Progress in Process Mechanism and Electrochemical Research of Bacterial Oxidation Leaching of Gold-containing Arsenite Pyrite

I. Introduction

With the increasing global ecological problems, the depletion of easy-to-select and manage gold ore resources and the improvement of metallurgical technology, metallurgical technologies with low environmental negative effects, good economic benefits and effective treatment of refractory gold ore have received increasing attention and become Possibly. Difficult to treat gold mines, also known as refractory gold or refractory metallurgical mines, refers to gold mines with a direct cyanidation rate of less than 70% in conventional cyanidation processes. About one-third of gold mineral resources belong to refractory gold mines. At present, gold refractory ore accounts for 60% of the world's gold reserves. There are many factors that cause gold mines to be difficult to handle. For example, gold is encapsulated in gold-bearing minerals with ultrafine particles, and the ore contains some elements that inhibit cyanide leaching (such as C). , As) and so on. In a large class of refractory gold sulfide ores are gold, pyrite and arsenopyrite FeAsS (arsenopyrite) is a common carrier gold sulfide ore, gold seq microscopic particulate inclusions therein. In order to increase the cyanide leaching rate of such ore gold, it is necessary to carry out pretreatment. Compared with traditional pretreatment methods, bacterial oxidation pretreatment has low environmental negative effects and good economic benefits, but due to its own shortcomings, such as long pretreatment time, exothermic oxidation process and arsenic to leaching bacteria produced by leaching process. The toxic effects and other problems limit its further application. The arsenic-bearing gold concentrate bacteria leaching pretreatment process strengthens, requires an in-depth understanding of the mechanism of bacterial oxidative leaching of sulfide ore, this process is essentially a redox reaction involving bacteria, involving electrons in minerals - Migration between the bacteria, mineral-leaching solution and leachate-suspended bacteria adsorbed on the surface of the mineral, and the electrochemical signal of the bacterial oxidation process can be obtained by modern electrochemical analysis technology, and the mechanism is effectively studied.

2. Bacterial oxidation pretreatment process of arsenic-containing gold concentrate

Bacterial oxidative leaching process can use a variety of bacteria, the most widely used is the strain of Thiothiobacillus ferrooxidans At. f. Currently, there are three direct, indirect and combined effects on bacterial leaching mechanism. view. Taking Thiobacillus ferrooxidans as an example, the direct and indirect effects are shown in Figure 1. The combined action mechanism means that the direct and indirect effects in the process of bacterial leaching are often present at the same time, sometimes with direct effects and sometimes with indirect effects. Bacteria adsorbed on the mineral surface initially oxidize the mineral while providing a growth substrate for the bacteria suspended in the leachate.

Figure 1 Comparison of direct and indirect effects

Although the mechanism research has not yet reached a general conclusion, the leaching process of refractory gold ore has obvious advantages compared with the traditional pretreatment process. Its main advantages are: (1) low investment and low cost (2) does not require complex and advanced technology; (3) equipment is easy to solve; (4) is conducive to environmental protection.

The initial bioleaching pretreatment process has achieved good results. Li Ximing et al. carried out a kilogram test of arsenic-containing gold concentrate. The arsenic removal rate of gold concentrate after bacterial pretreatment for 5 days was more than 80%, and the cyanide leaching rate was greater than 90. %; Tolan et al. used a leaching column leaching process to study the pretreatment of arsenic-containing gold concentrate bacteria. The leaching rate of the leaching of the ore cyanide diafiltration column without bacteria pretreatment for 44 d was 27.4%, and the treated cyanide The leaching rate can reach 66.8%~73.2%. These results provide a basis for further industrial application of bacterial pre-oxidation dearsenic-cyanide gold extraction. Since 1986, the world's first biological pre-oxidation plant was built in Fairvie, South Africa. In 1998, Shaanxi Bio-Mine Mining Engineering Co., Ltd., which is processing 10 t gold concentrate in China, was officially put into operation. In 2000, Yantai Gold Smelter The successful construction and commissioning of the bio-oxidation project marks that China has become one of the few countries in the world to have this high-tech. At present, bacterial pretreatment mainly includes the following processes: BIOX (R) process, BacTech process, Newmont process and Geobiotics process.

The leaching pretreatment process of arsenic-containing gold concentrates has its own disadvantages, such as long residence time and oxidation in acidic solution. Therefore, anti-corrosion materials must be used. The exothermic oxidation process leads to temperature rise and arsenic produced by leaching process. The toxic effects of bacteria limit its further industrial applications. The development and optimization of bacterial pretreatment requires an in-depth understanding of the mechanism of bacterial leaching of sulfide ore, and strengthens the kinetic process based on this, and promotes the further industrial application of bacterial leaching pretreatment under the guidance of specific mechanisms.

3. Study on bacterial oxidation mechanism of arsenic-bearing gold concentrate

(1) Bacterial oxidation process of arsenic pyrite

Arsenic pyrite (aromatic sand) is one of the most common minerals in arsenic-containing gold ore. The molecular formula is FeAsS, monoclinic system, which consists of cationic Fe ^{2 +} and anionic group [AsS]2-. There are many research reports on the mechanism of leaching arsenopyrite. In FeAsS, the As and S contents often change, from FeAs _0.9 S _1.1 to FeAs _1.1 S _0.9 . The arsenopyrite is a sulfide ore with higher oxidation activity. Edwards et al. traced the presence of At. f in the presence of At. The surface changes and found that the polished surface of the arsenopyrite passed through At. f for a long time, and there was no trace of oxidation of the shape and size of the bacteria around the adsorbed bacteria. Instead, a deep groove was formed on the surface, and the oxidation of the arsenopyrite along the deep groove was strengthened. It is thus known that At. f oxidation of arsenopyrite may be dominated by indirect effects. Yang Hongying et al studied the morphology and chemical composition of the polished surface of arsenopyrite in different periods, and found that the bacterial oxidation of arsenopyrite begins at the surface and gradually Cracking and cracking go deep into the crystal. During the oxidation process of the arsenopyrite, As exhibits the valence state change of [AsS] ^{2 -} →As(III)→As(V), and the yellow precipitate of the oxidation of the poisonous sand bacteria is analyzed. Potassium sulphate KFe ₃ (SO ₄ ) ₂ (OH) ₆ and arsenic As ₂ O ₃ , when they cover the surface of the arsenopyrite, inhibit the further oxidation of the bacteria. Jones et al studied the different parts of the crack formed on the surface of the poisonous sand during the bacterial leaching process and the chemical composition of the leachate. At the same time, the surface of the poisonous sand was detected by electron microscopy, and it was found that even the surface of the poisonous sand covered the precipitate film formed by oxidation. Prevents direct contact between bacteria and minerals, but as long as Fe ³⁺ and O ₂ in the solution can reach unoxidized crystals by diffusion, the oxidation of the arsenopyrite can continue until the precipitate film completely blocks Fe ^{3 +} and O ₂ Diffusion into unreacted crystals. Min et al. compared the leaching characteristics of arsenopyrite and pyrite, and obtained evidence of the indirect mechanism of leaching of toxic sand bacteria: (1) only a few bacteria in the leaching process are adsorbed on the surface of the arsenopyrite, while the bacteria The direct action must adsorb the participation of bacteria; (2) the leaching process exhibits selective preferential leaching of arsenic. Due to the toxic effect of arsenic on bacteria, this phenomenon is obviously unexplained by the direct mechanism; (3) poisoning during leaching The surface of the sand does not see the appearance of a corrosion pit of the shape of the bacteria, but exhibits an overall oxidative property, which can only be explained by the chemical oxidation behavior.

The above studies illustrate the important role of the indirect action of bacterial oxidation in the bacterial leaching process of arsenopyrite. However, these studies do not fully explain that At. f has only an indirect effect on the oxidation of arsenopyrite. The oxidative process of At. f on the arsenopyrite and the physicochemical properties of the surface, the distribution of bacteria in mineral particles and leachate, and The composition of the leachate was examined in more detail. It is believed that the At. f oxidized arsenopyrite can be divided into three stages. The first stage is to start the oxidation of the arsenopyrite. The bacteria adsorb to the mineral surface, the number of adsorbed bacteria increases rapidly, and the surface of the mineral is eroded. The direct effect of bacteria. The direct action of Fe ^{2 +} promotes the growth of bacteria in the solution, and the increase in the number of bacteria in the solution causes more bacteria to adsorb to the mineral surface. This process is primarily a direct effect of bacteria:

In the second stage, a large number of active bacteria oxidize Fe ²⁺ and As(III) to Fe ³⁺ and As(V), and the resulting Fe ³⁺ can oxidize As(III) and arsenopyrite crystals. This process is mainly bacterial. The indirect effect, that is, the main role of At. f is to regenerate Fe ³⁺ :

The increase of Fe ³⁺ and As(V) concentration in the third stage solution increases the concentration of precipitated iron arsenate in the leachate. The increase of precipitate reduces the concentration of Fe ³⁺ in the solution and inhibits the indirect oxidation of bacteria. effect:

The bacterial oxidation process can be expressed by the following general reaction equation:

The first and second stages are n=2, and the third stage is n=4. From the above research results, it can be concluded that At. f oxidation of arsenopyrite has different mechanisms of action at different stages. In order to clearly explain the leaching mechanism, the problem that needs to be further determined is: how the oxidation of the arsenopyrite in the first stage is carried out, and what medium is in the oxidized arsenopyrite crystal; how is the second stage Fe ³⁺ ion oxidized arsenopyrite crystal? According to the conclusions of the first two stages, how to avoid the inhibition of oxidation by sediment. The specific mechanism of each stage needs further research.

(2) Kinetic process of bacterial oxidation of arsenic sulfide ore

There are many researches on the kinetic model of leaching bacterium of sulfide ore. These results are helpful for the establishment of arsenic pyrite leaching kinetic model. The initial research is based on the traditional chemical model, focusing on the mass transfer factors of bacterial oxidation. Attempts to establish a widely applicable theory of leaching dynamics by establishing a model with universal significance. With the deepening of the research, the understanding of the process of bacterial leaching is more profound. Recent studies on bacterial leaching have shown that during leaching, vulcanization The leaching of the ore has two steps. On this basis, it can be considered that the leaching of the sulfide ore is mainly the chemical leaching of Fe ³⁺ , and the action of the bacteria is mainly the Fe ³⁺ ion in the regeneration system. Thus, the leaching effect of Fe ³⁺ on sulfide ore and the oxidation of Fe ³⁺ by bacteria can be relatively independently studied and strengthened. The oxidation of Fe ³⁺ by bacteria during leaching is accomplished by iron oxidase and is an enzymatic reaction. Most of the models describing the oxidation of Fe ³⁺ by bacteria were established by the Monod equation in combination with electrochemical theory. As shown in Table 1, different researchers only considered the different environmental parameters of the leaching process for the oxidation of Fe ³⁺ by bacteria. Inhibition or promotion, thus adjusting the mathematical expression of the model. It can be seen that the reaction mechanism obtained by different researchers has subtle differences. This is mainly because the bacterial leaching process involves the physical and chemical properties of minerals and the physiological characteristics of bacterial species. And the complexity of the environmental parameters used. Based on different experimental conditions, different researchers have obtained different experimental results. Under the guidance of basically the same mechanism, the interpretation of the experimental results leads to different adjustments to the basic mechanism. Therefore, The specific bacterial leaching process is studied, and the specific kinetic model of the leaching process is meaningful through experiments.

Table 1 Kinetic models of bacterial growth and oxidation of Fe ³⁺ in different studies

As for the conversion of elemental sulfur in the process of bacterial leaching, there is no unified theoretical basis for kinetics. During the oxidation of minerals, the elemental sulfur product may act as a precipitate attached to the surface of the mineral to prevent further oxidation of the mineral. The action of the bacteria may be to remove the inhibitory effect of the sulfide precipitation layer and promote the continuous leaching of the bacteria.

The leaching effect of Fe ³⁺ on sulfide ore can be studied by electrochemical theory. For the bacterial leaching process of arsenic-containing gold concentrate, Ruitenberg et al. in 1999 derived and verified the Fe ³⁺ leaching power of arsenopyrite. Learning model.

The ratio of Fe ³⁺ and Fe ²⁺ in the bacterial leaching system can be expressed by the Nernst equation:

Where E is the solution oxidation-reduction potential (mV), E0' is the standard electromotive force (mV), R is the universal gas constant [kJ/(mol.K)], T is the temperature (K), and z is involved in the redox reaction. The number of charges, F is the Faraday constant (C/mol).

The leaching rate expression of arsenic pyrite from the conservation of iron in the system is

The relationship between the leaching rate of arsenic pyrite and the Fe ³⁺ and Fe ²⁺ in the system is obtained from the above equation:

Further obtaining the final arsenic pyrite Fe ^{3 +} leaching expression

In the subsequent verification experiments, Ruitenberg et al. obtained the conclusion that the model basically conforms to the experimental results. Of course, the model is only a pure chemical and electrochemical derivation process, and it is only a description of the leaching dynamics on a macro scale, more accurate. The model should consider the leaching of minerals by the bacteria adsorbed on the mineral surface and the mass transfer of Fe ³⁺ and Fe ²⁺ .

(III) Biochemistry of bacterial oxidation of arsenic sulfide ore

During the leaching process, bacteria adsorbed on the mineral surface play a different role than bacteria suspended in the leachate. It is generally believed that the adsorbed bacteria act as a direct leaching function to suspend Fe ²⁺ in the bacterial oxidation system and function to regenerate Fe ³⁺ . This is based on different biochemical functions. Bacteria adsorbed to the mineral surface in the leaching system play an important role in the leaching process. Nemati et al. proposed a general procedure for the adsorption of bacteria on the mineral surface: first, the bacteria adsorbed on the mineral surface, and there is a balance mechanism between the free bacteria and the adsorbed bacteria; Second, the extracellular polymer (EPS) secreted by the bacteria forms a connection between the cell membrane and the mineral. Bacteria adsorbed to the mineral surface are surrounded by EPS produced by themselves, and EPS mediates the energy exchange between bacteria and sulfide minerals. It plays an important role in the formation of biofilm and the interface between bacteria and matrix. Hansford et al believe that only Bacteria secreting extracellular polymers can be adsorbed on the mineral surface to etch minerals. Different substrates may cause bacteria to secrete different extracellular polymers, such as extracellular polymers secreted by At.f on the surface of pyrite. There are glucuronic acid residues, these groups can form a complex with Fe ³⁺ , and the leaching of minerals has obvious effect only when the concentration of Fe ³⁺ reaches a certain value. When the concentration of Fe ³⁺ is low, no obvious observation is observed. Leaching effect. The main functions of Fe ³⁺ are: (1) formation of polymer-Fe ³⁺ complex, which may be the initial substrate for bioleaching, and the extracellular polymer also has the effect of enriching Fe ³⁺ . (2) The surface of the bacteria has a positive charge and can be adsorbed on the surface of the mineral with a negative charge. The bacteria growing on the surface of the elemental sulfur secrete different extracellular polymers, and the binding of the bacteria to the surface is mainly based on hydrophobic interaction. This kind of force is relatively weak. Tributsch et al. believe that the extracellular polymer containing thiol bond (—SH) amino acid (such as cysteine)-based substance is the key to the interaction between bacteria and minerals with special crystal structure. The class of compounds can leaching sulfur in the form of a colloid. None of the above studies involved the bacterial oxidation process in which extracellular enzymes are directly involved in the enzymes. The bacteria adsorbed to the mineral surface acted as a composite of Fe ³⁺ and glucuronic acid residues in the extracellular polymer. The key role; the indirect mechanism of action is currently the generally accepted mechanism of bacterial oxidation. This study believes that due to the physical and chemical properties of the target minerals and the complexity of At. f itself, there is no universal mechanism of action for bacterial leaching. Whether it is direct or indirect, it should be determined by the specific process of minerals and bacterial leaching.

Most researchers use chemical permeation theory to explain the coupling of ATP in the body during iron oxidation. It is believed that Fe ²⁺ enters the respiratory chain of bacteria at a suitable site, and the electrons released by it are transmitted to the final electrons in the bacteria along the respiratory chain. Body O ₂ , the energy produced by this process for the growth of bacteria. As shown in Figure 2, Xe represents the series of enzymes involved in the transfer of electrons from Fe ²⁺ to O ₂ in the plasma membrane of the cell, Xep and Xen represent their oxidation and reduction states, respectively; Xc represents the series of enzymes involved in CO ₂ bio-immobilization, Xc is its inactive state; Xn is the substance used to store carbon and energy in cells, and Xn' is the state in which it stores energy. Electrons are transported from Fe ²⁺ to O ₂ through a series of enzymes, causing proton and electron gradients inside and outside the plasma membrane. Protons are transported from the plasma membrane to the plasma membrane by ATP synthase (ATPase), providing energy for the synthesis of ATP; ATP Provides energy for the synthesis of cell-fixed CO ₂ and biomacromolecules.

Figure 2 At. f oxidation Fe ²⁺ reaction model

Lu Diankun et al. calculated by thermodynamics that the position of Fe ²⁺ entering the biological respiratory chain was before cytochrome C and after ubiquinone (coenzyme Q). The series of enzymes that explicitly participate in the transfer of electrons from Fe ³⁺ to O ₂ are the concerns of bacterial workers. Figure 3 shows the electron transfer lines proposed in the study. Some researchers believe that electrons from Fe ²⁺ to iron There is an electron transferase that has not been found between lansin, because the electron transfer rate calculated by kinetics is too slow compared with the Fe ²⁺ oxidation rate obtained in the experiment; unlike the above electron transfer order, Hazra et al believe that electrons pass Cytochrome C is transferred to ferrocyanin. The electron transport enzyme system of leaching bacteria also requires further research.

Figure 3 At. f oxidized Fe2+ electron transport chain

The biochemical characteristics of bacteria are the result of their genetic factors. To reveal the association and regularity of biochemical leaching of sulfide ore and the biochemical process of bacterial growth, it is necessary to uncover the bacterial oxidation mechanism at the molecular level, and then to carry out the genetic level of the leaching bacteria. The transformation of the foundation to create a new generation of high-performance leaching bacteria. The study of biochemical processes at the molecular level of bacteria reveals the mechanism of oxidative leaching of sulfide ore bacteria. The basic problems that need to be solved include: the genetic structure of the bacteria, which specific fragment of the gene is involved. The reaction, how the reaction process, the cloning and sequencing of the close-up gene, how to influence or change the role of specific genes, etc. Ayme et al. studied in detail the structure and characteristics of the gene operons encoding the components of the respiratory chain in At. f ATCC33020, Inferred that all electron transfer enzyme genes in the leaching process exist in the same operon in a certain order, and these genes are transcribed together; these genes can be transcribed when growing in iron or sulfur matrix, indicating the protein encoded by the operon It acts in both ferrous oxidation and sulfur oxidation.

In the study of the iron oxidation system of Thiobacillus ferrooxidans, the conclusions obtained by the researchers were different. The reason may be that they have different interpretations of the data obtained, and on the other hand, the genetic diversity caused by strong selection pressures in extreme growth environments, resulting in differences in energy metabolism systems between different populations.

(4) arsenic sulfide ore bacteria oxidation electrochemical (interface electron transfer)

The bioleaching of sulfide ore should be the intersection of chemical, solid surface chemistry, biochemistry and electrochemistry. Since this process is essentially a redox reaction, the transfer of electrons between the mineral surface and the leachate interface and the adsorption of the bacterial interface is the most reactive. For the root cause, it is extremely important to study the electrochemistry of the leaching process. The electrochemical principle of bacterial leaching mainly examines the role of the following two factors in bacterial leaching: (1) the main electrical pair in the system, E _ox (O ₂ /H ₂ O), E _sox (S component / adherent bacteria) And the change rule of E _EP (Fe ²⁺ /Fe ³⁺ ); (2) the electron transport chain of the reaction. As shown in Fig. 4(a), if the iron in the solution is mainly in the form of Fe ²⁺ , resulting in a relatively low E _EP in the system, the point difference between Eox and E _EP is the largest, resulting in the oxidation of bacteria. In the oxidation process of Fe ²⁺ , electrons are transferred from Fe ²⁺ to O _{2 in} bacterial protoplasts; Figure 4(b) and Figure 4(c) compare the presence or absence of sufficient O ₂ in the system. The difference in the form of Fe ²⁺ exists in the system, when electrons are transferred from sulfide to Fe ³⁺ and converted to Fe ²⁺ , such as O _{2 is} sufficient, and with the participation of bacteria, Fe ²⁺ can be reconverted into Fe ³⁺ allows the leaching process to continue. Conversely, the consumption of Fe ³⁺ will cause Fe ²⁺ in the solution to dominate, thereby interrupting the leaching.

Fig. 4 Relationship between main oxidation-reduction electricity pair and electron transfer in bacterial leaching system

The electrochemical action of the leaching bacteria and mineral interface in the leaching process can be considered from two aspects: on the one hand, changing the electrochemical factors in the leaching system to enhance the leaching effect of the bacteria; on the other hand, the electrochemical signal through the leaching process Detection, giving a reasonable explanation of the change of the detection signal with the process, and obtaining the possible mechanism of the bacterial leaching process. The above research can be considered by electrochemical methods: on the one hand, the relationship between electrochemical factors and bacterial activity, and on the other hand, the relationship between bacterial activity and mineral leaching, and the combination of electrochemical factors and minerals. The general rule of connection between leaching.

Modern electrochemical analysis technology can be used as an effective means to study the electrochemical behavior of the bioleaching interface of sulfide ore. The preparation of mineral electrode is the premise of electrochemical technology to study the process of bacterial leaching. According to the physical and chemical properties of minerals, minerals can be processed into minerals. A carbon paste electrode or a mineral crystal having good conductivity is processed into a mineral electrode.

Dan Shaoyuan using various electrochemical cyclic voltammetry method, potentiodynamic, potentiostatic AC impedance and studied iron sphalerite - electrochemical properties of the carbon paste electrode [FIG 5 (a)], revealing iron The electrochemical mechanism and microelectrochemical reaction steps of the sphalerite bioleaching process were investigated. The corresponding effects of various factors on the electrochemistry of the leaching system were investigated, and the reaction mechanism of mineral bioleaching was further revealed, and the enhancement measures for bioleaching were provided. Based on the potential sweep, potential step, constant potential Coulomb analysis, AC impedance and other methods, the electrochemical behavior of arsenic pyrite electrode in alkaline, especially ammonia solution, was studied. Cabral et al. [31] The interface mechanism for studying the pyrite bacterial leaching system describes three relatively mature electrode fabrications (Fig. 5). The improved electrode enhances conductivity and eliminates interference factors to the greatest extent possible. The bioleaching process of specific arsenic-containing gold ore should consider more complex factors. Taking arsenic pyrite as an example, Yang et al studied the submicrostructure of arsenopyrite. It is believed that most of the ultrafine gold particles are encapsulated in the arsenic pyrite crystal in a submicron state, and the distribution of gold particles is uneven. of. In general, minerals with high arsenic content contain high gold content, and the core region of mineral crystals has almost no gold component. In gold-containing mineral crystals, “gold/arsenic pyrite” electric pairs are naturally formed, and gold Compared with the inertia, arsenic pyrite has high activity, and it is very easy to be oxidized due to the action of the primary battery, thereby destroying the arsenic pyrite crystal lattice.

The gold particles are exposed. The gold-rich regions are generally at the lattice edge, crystal surface and surface cracks of the arsenopyrite, and there is substantially no gold component in the core region of the mineral crystal, thus for gold-containing arsenopyrite For the purpose of effective pretreatment, it is not necessary to completely oxidize the arsenic pyrite.

The above review of the study of leaching of sulfide ore bacteria, specifically to arsenic pyrite, has not yet been generally accepted. To understand the mechanism of bacterial leaching, at least three levels of problems should be explained: (1) What is the first electron acceptor in the oxidation process, and (2) the reaction pathway of this oxidation process is What is the end product of the reaction, what intermediate stages have been experienced before reaching the end product; (3) what role the bacteria plays and how it works. These problems are related to the electrochemical study between mineral surface, leachate and bacterial interface, so it can be concluded that electrochemical research technology can play an important role in the study of bioleaching.

Fourth, the strengthening of bacterial oxidation process

Changes in the parameters of the leaching system during actual production application and mechanism research can reduce production costs and facilitate the exploration and verification of mechanisms. Bacterial leaching must consider the effect of metal ions produced by different mineral leaching processes on bacterial activity. The ability of Thiobacillus ferrooxidans to resist metal ions is Zn 119, Cu 55, Mn 40, Ni 72g/T, respectively. Xiang Lan studied the effect of metal ions generated during different mineral leaching processes on bacterial activity, and believed that the tolerance of bacteria to specific metal ions can be improved by domestication, thereby improving the activity of bacteria in the leaching process. Compared with the process, the toxicity of arsenic to bacteria caused by the leaching process of arsenic-containing gold concentrate is an important factor restricting the use of high-concentration pulp in such mineral leaching. Excessive concentration of arsenic can inhibit the oxidation of Fe ²⁺ by At. f. Thus, the Fe ^{3+ is} inactivated, and the arsenic-resistant domestication of At. f can improve its tolerance to arsenic. Various physical and chemical factors in the bacterial leaching system may affect the leaching effect, such as treatment of flotation gold. Effects of flotation reagents on bacterial growth and decomposition of arsenopyrite during mineralization, behavior of elemental sulfur in microbial oxidation, and effects of As ³⁺ and As ⁵⁺ on bacterial oxidation. Deng et al. studied the effects of the following factors on bacterial leaching efficiency: 1) the use of arsenic-resistant domesticated bacteria; (2) the use of magnetized water technology; (3) the addition of surfactants; (4) the introduction of catalytic metal ions. The mechanism of action of these factors is either unclear or requires further validation. The results show that they all increase the effect of bacterial leaching to varying degrees.

The adoption of new technologies such as hydrothermal, ultrasonic, electric field, and magnetic field enhancement provides an opportunity for the development of new chemical and chemical technologies. In biometallurgy, the emergence of sonobioleaching indicates the broad development space of biometallurgy. Swamy et bioleaching investigated, and lead nickel ore leaching processes and effects associated with the ultrasonic technique, describes the role of strengthening the leaching effect of ultrasound on the proposed mechanism of action in metallurgical ultrasonic biological hypothesis. The adoption of new technologies in biometallurgy helps to promote the industrial application of biometallurgy and provides more means for its mechanism research.

V. Conclusion

Biometallurgy is an effective way to solve the negative effects of the metallurgical industry and reduce its cost, especially the application of bioleaching to the pretreatment of refractory gold ore. Due to the physicochemical properties of various mineral deposits and the complexity of the physiological characteristics of different leaching microorganisms, there is no universally applicable mechanism for the bioleaching of minerals. Arsenic pyrite and Thiobacillus ferrooxidans are one of the most common gold-bearing and leaching microorganisms, respectively. The mechanism of arsenic pyrite-oxidized arsenic pyrite is of great academic significance and application value. Biological oxidation is essentially an oxidation reaction of minerals, and the complexity of mineral components naturally forms various types of galvanic cells in the system, and the transfer of electrons plays an important role in these processes. Contemporary electrochemical analysis technology can provide comprehensive and accurate electrochemical signals, and provide an effective means for strengthening the effect of mineral leaching and research on leaching mechanism. It is foreseeable that the electrochemical method can effectively explore the bacterial leaching mechanism of refractory gold ore and propose strengthening measures.

Double Sided Film