Behavior of antimony(III) during copper electrowinning in chloride solutions
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I.
INTRODUCTION
Sb2OHCI5 (adsorbate)
ANTIMONY exists as an impurity in electrolytes of copper electrorefining and electrowinning from sulfate solutions. To prevent detrimental effects during copper electrorefining and electrowirming, antimony in the copper sulfate electrolytes is controlled within the range of 0.3 to 0.6 g/L. However, solubility of antimony is 1.0 to 1.5 g/L in a typical copper electrolyte containing 40 to 50 g/L Cu and 180 to 200 ~ free sulfuric acid at 323 to 333 K (50 to 60 ~ Therefore, the excessive antimony in the electrolytes has to be removed by hydrolysis, sulfde precipitation, solvent extraction, carbon adsorption, or ion exchange,tt~l Contamination of cathodic copper by antimony was observed in copper electrowinning from chloride electrolytes when the antimony concentration in the electrolytes was as low as 2 ppm. Obviously, antimony contaminates cathodic copper more severely in chloride electrolytes than in sulfate electrolytes. Muir and Senanayaket41 demonstrated that the reduction potential for antimony in chloride media lies close to the reduction potential of Cu(t). Therefore, the effect of antimony on copper electrowinning from chloride electrolytes is more significant than that in sulfate electrolytes. Recently, Lin et aLtO1 investigated the behavior of cathodic processes of antimony species in chloride solutions. Based on the results of the electrochemical study, a reaction mechanism, which corroborates the experimental results, was proposed as follows: SbCI3 + H 2 0 ~k,_Z SbOHCI, + H ~ + C I ShOHCI, + SbCI3 #
Sb,OHCI, (adsorbate)
[1] [2]
+ e ~ Sb, OHC14 (adsorbate)+ CI-
[3]
Sb201-IC14 (adsorbate)
k,
+ e ~_~ Sb,OHCI~ (adsorbate) + CI-
[4]
Sb2OHCI3 (adsorbate) + H § k, + e~Sb
+ SbCI3 + H20
[5]
The overall rate was expressed astS1 Rate =
k,[SbCI3]-'/[H-] [CI- ] kh[SbCl3l:/[H*][Cl--I + k~
[6]
where k,, ke, and k~. are constants at a fixed temperature. At lower concentrations of Sb species, the reaction orders with respect to [SbCI3], [H§ and [C1-] are 2, - 1 , and - 1 , respectively, while at higher concentrations of Sb species, the reaction order with respect to [SbCI3] leads to zero. These reaction orders were confirmed by experimental results/~7 However, antimony species may behave differently in copper electrowinning where electrolytes contain copper species which could interfere or react with the antimony species. The object of this study is to examine the behavior of antimony in the chloride electrolytes during the copper electrowinning. With a better understanding of the behavior of antimony in the electrolytes, some appropriate operating conditions of the electrowinning can hopefully be recommended. II.
EXPERIMENTAL
A. Electrowinning of Copper The electrolyzing cell is made of TEFLON* with an inILK. LIN, Associate Professor, is with the Mineral Industry Research Laboratory, University of Alaska Fairbanks, Fairbanks, AK 99775-7240. X. WU, formerly Research Associate with the Mineral Industry. Research Laboratory, University of Alaska Fairbanks, is Senior En
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