Converting wastes to resource: Preparation of NiO@γ-Al2O3 sludge composite from aluminum-containing sludge for cadmium removal from wastewater

Solid sludge waste and heavy metal water pollution have attracted great interest due to the adverse impacts on the ecological environment, which remains a significant challenge to environmental protection. Herein, with the concept of converting wastes to resources, this work presents a general procedure to fabricate NiO@γ-Al2O3 sludge composite derived from aluminum-containing sludge for efficient cadmium removal. During the procedure, the unstable metal compounds were converted into chemically stable metal oxides, and the organic components in sludge are decomposed via high-temperature treatment. Then, the NiO@γ-Al2O3 sludge composite was obtained by in situ growth of NiO nanocrystals using the calcined sludge as raw materials, followed by calcination to form a porous structure. The as-obtained NiO@γ-Al2O3 sludge composite with hierarchical porosity comprises self-assembled NiO nanosheets with sizes ranging from 1 to 3 μm. Compared with raw sludge particles, the specific surface area of NiO@γ-Al2O3 sludge composite is enhanced significantly (116.27 m2/g), revealing that the preparation procedure is favorable for the improvement of the surface properties of the sludge. The cadmium adsorption results showed that the maximum cadmium adsorption capacity of the sludge composite could attain 160.12 mg/g, and cadmium removal efficiency could reach 99.9% with an optimal dose of 1.5 g/L. Meanwhile, the sludge composite showed high adsorption capacity at the neutral pH condition, which was attributed to the exchange of cadmium ions in solution with the surface protons on the adsorbent. Significantly, a simple regeneration operation was used for the desorption of cadmium ions to realize the regeneration of adsorbents, and the regenerated sludge composite can be recyclable for continuous use. This work provides a waste-to-resource strategy for resource utilization of solid waste sludge and presents an adsorbent material with high surface activity for cadmium adsorption, which may inspire the development and application of other solid waste for wastewater treatment. [Display omitted] •A concept for converting waste into a useable resource is proposed.•NiO@γ-Al2O3 sludge composite was fabricated using aluminum-containing sludge.•The sludge composite exhibited large adsorption capacity and high removal rate for cadmium.•The sludge composite performed an excellent reusable characteristic.