Enhanced Adsorption of Cu2+ from Aqueous Solution by Sludge Biochar Compounded with Attapulgite-Modified Fe

Three types of modified sludge biochar were produced for the adsorption of copper in aqueous solutions via the calcium-based magnetic (CaCO3, Fen+) treatment (CA-BC), nanozero-valent iron (nZVI) treatment (nZVI-BC), and iron (Fe3+) treatment (FA-BC) of raw biochar. The results suggested that the adsorption capacity for Cu2+ of calcium-based magnetic attapulgite/sludge biochar (CA-BC) prepared from CaCO3, FeCl3, and FeSO4 is 38.01% greater than that of unmodified biochar and 6.41% to 17.5% greater than that of the other biochar. The CA-BC contained a variety of ferrite-containing and hydroxide-functional groups, as well as a more developed pore structure. The existence of H+ reduced the adsorption capacity of the biochar for Cu2+. A high initial concentration of Cu2+ could increase Cu2+ adsorption on CA-BC. Combined with theoretical calculations, the adsorption efficiency of CA-BC in different systems was explored. The results revealed that CA-BC achieved a maximum removal rate of 92.644% at a pH of 6 with a reaction time of 157 min and an initial Cu2+ concentration of 2.813 mg/L. These results suggest that CA-BC shows great potential for removing Cu2+ from aqueous solutions.