Catechol-Functionalized Chitosan Synthesis and Selective Extraction of Germanium (IV) from Acidic Solutions

Germanium (Ge) is one of the critical elements that lack an efficient economic recovery process from dilute sources. An improved catechol-based adsorbent, catechol-functionalized chitosan (C–Cat), was synthesized to recover germanium (Ge) from dilute acidic solutions. The adsorbent was also compared with an N-methylglucamine-based commercial adsorbent (Purolite S108) for optimum pH conditions, ion selectivity, adsorption isotherm, adsorption kinetics, and regeneration ability. The newly synthesized C–Cat exhibited higher selectivity against various competing ions than the commercial one (their respective Langmuir capacity was 22.72 and 79.66 mg/g at pH 3) and was more selective for Ge than other adsorbents reported in the literature. Linear free-energy relationships between the distribution coefficients and the metal hydrolysis constants were developed for both C–Cat and S108 at pH 3 and can be used for preliminary prediction of the selectivity of the adsorbents. Adsorptions data followed Langmuir isotherm for both adsorbents, and the kinetics data were well-fitted with pseudo-second-order kinetics. The C–Cat was proven to be completely reusable for multiple cycles after initial re-equilibration.