Thermal decomposition and leaching mechanisms of copper(II) oxalate (CuC2O4) raw material obtained from chalcopyrite concentrate

Abstract

A comprehensive understanding of the dissolution mechanisms of metal oxalates, both in their raw and thermally decomposed states, is critical for enhancing selective metal recovery in hydrometallurgical processes. The present study focuses on selective copper recovery from a CuC2O4-rich raw material obtained by leaching chalcopyrite concentrate with oxalic acid and hydrogen peroxide. The principal objective was to elucidate the dissolution behavior of low-solubility oxalate phases in various leaching media, before and after thermal decomposition. Leaching experiments were performed in two stages: (i) direct leaching of the raw material in HCl, HNO3, H2SO4, and NH3 solutions, and (ii) leaching after thermal decomposition at 200 - 400 degrees C. Phase transformations and dissolution mechanisms were systematically characterized using XRD, FTIR, SEM-EDS, and TGA - DTA analyses. Direct leaching achieved 52.1% Cu dissolution in 5 M HCl and 46.5% in 3 M NH3, whereas dissolution in H2SO4 and HNO3 remained minimal due to the limited solubility of CuC2O4. Upon thermal treatment at 400 degrees C, CuC2O4 fully decomposed into oxide and sulfate phases (Cu2O(SO4), Cu2O, and CuO). Under these conditions, leaching in 5 M NH3 resulted in up to 90.3% Cu dissolution with high selectivity. Overall, the findings confirm that metal oxalates generated from concentrates can be effectively and selectively dissolved in suitable solvents following controlled thermal decomposition, providing a viable strategy for improving hydrometallurgical copper recovery.