I. Introduction
Heap leaching is a simple and economical technique for recovering gold from low-grade ore. It has become an important method for recovering gold from low-grade ore, off-balance sheet ore, old mine waste rock pile and old tailings. The gold production produced by the heap leaching gold extraction process has been steadily increasing year by year. In order to adapt the heap leaching gold extraction process to the production needs, the scientific and technological workers of various countries have adopted different methods to carry out the precautions in the process of heap leaching and gold extraction from different angles. Research has enabled the heap leaching technology to be continuously improved and developed.
Second, the precautions in the process of heap leaching
According to the characteristics of heap leaching technology, this precaution mainly discusses the improvement and improvement of the heap leaching process and the cyanide agent action environment.
(1) Improving the heap leaching process
1. Correct application of granulation technology to improve gold leaching
Practice has proved that fine ore materials and ores with too high clay content should not be directly piled up. It is necessary to pretreat the granules first to improve the permeability of the heap to be heap leaching. The granulation pretreatment can greatly enhance the leaching of gold and accelerate the leaching speed of gold. In most cases, the leaching rate of gold can be increased.
According to reports, after granulation pretreatment in a US factory, the leaching rate of gold ore containing a large amount of fine ore fines has increased by 6000 times. After the granulation heap leaching of the Paradise Peak gold mine, the recovery rate was increased by 12%; after the granulation pretreatment in another gold selection plant, the leaching period was shortened from the original two months to three weeks, and the gold leaching rate was from 35 % increased to 90%, while production costs per ton of ore increased from only 80 cents to $1.30.
In 1991, the Xinjiang Saidu Gold Mine was the first in the country to carry out the largest scale (24,000 tons) of granulation heap leaching. The leaching time was 35 days shorter than non-granulation, and the leaching rate increased from 49.69% to 81.5%, an increase of 32%. The leaching leaching of 20,000 tons of low-grade (2.12g/t) gold ore in the Dorasai gold mine in Xinjiang has a gold leaching rate of 82%, and its tail slag grade is close to that of the ore. The Kanggur gold deposit in Shanshan County, Xinjiang, was the first to use salt water granulation instead of cement lime granulation in China. The gold leaching rate was 74.2%, which completely solved the problem of salt water leaching and scaling. Zhejiang Huzhou silver gold deposit using granulated with a solution of sodium cyanide heap leaching process, so that 65% of the gold extraction rate increased to 77.5% of the design.
Liquor and lime are usually used as binders, but the amount should be appropriate. New granulation auxiliaries have also been studied. According to reports, the Breway gold mine in South Carolina, USA, uses a granulating aid that increases gold recovery and reduces cement usage compared to cementing alone, while also increasing pellet strength. The Leach-It granulation auxiliaries from Chemstar Lime, Arizona, and the other Polymers granulating agent, which use a special granulating agent to increase the gold recovery rate by 20% compared to conventional cement-only granules; 1/2 leaching area; the amount of gold-containing solution is reduced by 1/2, and the grade is increased by two times; thereby reducing cyanide consumption and water evaporation.
2, using different heap leaching process to improve the leaching effect
Foreign heap leaching production does not use a pile of unloading methods, but a permanent yard. Usually, the yard is selected in a valley with a large area at the bottom, and the stratified partitions are alternately piled up or piled up. The dripping method greatly improves the economic benefits of the enterprise. The Girl Gold Mine in the United States adopts a typical layered partition alternately to build a spray method, which greatly improves the operation rate of mining, building equipment and sprinkler equipment, while ensuring expensive The liquid grade is relatively stable. China's Xinjiang Habahe Saidu Gold Mine adopts the process of “segmented stacking, cross-spraying, multi-stage countercurrent leachingâ€, and has achieved obvious economic benefits. The results are shown in Table 1.
The permeability of the heap and the permeability of the solution are key factors in determining the heap leaching effect. According to reports, Fegasus Gold's Florida Canyor gold mine uses a unique curved pile system; Round Mountain gold mine uses a bridge crane system; Buckhom and Grofoot gold mines use a wheeled self-adjustable conveyor. A mobile curved piler developed in China has a good effect.
The results of the study at the Hazen Institute in the United States indicate that increasing the oxygen content by introducing air into the heap can shorten the leaching period by nearly 1/3 and increase the leaching rate of gold. A patent invented by Kamyr in the United States, "the heap leaching method using oxygen", has increased the leaching rate of gold and silver; the other two patents in the United States introduce the designed device, which is installed in the heap during the pile-up. Conducive to the entry of oxygen, improve the permeability of the heap, and improve the leaching speed in the later stage. Some mines in China are buried in bamboo tubes and wooden sticks during the pile-up. After leaching for a period of time, these buried objects are pulled out to make some looseness of the heap, and the permeability is improved to facilitate the leaching of gold ore. After using the research institute for a period of ore heap leaching, partial loose blasting is applied to the part of the accumulated water, which also acts to loosen the heap and improve the permeability; in addition, a tube with many small holes is buried in the heap. The tube is filled with cyanide solution, and the cyanide solution permeates through the small holes; the top of the pile is divided into several areas according to the condition of rapid penetration, and the cyanide solution is supplied in the same volume in the same area to make the area with slow penetration The volume of the leachate is the same as that of the infiltration, so as to achieve the purpose of uniform permeation of the heap.
Laying a rich liquid collection tube at the bottom of the heap can speed up the solution flow, eliminate the mineral accumulation water, increase the gold leaching speed, and prevent the mine from falling down and landslide. In the foreign heap leaching production, almost all the bottom of the heap is covered with a liquid collecting pipe. In the domestic heap leaching production of Shanghang Zijinshan Gold Mine and Xinjiang Kanggur Gold Mine, the sump is designed and laid by itself, and the effect is good. No rich liquid is found around the heap immersion field. The effluent solution is also quite clear. This measure was also adopted during the granulation heap leaching of the Ministry of Geology and Mineral Resources, and achieved obvious results.
The cyanidation reaction should be carried out at a slightly higher temperature, so in cold climates, the main problems of heap leaching are solution and temperature. When the leaching temperature is lower than 10 ° C, the dissolution rate of gold sharply drops. In order to overcome this disadvantage, the heap leaching season is extended, and the solution is first heated and then sent to the heap. Some mines in Canada use waste heat to warm the solution, thus extending the heap leaching time; the Western Windfall gold mine in Eureka, Nevada, USA passes the solution through an immersion heater and stores the solution on the heap to avoid heat loss during spraying. And evaporation; the Richmand Hill gold mine in South Dakota, USA, uses continuous drip and heap heat sinks for continuous production throughout the winter.
3, using drip technology to improve the leaching effect
Spraying and dripping are two different methods of liquid immersion in the heap leaching process, which can produce a uniform liquid distribution effect, and uniform liquid distribution is one of the key factors to improve the gold leaching rate. At present, the rotary swing spray equipment widely used at home and abroad has the advantages of large spray area, uniform spray, no atomization, easy clogging, convenient loading and unloading, etc., but its disadvantage is that the surface impact force of the heap is large, and the solution is evaporated. Losses and wind entrainment losses are large. Drip is suitable for heap leaching production under the natural conditions of drought, high temperature and lack of water in the Gobi Desert. Due to the unique advantages of drip equipment, it has been widely used in foreign countries, such as 80% of the heap leaching in the United States. The drip method is used to raise gold. With the success of the first application of drip equipment in China, the drip technology has been gradually applied in China.
See Table 2 for the comparison of spray and drip in the Xinjiang Sadu Gold Mine.
The comparison shows that the drip is 40% less than the spray equipment investment, the solution evaporation is reduced from 27% to 6%, the gold leaching peak appears one week earlier, and the leaching time is reduced from 109d to 72d, and the leaching rate is 70.5%. Increased to 78.6%.
(2) Improving the working environment of the chemical agent and improving the gold leaching
Application of infusion
Oxygen plays an extremely important role in the cyanidation process. The use of oxidants is an important technical measure to improve gold heap leaching. Batt studied the promotion of cyanide leaching by peroxides of strontium , barium and calcium and found that they can release oxygen into solution. For example, for some ores, when 1.5kg/CaO 2 is added, heap leaching can be achieved. The process speeds up by 20d. U.S. Patent No. 4,421,724 also reports that the addition of KMnO 4 during heap leaching increases the leaching rate of gold by 5%.
Adding an appropriate amount of a hardening agent or a wetting agent to the cyanide solution facilitates the penetration of the cyanide solution and reacts with the encapsulated gold. It is reported that industrial trials of adding leachate and re-cyanide treatment on the tailings of the heap in the Cannes gold deposit and the Zhaizitou gold mine in southwestern Guizhou have shown that the tailing grades are reduced to 0.625g/t and 0.44 respectively. g/t, the leaching rate increased from 68.15% and 82.4% to 77.75% and 88.27%. The local mine and minerals department added a self-made soaking agent in the late stage of heap leaching in Sichuan. The gold content of the rich liquid in the field increased from 1.4-1.6mg/L to 2.19-2.93mg/L, which played a certain role in assisting leaching.
Pre-alkali treatment before heap leaching can reduce the influence of harmful metal ions on cyanide leaching, reduce the amount of cyanide and maximize the gold leaching rate.
Multi-stage leaching can obtain precious liquid containing up to 4 ppm of gold, which is significantly higher than single-stage heap leaching. The laboratory column dip test of Beijing Nonferrous Metals Design and Research Institute showed that the leaching rate of the two-stage leaching was 1.3% higher than that of the conventional and one-stage leaching gold, and the cyanide concentration was reduced from 0.09% to 0.05%.
Third, difficult to handle heap leaching of gold mines
Studies have shown that for many difficult ore, biooxidation pretreatment is carried out before heap leaching, and in most cases, leaching time and leaching rate can be shortened. U.S. Newmont Gold Company Gold Quarry treated with ferrooxidans ferrous carbonaceous sulfide ores, oxide 100d after 35% -40% of a sulfide, thiourea leaching and acidic, treated with charcoal and cation exchange resins from thiourea Gold is recovered from the leaching solution. According to reports, the test results are good. The ore grade used in the pretreatment process is as low as 0.62-2.1 g/t, and the gold recovery rate is between 60% and 70%.
Recently, a microbial treatment of passivated carbonaceous materials has been reported, which is used to treat a carbonaceous sulfide gold ore with a conventional cyanidation leaching rate of zero. After oxidation of the sulfide by microorganisms (H. thermophila), gold is reported. The leaching rate was 55.5%, and after the microbial oxidation was treated with the fungus composition to passivate the gold, the gold leaching rate could be increased to 74.4%. The domestic Shaanxi Geological Survey Bureau used the microbial oxidation heap leaching process for the first time to treat refractory gold ore, which has been successful in the Jiupinggou section of Shuangwang Gold Mine. In view of the characteristics of gold-bearing minerals being immersed in sulfide minerals such as pyrite, the microbial oxidation technology was used for industrial scale (2000t) heap leaching test. After 52d microbial oxidation of ore, the recovery rate of heap leaching gold was 32% higher than conventional. .
Chlorination pretreatment is also an effective method to solve the problem of carbonaceous materials preemptively adsorbing gold cyanide ions in ore. According to reports, Sawwyer et al. studied the process of pre-pile leaching of carbonaceous gold ore with sodium hypochlorite. The test used two kinds of gold ore from Nevada, USA. The total carbon content and organic carbon content in the ore were: I4.87%. 2.50%; II2.63%, 1.50%. The conventional leaching rates of the two gold ores are 1.7% and 0.0%. After the treatment with sodium hypochlorite and then cyanidation, the leaching rate of both samples is above 85%; while the leaching rate of gold is only above 60% when the ore sample is only leached with sodium hypochlorite, which indicates that sodium hypochlorite is also an effective gold leaching agent. Subsequent analysis concluded that the heap can be treated with sodium hypochlorite solution in the cold season (below 10 ° C), and then in the warm season when the temperature rises, the gold is leached with cyanide solution, which reduces the chlorine consumption and thus reduces Cost of production. In a sense, sodium hypochlorite is also a promising pretreatment agent for the pretreatment of carbonaceous gold ore oxidized ore heap leaching.
The use of certain organic or inorganic substances to inhibit the adsorption of gold by carbonaceous materials is also one of the effective ways to solve the problem of carbonaceous material robbing in ore. According to reports, a high-efficiency composite inhibitor developed by Chengdu University of Science and Technology has tested the heap leaching rates of two gold mines in Getang and Changkeng, Guizhou, with 29.8% and 39.9% leaching rates, respectively. In the heap leaching, the gold leaching rate was increased to 75.1% and 66.5%, respectively (immersion 240h).
One direction Heap Leaching Technology refractory sulfide gold ore containing arsenic also research, China's Liaoning Geological laboratories for this type of ore leaching water discharge, alkaline pretreatment eliminate the effects of harmful elements, combined with mechanical oxygenation Then, the granulation heap leaching rate can reach 72.22%.
Fourth, the conclusion
With the large-scale development of gold mines, the depletion of resources is becoming more and more serious, and the application of heap leaching and gold extraction technology will be more extensive, and the technology for improving leaching rate has been widely applied.
(1) For ore with high content of fine or clay and poor permeability, granulation pretreatment technology should be adopted to improve the permeability of the heap, speed up the leaching and increase the leaching rate. The ore may be fully granulated or sieved to obtain fine granulation.
(2) The method of pile-up is an important part of the process of heap leaching and gold extraction. The pile-up should consider eliminating segregation as much as possible, so that the entire pile has similar permeability and avoids channel flow or partial blockage. Therefore, during the pile-up process The use of advanced curved pile-building equipment, the use of "segmented layered pile, cross-spray, multi-stage countercurrent leaching" process; at the same time to solve the method of the mine into the air during the pile-up process; Solve the permeability of the heap and improve the leaching effect.
(3) For different situations, use drip and spray technology to evenly distribute liquid. Heap leaching in Gobi, desert, drought, high temperature and water shortage areas, in order to reduce the evaporation of the solution and save water, the use of dripping technology should be strongly advocated.
(4) Adding an oxidizing agent such as oxidant, infusion agent and wetting agent during the heap leaching process can accelerate the leaching of gold and increase the leaching rate of gold. This is also the focus of the technology of strengthening the heap leaching and gold extraction process. Research in this area.
(5) Dumping and gold extraction of refractory metallurgical mines should be carried out from the pretreatment technology to expand the research, expand the gold resources and improve the strategic reserve of gold resources.
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