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Do You Know How Is Gold Ore Mined?
The process of gold ore refining is usually divided into six steps: crushing, grinding, beneficiation, leaching, recovery, and refining, covering the entire process from raw ore processing to refining, and each step requires specific equipment and processes.
Process and equipment for gold ore refining
1. Crushing
The purpose of crushing is to crush the raw ore into smaller particles (usually ≤30mm) for subsequent processing.
There are three stages of crushing
| Coarse crushing | Use a jaw crusher to crush the ore to 100-150mm. |
| Medium crushing | Cone crusher further crushes to 20-50mm. |
| Fine crushing | Roll crusher or impact crusher crushes the ore to ≤30mm. |
2. Grinding
The grinding step is to grind the crushed ore into fine powder (particle size is usually ≤0.074mm) to fully dissociate the gold minerals and make the ore easier to process in the next step. Crushing and grinding is the process of crushing and grinding the ore into powder. The purpose of this is to make the ore easier to process in the next step. The most common method of grinding is ball milling, which is to put the ore and steel balls into a rotating container and use the impact and friction of the steel balls to grind the ore into powder.
This process requires wet grinding with a ball mill or a rod mill, which forms a closed loop with classification equipment (such as spiral classifiers and hydrocyclones) to ensure that the particle size meets the standard.
3. Ore dressing
Ore dressing is a key step in extracting gold. The purpose of ore dressing is to separate the gold from the ore. Ore dressing methods include physical ore dressing and chemical ore dressing. Physical ore dressing is a method of separating different minerals in the ore by using the physical properties of different minerals. For example, gravity separation is used to separate minerals with higher specific gravity.
Chemical ore dressing is a method of separating minerals by chemical reactions. For example, chemical reagents are added to the ore to make different minerals react chemically to separate gold.
This process requires ore dressing equipment.
Two common methods of ore dressing:
| a. Flotation |
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| b. Gravity separation |
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4. Leaching
Leaching is the process of extracting gold from ore. Leaching methods include cyanide leaching and gold leaching. Cyanide leaching is to mix the ore with a cyanide solution to ionize the gold and form a gold cyanide complex in the solution. Then, by adding activated carbon or other reducing agents, the gold cyanide complex is reduced to metallic gold. Gold leaching is to mix the ore with sodium hydroxide and mercury to form mercury hydride gold with the mercury, and then heat it with fire to evaporate the mercury and leave the gold.
This process requires a separator, a leaching tank (with a stirring device), an adsorption tank, etc.
5. Recovery
Recovery is to extract gold from a solution or activated carbon.
There are two ways to recover gold.
| a. Activated carbon adsorption method (CIP/CIL) |
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| b. Zinc powder replacement method (Merrill-Crowe) |
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6. Refining
Refining is the process of further purifying the extracted gold, the purpose is to purify the gold mud to a high purity of more than 99.9%. Refining methods include fire refining and wet refining. Fire refining is the process of heating gold to high temperature to oxidize or volatilize impurities.
For example, heating gold to high temperature to oxidize silver to form silver oxide, and then dissolving the silver oxide with hydrochloric acid to leave pure silver. Wet refining is to purify gold by dissolving and reducing.
For example, dissolving gold in sodium hydroxide, and then dissolving sodium hydroxide with hydrochloric acid to obtain pure gold.
This process requires the use of electric arc furnaces or induction furnaces, electrolysis cells, etc.
Extracting gold from gold ore is a complex process that requires a combination of multiple methods. Ore dressing, crushing and grinding, leaching and refining are the main steps in extracting gold. Different methods are suitable for different types of ores and gold content.
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