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The electrochemical oxidation behavior of Ce(III) in nitric acid and sulfuric acid media with various concentrations and compositions were investigated by cyclic voltammetry (CV) and potentiostatic electrolysis. In nitric acid media, the peak potential separation for the redox reactions of the Ce(III)/Ce(IV) couple shifted to base side with the increasing concentration of nitric acid from 1 to 6 M. The kinetics of the Ce(III)/Ce(IV) couple is rapid in high concentration nitric acid. The formal potential is independent of both proton and nitrate concentrations while the standard rate constant increases with added protons but is independent of nitrate concentration. Constant-potential electrolysis also shows that a high proton concentration is electrochemically favorable for the electron transfer of the Ce(III)/Ce(IV) couple and for a high Ce(IV) yield in nitric acid media. The current efficiency was ca. 75% for the oxidation process of Ce(III) at 298 K. A Ce(IV) yield of ca. 80% was achieved for the electrolysis of 100 mM Ce(III) in 6 M HNO 3 solution. In sulfuric acid media, the peak potential separation for the redox reactions of the Ce(III)/ Ce(IV) couple shifted to noble side with rising concentration of sulfuric acid from 0.1 to 2 M and then shifted to base side with further increase in the concentration. A Ce(IV) yield of ca. 95% was achieved for the potentiostatic electrolysis of 100 mM Ce(III) in 3 M H 2 SO 4 solution.

Successful amidoximation of SiO 2 / polyacrylonitrile composite (SiO 2 / PAO).• PAO/SiO 2 highly efficient for Ga (III) recovery from slightly acidic solution.• Ga(III) desorption using 0.5 M HCl solutions for sorbent recycling.• PAO/SiO 2 sorbent is selective for Ga(III) recovery from multi-metal solutions.• Ga(III) efficiently and selectively recovered from Bayer liquor using SiO 2 / PAO.