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Effect of the depressing agents FeSO4 and NaCN on the surface properties of galena in the flotation system
International Journal of Mineral Processing, 24 (1988) 111-123
111
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Effect of the D e p r e s s i n g Agents F e S 0 4 and N a C N on the Surface Properties of Galena in the Flotation S y s t e m S.R. POPOV, D.R. VUCINIC and N.M. CALIC
Faculty of Mining and Geology, University of Belgrade, Belgrade (Yugoslavia) (Received March 17, 1987; accepted after revision January 14, 1988)
ABSTRACT Popov, S.R., VuSini~, D.R. and Calid, N.M., 1988. Effect of the depressing agents FeS04 and NaCN on the surface properties of galena in the flotation system. Int. J. Miner. Process., 24: 111-123. The simultaneous effect of FeS04 and NaCN as depressing agents on the floatability and surface properties of galena at various pH values and with different concentration ratios of the two reagents has been determined. A good correlation between floatability, infrared data and zeta-potential measurements is obtained. The depressing action of FeSO4 and NaCN is observed for the pH range from 6.0 to 7.5. Under the depressed galena condition, and using KEX as a collector, a hydrophilic ferrocyanide compound is suggested as the species responsible for the mineral surface depression. In an alkaline medium, the flotation recovery of galena is not reduced in the presence of FeS04 and NaCN, but another kinetic of xanthate galena flotation is noted. Besides pH, the molar ratio of FeS04 and NaCN used is very important for the depressing effect of these reagents. The addition of Pb-acetate to a suspension of previously depressed galena causes a certain rise in the flotation recovery for the pH range from 5.5 to 7.0, at which the depression is obtained, but complete flotation (near 100% ) is not accomplished. The adsorption of Pb ~+ on pre-depressed galena is lower than that on undepressed galena, because the surface sites are occupied by the depressing compound.
INTRODUCTION
In several flotation studies on sphalerite, the hydrophilic properties acquired were found to be significantly affected by the addition of combined FeSO4 and NaCN reagents. The role of FeSO4-NaCN in a modifying sphalerite-xanthate collector system has previously been studied (Dra§kid et al., 1980, 1985). A new depressing procedure has been introduced in several flotation mills in Yugoslavia. FeSO4 and NaCN have several advantages over the application 0301-7516/88/$03.50
© 1988 Elsevier Science Publishers B.V.
112
of the pair ZnSO4 and NaCN: lower consumption of NaCN and other reagents, primarily that of CuSO4; high selectivity of the process; and higher recovery of silver in the lead concentrate. Moreover, the reduction in consumption of reagent has a beneficial effect on the environmental conditions (Pavlica et al., 1986). Consequently, for the study of lead-zinc ore, F e S Q and NaCN, when used as a modifying agent, depress the xanthate flotation of sphalerite and do not have a significant direct effect on the floatability of galena. It was observed, however, that the new pair of reagents had a certain effect on the kinetics of galena flotation under certain conditions of the flotation system. The present work is concerned with the effect of a new pair of depressing reagents (FeSO4 and NaCN) on galena xanthate flotation at various pH values, and with the effect of various proportions of FeS04 and NaCN reagents. Hence, it is a study of the influence of depressing agents, such as FeSO4 and NaCN, on the surface properties of galena. The zeta-potential measurements and infrared examination data are discussed in relation to the behaviour of the mineral in flotation. EXPERIMENTAL
Mineral and reagents A natural galena mineral was used. Specimens of ore were crushed, and the mineral grains picked were ground in a mortar. The mineral was then sorted into two particle-size fractions by sieving. The coarser fraction ( - 104 + 74 /~m) was used in the flotation test and a portion of the remaining - 7 4 ~m fraction was further reduced by grinding (for a few hours) in an agate mortar. This grain size was used in the infrared examination and in zeta-potential measurements. The mineral sample was stored in a vacuum desiccator. Chemically analysed, the galena sample contained 85.15% Pb and 13.31% S. For pH adjustment, NaOH and HeSO, of analytical-reagent grade were used. Commercial-grade potassium ethylxanthate (KEX), used as a collector in this study, was purified by multiple recrystallisation from acetone. It was stored in a vacuum desiccator over silica gel. Any other reagent used was also of analytical grade. Pb-acetate was used as the activating agent. The depressing reagents were combinations of FeSO4 and NaCN. Lead ethylxanthate, the spectrum of which is presented in this paper, was obtained from aqueous solution of Pb-acetate and potassium ethylxanthate by precipitation. The reaction product was washed with distilled water.
Methods and procedures The modified Hallimond-tube flotation technique was used. Approximately one gram of the mineral was conditioned in a 100-ml flask for three minutes
113
with a reagent (depressing and activating reagents, collector) at the desired concentration and pH. Then the suspension was transferred to a Hallimond tube and floated for 5 min at an air-flow rate of 10 ml per minute. Zeta potential was determined by means of the microelectrophoresis technique, using a Riddick Zeta-meter. A solution of the mineral was prepared and stirred, and samples of the colloidal supernatant were then charged in the electrophoretic cell. The zeta potential was measured after conditioning the suspension for 3 min upon each addition of reagents. The infrared spectrophotometric method was used in a qualitative analysis of surface products from the reaction between galena and the different flotation reagents. In order to increase the amount of reagent adsorbed on the mineral, it is finely ground, increasing the surface area and requiring the use of higher concentrations of reagents for infrared examination than for the flotation tests and zeta-potential measurements. For infrared examination, reagent concentrations ten times higher than those for flotation tests were used. The ratio of reagent concentrations used (depressing and activating agents, collector) and the solid/liquid ratio were the same as in the flotation tests. A Perkin-Elmer infrared spectrophotometer (type 397) with an ATR-attachment was used. The reflection elements used in the experiments were KRS5. The following procedure was applied in the experiment with powdered samples. A sample of 500 mg of galena was added to 50 cm ~ of distilled water and after a few minutes agitation, a portion of desired reagent was added and the agitation continued for another 5 min. After the addition of each reagent, the suspension was conditioned by a magnetic stirrer for another 5 min and the solution was decanted (after depression, activation or collection ). The purpose of the decantation was to prevent the formation of precipitates in the bulk of the solution, since high concentrations of reagents were used in the experiments. After the last decantation of the solution, the sample together with the remaining solution was put in contact with the surface of the reflexion element and examined spectrophotometrically. RESULTS AND DISCUSSION
Floatability tests The first set of tests included the galena floatability without (natural floatability) and with various flotation reagents (Fig. 1 ). It is evident that the natural floatability of galena is relatively high at all the pH ranges tested (Fig. 1, curve 1 ). The results show that a small rise in floatability above the natural floatability of galena occurs with KEX in the pH range from 6.0 to 10.0 (Fig. 1, curve 2). The effect of depressants (FeSOt and NaCN) on the flotation behaviour of
114
_9
100.
8C
>_n~ ~J > 0 0 iii nZ 0
40
LI_
20
[C] = [kmot m-'] KEX (1.5 x 10- 4 ) Fe SO4 ( 2.0,10 .4 ) Na CN ( 2.0 x 10-4 ) Pb- acetate ( 9.0 x 10-5 )
Fig. 1. Flotation recovery of galena as a function of pH in the presence of: 1--the natural floatability; 2=KEX; 3-- (FeSO4+NaCN) +KEX; 4 = (FeSO4+NaCN) +Pb-acetate+KEX (depression performed at pH 5.7).
>> O
60
uJ
u_
2C
;
½
:3
z,
;
TIME,
rain
Fig. 2. Flotation recovery of galena as a function of time at pH 8.0:1 = K E X ; 2 = (FeSO4 + N a C N ) (both 2.0" 10 -4 kmol m - a ) + KEX.
galena in the presence of KEX is also depicted in Fig. 1 (curve 3). The data indicate that a combination of the reagents, FeSO4 and NaCN, depresses galena flotation within the pH range from 6.0 to 7.5, with KEX as a collector. Recovery of galena was good (nearly 100% ) in the basic medium. The flotation
115 recovery of depressed galena is practically the same as that in the absence of a depressor at pH values above 7.5. However, a different kinetics of flotation between the depressed and undepressed galena in the basic pH range was observed. Fig. 2 shows the data from our examination of the depressing effect on the flotation kinetics. In order to compare the effect of depressing reagents on galena flotation kinetics, the flotation was tested as a function of time. The results show that the depressants had a certain effect on the galena flotation speed. Galena floats faster with K E X without depressants (curve 1 ) than in the presence of FeS04 and NaCN (curve 2). In fact, a longer time is necessary for complete flotation of depressed galena (about 100% ) t h a n for galena without depressants. The following step of the experiment was to test the influence of a Pb-acetate activating agent on the flotation of pre-depressed galena with K E X as a collector (Fig. 1, curve 4). The depression was always carried out at a pH of about 5.6, and the activation at various pH values. The results show the flotation recovery as a function of the activation pH. An activation, when Pb-acetate was added to the system of previously depressed galena, was noted in the pH range from 5.5 to 7.0, but full flotation was not accomplished. The test results on the influence of various proportions of depressing agents on the flotation recovery of galena at three pH values are shown in Fig. 3. It is evident that, with increasing FeSO4 concentrations, but with the same concentration of NaCN (2" 10 -4 kmol m - 3 ) , the flotation recovery decreases at each
I00
~___.._~,~_~-----'-~~o.~
!-
80
W
60
0 UJ Z 0
.J mJ
40
[c] ~[kr.ot m-~1 Na aN ( 2.0 x 10-4) KEX (1.56 x 10")
20
o.'i
'
'
'
oTs
. . . . . . . .1.0.
\/LP
1.4
CFeSOJZNaCN
Fig. 3. Flotation recovery of galena as a function of CFeSO4/CNaCN;I =pH=6.0; 2--pH=7.4; 3=pH=8.5.
116
of the tested pH values. Fig. 3 shows the flotation recovery of galena with KEX as a collector, where the FeSO4/NaCN concentration ratio is increasing. The maximum flotation recovery is clearly seen to occur at a ratio of FeSO4/ NaCN = 0.5, at any tested pH range. The plots demonstrate increasing amounts of FeSO4 to be required in depressing the mineral at pH values higher than 6.0.
Zeta-potential measurements The surface properties of galena with or without additives (depressing or activating agents, collector) were tested by determining the zeta potential. The zeta potential for galena, as a function of pH, is shown in Fig. 4 (curve I ). A negative surface is noted in the pH range tested. These results roughly agree with the published data (Solzhenkin et al., 1958; Yarar and Kitchener, 1970; Yiicesoy and Yarar, 1974; Pugh and BergstrSm, 1986). The addition of NaCN to a galena suspension results in a more negative zeta potential (Fig. 4, curve 2) than without additive in the entire pH range tested, indicating a low adsorption of C N - ions on the galena surface. The effect of FeSO4 on the zeta potential of galena is also illustrated in Fig. 4 (curve 3). Comparison of these results with the distribution diagram for Fe 2+ (Baes and Mesmer, 1976; Langmuir, 1969; Wagman et al., 1969) indicates that the zeta potential reverses its sign from - to + at about pH 5.4, due to the formation +3 0 -
NaCN (2.0x 10-4) Fe SO4 ( 2.0 x 10-~" ) KEX (1.5xi0 -4)
+ 20"
÷10-
E pH < x
UJ
u.l N
-TO-
- 20-
- 30-
Fig. 4. Zeta potential of galena as a f u n c t i o n of p H : 1 = w i t h o u t reagents; 2 = w i t h N a C N ; 3 = w i t h FeSO4; 4 = w i t h F e S 0 4 + N a C N ; 5 = w i t h (FeSO4 + N a C N ) + K E X .
117
of Fe 2+ and, to some extent, Fe (OH) + ions in the solution and their adsorption on the galena surface. At about pH 7.5, the zeta potential again reverses its sign (from + to - ) because the concentration of Fe 2+ ions decreases with increasing pH (according to the distribution diagram). At the same time, the concentration of Fe (OH)2 in the solution is increasing. In an alkaline medium, the galena surface is negatively charged in the presence of FeSO4, but it is less negative than without the additive. Curve 4 in Fig. 4 shows the zeta potential of galena treated with FeSO4 and NaCN. First, F e S Q was added to a galena suspension and, after conditioning the suspension for a few minutes, NaCN was added. The zeta potential was measured after the galena suspension had been conditioned for another 5 min. It is clear from a comparative scrutiny of curves 3 and 4 in Fig. 4 that the sorption process was a superficial reaction between Fe 2+ ions, previously adsorbed on the galena surface, and probably ferrocyanide ions, contained in the solution. Also that the depression of galena (by F e S Q and NaCN) in the pH range 6.0-7.5 was due to the formation of the hydrophilic ferrocyanide compound on the mineral surface. Its presence there reduces the floatability of the mineral. With increasing pH of the solution, the concentration of free Fe 2+ ions decreases and subsequently the hydrophilic ferrocyanide complex is not formed in sufficient amount, and the depressing action of F e S Q and NaCN ceases. The effect of KEX on the previously depressed galena (Fig. 4, curve 5) is seen in the increasing negative values of the zeta potential as compared with the same system without a collector (Fig. 4, curve 4). These results illustrate the adsorption of collector on the galena surface in the presence of the pair of depressing reagents. However, with a reduction of the pH from 7.0 to 5.5, a decrease in the negative values of the zeta potential is noted. At pH 6.0, the zeta potential of depressed galena with KEX is similar to that without. It corresponds to the pH range at which the galena flotation is reduced (Fig. 1, curve 3). The next experiments included examination of the surface properties of galena after the activation (with Pb-acetate) of pre-depressed and undepressed minerals (Fig. 5). For the latter (Fig. 5, curve 4) in the pH range 5.5-7.1, the zeta potential is positive due to Pb 2+ ion adsorption and, to some extent, Pb (OH) + ion adsorption on the galena surface. This is exactly the pH range at which Pb 2+ prevails and P b ( O H ) + ions begin to form in the bulk of the solution. Distribution diagrams for lead show these phenomena (Beas and Mesmer, 1976; Latimer, 1952; Pugh and BergstrSm, 1986). In an alkaline medium, with the pH increasing above 7.0, the free lead ion concentration decreases, because the equilibrium between it and other lead-containing species derived from it in aqueous solution ( H P b O [ , Pb (OH) +, etc. ) moves toward a decreasing Pb 2+ concentration. Consequently, the surface charge of galena remains negative in an alkaline medium, in the presence of Pb-acetate.
118
[c]=[kmol m"3] FeSO¢ ( 2.0x 10.4 ) NaCN I2.0 xlO-4) Pb- acetate ( 9.0x 10 -s )
÷20'
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E
.ji-.-
Z w
11
i
B I1_
-10
N
-20
g ""----o
-
pH
10
Q~(I
-30
Fig. 5. Zeta potential of galenaas a function ofpH in the presenceof: 1 = without reagents;2 = with FeSO4+ NaCN; 3 = with (FeSO4+ NaCN ) + Pb-acetate; 4 = with Pb -acetate. Comparative curves 3 and 4 (Fig. 5) show that the adsorption of lead ions (Pb 2+) and hydrolized lead species ( P b ( O H ) +) is much lower on the predepressed than on the undepressed galena surface. Subsequent to depression, the number of surface sites available for lead-ion adsorption is expected to be reduced. Consequently, in the presence of FeSO4 and NaCN, the density of surface-adsorbed lead ion is lower t h a n that without the depressing agents. This agrees with the flotation data. In the pH range 5.57.0, the activation of depressed galena is not fully achieved (Fig. 1, curve 4). It is evident that activation occurs when there is still an amount of depressor on the surface sufficient to cause some level of depression.
Infrared tests We have studied the adsorption p h e n o m e n a in galena with various flotation reagent systems, using the method of internal reflection spectrophotometry (Harrick, 1967; Mielczarski et al., 1979). The goal of the first set of experiments was the study of adsorption on galena in the presence of depressing agents. The spectra resulting from t r e a t m e n t with FeSO4 and NaCN at pH 5.7 and 8.7 are shown in Fig. 6. The band at 2045 cm-1 suggests that, after the depressing action at pH 5.7 (spectrum 2), the presence of a compound containing the ferrocyanide group/Fe ( C N ) / g - on the galena surface (Jones, 1963; Nyquist and Kagel, 1971; Tananaev et al., 1971 ).
119 T, %
2100 2000
Fig. 6. Reflection spectra of galena after a t r e a t m e n t with FeSO4 a n d N a C N (molar ratio 1.0): 1 = without reagents; 2 = at p H 5.7; 3 = at p H 8.7; 4 = at p H 5.7 (molar ratio 0.5 ).
The depressing action of FeSOa and NaCN evidently results primarily from the deposition of a hydrophilic ferrocyanide complex on the mineral surface. A somewhat lower amount of the adsorption product was observed at the same pH (about pH 5.7) when a different proportion of depressing reagents was used; the FeSO4 to NaCN ratio was 0.5 instead of 1.0 in the earlier experiment (spectrum 4 ). In contrast to the previous data, the absorption band at 2045 c m - 1, a characteristic of the ferrocyanide group, is almost nonexistent when the depression was performed in an alkaline medium (pH about 8.7) (spectrum 3). This indicates the absence of the hydrophilic ferrocyanide complex on the galena surface. After the treatment of pre-depressed galena (at pH about 5.7) with KEX, the xanthate bands were observed (Fig. 7, spectrum 3), but the ferrocyanide compound band at 2045 c m - 1 remained. Absorption bands for the frequencies 1020 and 1110 and 1202 cm-1 (C = S and C - O vibrations) may be associated with the presence of lead ethylxanthate on the galena surface (Little et al., 1961; Greenler, 1962; Poling and Leja, 1963). They can also be seen in the spectrum of precipitated lead ethylxantate (spectrum 4 ). Under the same condition, the xanthate flotation of galena was partly depressed. Galena is not depressed by FeSOt and NaCN when ethylxanthate adsorption on the galena surface is fully prevented, but probably by a strong hydration of the ferrocyanide compound adsorbed on the galena surface, whereby the hydrophobicity of the collector coating was partly overcome.
120 T, %
z// / / 2045
'a
f\
Ij
I
Ii IP I J J I I
1210'~J 1202
I/ ~/ v 1110
~1020
2;o0 26oo
~2bo
10b0
cni 1
Fig. 7. Reflection spectra of galena after various treatments: 1 = without reagents; 2 = with KEX at pH 8.0; 3 = w i t h (FeS04+ NaCN) + K E X at 6.9; 4 = w i t h precipitated Pb (EX)2.
The spectra resulting from galena treated with Pb-acetate after the depressing action of FeS04 and NaCN are shown in Fig. 8. The absorption band at 2045 cm-1, which remained in spectrum I even after mineral treatment with Pb-acetate, indicates that the adsorption of lead ion does not occur by replacing the ferrous ion previously adsorbed on the galena surface. Evidently, after activation, the galena surface remained partly covered with the depressing compound (spectra 2, 3, and 4). Nevertheless, spectra in Fig. 8 demonstrate the presence of lead enthylxanthate on the galena surface. Under the condition when the mineral was activated at pH values from 5.0 to 6.0, and again at a pH of about 9.0 (after the depression was carried out in the pH range 5.0-6.0), the absorption bands of lead ethylxanthate were noted. However, the xanthate absorption bands varied in intensity depending on the pH condition of activation or collection. A somewhat lower quantity of adsorbed lead ethylxanthate was observed when the pH activation was from 5.0 to 6.0. The quantity of the sorption product grows when the pH of activation or collection increases at the same pH of depression (about 5.7 ). But, the difference in the absorption band intensities of lead xanthate on the galena surface is not great. Therefore,
121 T,%
!11°2°I I
, t 121o\d 1202
l
/ j I/ IJ 1110
I
I
I ~ I J J
I I J /
I i
hs II ~j V1020
2200
2000
12oo
1~
cm-~
Fig. 8. Reflection spectra of galena after treatment with: 1 = (FeSO4 + NaCN, pH 5.6 } + Pb-acetare (pH 9.3); 2=(FeSO4+NaCN, pH 5.6)+Pb-acetate (pH 6.0)+KEX (pH 6.0); 3= (FeSO4+NaCN, pH 5.6)+Pb-acetate (pH 5.5)+KEX (pH 8.3); 4--(FeSO4+NaCN, pH 5.6) +Pb-acetate (pH 9.0)+KEX (pH 9.0); 5--(FeSO4+NaCN, pH 9.0)+Pb-acetate (pH 8.8 ) + KEX (pH 8.8 ); 6 = precipitated Pb (EX) 2.
from infrared data no essential difference was found in the quantity of surface product (Pb-ethylxanthate) for different pH conditions (activation or collection ). Furthermore, the experiment with a sample of depressed and then activated galena (both in alkaline pH range from pH 8.8 to 9.0) has shown that the influence of depression pH on the formation of the hydrophilic ferrocyanide complex is important. The absorption band at 2045 c m - 1 disappeared, and the only adsorption product was lead ethylxanthate (spectrum 5). CONCLUSIONS
( 1 ) The results presented in this study indicate that FeS04 and NaCN have a depressive effect on the xanthate flotation of galena within the pH range
122
from 6.0 to 7.5 at which, according to the distribution diagram, Fe 2+ ions are dominant in the solution. Based on zeta-potential measurements and infrared data, the following mechanism of depressing action is suggested: first, adsorption of Fe 2+ ion from the solution on the galena surface; then the reaction between Fe 2+ ion at the galena surface and ferrocyanide ion from the solution. The hydrophilic ferrous ferrocyanide compound produced at the interface is the species responsible for the depression of galena in the pH range from 6.0 to 7.5. The infrared reflection spectra clearly show that, in the condition of partly depressed galena, the surface is covered with two different adsorption products: ferrocyanide compound and Pb-ethylxanthate. (2) A good floatability of galena is attained in the alkaline medium, but a different kinetics of xanthate galena flotation is noted. Galena flotation is slower in the presence of depressing reagents than in their absence. (3) Besides pH, the molar ratio of reagents (FeS04 to NaCN) used is very important for a depressing effect on the xanthate flotation of galena. The depressing action is noted when the molar ratio of FeSO4 to NaCN was 1.0 or higher, depending on the pH. (4) Addition of Pb-acetate to a previously depressed galena suspension leads to an increase in the flotation recovery within the pH range from 5.5 to 7.0, in which the depressing action was observed. A full flotation effect is not achieved. Under the same condition, the zeta-potential data show a lower adsorption of Pb 2+ on pre-depressed than on undepressed galena. The desorption of depressing compound does not take place i n the presence of Pb-acetate, which reduces the free surface sites available for Pb 2+ adsorption. Infrared data show the presence of Pb-ethylxanthate on the galena surface, but also the band at 2045 cm-1, which is typical of the ferrocyanide group. (5) Since the combination of the reagents, FeSO4 and NaCN, is a good depressor for sphalerite, the results presented can be useful to those concerned with the problems of selective flotation of lead-zinc ores. ACKNOWLEDGEMENT
The authors are indebted to the Research Fund of the Republic of Serbia for financial support.
REFERENCES Baes, C.F. and Mesmer, R.E., 1976. The Hydrolysis of Cations. Wiley, Ner York, N.Y., pp. 364365. Dra§kid, D., Manojlovid-Gifing, M. and Pavlica, J., 1980. Cyanide depression of naturally floating sphalerite in the presence of ferrous ions. In: M.J. Jones (Editor), Complex Sulphide Ores. IMM, Rome, pp. 113-117. Dra~kid, D., Manojlovid-Gifing, M. and Pavlica, J., 1985. Ddpression de la blend prdsentant une
123 flottabilit~ naturelle dans les conditions de la flottation sdlective des minerals de plomb-zinc. Proc. 15th Int. Miner. Process. Congr., Cannes, Tome II, pp. 278-284. Greenler, R.G., 1962. An infrared investigation of xanthate adsorption by lead sulphide. J. Phys. Chem., 66: 879-883. Harrick, N.J., 1967. Internal Reflection Spectroscopy. Interscience Publishers Inc., New York, N.Y. Jones, L.H., 1963. Inorg. Chem., 2: 777. Quoted in: I.V. Tananaev, G.B., Seifer, h . Ia., Kharitonov, V.G. Kuznetsov, A.I. Korol'kov, 1971. Chemie of Ferrocyanide. Nauka, Moscow, pp. 149-150. Langmuir, D., 1969. U.S. Geol. Surv. Prof. Pap., 650-B, p. 181. Quoted according to M.C. Fuerstenau and B.R. Palmer, 1976. Anionic flotation of oxides and silicates. In: M.C. Fuerstenau, (Editor), Flotation. A.M. Gaudin Memorial. New York, N.Y., Vol. I, p. 164. Latimer, W.M., 1952. Oxidation Potentials. Prentice-Hall Englewood' Cliffs, N.J., p. 281. Quoted according to M.C. Fuerstenau and B.R. Palmer, 1976. Anionic flotation of oxides and silicates. In: M.C. Fuerstenau (Editor), Flotation. A.M. Gaudin Memorial. New York, N.Y., Vol. I, p. 162. Little, L.K., Leja, L. and Poling, G.W., 1961. Infrared spectra of xanthate compounds, II. Assignment of vibrational frequencies. Can. J. Chem., 39: 745-754. Mielczarski, J., Nowak, P., Strojek, J.W. and Pomianowski, A., 1979. Infrared internal reflection spectrophotometric investigations of potassium ethylxanthate sorption on sulphide minerals. In: J.S. Laskowski (Editor), Proc. 13th Int. Miner. Process. Congr., Warsaw. Elsevier, Amsterdam, pp. 35-53. Nyquist, R.A. and Kagel, R.O., 1971. Infrared Spectra of Inorganic Compounds. Academic Press, London, pp. 25-41. Pavlica, J., Calid, N., Dra§kid, D. and Cikid, M., 1986. Industrial application of ferro-sulphate and sodium cyanide in depressing zinc minerals. Proc. 1st Int. Miner. Process. Symp., E.U. Atattirk Cultural Centre, Izmir, Turkey, Vol. 1, pp. 183-189. Poling, G.W. and Leja, J., 1963. Infrared study of xanthate adsorption on vacuum deposited films of lead sulphide and metallic copper under condition of controlled oxidation. J. Phys. Chem., 67: 2121-2126. Pugh, R.J. and BergstrSm, L., 1986. Surface and solution chemistry studies on galena suspensions. Colloids Surfaces, 19: 1-20. Solzhenkin, N.M., Tikhonov, S.A. and Yasynkevich, S.M., 1958. Influence of flotation reagents on the electrokinetic potential of some minerals. Sb. Nauchn. Tr., Mosk. Inst. Tsvetn. Met., 31: 174-180. Tananaev, I.V., Seifer, G.B., Kharitonov, Iu.Ia, Kuznetsov, V.G. and Korol'kov, A.I., 1971. Chemie of Ferrocyanide. Nauka, Moscow, pp. 146-156. Wagman, D.D. et al., 1969. NBS Tech. Note, 74, p. 74. Quoted according to M.C. Fuerstenau and B.R. Palmer, 1976. Anionic flotation of oxides and silicates. In: M.C. Fuerstenau (Editor), Flotation. A.M. Gaudin Memorial. New York, N.Y., Vol. 1, p. 164. Yarar, B. and Kitchener, J.A., 1970. Selective flocculation of minerals. Trans. Inst. Min. Metall., 79: C23-33. Yiicesoy, A. and Yarar, B., 1974. Zeta potential measurements in the galena-xanthate-oxygen system. Trans. Inst. Min. Metall., 83: C96-100.
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Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Effect of the D e p r e s s i n g Agents F e S 0 4 and N a C N on the Surface Properties of Galena in the Flotation S y s t e m S.R. POPOV, D.R. VUCINIC and N.M. CALIC
Faculty of Mining and Geology, University of Belgrade, Belgrade (Yugoslavia) (Received March 17, 1987; accepted after revision January 14, 1988)
ABSTRACT Popov, S.R., VuSini~, D.R. and Calid, N.M., 1988. Effect of the depressing agents FeS04 and NaCN on the surface properties of galena in the flotation system. Int. J. Miner. Process., 24: 111-123. The simultaneous effect of FeS04 and NaCN as depressing agents on the floatability and surface properties of galena at various pH values and with different concentration ratios of the two reagents has been determined. A good correlation between floatability, infrared data and zeta-potential measurements is obtained. The depressing action of FeSO4 and NaCN is observed for the pH range from 6.0 to 7.5. Under the depressed galena condition, and using KEX as a collector, a hydrophilic ferrocyanide compound is suggested as the species responsible for the mineral surface depression. In an alkaline medium, the flotation recovery of galena is not reduced in the presence of FeS04 and NaCN, but another kinetic of xanthate galena flotation is noted. Besides pH, the molar ratio of FeS04 and NaCN used is very important for the depressing effect of these reagents. The addition of Pb-acetate to a suspension of previously depressed galena causes a certain rise in the flotation recovery for the pH range from 5.5 to 7.0, at which the depression is obtained, but complete flotation (near 100% ) is not accomplished. The adsorption of Pb ~+ on pre-depressed galena is lower than that on undepressed galena, because the surface sites are occupied by the depressing compound.
INTRODUCTION
In several flotation studies on sphalerite, the hydrophilic properties acquired were found to be significantly affected by the addition of combined FeSO4 and NaCN reagents. The role of FeSO4-NaCN in a modifying sphalerite-xanthate collector system has previously been studied (Dra§kid et al., 1980, 1985). A new depressing procedure has been introduced in several flotation mills in Yugoslavia. FeSO4 and NaCN have several advantages over the application 0301-7516/88/$03.50
© 1988 Elsevier Science Publishers B.V.
112
of the pair ZnSO4 and NaCN: lower consumption of NaCN and other reagents, primarily that of CuSO4; high selectivity of the process; and higher recovery of silver in the lead concentrate. Moreover, the reduction in consumption of reagent has a beneficial effect on the environmental conditions (Pavlica et al., 1986). Consequently, for the study of lead-zinc ore, F e S Q and NaCN, when used as a modifying agent, depress the xanthate flotation of sphalerite and do not have a significant direct effect on the floatability of galena. It was observed, however, that the new pair of reagents had a certain effect on the kinetics of galena flotation under certain conditions of the flotation system. The present work is concerned with the effect of a new pair of depressing reagents (FeSO4 and NaCN) on galena xanthate flotation at various pH values, and with the effect of various proportions of FeS04 and NaCN reagents. Hence, it is a study of the influence of depressing agents, such as FeSO4 and NaCN, on the surface properties of galena. The zeta-potential measurements and infrared examination data are discussed in relation to the behaviour of the mineral in flotation. EXPERIMENTAL
Mineral and reagents A natural galena mineral was used. Specimens of ore were crushed, and the mineral grains picked were ground in a mortar. The mineral was then sorted into two particle-size fractions by sieving. The coarser fraction ( - 104 + 74 /~m) was used in the flotation test and a portion of the remaining - 7 4 ~m fraction was further reduced by grinding (for a few hours) in an agate mortar. This grain size was used in the infrared examination and in zeta-potential measurements. The mineral sample was stored in a vacuum desiccator. Chemically analysed, the galena sample contained 85.15% Pb and 13.31% S. For pH adjustment, NaOH and HeSO, of analytical-reagent grade were used. Commercial-grade potassium ethylxanthate (KEX), used as a collector in this study, was purified by multiple recrystallisation from acetone. It was stored in a vacuum desiccator over silica gel. Any other reagent used was also of analytical grade. Pb-acetate was used as the activating agent. The depressing reagents were combinations of FeSO4 and NaCN. Lead ethylxanthate, the spectrum of which is presented in this paper, was obtained from aqueous solution of Pb-acetate and potassium ethylxanthate by precipitation. The reaction product was washed with distilled water.
Methods and procedures The modified Hallimond-tube flotation technique was used. Approximately one gram of the mineral was conditioned in a 100-ml flask for three minutes
113
with a reagent (depressing and activating reagents, collector) at the desired concentration and pH. Then the suspension was transferred to a Hallimond tube and floated for 5 min at an air-flow rate of 10 ml per minute. Zeta potential was determined by means of the microelectrophoresis technique, using a Riddick Zeta-meter. A solution of the mineral was prepared and stirred, and samples of the colloidal supernatant were then charged in the electrophoretic cell. The zeta potential was measured after conditioning the suspension for 3 min upon each addition of reagents. The infrared spectrophotometric method was used in a qualitative analysis of surface products from the reaction between galena and the different flotation reagents. In order to increase the amount of reagent adsorbed on the mineral, it is finely ground, increasing the surface area and requiring the use of higher concentrations of reagents for infrared examination than for the flotation tests and zeta-potential measurements. For infrared examination, reagent concentrations ten times higher than those for flotation tests were used. The ratio of reagent concentrations used (depressing and activating agents, collector) and the solid/liquid ratio were the same as in the flotation tests. A Perkin-Elmer infrared spectrophotometer (type 397) with an ATR-attachment was used. The reflection elements used in the experiments were KRS5. The following procedure was applied in the experiment with powdered samples. A sample of 500 mg of galena was added to 50 cm ~ of distilled water and after a few minutes agitation, a portion of desired reagent was added and the agitation continued for another 5 min. After the addition of each reagent, the suspension was conditioned by a magnetic stirrer for another 5 min and the solution was decanted (after depression, activation or collection ). The purpose of the decantation was to prevent the formation of precipitates in the bulk of the solution, since high concentrations of reagents were used in the experiments. After the last decantation of the solution, the sample together with the remaining solution was put in contact with the surface of the reflexion element and examined spectrophotometrically. RESULTS AND DISCUSSION
Floatability tests The first set of tests included the galena floatability without (natural floatability) and with various flotation reagents (Fig. 1 ). It is evident that the natural floatability of galena is relatively high at all the pH ranges tested (Fig. 1, curve 1 ). The results show that a small rise in floatability above the natural floatability of galena occurs with KEX in the pH range from 6.0 to 10.0 (Fig. 1, curve 2). The effect of depressants (FeSOt and NaCN) on the flotation behaviour of
114
_9
100.
8C
>_n~ ~J > 0 0 iii nZ 0
40
LI_
20
[C] = [kmot m-'] KEX (1.5 x 10- 4 ) Fe SO4 ( 2.0,10 .4 ) Na CN ( 2.0 x 10-4 ) Pb- acetate ( 9.0 x 10-5 )
Fig. 1. Flotation recovery of galena as a function of pH in the presence of: 1--the natural floatability; 2=KEX; 3-- (FeSO4+NaCN) +KEX; 4 = (FeSO4+NaCN) +Pb-acetate+KEX (depression performed at pH 5.7).
>> O
60
uJ
u_
2C
;
½
:3
z,
;
TIME,
rain
Fig. 2. Flotation recovery of galena as a function of time at pH 8.0:1 = K E X ; 2 = (FeSO4 + N a C N ) (both 2.0" 10 -4 kmol m - a ) + KEX.
galena in the presence of KEX is also depicted in Fig. 1 (curve 3). The data indicate that a combination of the reagents, FeSO4 and NaCN, depresses galena flotation within the pH range from 6.0 to 7.5, with KEX as a collector. Recovery of galena was good (nearly 100% ) in the basic medium. The flotation
115 recovery of depressed galena is practically the same as that in the absence of a depressor at pH values above 7.5. However, a different kinetics of flotation between the depressed and undepressed galena in the basic pH range was observed. Fig. 2 shows the data from our examination of the depressing effect on the flotation kinetics. In order to compare the effect of depressing reagents on galena flotation kinetics, the flotation was tested as a function of time. The results show that the depressants had a certain effect on the galena flotation speed. Galena floats faster with K E X without depressants (curve 1 ) than in the presence of FeS04 and NaCN (curve 2). In fact, a longer time is necessary for complete flotation of depressed galena (about 100% ) t h a n for galena without depressants. The following step of the experiment was to test the influence of a Pb-acetate activating agent on the flotation of pre-depressed galena with K E X as a collector (Fig. 1, curve 4). The depression was always carried out at a pH of about 5.6, and the activation at various pH values. The results show the flotation recovery as a function of the activation pH. An activation, when Pb-acetate was added to the system of previously depressed galena, was noted in the pH range from 5.5 to 7.0, but full flotation was not accomplished. The test results on the influence of various proportions of depressing agents on the flotation recovery of galena at three pH values are shown in Fig. 3. It is evident that, with increasing FeSO4 concentrations, but with the same concentration of NaCN (2" 10 -4 kmol m - 3 ) , the flotation recovery decreases at each
I00
~___.._~,~_~-----'-~~o.~
!-
80
W
60
0 UJ Z 0
.J mJ
40
[c] ~[kr.ot m-~1 Na aN ( 2.0 x 10-4) KEX (1.56 x 10")
20
o.'i
'
'
'
oTs
. . . . . . . .1.0.
\/LP
1.4
CFeSOJZNaCN
Fig. 3. Flotation recovery of galena as a function of CFeSO4/CNaCN;I =pH=6.0; 2--pH=7.4; 3=pH=8.5.
116
of the tested pH values. Fig. 3 shows the flotation recovery of galena with KEX as a collector, where the FeSO4/NaCN concentration ratio is increasing. The maximum flotation recovery is clearly seen to occur at a ratio of FeSO4/ NaCN = 0.5, at any tested pH range. The plots demonstrate increasing amounts of FeSO4 to be required in depressing the mineral at pH values higher than 6.0.
Zeta-potential measurements The surface properties of galena with or without additives (depressing or activating agents, collector) were tested by determining the zeta potential. The zeta potential for galena, as a function of pH, is shown in Fig. 4 (curve I ). A negative surface is noted in the pH range tested. These results roughly agree with the published data (Solzhenkin et al., 1958; Yarar and Kitchener, 1970; Yiicesoy and Yarar, 1974; Pugh and BergstrSm, 1986). The addition of NaCN to a galena suspension results in a more negative zeta potential (Fig. 4, curve 2) than without additive in the entire pH range tested, indicating a low adsorption of C N - ions on the galena surface. The effect of FeSO4 on the zeta potential of galena is also illustrated in Fig. 4 (curve 3). Comparison of these results with the distribution diagram for Fe 2+ (Baes and Mesmer, 1976; Langmuir, 1969; Wagman et al., 1969) indicates that the zeta potential reverses its sign from - to + at about pH 5.4, due to the formation +3 0 -
NaCN (2.0x 10-4) Fe SO4 ( 2.0 x 10-~" ) KEX (1.5xi0 -4)
+ 20"
÷10-
E pH < x
UJ
u.l N
-TO-
- 20-
- 30-
Fig. 4. Zeta potential of galena as a f u n c t i o n of p H : 1 = w i t h o u t reagents; 2 = w i t h N a C N ; 3 = w i t h FeSO4; 4 = w i t h F e S 0 4 + N a C N ; 5 = w i t h (FeSO4 + N a C N ) + K E X .
117
of Fe 2+ and, to some extent, Fe (OH) + ions in the solution and their adsorption on the galena surface. At about pH 7.5, the zeta potential again reverses its sign (from + to - ) because the concentration of Fe 2+ ions decreases with increasing pH (according to the distribution diagram). At the same time, the concentration of Fe (OH)2 in the solution is increasing. In an alkaline medium, the galena surface is negatively charged in the presence of FeSO4, but it is less negative than without the additive. Curve 4 in Fig. 4 shows the zeta potential of galena treated with FeSO4 and NaCN. First, F e S Q was added to a galena suspension and, after conditioning the suspension for a few minutes, NaCN was added. The zeta potential was measured after the galena suspension had been conditioned for another 5 min. It is clear from a comparative scrutiny of curves 3 and 4 in Fig. 4 that the sorption process was a superficial reaction between Fe 2+ ions, previously adsorbed on the galena surface, and probably ferrocyanide ions, contained in the solution. Also that the depression of galena (by F e S Q and NaCN) in the pH range 6.0-7.5 was due to the formation of the hydrophilic ferrocyanide compound on the mineral surface. Its presence there reduces the floatability of the mineral. With increasing pH of the solution, the concentration of free Fe 2+ ions decreases and subsequently the hydrophilic ferrocyanide complex is not formed in sufficient amount, and the depressing action of F e S Q and NaCN ceases. The effect of KEX on the previously depressed galena (Fig. 4, curve 5) is seen in the increasing negative values of the zeta potential as compared with the same system without a collector (Fig. 4, curve 4). These results illustrate the adsorption of collector on the galena surface in the presence of the pair of depressing reagents. However, with a reduction of the pH from 7.0 to 5.5, a decrease in the negative values of the zeta potential is noted. At pH 6.0, the zeta potential of depressed galena with KEX is similar to that without. It corresponds to the pH range at which the galena flotation is reduced (Fig. 1, curve 3). The next experiments included examination of the surface properties of galena after the activation (with Pb-acetate) of pre-depressed and undepressed minerals (Fig. 5). For the latter (Fig. 5, curve 4) in the pH range 5.5-7.1, the zeta potential is positive due to Pb 2+ ion adsorption and, to some extent, Pb (OH) + ion adsorption on the galena surface. This is exactly the pH range at which Pb 2+ prevails and P b ( O H ) + ions begin to form in the bulk of the solution. Distribution diagrams for lead show these phenomena (Beas and Mesmer, 1976; Latimer, 1952; Pugh and BergstrSm, 1986). In an alkaline medium, with the pH increasing above 7.0, the free lead ion concentration decreases, because the equilibrium between it and other lead-containing species derived from it in aqueous solution ( H P b O [ , Pb (OH) +, etc. ) moves toward a decreasing Pb 2+ concentration. Consequently, the surface charge of galena remains negative in an alkaline medium, in the presence of Pb-acetate.
118
[c]=[kmol m"3] FeSO¢ ( 2.0x 10.4 ) NaCN I2.0 xlO-4) Pb- acetate ( 9.0x 10 -s )
÷20'
-10-
E
.ji-.-
Z w
11
i
B I1_
-10
N
-20
g ""----o
-
pH
10
Q~(I
-30
Fig. 5. Zeta potential of galenaas a function ofpH in the presenceof: 1 = without reagents;2 = with FeSO4+ NaCN; 3 = with (FeSO4+ NaCN ) + Pb-acetate; 4 = with Pb -acetate. Comparative curves 3 and 4 (Fig. 5) show that the adsorption of lead ions (Pb 2+) and hydrolized lead species ( P b ( O H ) +) is much lower on the predepressed than on the undepressed galena surface. Subsequent to depression, the number of surface sites available for lead-ion adsorption is expected to be reduced. Consequently, in the presence of FeSO4 and NaCN, the density of surface-adsorbed lead ion is lower t h a n that without the depressing agents. This agrees with the flotation data. In the pH range 5.57.0, the activation of depressed galena is not fully achieved (Fig. 1, curve 4). It is evident that activation occurs when there is still an amount of depressor on the surface sufficient to cause some level of depression.
Infrared tests We have studied the adsorption p h e n o m e n a in galena with various flotation reagent systems, using the method of internal reflection spectrophotometry (Harrick, 1967; Mielczarski et al., 1979). The goal of the first set of experiments was the study of adsorption on galena in the presence of depressing agents. The spectra resulting from t r e a t m e n t with FeSO4 and NaCN at pH 5.7 and 8.7 are shown in Fig. 6. The band at 2045 cm-1 suggests that, after the depressing action at pH 5.7 (spectrum 2), the presence of a compound containing the ferrocyanide group/Fe ( C N ) / g - on the galena surface (Jones, 1963; Nyquist and Kagel, 1971; Tananaev et al., 1971 ).
119 T, %
2100 2000
Fig. 6. Reflection spectra of galena after a t r e a t m e n t with FeSO4 a n d N a C N (molar ratio 1.0): 1 = without reagents; 2 = at p H 5.7; 3 = at p H 8.7; 4 = at p H 5.7 (molar ratio 0.5 ).
The depressing action of FeSOa and NaCN evidently results primarily from the deposition of a hydrophilic ferrocyanide complex on the mineral surface. A somewhat lower amount of the adsorption product was observed at the same pH (about pH 5.7) when a different proportion of depressing reagents was used; the FeSO4 to NaCN ratio was 0.5 instead of 1.0 in the earlier experiment (spectrum 4 ). In contrast to the previous data, the absorption band at 2045 c m - 1, a characteristic of the ferrocyanide group, is almost nonexistent when the depression was performed in an alkaline medium (pH about 8.7) (spectrum 3). This indicates the absence of the hydrophilic ferrocyanide complex on the galena surface. After the treatment of pre-depressed galena (at pH about 5.7) with KEX, the xanthate bands were observed (Fig. 7, spectrum 3), but the ferrocyanide compound band at 2045 c m - 1 remained. Absorption bands for the frequencies 1020 and 1110 and 1202 cm-1 (C = S and C - O vibrations) may be associated with the presence of lead ethylxanthate on the galena surface (Little et al., 1961; Greenler, 1962; Poling and Leja, 1963). They can also be seen in the spectrum of precipitated lead ethylxantate (spectrum 4 ). Under the same condition, the xanthate flotation of galena was partly depressed. Galena is not depressed by FeSOt and NaCN when ethylxanthate adsorption on the galena surface is fully prevented, but probably by a strong hydration of the ferrocyanide compound adsorbed on the galena surface, whereby the hydrophobicity of the collector coating was partly overcome.
120 T, %
z// / / 2045
'a
f\
Ij
I
Ii IP I J J I I
1210'~J 1202
I/ ~/ v 1110
~1020
2;o0 26oo
~2bo
10b0
cni 1
Fig. 7. Reflection spectra of galena after various treatments: 1 = without reagents; 2 = with KEX at pH 8.0; 3 = w i t h (FeS04+ NaCN) + K E X at 6.9; 4 = w i t h precipitated Pb (EX)2.
The spectra resulting from galena treated with Pb-acetate after the depressing action of FeS04 and NaCN are shown in Fig. 8. The absorption band at 2045 cm-1, which remained in spectrum I even after mineral treatment with Pb-acetate, indicates that the adsorption of lead ion does not occur by replacing the ferrous ion previously adsorbed on the galena surface. Evidently, after activation, the galena surface remained partly covered with the depressing compound (spectra 2, 3, and 4). Nevertheless, spectra in Fig. 8 demonstrate the presence of lead enthylxanthate on the galena surface. Under the condition when the mineral was activated at pH values from 5.0 to 6.0, and again at a pH of about 9.0 (after the depression was carried out in the pH range 5.0-6.0), the absorption bands of lead ethylxanthate were noted. However, the xanthate absorption bands varied in intensity depending on the pH condition of activation or collection. A somewhat lower quantity of adsorbed lead ethylxanthate was observed when the pH activation was from 5.0 to 6.0. The quantity of the sorption product grows when the pH of activation or collection increases at the same pH of depression (about 5.7 ). But, the difference in the absorption band intensities of lead xanthate on the galena surface is not great. Therefore,
121 T,%
!11°2°I I
, t 121o\d 1202
l
/ j I/ IJ 1110
I
I
I ~ I J J
I I J /
I i
hs II ~j V1020
2200
2000
12oo
1~
cm-~
Fig. 8. Reflection spectra of galena after treatment with: 1 = (FeSO4 + NaCN, pH 5.6 } + Pb-acetare (pH 9.3); 2=(FeSO4+NaCN, pH 5.6)+Pb-acetate (pH 6.0)+KEX (pH 6.0); 3= (FeSO4+NaCN, pH 5.6)+Pb-acetate (pH 5.5)+KEX (pH 8.3); 4--(FeSO4+NaCN, pH 5.6) +Pb-acetate (pH 9.0)+KEX (pH 9.0); 5--(FeSO4+NaCN, pH 9.0)+Pb-acetate (pH 8.8 ) + KEX (pH 8.8 ); 6 = precipitated Pb (EX) 2.
from infrared data no essential difference was found in the quantity of surface product (Pb-ethylxanthate) for different pH conditions (activation or collection ). Furthermore, the experiment with a sample of depressed and then activated galena (both in alkaline pH range from pH 8.8 to 9.0) has shown that the influence of depression pH on the formation of the hydrophilic ferrocyanide complex is important. The absorption band at 2045 c m - 1 disappeared, and the only adsorption product was lead ethylxanthate (spectrum 5). CONCLUSIONS
( 1 ) The results presented in this study indicate that FeS04 and NaCN have a depressive effect on the xanthate flotation of galena within the pH range
122
from 6.0 to 7.5 at which, according to the distribution diagram, Fe 2+ ions are dominant in the solution. Based on zeta-potential measurements and infrared data, the following mechanism of depressing action is suggested: first, adsorption of Fe 2+ ion from the solution on the galena surface; then the reaction between Fe 2+ ion at the galena surface and ferrocyanide ion from the solution. The hydrophilic ferrous ferrocyanide compound produced at the interface is the species responsible for the depression of galena in the pH range from 6.0 to 7.5. The infrared reflection spectra clearly show that, in the condition of partly depressed galena, the surface is covered with two different adsorption products: ferrocyanide compound and Pb-ethylxanthate. (2) A good floatability of galena is attained in the alkaline medium, but a different kinetics of xanthate galena flotation is noted. Galena flotation is slower in the presence of depressing reagents than in their absence. (3) Besides pH, the molar ratio of reagents (FeS04 to NaCN) used is very important for a depressing effect on the xanthate flotation of galena. The depressing action is noted when the molar ratio of FeSO4 to NaCN was 1.0 or higher, depending on the pH. (4) Addition of Pb-acetate to a previously depressed galena suspension leads to an increase in the flotation recovery within the pH range from 5.5 to 7.0, in which the depressing action was observed. A full flotation effect is not achieved. Under the same condition, the zeta-potential data show a lower adsorption of Pb 2+ on pre-depressed than on undepressed galena. The desorption of depressing compound does not take place i n the presence of Pb-acetate, which reduces the free surface sites available for Pb 2+ adsorption. Infrared data show the presence of Pb-ethylxanthate on the galena surface, but also the band at 2045 cm-1, which is typical of the ferrocyanide group. (5) Since the combination of the reagents, FeSO4 and NaCN, is a good depressor for sphalerite, the results presented can be useful to those concerned with the problems of selective flotation of lead-zinc ores. ACKNOWLEDGEMENT
The authors are indebted to the Research Fund of the Republic of Serbia for financial support.
REFERENCES Baes, C.F. and Mesmer, R.E., 1976. The Hydrolysis of Cations. Wiley, Ner York, N.Y., pp. 364365. Dra§kid, D., Manojlovid-Gifing, M. and Pavlica, J., 1980. Cyanide depression of naturally floating sphalerite in the presence of ferrous ions. In: M.J. Jones (Editor), Complex Sulphide Ores. IMM, Rome, pp. 113-117. Dra~kid, D., Manojlovid-Gifing, M. and Pavlica, J., 1985. Ddpression de la blend prdsentant une
123 flottabilit~ naturelle dans les conditions de la flottation sdlective des minerals de plomb-zinc. Proc. 15th Int. Miner. Process. Congr., Cannes, Tome II, pp. 278-284. Greenler, R.G., 1962. An infrared investigation of xanthate adsorption by lead sulphide. J. Phys. Chem., 66: 879-883. Harrick, N.J., 1967. Internal Reflection Spectroscopy. Interscience Publishers Inc., New York, N.Y. Jones, L.H., 1963. Inorg. Chem., 2: 777. Quoted in: I.V. Tananaev, G.B., Seifer, h . Ia., Kharitonov, V.G. Kuznetsov, A.I. Korol'kov, 1971. Chemie of Ferrocyanide. Nauka, Moscow, pp. 149-150. Langmuir, D., 1969. U.S. Geol. Surv. Prof. Pap., 650-B, p. 181. Quoted according to M.C. Fuerstenau and B.R. Palmer, 1976. Anionic flotation of oxides and silicates. In: M.C. Fuerstenau, (Editor), Flotation. A.M. Gaudin Memorial. New York, N.Y., Vol. I, p. 164. Latimer, W.M., 1952. Oxidation Potentials. Prentice-Hall Englewood' Cliffs, N.J., p. 281. Quoted according to M.C. Fuerstenau and B.R. Palmer, 1976. Anionic flotation of oxides and silicates. In: M.C. Fuerstenau (Editor), Flotation. A.M. Gaudin Memorial. New York, N.Y., Vol. I, p. 162. Little, L.K., Leja, L. and Poling, G.W., 1961. Infrared spectra of xanthate compounds, II. Assignment of vibrational frequencies. Can. J. Chem., 39: 745-754. Mielczarski, J., Nowak, P., Strojek, J.W. and Pomianowski, A., 1979. Infrared internal reflection spectrophotometric investigations of potassium ethylxanthate sorption on sulphide minerals. In: J.S. Laskowski (Editor), Proc. 13th Int. Miner. Process. Congr., Warsaw. Elsevier, Amsterdam, pp. 35-53. Nyquist, R.A. and Kagel, R.O., 1971. Infrared Spectra of Inorganic Compounds. Academic Press, London, pp. 25-41. Pavlica, J., Calid, N., Dra§kid, D. and Cikid, M., 1986. Industrial application of ferro-sulphate and sodium cyanide in depressing zinc minerals. Proc. 1st Int. Miner. Process. Symp., E.U. Atattirk Cultural Centre, Izmir, Turkey, Vol. 1, pp. 183-189. Poling, G.W. and Leja, J., 1963. Infrared study of xanthate adsorption on vacuum deposited films of lead sulphide and metallic copper under condition of controlled oxidation. J. Phys. Chem., 67: 2121-2126. Pugh, R.J. and BergstrSm, L., 1986. Surface and solution chemistry studies on galena suspensions. Colloids Surfaces, 19: 1-20. Solzhenkin, N.M., Tikhonov, S.A. and Yasynkevich, S.M., 1958. Influence of flotation reagents on the electrokinetic potential of some minerals. Sb. Nauchn. Tr., Mosk. Inst. Tsvetn. Met., 31: 174-180. Tananaev, I.V., Seifer, G.B., Kharitonov, Iu.Ia, Kuznetsov, V.G. and Korol'kov, A.I., 1971. Chemie of Ferrocyanide. Nauka, Moscow, pp. 146-156. Wagman, D.D. et al., 1969. NBS Tech. Note, 74, p. 74. Quoted according to M.C. Fuerstenau and B.R. Palmer, 1976. Anionic flotation of oxides and silicates. In: M.C. Fuerstenau (Editor), Flotation. A.M. Gaudin Memorial. New York, N.Y., Vol. 1, p. 164. Yarar, B. and Kitchener, J.A., 1970. Selective flocculation of minerals. Trans. Inst. Min. Metall., 79: C23-33. Yiicesoy, A. and Yarar, B., 1974. Zeta potential measurements in the galena-xanthate-oxygen system. Trans. Inst. Min. Metall., 83: C96-100.