Extraction of copper from sulphate solutions by MOC 45: Application to Cu separation from leachates of a copper flue dust

hydrometallurgy Hydrometallurgy

47 ( 1997) 99-

1I2

Extraction of copper from sulphate solutions by MOC 45: Application to Cu separation from leachates of a copper flue dust M. Amores, A.G. Coedo, F.J. Alguacil

*

Centro National de Investigaciones Metalirgicas (CSIC), Avda. Cregorio de1 Amo 8, Ciudad lJnir:er.sitmiu. 28040 Madrid, Spain Received 23 January

1997; accepted 23 May 1997

Abstract The application of the new extractant MOC 45 (oxime derivative) as an extraction agent of copper (II) from sulphate media is studied. The extraction system is studied as a function of temperature, diluent of the organic phase, metal concentration, along with the copper stripping stage by sulfuric acid solutions. The data have been analyzed numerically to determine the stoichiometry of extracted species and their equilibrium constants. It was found that copper was extracted into the organic phase by the formation of the species CUR, (log K,,, = 0.62) and Cu(HR,), (log K,,, = 4.00). The performance of the system was studied using batch and continuous experiments. 0 1997 Elsevier Science B.V.

1. Introduction At the end of the 1960s a new period began in copper hydrometallurgy due to the introduction of solvent extraction to the electrolytic copper process using mainly hydroxyoximes as extractants [l-5]. From those days to the present the application of the sequence leaching-solvent extraction-electrowinning has produced the most economical copper in the world. The effectiveness of the operation is demonstrated by the increase of copper production by this method (Table 1). The implementation of hydrometallurgy for copper production using solvent extraction on a scale not encountered before, has led to the develop of new extractants to cope with the demands of the industry. One of the new extractants in this field is the MOC family, developed by Allied

’ Corresponding

author

0304-386X/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PI/ SO304-386X(97)00038-8

M. Amores et al. / Hydrometallurgy 47 (19971 99-l 12

100 Table 1 Worldwide

1981 1991 2000 Increment

production

of refined copper (ton) [6-81

1991-2000

Total

SX/EW

% SX/EW

7,350,ooo 8,863,OOO 11 ,ooo,ooo +2,137,000

700,000 950,000 2,310,OOO + 1,360,OOO

9.5 IO.7 21.0 64.0

over total

Signal Chemicals (Allco Chem.). The present work investigates the behavior and performance of MOC 45 oxime in the extraction of copper from sulphate solutions.

2. Experimental MOC 45 extractant was obtained from the Chilean branch of the former Allied Signal Chemicals manufacturer of this extractant. The agent is based on the 2-hydroxy-5-nonylacetophenone oxime (C ,7 H,,NOz) with an apparent molecular weight of 277 and density 900 kg/m3 [9]. The extractant was used as supplied by the manufacturer. The approximate oxime concentration in the organic phases was determined by the ultimate loading [ 10-121, as this appears to be of most practical use in determining oxime concentrations. Kerosene was obtained from CAMPSA, its main properties are: density 780 kg/m3, aromatic content lo%, boiling range 200-260°C flash point 80°C. All other chemicals were of AR grade. Copper extractions and/or stripping experiments were carried out by shaking equal volumes, unless otherwise stated, of the appropriate organic and aqueous solutions in separatory funnels, for the time and at the temperature required. Continuous experiments were conducted in a unit of 2 mixer-settlers thermostated at the required temperature. The unit had a maximum flow capacity of 100 ml/min for each phase. Mixing and settling volumes were 200 and 700 ml respectively.

Table 2 Analysis of copper flue dust and composition

of leach solution

Analysis of copper dust MO 0.45% Pb 0.08% As 0.90%

Cu 24.5% Fe 14.0% Zn 0.15% Composition Cu 0.26 g/l Fe 7.3 mg/l Zn 0.1 mg/l

of leach solution MO 0.05 mg/l Pb 0.06 mg/l As 0.1 mg/l

M. Amores et al. / Hydrometallurgy

0’ 0

lOI

47 C19971 99-I I -I

I

I

’

/

I

10

20

30

40

50

’ 60

Tlme,mln

Fig.

1.Influence of equilibration time in copper extraction by MOC 45. Equilibrium pH 0.9 f 0.05.

A leach solution was prepared dust whose composition is shown for 2 h with a solution of sulfuric leach liquor treated in continuous

by the following procedure: a copper flash furnace flue in Table 2 was leached under atmospheric conditions acid (approximately 45 g/l). The composition of the extraction is presented in Table 2.

6

Fig. 2. Plot of log II),, versus 1000/T for copper extraction by MOC 45. Equilibrium Equilibration time 20 min. Dotted line shows 95% confidence interval.

pH 0.9~0.05.

102

M. Amores

et al./Hydrometallurgy

47 (1997)

99-112

Metals were analyzed by atomic absorption or ICP-MS. The acidity of the aqueous phases was determined by titration with standard NaOH solution.

3. Results and discussions 3.1. Influence

of equilibration

time and temperature

Experiments on the influence of equilibration time and temperature on copper extraction have been carried out by shaking at 20°C for various lengths of time aqueous solutions of 0.1 g/l copper and organic phases of 10% v/v MOC 45 in kerosene. Results obtained are shown in Fig. 1; it is shown that the system approaches the equilibrium rather slowly (e.g., equilibrium is reached within 20 min of contact), although the difference between 10 min and 60 min is not marked. In these conditions, MOC 45 appears to have relatively poor extraction kinetics which do not compare favorably with other Cu extractants, especially salicylaldoximes with faster kinetics, although they are stronger extractants for copper.

100

90-

ao:

70-

cl :

bO-

: z k 0. a

so-

40-

u” s

30-

20-

0

decane

A

kerosene

0

xylene

lo-

03 0

Equilibrium

3. Variation of copper extraction Temperature 20°C.

Fig.

3

2

1

by MOC 45 in various

pH

organic

diluents.

Equilibration

time 20 min.

IO3

M. Amores et al. / Hydrometallurgy 47 (19971 99%Ill?

In addition the relationship between copper extracted into the organic phase and the temperature was studied, the organic and aqueous phases used being the same as above. Fig. 2 shows the variation of log D,, a g ainst 1000/T; in the range of temperatures used there is an increase of copper extraction with the increase of temperature. From this figure is obtained AH0 = 28.9 kJ/mol, so the extraction process is endothermic. 3.2. Injluence

of the organic phase diluent

Since the diluent of the organic phase can influence the extraction of metals, in the present work the performance of the MOC 45copper sulphate extraction system was tested using various diluents for the organic phase. Aqueous solutions contained 0.1 g/l Cu whereas organic solutions were of 5% v/v MOC 45 in each diluent. The results obtained are shown in Fig. 3 in which the per cent of copper extracted is plotted against equilibrium pH. The results obtained for the present extraction system showed that the change of the diluent influences copper extraction by MOC 45 since the pH,, values vary from 1.22 for xylene to 0.69 for n-decane. Accordingly it can be deduced that in this extraction system the best extraction results are obtained if mainly aliphatic diluents are employed.

100

90-

80-

70-

60-

c li

I 1

Fig. 4. Variation of copper Temperature 20°C.

extraction

1 2 Equilibrium

at different

0

0.1

0

2

g/L 0

g/L

I 3 pH

initial metal concentrations.

Equilibration

time 20 min.

104

M. Amores et al. / Hydrometallurgy

3.3. lnjluence

47 C1997) 99-l 12

of copper concentration

The influence of the initial copper concentration on the extraction by MOC 45 was investigated. This study was carried out at 20°C by shaking aqueous phases which contained various copper concentrations and organic phases of 5% v/v MOC 45 in kerosene. Fig. 4 shows that the variation of the initial copper concentration has no influence on the pH,, value. The independence of the percentage of extraction and consequently of the copper distribution coefficient with the aqueous pH indicates that there is no formation of polynuclear species in the organic phase. Similar results were obtained when different MOC 45 concentrations (1 to 10% v/v) were used to extract copper. 3.4. Reagent concentration

dependence

and copper extruction

mechanism

In Fig. 5 the variation in the percentage of copper extracted against pH at various extractant concentrations is shown. Experiments were carried out with aqueous solutions of 2.0 g/l Cu and organic solutions of MOC 45 at 1, 2.5, 5, and 10% v/v in kerosene.

100

go-

80-

k

70-

r lil

60-

: z

50-

kl :

40-

x

30-

:

MOC

20-

10

45

0

10%

a

5%

0

2.5%

0

1%

v/v v/v v/v v/v

-

1

0

Fig. 5. Copper extraction Temperature 20°C.

by various

3

2 Equtlibrium

MOC 45 concentrations

4

pH

in kerosene.

Equilibration

time 20 min.

M. Amores et al. / Hydrometallurgy 47 ( 19971 99-112

MOC: ??

a 0

10% 5% 25%

105

45 v/v v/v v/v

m n

0

1

3

2

4

ccul,s.s/tFig. 6. Equilibrium

loading isotherms for copper extraction

by MOC 45. Equilibration

time 20 min

The results show that the variation in the initial extractant concentration has a significance influence on copper extraction and that under the experimental conditions used it was possible to reach copper pH,, values near 0.6. Results also show that, as expected from the extraction reaction stoichiometry, a ten-fold increase in extractant concentration produced an increment in the pH,, of near one unit. Several copper extraction equilibrium isotherms were obtained by shaking at 20°C different volumes of organic phases of MOC 45 2.5, 5 and 10% v/v in kerosene and aqueous phases which contained 2.0 g/l copper. The results obtained are shown in Fig. 6. Sulfuric acid titration of the equilibrated aqueous phases showed that 1 mol of acid is liberated for 1 mol of copper extracted by MOC 45 as shown by the experimental values (Table 3) for MOC 45 5% v/v in kerosene. If we take into account the hydroxyoxime association in the organic phase and the solvation of the complex with hydroxyoxime molecules, the extraction of copper can be described by the expression: 2fs (HR) zorg@ CUR, . sHRO,, + 2H,t, + z where 2: denotes the degree of hydroxyoxime association solvation with extractant molecules. cll;;

(1) and s the degree of complex

M. Amores et al. / Hydrometallurgy 47 (1997) 99-112

106 Table 3 Experimental

values of H,SO,

liberated by the extraction

of copper

[Cd,,, m4)

[&SO& (fi)

[Cd,,, /h

14.6 26.3 31.3 43.3 46.6 44.7

14.3 26.8 36.9 42.0 46.6 45.2

1.02

Table 4 Equilibrium

constants

for the extraction

0.98 1.01 I .03

1.oo 0.99

of copper by MOC 45 from sulphate solutions

Species

log K,,,

&log

CUR,

0.62 LO.08 4.00~0.07

0.027 0.023

Cu(HR,),

SO&

K,,,)

l/= 0.061

3

-1.6

-12

-0.8 ‘og

Rig. 7. Copper distribution

diagram

as a function

-0

4

CHRI

of the total concentration

of MOC 45. Equilibrium

pH 0.5.

M. Amores et al./Hydrometallurgy

JO.7

47 (1997) 99-112

I-

CUR,

erg

/

>_

/

o.ot-2.0

-1.6

-12 log

Fig. 8. Copper distribution

diagram

-0.8 CHRI

as a function of the total concentration

-0.4

00

of MOC 45. Equilibrium

pH 2.1).

Experimental data were treated numerically using the program LETAGROP-DISTR [ 131 in order to define the species extracted in the organic phase and the corresponding values of K,,,. In these calculations several co-reactions of the oxime were also taken into account as follows: (i) Dimerization of the oxime in the organic phase: 2HR.,,

@ (HR)2”r,

(ii) Partition

K, = 31 dm3/mol

(2)

of the oxime into the aqueous phase: K, = 2.2 ’ 1O-4

HRW, + HR,, (iii) Dissociation

(3)

of the oxime in the aqueous phase:

HR,, * H& + Riq

K, = 5.3.

IO-”

mol/dm’

(4)

The K values were taken from literature considering the close resemblance between MOC 45 and SME 529 extractants [14]. The proposed stoichiometries for copper extraction by MOC 45 together with the corresponding values of log K,,, and g(log K,,,) are given in Table 4. Figs. 7 and 8 show the distribution of copper-MOC 45 species as a function of rhe total oxime concentration and the equilibrium pH. The dimer complex is predominant at

108 Table 5 Stripping

M. Amores et al./ Hydrometallurgy

of copper using H,SO,

47 C19971 99-l 12

solutions

H,SO,

% Cu stripped

125 g/l 150 g/l 175 g/l

91.7 93.3 92.5

Temperature

20°C. Equilibration

time 10 min. O/A

ratio 1.

high oxime concentrations and/or low pH values, whereas the monomer complex (CUR,) is predominant at low oxime concentrations and high aqueous pH values. In the case of the dimer complex the proposed stoichiometry is in agreement with the four coordination geometry preferred for copper (II). The Jahn-Teller effect is strong for this ion and thus the geometry of the complex should be considered as a distorted octahedral (close to square planar) [ 15-171. 3.5. Copper stripping The stripping stage was studied using sulfuric acid as this is the medium for copper electrowinning. Copper stripping experiments were carried out using an organic phase of

1 :

r2=

0967

1 ;

y” 01

-0

1

1.

2

1

1

3.0

31

I

3.2

1

3.3

I

3.4

:

5

lOOO/T.K-’

Fig. 9. Arrhenius plot for copper stripping. 95% confidence interval.

K, defined as [Cu],, /[Cu],,,

at equilibrium.

Dotted line shows

M. Amores et al. / Hydrometallurgy 47 (1997) 9% I !2

IOU

J 0

1

2

3

4

5

CCUl,~,.Gl/L

Fig. 10. Copper stripping isotherm using H?SO,.

Temperature

20°C. Equilibration

time IO min.

MOC 45 10% v/v in kerosene loaded with 0.6 g/l copper and different sulfuric acid solutions. Table 5 shows results obtained using different H,SO, concentrations for stripping: there is no appreciable difference in the per cent of copper stripped after one stage, thus this parameter seems not to be important for achieving good copper recoveries in one stage. Stripping equilibrium is obtained in all the cases within 5 min of contact. Temperature influences the extent of copper stripped using a solution of 150 g/1 H2S0, and 10 min of contact. Fig. 9 shows the Arrhenius plot for copper stripping; from this figure is obtained A Ho = 1 I .4 kJ/mol; the reaction is therefore endothemric. Fig. 10 shows stripping isotherms obtained using different H,SO, solutions: as mentioned above the initial sulfuric concentration appears not to have a great influence on copper stripping. 3.6. Extraction-stripping

cycles (batch)

These experiments were carried out to determine the performance of MOC 45 under continuous use. As organic phase a solution of MOC 45 10% v/v in kerosene was used, the aqueous

110

M. Amores 100

et al./Hydrometallurgy

47 (1997)

99-112

Y.

I-

o/+-----o

go-

80-

70-

60-

50-

40-

30-

20-

*

Extraction

0

Strlpping

10 -

0

1

0

1

I

I

I

I

I

8

1

I

2

3

4

5

6

7

8

9

1 3

Cycles

Fig. 11. Variation of copper extracted or stripped per cycle.

phase in extraction contained 0.1 g/l Cu and the stripping solution was 150 g/l H,SO,. In all cases temperature was 20°C and contact time 10 min. Fig. 11 shows the results obtained after ten cycles; it can be seen that there is no appreciable loss either in copper load or strip in the corresponding stage.

UNLOADED

LOADED

RAFFINATE 0 017g/L

cu

F&D 00939/L

C”

ORGANIC

cOOOlg/L

CU

ORGANIC

STRIP SOLUTION 0074g/L

cu

-ORGANIC

I t STRIP SOLUTION No Cu STREAM

-----AQUEOUS Fig.

12. Copper concentration synthetic solution.

in feed solutions

and mixer-settlers

for the experiment

STREAMS

carried

out with a

112

M. Amores et al. / Hydrometallurgy 47 (19971 9%112

using this leach solution. the complete test.

As in the above operation

good performance

was observed

for

4. Conclusions The results obtained show that the commercially available extractant MOC 45 (2-hydroxy-5nonylacetophenone oxime) can be used as a reagent for copper extraction in sulphate media at moderate acidic pH values. The extraction reaction is endothermic (AH” = 28.9 kJ/mol) and it is dependent on the organic diluent, the aqueous pH value and the extractant concentration. The extraction of copper proceeds by an ion exchange reaction (chelate formation). Copper is extracted into the organic phase by the formation of the species CUR, (log K,,, = 0.62) and Cu(HR,), (log K,,, = 4.00). No polynuclear copper complexes are formed in the experimental conditions used. The predominance of the different species depends on the extractant concentration and the pH of the aqueous solution. Sulfuric acid can be used as an effective stripping agent for copper, the reaction being endothermic (A H” = 11.4 kJ/mol). Batch and continuous studies showed that there is no appreciable loss of reagent copper loading or stripped over the period of the experiment, thus MOC 45 can be used effectively to separate copper from sulphate solutions and recover this metal by electrowinning.

References [I I G.M. Ritcey, A.W. Ashbrook, Solvent Extraction, Part II. Elsevier, Amsterdam, 1979, pp. 196-258. [2] J.F.C. Fisher, C.W. Notebaart, in: T.C. Lo, M.H.I. Baird, C. Hanson (Ed&.), Handbook of Solvent Extraction, J. Wiley & Sons, New York, 1983, pp. 649-671. [3] GM. Ritcey, A.W. Ashbrook, Solvent Extraction, Part I. Elsevier, Amsterdam, 1984, pp. X7-17 I, [4] M. Cox, in: J. Rydberg, C. Musikas, G.R. Choppin (Eds.), Principles and Practices of Solvent Extraction, Marcel Dekker, New York, 1992, pp. 357-412. [51 J. Szymanowski, Hydroxyoximes and Copper Hydrometallurgy, CRC Press, Boca Raton, 199.1. [6] C.A. Gomez, Mineria Chilena 12 (134) (1992) 13-21. [7] J. Herrera, Mineria Chilena 15 (171) (1995) 29-35. [8] P. Navarro, J.C. Cardenas, INDEMET ‘96, Universidad de Santiago de Chile. Santiago. 1996. pp. I i-33. [9] Allied Signal Chem., MOC 45 Technical Sheet, 1994. [IO] A.W. Ashbrook, J. Chromatogr. 105 (1975) 151-156. 1Ill R.J. Whewell, M.A. Hughes, C. Hanson, Proc. ISEC ‘77, CIM Special Volume 21, 1979. pp. 185-1Y2. [ 121 C.K. Lee, L.L. Tavlarides, Metall. Trans. B 14B (1983) 153-158. [ 131 D.H. Liem. Acta Chem. Stand. 25 (1971) 1521-1534. [ 141 K. Inoue, H. Tsunomachi, Hydrometallurgy 13 (1984) 73-87. [ 151 F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, Wiley, New York, 1980. [ 161 A.M. Sastre. N. Miralles, E. Figuerola, Solvent Extr. Ion Exch. 8 (1990) 597-614. [ 171 K.C. Sole, J.B. Hiskey, Hydrometallurgy 37 (1995) 129-147.

M. Amores et al. / Hydrometallurgy 47 (1997) 99-l 12 UNLOADED ORGANIC
LOADED ORGANIC

012g/L OOlmg/L

RAFFINATE 002g/L_ 68mg/L OOlmg/L O.O3mg/L OOBmg/L Olmg/L

cu Fe

Zn MO Pb As

Fig. 13. Metal concentrations solution.

3.7. Extraction-stripping

0.269/L

CL.

7.3mg/L

Fe

O.OlrnQ/L O.OSmg/L 0 Odmg/L O.lmg/L

Zn MO Pb As

111

CL. Fe

CL. MO

STRIP. SOLUTION 0 12g/L cu

OOlmg/L 0 lOmg/L

in feed solutions and mixer-settlers

MO Fe

for the experiment

ST&P. SOLUTION ~zzSO4

carried out with a leach

cycles (continuous)

To complete the information available, experiments were also carried out in a continuous mixer-settler equipment. In these experiments the organic solution was run directly from the extraction circuit to the stripping circuit and from here recycled back to the extraction circuit. The continuous operation was run for 20 h at 20°C. One stage was used for extracting copper from a synthetic solution of near 0.1 g/l copper by a solution of MOC 45 1% v/v in kerosene and one stage of stripping with a solution of 150 g/l sulfuric acid. The unit was operated at an organic:aqueous phase flow ratio of 1:l both in the extraction and stripping circuits. Fig. 12 presents the quantitative results obtained from these experiments; good performance in the extraction-stripping of copper and also in phase disengagement was observed throughout the operation. Another experiment was carried out with a leach solution whose composition is shown in Table 2 and the same organic solution as above. This operation was conducted continuously for 20 h. The organic:aqueous phase ratio was 2: 1 for the extraction circuit and 1: 1 for the stripping circuit using a solution of 150 g/l H, SO, as stripping agent. The results are shown in Fig. 13. The presence of molybdenum and iron in the stripping stream is probably due to the experimental conditions used since the organic phase was not completely loaded with copper and these metals were co-extracted with the copper. Table 6 shows the separation factors Cu-MO and Cu-Fe obtained from the experiment

Table 6 Separation

factors obtained

for extractions

in continuous

operation SF

Cu-MO G-Fe

18.2 150

(Fig. 13)