Evolution of Pb speciation in Portland cement during leaching

Heavy metals, coming from raw materials and combustibles, are present in trace amount in cement. This study aims at evaluating Pb long-term behaviour, linking the evolution of Pb speciation due to leaching, with changes in the structure of the bearing mineralogical phases of the cement. EXAFS experiments point out a Pb retention through calcium silicate phases, but also show changes in Pb atomic environment due to leaching. These changes would be due to evolution in calcium silicate hydrates (C-S-H) structure with alteration, as 29 Si NMR shows lengthening of the chains of silicon tetrahedron in the C-S-H.