Batch reactor studies of the leaching of a pyrite/chalcopyrite concentrate using thermophilic bacteria

摘要

The bio-oxidation of a pyrite/chalcopyrite concentrate under thermophilic conditions was studied in a 10 L stirred tank reactor and a 10 L airlift reactor. Two different cultures of mixed thermophiles (containing Sulfolobus, Acidianus and Metallosphaera) were studied, one producing elemental sulphur the other sulphates. Tests were conducted at 5% and 10% pulp density, 70℃ and initial solution pH of 2.0. The pH gradually decreased during the runs with the sulphate producing culture, but was maintained around pH 2.0 through the controlled addition of sulphuric acid in the runs employing sulphur-producing bacteria. Good Cu recoveries were achieved using either culture in either reactor, but bacterial growth was clearly retarded in some of the stirred tank reactor runs. The interactions between chalcopyrite leaching, bacterial counts and type, Fe in solution and solution potential are closely interlinked and complex. Trends observed in the experiments indicate that rapid chalcopyrite leaching coincides with exponential bacterial growth, but is independent of solution potential. Fe/Cu ratios indicate that continuous surface build-up of iron-sulphur compounds is likely to occur. These are associated with a premature cessation of Cu leaching. Sulphur assays indicate that chalcopyrite S react nearly completely to either elemental S or sulphate, depending on the type of bacteria employed. Sulphate producers previously grown on a pyrite concentrate, however, also leach significant quantities of pyrite, whereas those grown on chalcopyrite only leach this mineral.