Thermochemical study of Cr(VI) sequestration onto chemically modified and its recovery by desorptive precipitation method.

A new biosorbent for Cr(VI) sequestration was investigated from betel nut waste (BNW), , by HSO charring. Aqueous insolubility and Cr(VI) uptake capacity of native BNW were potentially improved after HSO modification due to cross-linking reaction of betel nut cellulose, thereby creating suitable complexation sites for Cr(VI) ion removal. Langmuir isotherm and pseudo second order (PSO) kinetic models described well with the experimental data. A trace amount of Cr(VI) was effectively removed below the safe drinking water standard (WHO, 0.05 mg/L) using charred BNW (CBNW). The negative value of ΔG° evaluated for all the temperatures suggested the spontaneous nature of Cr(VI) sequestration and positive value of ΔH° (42.43±0.13 kJ/mol) confirmed an endothermic reaction. Co-existing NO , Cl, Na and Zn ions showed negligible interferences, whereas SO and PO notably reduced Cr(VI) uptake capacity of CBNW. More than 98% of adsorbed Cr(VI) was desorbed using 1M NaOH solution. A light yellow precipitate of BaCrO was recovered from the desorbed solution after precipitation with BaCl solution. Therefore, the CBNW biosorbent investigated in this work is expected to be a promising material for Cr(VI) sequestration and its recovery from polluted water.