Abstraction of arsenic(III) on activated carbon prepared from Dialium guineense seed shell: kinetics, isotherms and thermodynamic studies

Abstract

Removal of arsenic(III) from aqueous solution has been studied using activated carbon produced from Dialium guineense seed shell by impregnation of carbonized sample with zinc chloride and thermal activation. The zinc chloride activated sample was selected because it produced the highest iodine number, mg/g (962.52) compared to the raw sample (601.57), phosphoric acid and nitric acid impregnated samples (802.10, 868.95). Proximate analysis of raw D. guineense seed shell revealed low ash content of 1.70% and moderate fixed carbon of 32.97%. The prepared adsorbent was characterized using Brunaeur–Emmett–Teller surface area, SEM and FTIR analyses. The surface area of the zinc chloride activated adsorbent was 533.94 m2/g and its micropore volume 0.475 cm3/g, with a porous structure that is well organized. Batch adsorption experiments were done by changing the following parameters: adsorbent dose, pH, contact time, initial metal ion concentration and temperature. Adsorption increased as each parameter was varied but decreased with increase in initial arsenic(III) concentration. The Freundlich model presented better fit with R2 of 0.998 compared to the Freundlich isotherm (0.991) and Tempkin isotherm (0.984). The positive value of ∆H° 51.68 kJ/mol showed the endothermic nature of adsorption. The study demonstrated the potential of D. guineense seed shell as low cost adsorbent for removing arsenic(III) from polluted water.