MICROSCOPY AND XRD INVESTIGATIONS OF THE PRODUCT LAYER FORMED DURING CHALCOPYRITE LEACHING IN COPPER(II) CHLORIDE SOLUTIONS

This study presents a microscopy investigation of chalcopyrite surface product layers formed in concentrated cupric chloride solutions, similar to those used in the HydroCopper® process. The physical appearance as well as chemical composition of chalcopyrite reaction product layers was studied as a function of pH (from 1 to 3) and leaching time. Microscopic methods, such as stereo-optical microscopy, scanning electron microscopy (SEM) analyses, and X-ray diffraction analyses were applied. To study the chalcopyrite reaction product layers, mineral surfaces were leached either at open circuit potential (OCP) or treated by anodic polarization. It was shown that at lower pH values, a gray elemental sulfur layer was the prevailing phase in the reaction product layer even with longer (22 h) leaching times. With increasing pH (from 2 to 3), the reaction product layer became more yellow-brown, and consisted mainly of FeOOH. Additionally, elemental sulfur was observed at higher pH. At pH 1, the thickness of the reaction product layer increased from approximately 1 to 9 μm with increasing leaching time up to 22 hours. At pH 2, the layer grew up to approximately 10 μm, and at pH 3, up to approximately 14 μm.