Valves for copper leaching, solvent extraction and electrowinning

Valves play an important role in the LX-SX-EW process by ensuring that various liquid flows are kept within the optimum range. Because of the demanding requirements for some of the valve installations and the constant acidity, selecting the optimal valves can have a positive impact on the plant’s overall profitability.

Valves for the pregnant leach solution

The pregnant leach solution is the output product of leaching. It forms as sulfuric acid percolates through the ore pile while the copper content of the ore is introduced in the aqueous solution. At some sites, drainage systems move the solution to the next processing stage using gravity; other sites use pumps.

Butterfly and ball valves are good choices for PLS flow control. Chloride sometimes poses a challenge in PLS feed, in which case the valve material selection is an important factor to be considered. For instance, hastelloy steel is a typical choice, as it exhibits a very high resistance against corrosion.

Valves for the raffinate feed

Raffinate is a mild solution of sulfuric acid with a pH typically between 1.2-2.0. When choosing a valve, many of the choices are typically straightforward in terms of size and pressure class, but there are also factors that may need a proper evaluation to ensure the best possible outcome. In addition to material selection, the right body and seat designs ensure that the valves perform at their peak.

Valves for the rich electrolyte solution

In the stripping stage of the process, the copper in the organic solution transfers to an aqueous solution, resulting in a rich electrolyte solution. This solution is piped to the electrowinning stage. Pipe sizes vary from site to site and can be DN1000 or even bigger. As pressures are typically in the lower range, butterfly valves are a good choice and provide the lowest total cost of ownership.

LX-SX-EW aims to concentrate the aqueous copper solution from a few g/l to around 40-50 g/l and to eliminate the chloride, ferrous, manganese and other impurities that may cause problems in the downstream electrowinning process.

There are six different methods for leaching: heap, dump, in-situ, agitation, autoclave and vat. The leaching method used at each processing plant varies based on the ore chemistry and local conditions. Heap and vat leaching are common leaching methods.

In vat leaching, the process starts with the crushing, grinding and separation circuit followed by thickening. The slurry then enters vat leaching tanks and moves to solvent extraction through dewatering.

Heap leaching starts with the sprinkling of a low concentration sulfuric acid and water solution on a stockpile (leach pad) of low-grade ore.

The liquid percolates through the stockpile and dissolves copper minerals, producing an approx. 60% copper concentration called pregnant leach solution (PLS). The PLS then flows to a collection reservoir and to the solvent extraction plant; the copper is then transferred from the mildly acid aqueous leach solution to an organic solution.

After extraction, the copper-loaded extractant is fed to the stripping unit, where it is transferred from the organic solution to a strongly acid aqueous electrolyte solution.

This is followed by the final stage, electrowinning, where metal is recovered from the acid solution as it deposits to the cathode plates. In this step, an electric current is passed through a bath of the extracted material causing the copper to deposit onto metal plates and results in a pure form of the metal.