High-capacity amino-functionalized walnut shell for efficient removal of toxic hexavalent chromium ions in batch and column mode

Abstract

This research investigated the feasibility of removing hexavalent chromium (Cr(VI) (e.g., HCrO4−, CrO42− and Cr2O72− ions) from water using walnut shells functionalized with amino groups (ACWNS) in a batch and continuous adsorption mode. The characterization of ACWNS was carried out utilizing FTIR, XPS, SEM, and BET methods. Adsorption was investigated in terms of pH, dose, concentration, and contact duration. Furthermore, at different temperatures, the adsorption isotherms, kinetics, and thermodynamics were studied. The Langmuir model described the experimental batch and column modes, while the Thomas and pseudo-second-order kinetics models predicted continuous and batch adsorption, respectively. The maximum uptake quantity toward Cr(VI) was 236.8 mg g–1 in batch mode and 308.4 mg g–1 in column mode at 303 K. There is some selective adsorption for Cr (VI) with some dyes coexisting in solution. Electrostatic interactions and the reduction process mediated Cr(VI) adsorption by ACWNS. The mass transfer potential (B) and the affinity between ACWNS and Cr(VI) (β) were computed using the modified mass transfer factor model. Since the attraction of Cr (VI) to ACWNS is more robust, the B value increases as the concentration increases. Again, MTZ assessment reveals that as MTZ length rises, diffusion resistance increases, resulting in increased adsorption. The adsorbent demonstrated improved regeneration capacity and therefore showed potential for the uptake of Cr(VI) ions from wastewater. Availability of data and materialThe dataset produced and processed during this research is available upon reasonable request from the corresponding author.