Leeching (Electro-winning)
Leaching and electrowinning are two interconnected processes widely used in gold mining to extract and purify gold from ore. During leaching, commonly through cyanidation, a cyanide solution dissolves gold from crushed and ground ore, forming a soluble gold-cyanide complex. The gold-laden solution is then transferred to an electrowinning cell, where an electric current causes gold ions to deposit onto a cathode, typically made of steel wool, as a solid metal. This process is highly efficient for recovering gold from low-grade ores but requires stringent environmental controls due to the use of cyanide. Together, leaching and electrowinning enable the economical recovery of gold from complex or low-concentration mineral deposits.
Leaching and electrowinning are critical processes in gold mining used to extract and purify gold from its ores or concentrates. Here’s an explanation of each:
1. Leaching
Leaching involves using chemical solutions to dissolve gold from ore. The most common leaching method is the cyanidation process, where a cyanide solution is used to extract gold. The steps include:
- Crushing and grinding: The ore is crushed and ground to increase surface area for chemical reactions.
- Leaching process: The ore is mixed with a cyanide solution in tanks, heap leach pads, or vat leaching systems.
- Gold dissolution: Cyanide binds with gold to form a soluble complex, usually gold-cyanide (Au(CN)₂⁻), allowing the gold to be dissolved into the solution.
2. Electrowinning
Electrowinning is a purification step that follows leaching. It uses an electrochemical process to recover gold from the cyanide solution:
- The gold-laden solution from leaching is transferred to an electrowinning cell.
- A current is applied through electrodes in the cell, causing gold ions in the solution to deposit onto the cathode (usually made of steel wool or a similar material).
- Gold accumulates on the cathode, while impurities remain in the solution.
- The cathodes are later processed to extract the purified gold.
Combined Process:
- Together, leaching and electrowinning form a system to efficiently extract and recover gold.
- Cyanidation dissolves the gold, and electrowinning retrieves it in a concentrated, solid form ready for smelting or further refining.
These processes are popular because they allow for the recovery of gold from low-grade ores and complex mineral deposits that would otherwise be uneconomical to process. However, environmental concerns, particularly related to cyanide use, require strict controls and regulations.