H3PO4-Activated Cattail Carbon Production and Application in Chromium Removal from Aqueous Solution: Process Optimization and Removal Mechanism

In this study, Box–Behnken design (BBD) was employed to optimize the process for H3PO4-activated Typha angustifolia activated carbon (TAC) production and Cr removal by TAC; the removal mechanisms were discussed based on TAC characterization, and the regeneration evaluation was also conducted. The optimum preparation conditions were activated time of 1.5 h, temperature of 469.02 °C, and incubation ratio of 4, resulting in an experimental carbon yield of 38.23% and Cr removal of 90.01%. The optimum adsorption parameters were found to be 0.02 g/50 mL TAC, 80 mg/L Cr(VI), and 2.21 pH with the observed Cr adsorption capacity of 59.54 mg/g. The removal mechanisms involved coulombic attraction, ionic exchange, surface complexation, and reduction. The process of Cr(VI) adsorption was feasible, spontaneous, and endothermic in nature, and the pseudo-second-order and Langmuir isotherm models were more appropriate for the removal process. After five adsorption/desorption cycles, the Cr adsorption capacity on TAC reduced by only 24.37%. The results showed that BBD could successfully optimize TAC production and Cr removal, and TAC could be developed as a promising, eco-friendly, and effective adsorbent for Cr pollution control