Highly selective ion precipitation flotation for ternary Co–Zn–Mn separation: Stepwise chelation capture of Co and Zn from simulated zinc hydrometallurgy wastewater

Abstract

Ion precipitation flotation technology was demonstrated to be an efficient method for the separation of valuable metals from low-concentration solution. However, the selective separation of three metals from mixing solution is a great challenge, and highly selective reagents are the key to polymetallic separation. In this work, stepwise separation of Co and Zn from the simulated zinc hydrometallurgy wastewater containing ternary Co–Zn–Mn metals by ion precipitation flotation process was proposed. It's demonstrated that organic reagents of 1-nitroso-2-naphthol (NN) and sodium dimethyldithiocarbamate (SDDC) had excellent selectivity for the capture of Co and Zn to form respective precipitate from wastewaters via the chelation reactions. After precipitation, dodecylpyridinium chloride (DPC) and tetradecyltrimethylammonium bromide (TTAB) were chosen as surfactants for the separation of Co and Zn sediments from the solution via the flotation process. The effects of solution pH, molar ratio, reaction temperature, and reaction time on the selective precipitation efficiencies of Co and Zn as well as the effects of surfactant dosage and flotation gas velocity on the flotation separation efficiencies were systematically investigated. It's demonstrated that the comprehensive recovery rates of Co, Mn, and Zn reach 98%, 90%, and 99%, respectively. After separation, oxidation calcination of the foam products was conducted to prepare high-purity Co3O4 and ZnO nanoparticles in which the organic matters were burnt out with gas emissions. The stepwise chelation capture mechanisms of Co and Zn by highly selective precipitation reagents were minutely discussed. It's demonstrated that the proposed selective stepwise precipitation and flotation method is suitable for recovery of critical metal ions from low-concentration polymetallic wastewaters.