Attapulgite-Supported Nanoscale Zero-Valent Iron Composite Materials for the Enhanced Removal of Ni2+ from Aqueous Solutions: Characterization, Kinetics, and Mechanism

This study focuses on addressing the pollution caused by Ni in water. To enhance the removal efficiency of Ni2+, attapulgite (ATP) from Linze County, Gansu Province, China, was used as a carrier to prepare attapulgite loaded with nanoscale zero-valent iron (nZVI@ATP) via a liquid-phase reduction. This approach aims to mitigate the aggregation and oxidation tendencies of nZVI, thereby improving its performance in Ni2+ removal. The results revealed that nZVI@ATP exhibited a mesoporous structure with a specific surface area and an average pore size of 51.79 m2/g and 9.22 nm. Notably, nZVI@ATP showed a remarkably reduced agglomeration phenomenon. In addition, nZVI@ATP demonstrated a considerably more excellent adsorption performance for Ni2+ than raw ATP and pure nZVI, as its highest adsorption capacity was 143.20 mg/g when the iron–ATP ratio was 2:1 (initial concentration: 200 mg/L, initial pH: 5, temperature: 298 K, and dosing amount: 1 g/L). The adsorption of Ni2+ by nZVI@ATP followed the quasi-secondary kinetic model, and the removal rate of Ni2+ was inversely proportional to the initial concentration and directly proportional to the dosage. The adsorption capacity tended to increase and then decrease as the pH increased. The removal mechanism of Ni2+ by nZVI@ATP involved adsorption, reduction, and precipitation, with the significant mechanism being the induced Ni(OH)2 precipitation on the nZVI@ATP surface.