Preparation of sludge-based activated carbon and its adsorption performance for Cr(VI) in wastewater

This study used excess sludge from urban wastewater treatment plants as a raw material to prepare sludge-based activated carbon (SAC) via ZnCl₂ activation and high-temperature carbonization. The structure of SAC was characterized using XRD, SEM, and FTIR, and the adsorption performance of SAC toward Cr(VI) in wastewater was systematically investigated. The results showed that, under the conditions of a ZnCl₂ activator concentration of 1 mol/L, a carbonization temperature of 550°C, and a heating rate of 10 ℃/min, the prepared SAC had a maximum adsorption capacity of 57.90 mg/g for Cr(VI) in wastewater, and could achieve 100% removal of Cr(VI) at an initial concentration of 10 mg/L. The adsorption process conformed to the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating that chemical adsorption was the rate-controlling step, and Cr(VI) was mainly adsorbed in a uniform monolayer on the SAC surface. This study provides a feasible technical route for sludge resource utilization and Cr(VI) wastewater treatment.Implications:In this study, activated carbon was prepared using sludge as the raw material, realizing the reduction and resource utilization of sludge. This method not only solves the problems of land occupation and secondary pollution caused by sludge storage and landfilling, but also reduces the preparation cost of activated carbon, which conforms to the environmental protection policies for solid waste recycling.To address the pollution of highly toxic Cr(VI) in wastewater, the as-prepared sludge-based activated carbon shows excellent adsorption performance, which can efficiently remove Cr(VI) from aqueous solution and significantly reduce the biological toxicity and environmental risks of heavy metals.This work constructs a cyclic utilization pathway of "sludge disposal-functional carbon preparation-heavy metal wastewater treatment," providing an economically feasible technical scheme for the treatment of chromium-containing industrial wastewater. It has important theoretical value and practical application significance for promoting solid waste resource utilization, improving the water ecological environment and ensuring water environmental safety.