Application of layer double hydroxide in cementitious matrices for the improvement of the double Barrier Technique in the immobilisation of lead waste

This research deals with the immobilisation of lead-contaminated waste by means of the Double Barrier Technique. Specifically, the integral treatment of lead-contaminated water is studied by incorporating Layer Double Hydroxides (one calcined and two uncalcined) into cement monoliths. The three Layer Double Hydroxides were composed of MgAl in the layer, the calcined with carbonate in the interlayer, and the other two with nitrate or meso-2,3-dimercaptosuccinic acid, respectively. In the first stage of research, the influence of Layer Double Hydroxides and lead on the heat of hydration in cement pastes was analysed. Subsequently, mortars were produced to evaluate compressive strengths, mineralogy and leaching behaviour in monolithic and granular state. The interaction of sulphate ion played an important role in delaying the first stage of hydration. However, the presence of Layer Double Hydroxides counteracted the detrimental effect of lead on the cementitious materials. The compressive strength was modified by Layer Double Hydroxides and lead, less than 5 MPa in all cases, being in line with the heat of hydration. The mineralogical study determined the formation of the same mineral phases in all cementitious systems (with and without Layer Double Hydroxides). Mortars were environmentally classified as “Inert” in monolithic state. Mortar with MgAl in the layer and meso-2,3-dimercaptosuccinic acid in the interlayer was classified as “Non-Hazardous” in granular state reducing the mobility of lead to the medium by 50% with respect to the lead-doped mortar without Layer Double Hydroxides content. The results obtained in this research show the sustainability of the Double Barrier Technique as it achieves an immobilisation of lead-contaminated water while maintaining the criteria of release levels below the established limits.