A comparison of microbial leaching and chemical leaching of arsenic and heavy metals from mine tailings

The aim of this research was to compare the efficiencies of microbial leaching and chemical leaching of As and heavy metals from mine tailings. A mixed culture of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans was used as a microbial lixiviant agent for microbial leaching, while sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) were used as the leachants for chemical leaching. The results showed that except for Zn, the microbial leaching achieved higher removal efficiencies than the chemical leaching with As, Cu, Mn, and Fe after 300 h of incubation. It was observed that 95% Mn, 38% Cu, 67% Zn, 41% As, and 47% Fe were removed from the mine tailings by the microbial leaching process. In chemical leaching, the addition of H2O2 enhanced the As removal efficiency significantly. The leaching with a solution of 2% H2SO4 yielded the higher removal efficiencies of Mn, Zn, As, and Fe in comparison to that with 1% H2SO4. A sequential extraction scheme was applied to determine the chemical forms of As and heavy metals in the mine tailings before and after the leaching processes. The results indicated that the chemical forms of heavy metals in the mine tailings affect significantly their extraction efficiencies.