49] Application of immobilized Thiobacillus ferrooxidans for large-scale treatment of acid mine drainage

Abstract

This chapter describes a large-scale treatment of acid mine drainage including a bacterial oxidation system, as an example of an effective and practical application of the bacteria. Thiobacillus ferrooxidans, found naturally in acid mine drainage, increases the oxidation of sulfide minerals and supplies ferrous ion in the acid drainage as the microbial catalyst. Utilizing these characteristics of Thiobacillus ferrooxidans, bacterial oxidation is being adopted in the treatment of acid mine drainage at some mines in Japan. To neutralize acid mine drainage and at the same time precipitate heavy metals, lime neutralization has been used for many years, employing calcium hydroxide in many cases. In comparison, neutralization by calcium carbonate has several advantages—such as lower cost, less volume, and faster settling of the resultant sludge. However, calcium carbonate simultaneously generates carbonic acid in the course of neutralization, which limits the maximum pH of the drainage to about 6.5. At this pH, the ferrous salt remains in solution and does not precipitate. If the ferrous salt can be oxidized to a ferric salt prior to neutralization, calcium carbonate is made available to neutralize acid mine drainage.