Editing Extractive metallurgy (section)

==== Metal recovery from oxide compounds with Ionometallurgy ====
Recovery of metals from oxide matrixes is generally carried out using mineral acids. However, electrochemical dissolution of metal oxides in DES can allow to enhance the dissolution up to more than 10 000 times in pH neutral solutions.<ref>{{cite journal |last1=Pateli |first1=I.M. |last2=Abbott |first2=A. |last3=Hartley |first3=J. |last4=Jenkin |first4=G.R.T |title=Electrochemical oxidation as alternative for dissolution of metal oxides in deep eutectic solvents |journal=Green Chemistry |date=2020 |volume=22 |issue=23 |pages=8360–8368 |doi=10.1039/D0GC03491F |s2cid=229243585 |url=https://pubs.rsc.org/en/content/articlehtml/2020/gc/d0gc03491f}}</ref>

Studies have shown that ionic oxides such as ZnO tend to have high solubility in ChCl:malonic acid, ChCl:urea and Ethaline, which can resemble the solubilities in aqueous acidic solutions, e.g., HCl. Covalent oxides such as TiO<sub>2</sub>, however, exhibits almost no solubility. The electrochemical dissolution of metal oxides is strongly dependent on the proton activity from the HBD, i.e. capability of the protons to act as oxygen acceptors, and on the temperature. It has been reported that [[eutectic]] ionic fluids of lower pH-values, such as ChCl:oxalic acid and ChCl:lactic acid, allow a better solubility than that of higher pH (e.g., ChCl:acetic acid).<ref>{{cite journal |last1=Pateli |first1=I.M. |last2=Thompson |first2=D. |last3=Alabdullah |first3=S.S.M |last4=Abbott |first4=A. |last5=Jenkin |first5=G.R.T. |last6=Hartley |first6=J. |title=The effect of pH and hydrogen bond donor on the dissolution of metal oxides in deep eutectic solvents |journal=Green Chemistry |date=2020 |volume=22 |issue=16 |pages=5476–5486 |doi=10.1039/D0GC02023K |s2cid=225401121 |url=https://pubs.rsc.org/en/content/articlelanding/2020/gc/d0gc02023k}}</ref> Hence, different solubilities can be obtained by using, for instance, different carboxylic acids as HBD.<ref>{{cite journal |last1=Abbott |first1=A. |last2=Boothby |first2=D. |last3=Capper |first3=G. |last4=Davies |first4=D.L. |last5=Rasheed |first5=R.K. |title=Deep Eutectic Solvents formed between choline chloride and carboxylic acids: Versatile alternatives to ionic liquids |journal=J. Am. Chem. Soc. |date=2004 |volume=126 |issue=29 |pages=9142–9147 |doi=10.1021/ja048266j |pmid=15264850 |url=https://pubs.acs.org/doi/10.1021/ja048266j}}</ref>