Bioleaching of highly concentrated arsenic mine tailings by Acidithiobacillus ferrooxidans

• A. ferrooxidans is first used for bioleaching of arsenic-rich mine tailings.
• Arsenic bioleaching is not sensitive to reaction temperature investigated.
• Arsenic bioleaching is largely affected by initial pH and pulp density investigated.
• Jarosite and cell activity are critical factors controlling arsenic bioleaching.

In this study, arsenic (As) leaching was conducted from highly concentrated As mine tailings using the iron-oxidizing bacteria (Acidithiobacillus ferrooxidans). The effects of temperature, initial pH, and pulp density on the As leaching were systematically investigated. At all reaction temperatures, the As leaching amount exceeded 85%. However, the As leaching was significantly affected by the initial pH and pulp density. In particular, the As leaching amount of 85% at initial pH ⩽ 2.0 decreased to as low as 40% at initial pH 2.2 due to the effects of the jarosite that was formed by the precipitation of the leached iron. The As leaching efficiency decreased from about 80% at the pulp density ⩽2.0% to as low as about 25% at pulp density 4.0% due to the low bacterial growth rate. Therefore, in the bioleaching process for highly concentrated As mine tailings, the pH range should be controlled to prevent the formation of jarosite, and it is important to maintain a high bacterial cell concentration at high-concentration pulp density.