Dissolution and Passivation Mechanism of Chalcopyrite during Pressurized Water Leaching

Abstract

In this study, chemical leaching, XRD, SEM, and XPS analyses were conducted to investigate the dissolution and passivation mechanisms of chalcopyrite under pressurized oxidative conditions in water. The chemical leaching results showed that the chalcopyrite could be dissolved by pressurized leaching without any acid addition, i.e., in an O2–H2O system, and the copper leaching rate reached 96.4% under the optimal conditions of 180 °C, 1.5 MPa, 900 rpm, and 90 min. The XRD, SEM, and XPS data suggested that a large proportion of the chalcopyrite dissolved in solution via the mineral phase transformation of CuFeS2→Cu2+ and CuFeS2→CuS→Cu2+, i.e., some of the chalcopyrite directly leached into solution as Cu2+, and some of it was first converted to CuS and then to Cu2+. The primary passivation layers during the chalcopyrite pressurized water leaching were hematite, pyrite, and covellite; however, none of them covered the un-leached mineral surface or inhibited chalcopyrite dissolution, as long as the agitation speed and leaching time were maintained over 700 rpm and 60 min, respectively. Finally, a model of chalcopyrite’s dissolution and passivation mechanism during pressurized water leaching was proposed.

The Effects of Chloride on the High Temperature Pressure Oxidation of Chalcopyrite: Some Insights from Batch Tests—Part 2: Leach Residue Mineralogy

“…Covellite is indicated to be the most stable copper sulphide, being the end product derived from various copper sulphide minerals as discussed by Muszer et al [17]. These researchers also demonstrated covellite persists as an intermediate product during pressure oxidation of a mixed sulphide concentrate in 120 g/L sulphuric acid at 180 • C with oxygen partial pressure of 5 atm for beyond 4 h, albeit at a moderate stirrer speed of 400 rpm, similar to the finding of Jiang et al [15]. Furthermore, covellinisation of copper sulphide minerals does not hinder copper extraction at temperatures of 160 • C and below: using a synchrotron technique, Majuste et.…”

“…This conclusion is not contradicted by the results of this, and the previous study [1]. In comparison, the recent study of Jiang et al [15] reported chalcopyrite leaching (with no added acid) conducted at 160-180 • C, typically with a total pressure of 1.5 MPa (including partial pressure of oxygen), no suggestion for phases that could inhibit the reaction. This conclusion was based upon XPS analysis of leach residues generated when the agitation speed in their reactor was 700 rpm (or greater); at lower agitation speeds the reaction of chalcopyrite was slower and significant amounts of covellite intermediate could be detected.…”

“…Even at high temperatures (180-200 • C), the formation of copper sulphide intermediates has been noted, e.g., [15]. An upgrade in the copper content of chalcopyrite has been described under oxidising conditions by Bartlett [16] and Muszer et al [17] who generated predominantly digenite and covellite, respectively.…”