Simultaneous removal of arsenic and cadmium in aqueous solution by a novel hydrotalcite-like absorbent FeMnCa-LDHs

Abstract

As(III) and Cd(II) pose a significant threat to the ecological environment and human health due to their high toxicity and carcinogenicity, the simultaneous removal of hazardous anions and cations in wastewater has always been a challenging problem. This study employed the co-precipitation method to synthesize FeMnCa-LDHs, a novel ternary metal material devoid of toxic metals, enabling simultaneous removal of As(III) and Cd(II) from aqueous solutions. The XRD patterns and SEM-EDS images showed that the prepared FeMnCa-LDHs exhibited characteristic peaks and a typical layered structure of hydrotalcite-like compounds with high crystallinity. In the composite adsorption system, FeMnCa-LDHs showed synergistic sorption of As(III) and Cd(II) in water, and their adsorption kinetics conformed to the quasi-secondary kinetic model, with adsorption rates of 0.31 and 0.136 g·(mg·h)−1, respectively, and the isothermal adsorption curves conformed to the Langmuir model, with the maximum adsorption amounts of 216.08 and 193.18 mg·g−1 (pH = 5.0, 25 °C), respectively, higher than those of the other LDHs. In the pH range of 3–6, FeMnCa-LDHs exhibited excellent adsorption performance on As(III) and Cd(II), and the adsorption capacity can reach 89.0 and 82.9 mg·g−1, respectively. The coexistence of both PO43− and CO32– ions in water had a competitive effect on the adsorption of As(III) but had little effect on Cd(II) adsorption. The main adsorption mechanism between Cd(II) and FeMnCa-LDHs was found to be isomorphic substitution and surface precipitation, as revealed by XRD, XPS, and FT-IR analyses. On the other hand, the adsorption mechanism that bonded As(III) involved oxidation, ion exchange, surface complexation, and surface precipitation. Furthermore, it maintains a specific adsorption capacity even after undergoing five adsorption cycles. This study demonstrates the potential of FeMnCa-LDHs in treating wastewater that contains As(III) and Cd(II).