Increasing the Duration of Dump Leaching of Copper Under Winter Conditions

The successful introduction of the technology of copper production using a dump leaching method is associated with low capital investments, low cost of copper extraction, quick payback, high labor productivity, and the absence of energy- and material-intensive operations. The experience of implementing dump leaching technology has shown that negative temperatures significantly worsen the conditions and the rate of migration of metal-bearing solutions, resulting in freezing of blocks in winter. Therefore, the main task of increasing the efficiency of dump leaching in Kazakhstan is to enable the successful use of the process under winter conditions in a sharply continental climate (at a temperature of –25°C). The article describes the commercial implementation of the model of winter leaching of copper from the overburden dumps of spent sulfide ores at the Kounrad mine at negative ambient temperatures. The method is applied to mature dumps of various heights, while employing a surface irrigation device and facilitating collection of the product solutions into a pit equipped with a secondary containment berm. In this case, the bottom of the pit and the sides of the berm are covered with a waterproof layer of clay and a geosynthetic screen. In order to organize a sustainable leaching process during winter, the evaporation surfaces of the leaching blocks are covered with a geocomposite having thermal insulation and waterproofing properties. Efficient and continuous flow of the dump-based production process throughout the calendar year is ensured by maintaining a process-favorable temperature regime of the solutions and dump surfaces under extreme winter temperatures and high winds. It was shown that the temperature of the solution supplied for leaching can be reduced by 3°C due to better thermal insulation properties of the geocomposite. The pressure drop in the lines of the block covered with geocomposite during the entire period of pilot tests did not exceed 0.5 MPa, which indicates excellent efficiency of the geocomposite and a large margin in terms of performance parameters of the block at extremely low temperatures.