Toward an efficient multi-step separation protocol to recover metallic components from waste leachates

Abstract

This work presents a study of the separation and recovery of metal elements, through a multi-step protocol based on solvent extraction, stripping and chemical precipitation processes. The waste leachate was produced during the treatment of the mixed solid waste from the decommissioning of a coal-fired power plant. The organophosphorus acid, di-(2-ethylhexyl) phosphoric acid (DEHPA) was investigated as organic extracting agent during the solvent extraction (Step 1). A factorial design with three levels for the organic phase/aqueous phase ratio (O/W), DEHPA concentration and contact time were carried out and a prediction model obtained using a neural-fuzzy approach. Optimized extraction values for Ti (93.4 %), (V) 94.6 % and (Zn) 89.8 % were obtained using 60min of contact time, a DEHPA concentration of 0.5M and O/W ratio of 4. Stripping tests were performed using HCl, H2SO4, NaOH and KOH as stripping agents. The stripping step (step 2) showed optimum results (82 % of Zn and 31 % of V) using 1M H2SO4 solution as stripping agent. A selective precipitation step (step 3) allowed the final separation of metals in aqueous solutions produced in Step 1 and 2. The results showed that an effective separation of Mn and Ni could be carried out at pH 9, while the best separation results for the solution obtained during the stripping step, which contains V and Ti, was obtained at pH 12.