Sorption Process of Date Palm Biochar for Aqueous Cd (II) Removal: Efficiency and Mechanisms

Date palm biochar (BC) was prepared at two pyrolysis temperatures of 300 degrees C (BC-300) and 700 degrees C (BC-700) as sorbents for removing Cd from aqueous solutions in batch experiments. The results indicated that Cd removal efficiency was significantly affected by the initial pH (2-7) of aqueous solutions, with the lowest Cd adsorption at initial pH of 2. BC-700 was more effective in removing Cd from aqueous solution than BC-300. The maximum adsorption capacity of 43.58 mg g(-1) was observed for BC-700 based on the Langmuir model, which was 1.6 times higher than that of BC-300 (26.96 mg g(-1)). Mechanistic evidences of Cd sorption onto BCs were identified by using the instrumental techniques of XRD and SEM or predicted from sorption isotherm and kinetic models. The Cd sorption onto BCs followed the pseudo-second order kinetics, suggesting chemisorption as one of the possible mechanisms of Cd interaction with BCs. However, XRD and SEM analyses of BCs before and after Cd sorption indicated that ion exchange and surface complexation could be the controlling mechanisms of Cd adsorption onto BC-300, while precipitation (as CdCO3) could be the operating mechanism of Cd sorption onto BC-700. Date palm waste, therefore, could possibly be converted to BC as an efficient sorbent for removal of Cd from aqueous media. However, the removal efficiency of BCs varies with different pyrolysis temperatures.