Heap leaching is a method used to recover metals like gold, copper and uranium, from oxide ores. After mining, crushed ore is stacked on a lined pad. A leaching solution is sprayed onto the ore and percolates through to dissolve specific minerals. The mineral-rich leach solution is collected around the base of the pad and piped to a SX-EW plant where pure metal is recovered.
Proposed Heap Leach Process video
Solvent extraction electrowinning (SX-EW) is the method of recovering pure metal from the leach solution. In the first step, solvent extraction (SX), the metal in the leach solution is extracted from the mineral using powerful solvents. In the second step, electrowinning (EW), pure metal is recovered from the solvent solution.
Electrowinning is based on the principles of electrolysis. The solvent solution contains positively charged metal ions and negatively charged anions. The purpose of electrowinning is to recover the postively charged metal ions.
To begin the process, two electrodes are inserted into the solvent solution and hooked up to a power source. When the electric current is turned on, the electrodes gain a charge. The positively charged electrode is called the anode, and the negatively charged electrode is called the cathode. The electric current passes through the solution and causes the positively charged metal ions to move towards the cathode and plate onto it. The solution is replenished with positive ions from the anode, and the process continues.
To use copper as an example: the process is complete when there are no copper ions left in the solvent solution; they have all been plated onto the cathode. The cathode copper (99.99% pure) is peeled from the cathode and used to manufacture goods.
Copper Heap Leach & SX-EW Slideshow
In situ leach is a method of mineral extraction similar to heap leaching, that is used to mine underground oxide deposits. The leaching solution is introduced into the deposit through bore holes. It percolates through the ore body and collects in wells constructed around the deposit. The metal-bearing solution is then pumped to the surface, and the metal is recovered by solvent extraction electrowinning (SX-EW).