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Due to the special role of gold , re-selection of gold from selected metal tailings has received more attention. Practice has proved that due to the backward mining and smelting technology, a considerable part of the valuable elements such as gold and silver are lost in the tailings. According to relevant information, for every 1t of gold produced in China, about 2t of gold reserves are consumed, and the recovery rate is only about 50%. That is to say, about half of the gold reserves remain in the tailings and slag. Foreign practice shows that about 50% of the gold in the metal mine can be recycled.
Mine production in the 1970s before the completion of China's gold, mineral processing flotation plant they use, re-election, amalgamation, amalgamation or + flotation + flotation re-election and other traditional technology, low level of technical equipment, production targets poor, The recovery rate of gold is low. The grade of gold in tailings is mostly above 1g/t, and some mines even reach 2~3g/t; the mines with high ore content are more complex mines or high-grade mines, and the gold grade in tailings is more than 3g/t. With the improvement of the level of smelting technology in recent years, especially after the introduction and promotion of the whole mud cyanide carbon pulp production process in China, this part of the old tailings has once again become an important resource for gold mines. The ore dressing cost is calculated according to the whole mud cyanide carbon slurry production process. Under the condition that the tailings transportation distance is less than 1km, the general breakeven point grade is 0.8g/t. Therefore, if the tailings gold grade is greater than 0.8g/t, it can be recycled again. At the same time, the recovery of associated components in gold tailings, such as lead , zinc , copper , sulfur, etc., should also be taken seriously.
1. Recovery of iron from gold mine tailings
(1) Magnetic-heavy combined recycling process
The Yuehe River in southern Shaanxi traverses the two cities and counties of Ankang and Hanyin. There are 4 gold mines in Wuli, Ankang, Hengkou and Hanyin along the river, 9 gold mining vessels and 3 onshore plants. There are 21 kinds of minerals in the tailings produced by the gold mining ship and the onshore selection plant. The minerals are mainly composed of ferromagnetic minerals, supplemented by weak magnetic minerals, and mixed with trace amounts of non-magnetic minerals. only 4: magnetite (42%), hematite (18%), titanium ore (18%), garnet (17%), of which aluminum garnet-based iron garnet. The iron ore-based iron concentrate is a strong magnetic mineral, which has the highest content in the gold tailings, generally 60%, and the content in the grain size is less than 90%.
Considering that the dust in the tailings of the plant has been re-elected (the gold mine is re-elected) medium-washed, the dry sorting process can be used to sort the iron concentrate, which can simplify the process equipment. It also reduces dewatering, concentration and filtration operations, reducing floor space and mineral processing water.
According to the characteristics of the tailings of the plant, Ankang Gold Mine adopts Φ600×600 (214.97kA/m) permanent magnet single-roller dry sorter and CGR-54 type (1592.36kA/m) hydromagnetic counter-roller strong magnetic dry sorter. The two-stage dry magnetic separation process of separating magnetite, hematite (collectively called iron concentrate) and ilmenite and garnet from the tailings is shown in Figure 1. At the end of the process, it is added. Two XZY2100×1050 shakers are used to sort the gold in the mudstone waste rock. Using this process, Ankang Gold Mine can obtain 1700t of iron concentrate from the tailings of the plant, recovering 2.187kg of gold, iron concentrate with a conservative price of 136 yuan / t, gold with 96 yuan / g, annual output value of 44.12 Ten thousand yuan.
The Hengkou Gold Mine in southern Shaanxi used a single Φ600×600mm (87.58kA/m) permanent magnet single-roller dry sorter to sort iron concentrate from the tailings of the plant. The concentrate yield reached 31.2%. The grade is 65%~68%. From the tailings, the iron concentrate can be produced at 1100t/a, and the shaker can be used to select 1.5309kg of sand gold to create a production value of nearly 300,000 yuan.
Figure 1 Ankang gold ore separation iron concentrate process
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(2) Magnetic separation-baking-magnetic separation process
According to the nature of tailings, Hanyin Gold Mine selected a wet magnetic separator with a field strength of 135.35kA/m to sort iron concentrate from tailings. The tailings after sorting iron concentrates were processed by roasting-magnetic separation. The ilmenite and garnet are sorted out, and the production process is shown in Figure 2. According to preliminary estimates, it can produce 360t of ilmenite, 468t of garnet and 216t of magnetite selected at the end of iron selection. From this, 1.218kg of fine gold chips will be sorted, and the total output value will reach 1.7 million yuan.
Figure 2 Process for sorting ilmenite and garnet in Hanyin gold mine
2. Recovery of gold and silver from gold tailings by carbon slurry method
The Yindongpo Gold Mine was completed and put into operation at 100t/d in 1981. After 1985, the beneficiation process was a carbon slurry process, and the production capacity was increased to 250t/d. Before the establishment of the new tailings pond in 1992, the old tailings pond stocked up to 900,000 tons of recoverable tailings with high gold content, containing about 1665kg of gold and 25t of silver.
In 1996, the ore dressing plant began to use the original 250t/d carbon slurry plant for industrial practice of tailings treatment. The whole mud cyanide carbon pulp gold extraction process was used to recover gold and silver from old tailings. The production process is as follows: for the mining of tailings, a simple chain bucket mining vessel with a capacity of 250t/d is used. The tailings are transferred from the sand pump to the 250t/d carbon slurry plant after being pulverized on the ship, and the Φ1500mm×3000mm is fed. The ball mill and the spiral classifier form a closed-circuit grinding. The overflow is fed into the Φ250mm cyclone, and the cyclone forms a two-stage closed-circuit grinding with the No. 2 (Φ1500mm×3000mm) ball mill. The graded overflow is fed into the Φ18m concentration tank, concentrated and leached for adsorption, during the leaching adsorption process. In order to expand the processing capacity, the index will be further improved, and the vacuum pump will be used instead of the vacuum pump. The gold-loaded charcoal produced by the side-dipping process will be used to produce the finished gold. The flow chart of the principle of the metallurgical process is shown in Figure 3.
Figure 3 tailings carbon slurry method gold extraction process
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After industrial production practice, the main indicators have achieved satisfactory results. The production capacity is above 250t/d, the tailings concentration is about 20%, the fineness is -0.074mm, which is about 55%, the double-helix classifier overflow is -0.074mm, accounting for 75%, and the cyclone graded overflow is -0.074mm. 93%, leaching concentration of 38% to 40%, leaching time of 32h or more, calcium oxide dosage of 3000g / t, sodium cyanide dosage of 1000g / t, five-stage adsorption average bottom carbon density of 10g / L. The main indicators are as follows: dip quality: gold 2.83g / t, silver 39g / t, gold leaching rate of 86.5%, silver leaching rate of 48%, gold smelting total recovery rate of 80.4%, total silver smelting recovery rate It is 38.2%.
According to the preliminary investigation of the tailings resources of the old tailings pond, the tailings with a gold grade of more than 2.5g/t are about 380,000 tons, which can be used for 4 to 5 years in the production of carbon pulp plants. According to the practice of industrial production, it can be extracted from tailings. The recovery of gold is 760kg, silver is 5t, and the output value is more than 70 million yuan. At the same time, it is pointed out that due to the low cost of processing tailings, the tailings treated with more than 1g/t are also slightly profitable. It not only increases the gold output, but also reduces the production cost of the enterprise. Therefore, it is more than 1g/t. The tailings are also advantageous.
Third, the recovery of sulfur from gold tailings
The type of ore in the Qibaoshan gold deposit in Shandong Province is gold, copper and sulfur symbiotic ore. The metal sulfide is mainly pyrite, and there are a small amount of chalcopyrite and porphyrite. The gold-bearing minerals mainly include natural gold and a small amount of silver and gold. mirror oxides, siderite main gangue minerals are quartz, sericite and the like. The selection process uses a grinding and preferential flotation process to obtain gold and copper concentrate products at one time. Since 1995, the sulfur concentrate has been recovered from the gold tailings. The sulfur recovery method was used to recover sulfur. However, due to the high cost, the cyclone pretreatment process was adopted in the second half of 1996, which reduced the cost of sulfur selection. 45%, achieved very good results.
Analysis of the tailings of the preferential flotation was found. The pulp not only has a high pH value, but also contains many fine lime particles. At the same time, due to the coarse particle size of the pyrite in the ore and the density is larger than that of the gangue mineral, the cyclone is used to concentrate and demineralize the gold ore tailings slurry and discard it. In the fine mud part, the sand and water can be stirred and scrubed to restore the floatability of the pyrite, and the sulfur concentrate can be obtained through the next flotation operation. The Φ350mm cyclone is installed above the agitation tank, the grit sand enters the agitation tank, and the fresh water is added. The sulfur flotation is selected by a rough selection and a sweeping process, and the xanthate is added 60g/t and the pine oil 40g/t.
The process does not use sulfuric acid, which reduces the cost of the sulfur-selected concentrate. The grade of the obtained sulfur concentrate is 37.6%, the recovery rate is 82.46%, and the concentrate contains less mud, which is easy to precipitate and dehydrate, and the annual benefit is about 1.2 million yuan.
Fourth, gold tailings heap leaching
A small heap leaching test was carried out on the amalgam-flotation tailings in the Andi gold mine in Sanmenxia City. A total of 1640t tailings were piled up. The gold content of the tailings was 4~5g/t. After the heap leaching, the gold content of the final tailings was obtained. 0.7 g / t, leaching rate of 80.56%, carbon adsorption rate of 99.30%, desorption rate of 99.30%, total recovery of 79.44% of technical indicators.
V. Foreign gold recovery from tailings
South Africa is the world's largest gold producer and the first country to start recovering gold from tailings on a large scale. In South Africa, there are an estimated 3.4 billion tons of gold ore tailings with a gold content of 0.2 to 2 g/t, and an annual output of about 80 million tons of tailings. Currently, 12 of the 19 flotation plants in South Africa are processing tailings. Among them, 6 treatments recycle old tailings, and 6 treat tailings in the production process, from which gold is recovered. South Africa built the world's largest tailings reprocessing project in 1985 (Anglo-American's Ergo tailings treatment plant), which can process 2 million tons of tailings per month.
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