| abstract |
This application relates to an improved method for oxidizing multimetallic sulphide ores and concentrates, using a combination chemical/biological leaching process and at least three different types of bacteria. The treatment process for multi-metallic ores such as arsenopyrite can be made to work rapidly and to as much as 98% sulphide oxidation, when the finely ground ore or concentrate is leached in agitated, air sparged tanks, with strains of three different bacteria, T. thiooxidans, T. ferrooxidans, and Leptospirillum ferrooxidans. L. ferrooxidans is quite similar to T. ferrooxidans and obtains its energy for growth from the oxidation of ferrous iron. The process of the invention may conveniently be a continuously operating process utilizing more than one stage. Most of the chemical/biological action using the bacterium T. thiooxidans preferably takes place in the first stage, while in the subsequent stages the activity of T. thiooxidans is decreased in favor of the activity of the bacteria T. ferrooxidans and L. ferrooxidans, which oxidize the by then more readily available sulphide portion of the pyrite minerals present in most arsenopyrite ores and concentrates. According to the invention, bacterial cultures of T. thiooxidans, T. ferrooxidans and L. ferrooxidans used are first adapted to high dissolved arsenic concentrations and low pH by subjecting the cultures in a solution containing dissolved arsenic, to successive incremental concentrations of arsenic while operating in a continuous mode. |