Removal of Cr(III) from aqueous solutions using waste kelp-derived biochar

This study aimed to investigate the feasibility of using biochar derived from waste kelp biochar (KB) to remove Cr(III) from aqueous solutions. Scanning electron microscopy-energy-dispersive X-ray spectroscopy analysis revealed that KB could successfully adsorb Cr(III), while Fourier transforms infrared spectroscopy characterization suggested that electrostatic interaction was the major mechanism for the adsorption of Cr(III) on KB. Kinetic and isotherm studies on Cr(III) adsorption revealed that the pseudo-second-order kinetic model and the Langmuir model could adequately explain the adsorption of Cr(III) on KB. The maximum adsorption capacity of KB for Cr(III) was found to be 39.16 mg/g, while 91.13% of Cr(III) removal could be achieved by adding KB to aqueous solutions with an initial Cr(III) concentration of 25 mg/L at 0.9 g/L. Our experiments on cation competition demon-strated that the presence of Ca²⁺ could markedly inhibit the adsorption of Cr(III) by KB, although the inhibition was not observed with the presence of K⁺, Na⁺, and Mg²⁺ in the solution. When monovalent anions such as C₅ H₇ O₅ COO^– and CH₃ COO^– were present in the solution, they reacted with Cr(III) to form stable complexes, thereby reducing the removal efficiency of Cr(III). On the other hand, the . of PO₄ 3– and SO₄ 2– did not cause any inhibition in the adsorption of Cr(III).