The calcined Mg-Al hydrotalcite for copper adsorption and passivation of copper-contaminated soil

Abstract

Excessive copper content in soil and water will cause critical pollution to the ecosystem. In this study, an innovative material for passivating copper in soil and removing copper in aqueous environments was prepared by calcining Mg-Al hydrotalcite at various temperatures. The results showed that the calcined Mg-Al hydrotalcite presented high adsorption ability for Cu(II), while the optimal Mg-Al hydrotalcite calcined at 600 °C (HT600) exhibited a maximum Cu(II) adsorption capacity of 188.53 mg·g⁻¹ at 45 °C. The adsorption process was spontaneous and endothermic, conforming to pseudo-second-order kinetics and the Langmuir isotherm model. The adsorption mechanisms primarily involve electrostatic attraction, surface adsorption, precipitation, complexation, and other interactions. Notably, the Mg-Al hydrotalcite exhibited excellent regeneration performance, with HT600 retaining approximately 87.51 % of its initial adsorption capacity after five regeneration cycles. The content of TCLP-Cu (toxicity characteristic leaching procedure-Cu) in contaminated soil amended with calcined Mg-Al hydrotalcite was significantly decreased. After adding calcined Mg-Al hydrotalcite into soil, the occurrence form of copper changed significantly under the action of electrostatic attraction, adsorption, precipitation, complexation, and so on, i.e., the proportion of acid soluble-Cu and reducible-Cu declined, and the proportion of oxidizable-Cu and residual-Cu rose, and the degree of change was dependent on the calcination temperature. HT600 showed excellent passivating effects on Cu in soil. The findings of this study may provide a new perspective on the remediation of copper-contaminated soils and water bodies by using calcined hydrotalcite with simple preparation, environmental friendliness, and low cost.