Removal of Copper (II) from Aqueous Solution by a Hierarchical Porous Hydroxylapatite-Biochar Composite Prepared with Sugarcane Top Internode Biotemplate

Porous hydroxyapatite-biochar composites with layered microstructures (SC-HA/C) were prepared by carbonizing sugarcane stem nodes and then soaking them in lime water and (NH4)(2)HPO4 solutions in rotation. The surface area of SC-HA/C ranges from 8.52 to 28.44 m(2)/g, and its microstructure inherits various macro-, meso-, and micro-pores in the cell walls of sugarcane and in the pits of the vessel walls. The maximum removal capacities were 11.50, 14.65, and 19.81 mg/g for the Cu (II) immobilization at 25 degrees C, 35 degrees C, and 45 degrees C with the solution Cu (II) concentration of 10-320 mg/L, respectively, which were in accordance with the copper sorption capacities of synthesized nano-hydroxylapatites. The Cu (II)-removal kinetics and isotherm followed the pseudo-second-order equation and the Langmuir equation very well. The formation of the Cu-containing hydroxylapatite solid solutions ((CuxCa(1)(-x))(5)(PO4)(3)(OH)) through adsorption, ion exchange (x = 0.01-0.04), and dissolution-coprecipitation (x = 0.13-0.35) was the dominant process for the Cu (II) removal by the SC-HA/C composite.