Physico-chemical Activation on Rice Husk Biochar for Enhancing of Cadmium Removal from Aqueous Solution

Abstract

The biochar was prepared from rice husk by pyrolysis at slow pyrolysis at 300, 400, and 500°C. The obtained biochars were activated by combined physico-chemical methods. An alkaline solution of 1.63 M of KOH was used for chemical pre-activation and made second pyrolysis at the same condition as first pyrolysis. Adsorption efficiency was studied using the batch static method under laboratory conditions. Cd(II) ion removal efficiency of activated biochars was increased from 13–20% to 95–97% over non-activated biochar. The activated biochar at a pyrolysis temperature of 300°C showed the highest Cd(II) ion removal efficiency of 97% at 180 min of contact time. Cd(II) ion adsorption isotherms of activated biochar were fitted well both in Langmuir and Freundlich model. The maximum Cd(II) ion adsorption capacity of activated biochar pyrolysis at 300°C was 45.87 mg g⁻¹, about six times higher than that of the non-activated biochar (7.76 mg g⁻¹). The activated biochar increased the BET surface area from 7.71 to 11.57 m²g⁻¹. It has been suggested that the simplicity of the physico-chemical activation technique, technically feasible, eco-friendly, and cost effective, can stimulate high Cd(II) ion removal efficiency of rice husk biochar.