I. Introduction
Mt. Zijinshan Gold Mine is a gold-bearing ore oxide ore beneficiation process currently used as a "crushing re-election + washing + + + heap leaching CIL" joint process. The heap gold leaching process accounts for more than 80% of the total gold production. In recent years, the scale of heap leaching in Zijinshan Gold Mine has been continuously expanded. The parameters of heap leaching determined by laboratory tests and expansion experiments have not been suitable for industrial production, which has affected the technical and economic indicators of heap leaching production, which is not conducive to the long-term healthy development of enterprises. For this reason, it is urgent to optimize the parameters of heap leaching process. In this paper, the factors affecting the ore leaching rate are optimized to guide production practice.
Second, the nature of the ore
(1) Multi-element analysis of ore (see Table 1)
(2) Mineral composition and the occurrence of gold
Gold - ores belonging cyanide leaching oxide ores easily, the main component of 65.5% silica, 10% sericite, mica, 12.2% water, 7.3% dickite; secondary minerals pyrite 0.1%, Limonite accounted for 2.8%, goethite accounted for 0.5%; a small amount of copper blue, blue copper, zircon and natural gold minerals were also seen.
Grain-size characteristics of gold-bearing minerals: natural gold appears as visible gold, fine particles, micro-fine gold, micro-particle gold, and micro-gold present in microscopic, a small amount of coarse gold exists, more than 10μm gold 55%, 0.5 ~10μm grain grade gold 40%, less than 0.5μm grain grade gold 5%.
Third, heap leaching test research
(1) Stack height test
Stacking height is an important parameter of the heap leaching process. Increasing the height of the pile can not only improve the production capacity of the yard, but also improve the grade of the heap leaching liquid. However, increasing the pile height will also lengthen the heap leaching period. In severe cases, it will affect the gas permeability of the yard and affect the leaching rate of heap leaching.
For this purpose, pile height tests of 6, 8, 10, and 12 m were carried out, and other process conditions were the same. The test results are shown in Table 2.
It can be seen from Table 2 that in the case of the same spray process conditions, the leaching of three ore heaps of 6 to 10 m is not much changed, while the heap leaching rate of 12 m of heap height is 7.51 lower than that of the 10 m heap. %. Therefore, when the height of the ore heap is about 10m, both the better leaching index and the more minerals can be processed.
(two) into the heap granularity
The gold-bearing ore used for heap leaching is usually crushed first. The crushing particle size depends on the ore property and the size of the gold-embedded cloth. Generally, the finer ore-grained ore size is finer, the ore structure is looser and porous, and the gold leaching rate is higher during heap leaching. However, if the particle size of the heap leaching ore is too fine, the leaching rate of the heap leaching and leaching will be slowed down, and even the leaching and leaching process will not be carried out, which seriously affects the leaching rate of gold. The original ore samples of a mine are screened in five levels of 150, 100, 80, 50, and 20 mm. The gold grades are measured separately for each grade of product, and then the pile is sprayed for 60 days, and the section of the exit is at the top of the section. At 4, 6, and 8m, the grid sampling method is used to sample 100kg separately. The samples are mixed and sieved at 150, 100, 80, 50, and 20mm levels. The grades of each grade are separately sampled and the gold grade is calculated. Leach rate at each level. Compare the leaching rate to select the optimum immersion particle size. The test results are shown in Table 3.
It can be seen from Table 3 that when the ore particle size is d<80mm, the leaching rate of each grade ore is relatively high, and the difference is not large; when the ore particle size is d>80mm, the leaching rate of each grade is lower. And the larger the particle size, the faster the leaching rate decreases. In order to obtain a better leaching rate and to ensure a certain degree of crushing and washing treatment capacity, the ore size of the ore is selected to be less than 80 mm.
(III) Effect of NaCN concentration on gold leaching rate
The cyanide concentration is the main parameter determining the dissolution rate of gold. In low concentration cyanide solution, the reason for the high dissolution rate of gold is due to the high solubility of oxygen and the faster diffusion of oxygen and cyanide in dilute solutions. To. In addition, in the low concentration cyanide solution, the dissolution rate and quantity of the base metal will be greatly reduced, thereby reducing the consumption of cyanide and facilitating the dissolution of gold. Some minerals in the ore are easily oxidized by oxygen in the cyanide solution, so that a large amount of cyanide is consumed, and the dissolution rate of gold is lowered.
The tests with NaCN concentrations of 59, 89, 109, and 129 were carried out separately, and other process conditions were the same. The test results are shown in Table 4.
It can be seen from Table 4 that in the spray 2d, the leaching speed is faster when the spray liquid [NaCN] is 109 and 129, and the leaching speed is faster when the spray liquid [NaCN]>89 is sprayed for 3~5d. At 89-129, the leaching speed did not change much; at the 6th to 20th day of spraying, the leaching speed of the spray liquid [NaCN] concentration of 59-89 and 109-129 was not much different. Therefore, in industrial production, the spray liquid [NaCN] should be controlled as follows: spray liquid [NaCN] is controlled at 109 to 129 for 2d before spraying; 89 to 109 for control at 35d; and 6th to 20d for control at 59 to 89. After the first 20 days of spray leaching, about 55% of the gold has been leached. During the subsequent spraying period, the leaching of the spray [NaCN] is gradually reduced.
(4) Sprinkler system
In order to ensure the ideal leaching speed, a reasonable spraying system must be determined. For this reason, relevant tests have been carried out. The test results are shown in Table 5.
It can be seen from Table 5 that 3d before spraying, a higher leaching rate can be obtained by spraying with continuous spraying. In the 4th to 10th day of spraying, the leaching rate of continuous spraying is the smallest, only 15.55%; h sprayed for 0.5h, the leaching rate increased by 17.77%; on the 11th to 30th, the fastest increase of leaching rate was achieved by spraying 1.5h for 1.5h. In the 31st to 50th, three kinds of spray methods are adopted, and the increase value of the leaching rate is similar, and the method of stopping for 1 hour by spraying for 1 hour can save power consumption. Therefore, in industrial production, the first stage of spraying (first 3d) uses continuous spraying; the middle stage of spraying (4th to 30th) adopts the spraying mode of spraying for 0.5h for 0.5h, and the spraying later adopts the method of spraying for 1h and stopping for 1h. A better leaching rate is obtained.
(5) Spray strength
If the spray intensity is too small, it will cause insufficient CN-supply to participate in the reaction, affecting the leaching speed of gold; if the spray intensity is too large, it will lead to CN-excess and aggravate the loss of NaCN. Therefore, it is necessary to determine the reasonable spray strength through experiments. The cyanide spray strength was tested at 12 L/(m 2 ·h), 20 L/(m 2 ·h), and 25 L/(m 2 ·h), and the other process conditions were the same. The test results are shown in Table 6.
It can be seen from Table 6 that in the pre-spray period, a high leaching rate can be obtained by using a spray intensity of 25 L/(m2·h); a spray strength of 20 L/(m 2 ·h) can be obtained in the middle of the spray. The highest leaching rate increase value (49.59%); the maximum increase in the leaching rate of spray rate of 12L/(m 2 ·h) was 13.52%. Therefore, in industrial production, the spray intensity is 25L/(m 2 ·h) in the early stage, 20L/(m 2 ·h) in the middle of the spray, and 12L/(m 2 ·h) in the later stage of spraying. .
(6) Protection of alkali
In order to prevent the leaching agent 2 from cyanide hydrolysis, the cyanide is fully dissociated into cyanide ions and the cyanide leaching of gold is at the optimum pH (pH=10-11). A certain amount of alkali must be added during cyanidation. The pH of the heap is adjusted, and the added base is often referred to as a protective base. Caustic soda, caustic potash or lime can be used as a protective base. For this purpose, a lime dosage test was carried out, and the test results are shown in Table 7.
It can be seen from Table 7 that the unit consumption of the protective alkali is lowered, and the consumption of NaCN is obviously increased. To reduce the unit consumption of NaCN, it is necessary to ensure that the amount of the protective alkali and lime reaches 0.5 to 0.6 kg/t.
(7) Leaching time
The leaching time refers to the time from the start of the yard to the end of the spray. The length of the leaching time is directly related to the various process technologies and economic indicators of the heap leaching. The leaching time test results are shown in Table 8.
It can be seen from Table 8 that the prolonged leaching time and the increase of the amount of ton ore spray can significantly increase the heap leaching rate; the leaching time is prolonged, and the ton mine spray amount is reduced. Although the heap leaching rate can be improved, the NaCN unit consumption is significantly increased. After comprehensive analysis with other economic and technical indicators, the leaching time was determined to be about 60d.
(8) Comprehensive condition test
In order to verify the leaching conditions and technical indexes in the heap leaching process, the process comprehensive condition test was carried out. From the analysis of the test results, the choice of comprehensive conditions is relatively stable.
Fourth, the conclusion
1. The ore grade of Zijinshan Gold Mine is low, but the ore is highly oxidized and broken, easy to heap and easy to leach, and the production cost is low, which is the basis for the development of the mine.
2. The content of harmful elements in the ore is low, and the impact on the spray is minimal.
3. The spray liquid [NaCN] is controlled at 109-129 2d before spraying; 89-109 at 3~5d; 59-89 at 6~20d; the subsequent [NaCN] leaching is gradually Reduce the adjustment.
4. In industrial production, the spray method is used in the pre-spraying mode, the spray intensity is controlled at 25L/(m 2 ·h); the spray medium is sprayed for 1.5h for 0.5h, and the spray intensity is controlled. 20L/(m2·h) or so; spraying at 1.0h for 1.0h at the late stage of spraying, the spray intensity is controlled at about 12L/(m 2 ·h); better technical and economic indicators can be obtained.
references:
[1] Editorial Board of Leaching Technology. Leaching Technology [M]. Beijing: Atomic Energy Industry Press, 1994.
[2] Dai Xiaotong. Influencing factors and improvement measures of heap leaching rate of gold deposits [J]. World Mining Express, 2000, 16 (12): 451 ~ 452.
[3] Song Jianbin 1 Application study of static adsorption of Zijinshan gold deposit [J] 1 Mining Express, 2006171
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