Dump Leaching

Low-grade porphyry copper mining generated large volumes of waste rock containing 0.1–0.4% copper, historically discarded in dumps and mined-out areas, causing underutilization of metal resources. This study aimed to evaluate the technical feasibility and mechanistic basis for dump leaching of copper-bearing wastes using acid ferric sulfate and bacterially regenerated ferric solutions to increase copper recovery and reduce reagent costs. The methodology combined thermodynamic analysis of chemical leaching reactions with examination of bacterial oxidation pathways for sulfide minerals and ferrous iron, and evaluation of operational leaching schemes including in-place, heap, percolation, and agitation leaching applied to heterogeneous mine wastes. Dissolution reactions for major copper sulfides and oxides were quantified using ferric sulfate, sulfuric acid, and ammonia–carbonate lixiviants, and the role of iron-oxidizing bacteria in regenerating ferric iron and sulfuric acid from pyrite was assessed. Copper produced from waste and leached areas increased from approximately 4% of total copper output at the end of World War II to 10% by the early 1960s, with projections of 20–30% by the early 1970s. Cement copper product from dump leaching operations assayed 70–90% copper. Bacterial regeneration of ferric sulfate eliminated most chemical oxidant replacement, enabling profitable treatment of 0.1–0.4% copper material and significantly reducing leach reagent consumption. These outcomes indicate that integrated chemical–bacterial dump leaching can convert previously uneconomic mine rejects into a major copper source while improving overall resource efficiency.