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Cyanide-containing wastewater recycling example
Akagi County, Hebei ore, is 50t / d mining smelt small businesses, all-clay mineral cyanide CIP process, process conditions: grinding fineness -0.074mm 90% to 94% pulp density of 40%, CaO The dosage is 9～10kg/t, the dosage of NaCN is 1.0～1.2kg/t, the leaching time is 12h, the pH value of the pulp is 10～11, the gold is adsorbed by coconut shell carbon, the carbon particle size is 6～20 mesh, the carbon density is 14kg/m 3 , the dipping Suction time 48h. Processing plant daily water 381.5m 3, wherein the use of fresh water 148m 3 / d, using a thickener overflow water 233.5m 3 / d, without using alkali treatment tailings chlorinated water returns 75m 3 / d.
The original set of living water treatment equipment originally installed is only treated with sewage in the rainy season from July to August each year, and recycled with tailings water for the rest of the time.
In the recycling of cyanide-containing tailings water, it is necessary to explore the extent to which the accumulation of cyanide and harmful heavy metals in the circulation affects the index and environmental factors.
1. Change law and elimination method of cyanide and heavy metals in the process of recycling cyanide-containing wastewater
By 20 consecutive tests cyanide-containing waste water recycling observed :( a) SCN - and other cyanate have gradually accumulated. (2) Heavy metals such as Cu, Pb, Zn and Fe are enriched with the increase of the number of cycles. (3) The tailings pond has a natural purifying effect on harmful elements such as cyanide and other heavy metals. In May 1989, the CN - purification rate was 65.38%, the Cu purification rate was 17.39%, and the August CN - purification rate was 77.78%, and the Cu purification rate was 30.35%. (4) CN - The growth trend is increasing with the increase of the number of cycles.
In order to solve the long-term accumulation of cyanide, cyanate and heavy metals, the environment and process are affected, and the tailings water is kept in circulation. The plant conducts a one-month alkaline chlorination treatment of sewage from July 15 to August 15, and the results can reduce the wastewater below the national required emission standards. This cycle can be used for a long time.
Second, the examination of the degree of environmental impact
The cyanide-containing wastewater is recycled and not discharged, and the impact on the environment is mainly studied, which is mainly the influence of the infiltration of sewage in the tailings pond on the groundwater. The three sides of the gold mine tailings reservoir in Chicheng County are 16m thick loess sub- clay layer, one side is tailings dam, the dam foundation is 80m, the dam height is 14m, the storage capacity is 90,000m 3 , and it can serve 11.2 years.
The nearest groundwater source downstream of the tailings pond is an eye well (300m from the dam). The wellhead is 7m lower than the dam foundation and the well water level is 23m. Therefore, this well is an excellent groundwater change observation point. The results of regular monitoring of the wells indicate that CN - ground has a slowly rising trend with an upward rate of 0.00041 mg/L per month, while the time in the CN - infiltrated wells in tailings is about one month. If the maximum CN - permissible concentration in the well is set to 0.03mg/L (below the national drinking water standard of 0.05mg/L), it should be 48 months, which means that 4 years of tailings treatment will not pollute the groundwater. .
Third, the impact on the process
The production practice of the first two years of the Chicheng gold mine proved that the use of tailings water recycling, because the tailings return water directly into the ball mill, increased the cyanide leaching time and increased the gold leaching rate; the welded cyanide wastewater concentrated in the tailings pond The slag still has the effect of re-leaching gold, so the tailings return water will dissolve the return of gold, so that the recovery rate of the actual gold received by the smelting is improved.
Fourth, technical and economic analysis (according to the use of tailings pond backwater statistics in 6 months)
(1) Multi-recovery of gold 1221g;
(2) Saving 62,360 yuan for sewage treatment;
(3) reducing the amount of sodium cyanide from 60 to 120 kg;
(4) Saving water resources and reducing costs by 9,700 yuan.
Xinqiao Gold Mine adopts cyanide tailings slurry after pressure filtration, and the tail liquid is returned to the operation system, which not only does not affect the cyanide operation, but also saves 20t of sodium cyanide every year, saves 300,000 yuan of sewage treatment fee, and adopts pressure filtration. After that, the washing rate is increased by 4%, and the annual benefit is 300,000 yuan.