Electrokinetic, infrared and flotation studies of scheelite and calcite with oxine, alkyl oxine, oleoyl sarcosine and quebracho

International Journal of Mineral Processing, 39 ( 1993) 275-290

275

Elsevier Science Publishers B.V., Amsterdam

Electrokinetic, infrared and flotation studies of scheelite and calcite with oxine, alkyl oxine, oleoyl sarcosine and quebracho O. Ozcan and A.N. Bulutcu lstanbul Technical University, Chemical Engineering Department, Maslak-IstanbuL 80626, Turkey (Received 10 July 1992; accepted after revision 7 May 1993)

ABSTRACT Oxine and alkyl oxine were used as scheelite modifiers in scheelite flotation and their adsorption mechanism was investigated. Electrokinetic and infrared studies on the pure scheelite and calcite surfaces have been carded out with oleoyl sarcosine, oxine, alkyl oxine and quebracho. These studies showed that alkyl oxine increases the negative zeta potential of scheelite to a less negative value whereas the negative zeta potential value of calcite was not changed with this reagent. On the other hand, zeta potentials of both calcite and scheelite became more negative upon treatment with quebracho. Conditioning of calcite and scheelite minerals individually with alkyl oxine before quebracho addition increased the flotation efficiency of oleoyl sarcosine in scheelite flotation but no changes occured in calcite flotation. Infrared studies also showed that, oxine and alkyl oxine were chemically adsorbed on the scheelite surface and not on the calcite surface.

INTRODUCTION

Flotation separation of scheelite from calcite creates difficulties because of the existence of the same cation in the minerals and similar physicochemical characteristics such as solubility, hardness, specific gravity, PZC (point of zero charge) etc. (Weiss, 1985; Sillen and Martell, 1964; Weast, 1969). The conventional collectors used in the flotation of scheelite ores are generally fatty acids or fatty acid derivatives (Atak et at., 1986; Agar, 1984; Beyzavi, 1985 ). It is difficult to separate scheelite especially from calcite with these reagents because the adsorption mechanism of these collectors occurs through chemisorption of the oleate ion onto the mineral surface (Rao and Forssberg, 1991; Atak, 1979; Fuerstenau, 1962; Atademir et at., 1981 ). Therefore, it is almost impossible to separate them by fatty acid flotation without using any selective depressant. Although oleoyl sarcosine was used as a selective collector in the flotation of fluorite and siliceous scheelite ores (Baldauf et al., 1986; Ozcan et al., 1988), this selectivity is not adequate for a low-grade calcitic scheelite ore. Unfortunately, the reagents such as organic colloids (dextrine, 0301-7516/93/$06.00 © 1993 Elsevier Science Publishers B.V. All fights reserved.

276

c). OZCAN AND A,N. BI TLUI'( U

starch), quebracho, sodium phosphates, sodium silicate solutions containing polyvalent cations (hydrosols), etc. (Mercade, 1983; Schubert and Baldauf, 1990; Fuerstenau, 1985 ) used for calcite depression also depress scheelite to a large extent. On the other hand, oxine and alkyl oxine (pentylated 8-hydroxyquinoline) were effectively used as scheelite modifiers to prevent the depression effect of quebracho in scheelite flotation in our laboratory (Ozcan, 1992; Ozcan et al., 1990 ). The aim of this study is to show the selective adsorption ofoxine and alkyl oxine onto the scheelite surface and hence increase the selective flotation of scheelite from calcite using oleoyl sarcosine as collector. Zeta potential measurements and infrared studies of pure scheelite and calcite conditioned with oleoyl sarcosine as collector and alkyl oxine as modifier were conducted to define the adsorption mechanism and flotation responce of a siliceous scheelite and a calcite ore.

Some theoretical explainations on the adsorption mechanism of oxine on scheelite surface Oxine, C 9 H 7 O N ( 8 - h y d r o x y q u i n o l i n e ) is an amphoteric compound which has found an application as a complexing agent in the hydrometallurgical extractions of heavy metals (Morrison and Freiser, 1957; Phillips, 1956). In the analytical determination of tungsten, it is used as precipitating agent in acidic solutions (Snell and Ettre, 1974; Bailar et al., 1973 ). It has a powerful complexing effect for various elements because of its amphoteric character in its chemical structure as shown below:

O- H

Although there are seven types of hydroxyquinolines, only 8-hydroxyquinoline (shortly known as oxine in analytical chemistry) gives complexing reactions with polyvalent cations. This is attributed to the presence of the O H - functional group at the 8th position compared to the nitrogen atom in the molecule. The metal complexes of oxine are named as metal oxinates and formed through an electrovalent bond of the metal to oxygen and a coordinate bond to nitrogen in the molecule as can be written below: n-I

O-H

-

Oxine has two acid dissociation constants, K ~ = I 0 -5'° and K2=10 -98

ELECTROKINETIC, INFRARED AND FLOTATION STUDIES OF SCHEELITE AND CALCITE

277

(Rappoport, 1967). The pH-pC diagram of oxine can be drawn as in Fig. 1 using the minus logarithms of these values (pK) and solubility of oxine in water, 3.0 X l0 -3 M, which was determined in our laboratory. In general, dissociation equations of an amphoteric compound are as follows (Sillen and Martell, 1964; Skoog and West, 1982 ): H2 L+ = H L + H + HL=H++L -

K1 K2 -

[HL] [H + ] [H2L + ]

( 1)

[H+] [L - ] [HE]

(2)

where L is C 9 H 6 O N for oxine in these equations. It is clear from Fig. 1 and equations above that, oxine is in neutral (HL) form besides cationic and anionic species in the pH ranges between pKI ( 5.0 ) and pK2 (9.8) where flotation experiments were carded out. Oxine forms a chelate compound with hexavalent tungsten having the formula of WOE (C9H6NO) 2 in acidic or neutral pH's (Phillips, 1956 ). Scheelite mineral has a negative zeta potential in all practical flotation pH ranges and therefore, its surface must have WO 2- anions (Ozcan et al., 1988; Ney, 1973 ). And these ions are expected to give chelating reactions with oxine on the surface. The pH-pC diagram of scheelite can be drawn as in Fig. 2. In this diagram, the solubility product of scheelite (K~v) was taken as 9.8

5 '

Or'~ i x H+

.

/\

, .L

.

",,,x"/

??/

0

\e

"

,

13 14

/L-

//

.

1

2

3

\

. . . . . . . 4 5 6 7 8 9 pH "-

Fig. 1. The p H - p C diagram o f o x i n e .

10 11 12 13 11,

278

~ 1. O Z C & N :XND A . N , B I ) L U 7 ( . k

23

2

a.7

~,

\

3'

~

7

~," .~,,~,,

/¢

pCZ, 5 ~03 ppt 6

,'

Ca÷z, WO4

/

,/

B 9 10

,

,

,

pH Fig. 2. The p H - p C diagram o f scheelite in water at 25 °C.

4.9 ×10 -~° from Atademir's study (Atademir et al., 1979) and WO3 formation equation from WO~anions in acidic solutions (WO3-t-H20-WO 2 - +2H ÷ ) was taken from Pourbaix (Pourbaix, 1966). It is clear from Fig. 2 that WOg is the anionic species on the scheelite surface at pH 7 or higher. Oxine was used as collector in the flotation of lead, zinc, copper etc. carbonate and sulfides in 1940's (Erlenmeyer et al., 1942 and Steiger and Bayramgil, 1943 ). Kennecott Copper Corp. ( 1958 and 1960) also used oxine and methyl oxine as collector in the flotation of niobium minerals. Oxine and alkyl oxine (penthyl oxine) were used as scheelite modifiers in the present study and their adsorption mechanism on scheelite surface was investigated. EXPERIMENTAL

Materials High purity scheelite and calcite mineral concentrates were prepared in our laboratory. The scheelite concentrate was prepared from a final gravity concentrate from Turkish Tungsten Plant at Uludag containing about 18 % WO3. Further hand sorting under a UV lamp of the calcite free scheelite gave a product that was used in the electrokinetic and infrared studies. Calcite sample was also prepared by hand sorting of the scheelite free particles of a low grade calcitic run-of-mine scheelite ore from Nigde region in Turkey under UV lamp. These samples were then ground to < 38 microns and used in the electrokinetic and infrared studies. The X-ray powder diffraction and chemical analysis and scanning electron microscopic studies showed that the prepared scheelite sample consisted of only scheelite (CAW04) particles. Chemical and X-ray powder diffraction

ELECTROKINETIC, INFRARED AND FLOTATION STUDIES OF SCHEELITE AND CALCITE

279

analysis of the calcite sample also showed calcite with a chemical composition of 98.7 % CaCO3 and 0.91% SiO2. Flotation experiments were conducted with a hand sorted rich siliceous scheelite ore from the Nigde region. This ore assayed 24.6 % WO3, 57.32 % SiO2 and 4.7 % CaO. The calcite samples used in the flotation experiments were the same samples as used in electrokinetic and infrared studies. Oxine was used in both oxine and alkyl oxine forms in the infrared and flotation studies. The synthesis of alkyl oxine (penthyl oxine ) was performed in our laboratory by an alkylation reaction given in literature (Hartlage, 1978; Ozcan, 1992). In this reaction, oxine was reacted with n-pentanal (pentaldehyde) in the stoichiometric ratios using KOH as catalyst and toluene as solvent for 21 hours at 114 ° C (for more information on the synthesis of alkyl oxine the reader should refer to the references above ). Oxine (8-hydroxyquinoline) used for the synthesis of alkyl oxine was of analytical grade (Merck), oleoyl sarcosine was acquired from Hoechst Co. The reagents used for the synthesis of alkyl oxine such as n-pentanal, toluene, KOH were all analytical grade (Merck). Quebracho was used as 5 % aqueous solution and oleoyl sarcosine was used upon emulsification with 1% NaOH solution. Methods The zeta potential measurements (electrokinetic studies) were performed by a Zeta Meter 3.0+ unit. Pure scheelite and calcite samples (ground to < 38 microns) were conditioned with alkyl oxine, quebracho and oleoyl satcosine individually for a definite time and then their zeta potentials were measured. In each test, 0.5 g of sample was suspended in 200 ml of distilled water (conductance of 1.2 × 10 -6 ohms-~ cm). The reagent additions were continuously carded out using the Zeta Meter 3.0 + unit's AST (Automatic Sample Transfer) system. Reagents were added dropwise into the mineral suspensions. For the infrared studies, 0.5 g pure scheelite and calcite (ground < 38 microns) were individually suspended in 200 ml of oxine and alkyl oxine solutions for 25 minutes at pH 8 and pH 3.5 under ambient conditions. The pulps were then centrifuged and washed at least three times with distilled water and dried in a vacuum oven at 40 ° C. The infrared spectra were obtained by transmission after pressing in a KBr pellet using a Perkin-Elmer spectrophotometer, Model No. 983. Flotation experiments were carried out on 50 gram samples using a 250 ml capacity Denver flotation cell. The solid/liquid ratio was 1:4. Rougher flotation was employed in each experiment. Samples were conditioned with oleoyl sarcosine and quebracho for 2 minutes, whereas this time was 25 minutes for oxine and alkyl oxine.

280

O, OZCAN AND A, N. BU LUTC t

RESULTS AND DISCUSSION

Electrokinetic studies 1. Zeta potential measurements of scheelite and calcite with alkyl oxine Pure scheelite and calcite samples were conditioned with solutions of alkyl oxine with concentrations from 125 p p m to 2375 p p m for 25 minutes at the natural pH's of the suspensions (pH was 6.9-7.1 for scheelite suspension and 8-8.7 for calcite suspension) and their zeta potentials were measured. Pure scheelite gave a - 15.63 mV zeta potential in distilled water. The addition of alkyl oxine into the sample suspension increased the zeta potential of scheelite up to - 4.19 mV for 2375 p p m concentration. On the other hand, the zeta potential of the calcite sample was - 12.5 mV and the additions of alkyl oxine did not give any changes. The changes in the zeta potentials of scheelite and calcite versus alkyl oxine concentration are shown in Fig. 3.

2. Zeta potential changes of scheelite and calcite with quebracho Pure scheelite and calcite samples were conditioned individually with different amounts of quebracho for 5 minutes and then their zeta potentials were measured. From 10 p p m up to 250 p p m concentrations of quebracho were used. The changes in the zeta potentials of scheelite and calcite with the concentration of quebracho are given in Fig. 4. It is interesting to see that at lower concentrations of quebracho, i.e. from 10 p p m to 150 ppm, zeta potentials of scheelite become more negative than those of calcite, which means that quebracho will depress scheelite rather than calcite in these concentrations (25-50 ppm, as used in flotation). Above 150 ppm, however, zeta potentials of these two minerals approach the same value Zeta potentiat (mY) 0 -2 -4

-6 -8 -10 -12 z -14 _16 < -18

I

I

I

S0O

1000

150O

I

20O0

2500

Amount of atkyt oxine ( pprn )

Fig. 3. Variation of the zeta potentials of scheelite and calcite with alkyl oxine concentration.

ELECTROKINETIC, INFRARED AND FLOTATION STUDIES OF SCHEELITE AND CALCITE

281

Zeta potentiat (mY) 0

I O 5CHEELITE rlCkl-ClrEl -S -10 -15 -20 -25 - 30

I

I

I

20 40 60

~

oI I I I I I 0 100 120 140 160 180 200

12

l

0 240

Amount of quebracho (ppm)

Fig. 4. Zeta potential changes of scheelite and calcite versus quebracho concentration.

around - 2 3 mV. At these concentrations the two mineral will be equally depressed together and thus selectivity will be lost. This behavior was also observed in the flotation experiments which are discussed in the following pages.

3. Zeta potential measurements of scheelite and calcite with quebracho after treatment first with alkyl oxine The effect of pretreatments of alkyl oxine on the calcite and scheelite surfaces in the presence of quebracho was examined. Mineral samples were conditioned with 500 ppm alkyl oxine before quebracho addition into the suspensions. Then quebracho was added and zeta potentials of the samples were measured. The changes of their zeta potentials at these conditions are given in Fig. 5. It is clear from Fig. 5 that conditioning in 250 ppm quebracho changes the zeta potential of calcite from - 12.5 mV to - 2 1 . 5 mV which is the same value measured with quebracho alone (see Fig. 4). Conditioning of calcite with alkyl oxine prior to quebracho addition does not prevent the depression effect of quebracho on calcite. On the other hand, conditioning of scheelite with alkyl oxine prior to quebracho treatment prevents the negative action of quebracho on scheelite giving - 17.2 mV zeta potential which is about the same value obtained for scheelite in water alone ( - 15.3 mV). This result is very important for flotation studies because of the difficulty in selective depression of calcite when using quebracho as a depressant. Conditioning of the minerals with alkyl oxine before quebracho addition will prevent the depressing effect of quebracho on scheelite. Thus better selectivity will be achieved. In summary, these results reveal a competition between quebracho and alkyl oxine for the scheelite surface.

282

C.

OZCAN AND A N BI L u - r ( ' u

Zeta potentia((rnV) 0

I O SCHEELITE [] CALCITEi -5

-10,

I -IS

0

-.20 -25

0

I

I

20

/.,0

I

60

I

80 100 120 t40 160 180 200 220 2&O

Amount of quebracho ( pprn )

Fig. 5. Zeta potentials of scheelite and calcite versus quebracho concentration after treatment with 500 ppm alkyl oxine.

Infrared studies Pure scheelite and calcite minerals were treated with oxine and alkyl oxine for 25 minutes and then their infrared spectra were obtained. The infrared spectra of scheelite with oxine at pH 8 and 3.5 are given in Fig. 6. In the results of the present spectra, the following conclusions will be observed: 1. The spectra of scheelite and synthetic tungstic acid treated with oxine at pH 3.5 (spectra Nos. 2 and 4, respectively) show a shift, in the aryl-oxygen (C-O) stretching vibration band assigned in oxine at 1200-1220 cm-1 (see Fig. 7 ), to 1100 c m - 1 due to chelate formation. This result is in good agreement with those in the literature. Charles et al. (1956) in their examination of metal oxinates showed that the 9-/tm ( 1100-1110 cm -1 ) peak which occurs in the spectra of all the metal oxinates, but not in oxine itself, is associated with C-O vibrations in the molecule. These workers found that the 9/tm peak is characteristic for metal chelate formation and varied by a small amount from one metal oxinate to another, being displaced to lower frequencies as the atomic weight of the metal was increased. Magee and Gordon ( 1963 ) however, found that the position of the peak did not vary markedly from metal to metal being 1106-1113 c m - 1. 2. The C-H deformation and ring vibrations in the region 700-800 cm-1 in the metal oxinates assigned by Magee and Gordon, 1963, could not clearly be distinguished due to the superposition of W=O stretching vibrations (Nakamoto, 1978 ). 3. The O - H stretching band of oxine in the region 3050 cm-1 (see Fig. 7 )

ELECTROKINETIC,INFRAREDAND FLOTATIONSTUDIESOF SCHEELITEANDCALCITE 1

2

3

4

5

6

283

nl JO J3

<~

(11 J~ to JO

<~

== o

~000 30OO 2000 1600 1200 B]O 400 4000 3000 2000

1600 1200 800 /400

Freouency ( crn "1 )

Fig. 6. Infrared spectra of pure scheelite and some references treated with oxine at pH 8 and 3.5. ( 1 ) Pure scheelite treated with the saturated aqueous solution of oxine at pH 8. (2) Pure scheelite treated with oxine at pH 3.5 (in acetic acid). (3) The spectrum of synthetic tungstic acid which was precipitated by the treatment of Na2WO4 solution with HC1. (4) Synthetic tungstic acid after treatment with oxine at pH 3.5. (5) Pure scheelite. (6) Scheelite treated with oxine at pH 8 (5 times washed).

is not present in spectra 2 and 4. This is also due to the reaction of the reagent with WO 2- anions on the scheelite surface and with the tungstic acid. On the view of these spectral data results, it can be said that oxine is chemically adsorbed on the scheelite surface via the chelate mechanism with WO42- anions at pH 3.5. From the spectra of No. l, however, there is not any adsorption on scheelite surface at pH 8. Oxine is not chemically adsorbed on scheelite surface at pH 8. The infrared spectra of calcite-oxine system at pH 3.5 and 8 are given in Fig. 8. Because calcite is very soluble in acid solution (below pH 8), calcite

284

o, OZCANANDA.N, BULU-rcL

1

io

4000 3 oo

2 oo

, oo

,& .o

& 200

Frequency (cm -1)

Fig. 7. Infrared spectrum of oxine given in literature (Simons, 1978 ). (a)

(bl .cl

Frequency ( cm -1 )

Fig. 8. Infrared spectra of calcite treated with oxine at pH 3.5 (3.5) and pH 8 (b).

was added into the acidic solution as 0.5 g portions and the pH was kept constant around pH 3.5 by continuously addition of acetic acid. It is clear from Fig. 8, there is no difference in the spectra obtained at pH 3.5 and pH 8 compared to pure calcite alone (see Fig. 9b ). Oxine is not chemically adsorbed on the calcite surface at these two pH's. Infrared studies with alkyl oxine on the pure scheelite and calcite surfaces were carded out by the same method employed for oxine as described in the methods section. After 25 minutes conditioning with alkyl oxine, washing, centrifuging and drying procedures were employed to the treated suspensions and then their infrared spectra were obtained as given in Fig. 9. It can be seen from Fig. 9a, alkyl oxine is adsorbed on the scheelite surface at pH 8. The peaks on the spectrum $2 between 1000 and 1600 cm-1 show the adsorption of the reagent at pH 8.0. Especially, the peak at 1100 erawhich is characterising the metal-chelate formation is very clear. These absorbances were not present after treatment at pH 3.5. This behavior is oppo-

285

ELECTROKINETIC, INFRARED AND FLOTATION STUDIES OF SCHEELITE AND CALCITE

(a)

(b)

4000

3500

3000

2500

2000 1800 1600 1/00 1200 1000

800

600

~

200

Freouency (crn -I )

Fig. 9. Infrared spectra of pure scheeliteand calcite after treatment with alkyl oxine at pH 3.5 and pH 8. (a) Scheelite.SI: pH 3.5; $2: pH 8. (b) Calcite. CI: pH 3.5; C: Pure calcite; C2: pH 8. site to the behavior of oxine on scheelite where oxine was adsorbed onto the scheelite surface at pH 3.5 (see Fig. 6). This can be explained by the tautomeric effect of the alkyl chain in the molecule at acidic pH (Rodd, 1957). There was no adsorption of alkyl oxine on the calcite surface. From spectral data, the chemical reaction mechanism between the surface ion, WO 2- and oxine or alkyl oxine can be explained as follows: One WO E- anion on the surface reacts with two molecules of oxine or alkyl oxine by complexing through - N and - O H functional groups of the reagent and gives one molecule of tungsten oxinate. It is bounded to - N by a coordination bond and to - O H by an electrovalent bond, in the formula of WO2 (C9H6NO)2.

The possible reaction equation for this structure can be written as follows: 2C9 H7 ON + WO 2-

~ WO 2 (C 9n

6NO ) 2 + 2 O H -

(3)

A pH increase was observed during the conditioning of the scheelite pulp with oxine and therefore Eq. 3 is the most probable mechanism between the scheelite surface and the reagent. This structure is also discussed in the literature (Duval, 1963 ).

286

o. ()ZCAN AN[) A.N. BU[ U 1(3{

Flotation experiments with oxine and alkyl oxine as modbqers The behavior of oxine and alkyl oxine on flotation was assessed using the siliceous scheelite ore (24.6 % WO3, 57.32 % SiO2 and 4.7 % CaO), the reason for the choice of this rich siliceous ore was to determine the behavior of the reagents under real flotation conditions for scheelite and pure calcite ore.

1. The effect of ph in the flotation of siliceous scheelite ore To determine the effect ofpH, a series of experiments were conducted using 400 g/t oleoyl sarcosine as collector (this is the optimum concentration which was determined in our laboratory and by Baldauf and co-workers, Ozcan, 1992; Baldauf et al., 1986) and 500 g/t oxine as modifier. In these experiments, pulp was conditioned with 500 g/t oxine for 25 minutes first and then 25 g/t quebracho was added. After 2 minutes conditioning with quebracho, oleoyl sarcosine was added and flotation was performed, pH adjustments were made by HC1 or sodium hydroxide. The flotation conditions and the results obtained in these experiments are given in Table 1 and in Fig. 10. Table 1 and Fig. 10 show, the grade and the recovery of rougher concentrate reaches a maximum around pH 7.5-8 having the highest values of 50.13 % WO3 grade and 95 % recovery using oxine. In addition, it was found that recovery and grade is always higher when oxine is used for all pH's, and thus, oxine increases the flotation efficiency of sarcosine for scheelite. 2. Determination of optimum oxine concentration To determine the optimum oxine concentration in scheelite flotation, some tests were conducted using between 50 g/t to 750 g/t oxine at pH 8 in the TABLE 1 Effect o f p H on scheelite recovery and grade using quebracho, sarcosine and oxine. Input assay: 24.6% WO3 pH

6 6 7 7 8 8 9 9 10 10

Exp. No.

1 2 1 2 1 2 1 2 1 2

Anal. of rougher concent.

Reagent type and amount ( g / t ) Oxine

Quebr.

Sarcos.

% WO3

% Recovery

500 500 500 500 500

25 25 25 25 25 25 25 25 25 25

400 400 400 400 400 400 400 400 400 400

33.70 48.06 44.51 49.90 39.68 50.13 37.21 47.76 34.19 39.40

78.5 92.0 73.0 90.4 79.8 95.0 79.7 89.5 83.4 81.1

ELECTROKINETIC, INFRARED AND FLOTATION STUDIES OF SCHEELITE AND CALCITE

Grade(,I, WO3 )

287

Recovery ( '/,

60

100

90 SC

18o

40

,70 '60

30

I O Gradewith oxine •

• Rmy with atine j rl Recovery without mine I I

Grade without oxine

20

,

7

6

I

L

8

9

50 40

10

pH Fig. 10. The changes of the grade and the recovery of rougher scheelite concentrate versus p H in the presence and absence of oxine.

Grade(*l*WO 3)

Reco~try ( '1, 100

59

57

95 55 53

)0 51

49 [

8S

I II •

47 45

SO

l

!

150

250

350 450 Oxine amount (g/t)

Grade 550

[] I~cov. i 650

750

Fig. 11. The variationof the grade and the recovery of rougherconcentrateversusoxine amount in scheelite flotation. presence of 400 g/t oleoyl sarcosine and 25 g/t quebracho. The changes of the recovery and the grade of obtained rougher concentrates are represented graphically in Fig. 11. It is clear from Fig. 11 that, there is rapid increase in both recovery and

288

( . O Z C A N A N D A,N. B~II2JT('I~

grade of the concentrate up to 250-300 g/t oxine addition and above this amount the rate decreases. Therefore, about 300 g/t of oxine is sufficient for the flotation of this ore.

3. Flotation of scheelite and pure calcite with alkyl oxine To make a comparison between oxine and alkyl oxine in scheelite flotation and also to determine the effect of the reagent in calcite flotation, experiments were conducted using 350 g/t alkyl oxine, 400 g/t oleoyl sarcosine and 25 g/ t quebracho at pH 8. Experimental conditions and the results obtained are given in Table 2. It is clear from Table 2 that, alkyl oxine increases the recovery of scheelite from 89.4 % to 97.2 % when it is used together with sarcosine. The use of quebracho however, decreases the recovery to 80.8 % when oxine is not present in the system. In the experiment No.S4, alkyl oxine was added to the pulp before quebracho addition and the recovery was obtained as high as 93.0 %. In other words, the recovery and the grade of the rougher scheelite concentrate did not decrease despite quebracho addition into the pulp. From experiment No. $5, however, alkyl oxine is not floating scheelite, i.e. it is not acting as a collector for scheelite. But it has a modifying effect on scheelite flotation when it is used together with sarcosine and prevents the depressing action of quebracho on scheelite. From the comparison of Table 1 with Table 2 it is seen that, alkyl oxine increases the recovery and the grade of scheelite concentrate more than oxine does. This is an expected result because alkyl oxine has a penthyl group attached to the structure and it is more hydrophobic than oxine. TABLE Flotation

2 conditions

of siliceous scheelite and pure calcite ores at pH 8 and the metallurgical

data of

the rougher concentrates Exp.

Reagent type and amount

(g/t)

Assay (%)

Recovery (%)

No. Alk. oxine

Quebr.

Sarcos.

WO3

CaCO3

WO3

CaCO3

SI

-

-

400

47.13

-

89.4

-

$2

350

-

400

46.03

-

97.2

-

$3

-

25

400

50.48

-

80.8

-

$4

350

25

400

54.74

-

93.0

-

$5

350

-

-

-

none

-

C1

-

-

400

100.0

-

98.0

C2

350

-

400

100.0

-

97.4

C3

-

25

400

100.0

-

83.7

C4

350

25

400

100.0

-

94.8

C5

350

-

-

none

-

none

none

ELECTROKINETIC, INFRARED AND FLOTATION STUDIES OF SCHEELITE AND CALCITE

289

Calcite flotation however, was not affected by alkyl oxine addition and quebracho showed depressing effect for calcite. In conclusion, alkyl oxine or oxine addition to the pulp before quebracho treatment increases the selective attachment of oleoyl sarcosine to the scheelite surface and prevents the depression of scheelite by quebracho, while the depression of calcite is still preserved. Hence, oxine and especially alkyl oxine can be used as scheelite modifiers in a calcitic scheelite flotation with oleoyl sarcosine. Selective flotation scheme of a low-grade calcitic scheelite ore with sarcosine and alkyl oxine is given elsewhere (Ozcan, 1992). CONCLUSIONS

Alkyl oxine and oxine can be used as scheelite modifiers for the separation of scheelite from calcite by flotation. The main mechanism governing the modifying action of oxine and alkyl oxine is the competition of the reagents with quebracho for the scheelite surface. These reagents chemically adsorb on scheelite surface by decreasing the negative charge on the surface and hence prevent the depressant action of quebracho. Thus, separation of scheehte from calcite is possible, through the scheme developed in this study. REFERENCES Agar, G.E., 1984. Scheelite Flotation. U.S. Patent US 4,488,959 A, 17 pp. (Chem. Abstr., 102(20): 170318b). Atademir, M.R., Kitchener, J.A. and Shergold, H.L., 1979. The surface chemistry and flotation of scheelite. J. Colloid Interface Sci., 71 (3): 466-476. Atademir, M.R., Kitchener, J.A. and Shergold, H.L., 1981. The surface chemistry and flotation of scheelite. II: Flotation collectors. Int. J. Miner. Process., 8: 9-16. Atak, S., 1979. Flotation Behavior of Calcite and Scheelite. Ph.D. Thesis, Istanbal Technical University, Mining Eng. Department, Istanbul. Atak, S., Gurkan, V. and Yafawi, A., 1986. Effects of various fatty acids on separation of scheelite from calcite. In: Y. Aytekin (Editor), 1st Int. Miner. Process. Syrup., Izmir, pp. 94-103. Bailar, J.C., Emeleus, H.J., Nyholm, R. and Trotman-Dickenson, A.F. (Editors), 1973. Comprehensive Inorganic Chemistry. Part 2, Pergamon Press, Oxford. Baldauf, H., Schubert, H. and Kramer, H., 1986. N-Acylamino carboxylic acids, collectors for the flotation separation of fluorite and calcite. Aufbereitungs-technik, 5:235-241. Beyzavi, A.N., 1985. Flotation of calcite containing scheelite ores. ErzmetaU, 38 ( l 1 ): 543-549. Charles, R.G., Freiser, H. and Friedel, R., 1956. Infra-red absorption spectra of metal chelates derived from 8-hydroxyquinoline, 2-methyl-8-hydroxyquinoline, and 4-methyl-8-hydroxyquinoline. Spectrochim. Acta, 8: 1-8. Duval, C., 1963. Inorganic Thermogravimetric Analysis. Second and Revised Edition, Elsevier, New York. Erlenmeyer, H., Steiger, J.V. and Theilheimer, W., 1942. Flotation experiments with 8-hydroxyquinoline as collector. Helv. Chim. Acta, 25:241-245. Also in: Hollingshead, R.G.W., 1954-1956. Oxine and Its Derivatives. Vols. 1-4, Butterworths, London. Fuerstenau, D.W. (Editor), 1962. Froth Flotation 50th Anniversary Volume. AIME, New York. Fuerstenau, M.C., 1985. Chemistry of Flotation. SME-AIME, New York.

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