INDUSTRIAL AND ENGINEERING CHEMISTRY
426
Kfiding to eliminate large quantities of silica by fuming with hydrofluoric and sulfuric acids, a troublesome operation on a technical scale. Furthermore these workers used exceedingly large amounts of zirconium oxide (25 kg.) which causes great difficulties in filtration and handling and which are absolutely unnecessary. One-tenth of this quantity would be sufficient, as can be seen from the present results.
Acknowledgment The funds necessary to accomplish the work here described were generously donated by Hiram J. Halle of New York, K. Y., to whom the writers wish to express their sincere thanks. They are indebted to A. C. Ratchesky, U. S. Minister to Czechoslovakia, and to F. Novotny, of the U. S. Legation in Prague, for their efficient support in obtaining the raw material from the Czechoslovakian Government. The authors are also indebted to Julius Stieglitz for his personal interest and helpful advice during the course of this work. They wish to thank the Lindsay Light and Chemical Company, as well as M. W. Eichelberger and C. W. Stabenau, for their cooperation and assistance in carrying out the process a t their plant. Due thanks are given to
VOL. 27, NO. 4
Herbert N. McCoy for his technical advice and to D. R. Sperry, of D. R. Sperry and Company, for his coijperation in the use of a filter press. The authors are also grateful to the management of the Universal Oil Products Company and to Gustav Egloff for their continuous and many-sided help. Acknowledgment is due F. Benson who carried on most of the operations a t the plant very efficiently. At the present time the work is being supported by a grant from the R. A. F. Penrose Fund of the American Philosophical Society.
Literature Cited Graue, G., and KLding, H., Nutunoissenschaften,22, 386 (1934); 2. ungew. Chem., 47, 650 (1934). Grosse, A. V., Ber., 61, 233 (1928). Grosse, A. V.,J. Am. Chem. SOC.,52, 1742 (1930). (4) Grosse, A. V., Phgs. Rev., 42, 565 (1932). (5) Grosse, A. V., Science, 80, 514, Table 3 (1934). (6) Grosse, A. V., and Agruss, M. S., J. Am. C h m . SOC.,56, 2200 (1934). RECEIVED December 27, 1934. This paper is taken partly from a thesis submitted by M. S.Agruss to the faculty of the Division of Physical Sciences, University of Chicago, in partial fulfilment of the requirement8 for the degree of doctor of philoeophy.
Behavior of Oxidizing Agents with Activated Carbon A. S. BEHRMAN AND H. GUSTAFSON, International Filter Company, Chicago, Ill.
W
ITHIN the past few years the water purification world has become well acquainted with activated carbon and is now employing this new reagent in an ever-increasing number of applications. Generally speaking, activated carbon is utilized in water purification in two ways. In the first, the carbon is employed for removing from the water by direct adsorption in the carbon those substances which give to the water undesirable taste, odor, color, or other objectionable characteristics. Among the taste- and odor-producing substances commonly removed in this fashion are the phenols and chlorophenols, as well as certain tastes and odors arising from a variety of organic sources, such as the decomposition products of algae and other microorganisms. In the second method the carbon is employed primarily for the removal of free chlorine. This free chlorine may be either the relatively small residual amount (ordinarily a small fraction of a part per million) intentionally left in a community water supply as a protective measure t o assure continuous sterility; or it may be the considerably higher amount-frequently as much as 1 or 2 parts per million, and sometimes more-following a heavy dosage of chlorine applied usually for the purpose of effecting the oxidation of organic matter responsible for the objectionable taste, odor, color, or other of the undesirable characteristics mentioned. I n this second method of utilization the carbon functions not simply as an adsorbent but as a chemical reagent as well, acting as a reducing agent to convert the applied free chlorine to the chloride ion. Theoretically, 1 part by weight of pure carbon, completely reactive, could thus convert about 12 parts of free chlorine to the chloride ion. It is not the purpose of this paper to discuss in detail the I
application of these known methods of water purification employing activated carbon. Several very full discussions of this sort have already appeared in the literature (1). The object is to point out that the chemical reaction of the carbon and the free chlorine, employed in the second method described, is not an isolated phenomenon but is in agreement with a theory of behavior that was worked out several years ago in this laboratory; that is, activated carbon exhibits a marked adsorption tendency toward oxidizing agents in aqueous solution in general, and the adsorbate may or may not react with the carbon, depending partly on concomitant conditions and principally on the nature of the oxidizing agent itself. There is an important and practical development of this theory: In those cases in which the adsorbed oxidizing agent is retained in the carbon, it is possible to treat other fluidsboth liquid and gaseous-for a variety of purposes merely by bringing them in contact with the carbon containing the adsorbed oxidizing agent. Under proper operating conditions, the adsorbed oxidizing agent is retained by the carbon and is released in appreciable amount only as required by the presence of some reactive substance in the fluid being treated. For convenience in this discussion we may divide into three types of behavior the action of various oxidizing agents with activated carbon: 1. Adsorption and catalytic decomposition of the oxidizing agent. 2. Adsorption of the oxidizing agent accompanied by its reaction with the carbon: a. With release of the reaction products from the carbon. b. With retention of at least one reaction product in the
carbon.
3. Adso tion and retention of the oxidizing agent unaccompa-
nieTby chemical reaction with the carbon.
427
INDUSTRIAL AND ENGINEERING CHEMISTRY
APRIL, 1935
Adsorption and Catalytic Decomposition One of the best examples of the first type of behavior is the case of an aqueous solution of hydrogen peroxide. Such a solution can be freed of peroxides by contacting it with activated carbon. The carbon may be either in powdered or coarsely granular form, thus demonstrating that the decomposition does not result merely from the known general tendency of fine particles to promote peroxide decomposition. That sorption plays an important part in this reaction is readily demonstrated by comparing the action of activated carbon and graphite; with graphite, there is no appreciable decomposition even in powdered form. The action of activated carbon with an aqueous solution of ozone has not been studied quantitatively, but we might expect its behavior to be similar to that exhibited by the peroxides. Various practical applications of this first type of behavior at once suggest themselves. One is the removal of peroxides-and ozone-from solutions containing these reagents. A second is the purification of gases containing these substances. A third is the production, for very special purposes, of oxygen from peroxides by means of activated carbon. It is obvious that, since removal of this type of oxidizing agent is so readily accomplished, liquids and gases may be treated with a considerable excess of these reagents for a given effect, such as sterilization, bleaching, etc., with impunity, since there need be no fear of an undesirable residue in the final fluid.
Adsorption and Chemical Reaction with Carbon The second type of behavior is one with which water purification chemists are now quite familiar, since the dechlorination of water with activated carbon is an excellent example of one of the two species of reactions included under this heading. The reaction taking place in this case is represented by the following equation : 4HC1 COr 2C12 + C 2H20
+
+
Adsorption here is a very definite preliminary t o the chemical reaction just illustrated. Baylis (2), for example, found a considerable lag between the time of application of chlorinated water to a carbon bed and the time a t which the chloride content of the effluent water showed an increase corresponding to the applied chlorine. It is probably due to the adsorption and concentration which occur during this time lag that it is possible to keep a carbon bed in good bacteriological condition. Evidently the relatively tiny amount of chlorine in the water applied to the carbon is concentrated tremendously in the pores and exerts a sterilizing effectbefore reacting chemically with the carbon. In its behavior towards activated carbon, bromine acts much like chlorine, except that its chemical reaction with the carbon proceeds more slowly. The conversion of the free halogen t o the halide is in both cases favored by low pH and retarded by high pH. Mono- and dichloramines in water applied t o activated carbon are converted t o the chloride, though not as readily as chlorine. This behavior would be expected from the known fact that chloramine has a lower oxidation potential than chlorine. The type of behavior described is utilized by one of the present authors in processes for the production of hydrochloric acid, hydrobromic acid, and certain halides (3). The second species in this category of adsorption accompanied by chemical reaction with the carbon is less familiar t o water works chemists, but is very interesting. Whereas in the case of dechlorination, typical of the first species just
discussed, the principal reaction product is released and appears in the effluent liquid, in the second case a t least one of the principal reaction products is retained tenaciously by the carbon. An excellent case in point is that of a solution of potassium permanganate. Such a solution can, under proper conditions, be completely decolorized by contact with activated carbon; and the decolorized solution will be found substantially free of manganese. Contrary to what might be expected, however, potassium permanganate is not retained as such by activated carbon. The authors’ studies have shown that what is left in the carbon is manganese dioxide, resulting from the reduction of the permanganate by the active carbon. Activated carbon thus charged with a thin layer of manganese dioxide distributed over its tremendous internal surface may be employed in a variety of ways. It may be used for the purification of liquids containing impurities capable of oxidation by the manganese dioxide. It may be likewise utilized in the purification of gases containing similar types of impurities-notably sulfur dioxide, hydrogen sulfide, and the mercaptans.
Adsorption without Chemical Reaction with Carbon The third type of behavior presents a most inviting field of investigation because of the variety and practical utility of the possibilities it offers. One extremely useful example of this type of behavior is the adsorption of iodine. This adsorption, under proper conditions, affords a practical method of recovery of iodine from extremely dilute solutions, such as from oil well brines in which the iodine content (usually present as iodide) rarely exceeds 50 parts per million. As a matter of fact, substantially complete recovery can be secured from much lower concentrations. The adsorption of iodine is favored by low pH and hindered by high pH. The influence of pH is illustrated in the following table, in which is summarized the results obtained by treating a solution containing only about 12 parts per million iodine with activated carbon (Hydrocarco) ; the data show that the removal of iodine is substantially complete a t pH 6.9 or below but becomes increasingly incomplete as the pH is elevated above that point: (0.050 gram carbon per 250 co. agueoua iodine solution) Iodine Concn., Mg. per Liter Before After
11.7 11.8 11.6 11.7 11.8 11.7
1.8
0.7 0.0 0.0 0.0 0.0
PH 8.0 7.0 8.9
6.4 5.4
3.9
Incidentally, a good grade of the proper type of activated carbon can be made to adsorb as much as 25 to 30 per cent by weight of iodine. Activated carbon containing adsorbed iodine has a great variety of possible uses in the purification or treatment of liquids and gases. In the treatment of gases, for example, the removal or conversion of objectionable impurities especially susceptible to oxidation by, or to combination with, iodine is readily accomplished. Similar broad utility exists in the treatment of liquid,. In the treatment, of aqueous solutions: the favorable effect of low pH on the retention of the iodine in the carbon should be borne in mind in order to avoid undue loss of iodine. An interesting example (though not one necessarily of any great utility under ordinary circumstances) of the treatment
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 27, NO. 4
of aqueous liquids by means of carbon containing adsorbed iodine is the sterilization of water. Baylis, physical chemist of the Experimental Filter Plant of the City of Chicago, was kind enough to test a sample of granular carbon (Hydrodarco) containing adsorbed iodine which had been prepared in this laboratory. This carbon, containing approximately 25 per cent by weight of adsorbed iodine, was placed in a straight-
gasoline, the liquid-phase sweetening process of Zurcher was studied. He saturates activated carbon (6) with a solution of sodium plumbite (doctor solution) and then uses the carbon containing the plumbite for the sweetening of liquid petroleum products. Although sodium plumbite cannot be considered, in the usual sense, as an oxidizing agent, it was decided as a matter of interest to ascertain whether the carbon saturated with sodium plumbite held the reagent purely mechanically or whether true adsorption might not be inTABLE I. STERILIZATION OF WATER WITH CARBON CONTAINING volved. ABSORBEDIODINE Accordingly, the following simple experiment was carried Bacteria per Cc. out: Doctor solution was prepared by dissolving litharge in an -At 37‘ C.---At 20’ (2.5. coli per 100 Cc. Applied Applied Applied excess of sodium hydroxide solution. A portion of the clariDate liquid Effluent liquid Effluent liquid Effluent fied solution was then passed through a bed of granular acti2-28-30 25 19 0 5000 120 0 vated carbon (Darco) and followed by a small quantity of 27 275 0 0 20 1 0 0 28 2 0 350 10 0 wash water. Influent and effluent solutions were analyzed 0 00 1 3- 1 2 3 0 for sodium oxide and lead oxide. Pertinent analytical data 3 1 2 so 2 0 0 are as follows: 2 1 90 0 0 4 0 0
?
0 2
1 0 0 0
4 75 10 200
LO
2 0 1 1 1
0 0 0 1 0
-
5 6
0
0
0
0 0
0 1
0
210 11 21 13 95
0
0
-
-
-
0 0 1 0
0 0 1 0
S 14 00
20 21 22 24 25
0 1 2 2 0
1 0 1 0 1
21 130 200 10 25
100 1 40
20 27 28 29 4- 1
3 4
0
70 80 110 1200 65
5 2 2 00 8
8
11 12 13
14
14“ 15 17 18 19
8 7 9
0 1 1 2
0
0
0 0 0 0
0 0 5 0
0 0 0 0 0
0 1 0 0
3,500,000 0 2 2 0
1,050 0 0 0 0
0 16
0 0 2
0 0
0 0 0 0 0
0 2 2 25 2
0 0 0 0 0
0 1 1 2
50 7 0 2 4 3 25 2 2 2 21 8 45 3 4Gtb 02,OM),OOO 14,400 4a.c 330 02,000,000 35 2 14 180 5 2 3 0 3 1 25 0 35 7 4 Water was highly contaminated for this experiment by inoculation with B. coli. b Two gallons were run through the unit at the usual rate of 100 cc. per minute. The rate wa8 then cut to 25 cc. per minute and 2 additicnal gallons were run through.
-
-
__ -
sided percolator, forming a bed 2 inches in diameter and 12 inches deep. Raw, unchlorinated Lake Michigan water was passed through the bed a t the rate of approximately 1 gallon per square foot per minute. The experimental run was continued for well over a month, with the striking results shown in Table I. The data are presented, with Baylis’ permission, primarily for their indicative value. Obviously, they are not to be taken as a recommendation for the widespread employment of carbon containing adsorbed iodine for water sterilization. Thus far the discussion has been principally of the adsorption of the halogens and of potassium permanganate; but many other oxidizing agents might be mentioned. Nitric acid, potassium dichromate, and ammonium persulfate are a few whose adsorption characteristics have been studied. In view of the generic adsorption tendency of activated carbon towards oxidizing agents, and with Kruyt’s statement (4) in mind that “the adsorption is slight for all inorganic substances with the exception of the halogens,” it seems reasonable to raise the question as to whether the halogens are adsorbed because they are halogens or because they are oxidizing agents. In connection with the use of carbon containing manganese dioxide (from potassium permanganate) for the sweetening of
Original mln., grams/100 00,: PbO NaaO Molar ratio, Naz0:PbO Effluents o h . (without washing), g r a m d l 0 0 00.:
PbO
NatO Molar ratio, Naa0:PbO Retained in carbon (without washing), grama:
PbO
NalO Molar ratio, Naz0:PbO
3.86
7.70 7.2:l 2.27 7.27 11.6:l 1.59 0.43 0.973: I
From these data it will be noted that, although the molecular ratio of sodium oxide to lead oxide in the applied liquid is 7.2 to 1, the constituents were actually retained in the carbon in the ratio of almost exactly 1 to 1-in other words, in the same ratio as in sodium plumbite. This ratio may or may not have been purely coincidental, since washing of the carbon with distilled water removed considerable soda and comparatively little lead oxide. In any case, however, the adsorption by the carbon of a t least the lead oxide is unmistakable. Under the experimental conditions employed, the amount of lead oxide retained by the carbon was equivalent roughly to about 8 per cent by weight. Space does not permit the detailed discussion of the adsorption of other oxidizing agents or the utility of the processes and products involved. However, two or three other general considerations should be pointed out briefly and one or two rather broad applications suggested. One point worth mentioning is the function of the carbon as an oxidation catalyst in certain types of chemical reactions between the adsorbed oxidizing agent and the substances in the fluids with which the carbon is brought into contact. Again we may point out that the adsorbed oxidizing agent frequently has a dual nature and may therefore be utilized for purposes other than oxidation. For example, adsorbed nitric acid is obviously acidic as well as oxidizing; and the acidic part of its character permits its utilization in the automatic neutralization of undesirable alkalinity in liquids and gases. Finally, it had been the writers’ hope to relate more or less definitely the types of behavior described in the foregoing discussion to the oxidation potentials of the substances involved, with the expectation of finding a decreasing order of chemical reactivity (or absence of it) with the carbon with diminishing oxidation potentials of the oxidizing agents involved. Unfortunately, however, as far as it has been possible to determine, the fundamental concepts, as well as the technic of the determination, of oxidation potentials are not sufficiently clarified to permit the establishment of such a relationship, if any; but in due course of time it is hoped that
APRIL, 193.5
INDUSTRIAL AND ENGINEERING CHEMISTRY
the situation will improve sufficiently for the investigation to be carried out. NOTE. The new processes and products disclosed in this paper have been covered by issued or pending patents.
42 9
(2) Baylis, private communication. (3) Behrman, U. S.Patents 1,843,196 and 1,843,355 (Feb. 2, 1932); 1,870,308 (Aug. 9, 1932). (4) Kmyt, “Colloids,” New York, John Wiley & Sons, 1930. (5) Zurcher, Paul, paper presented before the regional meeting, American Chemical Society, Ponca City, Okla., Dec., 1932.
Literature Cited (1) Baylis, J . Am. Wufer Works Assoc., 21, 787 (1929); Spalding, Ibid.. 22, 646 (1930): Behrman and Crane, Ibid., 22, 1399 (1930); Behrman, Water W o r k s and Sewerage, 80, 55 (1933).
R E C E I V October ~D 8, 1934. Presented before the Divieion of Water, Sewage, and Sanitation Chemirrtry at the 88th Meeting of the American Chemioal Society, Cleveland, Ohio, September 10 to 14. 1934.
Extraction of Georgia Shale and
Wyomingite with Hydrochloric Acid S. L. MADORSKY AND J. RICHARD -4DAMS
Fertilizer Investigations, Bureau of Chemistry and Soils, Washington, D. C.
On t,he basis of the following data, Georgia shale and Wyomingite are susceptible of extraction with hydrochloric acid. Assuming an interrupted countercurrent application of hot saturated acid, in the ratio of about 2.5 cc. of constant-boiling acid to 1 gram of 200-mesh mineral, with 3 hours of stirring in the case of the shale and 1 hour in the case of Wyomingite, an extraction of about 66 per cent alumina, 80 per cent potassium oxide, and 73 per cent ferric oxide could be expected in case of the
HT
HE problem of treating potassium aluminum silicates with acids for the recovery of potash and alumina has been discussed extensively in the technical literature (1-4, 7-1 1, 13). Blanc (5) describes the large-scale extraction of Italian leucite by circulating hot hydrochloric acid through a bed of the granular mineral; on cooling the solution, potassium chloride crystallizes out. The mother liquor is then saturated with hydrogen chloride to precipitate aluminum chloride, and the mother liquor from this precipitation is recycled in treating fresh quantities of leucite. The aluminum chloride thus obtained is changed t o alumina by hydrolysis a t 300” to 400” C. Since the Italian leucite, after magnetic concentration, is practically free from iron, the resulting alumina is of high purity. Few details are given in the literature as to the optimum conditions of extraction, particularly those details pertaining to the effect of time of treatment, of temperature, and of concentration of the acid on the yield of potassium chloride and alumina. Wyoming leucite (Wyomingite) differs from the Italian leucite (12) in that its crystals are apparently too minute t o admit of ready magnetic or flotation concentration. They are imbedded in a matrix of other minerals of different solubilities, some of which contain iron. This element, accordingly, appears among the products to be separated if the
former, and 100 per cent alumina, 85 per cent potassium oxide, and 50 per cent ferric oxide in the case of the latter, yielding a solution of such concentration (in case of the shale) that 50 per cent of its alumina, 75 per cent of its potassium chloride, and 20 per cent of its ferric chloride could be precipitatedwith hydrochloricacid. The selective hydrolysis of the precipitated salts to yield potassium chloride and alumina with the recovery of hydrochloric acid was discussed in a previous paper ( 8 ) .
alumina constituent is to be utilized as a marketable byproduct. Since the work by Blanc, the technic of hydrogen chloride utilization has been advanced in connection with the process of converting potassium chloride into potassium sulfate by means of sulfuric acid (6). Methods of production have been described which hold the distinct promise of low-cost acid, in gaseous or solution form, warranting its consideration as applicable in those operations where a low-cost, highly active solvent acid is required. Accordingly the data presented here are designed as fundamental to proposals contemplating the hydrochloric acid extraction of the potassium aluminum silicates; of these, wyomingite, Georgia shale, and greensand (12), from the viewpoint of size of deposit and ease of mining, are outstanding examples. A previous paper (8) describes experiments on the extraction of Georgia shale with hydrochloric acid and, on the separation of potassium chloride and iron-free aluminum oxide from the mixture of chlorides thus obtained; the paper deals particularly with the separation of alumina from ferric chloride by heating a mixture of the two chlorides in an atmosphere of hydrogen chloride. In the present paper a study is made of the solubility of Georgia shale and Wyomingite in hydrochloric acid, the method of leaching, and the effect of a preliminary heat treatment to increase solubility of the minerals.
