Low-grade chalcopyrite ore, heap leaching or smelting recovery route?

Abstract

Chalcopyrite, the major mineral source of copper, is commonly treated pyrometallurgically, using froth flotation, smelting, converting and electrorefining processes. The ore treatment however is limited to the cut-off grade concentration below which the extraction is not economically viable. In this study a comparison of feasibility of the pyrometallurgical and hydrometallurgical treatment of low grade (0.23%–0.35% Cu), high content chalcopyrite (>90% CuFeS2) ore were studied from both technical and economic viewpoints. On a technical stance, the results of a pilot test on froth flotation of 100 t of low-grade ore are presented. The pilot test results confirm the generation of a Cu concentrate of a grade range 23.3–19.6% Cu with a copper recovery in the range 90.9–78.1%. For the hydrometallurgical treatment, bio heap leaching of 40,000 t of low-grade ore using agglomeration and aeration was proven to achieve a copper recovery of 32.6% for the chalcopyrite portion of the ore over 326 days of operation.On the economic side, the operating cost of the process per tonne of copper cathode for both processes were reported. The operating cost for the pyrometallurgical (PM) processing plant was calculated to be 1.4 times less than the hydrometallurgical (HM) processing plant. The sales revenue of the PM route was also higher than that of the HM route due to the byproducts credit. Capital cost estimates were made assuming that the current solvent extraction/electrowinning (SX/EW) facilities in a HM route and the current smelting and electrorefining plants in the PM route have enough free capacity to absorb the upstream outputs. Applying the copper extraction efficiencies of the pilot plants, the profitability indicators for both routes in treatment of 3000,000 t ore/year was studied. The impact of the interest rate was found significant in economic preference of the HM route over the PM route. This is due to the high capital cost of the mineral processing plant despite of the higher operating cost of the HM plant. The capital cost of the mineral processing plant can make the HM route feasible at interest rates higher than 27.5%. At discount rates lower than 27.5%, the PM route process is viable over the HM route at copper market price of US$9500/t. A drop in copper selling price to US$6000/t acts in favor of the HM route, making it feasible at interest rates higher than 22.4%. For a general scenario where the construction of SX/EW and smelter/refinery plants are required, the discount rate at which the net present value (NPV) of the two routes are equal has decreased from 27.5% to 17%. In this scenario, for discount rates higher than 17%, the HM route with 31% total copper recovery is more feasible than the PM route with 79% recovery.