Highly adsorptive pristine and magnetic biochars prepared from crayfish shell for removal of Cu(II) and Pb(II)

Background Biochar has attracted considerable attention as a low-cost adsorbent comprised of carbon matrix and mineral for treatment of wastewater. The main purpose of this work was to manufacture CaCO 3 -rich biochars using crayfish shell as feedstock for removal of Cu(II) and Pb(II) from aqueous solution. Methods Pristine and magnetic biochars were prepared via direct pyrolysis and K 2 FeO 4 -promoted pyrolysis , respectively, and characterized by element analysis, BET, FTIR, SEM-EDS, XRD and XPS. Moreover, their adsorption capabilities toward Cu(II) and Pb(II) were investigated in aqueous solution. Findings A large amount of CaCO 3 was assembled on the pristine biochar pyrolyzed at 600 °C, leading to 715.10 mg/g and 1682.87 mg/g adsorption capacities for Cu(II) and Pb(II), respectively. Whereas, CaCO 3 and single phase Fe 3 O 4 were simultaneously introduced into the magnetic biochar with K 2 FeO 4 -promoted pyrolysis at 600 °C using 1/1 (g/g) ratio of K 2 FeO 4 to crayfish shell, where 417.05 mg/g and 974.10 mg/g maximum adsorption capabilities were obtained for Cu(II) and Pb(II) with 29.66 emu/g saturation magnetism, respectively. Cu(II) and Pb(II) were mainly adsorbed onto the biochars as carbonates and oxides by their interaction with CaCO 3 and carbon matrix.