Study on Bio-preoxidation and Gold Extraction Technology of Low Grade Gold-Sulfur Concentrate

I. Introduction

With the exploitation of mineral resources of gold, easy to deal with dwindling ore; currently 60% of the refractory gold ores of gold reserves Jin Zhanshi sector. The so-called "difficult to handle" means that the gold in the ore cannot be effectively extracted by conventional cyanidation leaching. The factors that cause the gold mine to be difficult to dip are mineralogical, chemical and electrochemical.

Our study is the object Qinghai gold sulfur concentrate the tin Hill, main mineral component of the sample was pyrite (about 95%) and a small amount of silicate material, wherein the pyrite (FeS ₂₎ is a gold-bearing minerals, This gold-containing inclusion is very small and is often referred to as a fine inclusion or submicron inclusion. The water-soluble substance of the leaching agent cannot directly contact the gold particles during direct cyanidation leaching. Therefore, it is necessary to carry out biological pre-oxidation treatment of such a gold-containing sulfur concentrate.

The bio-pre-oxidation refractory gold mining technology has developed rapidly in the 1990s, the bacterial oxidation process has become increasingly mature, and its industrial application has also been rapidly popularized. The number of bacteria in the biological pre-oxidation refractory gold ore and the oxidative capacity of the bacteria on the sulfide ore are all affected by the environment. Environmental factors that affect the number of flora are temperature, nutrients, acidity, medium (energy), and dissolved metal ions. According to the temperature range, microorganisms that act on the biological pre-oxidation process can be mainly classified into the following three categories: (1) mesophilic bacteria. The optimal growth temperature is 30 to 45 ° C, including Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and micro-spirulina. (2) Moderately thermophilic bacteria. The optimum growth temperature is 45 to 55 ° C, such as B. sulfa. (3) Thermophilic bacteria at high temperature. The optimal growth temperature is 60-85 ° C, including S. sphaericus and S. sphaeroides. At present, the biological oxidation process mainly includes: refractory gold concentrate ore leaching, difficult to treat raw ore agitation leaching, and original ore heap leaching. The gold concentrate has the highest recovery rate of mixing and immersion gold, and the leaching period is short, less than 4-6 days. The investment in acid-resistant tank and mixing system is less, and the main operating cost is used for concentrate production, mixing and aeration. Typical processes are the BIOX process and the Bac Tech process. However, with the depletion of resources and the reduction of ore grades, the ore heap leaching has attracted more and more attention when it is economically inefficiently extracted by other methods. The typical process is: crushing, building, or forming of ore. Do not form a group, inoculate bacteria. The typical process is MINBAC process and Geobi-Otics process. In 2008, Changchun Gold Research Institute made a new breakthrough in the research of bio-oxidation and gold extraction of refractory gold concentrate, which made the recovery rate of gold reach 95%, and the highest arsenic resistance of bacteria reached 22g/L. Several characteristics of biological pre-oxidation technology: (1) The industrial scale is getting bigger and bigger. From the 10t small factory in 1986, it has developed to the scale of 750t of daily processing flotation concentrate. According to the current information, more large-scale bacterial oxidation plants will be built in the future. (2) The working temperature of bacteria is getting higher and higher. It has been raised from the previous 35 to 40 ° C to 45 to 50 ° C, and bacteria that are operating at a temperature of 60 ° C are being tested, from medium to high temperature bacteria to extremely high temperature bacteria. (3) The oxidation time is getting shorter and shorter. From the previous 6 to 10 days has been shortened to 5 days, reducing production costs and improving the economic benefits of the mine. (4) Adapting to minerals is becoming more and more complicated. It has evolved from simple sulphide to low-grade complex refractory gold ore containing arsenic, sulfur, and carbon. (5) Engineering technology, engineering equipment and engineering materials are increasingly advanced. For example, the mixing system, the gas supply system, the cooling system, the control system, and the acid balance system have all been greatly improved. (6) With the adoption of high temperature bacteria, more and more metals can be extracted by biometallurgical methods, such as copper , gold, silver , uranium , nickel , cobalt , zinc, etc., and will obtain great economic benefits.

Second, the test method

The samples containing different properties of gold-containing sulfur concentrate are divided into two representative parts, one part is preserved, and the other part is divided into different particle sizes by wet sieve method to analyze the content of precious metals and valuable metal elements.

The biological pre-oxidation test was carried out in a 2.5 L stirred tank at a stirring speed of 170 r/min and a temperature of 33 °C. The initial inoculum containing bacteria per ml ¹⁰⁶ units. The pH measured periodically leaching solution, and ⁺ redox potential and the amount of total iron Fe ^2. After the bacterial oxidized slag is dried at a low temperature, it is weighed and analyzed for its precious metal content. The oxidized solid is neutralized with an alkaline solution to a pH of about 10, and the cyanide solution is diluted to extract gold, and the gold extraction rate is calculated based on the assay nucleus.

Third, the results and discussion

(1) Relationship between pH value and ore oxidation rate

The initial pH value of bacterial pre-oxidation has a certain influence on the oxidation rate. Many experiments have found that when the initial pH value is adjusted to about 1.8, the subsequent oxidation is most beneficial.

(2) Relationship between bacterial inoculum and ore oxidation rate (see Figure 1)

Increasing the amount of bacterial inoculation can, to a certain extent, allow bacteria to enter the logarithmic growth phase in advance and shorten the ore oxidation time. Therefore, examine the effect of inoculum on the ore oxidation rate to determine the appropriate bacterial inoculum.

It can be seen from the test results that when the inoculation amount is less than 20%, increasing the inoculum can effectively shorten the stagnant period of bacterial growth and increase the oxidation rate of the final ore; when the inoculum is greater than 20%, increase the inoculum to shorten the growth time of the bacteria. The effect is significantly reduced. Therefore, the test or production process should be calculated to ensure that the bacterial inoculum is greater than 20%.

(3) Relationship between slurry concentration and ore oxidation rate (Figure 2)

It is well known that the concentration of pulp can strongly affect the gas transmission rate in the slurry. Increasing the concentration of the slurry will increase the viscosity of the solution, reduce the gas transmission rate, and increase the shearing force during the agitation; all of the above are extremely unfavorable for the growth and reproduction of the bacteria; Reducing the slurry concentration will reduce production capacity and increase energy consumption. Therefore, it is necessary to determine the appropriate slurry concentration.

It can be seen from the test results that the lower slurry concentration is beneficial to bacterial growth and ore oxidation, but with the increase of pulp concentration, the ore oxidation rate gradually decreases. When the slurry concentration is higher than 15%, the effect is extremely obvious. During the test, it was also found that in the early stage of leaching of 20% pulp concentration, the number of bacteria in the solution was significantly smaller than the number of bacteria with low pulp concentration. For the experience of pre-oxidation of difficult gold mines at home and abroad, it is recommended to control the concentration of pulp in the production process between 10% and 15%.

(4) Relationship between ore particle size and ore oxidation rate (see Figure 3)

Reducing the ore particle size can increase the surface area of ​​the ore, which is beneficial to the adsorption and reproduction of bacteria on the mineral surface and accelerate the oxidation rate of the ore. Therefore, the effect of ore particle size on the oxidation rate of bacteria was tested to determine the grinding time and the grinding size.

From the test results, the ore particle size has a significant effect on the bacterial oxidation efficiency, but the fine grinding of the grinding results in high energy consumption and high cost. For the nature of the samples used in this test, it is recommended to grind for about 5 minutes, that is, to control the ore particle size of -0.047 mm (-300 mesh) not less than 80%.

(5) Relationship between oxidation time and ore oxidation rate

The oxidation time is closely related to the ore oxidation rate. The ore is completely oxidized from the beginning to the gradual oxidation, and the time is a construction factor. The relationship between oxidation time and ore oxidation rate is examined, and the purpose is to provide a simple basis for determining the actual oxidation rate. The oxidation rates of ores with different oxidation times are shown in Table 1.

From the test results, the oxidation time has a very close relationship with the ore oxidation rate. In the early stage of mineral oxidation, the mineral surface area is large, the area for bacteria adsorption, the rapid proliferation of bacteria, and the oxidation rate of ore gradually increase. With the gradual oxidation of ore, the mineral particles shrink and the surface area decreases, and the ore oxidation rate gradually decreases.

(6) Relationship between ore oxidation rate and gold leaching rate (see Figure 4)

Because the test sample is a pyrite-coated refractory gold deposit; therefore, the oxidation rate of pyrite has a significant effect on the leaching rate of gold. After the pyrite is oxidized, the gold encapsulated can be completely exposed, and the natural gold can be combined with the cyanide ion in the solution to enter the solution. In order to reduce the oxidation time, save production costs, and ensure the gold in the ore can be better recovered, it is necessary to examine the relationship between the ore oxidation rate and the gold leaching rate. Only the test conditions are listed here. For the specific test procedures, refer to the relevant literature.

The test results show that the ore oxidation rate and the gold leaching rate are linearly related, and the cyanide time has little effect on the gold leaching rate; it is further confirmed that the ore is a pyrite-coated refractory gold deposit. After the ore is oxidized in the outer layer of pyrite and the brown gold is naturally gold, cyanide leaching is very easy. Since the ore after oxidation is fine in size, ion diffusion is easy; the cyanide time has little effect on the leaching rate. In the case of ensuring sufficient cyanide ions and dissolved oxygen, the gold leaching rate is only related to the ore oxidation rate.

Fourth, the conclusion

The experimental results show that the suitable conditions for biological pre-oxidation treatment of the refractory gold concentrate are: pH=2.0, inoculum 10% (volume fraction), grinding fineness-0.047mm (-300 mesh) accounted for 80%, ventilation The amount of 0.1 L / (L · min), under these conditions, 21 days after the action of bacteria, the oxidation rate of Fe can reach more than 90%.

V. Outlook

The biological pre-oxidation gold extraction method is a potential industrial technology. The key is to develop strains with good heat resistance, achieve high economic benefits in difficult gold concentrate treatment, and reduce the difficulty of engineering practice. China's arsenic-containing refractory gold concentrate is rich in resources, but due to the high-efficiency industrialization of gold extraction technology, it is just in its infancy, so many refractory gold mines with preliminary proven reserves cannot be fully developed. To this end, while striving to introduce foreign advanced technology, we should vigorously push the scientific research achievements that have made breakthroughs in China's metallurgical technology to industrialization.

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