Fabrication of CaCO Microcubes and Mechanistic Study for Efficient Removal of Pb from Aqueous Solution.

Pb(II) contamination in aquatic environments has adverse effects on humans even at a low concentration, so the efficient removal of Pb at a low cost is vital for achieving an environmentally friendly, sustainable, and healthy society. A variety of CaCO-based functional adsorbents have been synthesized to remove Pb, but the adsorption capacity is still unsatisfactory. Herein, calcite CaCO microcubes/parallelepipeds are synthesized via simple precipitation and a hydrothermal approach and found to outperform previously reported nano-adsorbents considerably. The CaCO achieves a high removal efficiency for Pb(II) (>99%) at a very low dosage (0.04-0.1 g/L) and an initial Pb(II) concentration of 100 mg/L. The CaCO presents an excellent adsorption capacity of 4018 mg/g for Pb(II) removal and depicts good stability over a wide range of pH 6-11. The maximum adsorption kinetics are fitted well by the pseudo-second-order kinetic model, whereas the Freundlich isotherm delineates the adsorption data at equilibrium well, indicating a multilayer adsorption process. The ex situ study confirms that the Pb(II) adsorption mechanism by CaCO can be attributed to the rapid metal-ion-exchange reaction between Pb(II) and Ca. Furthermore, a red shift in the Fourier Transform Infrared (FTIR) spectroscopy peak from 1386 cm to 1374 cm of CaCO after Pb removal indicates the adsorption of Pb onto the surface. This adsorbent provides an opportunity to treat wastewater and can be extended to remove other toxic heavy metals.