The crud formation during the long-term operation of the V(V) and Cr(VI) extraction

The roles of the emulsifiers in the crud formation during the long-term operation during the vanadium and chromium extraction were studied. The crud produced in the long-term operation of extraction was determined by GC–MS for organic phase and XPS for solid particles. The results indicate that the redox reaction occurs between Cr(VI) and organic compounds, and the reduction products of Cr(VI) induce more stable emulsion. Additionally, the roles of other types of solid particles and organic compounds confirmed before were carried out by thermodynamic calculation and experiments combined with discussion. Three-dimensional network structure of silica and precipitation of various cations act as the major incentives to stimulate the emulsion. Whereafter, crystallization of sodium sulfate and the reduction of Cr(VI) take place at the surface of emulsion droplet, and the organic compounds are prone to be adsorbed by these fine solids which subsequently consolidate the newly formed surface of droplet. The interactions between emulsion droplets were calculated according to the extended DLVO theory. The comprehensive stabilization mechanisms were also proposed, including the composite interfacial film mechanism, the steric hindrance mechanism and the double electric layer mechanism.