Fowler and Crundwell by oxidation or reduction of dissolved iron ions to the solution to maintain the oxidation-reduction potential of the same, and further Bacterial Effect of sphalerite microbial leaching. Through research, they believe that the dissolution of sphalerite is an indirect mechanism of action by the oxidation of Fe ³⁺ in solution, and direct leaching by bacterial contact is not possible. During the leaching process, the bacteria act to oxidize the ferrous ions in the solution, thereby regenerating the ferric oxidant. Through research, Fowler and Crundwell also pointed out that in the process of microbial leaching, sulfur-oxidizing bacteria can oxidize the sulfur product layer formed during the leaching process, thereby increasing the leaching rate of zinc. Schippers and Sand found that the indirect mechanism of microbial leaching of metal sulphide minerals in two ways: thiosulfates and polysulfides mechanism Mechanism. Through research, they pointed out that sphalerite can be dissolved by iron (III) ions and hydrogen ions, and polysulfide and metasole sulfur are formed in the process.

Recently, Rodriguez et al. proposed a combined mechanism of sphalerite bioleaching by studying the bioleaching of sphalerite at different temperatures, that is, the contact leaching of bacteria and the indirect oxidative leaching of Fe ^{3 +} exist simultaneously.

1 in the external control voltage of the zinc sulfide ore bioleaching

In the process of microbial leaching, the application of a suitable external control potential can significantly increase the leaching rate of sulphide ore and the yield of bacteria, and achieve selective leaching in the presence of polymetallic sulphide ore. Natarajan found in providing -0.5V (vs.SHE) external control potential from brass ore, sphalerite, pyrite ore mixing selectively sphalerite bioleaching of zinc.

2    Effect of galvanic effect on bioleaching of zinc sulfide ore

Jyothi, who studied the effects of galvanic effect of pyrite, chalcopyrite, galena and sphalerite bioleaching process. It has been found that when sphalerite is contacted with three other sulfide minerals, it will dissolve preferentially as an anode; in different combinations, pyrite will always be insoluble as a cathode; when chalcopyrite is in contact with sphalerite or galena It will become a cathode that will be protected, but will preferentially dissolve as an anode when it comes into contact with pyrite.

At the same time, Jyothi et al. also measured the electrostatic potential of pyrite, chalcopyrite, sphalerite and galena in 0.9K medium. It can be seen that when the bacteria are present, the electrostatic potential of the mineral measured under the same conditions rises, thereby strengthening the galvanic effect in the leaching process of the polymetallic sulfide ore.

Da Silva et al. studied the electrochemical passivation during the bioleaching of sphalerite in the presence of galena, indicating that galena was selectively oxidized to lead sulfate and promoted zinc leaching during the entire leaching process. Dissolution of the mine. This selective dissolution is caused by the action of the galvanic cells between the two minerals. In this process, the galena is dissolved and the sphalerite is passivated. This result is consistent with the electrostatic potential of the mineral measured in the solution (gallium 325 mV (vs. SHE); sphalerite 375 mV) (vs.SHE)).

3    Electrochemical Mechanism of Biological Leaching of Zinc Sulfide Ore

The zinc sulphide ore bioleaching has the following processes: bacterial oxidation of Fe ^{2 +} , Fe ^{3 +} chemical leaching of zinc sulfide ore, reaction of reduced sulfur and elemental S ⁰ bacterial oxidation process, bacterial respiratory oxygenation of electrons and bacteria to minerals Direct decomposition process, etc., Choi et al. used ZnS-carbon paste electrode as working electrode, and used cyclic voltammetry, chronoamperometry and chronopotentiometry to study the possible intermediates in the bioleaching process of sphalerite flotation concentrate under sulfuric acid system. Reaction process and its kinetic behavior. Cyclic voltammetry results indicate that the overall reaction of sphalerite biooxidation is not a one-step process involving a series of intermediate electrochemical reactions. Test results of chronoamperometry and chronopotentiometry indicate that the dissolution rate of sphalerite is controlled by the diffusion process.

Shi Shaoyuan et al. studied the electrochemical behavior of iron sphalerite using iron sphalerite-carbon paste electrode. Cyclic voltammetry results show that the cyclic voltammetry curves exhibit different characteristics under different leaching conditions, which means that the leaching of iron sphalerite is achieved by different reactions. When the redox potential value of the leaching system is high, the reducing substance which is difficult to be formed or generated by the reducing substance is rapidly oxidized by Fe ^{3 +} . Trivalent iron ions are very important in the dissolution process of iron sphalerite, especially in the early stage of leaching, when the concentration of bacteria is low. Studies have also shown that the adsorbed bacteria may promote the oxidation reaction of iron sphalerite during bioleaching. The etch pit formed during leaching is different, but similar to the shape and size of the adsorbed bacteria. The AC impedance spectroscopy (EIS) test results of iron sphalerite-carbon paste electrode under bacteria and aseptic conditions show that the shape of the AC impedance spectrum of the iron sphalerite-carbon paste electrode in different electrolytes is similar, both from the high frequency region. The two semicircles are composed of a straight line in the low frequency region. This indicates that the dissolution process of iron sphalerite in different electrolytes has the same kinetic control step, that is, the dissolution process of iron sphalerite is controlled by the mass transfer process of the reactants to the mineral surface or the reaction product leaving the mineral surface.

4    Effect of Leaching Conditions on Bioleaching of Zinc Sulfide Ore

In the zinc sulphide microbial leaching process, in addition to the characteristics of the leaching microbial strains, minerals and the addition of metal ions and surfactants will have a certain impact on the leaching effect, leaching conditions such as temperature, pH, available nutrients The concentration of pulp, the supply of O ₂ and CO ₂ , the amount of bacteria inoculated and the way of leaching also affect the bioleaching of minerals.

Under the conditions of aeration or different pulp concentration, Shi Shaoyuan et al. compared the bioleaching effect of iron sphalerite flotation concentrate in shake flask test and magnetic stirring reactor. The results showed that the amount and biological activity of Thiobacillus ferrooxidans in the solution were improved under aeration conditions, and the leaching effect of iron sphalerite flotation concentrate in different reactors was larger after inoculation with Thiobacillus ferrooxidans. The difference. Konishi et al

Human studies have found that when the initial concentration of Acidianus brierleyi bacteria in the leaching system increases from 1.0 × 10 ¹² per cubic meter to 1.1 × 10 ¹³ per cubic meter, the free bacterial concentration in the liquid phase and the zinc leaching rate in sphalerite The increase is, and when the inoculum is further increased to 5 × 10 ¹³ per cubic meter, the zinc leaching rate is not much increased compared to 1.l × 10 ¹³ per cubic meter. Similarly, Zhang Guangji et al. also found that with the addition of Fe ^{2 +} , the bioleaching rate of iron sphalerite increased with the initial inoculum of bacteria, but when the inoculum was too high, it increased the iron sphalerite. The effect of the leaching speed is diminished.

Each type of bacteria has an optimum pH for its growth, and the range of pH values ​​suitable for the survival of different bacteria varies. The pH value in the solution can not only affect the growth and reproduction rate and oxidation activity of the bacteria, but also have an important influence on the formation of ferric iron precipitates (especially jarosite). Therefore, pH is a very important parameter in the process of zinc sulphide microbial leaching.

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