Selective and Competitive Adsorption of Anions in Solution on Porous Adsorbent from Zea mays Steams: Kinetic and Equilibrium Study

Abstract

Surface modification can improve the adsorption capacity of biochar. Biochar was produced from corn stalks (Zea mays) by pyrolysis at 520 °C, activated with sulfuric acid (H2SO4) using impregnation ratios of biomass weight: volume 1:2 (B 1:2) and 1:3 (B 1:3). The kinetic study showed that the equilibrium is reached at 180 min; the maximum adsorption capacity of nitrate and sulphate was obtained with B 1:2 and for phosphate with B 1:3. The adsorption of nitrate and phosphate with the two biochars presented a good fitting to the pseudo-first order and pseudo-second-order model, while that of sulphate for B 1:2 is described by Elovich’s model. Freundlich’s model describes the equilibrium of adsorption of nitrate and phosphate using B 1:2 and B 1:3, while Dubinin–Radushkevich adjusts the removal of sulphate for C 1:2 and C 1:3; therefore it is suggested that adsorption occurs in multilayers. The multicomponent study evidences the preference of biocarbon for phosphate, without indicating competition for the active centers of the material among the anions studied.