Abstract: 【Objective】Effects of Aspergillus niger on weathering of potassium-bearing minerals and leaching rates of potassium and silicon are closely related to the ability of producing acids and extracellular metabolites (mainly including polysacchrides and proteins) by it. Now little is known about the relationships between potassium or silicon leaching rate and mineral crystal structure, and about the relationships between mineral crystal structure and growth metabolism of fungi. A strain of A. niger was used to leach potassium and silicon, respectively, from orthoclase and muscovite. 【Method】 A strain of A. niger was cultivated in solid and liquid Czapek’s media containing bauxite, orthoclase and muscovite powders and free-mineral powder, respectively, in order to survey the growing characteristics of A. niger in different mineral environments. Bioleaching experiments of potassium-bearing minerals were carried out in shake flasks to investigate the effects of mineral weathering and extraction of potassium and silicon by the strain. By measuring the contents of polysaccharides, proteins, organic acids, K2O, SiO2 , and pH values in culture media, and by observing the change of mineral surfaces before and after bioleaching with X-ray diffraction and scanning electron microscope, the difference of A. niger’s growth and metabolism and ability of mineral bioleaching was analyzed, when A. niger was cultured in different media containing orthoclase and muscovite respectively. 【Result】 Potassium-bearing minerals with different crystal structures promoted A. niger’s growth and metabolism to different extents. The strain of A. niger reproduced and grew faster in media containing potassium-bearing minerals than in media containing free mineral and a small amount of potassium-bearing bauxite. A. niger cultivated in potassium-bearing solid media in growth process exhibited a more obvious chemotaxis of minerals than in free mineral and bauxite solid media, and more obvious in the muscovite medium than in the orthoclase medium. Meanwhile, A. niger’s mycelium-mineral aggregation was formed much more obviously in liquid media containing potassium-bearing minerals, especially containing muscovite powder, than in media containing free mineral and a small amount of potassium bearing bauxite. A. niger produced 1.45, 1.97, and 2.45 g•L-1 of mixed organic acids, and 5.11, 9.96, and 12.25 g•L-1 of polysaccharides, and 6.25, 13.78, and 16.97 g•L-1 of proteins, respectively, after culturing for 10 days in potassium-free Czapek’s medium, orthoclase medium and muscovite medium. The contents of K2O and SiO2 released from muscovite were 79.10 and 57.78 mg•L-1 higher than from orthoclase by A. niger. The SEM images and XRD patterns of muscovite and orthoclase powders before and after bioleaching showed that the surface of muscovite was etched much more obviously and formed much more amount of amorphous substance or imperfect crystal particles than that of orthoclase. The characteristic peaks reflecting muscovite were obviously weakened and some of them were faded away, but the characteristic peaks reflecting orthoclase were slightly enhanced in XRD patterns of muscovite containing a small amount of orthoclase or orthoclase containing a small amount of muscovite. 【Conclusion】 The difference of crystal structures of potassium-bearing minerals is one of important factors resulting in the difference of mycelium-mineral aggregation, metabolites and acidic microenvironment formed in the interaction between fungi and mineral, when A. niger is cultured in media containing different potassium-bearing minerals. And then, maybe, the difference is one of the key factors interfering with A. niger’s mineral weathering ability and extraction of potassium or silicon. Potassium-bearing minerals can excite and promote A. niger’s growth and metabolism in media containing free available potassium. Muscovite can promote A. niger to produce much more amount of organic acids, polysaccharides and proteins in comparison with orthoclase. A. niger can selectively decompose different minerals according to the stability of the mineral crystal structure in the bioleaching system containing mixed minerals. A. niger can give preference to weather muscovite, when orthoclase with framework structure and muscovite with stratified structure coexist in a same leaching system.

Key words: potassium mineral , crystal structure , Aspergillus niger , metabolite , bioleaching , potassium , silicon