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COPPER RECOVER AND COPPER RICH SOLUTION

The images on the left showcase the heap leach pads, equipped with a sprinkler system, and the associated collection ponds containing the leached Copper solution. In the center, a simplified diagram illustrates the Copper extraction process. The upper photo on the right displays the solvent extraction plant (left) and the electrolytic plant (right). Finally, the bottom right-hand photo captures a Copper-rich solution just before it enters the second phase (stripping) at the solvent extraction plant – notice the stirrer assembly.

The heart of the hydrometallurgical process at Milpillas was heap leaching. On specially constructed, impermeable pads, the crushed ore was irrigated with a dilute sulfuric acid solution, known as the lixiviant. As the acid solution percolated through the ore pile, it selectively dissolved the Copper minerals, forming a Copper-rich solution called the pregnant leach solution (PLS). The efficiency of this stage depended on several factors, including the permeability of the ore heap, the concentration of the acid, and the contact time between the lixiviant and the Copper minerals. The Milpillas mine specifically targeted soluble Copper minerals, making heap leaching an ideal and cost-effective method for their extraction.

Following the leaching process, the pregnant leach solution, now laden with dissolved Copper, was directed to the solvent extraction (SX) plant. Solvent extraction is a purification and concentration step. In this stage, the PLS is mixed with an organic based solvent (i.e., alkyl Salicylaldoximes), which have a strong affinity for Copper ions. The Copper ions transfer from the aqueous PLS to the organic phase, leaving behind impurities in the aqueous phase now called the raffinate. This process effectively separates Copper from other undesirable elements that might have been leached from the ore. After the Copper is loaded into the organic solvent, the loaded organic phase is then stripped with a strong sulfuric acid solution, which reverses the process, transferring the concentrated Copper ions back into an aqueous solution. This resulting highly purified and concentrated Copper solution is known as the electrolyte. The final electrolytic cells then deposited high-purity Copper onto cathodes, a process that relied on a consistent and clean electrolyte composition to achieve "Grade A cathodic Copper."

Original photos courtesy of Jose Vazquez, diagram by Silvia. (Author: silvia)