Functionalization of Cellulose Adsorbents with Catechol derivatives for the Effective Separation and Recovery of Gallium from Acidic Solutions

The selective extraction, separation, and recovery of gallium (Ga), one of the critical elements, is essential due to its role in clean energy technologies and its low reserves. Herein, different catechol derivatives (Pn)-functionalized cellulose substrates were developed using 3,4 dihydroxybenzoic acid (P1), 3,4,5-trihydroxybenzoic acid (P2), and 3,4-dihydroxyhydrocinnamic acid (P3) through esterification reaction and used for selective extraction of gallium from dilute acidic solutions. Adsorption experiments at pH 3 displayed a maximum Ga adsorption capacity of 31.50, 14.22, and 29.50 mg g-1 for P1, P2, and P3, respectively. Langmuir isotherm was illustrated as the best-fitting model to explain the equilibrium adsorption. Kinetic data were best fitted with pseudo-second order and intraparticle diffusion model, indicating that the adsorption process involves chemisorption as well as intraparticle diffusion. The newly synthesized adsorbents P1 and P3 are 10-300 times more selective for Ga than As, Fe, Al, Cd, and Ge from the mixed solution (pH 3.0) of 1:1 metal ratio. Moreover, high selectivity for gallium was achieved from binary solutions of Ga:Zn, Ga:Ge, and Ga:As in 1:10 (SelGa/M >5), 1:50 (SelGa/M >2), and 1:100 (SelGa/M >2) metal ratio, suggesting that the adsorbent can separate Ga (III) from Zn (II), Ge (IV), and As (III) at the optimal conditions. The adsorbents (P1-P3) were characterized with various spectroscopic and microscopic techniques showing that the surface morphology of cellulose was greatly changed after functionalization. The Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis demonstrated that the adsorption of Ga onto the developed adsorbers was attributed to chelation between hydroxyl groups of catechol and gallium ions. This study shows the synthesis of low-cost, sustainable adsorbents for the selective recovery of gallium in dilute acidic solutions.