Heap leaching method
Heap leaching (HL) technology of gold extraction has been known for about a hundred years. In the second half or XX century this technology became widely used for extraction of precious metals from ore deposits in the United States. Presently HL is a leading technology of gold extraction from the ore in the United States.
The technology is based on hydrometallurgical procedures essentially consisting of various chemical reactions and electrophysical processes. The precious metal is extracted from the ore being dissolved in sodium cyane solution during ore spraying. Thereafter the solution is purified (adsorption-desorption) in special filters. Subsequently the purified solution undergoes electrolysis – the process whereby the metal is extracted.
Experts identify the following major advantages of HL method:
- feasibility of application at small-size ore deposits, where the use of other traditional methods is not economically justifiable;
- low capital costs;
- relatively low prime cost of the final product;
- fast ROI.
However, there are some limitations of this technology:
- ore processibility (i.e., ore cyanation has to be possible);
- certain difficulties in implementing the technology in the local climatic conditions.
In 1970ies the soviet scientists made an attempt to implement the HL technology in the condition of Far North. The experiment ended up as a failure, whereafter no further attempts to investigate or implement this method were made. In 1996, Seligdar placer miners guild, taking into account depletion of the placer gold deposits selected new strategic production direction – gold extraction from lode deposits.
Construction of the HL plant with the throughput of 100 thousand tons per year started in 1996. The pilot site at Lopukhovskoye deposit was in operation for 3 years.
In 1999, a heap leaching plant with the throughput of 350 thousand tons per year was commissioned at Samolazovskoye deposit site. Over this year, 208 kilograms of the precious metal was extracted by HL method.
In 2003, the issue of regeneration of active carbon used in the process was resolved. Thermal reactivation module was designed, installed and commissioned.
A significant improvement of the technology of oxidized gold ore processing at the HL plant of Samolazovskoye mining complex was implementation of the recirculation system for the gold-enriched solutions on the stacks with low gold content (additional gold recovery). This approach allowed increasing the throughput in the summer period without renovating the HL plant and without involving recirculation solutions into continuous adsorption cycles, periodically performing adsorption of the sections with relatively high gold content.
In 2005, filtration plant for the process solutions fed to ore stack spraying module was installed. Implementation of the filtration unit with a drum cage screen helps to prevent clogging the spraying system and improves operation of the system during winter period when the spraying system cleanup is impossible due to snow blanket on the ore stacks.
Present ore throughput of the heap leaching plant at Samolazovskoye is 700 thousand tons per year.