Simultaneous removal of Cr(VI), Cd, and Pb from aqueous solution by iron sulfide nanoparticles: Influencing factors and interactions of metals

Abstract

• Cr(VI), Cd, and Pb may be removed from aqueous solutions simultaneously by FeS NPs. • Acidic pH values favor Cr(VI) removal, and alkaline pH values favor Cd and Pb removal. • Oxygen inhibits Cr(VI) removal, but does not influence Cd and Pb removal. • The interactions between Cr(VI), Cd, and Pb involve enhanced adsorption and precipitation. Cadmium (Cd), lead (Pb), and hexavalent chromium (Cr(VI)) are often found in soils and water affected by metal smelting, chemical manufacturing, and electroplating. In this study, synthetic iron sulfide nanoparticles (FeS NPs) were stabilized with carboxymethyl cellulose (CMC) and utilized to remove Cr(VI), Cd, and Pb from an aqueous solution. Batch experiments, a Visual MINTEQ model, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectrometer (XPS) analysis were used to determine the removal efficiencies, influencing factors, and mechanisms. The FeS NP suspension simultaneously removed Cr(VI), Cd, and Pb from an aqueous solution. The concentrations of Cr(VI), Cd, and Pb decreased from 50, 10, and 50 mg·L −1 to 2.5, 0.1, and 0.1 mg·L −1 , respectively. The removal capacities were up to 418, 96, and 585 mg per gram of stabilized FeS NPs, respectively. The acidic conditions significantly favored the removal of aqueous Cr(VI) while the alkaline conditions favored the removal of Cd and Pb. Oxygen slightly inhibited the removal of Cr(VI), but it had no significant influence on the removal of Cd and Pb. A potential mechanism was proposed for the simultaneous removal of Cr(VI), Cd, and Pb using FeS NPs. The interactions of the three heavy metals involved a cationic bridging effect on Cr(VI) by Cd, an enhanced adsorption effect on Cd by [Cr,Fe](OH) 3 , precipitation of PbCrO 4 , and transformation of PbCrO 4 to PbS. Therefore, FeS NPs have a high potential for use in the simultaneous removal of Cr(VI), Cd, and Pb from contaminated aqueous solutions.