Heap Leaching Problems: Practical Considerations, Such As Loss of Water in Leaching, conflict with Proposal Not to Recirculate Solution-Further Contributions to Theory of the Process

This document is a technical discussion of heap leaching, focusing on the chemistry and economics of copper recovery from low‑grade ores. The authors respond to Posnjak’s laboratory work on the catalytic acceleration of ferrous iron oxidation by copper, arguing that in real heap-leach solutions copper is already present in sufficient concentration, so further acceleration offers limited practical benefit. They emphasize that heap leaching and leaching in place are inherently “rough” methods, justified only for ore grades too low to support the costs of mining, crushing, and controlled tank leaching, and that economic constraints, not lack of chemical knowledge, limit process refinement. The paper challenges recommendations against recirculating solutions after cementation on iron, citing water-loss, iron-supply, and waste-disposal problems, and contends that returning such liquors to the heaps is the only broadly practical approach. It also critiques certain assumptions about iron and acid generation from pyrite, the role of ferric iron in copper dissolution, and the physical constraints (e.g., capillarity, particle size) that differentiate true heap leaching from more intensive leaching practices. Finally, it examines the Fe–Cu redox equilibrium thermodynamically to estimate cuprous ion concentrations in typical liquors, showing that the theoretical equilibrium behavior must be considered when evaluating proposed changes in heap-leach practice.