We produce our copper by leaching the metal from the waste dumps generated by previous mining activities
This process is far less cost intensive than traditional mining, as there is no need to drill, blast or transport ore – the waste dump rocks can be leached in-situ. This allows us to produce copper cheaply and efficiently.
The process we use to produce copper is called Solvent Extraction and Electrowinning (SX-EW). SX-EW is a two-stage hydrometallurgical process that first extracts and upgrades acid-soluble copper from low-grade waste dumps, using dilute sulphuric acid, followed by extraction and upgrading of the leached copper solutions into an organic solvent mix containing a chemical that selectively reacts with and removes the copper. The copper is then extracted from the organic solvent using a strong solution of acid which is then plated as very high purity copper onto stainless steel cathode blanks using an electrolytic procedure (electrowinning).
At the Kounrad SX-EW project, the process consists of delivering the weak acid solution to the top of the waste dumps and irrigating the surface of the dump, through a pump and pipeline system.
The solution is distributed evenly and at a controlled rate via an extensive network of dripper pipes, which are similar to those used by gardeners for watering flower beds.
The very extensive (over 3,900km) network of drippers is mobile and can be relocated to a new area (leach pad) once the previous area has been leached out, which normally takes six to twelve months.
Copper contained in the rock is dissolved by the acidic solution that slowly drains through the dump until it reaches the natural ground level, and then flows out from under the dump, following the natural bedrock gradient, into a thick-plastic lined collector trench which runs along the edge of the dump.
From the collector trench the solution (now called “pregnant leach solution” or PLS) is pumped into storage ponds within the plant’s perimeter. These ponds not act only as a large buffer store but also assist with settling out any fine clay or rock particles, which can upset the SX process if not removed.
From the ponds, the copper-bearing PLS is pumped through the SX stage of the process. The equipment in this section looks like six large swimming pools and in these the PLS is intensively mixed with the organic reagents, and then allowed to flow and split into a copper-rich organic phase and a low-grade acidic aqueous phase. The aqueous solution is then recycled back to the dumps to dissolve more copper, whilst the organic reagent is treated further to increase the copper content in a high-strength acid solution.
This rich copper solution, known as rich electrolyte, is then pumped to the nearby EW building where it is plated by electrolysis in 74 cells that are similar in look to a large car battery. Placed inside these cells are 2,550 lead anode plates and 2,500 stainless steel cathode sheets.
As the electric current runs through the electrolyte the copper molecules attach themselves to the cathodes and sheets of at least 99.99%-purity copper are formed. Every three days on a planned schedule a third of the stainless steel cathodes are lifted from the cells and the copper is removed (stripped) from them. Once the copper is removed the cathodes are returned to the cells and the cycle is repeated.
The leaching, SX and EW processes run simultaneously and continuously for 24 hours a day, 7 days a week, and the copper plates that are harvested each day are stored in a secure area, prior to being shipped by rail to the end customer – normally once or twice per month.