Selective recovery of germanium with N-methylglucamine functional resin from sulfate solutions

Growing demand of germanium and uncertainties in supply create a need for research into efficient separation methods. Ion exchange recovery of germanium from sulfate solutions was studied with equilibrium experiments, column experiments, and modeling. Based on screening of four commercial resins by equilibrium experiments, a bifunctional N-methylglucamine resin was selected for dynamic adsorption studies and modeling. The adsorption of germanium onto the resin depended strongly on pH. The first pKa value of germanic acid, Ge(OH)4, is 9 and its anionic dissociation products (oxoanions) were adsorbed to the nitrogen containing groups by anion exchange mechanism. The germanium species were all adsorbed to glucose sites. Other metal ions in the studied multimetal feeds decreased the Ge adsorption directly by competition, and indirectly by acting as buffers to prevent pH increase and the dissociation of germanic acid. Iron was found to have a particularly detrimental effect on the adsorption.A competitive adsorption model was used to describe the sorption equilibrium of germanic acid and its dissociation products to glucose sites and to amine groups. A transport-dispersive model with a solid film linear driving force model was employed for the dynamic modeling. Authentic and simulated feed solutions were used to study the effect of competing metals. The feed solutions contained 63–490 mg/L Ge and metal sulfates so that ionic strengths were between 0.58 and 5.82 mol/L. The constructed simulation model predicted the equilibrium isotherms and the breakthrough curves of germanium well.

► N-methylglucamine resin was found to have good potential in recovery of germanium.
► Competitive isotherms were used to describe Ge adsorption to both functional groups.
► Other metals affect the adsorption also by acting as a pH buffers.
► Both Fe2+ and Fe3+ were found to have detrimental effect on germanium adsorption.
► Transport-dispersive model was used for describing dynamic adsorption.