I AMERICAN INSTITUTE OF h.IINISG AND hIETAT,I.URGIC.XT, GXGINEERS ! Contribution No. 26 (CLA~S B, MILLING AND CONCENTRATIOS). FEBRUARY. 1933 DISCUSSION OF THIS PAPER IS INVITED. It shouId preferably be presented a t the New York Meeting. February. 1933, when an abstract of the paper will be read. If this is impossible. discussion in writing may be sent to the Editor. American Institute of Mining arid Metallurgical Engi- neers. 29 West 39th Street. New York. N. Y.. for presentation by thc Secrctary or othcr representative of its author. Unlcss special arrangement is made the discursion of this paper nil1 close April 1, 1933. Any discussion offered thereafter shouId preferably be in the form of a ncw papcr. Action of Alkali Xanthates on Galena* ! BY T. CLINTOX TAT LOR^ AND A. F. ~<ZIOLL.$ NEW YORK, N. Y. (New York Meeting, February. 1933) QUALITATIVELY, galena (native lead sulfide) reacts with aqueous solutions of the xanthates,' and has its surface sufficiently altered so that there is a tendency for air bubbles to attach themselves to the mineral crystals where there was no such effect before the treatment. This property is utilized in froth flotation operations where the mineral sulfide particles are raised into the froth and the gangue whose surface is not -- altered remains behind. The results of a study of this reaction were reported2 recently and certain tentative suggestions about the interaction of gxlena and the alkali xanthates were offered. In this paper, there is set down the results of a detailed quantitative investigation of the ions involved in this inter- action with a view to finding out more about the condition existing imme- diately at the surface of a crystal like a heavy metal sulfide after treatment with an organic reagent. Past experimental experience showed that finely ground galena shaken with aqueous potassium xanthate abstracts xanthate ion and at the same time sulfate ion, reducing ions of the type (S,O,)= where the ratio of m to n is less than 4:l (as in sulfate), sometimes hydroxyl ion are thrown into s~lution.~ The present quantitative study of the galena-aqueous potassium xan- thate system shows that at the lower concentrations of potassium xan- thate (less than about 25 mg. per liter) the amount of xanthate ion abstracted by the galena can be accounted for by the amount of reducing ions of the (S,O,)= type and sulfate ion thrown into solution. At these * The material reported here is taken from a dissertation presented by A. F. Iinoll to the Faculty of Pure Science, Columbia University, in partial fulfillment of the requirements for the degree of Doctor of Pl~ilosopl~y. For details see original dissertation. Associate Professor of Chemistry, Columbia University. 1 Department of Chemistry, Columbia University. A. F. Taggart, T. C. Taylor and C. R. Ince: Trans. A. I. M. E. (1930) 87, 285. Milling Methods. A. F. Taggart, T. C. Taylor and A. F. Knoll: Trans. A. I. R4. E. (1930) 87, 217. Milling Methods. Reference of footnote 2. Copyright, 1933, by the American Institute of Mining and hfetallurgical Engineers, Inc. Printed in U. S. A.
Transcript
I AMERICAN INSTITUTE OF h.IINISG A N D hIETAT,I.URGIC.XT, GXGINEERS
! Contribution No. 26 ( C L A ~ S B, MILLING A N D CONCENTRATIOS). FEBRUARY. 1933
DISCUSSION O F THIS PAPER IS INVITED. It shouId preferably be presented a t the New York Meeting. February. 1933, when an abstract of the paper will be read. If this is impossible. discussion in writing may be sent to the Editor. American Institute of Mining arid Metallurgical Engi- neers. 29 West 39th Street. New York. N. Y.. for presentation by thc Secrctary or othcr representative of its author. Unlcss special arrangement is made the discursion of this paper nil1 close April 1 , 1933. Any discussion offered thereafter shouId preferably be in the form of a ncw papcr.
Action of Alkali Xanthates on Galena*
! BY T. CLINTOX TAT LOR^ AND A. F. ~ < Z I O L L . $ NEW YORK, N. Y.
(New York Meeting, February. 1933)
QUALITATIVELY, galena (native lead sulfide) reacts with aqueous solutions of the xanthates,' and has its surface sufficiently altered so that there is a tendency for air bubbles to attach themselves to the mineral crystals where there was no such effect before the treatment. This property is utilized in froth flotation operations where the mineral sulfide particles are raised into the froth and the gangue whose surface is not
-- altered remains behind. The results of a study of this reaction were reported2 recently and
certain tentative suggestions about the interaction of gxlena and the alkali xanthates were offered. In this paper, there is set down the results of a detailed quantitative investigation of the ions involved in this inter- action with a view to finding out more about the condition existing imme- diately a t the surface of a crystal like a heavy metal sulfide after treatment with an organic reagent.
Past experimental experience showed that finely ground galena shaken with aqueous potassium xanthate abstracts xanthate ion and a t the same time sulfate ion, reducing ions of the type (S,O,)= where the ratio of m to n is less than 4 : l (as in sulfate), sometimes hydroxyl ion are thrown into s ~ l u t i o n . ~
The present quantitative study of the galena-aqueous potassium xan- thate system shows that a t the lower concentrations of potassium xan- thate (less than about 25 mg. per liter) the amount of xanthate ion abstracted by the galena can be accounted for by the amount of reducing ions of the (S,O,)= type and sulfate ion thrown into solution. At these
* The material reported here is taken from a dissertation presented by A. F. Iinoll to the Faculty of Pure Science, Columbia University, in partial fulfillment of the requirements for the degree of Doctor of Pl~ilosopl~y. For details see original dissertation.
Associate Professor of Chemistry, Columbia University. 1 Department of Chemistry, Columbia University.
A. F. Taggart, T . C. Taylor and C. R. Ince: Trans. A. I . M. E. (1930) 87, 285. Milling Methods.
A. F. Taggart, T. C. Taylor and A . F. Knoll: Trans. A. I. R4. E. (1930) 87, 217. Milling Methods.
Reference of footnote 2.
Copyright, 1933, by the American Institute of Mining and hfetallurgical Engineers, Inc. Printed in U. S. A.
2 ACTION O F ALKALI XANTHATES ON GALENA
low concentrations of xanthate ion, hydroxyl ion is not in evidence. At higher concentrations of xanthate ion (greater than about 25 mg. per liter), the amount of xanthate ion abstracted cannot be accounted for by liberated sulfate ion'and the reducing ions (S,O,)= together, and it is only a t these higher xanthate-ion concentrations that hydroxyl ion can be found. That reducing ions of sulfur-oxygen type are associated with galena is evidenced by the fact that aqueous extracts of galena that had been exposed to air for a long time reduced iodine and permanganate solutions. A precipitate (BaSO.,) is also obtained if barium ion is added to the acidified a h e o u s extract. If precipitated BaS04 is filtered off and the filtrate oxidized with HzOz more Bas04 is obtained. The aqueous extract also gives a white precipitate with AgNOs, which rapidly turns brown and then black. This indicates thiosulfates or t h i ~ n a t e s . ~ The aqueous extract of freshly ground galena generally gives almost negative results when tested as described above, although, as will be shown later, detectable amounts of the above ions may ultimately be displaced from it.
Ezperimental Procedure
The experimental procedure followed by the authors in the tests described in this paper was as follows:
Large pieces bf galena,5 (about 2-in. cubes) were broken down to pieces >Q to )/4 in. on edge. The pieces that had bright clean surfaces and contained no inclusion^,^ were ground by hand in u porcelain mortar and passed through a 200-mesh brass sieve.
Thirty grams of the powdered galena was put, into a 500 C.C. Pyrex glass stoppered Erlennleyer flask, containing 300 C.C. of aqueous potassiunl xanthate solution. The flask was then fastened to the of a wheel 3 ft,. in diameter and slowly revolved so that t.he powdered galena kept'falling through the solut.ion. Controls containing potassium xanthate solution alone were run also, and were carried through the same process (mixing, filtering, etc.) as the actual experimcnt,~. The galena was then filtered off on an asbestoc mat7 in a Gooch erucihle.
The following determinations werc attempted on aliquot portions of the filtrate: (a,) The total reducing capacity in terms of 0.002N iodine, which was the sum of
that due to xanthnte ion and the ions (S,O,)-. (b) The reducing capacity after the removal of xanthate ion as xanthic acid is
due to the ions (S,O,)'. The xanthate ion equivalency in terms of 0.002N iodine 1s given by the differencc between determinations n and 6 .
(c) Sulfate ion. (d) Hydroxyl ion. ( e ) Sulfide ion (qualitative). (f) Carbonate ion.
T. Takamatsu and W. Smith: Chem. Soc. (1880) 37, 592. Galena obtained from tshc Ward Scientific Establishment, Rochester, N. Y.,
was marked as coming from Ottawa County, Oklahoma. The asbestos used showed no abstraction of xanthate when shaken with aqueous
potassium xanthate. Filter paper is uncertain in its action. Some of it is acidic, and weakly alkaline sol~itions filtered through it become acid.
7 Reference of footnote 6.
T. CLINTON TAYLOR AND A. I?. KNOLL 3
Because of the low concentrations worked with, it was found necessary to employ 0.002N iodine solution in the iodine titrations with starch as an indicator.
The volume of 0.002N iodine necessary to give a visible blue c.olor with a starch suspension is appreciable. This factor must, therefore, be compensated for in the iodine titration. For example, 50 C.C. of water containing 2 C.C. of a 1 per cent potato starch paste required 0.75 C.C. of 0.002N iodine solution. The volume of iodine needed to give a visible blue color varied with the kind of starch used and with the ionic strength of the solution, and a blank correction is made to avoid error here.
I t is possible to get a sharp end point with the minimum amount of iodine by adding for each 50 c.c. of solution to be titrated 5 C.C. of KzSOr. This salt affects tho formation of the starch iodine complex.
The filtrates from the treatment of galena with high concentrations of alkali xanthate are alkaline (pH = 9). At this alkalinity iodine is changed to hypoiodite, iodate, etc., so it is necessary to bring the filtrate to a pH of 7.5 or 8 with 0.05M acetic acid (amount determined by a side titration with phenophthalein) before addition of the iodine. If the filtrate is made too acid (pH = 5 or less) xanthic acid is formed and decomposes to non-iodine consuming products.
Determination of Total Reduding Ions.-A 50-C.C. aliquot of the filtrate to which were added (after neutralization with 0.05 acetic acid) 5 C.C. of 0.2M ICZSOI and 2 C.C.
of 1 per cent potato starch paste was titrated with 0.002N iodine. The titration was corrected by subtracting the value from a blank run as mentioned above.
The iodine titer is due to the interactions described by the following equations:
The precision that could be obtained using 0.002N iodine was determined by means of potassium xanthate as a standard. On 50 C.C. of solution representing 1 to 10 mg. of potassium xanthate checks could be obtained within 0.3 per cent.
Determination of Reducing Ions No' Xanthate (S,O,)'.-For the determina- tion of reducing ions not xanthatc, a 50-c.c. aliquot of the filtrate mas acidified with 50 C.C. of 0.3M tartaric acid. The xanthic acid thus formed deco~nposed almost instantaneously. In order to insure complete removal of the xanthic acid, the acidi- fied aliquot was extracted in a separatory funnel with two 20 c . ~ . portions of toluene (xanthic acid is insoluble in water and miscible with organic solvents). The aqueous layer of the extraction to which was added one water nPashing of the toluene layer was titrated after the addition of 5 C.C. of 0.2M KzSO4, with 0.002hl iodine. A blank cor- rection was applied as before. The applicability of this method to mixtures of potas- sium xanthate, sodiurn sulfite and sodium thiosulfate is illustrated below.
50 C.C. aliquots of a potassium xanthate mixed with either NazSz03 or Na2S03 solution were titrated with 0.002N iodine. Other 50 C.C. portions were acidified with 6 C.C. of 0.3M tartaric acid. These were then extracted with toluene as above. The aqueous layer was titrated with 0.002N iodine in each case.
The results of these experiments show that xanthic acid is completely removedby-the toluene from the water layer so that in subsequent titra- tion of the water layer only the inorganic ions such as sulfite, etc., when present, are titrated with iodine. Thus it is possible to differentiate between residual xanthate ion and other iodine-reducing ions.
Determination of Sulfate Zwn.-A 100-C.C. aliquot of the filtrate was transferred to a steamed Pyrex Erlenmeyer flask acidified with 0.5 C.C. of 6M HC1 and evaporated
4 ACTION OF ALKALI XANTHATES ON GALENA
to about 15 C.C. on an electric hot plate, whereupon i t was filtered and washed into a 50 c.c. steamed Pyrex beaker. The sulfate ion was then precipitated and weighed as BaS04 according to the micro method of Pregl.8 Duplicate determinations agreed within about 2 per cent. Blanks on the potassium xanthatc solution used were run along with the actual determination.
Delermination of Alkalinity.-Because of the low buffering capacity of the fil- trates, the pH was determined calorimetrically on 10 C.C. by means of the Net t - Beaver col~rimeter .~ Although precision within a few hundredths of a pH could be obtained on a single set of readings, duplicate determinations varied generally in the direction of a decrease in pH due probably to carbon dioxide from the breath of the operator and from the air. Accordingly, results are reported to the nearest tenth of a pH unit.
Quditative Test of Suljide Ion.-A 25-C.C. aliquot of the filtrate was tested for sulfide by the method involving n change of the sulfide ion to a blue thiazine dye.lO This test was shown to be applicable in the presence of xanthate ion, a t concentrations of as low as 0.06 mg. per liter of S' calculated as H2S. This is equivalent to the sulfide ion that would result if the interaction of about 0.6 mg. per liter of potassium xanthate with lead sulfide took place.
From a series ofruns the data given in Table 1 were obtained. The equations that were the basis for the calculation in equivalencies in columns 4 and 5 of Table 1 are:
No sulfide ion was found in any of the above experiments. The failure to detect sulfide ion cannot be accounted for on the basis of its disappear- ance caused by the following interaction of sulfide with sulfite to form free sulfur, for this would go on only if supplied with sufficient hydrogen ion," and experiments made with mixtures of sulfide and sulfite indicate that it does not go to any abpreciable extent above pH of approximately 7.
Examination of the data shows that a t the lower concentrations of potassium xanthate in the neighborhood of about 25 mg. per liter the removal of the xanthate ion can be accounted for by sulfate ion and reducing ions (SmOn)- thrown into solution. At the higher xanthate-ion concentrations the above ions do not account completely for the amount of xanthate ion abstracted and the mixture becomes progressively more
F. Pregl: Quantitative Organic Microanalysis, 139. Philadelphia, 1930. Blaki- ston and Son.
9 J. J. Beaver: Optical Soc. Amer. (1929) 18,. 41. 10 J. H. Yoe: Photometric Chemical Analysis, 1, 373. New Yorlr, 1928. John
Wiley & Sons. , '
l1 F. P. Treadwell and W. T. Hall: Analytical Chemistry, 1, 372. New Irork, 1921. John Wiley & Sons.
T. CLINTON TAYLOR AND A. F. KNOLL 5
TABLE 1.-Metathetical Reactions between Galena and Xanthate Ion at Various Concentrations
alkaline. The assumption may be made that the unaccounted-for xanthate ion is involved through metathetisis, such as the following:
E a;: pen- merit No'
New batch of galena.
2K+ + COa' + H20 -+ OH- + 2K+ + H2C03 [3]
Original Solution
Potaaaium Xanthate. Mg. per
Liter
L M N 0 P
Reaction 1 would be a possible explanation if the galena had associated with the oxide ion. This possibility can be rejected however, since the hydroxyl ion resulting from such a metathetical reaction would explain only a small part of the equivalent xanthate ion not accounted for by the other ions, even though there would be some slight buffering of the hydroxyl ion by the reducing ions.
Reaction 2 can be dismissed as a possibility on the basis of experiment. In no case was sulfide ion found in the filtrate- from one-of the above experiments, even though the sensitivity of the test was extremely great.
Reaction 3, where the hydroxyl from the ion hydrolysis of potassium carbonate, which in turn would come from the double decomposition of
Potaasium Xanthate Removed, hlg. per 100 Grams Galena
lead carbonate, associated with galena and xanthate ion, is possible. If an amount of potassium carbonate is taken such that its concentration'is equivalent to that of the unaccounted for xanthate ion in Table 1, items G and H, its solution has a pH of 9.2 .when measured col~rimetrically.12 This pH is about that developed with the high concentrations of xanthate on galena. The results are to be regarded as only approximate, however, as pH determinations in carbonate solutions of this concentration are difficult to obtain with any assurance of accuracy, though good precision can be obtained with care.
During these interactions, the sodium or potassium ion concentration in the filtrate of whatever alkali xanthate is used with the galena does not change appreciably, showing that the alkali xanthate salts are not removed as such but only the xanthate ion is abstracted. This is proved by the following experimental work:
30 grams of galena (through 200 mesh) washed with water several times by decan- tation was shaken for 1 hr. with 300 C.C. of water containing 20 mg. of sodium xanthatc. The galena was filtered off on an asbestos filter. 100 C.C. of the filtrate was acidified and evaporated carefully to dryness, then the residual sodium chloride was dissolved in 10 C.C. of water and the sodium determined by the method of Kolthoff and Barber.13
A similar experiment was carried out using 67 mg. of potassium xanthate in 300 C.C. of water. Potassium ion was determined in the filtrate by the micro method of Emich.14 (The galena used was not of the same batch in both cases.)
The method used for the determination of sodium could be used over a range of from 0.6 to 5 mg. Na with an average precision of f 2 per cent. The method used for the determination of potassium could be used over a range from 1 to 10 mg. K with an average precision of f 1 per cent.
In the experiment with sodium xanthate the amount of that reage&, removed as calculated from the iodimetric titration was 8 of the 20 mg. put into the system. The determined sodium ion in the original sodium xanthate solution corresponded to 20.4 mg. of sodium xanthate. After the treatment with galena the filtrate showed sodium ion equivalent to 20.6 mg. of sodium xanthate, which is no appreciable change. Obviously other ions took the place of the xanthate ions removed.
With potassium xanthate, by iodimetric determination 60.6 mg. of potassium xanthate went in, 35.2 mg. was abstracted. The potassium ion in the original amount of reagent was 61.2 mg., while that after the reac- tion corresponded to 60.6 mg. of potassium xanthate. The results are similar to those in previous experiments with the sodium xanthate.
-
* Reference of footnote 9. 13 H. H. Barber and I. M. I<olthoff: Jnl. Amer. Chem. Soc. (1928) 60, 1625. l4 F. Emich: Mikrochemisches Praktikum, 129. Munich, 1931. J. F. Bergmann.
T. CLINTON TAYLOR AND A. F. KNOLL
ALKALINITY AND ITS CAUSE
The alkalinity that is developed in the interaction of higher concentra- tions of alkali xanthates and galena is also developed in the interaction of galena with other ions of widely different types which cannot themselves decompose to give hydroxyl ions. For example, a sample of galena that gave a filtrate after the galena xanthate interaction, with,a pH of 9.2, gave a pH of 9.3 when a new sample was treated with potassium oxalate (104 mg. per liter) and a pH of 9.4 when still another sample was treated with potassium chromate (121 mg. per liter). Solutions of each of the original reagents had a pH of 6.8 to 7.1. Repetition of these experiments gave similar results. Oxalate and chromate like xanthate form insoluble lead salts.L6
The indirect evidence that higher concentrations of alkali xanthate on galena gives rise to carbonate ion is corroborated further by the fact that powdered cerussite when treated with aqueous solution of potassium xanthate (300 C.C. of water and 60 mg. xanthate for 30 grams of cerussite) removes xanthate ion and the filtrate becomes alkaline (pH = 9.2).
That lead carbonate is actually associated with galena is demonstrated by the results of a direct microdetermination of the carbon dioxide liberated from the displaced carbonate ion.
A direct determination of carbonates in the small quantities that might be present in the filtrate from galena treated with aqueous potassium xanthate must necessarily be done under conditions. where all possible chance of carbonate ion, or carbon dioxide contamination, can be avoided or accounted for. Briefly, galena ground in air to smaller than 200 mesh, as before, was introduced into a flask and shaken with potas- sium xanthate solution made up with COz free water. The galena was filtered under conditions excluding carbon dioxide contamination. An aliquot portion of the filtrate was treated with acid to destroy xanthate ion. Because xanthates hydrolyze to carbonatesL6 on boiling with water, especially in the presence of hydroxyl ion, means had to be taken to circumvent the possibility. of contamination of the solution by carbonate ion from the source. Therefore the solution containing the filtrate from a treatment of galena with aqueous potassium xanthate was acidified with
and allowed to stand 1 hr. in a closed system." The liberated
'5 I t is interesting to note that the concentration of xanthate used in the flotation of sulfide ores is 0.1 lh. per ton, which with t,he water used is equivalent to 13 mg. per liter. In the technical use of xanthate for flotation, therefore, the concentration of 'the reagent is such that no alka,linity can he expected from the reaction of galena with xanthate ion. For other reasons,however, it is customary to work in slightly alkaline solution through the addition of lime.
16 M. Ragg: Chem. Zeil. .(1908) 32, 630, 654, 677. 17 For details see A. F. Knoll, Columbia Dissertation, 1932.
8 ACTION OF ALKALI. XANTHATES- ON GALENA
xanthic acid decomposed to carbon disulfide and alcohol according to the equation:ls
In order to fix the C 0 2 liberated from the carbonate ion in the filtrate by the acid, so that i t could be concentrated, the solution in the closed system was made slightly alkaline with carbonate-free 0.5N alcoholic potash. A small amount of extraneous carbonate ion, which was allowed for by means of blank experiments, probably arose from the hydrolysis of carbon disulfide by hydroxyl ion:
The alkaline carbonate solution was concentrated in the closed sys- tem, the solution cooled and acidified and the liberated C 0 2 transferred to a Van Slyke gasometer,19 to be measured volumetrically. Corrections were made. for the.extraneous CO2 from the carbonate ion mentioned above, for the solubility of the CO2 in the water and for other errors from blank determinations and from ones with known pure sodium carbonate in the system. . From the amount of carbon dioxide obtained, the equiva- lent in terms of potassium xanthate was calculated:
PbC03 + 2K+ + 2X- = PbXi + 2Kf + COJ- . (CO,)= EZ CO, ZE 2KX
X xanthate radica120 . '
Total reducing ions, that is, the sum of the unused excess xanthate ion and the new (S,O,)=, were determined iodimetrically on an aliquot . of the filtrate. After destruction of xanthate ion in another aliquot of the filtrate (by conversion into xanthic acid which decomposes into carbon bisulfide and alcohol),21 the residual reducing ions @,On)= were determined by an iodimetric titration. Sulfate ion and p H were also determined on separate portions of the filtrate. The results are given in Table 2.
Apparently the carbonate associated with a given sample of galena is initially with it and is constant in amount. When the concen- tration of the reacting xanthate reaches the point where the carbonate is displaced all of this ion is removed. No more seems to form as the galena stands exposed to air. On the other hand, the amount of other
. 18 H. Holban and A. Kirsch: Ztsch. physik. Chem. (1913) 82, 325.. '9 D. D. Van Slyke: Jnl. Biol. Chem. .(1917) 30, 347.
J. F. McClendon: Zbid., 259. 20 Reference of footnote 17. . . 11 Reference of footnote 18. .. . .
T. CLINTON TAYLOR AND A. F. KNOLL 9
TAEILE 2.-Metathetical Reactions between Galena and Xanthate Ion . i n C 0 2 Free System
Potassiu~n Xanthate Removed. Mg. per 100 Grams Galena Alkalinity
a Determinations spoiled. Orig. conc. potass. xanthate 200 mg, per liter.
ions displaced by xanthate increases. on standing. This phenomenon will be discussed in a later section.
I Time of
The amount of xanthate ion abstracted by galena can be accounted for now on the basis of metathetical reactions between the potassium xanthate and lead sulfate, other lead-sulfur-oxygen compounds and lead carbonate associated with the galena. There is no indication that reac- tion takes place between xanthate ion and lead sulfide itself. Apparently the sulfate ion is displaced from the surface first, then the somewhat less soluble sulfur-oxygen reducing ions, and finally the carbonate ion. This is in agreement with order of the solubility products of lead salts of these "
ions, if we assume that this product holds at least qualitatively for these salts when associated with the galena crystal lattice. Because of the small solubility product of lead sulfide, the amount of sulfide ion, if any, that comes from the interaction of the potassium xanthate and lead sul- fide is below the detectable limit.
F 3 wks. 57.6. New batch of galena exposed to air about one month.
G 87.0 19.2 26.4 9.8+ !8.8 1 19.1 1 27.1 1 4; 1 87 1 9 8 + I
Expcri- merit No.
The falling off in the'amount of xanthate ion abstracted by galena from the solutions of higher concentrations of potassium xanthate is evidently due to the formation of soluble complex ions. As a matter of fact, the otherwise insoluble crystals of pure precipitated lead xanthate disappear readily when shaken with an excess of a concentrated aque-ous solution of potassium xanthate. Apparently this is the same phenomenon
Total
Exposure after
Grinding
Accounted for as
Reduced ate Ion
Original S O ~ U - tion. pH
Total (SmOn): + (SO4 j- (Cod
Actual Filtrate,
pH
10 ACTION O F ALKALI XANTHATES ON GALENA
as that referred to above. In connection with this it may be noted that the "captive bubble test"22 shows smaller. and smaller bubble attachment a t the treated galena surface as the xanthate concentration of the solution used to treat the galena is increased, until finally it is negligible.
Two TYPES OF LEAD-OXYGEN IONS ASSOCIATED WITH GALENA
If powdered galena which has been exposed to filtered air for several hours is treated for long periods with water, lead sulfafe, sulfite and other lead-sulfur-oxygen salts are dissolved off until the solution apparently is saturated with these salts. Both the negative radicals on one hand, and the lead ions on the other, may be formed and the former are approxi- mately equivalent to the latter. In the case of lead sulfate, the amount formed (42.8 mg. per liter a t 23" C.) corresponds to the solubility of ordinary orthorhombic lead sulfate (41 mg. per liter a t 20" C., 45 mg. per liter a t 25" C.).23
The reducing ions obtained in shaking (1) 20 grams of oxidized galena with 200 C.C. of water, (2) 50 grams of galena with 200 C.C. of water were equivalent (after 2 hr. shaking) to:
(1) 29.4 C.C. of 0.002N I per liter,
I (2) 30.0 C.C. of 0.002N I per liter. I t is, of course, impossible to designate these ions as sulfite, thiosulfite,
etc., but the mixture (no sulfide) is constant and a determination of the lead ion shows that there is enough of these metal ions over and above those necessary to pair off with the sulfate, to be allocated to these sulfur- oxygen reducing ions.
Newly ground galena, however, gives smaller values for the solubility of the lead sulfate and the other lead-sulfur oxygen compounds associated with it, and in this case sulfate, sulfite and other lead-oxygen ions may be displaced from galena by xanthate in amounts in excess of that which can be dissolved off with water alone. The following experiment illus- trates this.
20-gram portions of galena (through 200 mesh) were shaken with 200 C.C. of ~vater N . .
for increasing time periods. Reducing ions measured in terms of - ~odlne and sul- 500
fate ion (calculated as PbSO,) were determined on aliquot portions of the filtrate. At the same time, 30-gram porlions of the galena were shaken with aqueous potassium xanthate (200 mg. per liter) in order to determine (bx displacement of the anions) approximately the total quantity of soluble lead salt associated with the galena. This was done by determining the sulfate and sulfur-oxygen-reducing ions in the filtrate from the galena-xanthate mixture. The results are summarized in Table 3.
22 Reference of footnote 1. 23-A. Seidell: Solubilities of Inorganic and Organic Substances. New York, 1919.
D. Van Nostrand. :
\ T . CLINTON TAYLOR AND A. F. KNOLL I
11
TABLE 3.-Lead Sal ts Dissolved by Water and Displaced by Xanthate I o n f rom Galena
Another batch of galena.
While the experimental data given can by no means be regarded as conchlsive, the indications are, from the above experiments, that the compounds formed by the initial oxidation of galena are more firmly anchored to the surface of the galena particle, and differ in structure from the compounds in their normal state. I t is interesting to note in this connection that Menzies and have found that the evaporation of solutions of salts on a clean galena surface results in orientation of the salt being deposited if the latter is isomorphous with the galena (sodium chloride, for example) whereas if the salt is not isomorphous with the galena no orientation takes place. In the light of the experimental work reported here, and of the experiments of Taggart, Taylor and Ince,Z5 it is highly probable that the surfaces used by Menzies had undergone some oxidation. If this is so, the conclusion follows that the lead-sulfur- oxygen compounds (lead sulfate, etc.) first formed are probably isomorph- ous with the galena. I t might be expected also that this anchored "cubic" lead sulfate would have a different solubility from the common (orthorhombic) lead sulfate. The solubility might be expected to be intermediate between lead sulfide and lead sulfate; in other words, less than the solubility of common orthorhombic lead sulfate.
On continued oxidation, the lead-sulfur-oxygen compounds (being farther removed from the surface of the lead sulfide and therefore from its sphere of influence) change over into their normal orthorhombic form.
C. A. Sloat and W. C. A. Menzies: Jnl. Phys. Chem. (1931) 36, 2008. 56 Reference of footnote 1.
~ i m e , Hr.
% 1 2 4
PbSo4, hlg. per Liter Reducing Ions Iodine per Liter, c.c. 500
Diaaolved by Water
9 . 9 9 . 5 9 . 6 9 . 8
Disaolved by Water
3 . 0 4 . 0 4 . 2 4 . 1
Displaced by Xanthate Ion
12.5
13.2
Displaced by Xanthate Ion
24.2
28.2
12 ACTION O F ALKALI XANTHATES ON GALENA
This is indicated by the fact that highly oxidized galena surfaces give normal solubility for lead sulfate.
I t is probable that these adherent "cubic" lead-sulfur-oxygen com- pounds are the ones that are most effective in attaching and orienting the xanthate ion to the crystal lattice of galena.
The fact that the amounts of xanthate ion removed by freshly ground galena (through 200 mesh) on several different batches were fairly con- stant in amount seems to preclude the possibility of irregular contamina- tion by inclusions. Different samples of freshly ground galena, for example, abstracted 40, 37,45, 39 and 34 mg. of xanthate ion (calculated as potassium xanthate) per 100 grams of galena.
1
SOTJRCE OF IONS. ASSOCIATED WITH GALENA
In the previous experiments on carbonate ion it was implied that the amount of this ion associated with a batch of galena is constant but that the amount of other ions formed on the galena surface was a function of time of exposure to air. The rate of oxidation of a sample of powdered galena in air can be followed by noting the abstraction of anth hate.^^
For example, the abstraction of xanthate initially on a 100-mg. sample of powdered galena was 24.1 mg., which became successively 25.3 for 3 hr.; 35.9 for 1 day; 41.1 for 2 days; 41 for 3 days; 48.0 for 7 days; 53.2 for 16 days; and 60.5 for 32 days exposure to COz free air. The pH of the filtrate remained a t about 9.3 throughout.
The amounts of sulfate and iodine-reducing sulfur-oxygen ions increased steadily during this time but the carbonate ion and concurrent alkalinity remained substantially constant. Even when the powdered galena is exposed to ordinary air laden with the usual amount of carbon dioxide, there is no appreciable increase in the amount of carbonate ion displaced by the xanthate.
If the massive galena is dry ground in nitrogen instead of in air, there is a great decrease, as might be expected, in the subsequent xanthate removed by the sample when compared with an air-ground sample. After one hour's grinding in air the abstraction was about 16 mg. per 100 grams of galena compared to 5.5 mg. of xanthate with nitrogen-ground galena. Wet grinding under corresponding conditions also shows that
'oxidation is rapid in air. 8
ORIENTATION OF SULPHYDRYL RADICAL
Turning to the xanthate radical that takes part in these reactions, it follows that that portion of the xanthate ion that displaces the "anchored" sulfate and sulfite becomes itself firmly anchored and thereby oriented.
_ _ ._ _ ._ . .. . . - - .
Ze Since iodine-consuming ions such as sulfite, etc., are thrown into solution as the xanthate is abstracted, a direct iodimetric titration mill often show no apparent xanthate removal. This must be considered and allowed for as in previous instances.
T. CLINTON TAYLOR AND A. F. KNOLL 13
I t is this film that is water-repellent, the remainder of the xanthate that is removed having nothing to do with the alteration of the surface of the galena. So firmly is the xanthate radical anchored that washing in running water does not remove it.
If we assume that the water-repellent capacity of the lead xanthate lies in the ethyl grouping, a change in the character of this grouping, from a water-repellent type to one that is water avid should result in change in the character of the surface. The hydroxyl (-OH) grouping is one that carries with i t water-avid properties, as evidenced by the fact that organic compounds assigned this grouping are characterized (other things being equal), for example, by greater solubility in water than one not assigned this grouping.
Accordingly, an attempt was made td prepare a compound having a hydroxyl group in place of one of one hydrogen atom in the ethyl grouping:
C=S (a glycol xanthate)
5 grams of sodium was dissolved in an amount of redistilled ethylene glycol in excess of that necessary to give the monosodium derivative of ethylene The rather viscous, clear, pale yellow liquid resulting was shaken with an excess of carbon bisulfide (25 c.c.) for 10 hours:
C2H4(OH)2 + Na = C2H4. OH . ONa CzHl . OH ONa + CS? = [(CS)(OCZHIOH)S] Na
Some of the carbon disulfide evidently reacted with the monosodium glycoxide, as the glycol layer slowly changed to a deep orange color. The mixture of carbon disulfide and glycol was extracted with ethyl ether to remove the excess carbon disul- fide. The mixture of glycol and what was presumably the sodium salt of glycol xanthic acid was soluble in water. The fact that the aqueous solution was only slightly alkaline indicated that practically complete reaction took place between the carbon disulfide and the monosodium glycoxide. The sodium salt of glycol xanthic acid could not be separated from the glycol mixture.
Solutions of the presumed glycol xanthate gave a red precipitate with lead ion and a white precipitate with zinc ion. A few drops of the "glycol xanthate" were dissolved in 1 liter of water and 300 c.c. of this were shaken with 30 grams of galena. No collection of a froth containing galena particle took place a t the surface of the solution. This indicated that the surface of the galena had changed little or not a t all in wet- ability. (The small amount of glycol present would have no effect). That some of the "glycol xanthate" had been abstracted by the galena is evidenced by the following iodine titretion.
. 27 A. Wurtz: i n n . Chem. [3] (1859) 55, 429. .
14 ACTION OF ALKALI XANTHATES ON GALENA
"Glycol xanthate" solution before shaking with galena used 170 C.C. 0.002N iodine per liter of solution after shaking with galena = 117 C.C. 0.002N iodine.
An ethyl xanthate solution of the equivalent concentration would have been affected to about the same extent.
As further evidence of the effect of the hydrocarbon grouping of the xanthyl radical on the degree to which this ion changes the wetability of minerals, Wark and Cox28 report that contact angle between the mineral and water increases (the mineral becomes less wetable) as the length of the hydrocarbon chain increases; for example, a butyl xanthate gives a higher contact angle than an ethyl xanthate when used in equiva- lent concentrations.
STAB~LITY OF ALKALI XANTHATES
Because of the confusion of data on the stability of the alkali xan- thates, and because in certain types of decomposition of the alkali xanthates alkalinity is developed, and further because the possible devel- opment of alkalinity from the xanthate has bearing on the results of the experiments, i t was thought desirable to include a short discussion of the reagent here.
Potassium ethyl xanthate may be taken as the example. 1t was pre- pared in the usual way,29 recrystallized twice from alcohol and kept in a vacuum dessicator over concentrated sulfuric acid for 24 hr. The salt is almost white and nearly odorless. I ts water solution has a pH = 7.2 and its conductivity shows that xanthic acid is a strong acid. The precipitated lead salt dried a t 60" C. contained 45.8 f 0.005 per cent lead against 46.1 per cent theoretical. Iodine titration, 99.5 per cent + 0.10 per cent xanthate.
As pointed out by Von Holban and Kirschsa and others, alkali xan- thates do decompose when acidified to give CS2 and alcohol, but i t has been found that the pH must be less than 5 and the temperature above 5" C. for this to happen. Below this temperature, the very water-insoluble xanthic acid is stable (and may be extracted with organic solvents). To carbon bisulfide and alcohol produced in this way, and by reaction 8 below, Kellerman and Bender31 ascribe the surface alteration of galena. That CS2 is not present in sufficient quantity to alter the surface proper- ties of galena comes also from the work of Wark and Cox," who find that carbon bisulfide has no measurable effect on the contact angle between galena and water, until the amount of carbon bisulfide added to the
28 I. W. Wark and A. B. Cox: A. I. M. E. Tech. Pub. 461 (1932). 29 P.-J. Beilstein: Organische Chemie (1921) 3, 209. J0 Reference of footnote 18. J1 K. Kellerman and E. Bender: Kollpid. Zlsch. (1930) 62, 240. 32 Reference of footnote 28.
T. CLINTON TAYLOR AND A. F. KNOLL 15
water exceeds its solubility, whereupon a visible coating of carbon bisulfide on the galena results. It is well known that liquids like carbon disulfide, which have a high interfacial tension measured against water, and oily substances in general, when applied to solids, raise materially the contact angle between the solid and water.33 In an alkaline solution (1 to 2N) according to Ragg,34 there is extensive decomposition of xanthate ion when judged by the composition of the insoluble cuprous salts which precipitate from the decomposed solutions and which are probably in the main th io~arbona tes .~~ This alkalinity is beyond that reached in any of the present experiments and again beyond that in usual flotation practice.
The equations describing the most likely react.ions by which alkali xanthates may decompose are :36
According to experience in this laboratory, the only commonly met decompositions are those taking place around the neutral point; namely those recorded in equations (8) and (9). The determinations to prove this follow :
1. Iodimetric titration will detect changes as in equations 4 and 8, since nothing except xanthate is affected by iodine.
2. Iodimetric determination of the aqueous layer after acidification and extraction with toluene will detect sulfide ion. Unchanged xanthate on acidification is either destroyed to give non-iodine-consuming sub- stances (equation 4) or xanthic acid, which is very soluble in toluene. Sulfide ion if present would be titrated in the water layer.
3. Determination of pH colorimetrically37 would indicate any reaction giving hydroxyl ion either directly as in equations 4 and 9, or indirectly.
4. Qualitative test for sulfide ion3s would show reaction. 5. Color of precipitate on adding lead ion is white for lead xanthate;
for thiocarbonates brown, and for sulfide, black. The amount of lead xanthate precipitated also serves as a guide.
The results are given in Table 4.
33 A. F. Taggart: Handbook of Ore Dressing, 777. New 'lrork, 1927. John Wiley & Sons.
34-3s.36 Reference of foot,note 16. 37 Reference of footnote 9. j8Reference of footnote 10.
16 ACTIOK OF ALKALI. XANTHATES ON GALENA
TABLE 4.-Stability of Potassium Xanthate Solution at pH 7* 1.1526 grams per liter
At pH = 8, and at 10, the results are substantially the same, showing that the decomposition of alkali xanthate in water solution is slow. The principal reaction is probably the one of oxidation t o ' d i ~ a n t h o ~ e n .
1. The action of alkali xanthates with galena is one of ionic inter- change. The alkalinity developed in the interaction is due to lead carbonate.
2. Alkali xanthate is not adsorbed as such. 3. Sulfide ion from the galena crystals does not take part in the
interaction. 4. A set of sulfur-oxygen ions closely related to the galena crystal
is postulated as being present. These are displaced by the sulphydryl radical but not dissolved off by water.
5. By virtue of the displacement of these anchored sulfur-oxygen ions, the xanthate ion is oriented.
6. The stability of alkali xanthates is discussed.
![xanthate - Krishna districtkrishna.nic.in/PDFfiles/MSME/Chemical/xanthate[1].pdf · Xanthate content 80% minimum ... Flash point 205 Deg.F ... the product would be dried in a vacuum](https://static.documents.pub/doc/80x56/5ab894a07f8b9a28468d0215/xanthate-krishna-1pdfxanthate-content-80-minimum-flash-point-205-degf.jpg)
