Synthesis, analysis and characterisation of CuFeS2(s) towards superior, green Cu(aq) leaching
Creators: name: Godfrey, Daniel
Publisher: name: Imperial College London
Year: 2016

description: Efforts to decrease reliance on traditional high-consumption CuFeS2(s) pyrometallurgy, have focused on delivering hydrometallurgic solutions to the beneficiation of sulfide ores. Ionic liquids (IL) have been proposed as a potentially higher performance and more benign alternative to conventional acid-SO42-(aq) for CuFeS2(s) dissolution, although the sheer number of IL variants complicates the search for the most efficient systems. This study focuses on Cu2+(aq)-leaching performance in hydrogensulfate IL(aq)-CuFeS2(s) systems and comparisons with equivalent acidity conventional-SO42-(aq) references. A single commercial CuFeS2(s) ore source is used throughout. A combinatorial strategy is applied to low-volume scale identification of high performance IL(aq) lixiviant systems. Implementation of a high performance, flexible automated workstation is presented with broad applicability to study of acidic-CuFeS2(s) dissolution. Electrochemical ASV is demonstrated to be an effective screening tool for [Cu2+](aq) extraction quantification, as verified by ICP-AES measurements throughout. Successfully ASV modifications are described; most notably a procedure for automated in situ electrochemical monitoring of 120 mL-scale CuFeS2(s) dissolution. High accuracy reconstructed (continuous) Cu2+(aq) extraction profiles offer precise rate determinations and treatment of previously unconsidered profile features. Application of the robotic custom instrument demonstrates high-throughput electrochemical screening of IL(aq) sample arrays with minimal consumption and precise [Cu2+](aq) measurements. Proof-of-concept screening assays find &gt;102 difference in IL(aq) activities in equivalent conditions and at least 35-fold larger than sample-to sample variability. A large degree of variability in IL(aq) lixiviant activity is presented at nominal [HSO4](aq) and acidity for closely structurally-related ILs. Best performing [CnCmim][HSO4](aq) and [NR4∙HSO4(aq)](aq) IL(aq) systems are presented, alongside the confirmation of a non-trivial [IL](aq) dependence, which is a contrasting result to previous work with Cu flotation concentrates. Several ILs have been found to provide significant leaching at low acidity, ‘additive-quantity’ [IL](aq). Best performing IL(aq) systems have been scrutinised in an up-scaled tank leaching configuration for ~1 month leach durations. 450 mmol∙dm-3 NH4∙HSO4(aq) is demonstrated to enhance CuFeS2(s) dissolution compared with equivalent acidity H2SO4 under otherwise equal conditions. A combination of surface, bulk and solution speciation studies are untaken to obtain a global view of the IL(aq)-CuFeS2(s) dissolution process, with continuous in situ monitoring of key physical conditions ([Mn+](aq), [H+](aq), T, Eh). The role of surface oxygen and sulfur in CuFeS2(s) dissolution hindrance is examined. Experimental insights provided by consideration of the effect of SO42-(aq) and base addition to the primitive IL(aq) lixiviant media has led to the proposal of a HSO4-IL dissolution mechanism for CuFeS2(s).