Study On Leaching Of Copper From Highly Alkaline Copper Oxide Tailings By Aspergillus Niger

There are large quantities of available metals embodied in the tailings. Extraction of valuable metals from the tailings is of great significance for reducing the environmental impact of heavy metals and improving the secondary resources utilization. This study aims to develop a method for bioleaching of copper tailings. Taking the highly alkaline copper oxide tailings from a mine located in Hunan as research object, the copper tailings leaching behavior was investigated under two leaching systems, which contain Aspergillus niger fermentation broth indirect leaching and A.niger direct leaching, and the achievements are summarized as follows:Firstly, the A.niger fermentation broth leaching experiments were carried out to investigate the effects of temperature, fermentation time, inoculum size and medium components on the pellet morphologies of A.niger, and the leaching of copper from its mill tailings was conducted using the fermentation broths of A.niger with different pellet morphologies. The results showed that copper extraction gradually increased with reduction in the pellets diameter of A.niger. And a large number of compact smooth pellets were obtained under the optimum fermentation conditions of 30℃, 0.8% inoculum size(OD600=0.1), 30% potato-sucrose contents, 65 h fermentation time. After 3 d of leaching, the copper extraction reached 83.25% with the fermentation broths aforementioned at 30℃, 180 r·min-1.Secondly, direct bioleaching was investigated on copper tailings. The effects of culture time, medium components, inoculum size, temperature, shaker speed and pulp density of copper tailings were studied on the pellet morphologies of A.niger and copper extraction. The results showed that the formation of A.niger-copper tailings pellet could reduce the viscosity of the leaching solution and improve the copper extraction. A substantial number of compact smooth pellets with little diameter were obtained under the optimum culture conditions of 7 d cultured time, 20 g·L-1 sucrose content, 0.02%(OD600=1.0)inoculum size, 25℃, 180 r·min-1 and 5% pulp density. At the same time, the leaching efficiency of copper reached a maximum of 89.45%.Finally, the structure and formation process of A.niger-copper tailings pellet were studied. The experimental results showed that when A.niger and copper tailings were co-cultivated the formatin of A.niger-copper tailings pellet involved following three stages: germination of A.niger spores to form the hyphae; under the shear stress, extension of hyphae around the nucleus to enwrap the copper tailings forming the A.niger-copper tailings pellet; autolysis of the pellet owing to changes in nutrient components of the culture medium. The sturcture of A.niger-copper tailings pellet had three layers: the surface layer being hyphae, the middle layer of copper tailings, and inside layer being the core-shell structure.