Pilot experiments to reduce environmental pollution caused by acid rock drainage

Abstract

Bacterial leaching experiments were performed with sulfidic mine waste from dumps located adjacent to Ilba Mine, a Romanian base metal mining operation, to test techniques for reduction of environmental pollution by acid rock drainage. Two countermeasures had an effect: o 1. Inhibition of bacterial leaching by incorporating three alkaline layers in the waste heap 2. Purification of acid rock drainage by removal of metal ions through the use of a chemical barrier (buffer) at the base of the waste heap. Experiments proceeded “in situ” in the dump in a four-chamber percolator with 65 m 3 volume per chamber. Parameters of the chemical and microbial processes have been monitored for 630 days. The application of the first measure caused an increase of the pH. As a consequence, bacterial activity was reduced, the ratio between the several Thiobacillus species was modified, and the metal content in the effluent was reduced, because solubilization became inhibited and metallic ions precipitated in the alkaline layers. The result of the second method was a stopped percolation due to precipitations in the chemical barrier.