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Biogenic Calcium Carbonate with Hierarchical Organic–Inorganic Composite Structure Enhancing the Removal of Pb(II) from Wastewater

Zhou, Xueli, Liu, Weizhen, Zhang, Jian, Wu, Can, Ou, Xinwen, Tian, Chen, Lin, Zhang, Dang, Zhi
ACS applied materials & interfaces 2017 v.9 no.41 pp. 35785-35793
Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, active sites, adsorption, aragonite, calcite, calcium carbonate, crystal structure, desorption, heavy metals, lead, mercury, nitrogen, pollutants, scanning electron microscopy, shell (molluscs), sludge, thermodynamics, wastewater
Calcium carbonate from geological sources (geo-CaCO₃, e.g., calcite, aragonite) is used extensively in removing heavy metals from wastewater through replacement reaction. However, geo-CaCO₃ has an intrinsically compact crystalline structure that results in low efficiency in pollutant removal and thus its use may produce enormous sludge. In this work, biogenic calcium carbonate (bio-CaCO₃) derived from oyster shells was used to remove Pb(II) from wastewater and found to significantly outperform geo-CaCO₃ (calcite). The thermodynamics study revealed that the maximum adsorption capacity of bio-CaCO₃ for Pb(II) was three times that of geo-CaCO₃, reaching up to 1667 mg/g. The kinetics study disclosed that the dissolution kinetics and the rate of intraparticle diffusion of bio-CaCO₃ were faster than those of geo-CaCO₃. Extensive mechanism research through X-ray powder diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption/desorption test and mercury intrusion porosimetry showed that the hierarchical porous organic–inorganic hybrid structure of bio-CaCO₃ expedited the dissolution of CaCO₃ to provide abundant CO₃²– active sites and facilitated the permeation and diffusion of Pb(II) into the bulk solid phases. In addition, Fourier transform infrared spectroscopy (FTIR) study, X-ray photoelectron spectroscopy (XPS) analysis, and the examination of Pb(II) removal ability of bio-CaCO₃ after calcination indicated that the organic functional groups of bio-CaCO₃ also facilitated the immobilization of Pb(II) into CaCO₃ particles, although the major contribution was from the hierarchical porous structure of bio-CaCO₃.