Preparation of calcite/biochar composite by co-pyrolysis and its adsorption properties and mechanism for Pb(II)

In order to obtain a biochar material which adsorbs PB (II) in wastewater efficiently, calcite/biochar (CAL/BC) composite was prepared by co-pyrolysis at 500℃, 600℃ and 700℃, using coconut shell (CS) and calcite (CAL) as raw materials. The surface morphology and structure of CAL/BC composites were characterized by SEM, ICP-MS, BET, XRD and FTIR. The results show that CAL and CS combine tightly under the three pyrolysis tempera-tures, and CAL/BC has a large specific surface area and a large number of functional groups. The maximum adsorption capacities of PB (II) on CAL/BC composite (CAL∶ CS=1∶ 2, mass ratio) prepared at 500℃, 600℃, and 700℃ are 95.24 mg·g⁻¹, 99.01 mg·g⁻¹, and 185.19 mg·g⁻¹. The optimum adsorption condition is pH=5.5 and the amount of adsorbent is 1.5 g·L⁻¹. The adsorption process conforms to the second-order kinetic model and Langmuir isotherm model. The mechanisms of adsorption of Pb(II) on CAL/BC composites are precipitation, ion exchange, cation-π action, pore filling and electrostatic gravitation. In addition, the removal rate of Pb(II) by CAL/BC composite remains high level after 4 adsorption-desorption cycles. Therefore, the CAL/BC composite prepared by co-pyrolysis has a excellent application prospect in the treatment of Pb(II) in wastewater.