Roasting of Cu-rich complex concentrates - A mineralogical investigation

Copper has assumed importance as a metal which is essential for realization of a sustainable modern society. Demand for copper is sharply increasing, and a supply shortfall is shortly anticipated. Such a scenario could adversely affect some of the major transformations directed toward reversal of climate change. Consequently, it is crucial to efficiently utilize all the resources available for copper extraction. This thesis investigates the challenges associated with Cu-rich complex concentrates, which are scantily used in the mainstream pyrometallurgical route of Cu-extraction. The roasting step, at the start of the pyrometallurgical-route is expected to resolve certain complexities in the incoming concentrate feed, for instance, through partial volatilization of the minor deleterious elements – As, Sb. Therefore, evaluation of the behavior of Cu-rich complex concentrates during roasting is the focus of the current study. Cu-rich complex concentrates are generally polymetallic, containing numerous major, minor and trace elements. In reality, these numerous elements in a complex concentrate occur as multiple sulphide and sometimes also as non-sulphide minerals. In this work, four Cu-rich complex concentrates are investigated for their initial mineralogy, followed by their evaluation in laboratory-scale roasting experiments between 200-700oC in inert atmosphere. These complex concentrates were produced from the Rockliden, Garpenberg and Maurliden deposits of Boliden Mineral AB in Sweden. Though industrial roasting involves a partially oxidative environment, the roasting experiments in this work were performed in an inert atmosphere which could be collectively used as a reference for future roasting experiments at higher oxidation potential. The main objective of the roasting experiments in inert atmosphere was to determine various features of the mineralogical interactions which could occur up to 700oC. The selected concentrates were found to comprise the: (1) major minerals – chalcopyrite, sphalerite, pyrite and galena; (2) minor minerals – sulfosalt and sulfarsenide minerals of As and Sb, also including a non-sulphur bearing mineral – silver antimonide, and; (3) trace elements – Cd, Mn, Hg (hosted by sphalerite) and Tl (hosted by galena). The high-temperature physicochemical interaction between the different minerals mainly involved – (1) solid-state assimilation of Cu-, Fe- and Zn-bearing minerals to form the ‘iss-phase’ existing in CuS-FeS-ZnS ternary