Mechanism Research And Leaching Technology Of Complicated Cu-Co Sulfide Ore Bioleaching

The application of the important strategic elemental cobalt is widely extensive. Since cobalt mineral resources are lean and few rich ore, the traditional technologies of extracting metal cobalt from ore are poor economic and environmental pollution. The bioleaching technology gets increasingly attention in recent years, due to inherent advantages such as low investment cost and energy consumption and the attendant benefits to the environment. For example, the bioleaching technology was used to copper leaching from copper sulfide minerals and got positive evaluation. However, to our best knowledge, most of the previous studies have focused on the copper sulfide minerals and the bioleaching of cobalt sulfide mineral has hardly been investigated. So the further development of research on cobalt ore bioleaching is desirable. In this paper, the bioleaching of Zambian cobalt concentrate, leaching mechanism and improvement of leaching are investigated.The cobalt concentrate used in this study was provided by the Luanshya mine in Zambia, and the mass fraction of cobalt and copper content are 1.63% and 1.05%, respectively. Mineralogy analysis indicated that the dominant sulfide minerals are carrollite, chalcopyrite, bornite, chalcocite, covellite and pyrite. Most of carrollite, chalcopyrite and pyrite are simplex, while paucity samples are intergrowth with other sulfide minerals or gangue minerals. Most of bornite, chalcocite and covellite, in contrast, are intergrowth with other sulfide minerals or gangue minerals. About 96.24% cobalt and 83.38% iron are occurrence in ore particles, which sizes are less than 150 μm, while the distribution of elemental copper is average.The leaching mechanism, dissolution process and reaction pathway for carrollite dissolution during bioleaching are investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The results indicate that both indirect and contact mechanisms caused the leaching process. Moreover, the dissolution of carrollite was significantly promoted in the case of bacteria and mineral contacted. The oxidation state of the sulfur moiety in carrollite was transformed as follows:S2-â†'>S0â†'S4+â†'S6+, and elemental sulfur, sulfate and sulfite were produced on the surface of mineral during bioleaching, for which indicates that the dissolution of carrollite through the polysulfide pathway.SEM images demonstrate that the carrollite surface is selectively corroded in the presence of bacteria, and some etch pits of different size are observed at various sites. As more of compounds adhere to the mineral surface, they can form an oxidation product layer on the surface of carrollite. The chemical composition and structure variation law of oxidation product layer are:Initially, the layer composed by jarosite and sulfite is loose and pockety, and the layer thickness is less than 2 μm. In the middle stage, the layer is composed of elemental sulfur, jarosite and sulfite, and the structure of the layer becomes compact. The surface of carrollite was covered by the layer. Lastly, the layer is mainly composed of jarosite, and the layer thickness can reach over 6 μm.The comparison of the bioleaching and chemical leaching cobalt concentrate was studied. Compared with chemical leaching, the leaching efficiencies of cobalt and copper were increased by 63.26% and 27.62%, respectively. The optimum technology parameters are that the domesticated bacteria is employed, and the pH value of pulp is adjusted between 1.1 to 1.7, and constant temperature is at 45℃, and the grinding time is 30 min (the particle size is above 70% of 38 μm). In the amplified experiment with 15% pulp density, leaching efficiencies of cobalt and copper reach 86.75% and 70.35%.In order to improve the dissolution of oxidation products layer, the surfactant are employed. Results show that when 0.1 g·L-1 Tween-20 (or Tween-80) or 0.25 g·L-1 RB-1181 is added, the cobalt leaching efficiency can improve by more than 34% and that of copper can increase by more than 15% after leaching for 15 days. In addition, when an optimum concentration of 1.0 g·L-1 activated carbon is put in, the leaching ratio of cobalt can be enhanced from 72.92% to 94.98%, and that of copper increases by 15.43% after leaching for 18 days. Such an improvement can be attributed to the galvanic interaction between activated and carrollite. When using a combination catalyst of activated carbon and surfactant, it is interesting to note that the leaching efficiencies of cobalt and copper are enhanced by more than 20.50% and 13.62%, respectively. Moreover, it should be emphasized that the leaching time reduced by approximately one-third of that without the addition of activated carbon and/or surfactant. By the addition of catalysts, the leaching efficiencies of cobalt and copper increase significantly, and the production costs decrease due to the reduction of leaching time, indicating that a new technology of bioleaching cobalt concentrate is formed.