Koichi Arai1, Sumiko Sanuki1, Koji Itakura2, Tomonao Sanga2 and Satoshi Sunada1
1Department of Metallurgical Engineering, Faculty of Engineering, Toyama University, Toyama
The feasibility of an electro-winning process of Ag for lead anode slime was investigated from the electrochemical and kinetic points of view based on the experimental results of nitric acid leaching of lead anode slime, the stoichiometry of electro-winning of Ag recovery, the determination of cathodic polarization curves of the Pt electrode in the thiocyanate solution containing complex ions of metal-thiocyanate, the selective separation of AgX from the leach solution and thiocyanate leach of AgX.
The experimental results are summarized as follows:
(1) The leaching rate of Ag component from the lead anode slime in a nitric acid solution is fast, and the leaching degree of Ag reaches about 100% for the retention time of 10.8 ks at 323 K. However, the dissolution of precious metals such as Au and Pt are not detected in the leach solution.
(2) The selective separation of AgX from the leach solution is easily, and the recovery of AgX from the leach solution reaches 100% for the retention time of 3.6 ks at ambient temperature.
(3) The electrochemical reaction for Ag deposit starts at about 0.05 volt and the reaction rate increases with an increase in the concentration of Ag(SCN)nn-1 ions in the solution. The reaction rate is controlled by the rate of Ag(SCN)nn-1 ions from the bulk solution to the solid interface, and the metallic Ag of more than 99.5% purity can be recovered from the thiocyanate electrolyte.
(4) The electrochemical consideration and other observations have proved the effectiveness of the above electro-winning process of Ag from the lead anode slime.
(Received 1990/3/8)
lead anode slime, thiocyanate, leaching, silver recovery, electro-winning, electrochemical kinetics, nitric acid
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