Biosorption of tungstate onto garlic peel loaded with Fe(III), Ce(III), and Ti(IV)

In present study, garlic peel (GP) was modified by loading with Fe(III), Ti(IV), and Ce(III) through a cation exchange process, i.e., nGP-COOH + Mⁿ⁺ = (nGP-COO)-Mⁿ⁺ + nH⁺ (M = Fe, Ce, Ti), which could adsorb tungstate effectively under the weakly acidic conditions. The optimal initial pH for maximum adsorption of W(VI) was determined at 1~3 for Ti-GP, 1~4 for Fe-GP, and 3 for Ce-GP, respectively; and at pH 2.5, the corresponding maximum adsorption capacity for Fe-GP, Ti-GP, and Ce-GP was evaluated as 91.5 mg/g, 83 mg/g, and 84 mg/g tungsten respectively. Coexisting anions like chloride, sulfate, and carbonate showed little effect on tungsten adsorption, while fluoride and phosphate inhibited the adsorption drastically. The column adsorption showed that the breakthrough point for Ce-GP, Ti-GP, and Fe-GP was 180 min, 200 min, and 270 min respectively. And 0.1 mol/L NaOH effectively eluted the adsorbed tungsten, and concentration of the eluted solution had almost 6, 19.9, and 22 factors of the initial tungstate concentration correspondingly.