Multiple chemical modifications and Cd2+ adsorption characteristics of sludge-based activated carbon

Abstract

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 SACU-PF′ was synthesized by activating sludge simultaneously with uric acid and potassium ferrate. Moreover, SACN′, SACU, and SACPF′ 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 SACU-PF′ was 56.73 m2 g−1, which was higher than that of SACN′ and SACPF′. SACU-PF′ possessed abundant functional groups, such as C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 N and C-O. The adsorption capacity of SACU-PF′ for Cd2+ was 9.69 mg g−1, 5.5 times that of SACN′, the adsorption process of Cd2+ by SACU-PF′ fitted well for the second-order kinetic model and Langmuir isothermal adsorption model. The XPS and chemical analysis revealed that SACU-PF′ and Cd2+ were bonded by functional groups, and the Cd2+ removal by SACU-PF′ was through complexation, anion exchange, electrostatic attraction, and pore filling. The SACU-PF′ was exhibited different removal capacities for different metals, Pb2+ and Mn2+ correspond to adsorption capacities of 4.9 and 8.1 mg g−1. In addition, the adsorbed SACU-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.