Process and Kinetics of Extracting Cobalt from Complex High-Silicon White Alloy by Sulfuric Acid Oxidation Leaching

Abstract

A sulfuric acid system was used to recover Co from cobalt white alloy, and the leached cobalt was electrochemically dissolved.i This is a key step to separate the iron-silicon alloy phase from valuable metals when leaching cobalt white alloys with high silicon and iron contents. As an additive, sodium hypochlorite (NaClO) acts as an oxidant to break cobalt encapsulation and enhances leaching. It generates chloride ions, which further enhance Co leaching based on their corrosive ability. The results showed that the maximum leaching ratio of Co from the waste cobalt white alloy was 97.76%. Kinetic analysis showed that the apparent activation energy of Co leaching was 34.58 kJ/mol, and the surface chemical reaction was a controlling step for this process. The kinetic equation for the leaching of Co can be expressed as $$1 - \left( {1 - \alpha } \right)^{\frac{1}{3}} = 0.065t \times \left( {r_{0}^{ - 1} } \right) \times \left[ {{\text{H}}_{2} {\text{SO}}_{4} } \right]^{2.44} \times \exp \left( {\frac{ - 34580}{{8.314T}}} \right)$$ .