Potential application of ettringite generating systems for hazardous waste stabilization

The potential of ettringite generating systems in hazardous waste stabilization processes is studied by means of a mixture of anhydrous calcium sulphoaluminate and anhydrite doped with the nitrates of the six heavy metals Cu, Cr, Cd, Pb, Zn and Fe. The study has been carried out by means of differential thermal and X-ray diffraction analyses, infra-red spectroscopy, scanning electron microscopy coupled with an energy dispersion system and three different leaching tests. The presence of the metals has only a small negative effect on the hydration kinetics. The hydrated samples retain their structural integrity when submitted to the dynamic leaching test in water and pH 4 HNO3 solution, while they are disintegrated when the leachant is a pH 4.74 acetate buffer. The sulphoaluminate phases can partially accommodate any metal in the crystal lattice, thus giving rise to chemical entrapment.