Chemical Entrapment of Divalent Lead By Ettringite

This work aims to make clear whether Pb(II) can be chemically entrapped by ettringite and find out under what conditions this entrapment can take place. In experiment condition, several chemical analytical reagents were used to synthesize the lead analog of ettringite {Pb₆[Al(OH)₆]₂ldr3SO₄ldr26H₂O}, Ca-Pb ettringite {(Ca,Pb)₆ [Al(OH)₆]₂ldr3SO₄ldr26H₂O} and plumbite ettringite {3CaOldr Al₂O₃ldr3CaPbO₂ldr31H₂O}. The results showed that the lead analog of ettringite and the plumibte ettringite couldn´t be synthesized, while Ca-Pb ettringite could be made. This indicated that Pb(II) couldn´t be chemically entrapped by ettringite when divalent calcium or sulfate was absent in liquid phase. However, Pb(II) could entrapped into ettringite lattice when calcium ions existed in liquid phase to formed Ca-Pb ettringite. The X-ray diffraction patterns of Ca-Pb ettringite were significantly different from that of Ca-ettringite, indicating that ettringite´ lattice been varied after accommodating divalent lead. Experiments on Pb(II) solidified by 100% type I clinker showed that the XRD patterns of the paste at 7-day storage period changed after they doped divalent lead, These further confirmed that Pb(II) could be entrapped into cement minerals including ettringite.