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

摘要

Leaching tests were performed in citrate solution with Fe~(3+) 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 Fe~(3+) was selected based on the previous study, which reported that the oxidants such as Fe~(3+) 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 Fe~(3+) concentration, temperature, but decreasing pulp density; e.g. the efficiencies of Zn, Pb, Cu were almost 100% in the 1M citric solution with 3 M Fe~(3+) 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 FeCl_3 solution to 656.1 mV in citrate solution with FeCl_3, 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 Fe~(3+).