Heap Leaching of Gold Ore
Heap leaching is an effective gold ore processing technology for low grade gold ores.Heap leaching is also one of the cyanide leaching methods.This method is mainly used to deal with oxidized ore, by-product ore or off-balance ore produced in the process of shaft opening up, which all contain low-grade gold, and also used to deal with gold-bearing tailings and gold-bearing cinders from non-ferrous smelters and chemical plants.Heap leaching is actually the leaching of gold - bearing rock piles by cyanide solution on impermeable site.
Heap leaching is an effective gold ore processing technology for low grade gold ores.Heap leaching is also one of the cyanide leaching methods.This method is mainly used to deal with oxidized ore, by-product ore or off-balance ore produced in the process of shaft opening up, which all contain low-grade gold, and also used to deal with gold-bearing tailings and gold-bearing cinders from non-ferrous smelters and chemical plants.Heap leaching is actually the leaching of gold - bearing rock piles by cyanide solution on impermeable site.After the gold and silver in the ore is dissolved, the gold and silver flow into the expensive liquid storage tank along the pre-designed groove on the site.The precious liquid containing gold and silver is adsorbed by activated carbon and then desorbed to recover gold and silver.The process from expensive liquid to gold ingots is the same as cyanidation.(cyanide leaching process for gold extraction)
Selection and construction of leaching site:
The selection and construction of impermeable leaching sites is critical.If the site is not suitable or the construction quality is not good, the gold and silver will be lost.Heap leaching site site site, sometimes selected in the mine near the mouth of the "waste rock" pile.The materials for the site are also locally sourced.Use soil, clay, plastic film or asphalt to build impervious liners.To ensure that the heap leaching site is watertight, the ore to be processed is stacked on this site.The production scale can be determined according to the ore supply situation, site size, heap leaching after the waste rock or tailings transport and unloading storage plan.(a traditional example of gold extraction by cyanidation)Heap leaching sites are to be repeatedly used, to use artificial film matting.As a disposable site, natural clay can be used as the liner and sodium carbonate solution can be sprayed, which can improve the viscosity and permeability.
Process Flow Chart
Heap leaching process:
With the site, hundreds of tons or even thousands of tons of low-grade gold ore were piled into 1.2-12m high ore piles.The solution containing sodium cyanide is sprayed evenly and comprehensively on the pile with a sprinkler, and a layer of mesh system is installed on the top of the pile to ensure uniform spraying.The heap leaching site is slightly sloped, with plastic-lined gutters designed to allow the dissolved gold to flow into the storage tank.The particle size composition of raw ore or raw material, the lowest leaching grade and the leaching processing conditions are usually determined by experiments.Heap - leached ores are porous oxidized ores and do not need to be crushed.Ore larger than 300mm needs to be crushed.Powder ore and fine powder containing gold material also through granulation (pellet), too large, cyanide can not fully dissolve the gold ore;The material is too fine, water permeability is not good, heap leaching can not be carried out.(gold extraction technology by carbon leaching)The concentration of sodium cyanide in heap leaching solution is usually kept within the range of 0.01%-0.05%, and the pH is adjusted to 11 to make the cyanide stable.NaOH is often used for pH adjustment. Although it is more expensive, lime cannot be used because lime tends to scale and makes percolation difficult (if percolation performance is good, lime is still used for pH adjustment).The cyanide solution is uniformly sprayed over the entire heap under pressure.Continuous spraying or intermittent spraying can be adopted to maintain the spraying time of at least 8-12h every day, and the spraying intensity is generally about 6L/ (m ·h).During the first few days of heap leaching, the cyanide and lime (CaO) contents in the discharged liquid decreased rapidly, but the gold content was high.In order to ensure the necessary concentration of flotation agent, need to be added at any time.Additional, as a result of open-air job, moisture evaporates fast, also should fill at any time add the clear water of certain amount.The leaching liquid generally contains higher grade of gold within 5-10 days, and then the grade gradually decreases.When the grade is lower than 0.1g/m, if the heap leaching time continues to be extended, it will not be economical, and the production can be stopped at this time.(amalgamated gold from gold ores and concentrates)
Heap leaching of gold is to build a heap of low-grade gold ore or flotation tailings on the bottom material, and then dissolve the gold and silver in the ore by circulating spray of sodium cyanide solution.The gold - containing liquid can be recovered by activated carbon adsorption, zinc replacement precipitation or direct electrodeposition.Gold extraction by heap leaching is characterized by simple process, easy operation, less equipment, less power consumption, less investment, quick effect and low production cost.Heap leaching is used to treat low grade ore of 0.5 ~ 3g/t, the recovery rate of gold is 50% ~ 80%, even can reach 90%.As a result, heap leaching has made it possible to economically recover many small gold mines, low-grade ores, tailings or waste rocks that were previously considered to be of no economic value.Heap leaching was widely used in industrial production in China in 1980s.
Heap leaching is suitable for the treatment of the following mineral resources:
1. Low-grade gold and silver ores that are large in scale and previously considered unexploitable;
2. Low-grade gold-bearing "waste rock" stripped in the mining process;
3. Middle and low-grade gold-bearing ores extracted from geological pit exploration and mining;
4. gold grade is slightly higher, but the scale is small, should not be built in mechanized dressing plant gold and silver ore;
5. Use conventional cyanidation method to treat economically disadvantageous gold mines;
6. gold smelting slag, high grade tailings and gold containing large waste yard.
The production process of heap leaching gold mainly consists of the construction of heap leaching site, the pretreatment of ore (crushing or granulating), the construction of heap, the spraying leaching, the recovery of gold in gold-bearing liquid and the disinfection and unloading of waste ore heap.Heap leaching production cost: the heap leaching cost of tailings is about 30 ~ 40 yuan/ton, and the heap leaching cost of raw ore is about 40 ~ 50 yuan/ton.