SURFACE ACTIONS OF SOME SULFUR-BEARING ORGANIC

SURFACE ACTIONS OF SOME SULFUR-BEARING ORGANIC COMPOUNDS ON SOME FINELY-GROUND SULFIDE MINERALS A. M. GAUDIN AND WALTER D. WILKINSON Ore Dressing Laboratories of the Montana School os M i n e s , Butte, Monlana Received September 19, 1996

The fine grinding required to liberate ore minerals so as to permit' the fullest application of mineral separation by flotation produces particles of all sizes, frbm those having a diameter of about 100 microns to those of truly colloidal dimensions. The surface area of the solid phases is large in relation to their bulk, so that actions taking place a t the interface between the solids and the liquid in which they are immersed may involve a substantial amount of the agent in question, even though the action-or reaction-does not proceed on the solid to a depth greater than that corresponding to one or two atomic diameters. The physicochemical effect of these reactions on mineral surfaces is known to be tremendous: indeed many of the actual reactions have been surmised from observed physicochemical phenomena. The action (on the mineral surfaces) of the organic compounds that promote attachment of minerals to gas bubbles is of particular interest to the student of physical chemistry, as the discovery of the actual modus operandi may have applications in many fields of colloid chemistry not directly related to flotation. Establishment of the mode of action of these organic compounds-generally called collectors-on the minerals is, of course, of paramount interest to the flotation engineer, While it is generally acknowledged that collector molecules, being heteropolar, adhere to the mineral surface with their hydrophobic ends oriented away from the mineral, the mechanism of this attachment has been until quite recently a matter of Rpeculation. The simplest collectors are possibly the fatty acids and their alkali soaps, which are used principally in the flotation of non-sulfide minerals. More complex organic compounds whose molecules contain sulfur, nitrogen, or phosphorus are used for the flotation of sulfide minerals and of the oxidized minerals of lead and copper. Finely ground apatite' abstracts a considerable quantity of palmitate ion from an aqueous solution of sodium palmitate, while quartz does not Calcium phosphate in which some phosphate is replaced by fluorine or chlorine; the formula is often stated to be Ca6(F,C1) (PO&. 833 T H E J O C R N A L OF PHSSICAL CHEMISTRY, VOL. X X X V I I . NO,

7

834

A. M. GAUDIN AND WALTER D. WILKINSON

act in this manner. Although quartz sometimes appears to be floatable with sodium oleate as the collector, it has been shown (la) that flotation takes place to a substantial extent only when quartz has been activated by a cation, such as Pb++, Zn++, Ba++, Ca++, or Fe+++, which is capable of forming an insoluble soap. The fact that oleate ion, as such, adheres only to surfaces that have cations capable of forming insoluble oleates suggests that the mechanism of the abstraction is chemical. The action is practically irreversible and does not take place in accordance with the Freundlich adsorption isotherm (2). The behavior of some sulfur-bearing collectors, such as xanthates, toward oxidized lead and copper minerals is also well known (lb). These substances react metathetically with the surface of the mineral, forming thereon heteropolar coatings with the water-repellent end of the molecules of the coating oriented toward the water (3). The mechanism of the action of the sulfur-bearing collectors (e.g., thioureas, mercaptans, thiophenols, or xanthates) on sulfide minerals is less accessible t o investigation, and apparently more complicated, than the action of fatty acids and soaps. In spite of the evidence adduced by Taggart and his associates (4) of the strictly chemical character of the reaction between some collectors and some sulfide minerals, there are investigators who still adhere to the view that the phenomenon is one not involving primary valence forces. Holman (5), for instance, favors the secondary valence theory of adsorption, in that he assumes that xanthate molecules or ions are oriented at the mineral surfaces so that the double-bonded sulfur atoms, which he considers to be air-avid, are away from the mineral surface. Ostwald (6), on the other hand, considers that it is the double-bonded sulfur atom which has an affinity for the mineral, and a t least in the case of sodium dicresyl dithiophosphate (“aerofloat”), S

\\ /°CaH4CHs P / \

NaS

OCeH&Ha

and with xanthates, OR

/ s=c \

SNa

that it is the hydrocarbon group that is hydrophobic. The majority of investigators are in accord with this latter opinion. But Ostwald goes

SURFACE ACTIONS OF SULFUR-BEARING COMPOUNDS

835

further and imagines that a collector must be “triphilic,” that is, that each of its molecules must have a water-avid group, an air-avid group, and a mineral-avid group. Ostwald appears to support the view that the adherence of the reagent is a matter of residual valence. With those who believe that the abstraction of reagent from solution or suspension by the mineral is the result of a chemical reaction, it is still a question whether the major reaction is with the mineral itself, or with a mineral surface that has become oxidized (Taggart and coworkers), and whether it is the reagent itself, or a product resulting from the oxidation or decomposition of the reagent, which reacts with the mineral. An investigation of the action of xanthates, OR

s=c

/

\

SM

and of dixanthogens, OR

S=C

/

\

S

S

s=c

/

\

OR

on galena and pyrite has been conducted a t the Montana School of Mines. Work is now in progress in which experimentation is conducted with a wider variety of minerals and reagents. THE SURFACE REACTIONS OF XANTHATES AND DIXANTHOGBNS ON GALENA

In regard to the action of xanthate on galena it is known (3) that: (a) the surface of galena oxidizes rapidly in the presence of moist air or of water exposed to air, to form a film of lead sulfate, basic lead sulfate, or a compound of lead, sulfur, and oxygen of indeterminate composition containing less oxygen in relation to sulfur than the sulfate or basic sulfate; (b) this oxidized coating penetrates cleavage planes to an unknown but substantial extent; (c) the oxidized coating reacts with alkali xanthates, forming lead xanthates, which are less soluble in water than lead sulfate or basic lead sulfate; (d) slightly oxidized galena abstracts xanthate ion from solution and yields sulfate and other anions in approximately equivalent amount.

836


It was proposed to investigate further the action of xanthates on galena with particular reference to the effect of oxidation on the reaction products. In most cases the galena was finely ground, so that the final surface area of the mineral particles was several hundred times the original area. This made possible the recovery of sizable amounts of reaction products from quantities of galena that were not excessively large. The reaction products were recovered from the mineral by leaching with carefully purified acetone or benzene. The solvent was then evaporated quickly with a fan, so as to prevent as far as possible decomposition of the solute while in solution. Lead xanthates, particularly the higher xanthates and the branching or secondary compounds, are prone to decompose in solution, especially if warm ; consequently any method of concentrating the leach liquor by the application of heat, such as distillation, is out of the question. The raw galena was a jig concentrate from the Tri-State district. Before cleaning (see below) the galena was crushed, concentrated by tabling, and sized to 20/65 mesh by screening. After this preliminary purification the impurities were iron oxides and sphalerite, together with minor amounts of pyrite, calcite and silicates. Of these the ferric oxides were suspected of being the most harmful. However, their removal in the subsequent cleaning step was almost complete. After the preliminary cleaning just described, the galena was cleaned with an ammonium chloride-hydrochloric acid solution and with 0.5 N redistilled hydrochloric acid. The pH of the ammonium chloride-hydrochloric acid stock solution was 1.4, but before use the solution was diluted with thrice its volume of distilled water; a much greater concentration of cleaning solution results in undue metathesis of the hydrochloric acid with the galena, and in precipitation of salts on the mineral. The galena was washed with distilled water until the rinse was clear, then boiled gently for four hours in 400 cc. of the diluted ammonium chloride-hydrochloric acid solution. The operation was repeated until examination with a binocular microscope showed the galena to be substantially free from impurities other than a little quartz, pyrite, and sphalerite; total impurities usually were about 0.3 per cent. The sample was next boiled gently for two hours with 400 cc. of 0.5 N hydrochloric acid, and then was washed with distilled water. The hydrochloric acid treatment and subsequent washing were repeated. The object of this procedure was to remove the lead sulfate coating from the galena surface and to dissolve ferric impurities. This method was preferred to the use of ammonium acetate, for it was thought ammonium acetate might contain organic impurities difficult to remove. Also, hot hydrochloric acid (7) dissolves lead sulfate, especially if a large concentration of chloride ion is maintained by the addition of an alkali chloride or ammonium chloride.

SURFACE ACTIONS O F SULFUR-BEARING COMPOUNDS

837

After the special cleaning treatment just described, the mineral was ground in a closed porcelain jar of the type known as an assay mill. The jar was filled half-way with pebbles and pulp, the remainder of the space being occupied by air. In some tests a nitrogen atmosphere was used; this is specifically stated in every instance. Every grind was, of course, a wet grind. It was found that galena treated in this manner abstracts almost as much xanthate after it is ground as galena that has not been cleaned. This indicates that galena almost completely reoxidizes on a few hours’ exposure to air. The amount of oxygen in an assay mill is of an order of magnitude sufficient to oxidize the fresh galena surface produced by a six-hour grind. The followjng experiments were singled out from among many as of especial significance in ascertaining the true action of xanthates and dixanthogens on galena.

Experiment No. 1 Five hundred grams of cleaned galena was ground for six hours in the presence of 500 cc. of water; 2.50 g. potassium ethyl xanthate was added to the pulp of ground mineral. The mixture was stirred, allowed to stand for fifteen minutes and filtered. It was found by titration that approximately 1.0 g. of the reagent remained in the filtrate in the form of potassium ethyl xanthate; in other words, ethyl xanthate ion corresponding to 1.5 g. of molecular potassium ethyl xanthate had been abstracted or decomposed. After dewatering, the treated mineral was leached with nearly one liter of acetone; about one-half of the acetone was stirred with the mineral for fifteen minutes, and the mixture was filtered, and the rest of the acetone was used in washing the filter cake. The filtrate was evaporated with an electric fan. During the process characteristic crystals of lead xanthate (8), arranged in lily-pad fashion, appeared on the surface of the leach liquor. Besides the lead xanthate, there was found in the leach residue some oil, possibly ethyl dixanthogen, and a trace of lead sulfide, but no potassium ion. Methods of identification of these and other leach residues are presented elsewhere (8). This experiment was repeated, except that 1.50 g. of xanthate was used in place of 2.50 g. Only 0.22 g. of potassium xanthate was found in the aqueous filtrate, hence 1.28 g. was abstracted by the mineral. The dewatered, treated mineral contained the same substances as before. This experiment was again repeated, except that the amount of xanthate was reduced further to 1.0 Q., and that the grinding time was increased to eight hours. All the xanthate was abstracted. The dewatered, treated mineral contained the same substances as before. These experiments show that xanthate ion corresponding to one gram or more of potassium ethyl xanthate is abstracted in fifteen minutes by

838


500 g. of galena ground from six to eight hours in contact with a limited volume of air. These experiments also show that a considerable excess of xanthate ion is required to increase greatly the amount abstracted,

Experiment No. $2 Experiment No. 1 was repeated, except that the grinding time was increased threefold to eighteen hours. Of 2.50 g. of potassium ethyl xanthate added initially, but 0.42 g. remained in the aqueous filtrate, indicating that xanthate ion corresponding to 2.08 g. of the agent had been abstracted or decomposed. In this case the amount of xanthate abstracted did not increase in proportion to the added surface produced by the longer grind (9). This is perhaps because some of the freshly produced surface was not completely oxidized, and therefore did not react to the extent that a completely oxidized surface would react. Experiment No. 3 Five hundred grams of cleaned galena was ground for eighteen hours in the presence of 1.00 g. of potassium ethyl xanthate. The xanthate ion disappeared completely. However, the amount of lead xanthate recovered from the treated mineral was very small. In this case the xanthate had apparently decomposed, either while in the solution or while a t the mineral surface as solid xanthate. I n this, as in other tests in which the mineral was ground in the presence of the reagent, various decomposition products were noted, especially an oil, possibly ethyl dixanthogen, and elemental sulfur, and perhaps lead ethyl mercaptide (8). This test shows that potassium ethyl xanthate or lead ethyl xanthate decomposes much faster if in association with a galena surface, moisture, and atmospheric gases than if in bulk in the solid state or in pure aqueous solution or suspension. Experiment No. 4 Five hundred grams of cleaned galena was ground four hours and then treated with 2.00 g. of potassium n-amyl xanthate, in place of ethyl xanthate. Lead n-amyl xanthate was the chief product extracted by leaching the mineral. This test shows that the primary reaction between dissolved xanthate and galena is the same whether n-amyl or ethyl xanthate is used. Experiment No. ,$a Experiment No. 4 was repeated except that the amount of xanthate was reduced to 1.00 g., and that, after treatment, the mineral was exposed in aqueous pulp to the atmosphere for a day before filtering. As the galena was unusually dry after this treatment, it was leached with benzene instead

S U R F A C l ACTIONS O F SULFUR-BEARING COMPOUNDS

839

of acetone. Sulfur corresponding approximately to one sulfur atom per xanthate molecule abstracted was the only product identified; however, a strong odor suggestive of a mercaptan or of a xanthic ester was noted. These tests show that lead amyl xanthate decomposes rapidly, and in a well-defined way, when in contact with lead sulfide, moisture, and air.

Experiment No. 4b Experiment No, 4a was repeated with phenyl thiourethan, CaHs

H

\ /OCqH5 /"-"\ S

used in place of xanthate. Sulfur corresponding to approximately one atom per molecule of reagent was obtained in the leach liquor.

Experiment No. 5 One hundred grams of uncleaned galena, ground thirty hours with 400 g. of granite in the presence of n-amyl dixanthogen, CJL0

\ S//c-s-s-c

OCsHii

/ B

S

was floated, filtered, and then leached with benzene. The benzene left a residue of sulfur plus some volatile material, possibly the amyl ester of amyl xanthic acid (8). The amount of sulfur recovered was approximately that which would be contributed by two of the sulfur atoms in each dixanthogen molecule. This test shows that dixanthogen, which is the direct oxidation product of xanthate, is itself decomposed when allowed to remain in contact with a large amount of galena surface.

Experiment No. 5a If amyl formate disulfide, csH110

\ //

0

c-s-s-c

\\

0

840


be substituted for amyl thioformate disulfide (amyl dixanthogen), CsHiiO

\ S//c-s-s-c

/OCbH1'

\\

S

sulfur appears again as the only solid reaction product. The amount of sulfur obtained is again approximately that corresponding to two sulfur atoms per molecule of reagent, showing that in this case, as probably in that involving dixanthogen, the sulfur left with the mineral after reaction is the single-bonded, or disulfide, sulfur. Experiment No. 6 Seven hundred grams of uncleaned galena was ground for four hours in an atmosphere of nitrogen in the presence of 1.00 g. of potassium ethyl xanthate which had been added in oxygen-free solution. The assay mill was emptied in a nitrogen atmosphere, and the slime was filtered and washed with acetone, also in an atmosphere of nitrogen. The aqueous filtrate was titrated immediately for xanthate. It was found that xanthate ion corresponding to 0.99 g. of the reagent had disappeared. Sulfate ion was found in the aqueous filtrate, and lead xanthate was recovered from the treated mineral. A similar experiment was conducted with cleaned galena in a nitrogen atmosphere. Again a substantial disappearance of xanthate ion was noted. Xanthate disappearance, sulfate evolution, and lead xanthate extraction from the mineral were much smaller in this experiment than in corresponding experiments conducted in air. Taken as a whole these experiments confirm the view of Taggart and his associates, in so far as galena and xanthates are concerned, that the reaction is essentially a metathesis between oxidized coatings on the mineral and the xanthate in solution, although they do not exclude the possibility of reaction between galena itself and the xanthate in solution. From the experiments described in this paper, it would appear that the following reactions take place:

+

1. Galena oxygen -,lead sulfate coating on galena. 2. Galena coated with lead sulfate potassium xanthate in aqueous solution-, galena coated with lead xanthate potassium sulfate in solution. 3. Lead xanthate coating on galena oxygen (1) -, dixanthogen coating on

+

+ + galena + oxidized lead salt. 4. Galena not coated with lead sulfate + dixanthogen suspended in pulp galena coated with dixanthogen. 5. Dixanthogen coating on galena + oxygen (1) +elemental sulfur corresponding t o the two single-bonded (disulfide) atoms of sulfur per dixanthogen molerule + volatile sulfur organic compounds (xanthic esters and mercaptans?). +


84 1

The reactions are purposely not formulated because of the uncertainty which at present surrounds some of them. It appears that steps 2 and 5 are relatively rapid, that 3 is rather slow, and that the speed of 4 depends on physical rather than chemical circumstances. T H E SURFACE REACTIONS O F XANTHATES AND DIXANTHOGENS ON PYRITE

From what is known concerning galena it is tempting to conclude that similar reactions take place with other sulfide minerals. In the case of pyrite, however, it is difficult to postulate the formation of iron xanthate as a first step in a chain of reactions because ferrous xanthate is quite soluble2 and because ferric xanthate hydrolyzes to ferric hydrate and xanthic acid. Since, however, xanthates are very effective in floating pyrite, and since xanthates are abstracted by the mineral, it is evident that xanthate ion or some decomposition product must attach itself to the surface of the mineral. The most probable substance seems to be dixanthogen. The experiments described in the following pages, however, indicate that the reactions involved are somewhat more complicated than is implied by the view that the active collector is dixanthogen. The experimental procedure for testing pyrite was essentially the same as that used in Experiment No. 1, in which galena was used. The pyrite was hand-picked mineral from Butte. After being cleaned it Contained a trace of arsenic, less than 0.05 per cent copper, and no zinc. The pyrite was cleaned with 1:1 hydrochloric acid according to the method recommended by C. W. Orr (12) except that the mineral was first washed, a t a coarse size, with redistilled acetone. This step was designed to remove oily compounds possibly deposited from suspension in air while the mineral was stored in the laboratory (3). Unless otherwise stated, the experiments were performed in air and a 500-g. sample of pyrite was used in each case. All the grinds were wet grinds; during grinding the pulp dilution was 1 :1.

Experiment N o . 7 To 20/65 mesh cleaned pyrite ground for eight hours was added 1.00 g. of potassium ethyl xanthate. Immediately after the addition of xanthate there was an odor resembling that of commercial carbon disulfide. The xanthate was completely abstracted or destroyed. The aqueous filtrate contained ferric ion, chloride ion, sulfate ion, but no sulfide ion. The acetone leach liquor contained elemental sulfur.

* The solubility of ferrous ethyl xanthate exceeds one part per thousand, whereas the solubility of lead ethyl xanthate is less than one part per million.

842


Experiment No. 7a Experiment No. 7 was repeated, except that the pulp was allowed to stand in the assay mill for two days before opening the mill. A much stronger vacuum than usual was noted on opening the mill. This indicates that the freshly produced pyrite surfaces, the reagent, or both had been more completely oxidized by the oxygen in the mill than if the mill had been opened immediately. Besides sulfur, the following substances appear to have formed during the reaction :-carbon dioxide, carbon disulfide, carbonyl sulfide, and a relatively complex organic acid (8). These experiments show that potassium ethyl xanthate is abstracted by pyrite ground in a limited volume of air, from a pulp slightly acid in the vicinity of the mineral particles, probably because of oxidation of the pyrite, to yield principally elemental sulfur, but also miscellaneous volatile organic compounds as yet incompletely determined. Experiment No. 8 Acid-cleaned pyrite was ground eighteen hours with 2.00 g. of potassium n-amyl xanthate. The aqueous mixture was agitated with redistilled benzene in a closed jar, on agitating rolls. All the pyrite went into the benzene phase. The benzene was evaporated with a current of air; the resulting residue contained sulfur and something that smelled like an ester. This experiment shows that the reactions with amyl xanthate are similar to those with ethyl xanthate. Experiment No. 9 Five hundred grams of cleaned pyrite and 1 g. of ethyl dixanthogen in 20 cc. of ethyl alcohol was added to one-half liter of water. The mixture was ground for six hours. The mill was opened and a sample of the pyrite, which formed a dry froth (14), was immediately shaken with ether and the sample was tested for dixanthogen. No dixanthogen or xanthate was found,-only sulfur. The amount of sulfur recovered from the total pulp was 0.210 g., which corresponds nearly to two atoms of sulfur per dixanthogen molecule. This experiment shows that dixanthogen in contact with pyrite is decomposed to yield elemental sulfur. Experiment No. i0 Five hundred grams of pyrite was ground twelve hours in a normal potassium hydroxide solution, After this preliminary grind 1 g. of ethyl dixanthogen was added and the mixture was ground further for eight hours. The leach liquor contained some oil, possibly dixanthogen, together with


843

sulfur. The sulfur was less abundant than in experiments conducted in pulps not made alkaline. This experiment suggests that if the sulfuric acid formed by the reaction of atmospheric oxygen with pyrite in the presence of water is neutralized and an excess of alkali is present, the dixanthogen msy not decompose so readily, nor perhaps be abstracted so readily.

Experiment No. 11 Five hundred grams of cleaned pyrite was ground for six hours to be tested as a blank. In the acetone leach there was found a small amount (less than 0.020 g.) of sulfur and traces of ferric chloride. The amount of sulfur found was less than one-tenth the amount found in corresponding experiments with a xanthate or dixanthogen. This experiment shows that the sulfur observed in experiments 7 to 10 is essentially not an impurity derived from the mineral. Experinmt No. 12 Seven hundred grams of uncleaned pyrite was ground in a nitrogen atmosphere to parallel experiment No. 6 carried out with galena, except that amyl xanthate was used in place of ethyl xanthate. Of the 0.991 g. of xanthate added, 0.986 g. was abstracted or decomposed. Less sulfur was found than in other experiments, and the sulfur was sticky with an oil. This experiment shows that amyl dixanthogen is formed when amyl xanthate is added to pyrite, but that the dixanthogen is subsequently decomposed to yield sulfur. From the above experiments it is clear that the product of the reaction of a xanthate with pyrite, or of a dixanthogen with pyrite, is in the end sulfur, together with some as yet incompletely identified volatile compounds. If the quantity of oxygen or other oxidizing agent is minimized, the reaction chain may be limited merely to the production of dixanthogen. It is not known whether xanthate ion is adsorbed momentarily a t the pyrite surface where it becomes oxidized to dixanthogen, or whether soluble iron salts are responsible for the change of the xanthate in solution. In the absence of definite evidence as to the mode of oxidation of the xanthate, the following reaction steps appear likely:

+ +

+

+

1. Pyrite oxygen xanthate ion -+ dixanthogen-coated pyrite sulfate ion; 2. Pyrite dixanthogen suspension in water -+ dixanthogen-coated pyrite; 3. Dixanthogen-coated pyrite oxygen -+ sulfur miscellaneous volatile compounds.

+

+

T H E SURFACE REACTIONS O F OTHER SULFIDE MINERALS

Preliminary experiments in need of duplication and extension have been conducted with chalcocite, CuzS, chalcopyrite, CuFeSz, and sphalerite,

844


ZnS. In view of the interest presented by these incomplete experiments, some of the results are presented here. Sphalerite does not abstract xanthates from solution (Id); no reaction product can be extracted from the mineral. Chalcocite abstracts isoamyl monosulfide from aqueous suspension. Part of the reagent, unchanged, can be extracted from the treated mineral. Chalcocite abstracts isoamyl disulfide from aqueous suspension. The reagent is changed to the monosulfide and sulfur. Chalcocite abstracts isoamyl mercaptan from aqueous suspension or solution. The reagent appears changed to isoamyl monosulfide and sulfur (13). Chalcopyrite abstracts isoamyl monosulfide from aqueous suspension. The reagent appears changed to a mixture of sulfur and an oily substance as yet unidentified. SUMMARY

Much work remains to be done to complete the investigation which has been undertaken. However, the following conclusions summarize the results obtained so far. 1. Galena reacts with xanthates to form lend xanthates, principally by metathesis of oxidized coatings with the xanthate. Subsequently the xanthate changes to sulfur and unidentified oils. Some of the changes appear to require atmospheric oxygen. Because of the great area over which the lead xanthate or dixanthogen is assumed to be spread, the galena may well be regarded as a catalyst in the decomposition of the primary reaction product. 2. Galena abstracts dixanthogen from aqueous suspension, and apparently catalyzes the decomposition or oxidation of the dixanthogen to yield principally elemental sulfur. 3. Pyrite, or ferric ion derived from it by oxidation, changes xanthate to dixanthogen; the dixanthogen can be extracted from the mineral surface provided oxidation of the dixanthogen is prevented. 4. If oxidation a t the surface of pyrite is not restricted, the dixanthogen formed there by preliminary oxidation of xanthate, or that abstracted directly from a suspension of dixanthogen, breaks down to elemental sulfur and miscellaneous volat,ile compounds. 5. Reactions of the copper and zinc sulfides appear to be different from those of galena and pyrite. In general, indeed, it may be said that each mineral-reagent combination requires a special investigation. The writers wish to express their appreciation to Mr. M. S. Hansen and Mr. L. J. Hartzell, Jr., for the use of unpublished data.

SURFACE ACTIONS OF SULFUR-BEARING COMPOUNDS

845

REFERENCES (1) GAUDIN,A. M.: Flotation. McGraw-Hill Book Co., New York (1932). (a) p. 361; (b) pp. 64,296, 308; (c) pp. 65-6; (d) p. 205. (2) LUYKEN,W., AND BIERBRAUER, E.: Flotation in Theory and Practice. Julius Springer, Berlin (1931). (3) TAGGART, A. F., TAYLOR, T. C., AND KNOLL,A. F.: Am. Inst. Mining Met. Engrs., Milling Methods, p. 223 (1930). Chemical Reactions in Flotation. (4) TAGGART, A. F., TAYLOR, T. C., AND INCE,C. R.: Am. Inst. Mining Met. Engrs., Tech. Pub. No. 204 (1929). Experiments with Flotation Reagents. (5) HOLMAN, B. W.: Trans, Am. Inst. Mining Met. Engrs., p. 613 (1930). Flotation Reagents. (6) OSTWALD, WOLFGANG: Kolloid-Z. 68, 179 (1932). On the Theory of Flotation. (7) MELLOR,J. W.: Comprehensive Treatise on Inorganic and Theoretical Chemistry, Vol. VII. Longmans, Green and Co., New York (1927). (See “lead sulfide,” also “galena.”) (8) WILKINSON, W. D. Master’s thesis, Montana School of Mines, 1932. Certain Sulfur-Bearing Flotation Collectors and Their Reactions with Sulfide Minerals. (9) GROSS,JOHN, AND ZIMMERLEY, S. R.: Am. Inst. Mining Met. Engrs., Milling Methods, p. 30 (1930). (IO) NORRIS,JAMES F.: Organic Chemistry, p. 240. McGraw-Hill Book Co., New York (1922). (11) SHCHERBAKOVA, E. A.: Tzvetnuie Metalli, 1932, 8. Xanthates, their Properties and Importance for Flotation. (12) GAUDIN,A. M., GLOVER,HARVEY, HANSEN, M. S., AND ORR, C. W.: Flotation Fundamentals, University of Utah Tech. Paper No. 1, 1928. (13) SLAGLE, KENNETH H., AND REID,E. EMMET: Ind. Eng. Chem. 24,448-51 (1932). Action of Some Mercaptans in Hydrocarbon Solution on Copper and Copper Sulfide. (14) GAUDIN,A. M., AND MALOZEMOFF, P.: J. Phys. Chem. 37, 597-607 (1933). Recovery by Flotation of Mineral Particles of Colloidal Size.

SURFACE ACTIONS OF SOME SULFUR-BEARING ORGANIC

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