Gallium extraction from synthetic Bayer liquors using Kelex 100-kerosene, the effect of loading and stripping conditions on selectivity

Solvent extraction with Kelex 100 has been recognised as a possible method for recovering gallium from Bayer liquors, but the practical process has not been so attractive as to cause a general technological break-through. The purpose of this research was to enhance the Ga/Al selectivity and efficiency of the extraction and re-extraction processes, while making the method as simple as possible. Instead of applying various additives and modifiers, the approach was based on the fundamental extraction kinetics with the pure kerosene/Kelex 100 system and a method of selective re-extraction boosted by possible chloro-complex formation in HCl media. The main factors examined during the extraction tests were solution pH, concentration of Al, amount of the reagent and the intensity of agitation, whereas HCl concentration was varied to improve the performance of the re-extraction step. The extraction results were interpreted in terms of the heterogeneous transfer mechanism. A Ga/Al selectivity index of almost 100 could be achieved at a Ga yield of ∼70% with 10–20% Kelex 100 in kerosene and the pH set to ∼14.3 from a NaOH solution containing 100 ppm Ga and 1100 ppm Al. As a practical source, the zeolite mother liquor has also proved suitable for the procedure. Aluminium carried over to the extractant can be separated from gallium during the combined re-extraction procedure, removing aluminium with 5–6 M HCl from the organic phase, then eluting gallium with ∼2 M hydrochloric acid solution.