Investigation of the kinetics and mechanisms of nickel and copper ions adsorption from aqueous solutions by date seed derived biochar

This paper reports on Ni2+ and Cu2+ adsorption kinetics and mechanisms by date-seed derived biochar. Biochar was prepared at different temperatures (350-550 degrees C), heating times (1-3 h) and particle sizes (< 0.3- > 2.0 mm). Biochar prepared at 550 degrees C and 3 h heating time with particle size range of 0.6-1.4 mm had the highest adsorption capacity for both ions. Further batch experiments revealed that optimal adsorption occurred around pH 6 with maximum adsorption capacity of 0.421 and 0.333 mmol g(-1) for Cu2+ and Ni2+, respectively. The experimental data were best fit by the Sips isotherm model and the pseudo-second order kinetics models. Ion exchange mechanism accounted for more than two thirds of the ions removal. Complexation with carboxyl and hydroxyl groups also played significant role in ion removal. Column experiments showed that the effluent pH fluctuated overtime buffering to level slightly above 6 which may have facilitated surface precipitation and resulted in the apparent increase in adsorption capacity. The breakthrough curve obtained in the column experiment was reasonably fit by the Adam-Bohart model. Date-seed derived biochar is a promising material for adsorption for heavy metals from aqueous solutions.