Since all gold recovery processes wants to reduce the consumption of reagents, the recycle of cyanide from tailings is probably the most useful idea to be considered in the design of any gold operation with cyanidation. The typical methods employed to reuse cyanide are direct reuse, AVR process, ion exchange resins and activated carbon.
- Direct reuse
Probably this is the most common idea employed in gold operations. Cyanidation tailings contain free cyanide and lime, which may be recycled directly from the tailing pond solution. Heap leaching operations generates barren solutions from electrowinning and the solution is usually recycled to the any part of the process. One option is to send the solution to the pad. In this case, the free cyanide and alkalinity must be corrected to the right level and restart all the process again. Obviously, the system must be design to eliminate the solution when the presence of any undesirable metal is high. In other words the process design must include alternatives to the cyanide solution. A similar criterion is adopted in Carbon-In-Pulp or Carbon-In-Leach operations. These processes need to recycle the solution from the tailings pond and/or tailings thickener overflow.
Also, tailings systems are considered an extra leaching reactor due to gold particles continue reacting with free cyanide. Then, when the solution is recycle, the process gains a little more of gold (e.g. 0.5%). The presence of other metals is influenced by their solubility in cyanide and the equilibrium reached in the system.
Leaching operations are used to store the solution from tailings in tanks so that they can deliver the solution to the right point. Fresh and recycled water can be mixed in order to get a balance between the desired concentration of cyanide and the recycled flow. It is important to take a control of the pH, free cyanide and dissolved metals so that the information on water quality can be accessed immediately.