Editing Extractive metallurgy (section)

==== Metal recovery from sulfide minerals with ionometallurgy ====
Metal sulfides (e.g., pyrite FeS<sub>2</sub>, arsenopyrite FeAsS, chalcopyrite CuFeS<sub>2</sub>) are normally processed by chemical oxidation either in aqueous media or at high temperatures. In fact, most base metals, e.g., aluminium, chromium, must be (electro)chemically reduced at high temperatures by which the process entails a high energy demand, and sometimes large volumes of aqueous waste is generated. In aqueous media chalcopyrite, for instance, is more difficult to dissolve chemically than covellite and chalcocite due to surface effects (formation of polysulfide species,<ref>{{cite journal |last1=Ghahremaninezhad |first1=A. |last2=Dixon |first2=D.G. |last3=Asselin |first3=E. |title=Electrochemical and XPS analysis of chalcopyrite (CuFeS2) dissolution in sulfuric acid solution |journal=Electrochimica Acta |date=2013 |volume=87 |pages=97–112 |doi=10.1016/j.electacta.2012.07.119 |url=https://www.sciencedirect.com/science/article/pii/S0013468612012996}}</ref><ref>{{cite journal |last1=Dreisinger |first1=D. |last2=Abed |first2=N. |title=A fundamental study of the reductive leaching of chalcopyrite using metallic iron part I: kinetic analysis |journal=Hydrometallurgy |date=2002 |volume=60 |issue=1–3 |pages=293–296 |doi=10.1016/S0304-386X(02)00079-8 |bibcode=2002HydMe..66...37D |url=https://www.sciencedirect.com/science/article/pii/S0304386X02000798}}</ref>). The presence of Cl<sup>−</sup> ions has been suggested to alter the morphology of any sulfide surface formed, allowing the sulfide mineral to leach more easily by preventing passivation.<ref>{{cite journal |last1=Pikna |first1=L. |last2=Lux |first2=L. |last3=Grygar |first3=T. |title=Electrochemical dissolution of chalcopyrite studied by voltammetry of immobilized microparticles |journal=Chemical Papers |date=2006 |volume=60 |issue=4 |pages=293–296|doi=10.2478/s11696-006-0051-7 |s2cid=95349687 }}</ref> DESs provide a high Cl<sup>−</sup> ion concentration and low water content, whilst reducing the need for either high additional salt or acid concentrations, circumventing most oxide chemistry. Thus, the electrodissolution of sulfide minerals has demonstrated promising results in DES media in absence of passivation layers, with the release into the solution of metal ions which could be recovered from solution.

During extraction of copper from copper sulfide minerals with Ethaline, chalcocite (Cu<sub>2</sub>S) and covellite (CuS) produce a yellow solution, indicating that [CuCl<sub>4</sub>]<sup>2−</sup> complex are formed. Meanwhile, in the solution formed from chalcopyrite, Cu<sup>2+</sup> and Cu<sup>+</sup> species co-exist in solution due to the generation of reducing Fe<sup>2+</sup> species at the cathode. The best selective recovery of copper (>97%) from chalcopyrite can be obtained with a mixed DES of 20 wt.% ChCl-oxalic acid and 80 wt.% Ethaline.<ref>{{cite journal |last1=Abbott |first1=A. |last2=Al-Bassam |first2=A.Z.M. |last3=Goddard |first3=A. |last4=Harris |first4=R.C. |last5=Jenkin |first5=G.R.T. |last6=Nisbet |first6=J. |last7=Wieland |first7=M. |title=Dissolution of pyrite and other Fe – S – As minerals using deep eutectic solvents |journal=Green Chemistry |date=2017 |volume=19 |issue=9 |pages=2225–2233 |doi=10.1039/C7GC00334J |url=https://pubs.rsc.org/en/content/articlelanding/2017/gc/c7gc00334j|hdl=2381/40192 |hdl-access=free }}</ref>