A new heterotrophic strain, named Providencia sp. JAT-1, was isolated and used in bioleaching of low-grade complex copper ore. The strain uses sodium citrate as a carbon source and urea as a nitrogen source to produce ammonia. The optimal growth condition of the strain is 30 C, initial pH 8, sodium citrate 10 g/L and urea 20 g/L, under which the cell density and ammonia concentration in the medium reached a maximum of 4.83 × 108 cells/mL and 14 g/L, respectively. Ammonia produced by the strain is used as the main lixiviant in bioleaching. Bioleaching results revealed that higher strain growth led to a higher copper recovery, while higher pulp density will cause a greater inhibitory effect on strain growth and ammonia production. The copper extraction reached the highest value of 54.5% at the pulp density of 1%. Malachite, chrysocolla and chalcocite are easy to leach out in this bioleaching system while chalcopyrite is difficult. Results of comparative leaching experiments show that bioleaching using JAT-1 is superior to ammonia leaching at the same condition. The metabolites produced by the strain other than ammonia are also involved in bioleaching.

Mineralogical and geochemical analyses of the Dopolan karstic bauxite ore were performed to identify the characteristics of four bauxite horizons, which comprise from top to bottom, bauxitic kaolinite, diaspore-rich bauxite, clay-rich bauxite, and pyrite-rich bauxite. Diaspore, kaolinite, and pyrite are the main minerals; böhmite, muscovite, rutile, and anatase are the accessory minerals. The main minerals of the Dopolan bauxite deposit indicate slightly acidic to alkaline reducing conditions during bauxitization. Immobile elements (Nb, Ta, Zr, Hf, and rare earth elements) are enriched in the diaspore-rich horizon, which also has the highest alumina content, whereas redox sensitive elements (e.g., Cr, Cu, Ni, Pb, Zn, Ag, U, and V) are enriched in the lowest horizon of pyrite-rich bauxite. The presence of a high content of organic matter was identified in different horizons of bauxitic ore from wet chemistry. The presence of organic matter favored Fe bioleaching, which resulted in Al enrichment and the formation of diaspore-rich bauxite. The leached Fe²⁺ reacted with the hydrogen sulfur that was produced due to bacterial metabolism, resulting in the formation of the pyrite-rich horizon towards the bottom of the Dopolan bauxite horizons. Biogeochemical activity in the Dopolan bauxitic ore was deduced from the reducing environment of bauxitization, and the deposition of framboidal and cubic or cubic/octahedral pyrite crystals, with large negative values of δ³⁴S of pyrite (−10‰ to −34‰) and preserved fossil cells of microorganisms.