Bacterial leaching processes are various. According to the different ways of contact between bacteria and ore, they can be roughly divided into two categories: bacterial heap leaching and stirred leaching. Bacterial heap leaching refers to a method of leaching bacteria liquid through the ore heap by gravity and pressure. The most typical leaching leaching is bacterial heap leaching. Bacteria have been widely used in heap leaching of low grade copper ore, bacterial leaching of uranium ore, in refractory gold ore pretreatment has been applied. For heap leaching, it has the characteristics of simple process, low investment and low cost. However, due to the low temperature of the heap, the leaching cycle usually lasts for several months or even years. The material used for agitation leaching is generally very fine-grained, and leaching is carried out at relatively low concentrations because microorganisms are more sensitive to shearing effects in high-concentration pulps, prone to cell damage, and thus bacterial growth. The situation is not good. However, the effect of agitation is to fully mix the leached ore with the bacterial leaching agent, and the slurry inhales more air, so that the three-phase turbulent system containing solid, liquid and gas is fully contacted, and sufficient oxygen and carbon dioxide are provided for the growth of the bacteria. Improve mass transfer and leaching rates. Compared to bacterial heap leaching, the production cost of agitation leaching is high (requires stirring, heating, cooling and aeration equipment, acid-resistant reaction tanks, etc.), so it is only suitable for processing minerals with high unit prices, such as Gold mine. The process of microbial pre-oxidation treatment of sulfide ore leaching gold is shown in Figure 5-5.
In industrial applications where high-grade sulfide minerals such as flotation gold concentrates are pre-oxidized and cyanide leached, the construction of high-efficiency reactors is the key to improving production efficiency. However, in the papers published in foreign bioleaching, the papers on reactors are less than 6%, and domestic papers in this area are even rarer. At present, in the bioleaching treatment of gold concentrates, due to the limitations of the strains, the reaction temperature of the normal temperature bacteria is 40-45 ° C, and the reaction temperature of the medium-temperature bacteria is only 50-60 ° C. The oxidation rate (65% to 95%) generally takes 4 to 7 days, while other hydrometallurgical techniques only take several hours. On the other hand, the concentration of the slurry during bioleaching is limited to less than 20%, resulting in unit processing of the equipment. The ability is small. Therefore, the high-grade sulphide ore bioleaching technology has a competitive advantage in comparison with other hydrometallurgical methods in terms of production and production costs. It is urgent to solve the process engineering problem, develop a high-efficiency bioleaching reactor, and shorten the leaching. Cycle, increase pulp concentration and reduce production costs.
So far, there have been few studies on microbial metallurgical bioreactors. The most commonly used in the laboratory is the triangular shake flask, followed by the column reactor and the trough reactor with or without agitation, which is commonly used in industrial production. For reactors without or without agitating devices, the working volume is generally in the range of several hundred cubic meters, and the agitation can be achieved by mechanical or air. At present, the most commonly used reactors are a stirred tank reactor (STR) and an airlift reactor (ALR), in addition to a foam column reactor (BCR), a Bachelor tank, a low energy reactor, a drum type organism. A new type of reactor designed for bioleaching processes such as reactors.
(1) Mechanically stirred tank reactor (STR). A mechanically agitated tank reactor is a reactor that is applied from a chemical process. Its propeller plays the most important role, at least three major tasks are required: suspension of solid particles, mixing of air and water phase, and dissolution into the aqueous phase, the interface between the atmosphere and the aqueous phase. Turboprops are more commonly used in these reactors, and axially propellers with curved blades have recently been used because the latter requires less power and a lower shear force when the same level of agitation is achieved. Although the stirred tank reactor has long-term experience, it also has some obvious shortcomings, such as large power consumption, difficult processing, high investment, troublesome maintenance, large stirring shear force, large damage to cell growth, and large-scale The mixing is uneven, the heat transfer area is insufficient, and the mass transfer efficiency is lowered.
(2) Air-open reactor. Airlift reactor (ALR) principle: The solid particles are maintained in suspension by the rising motion of the fluid (gas, liquid). The gas, liquid and suspended solid particles move upward together in the upflow zone of the reactor. In the downflow zone, the liquid phase and the solid particles flow down to the bottom of the reactor, and the pressure difference generated by different gas phase contents in the ascending and descending zones is forced to drop. The liquid phase and solid particles in the flow zone flow into the upflow zone, thereby forming a circulating flow of gas, liquid and solid three phases in the reactor, generating a fluidization effect and reaching a turbulent state. Fang used At.tTs6 and Brettanomyces B65 mixed bacteria to leach the chromium in the activated sludge in a single-stage airlift reactor (see Figure 5-6), maintaining the reaction temperature at 30 °C, and the leaching rate exceeded over 3 days. 95%, but the cost of construction airlift reactor is too large, and a small amount of processing, therefore Mousavi et al bioleaching process for the establishment of Figure 5-7 shows for leaching of sphalerite.
The specific process flow is: maintaining the growth temperature of At.f by a water bath at 28 ° C, and then inputting the bacterial culture liquid from the reservoir into the mineral filler column through a constant flow pump, wherein the leaching liquid and the gas flow back to each other in the packed column, and the packed tower is used. The insulating material prevents the heat generated by the mineral from being lost. The solution flowing out of the leaching column is re-flowed into the reservoir by the action of gravity, and thus circulates. At 28 ° C, the leaching rate of zinc reached 72% after 120 days of leaching. This process, while increasing the leaching cycle relative to the airlift reactor, reduces the cost of mineral agitation. However, since the immersion column is not properly stirred, when the leaching solution flows through the leaching column from top to bottom, the gully is easily formed, which restricts the sufficient contact between the mineral and the leaching solution, and reduces the leaching rate.
(3) Membrane bioreactor. Membrane bioreactor (MBR) is a high-tech developed at the end of the 20th century. It combines membrane separation technology and biotechnology organically. It has the incomparable advantages of traditional technology and has become a hot research topic in the field of biotechnology in recent years. Membrane bioreactor applications have the following advantages: 1) Increase the reaction rate. Many reactions in biology are product inhibition, that is, as the reaction progresses, the product concentration increases and the reaction rate decreases. The membrane bioreactor can be used to remove the product during the reaction, keeping the product concentration constant and increasing the reaction rate. 2) Increase the conversion rate of the reaction. The membrane bioreactor can continuously separate the product or by-product from the reaction zone, and balance the reaction, thereby greatly improving the reaction conversion rate, increasing the yield or the processing capacity, and the process energy consumption is low and the efficiency is high. 3) Simplify the production steps. The membrane bioreactor completes the reaction and separation in the same step, simplifies the production steps, reduces labor and improves labor efficiency. 4) The biocatalyst is retained to allow the cells or enzyme to be carried out at a high concentration. 5) Reduce energy consumption and save costs. However, in the field of biometallurgy, the membrane bioleaching reactor has rarely been reported. It has been reported that the membrane bioleaching reactor is used to leach nickel- molybdenum ore. The leaching rate of nickel and molybdenum is higher than that of the column under the same conditions. If the future research in this area can be further strengthened, MBR will surely make a great contribution in the field of bioleaching.
The microorganisms that act on the biological pre-oxidation process can be mainly classified into three groups: Mesophile, Moderate thermophile and Exterme thermophile according to their suitable temperature ranges. At present, more than 20 kinds of microorganisms have been reported for biohydrometallurgy, and there are mainly four kinds of bacteria used for pre-oxidation of gold ore in industrial production: Oxide
Thiobacillus iron (Acidithiobacillus ferrooxidans, bacteria referred Af), Thiobacillus thiooxidans (Acidithiobacillus thiooxidans, referred At bacteria), spirochetes oxyalkylene hook end (Leptospirillum ferrooxidans, referred to as Lf Yin) and heat Thiobacillus ferrooxidans (Sulfobacillum thermosul fidooxidans The above several bacteria are acidophilic, aerobic, inorganic and self-supporting, taking CO2 in the air as the carbon source, the first three are moderate temperature bacteria, the most suitable pH for growth is 1.5~2.0, the temperature is 25~35°C. The most used ones are Af and At. At present, the dominant bacteria in oxidative leaching in acidic environment is Af. Af is easy to separate and culture, and the metal ions in solution are Cu2+, Mg2+, Fe3+, etc. It has certain tolerance, but it is not heat-resistant, and the temperature used should not exceed 40 ° C. Brierley believes that the mixed bacteria of iron oxide bacillus and iron oxidized Helicobacter pylori are oxidized in the sulfide mineral biooxidation system in a strongly acidic environment. The best results. Schrenk et al. pointed out that Lf and Af are widely distributed, and have great industrial application prospects for the biooxidation of sulfide minerals. From the kinetics of leaching reaction At higher temperature conditions, medium-high temperature bacteria can not only significantly accelerate the reaction rate, shorten the pre-oxidation cycle, but also prevent excessive passivation of sulfide minerals and hinder the leaching reaction. Therefore, people pay more and more attention to the field of bio-metallurgy. The application of Henry et al. showed that highly thermophilic bacteria grown at temperatures above 60 °C are difficult to apply in the sulphide ore bioleaching industry, while moderate thermophilic bacteria with optimal growth temperatures between 45 and 55 °C are in the industry. It is very advantageous in application because most of the thermophilic bacteria are archaea, most of which lack cell walls, and it is often difficult to tolerate the high shear force caused by high pulp concentration. Relatively speaking, moderate thermophiles have higher pulp. Tolerance of concentration. BacTech Australia has developed a high-temperature heat-resistant bacteria with a heat-resistant temperature of 45-90 ° C and an optimum temperature of 60 ° C, and can survive for several hours under anoxic conditions. Semi-industrial experiment of bacteria and plans to use this process to build factories in Kazakhstan. T-901 strain and Li Yaxu et al. isolated from Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences The 10-year-old MP30 strains are moderately thermophilic bacteria, which can simultaneously oxidize iron and sulfur, and the optimum temperature for oxidizing metal sulfide minerals is 45-50 ° C. Researchers such as Yao Guocheng also carried out research on enhanced leaching of medium-high temperature bacteria. Work, and in order to adapt to the North American climate, Canadian scholars have developed high-activity Af bacteria at low temperature, the suitable temperature range is 5-35 ° C, and the low temperature oxidation behavior of the Af bacteria on refractory sulfide ore is studied.
As a living organism, bacteria need various nutrients to ensure their own growth, and on the other hand, they participate in the reaction as a catalyst. Therefore, the acquisition of excellent strains is the key and core of microbial technology. The nutrient medium on which microorganisms depend for survival and reproduction is the medium, which is mainly composed of nitrogen, potassium, phosphorus and trace elements. The medium is divided into liquid medium and solid medium. The liquid medium is mainly used for rough separation and cultivation. Microorganisms, while solid media are primarily used for pure seed isolation of microorganisms. Commonly used leaching media are 9K and Leathen media. Studies by scholars at home and abroad have shown that there is a significant positive correlation between the biomass of the leaching bacteria and the leaching rate and leaching rate. The activity, concentration and biomass of the bacteria directly affect the effect of biooxidation, so many scholars have passed the leaching microorganisms. Nutritional research attempts to promote the problem of low biometallurgical efficiency is effectively addressed. Russian scientists have degraded the discarded collagen in the feed industry into preparations for use in metallurgical microbial leaching processes, which have a good effect on the leaching effect. There is less than 5% yeast hydrolysate in the nutrient solution of the BIOX process. At present, there are few studies in the domestic perspective on the nutritional conditions required for microbial growth. Before using the leaching bacteria, it is necessary to adapt and acclimate various conditions in the industrial environment so that the bacteria enter the logarithmic phase as soon as possible. Liao Mengxia and others have been breeding, separating and domesticating for nearly 10 years. High-efficiency leaching engineering strain Mdl of arsenic 18g/L.
The biological oxidation pretreatment process is a complex reaction process, which needs to be completed by bacteria. Its essence is the life activity of bacteria. The leaching mechanism exhibited by bacteria is direct or indirect, and its internal physiological and biochemical characteristics are It is determined that the number of bacteria used for biological pre-oxidation refractory gold ore and the ability of bacteria to oxidize minerals are affected by the environment. It can be seen that only the strains with strong oxidizing ability and fast propagation speed can be used as strains to ensure cell growth and breeding environment, and the oxidation rate and oxidation rate can be improved.
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