Thermochemical study of Cr(VI) sequestration onto chemically modified Areca catechu and its recovery by desorptive precipitation method
2022
Basnet, Prabin | Ojha, Pawan Kumar | Gyawali, Deepak | Ghimire, Kedar Nath | Paudyal, Hari
A new biosorbent for Cr(VI) sequestration was investigated from betel nut waste (BNW), Areca catechu, by H₂SO₄ charring. Aqueous insolubility and Cr(VI) uptake capacity of native BNW were potentially improved after H₂SO₄ 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 NO3−, Cl⁻, Na⁺ and Zn²⁺ ions showed negligible interferences, whereas SO42− and PO43− 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 BaCrO₄ was recovered from the desorbed solution after precipitation with BaCl₂ 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.
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