Efficient recovery of aluminum, lithium, iron and gallium from coal fly ash leachate via coextraction and stepwise stripping

The recovery of critical metals from industrial waste is very important and challenging. This work proposed an efficient process for recovering aluminum, lithium, iron and gallium from coal fly ash leachate. Firstly, 98.1 %, 86.6 % and 99.8 % of iron, lithium and gallium are coextracted by tributyl phosphate (TBP), facilitating the subsequent use of the aluminum raffinate. The spectroscopic analysis verifies the formation of [Li(TBP)2][FeCl4] and [Li(TBP)2][GaCl4]. Afterwards, the effective separation of lithium, iron, gallium in TBP is achieved by stepwise stripping. Lithium can be almost completely stripped using 6 mol/L HCl with free iron and gallium of loss. An extremely high separation factor of iron and gallium (αFe/Ga, 1175) can be achieved through reduction stripping by precisely controlling pH value and oxidation–reduction potential. Finally, about 99.5 % of gallium can be stripped with 0 ∼ 1 mol/L HCl. This work realizes the synergistic recovery of valuable metals from waste resources.