The sensitive mobility of Cr in ashes studied by SiO-AlO-FeO-CaO system.

Since incineration is a feasible method for stabilization/solidification of chromium (Cr)-enriched wastes, the species, distribution, and mobility of Cr in ashes deserve more studies, especially as the function of ash composition. Synthetic Cr-bearing ashes (SAs) were synthesized by SiO-AlO-FeO-CaO systems to investigate Cr mobility under 1100 °C. A study from simplicity to complexity. The Cr in SiO-CaO is of high mobility with CrO formation, in contrary to the moderate mobility in SiO-AlO and poor mobility in SiO-FeO. However, species and mobility of Cr are affected by the values of CaO/SiO, AlO/SiO and FeO/SiO ratios. When other oxides are added to the two-phase systems above, the fate of Cr is affected more considerably. With the SiO content of 70%, adding a slight amount of CaO (<10%) strengthens the stabilization/solidification of Cr, due to the favorable solid integration under Ca fusion. However, the Cr mobility is higher with increasing the CaO content further. The minimum content of CaO is ∼20% to sufficiently decrease the proportion of residual Cr (QCr-S5) in SiO-AlO-CaO, much lower than in SiO-FeO-CaO, which confirms the easier release of Cr immobilized in Si-Al matrixes. Considering the opposite effects of FeO and CaO on Cr mobility, increasing FeO/CaO ratios >3/2 can limit the effect of CaO, leading to the efficient stabilization/solidification of Cr waste. Additionally, the QCr-S5 is 83% with the FeO content of 15% in SiO-AlO-FeO, higher than in SiO-AlO and SiO-FeO. This suggests the intense stabilization/solidification of Cr, probably due to the formation of amorphous Fe-rich glass. Based on these above, an equation is developed to describe the relationship between ash compositions and QCr-S5 (QCr-S5 = -39.37X + 24.96X + 5.34X - 2.51X + 54.29).