Mercury sequestration from synthetic and real gold processing wastewaters using Fe–Al bimetallic particles

Abstract

The Fe–Al bimetallic material was synthesized, and its capability to eliminate mercury (Hg) pollution from both simulated and real gold processing wastewaters containing other heavy metals was examined. A high Hg removal from a chloride solution was achieved at a wide range of initial pH (3–11) and Cl− concentrations (0.2–3 M). The best result (99.9% of Hg removal) was obtained at pH of 3, Cl− concentration of 1.7 M, and bimetal dosage of 10 g/L. The removal of Hg(II) from nitrate solution decreased, while the presence of other metal ions did not interfere. It can be attributed to higher redox potential and, therefore, an increased affinity of nitrate for electrons than Hg and the other metals studied. A redox reaction involving electrons transfer to Hg(II) from Al and Fe, and Hg adsorption by Fe oxy-hydroxides were identified as the main pathways for Hg removal. XPS examination detected oxidized Hg on the bimetal surface (HgCl2) in addition to elemental Hg, which is likely due to re-oxidation of Hg0 by active Cl atoms on the bimetal. In addition, leaching tests on Hg loaded bimetal in acidic and neutral pH conditions indicated a strong bond between Hg ions and the bimetal. The bimetal was also shown to be highly effective for repeated use (≥90% of Hg removal after 4 cycles). On gold processing wastewater containing stable Hg-cyanide complexes, the Hg removal of 82% was achieved after 120 min using 20 g/L of bimetal dosage at an initial pH of 8. This study has provided evidence for the potential application of the Fe–Al bimetal for removing heavy metals from complex wastewater under varying conditions.