Dissolution of low-grade chalcopyrite concentrate in acidified nitrite electrolyte

Copper sulfides are generally treated by flotation followed by smelting. However, concerns over air pollution have made governments tighten their regulations regarding the emission of sulfur dioxide. Thus, hydrometallurgical techniques seem to be the most convenient methods to selectively extract non-ferrous metals. In this study, the leaching kinetics of copper from low-grade concentrate by nitrite salt was investigated. The probabilities of several chemical reactions and the products formed were explained based on literature data and thermodynamic analysis. The copper concentrate was obtained from a flotation plant in the Kastamonu region of Turkey. Leaching experiments were conducted in sulfuric acid electrolyte (0.5 M–2.0 M) containing nitrite compounds (0.025 M–0.15 M) at a moderate temperature (80–120 °C). A high level of copper recovery (96%) from low-grade chalcopyrite concentrate was obtained under a total pressure of 6 atm at 120 °C within 2 h when using small amounts of nitrite species due to their autocatalytic behavior in acidic solutions. Elemental sulfur was the primary leaching product on the mineral surface, as confirmed using XRD and SEM/EDX analysis, and the formation of the sulfur layer inhibited leaching rate at later stage of dissolution process.

► Even small amounts of nitrite were found to be capable of leaching chalcopyrite.
► Oxy-nitrogen species have a catalytic effect on the dissolution of copper.
► The best results were obtained with 0.1 M NaNO2 at 120 °C after 4 h.
► The sulfur layer inhibited leaching rate at later stage of dissolution process.