Evaluation of effect of reducing additives during vitrification via simulation and experiment

Abstract

This study investigates how reducing additives governed the vitrification of prepared specimens. In the experiments, pure CaO/CaCO3 and SiO2 served as the major components of glassy matrix (basicity = mass ratio of CaO/SiO2 = 2/3) with doping of hazardous metals (Cr, Cu, and Ni). The substitution ratio of CaCO3 for CaO was used as an operating parameter. The specimens were vitrified at 1400°C and a sequential extraction protocol was used to determine the phase distribution of Cr, Cu, and Ni. The volume fractions of crystalline and amorphous phases were measured using semiquantitative x-ray diffraction (XRD) analysis. A commercial software package (HSC Chemistry 6.0) was used to simulate the experiment to acquire additional information. The simulation results showed the addition of CaCO3 generated CO and CO2 at high temperature. This reducing atmosphere might enhance Cu and Ni to be easily separated from slags and elevated the levels of Cu and Ni in ingots. At higher CaCO3 mol(%), the polymerization of silicate (from sorosilicate to inosilicate) in slag rose and the CaSiO3 amount increased. In addition, the immobilization of metals and the acid resistance of slags were improved. The results indicate that CaCO3 addition is favorable for increasing the metal level in ingots and the metal encapsulation in slag in vitrification. Implications: Vitrification techniques are often used to treat hazardous materials. The additives used in vitrification processes play an important role in vitrification. This study combines simulations (based on HSC Chemistry) and experiments to evaluate the effect of CaCO3 addition (creating a reducing atmosphere) on toxic metal stabilization in vitrification. This way, the effects of different parameters on toxic metal stabilization in vitrification can also be evaluated.