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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.