Removal of Heavy Metals from Tailing in Citrate Solution with Ferric Chloride

Abstract

Leaching tests were performed in citrate solution with Fe³⁺ to investigate the leaching behaviors of As, Zn, Pb, and Cu from tailings, which has been known as soil contaminant sources near abandoned mines. The combination of citrate and Fe³⁺ was selected based on the previous study, which reported that the oxidants such as Fe³⁺ was required to remove heavy metals from stable forms like sulfides because citrate could leach metals only in carbonate and oxide forms. The leaching efficiencies of heavy metals except As increased with increasing agitation speed, initial Fe³⁺ concentration, temperature, but decreasing pulp density; e.g. the efficiencies of Zn, Pb, Cu were almost 100% in the 1 M citric solution with 3 M Fe³⁺ at 400 rpm and 50°C with 0.25% pulp density within 3 hr, but 7.4% for As. The initial oxidation-reduction potential (vs Ag/AgCl) was reduced from 713.5 mV in FeCl₃ solution to 656.1 mV in citrate solution with FeCl₃, which would inhibit the dissolution of As because As mineral such as arsenopyrite has high open circuit potential. These results indicate that As could be selectively left in the leach residue using citrate solution with Fe³⁺.

Fig. 4 The effects of addition of citrate on the leaching efficiency of metals at 50°C and 400 rpm with 3 h leaching time, 1 M Fe³⁺ and 0.25% pulp density.