Adsorption behaviors of paper mill sludge biochar to remove Cu, Zn and As in wastewater

Paper mill sludge biochar (PMSB) was produced via pyrolysis in a muffle furnace at 750 °C. Subsequently, PMSB was soaked in the HCl solution and washed by deionized water to obtain minerals and organic materials. The organics were named as demineralized paper mill sludge biochar (DPMSB). It was found that PMSB and minerals had larger pore diameters than DPMSB. Also, the removal efficiencies of Cu, Zn and As were above 95.00% by using PMSB and minerals because of the large pores, abundant carbonates and OH groups, while the removal efficiencies of Cu, Zn and As by using DPMSB were 40.92%, 87.93% and 94.99%, respectively, owing to the H + competition to Cu and Zn adsorption but more micropores to enhance As adsorption. The adsorption behavior of PMSB showed that the adsorption isotherms of Cu, Zn and As could be well simulated by the Freundlich model, and the pseudo-second-order model fitted the adsorption kinetics of Zn and As, and the Elovich model fitted the adsorption kinetics of Cu. Moreover, the optimal dosages of PMSB to adsorb Cu, Zn and As were 0.3, 0.3 and 0.1 g/L, respectively. And the pH values of the solution for the efficient adsorption of Cu, Zn and As were 4.00, 6.00 and 2.00, respectively. This work provided basic data for the potential commercial application of PMSB for heavy metals removal from wastewater.