Optimization of separation processing of copper and iron of

dump bioleaching solution by Lix 984N in Dexing Copper Mine

LIU Qing-ming(刘清明)^{1, 2}, YU Run-lan(余润兰)^{1, 3}, QIU Guan-zhou(邱冠周)^{1, 3},

FANG Zheng(方 正)^{1, 2}, CHEN Ai-liang(陈爱良)⁴, ZHAO Zhong-wei(赵中伟)⁴

1. Key Laboratory of Biometallurgy, Ministry of Education, Central South University, Changsha 410083, China;

2. School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China;

3. School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China;

4. School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China

Received 3 September 2007; accepted 19 December 2007

Abstract: The effects of the concentration of Lix 984N, phase ratio, initial pH value of aqueous phase and extraction time on the extraction of copper and iron under the condition of low Cu²⁺ /Fe³⁺ ratio in dump bioleaching solution of Dexing Copper Mine were explored. The optimal conditions of extraction are as follows: the concentration of Lix 984N 10%; the phase ratio (O/A) 1?1; the initial pH value of aqueous phase 1.5 and the mixing time 2 min. The stripping experiments show that H₂SO₄ solution could efficiently recover copper from the organic phase under the optimal conditions.

Key words: copper solvent extraction; processing optimization; Lix 984N; bioleaching solution

1 Introduction

Bioleaching—solvent extraction—electrowinning (BL-EX-EW) has become a key process for recovering copper from the bioleaching solution of low-grade ores in the last two decades[1]. The separation of copper and iron with solvent extraction is basic in biological metallurgy. In recent years, a lot of studies on copper solvent extraction in acid or ammoniacal medium using Lix series extractants have been reported[2-15]. Now, Lix 984N and M5640 are widely used as extractive reagents.  Lix 984N is a mixture of Lix 860N and Lix 84 in kerosene. The active ingredients are 2-hydroxy-5- nonylacetyloxime and 2-hydroxy-5-dodecalkyl salicyl- aldoxime. The extractive reactions are as follows[16]:

Cu²⁺+2HR⁰=CuR₂⁰+2H⁺                      (1)

Cu²⁺+4HR⁰=CuR₂2HR⁰+2H⁺                   (2)

In dump bioleaching solution of Dexing Copper Mine, the concentration of Cu²⁺ was designed as 1 g/L. Now it maintains about 0.3 g/L for several years. The concentration ratio of Cu²⁺ to Fe³⁺ is very low. The accumulated concentration of Fe³⁺ in the electrowinning solution is up to 6-8 g/L. Therefore, it is necessary to study the separation behaviors of copper and iron from the bioleaching solution with low Cu²⁺/ Fe³⁺ ratio by Lix 984N by optimization of the extractive parameters.`

2 Experimental

2.1 Raw material and chemical reagents

The aqueous phase was prepared by CuSO₄·5H₂O, Fe₂(SO₄)₃ and H₂SO₄ (all in AR grade) according to the composition of solution of Dexing Copper Mine. The solution contained Cu²⁺ 10 g/L, Fe³⁺ 20.4 g/L and its pH is about 2. The copper extractive reagent was Lix 984N (Germany Henkel Corporation) with kerosene as the diluent reagent. The stripping reagent was 180 g/L H₂SO₄ solution.

2.2 Analytical method

The concentration of copper and iron in the aqueous phase was measured by 3510 atomic absorption spectrophotometer. The concentration of copper and iron in the organic phase was calculated based on the mass balance.

2.3 Condition experiments

The experiments were carried out in a separatory funnel. Before each run, the funnel was washed with kerosene. The aqueous phase and the organic phase were added into the funnel. Then the cone was vibrated under 200 r/min at (25±1) ℃. The phases were disengaged after vibrating for a certain minutes. The concentration of Cu²⁺ and Fe³⁺ in the aqueous phase was measured and that in the organic phase was calculated. The extraction rate and the separation coefficient of copper and iron were determined under different conditions of extractive reagent, phase ratio, pH value and extractive time, respectively. The organic phase was further stripped by 180 g/L H₂SO₄ solution. The conditions of counter extraction were similar to the extraction experiments.

3.1 Solvent extraction behaviors of copper and iron

Fig.1 shows the change in the extraction rate of copper and iron with Lix 984N concentration. The extraction rate of copper increases as the concentration of extractive reagents enhances. When the concentration of Lix 984N is 10%, the extraction rate of copper reaches about 98.5%, then remains stable. Simultaneously, the extraction rate of iron stays very low, and keeps constant over the concentration of 30% Lix 984N. The extraction rate of iron slightly increases as the concentration of Lix 984N enhances. The largest separation coefficient of Cu/Fe occurs in the Lix 984N range from 10% to 12.5%. The optimal concentration of Lix 984N is suggested to be about 10%.

Fig.1 Effect of Lix 984N concentration on separation of copper and iron (Initial pH value of aqueous phase 1.5; time 2 min; O/A=1?1; 298 K)

Fig.2 shows the effect of the phase ratio (O/A) on the separation of copper and iron. When the phase ratio(O/A) is lower than 1?1, the extraction rates of both copper and iron ascend rapidly with the increase of the phase ratio, reaching about 96.3% for copper. Then, they maintain only a slight increase over the phase ratio of  1?1. Basically, the phase ratio almost does not influence the separation coefficient of Cu/Fe. The optimal phase ratio is suggested to be 1?1.

Fig.2 Effect of phase ratio on extraction rates of copper and iron (Time 2 min; 10% Lix 984N; 298 K)

The effect of the initial pH value of aqueous phase on the extraction rates of copper and iron is shown in Fig.3. There is an obvious increase in the extraction rate of copper with the increase of initial pH value. During the extraction process, reaction (1) happens between Cu²⁺ and Lix 984N, so the initial pH value of the aqueous phase plays an important role in the reaction. The extraction rate of iron also slightly increases with the increase of the pH value. However, it begins to decrease rapidly when pH is over 2.0. The reason is that the aqueous phase becomes turbid because of the hydration of Fe³⁺ as follows.

Fe³⁺+H₂O=Fe(OH)²⁺+H⁺                      (3)

Fe(OH)²⁺+H₂O=Fe(OH)₂⁺+H⁺                  (4)

Fe(OH)₂⁺+H₂O=Fe(OH)₃+H⁺                   (5)

Fig.3 Effect of initial pH value of aqueous phase on extraction rate of copper and iron (Time 2 min; 10% Lix 984N; O/A=1?1; 298 K)

Although the separation coefficient of Cu/Fe keeps ascending with the increase of the initial pH value, the hydration of Fe³⁺ is accelerated at the high pH value, resulting in the formation of the third phase. So the optimal initial pH value of aqueous phase is 1.5. If the third phase can be treated by other method, the higher initial pH value of bioleaching solution is advantageous in the selective separation for Cu/Fe and the extraction rate of Cu.

Fig.4 shows the effect of mixing time on the extraction rate of copper and iron. The extraction rate of copper increases with the prolonging of time. The reaction is so rapid that it almost finishes within 1 min. Meanwhile, the extraction rate of iron is 20%. The separation coefficient of Cu/Fe does not change a lot after 2 min. The optimal mixing time is 2 min.

Fig.4 Effect of mixing time on extraction rate of copper and iron (Initial pH =1.5; 10% Lix 984N; O/A=1?1; 298 K)

3.2 Stripping behaviors of copper and iron

As shown in Fig.5, the stripping rate of copper goes up with the rise of H₂SO₄ concentration from 1 to 1.5 mol/L, and reaches 97.8% when H₂SO₄ is 1.5 mol/L. But the stripping rate of iron also increases and almost attains the maximum at 2.5 mol/L H₂SO₄, then it is stable over the H₂SO₄ concentration. Only about 60% of iron is stripped into the aqueous phase during stripping. Obviously, the behavior of iron differs from that of copper in the stripping process. The appropriate H₂SO₄ concentration for the stripping is from 1.5 to 2.0 mol/L.

Fig.5 Effect of H₂SO₄ concentration on stripping rate of copper and iron (Reaction time 2 min; O/A=1?2; 298 K)

As illustrated in Fig.6, the stripping rate of copper increases sharply with prolonging the time, and reaches 94.2% in 2 min. Then it increases slightly. The optimal time is 2 min.

Fig.6 Effect of stripping time on stripping rate of copper and iron (H₂SO₄ concentration 1.5 mol/L; O/A=1?2; 298 K)

Fig.7 shows that the stripping rate of copper increases with the phase ratio increasing. When the ratio is below 0.5, the rates of both copper and iron increase rapidly. The highest value is 97.8% when the phase ratio is 1?2. At the same time, the stripping rate of iron remains very low. Thus, the proper phase ratio (O/A) is 1?2.

Fig.7 Effect of phase ratio on stripping rate of copper and iron (H₂SO₄ concentration 1.5 mol/L; time 2 min; 298 K)

1) The extraction rate of copper increases with the increase of the Lix 984N concentration. It reaches 98.5% at the optimal Lix 984N concentration of 10%. When the proper phase ratio(OA) is 1?1, the extraction rate of copper can reach a high value with a low cost of production. The initial pH value of aqueous phase obviously affects the extraction rate of copper and the separation of copper from iron. The optimal initial pH value for the extraction is 1.5. The extraction can be completed in 1 min and the extraction rate of copper is 96.5%.

2) H₂SO₄ solution is high-efficient stripping reagent. The optimal condition of stripping of copper is O/A=1?2 with 1.5 mol/L H₂SO₄ for 2 min.

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Foundation item: Project (2004CB619200) supported by the National Basic Research Program of China

Corresponding author: Yu Run-lan; Tel: +86-731-8836943; E-mail: yrl715@sina.com

(Edited by YUAN Sai-qian)