Solvometallurgical Process for the Recovery of Copper from Chrysocolla in Monoethanolamine

Difficulties in beneficiation and hydrometallurgicalprocessinglimit the potential of chrysocolla as a copper ore mineral. Solvoleachingin a solution of 3 M NH4Cl in monoethanolamine (MEA) enabledefficient and selective copper extraction from high-grade chrysocollaore. The leaching temperature was a decisive parameter; leaching atelevated temperatures progressively improved copper extraction yields,with the highest yield of 88% obtained by leaching at 100 & DEG;Cfor 4 h. SEM-EDX analysis indicated the presence of copper-depletedsilica surface layers in residual copper-containing chunks that eventuallyhinder complete copper extraction. However, it was demonstrated thateither milling the leach residue to create fresh accessible surfacesor milling the starting material into finer particle size could improvecopper extraction yields. FTIR analysis suggests that the leachingmechanism occurs via coordination of the amine functional group ofMEA to copper(II) ions. The ammonium chloride salt in the lixiviantis expected to have provided chloride counteranions that kept theformed copper-ammine complex in solution. Copper was recoveredfrom the pregnant leach solution by sulfide precipitation with anaqueous (NH4)(2)S solution. Copper was precipitatedas a covellite phase, with more than 98% recovery yield. Furthermore,reusability of the lixiviant was demonstrated by four leaching-precipitationcycles.