obtain an even flow of liquid by means of a n ordinary glass stopcock. The apparatus described below will deliver liquid a t a constant rate over any desired length of time. It operates on the principle of opposing a constant liquid head to a constant resistance. Somewhat similar devices have been described by Sabatier (1) and by Vaughen (8).
For an all-round buret capable of delivering from 15 to 60 cc. per hour, the capacity of A is 500 cc., the length of C is 60 cm., the bore of capillary D is 0.25 to 0.5 mm., and the length of the capillary is 40 em., the vertical height of the spiral being 5 cm. Tube E is of convenience in venting the pressure caused by the insertion of stopper F , and with liquids which tend to deposit solid matter, it is well to protect the capillary by a small filter plug of cotton, G.
The liquid reservoir of the constant feed-buret is essentially a Mariotte bottle, and the head of liquid can be varied at will by raising or lowering tube A ; the effective head is at B, the lower end of tube A, and the range through which the head can be varied depends on distance C . The constant resistance is furnished by capillary spiral D through which the liquid must travel. The choice of feed rate is wide, depending as it does on two variables, the liquid head and the resistance, the latter being governed by the length and the bore of the capillary.
This apparatus has a general application for catalytic reactions in which a liquid is vaporized and the resulting gas passed over a solid catalyst. It is especially convenient for the dehydration of alcohols over alumina. The buret is connected t o the catalyst tube by means of mercury seal H , which is designed along the conventional lines of a mercury seal for a mechanical stirrer. The alumina catalyst is introduced through the open end of the tube a t I , which is then
IK
CATALYTIC DEHYDRATION OB ALCOHOLS
