Multiple chemical modifications and Cd(2+) adsorption characteristics of sludge-based activated carbon

Sludge resource utilization is commonly realized through carbonization, but the use of direct carbonization to obtain sludge-based activated carbon (SAC) is not functional yet. The multiple chemical modifications were carried out to achieve N-doping and pore-making to modify SAC. The SAC(U–PF′) was synthesized by activating sludge simultaneously with uric acid and potassium ferrate. Moreover, SAC(N′), SAC(U), and SAC(PF′) were prepared with no additives, uric acid, and potassium ferrate, respectively. The results indicated that the different modifications affected the chemical properties and structure of SAC. The BET of SAC(U–PF′) was 56.73 m(2) g(−1), which was higher than that of SAC(N′) and SAC(PF′). SAC(U–PF′) possessed abundant functional groups, such as C[double bond, length as m-dash]N and C–O. The adsorption capacity of SAC(U–PF′) for Cd(2+) was 9.69 mg g(−1), 5.5 times that of SAC(N′), the adsorption process of Cd(2+) by SAC(U–PF′) fitted well for the second-order kinetic model and Langmuir isothermal adsorption model. The XPS and chemical analysis revealed that SAC(U–PF′) and Cd(2+) were bonded by functional groups, and the Cd(2+) removal by SAC(U–PF′) was through complexation, anion exchange, electrostatic attraction, and pore filling. The SAC(U–PF′) was exhibited different removal capacities for different metals, Pb(2+) and Mn(2+) correspond to adsorption capacities of 4.9 and 8.1 mg g(−1). In addition, the adsorbed SAC(U–PF′) can be regenerated by sodium hydroxide. The study highlights the importance of multiple chemical modifications performed on SAC, the double coupled chemical modifications to ensure its good performance in the treatment of heavy metals in wastewater treatment.