Theoretical Basis for the Separation of W and Mo with Manganese Dioxide: A Speciation-Based Approach

Abstract

The separation of W and Mo has been a technical problem in extractive metallurgy. It is known that manganese nodule (mainly manganese oxides) can adsorb W efficiently in the thalassochemistry; if there exists a difference between the adsorption behaviors of W and Mo onto manganese dioxide, then W/Mo separation may be achieved using manganese dioxide. In this paper, the adsorption characteristics of W and Mo onto ‘‘nascent’’ manganese dioxide were studied under different pH, ionic strength, and different concentration. The results showed that the adsorption of W onto manganese dioxide was higher than Mo both in single-sorbate solution and mixed solution. Besides, ionic strength had no impact on the W and Mo adsorption, while pH significantly affected the W and Mo adsorption. The adsorption of W followed the Freundlich isotherm, indicating that the surface of manganese dioxide was heterogeneous. Speciation-based model was developed to describe the W and Mo adsorption onto manganese dioxide. This model can be well applicable for describing the adsorption behavior of W and Mo in a wide pH range of 2 to 12 and a wide surface loading range. Besides, the optimum pH range of W/Mo separation in mixed solution predicted by this model was 6 to 6.5, which agrees well with the experimental results, and the separation factor achieved the maximum value 7 at this optimum pH range. Such model offers an important insight into the adsorption mechanism of W and Mo onto manganese dioxide, and lays a theoretical foundation for the process of separating W and Mo with manganese dioxide.