Removal of Cu2+ in Aqueous Solution with Nano-zero-Valent Iron (nZVI) Supported by Alkali-Modified Sludge Biochar.

In this study, an efficient nano-zero-valent iron supported by alkali-modified sludge biochar (nZVI@NaOH-SBC) composites were synthesized by a liquid-phase reduction method for Cu²⁺ removal. The preparation conditions (sodium hydroxide concentration, pyrolysis temperature, solid–liquid ratio, and modification time) of sludge biochar (SBC) were optimized by orthogonal experiments. The results showed that the best SBC was prepared under the conditions of sodium hydroxide concentration of 3 mol/L, pyrolysis temperature of 500 °C, a solid–liquid ratio of 1:20, and modification time of 24 h, and a maximum adsorption capacity was 183.22 mg/g, which is 2.43 times that of the pristine sludge biochar. The adsorption behavior was in accordance with a pseudo-second-order kinetic model, indicating that the removal of Cu²⁺ was mainly affected by chemisorption. The adsorption isotherm conformed to the Langmuir model, and the maximum adsorption capacity of Cu²⁺ was 358.42 mg/g at pH = 5, and 25 °C. Reusability tests confirmed the good reusability and stability of the material. Batch experiments and characterization reveal that the mechanism of Cu removal by nZVI@NaOH-SBC composites involves multiple processes: adsorption, precipitation, electrostatic attraction, and reduction. This study proposes a new biochemical adsorbent, which provides a good choice for the treatment of copper-containing wastewater and the resource utilization of sludge. [ABSTRACT FROM AUTHOR]