Zinc Recovery from an Extreme Copper-Free Acid Mine Drainage: Studying the Prior Separation of Ferric Iron by Solvent Extraction using AliCy and/or Alkalinization

Zn recovery attempts from a copper-free extreme Acid Mine Drainage with ~ 53 g/L Fe and ~ 2 g/L Zn revealed Fe co-extraction in solvent extraction with 0.9 M D2EHPA or a mixture of 0.72 M D2EHPA and 0.18 M Cyanex 272, and simultaneous precipitation of Fe during zinc sulfide recovery through biogenic sulfide addition. Therefore, alkalinization, solvent extraction with the self-prepared ionic liquid AliCy diluted in kerosene, and combinations of both these methods were studied for the separation of ferric iron (Fe 3+ ) from such water, prior to Zn recovery. The most efficient strategy tested was a solvent extraction cycle with AliCy followed by alkalinization of its aqueous raffinate to pH 3.25 or 3.5. As a result of this approach, ~ 92% of Fe 3+ is separated by SX and the remaining is removed by precipitation, with just ~ 12% or ~ 17% Zn losses, respectively. Afterwards, the highest Zn recovery from water resulting from such combination of processes was achieved by precipitation through addition of biogenic sulfide at pH = 3.5. The obtained precipitates are nanoparticles of Wurzite and Sphalerite (ZnS) of sizes between 2 to 22 nm agglomerated into larger structures. This work shows for the first time the potential of AliCy to separate Fe 3+ from acidic multimetallic solutions, a known contaminant of several metal recovery processes. Graphical Abstract