Immobilization of lead from aqueous solution by using carboxymethyl cellulose stabilized iron sulfide nanoparticles

Abstract

Lead pollutant has attracted more attention recently. Moreover, the use of patent iron sulfide nanoparticles is more and more extensive for various contaminants removal. In this study, FeS nanoparticles is prepared with carboxymethyl cellulose (CMC) as a stabilizer, which can be used for improving removal of aqueous lead (Pb2+). Firstly, to find the specific mechanism during the removal, batch tests such as kinetic with curve fitting, isotherm with model fitting, FTIR spectra and XRD have been done. In these experiments, the pseudo-second-order kinetic curve fitting indicates that the reaction is rapid in the beginning, and the rate-controlling step for adsorption is chemical interaction. The isotherm curve shows S-shape with Sigmoidal isotherm model fitting, which means at low Pb2+ concentration the complexation between Pb and CMC phase competes with the Pb sorption, and the main adsorption mechanism is surface complexation. FTIR and XRD analyses indicate the same results that precipitation (formation of Galena PbS) and surface complexation are important mechanisms for lead removal. Secondly, for obtaining the optimal removal conditions, FeS dosage test, CMC-to-FeS molar ratio test, DLS size and zeta potential test and effect test of pH, coexisting ions and leonardite HA have been done. The best FeS dosage and CMC-FeS molar ratio are 50 mg/L FeS and 0.0005 (50 mg/L FeS: 0.0025 wt % CMC). When the CMC-to-FeS molar ratio ≥ 0.0005, the particles are fully stabilized. High lead uptake is observed over the pH range of 6.5~7.0, whereas significant capacity loss is observed at pH < 6 since the large amount of FeS particle leaching in the acid environment. And the result of DLS size and zeta potential test demonstrate that the CMC-FeS particles are nanoscale with larger specific surface area, and the zeta potential is negative for effective Pb2+ adsorption. High concentrations of Na+ and Ca2+ (≥ 10 mM) and leonardite HA (10 mg/L as TOC) modestly inhibit the lead uptake. Thus, the experimental results verify that the proposed CMC-FeS nanoparticles can remove Pb2+ efficiently with the main mechanisms of precipitation and surface complexation.