Formation of leadhillite and calcium lead silicate hydrate (C–Pb–S–H) in the solidification/stabilization of lead contaminants

In this study, we have investigated the structure of Pb-doped solidified waste forms (SWF) for assessment of lead fixation. A large quantity of lead precipitates produced during the S/S, based upon the results of cement–water solution analysis, X-ray diffraction and electron probe microanalysis/electron dispersive spectroscopy investigations, have been shown to be principally leadhillite (lead carbonate sulfate hydroxide, Pb4SO4(CO3)2(OH)2), lead carbonate hydroxide hydrate (3PbCO3 · 2Pb(OH)2 · H2O) and two other unidentified lead salts. In the long curing, the lead species dissolved from the lead precipitates are fixed into the cement matrix, forming a gelling calcium lead silicate hydrate during cement-based solidification. On leaching the lead precipitates such as leadhillite were markedly dissolved/released and some dissolved lead species were adsorbed to silicate-rich surface of leached SWF with the subsequent formation of mainly amorphous gel of calcium lead silicate hydrate.