A new biochar from cotton stalks for As (V) removal from aqueous solutions: its improvement with H3PO4 and KOH

The present study is the first attempt to evaluate the potential of acid and base activated biochar derived from cotton stalks (CSB) for the removal of As from contaminated water. The CSB was treated with 0.5 M KOH (BCSB) and H3PO4 (ACSB) separately to change its surface properties. The CSB, ACSB and BSCB were characterized using BET, FTIR, and SEM analysis to check the effectiveness and insight of the main mechanisms involved in the removal of As. A series of batch experiments was performed using As-contaminated synthetic water and groundwater samples. The effects of initial concentration of As, contact time, dose of the biochars, solution pH, type of the biochar and coexisting ions on the removal of As were investigated. Results revealed that BCSB efficiently removed As (90-99.5%) from contaminated water as compared with ACSB (84-98%) and CSB (81-98%) due to improved surface properties when As concentration was varied from 0.1 to 4.0 mg/L. The experimental data were best fitted with Freundlich adsorption isotherm as compared with Langmuir, Temkin and Dubinin-Radushkevich models. However, kinetic data were well explained with pseudo-second-order kinetic model rather than pseudo-first-order, intra-particle diffusion and Elovich models. The sorption energy indicated that physical adsorption was involved in the removal of As. The comparison of adsorption results with other biochars and their modified forms suggests that activation of CSB with base can be used effectively (4.48 mg/g) as a low-cost adsorbent for maximum removal of As from contaminated aqueous systems.