Reactions of lead ion in mixtures of silica and magnesia

Lead (Pb) is one of the toxic heavy metals found in many cases of soil pollution. Stabilization of lead contaminated soils by use of cement is the most popular way of remediation. However, in cases of multiple contaminations by lead and fluorine, magnesia may be superior to cement. To explore the possibility of immobilization of lead with magnesia, we mixed silica, magnesia and solutions of lead nitrate at a solid: solution ratio of 1 kg:2 L and the reaction products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and sequential extraction of lead. The reaction of the mixture was alkaline just after mixing and became neutral after 5 days. After 5 days and on, only 0.0018 to 0.0051% of the lead in the mixture was extractable in water, 1 mol L^-1 MgCl₂ and NaOAc, whereas 25 to 30% was extractable in HCl. The XRD and FTIR spectra showed that lead was stabilized as carbonates and hydroxides.