Effective Removal of Toxic Heavy Metal Ions from Aqueous Solution by CaCO3 Microparticles

Abstract

Heavy metals are a common contaminant in water supplies and pose a variety of serious health risks to nearby human populations. A promising approach to heavy metal decontamination is the sequestration of heavy metal ions in porous materials; however, current technologies involve materials which can be difficult to synthesize, are high-cost, or are themselves potentially toxic. Herein, we demonstrate that rapidly synthesized calcium carbonate (CaCO3) microparticles can effectively remove high quantities of Pb2+, Cd2+, and Cu2+ ions (1869, 1320, and 1293 mg per gram of CaCO3 microparticles, respectively) from aqueous media. The CaCO3 microparticles were characterized with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Brunauer–Emmett–Teller (BET) N2 sorption–desorption. It was found that the Ca2+ ions of the microparticles were replaced by the heavy metal ions, leading to partially recrystallized nanoparticles of new compositional phases such as cerussite (PbCO3). The adsorption, surface dissolution/re-precipitation, and nucleation/crystal growth mechanisms were determined by investigating the Ca2+ released, along with the changes to particle morphology and crystal structure. Importantly, this study demonstrates that the porous CaCO3 microparticles performed well in a system with multiple heavy metal ion species: 100% of Cu2+, 97.5% of Pb2+, and 37.0% Cd2+ were removed from an aqueous solution of all cations with initial individual metal concentrations of 50 mg/L and 1.5 g/L of CaCO3 microparticles. At this concentration, the CaCO3 microparticles significantly outperformed activated carbon. These results help to establish CaCO3 microparticles as a promising low-cost and scalable technology for removing heavy metal ions from contaminated water.