Study On The Formation Mechanism Of Emulsion In Impurity Extraction Process Of Cobalt And Nickel Sulfide Ore Bioleaching

Bioleaching technology has been widely used in leaching of copper in the primary copper sulfide ores since the1990s. Then, the method was gradually extended to leach the cobalt, nickel from cobalt and nickel sulfide ores. The concentration of valuable metal ions is generally low in bioleaching solution, and solvent extraction was usually adopted to separate the valuable metal ions from the bioleaching solution. However, interfacial emulsion was always produced in the solvent extraction process of industrial production, bringing severe problems such as a loss of extractant and prolonged split phase time and so on. The effect of bacteria and bacteria-mineral absorption on emulsion has not been reported at present. It is imminent to solve interfacial emulsion in the bioleaching solution during the extraction process, which would improve the extraction efficiency and reduce the loss of organic phase.This study examined the major factors of causing the interfacial emulsion such as solid particles, colloid and metal ions on the basic characteristics of bioleaching solution. IR, Zeta potential and SEM were used as characterization methods. Extended DLVO theory and Ac impedance test were introduced to study the effect of bacteria, bacteria-solid absorption and bacteria coexist with impurity ions on the emulsion stability was studied.There are a large number of bacteria in the bioleaching solution, which influences aqueous phase properties and emulsion of oil-water system. The density and viscosity of aqueous phase increased and surface tension of aqueous phase decreased with bacteria density increasing. And the oil content in water was influenced by solution pH, bacteria density and electrolyte concentration. It was found that the oil content in water increased obviously at high pH, high bacteria density and low electrolyte concentration. The oil content in water increased from0.07%(v/v) to0.14%(v/v) with pH increasing, duo to the formation of hydrogen bonds on the bacteria surface and the adsorption potential. And the oil content in water was increased from0.064%(v/v) to0.078%(v/v) as bacteria density increased from2.4x107cells/mL to7.2x107cells/mL corresponds to the amount of hydrophobic functional groups on the bacteria surface. Ion-permeable model was introduced to simulate the electrical double layer structure of bacteria surface. It was found that the adsorption potential of bacteria surface increased with pH increasing, increasing the adsorption of charged group on bacteria. The growth and surface properties of bacteria were affected by environment in the solution. The adsorption behavior of bacteria to solid particles (mineral, jarosite and silica) was investigated under different solution pH, bacteria density and electrolyte concentration. It was found that the absorption rate of bacteria on mineral and jarosite surface was high at pH2-3. While the absorption of bacteria onto silica surface was low and did not change in the pH range. The adsorption quantity of bacteria at solid surface tended towards saturation with bacteria density increasing. The adsorption rate of bacteria onto mineral increased with electrolyte solution concentration increasing, but the adsorption rate of bacteria onto jarosite and silica did not change much. The extended DLVO theory was used to analyze the interaction energy between bacteria and solid particles. It indicated that the influence of acid-base interaction is significantly greater than the electrostatic interaction and Van Der Waals interaction. Bacteria can easily adsorb on the surface of mineral and jarosite because of the strong acid-base attraction interactions between them. Adhesion of bacteria onto silica particles is difficult due to the acid-base repulsion interaction between bacteria and silica. In addition, Ac impedance tests show that solid electric double layer capacitor was decreased by adsorption of bacteria, verifying the law of absorption of bacteria on solid surface obtained from experiments.Based on the study on the rules of bacteria-solid adsorption, the effect of bacteria-solid absorption on the emulsion stability was further studied. After bacteria absorbed to the solid particle surface, the coalescence rate of emulsion droplet is accelerated in the extraction process and the stability of interfacial layer was enhanced. Extended DLVO theory can be used to describe the interaction energy between two emulsion droplets. It was found that the coalescence barrier reduced after bacteria adsorbed and the repulsive force between droplets transformed into the attractive force, which speeded up the droplet coalescence. Ac impedance analysis showed that the adsorption of organic phase on the surface of mineral and jarosite increased obviously after bacteria-solid absorption. But the presence or not of bacteria had quite small impact on the absorption of organic on the silica surface. The coalescence rate of emulsion droplet is also significantly accelerated in the extraction process when bacteria and colloidal silica coexist. This is mainly due to the hydrogen bonding between the functional groups located on the surface of bacteria and the silanol groups (Si-O-H) on the colloidal silica surface. It would reduce the amount of siloxane and destroy the long chain or mesh structure of colloidal silica, accelerating the emulsion droplet coalescence.In addition, impurity metal ions in bioleaching solution are also an important factor of leading interfacial emulsion formation. There is generally a lot of Ca2+, Mg2+in the leaching solution. When bacteria coexist with Ca2+, the existence of bacteria increased the adsorption of CaSO4crystals on the interface, making the product rate of emulsion increase.The emulsification property of nickel sulfide ore bioleaching in baishan was investigated after extraction process. It was found that bacteria, jarosite and silica gradually accumulated in the interface layer. In addition, the results show that the structure and properties of organic phase changed by formation of complexes due to P204combined with Fe3+in the extraction process. The complex reduced the interface tension and increased the difficulty of split phase. The presence of bacteria in the extraction process would enhance the emulsion stability after the bacteria absorption, and result in an increase of organic phase in interfacial emulsion layer.