Preparation of high-efficient MgCl2 modified biochar toward Cd(II) and tetracycline removal from wastewater

MgCl2-modified biochar (MgC700) derived from cotton stem is prepared by microwave heating to investigate Cd(II) and tetracycline (TC) adsorption performance. The adsorption isotherm analysis indicates the Cd(II) and TC adsorption capacity of 178.17 and 201.85 mg/g at pH of 5 and 6, respectively. Cd(II) adsorption mechanism includes precipitation, cation exchange, etc. While, the electrostatic attraction, π-π, interaction etc. are responsible for TC adsorption. TC slightly enhances Cd(II) adsorption on MgC700 at concentration of 10–40 mg/L, while TC adsorption amount is inhibited at high Cd(II) concentration in binary contaminant system. Cd(II) and TC adsorption mechanism are further investigated using density functional theory calculations. MgC700 shows excellent Cd(II) and TC adsorption performance after three cycles. Based on a preliminary economic analysis, the production cost of MgC700 is calculated to be $332/t. These results demonstrate that MgC700 can act as low-cost adsorbent for Cd(II) and TC removal.