Introduction of Heap Leaching Process For Gold Extraction
While there are many different processes to remove gold from its encapsulating ore, cyanide heap leaching (cyanidation) is perhaps the most flexible and economic gold ore processing method used to extract gold from low-grade gold ores. In this process, ore is firstly crushed to fine particles. By spraying leaching solution to the large piles, the gold-containing solution is leached, A cyanide solution (NaCN or KCN) is elevated to a high pH level (>10.5pH) so that free cyanide (CN-) will dissolve the gold in the ore. Then used the gold processing method of carbon adsorption, zinc powder displacement device and so on to separate gold from the liquid.. The main process as bellow:
1. Ore Preparation: The preparation stage of ore mainly includes crushing, granulation and pretreatment. The purpose is to improve the leach ability of the ore and the permeability of the leach heap, avoid uneven liquid flow, blockage, channeling and other phenomena, improve the recovery rate of gold ore and reduce the leaching rate. fluid consumption.
2. Ore Broken: According to the nature and process requirements of gold ore, different crushing processes are implemented. The heap leaching of waste ore is generally not broken (30%), the ore particle size after the second-stage crushing is 30–50mm (53%), and the ore particle size after the third-stage crushing is 9–19mm (17%). Practice has proved that crushing is one of the key technical links to ensure good permeability of ore and improve the leaching rate of gold ore.
3. Ore Granulation: For powder ore and ore with high clay content, granulation operation is required first. Add a certain amount (3–6kg/t) of cement and lime adhesives to the ore, and add an appropriate amount of sodium cyanide solution to keep the ore at 8–12% humidity, solidify for 8–12 hours, and form agglomerates. Through the granulation treatment, the permeability of the ore heap is improved, the oxygen supply is sufficient, and the gold is dissolved by cyanidation in advance, which greatly improves the leaching rate of gold. This process often uses a cylindrical granulator, a disc granulator, and a multi-section belt granulator. Among them, the belt granulator can granulate the fine ore and send it directly to the heap leaching field, and the cylindrical granulator is especially suitable for the ore with high clay content.
4. Building the Heap Pool: The purpose of building the pile is to make the ore pile have good and uniform permeability, and to ensure that the slope will not collapse. The height of the ore pile mainly depends on the permeability of the ore pile, the content of the leaching agent in the leaching solution, and the equipment and method of building the pile.
5. Solution Preparation: Water and leaching agent are formulated into a solution or leaching solution for leaching useful components from gold ore according to a certain formula. Most Common leaching agents include sulfuric acid, nitric acid, hydrochloric acid, sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, ferric sulfate, chloride, sodium iodide, potassium iodide, ammonium sulfate, air, oxygen, permanganate, Contains nitrogen oxides, hydrogen peroxide and chlorates, etc. The formula and dosage of the solution leaching solution should be determined according to the ore type, mineral composition and chemical composition. Alkaline sodium cyanide solution is often used as the leaching solution for heap leaching of gold mines.
6. Distributing and collecting liquid: Liquid distribution is to spray the leaching liquid evenly on the top surface of the ore pile.Taking spraying as an example, the spraying pipe network is made of high-strength polyethylene plastic pipes, and the spray head adopts a rotating and swinging spray head, with a large spray radius, large and uniform spray droplets, not easy to atomize, and easy to install. In the spraying process, one is to make the solution spray evenly on the ore pile, and the other is to achieve the required spraying intensity, that is, the spraying volume per unit time per unit area, usually 0.1–0.4L /m•min, the spraying time is about 1/3–1/2 of the total time. After spraying, the rich liquid from the bottom of the pile flows into the liquid collecting tank through the liquid ditch, and then is pumped to the workshop for processing.
7. Rich Liquid Processing: Gold ore is extracted by carbon adsorption and (or precipitation). Activated carbon becomes gold-loaded carbon due to the adsorption of gold in pulp. After the adsorption operation is completed, the pulp containing gold-loaded carbon is sent to the carbon extraction screen through the air lifter to separate the pulp and activated carbon. After screening and washing, the pulp is sent to the desorption electrolysis operation. Under the condition of high temperature and high pressure, anions that are easily adsorbed by activated carbon are added to the desorption system, and Au(CN)2- is replaced to obtain gold mud and lean carbon, thereby realizing gold desorption. The precious liquid obtained by desorption of gold-loaded carbon is recovered by ionization method to obtain solid gold.
