Carbide slag generated from industrial sites can contain many organic and inorganic impurities such as toxic metals and organic compounds, which should be treated before disposal. Bioleaching using Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and their combination was investigated. The effects of important factors including pH and pulp density were assessed. It was found that under optimal conditions 100% Zn, 41.9% Ba, 98.5% Ni and 97.8% Li were extracted with the mixed culture of Acidithiobacillus at pH 1 with pulp density 0.5% (w/v) after 14 days. To ensure risk reduction of the carbide waste for the soil environment, ecological risk criteria and plant seed germination potentials were evaluated. The results showed that bioleaching significantly reduced slag toxicity, and plant seed germination from leached waste was observed.
