Recovery of gallium from leach solutions of zinc refinery residues by stepwise solvent extraction with N235 and Cyanex 272

A novel approach was proposed for the extraction of gallium from high-ferric and strongly acidic sulfate leach solutions from zinc refinery residue. The stepwise separation was carried out using N235 and Cyanex 272 in the first and second steps, respectively. The results showed that N235 could selectively remove iron and H2SO4 and provide suitable conditions for the subsequent extraction by Cyanex 272. The co-extracted zinc, gallium, and iron were separated by stepwise stripping. In batch tests, 97.9% of iron was selectively extracted from solutions through three-stage cross-current extraction by using an organic system consisting of 30% (v/v) N235 and 10% (v/v) tributyl phosphate in sulfonated kerosene with an aqueous/organic (A/O) ratio of 1:1, while the percentage extractions of other metals were <3% (the separation factors of beta(Fe/Ga), beta(Fe/Zn), beta(Fe/Cu), and beta(Fe/Cd), were determined to be 4.1x10(3), 1.7x10(3), 1.8x10(3), and 2.3x10(3), respectively). In the loaded organic system, 99.7% of iron was stripped using 0.5 mol/L H2SO4 followed by treatment with a sodium carbonate solution for regeneration. The raffinate with pH = 2.67 could be directly used for the extraction by Cyanex 272. A total of >99.9% gallium, >99.9% remaining iron, and 49.7% zinc were co-extracted through four-stage counter-current extraction by using an organic system consisting of 30% (v/v) Cyanex 272 in sulfonated kerosene with an A/O ratio of 1:1, while the percentage extractions of other metals (copper and cadmium) were negligible (the separation factors of beta(Ga/Zn), beta(Ga/Fe), beta(Ga/Cu), and beta(Ga/Cd), were determined to be 6.1x10(3), 2.7x10(-1), 3.3x10(6), and 8, respectively). Furthermore, >99.9% zinc, 99.7% gallium, and 98.9% iron in the loaded organic system were efficiently separated through a stepwise stripping process by using 6 mol/L HCl, 0.5 mol/L H2SO4, and 0.6 mol/L H2C2O4 (the separation factors of beta(Zn/Ga), beta(Zn/Fe), and beta(Ga/Fe), were determined to be 1.1x10(6), 4.4x10(4), and 6.4x10(4), respectively). Overall, 99.7% of gallium was separated and extracted into the strip liquor, resulting in a concentration of 1502 mg/L.

Automated summary

A novel method was proposed for the extraction of gallium from high-ferric and strongly acidic sulfate leach solutions, achieving efficient separation of metals through multiple stepwise processes. The method demonstrated high selectivity for iron removal and gallium extraction, leading to a concentrated gallium solution with a concentration of 1502 mg/L.