Synergistic dual mechanisms in SiO2-Activated CaCO3 composites: Enhanced Pb(II) removal and trace contaminant purification

Lead ions (Pb(Ⅱ)) cause serious environmental pollution and endanger human health and it is urgent to carry out efficient treatment. Herein, a strategy was proposed to enhance the immobilization and removal of Pb(Ⅱ) (including trace Pb(Ⅱ)) from water by coating SiO 2 on the surface of CaCO 3 to prepare CaCO 3 @SiO 2 composites using the carbonation method. The findings revealed that SiO 2 coating exhibits strong activation effects on CaCO 3 . The SiO 2 coating (loaded at 8.62 wt%) increased CaCO 3 specific surface area by over 20-fold, confirming its activating effect. The maximum immobilization amount of Pb(Ⅱ) by CaCO 3 @SiO 2 reached 3354 mg/g (over twice that of CaCO 3 ), and the removal rate of trace Pb(Ⅱ) (100 μg/L) was 99.5 %. The residual Pb(Ⅱ) concentration (5.5 μg/L) complies with WHO drinking water standard. Furthermore, CaCO 3 @SiO 2 showed selective removal of Pb(II), maintaining an 87 % percentage removal after 5 cycles of recycling. This study quantified dual mechanisms: surface adsorption-complexation dominated at low concentrations (100 % at 10 mg/L), while dissolution-precipitation plays the primary role at high concentrations (99.39 % at 500 mg/L), the removal mechanism of CaCO 3 @SiO 2 was greatly affected by the initial concentration of Pb(Ⅱ), therefore, the accurate contribution rate of each mechanism at different concentrations was calculated. The synergistic effect of CaCO 3 , its surface coated SiO 2, and the rate of increase in the system pH value was found to be the fundamental reason for the significant increase in the immobilization of Pb(Ⅱ) by CaCO 3 @SiO 2 .