Enhanced Cu²⁺ and Cd²⁺ removal by a novel co-pyrolysis biochar derived from sewage sludge and phosphorus tailings: adsorption performance and mechanisms

The reutilization of municipal wastes has always been one of the hottest subjects of sustainable development study. In this study, a novel biochar co-pyrolyzed from municipal sewage sludge and phosphorus tailings was produced to enhance the adsorption performance of the composite on Cu²⁺ and Cd²⁺. The maximum Cu²⁺ and Cd²⁺ adsorption capacity of SSB-PT were 44.34 and 45.91 mg/g, respectively, which were much higher than that of sewage sludge biochar (5.21 and 4.58 mg/g). Chemisorption dominated the whole adsorption process while multilayer adsorption and indirect interaction were also involved. According to the result of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectrum (XPS), the load of CO₃²⁻, Mg²⁺, and Ca²⁺ on the surface of SSB-PT enhanced the precipitation and ion exchange effect. Posnjakite and CdCO₃ were formed after the adsorption of Cu²⁺ and Cd²⁺, respectively. Besides, complexation, and metal-π interaction were also involved during the adsorption process. Therefore, this study offered a promising method to reuse sewage sludge and phosphorus tailings as an effective adsorbent.