Effect of B_2O_3 addition on mineralogical phases and leaching behaviorof synthetic CaO–SiO_2–MgO–Al_2O_3–CrOx slag

摘要

Boron oxide is frequently applied in modification of stainless steelmaking slag to mitigate the disintegration of slag. In thiswork, the effect of B_2O_3on mineralogical phases and hexavalent chromium leaching behavior of synthetic CaO–SiO_2–MgO–Al_2O_3–CrO_x slag was investigated. Di-calcium silicate, merwinite, spinel, akermanite, and matrix phase were observed asmain minerals in slags by scanning electron microscope (SEM) equipped with energy-dispersive spectrometry (EDS) andX-ray diffraction (XRD) techniques. It was found that 2% B_2O_3addition is sufficient to eliminate the disintegration of syntheticslag by suppressing the phase transition to γ-Ca_2SiO_4. The size of spinel phase increases with increasing B_2O_3,whichcould be well interpreted by enhanced Ostwald ripening. The amount of Ca_2SiO_4phase in slag was reduced by addition ofB_2O_3;however, excess B_2O_3(> 2%) addition would significantly increase chromium concentration and overall chromiumdistribution in Ca_2SiO_4phase. Leaching results according to US-EPA-3060A method indicated that excess boron oxideaddition (> 2%) leads to a significant increase of hexavalent chromium leaching concentrations and should be avoided forstabilizing stainless steel slag.