Effects of P_(O_2) at Flux State on the Fluorine Dissolution from Synthetic Steelmaking Slag in Aqueous Solution

摘要

This paper studies effect of oxygen partial pressure at molten flux state on the fluorine dissolution from synthetic steetmaking slag solidified from the flux. The P_(O_2)'s were set as 6.6×10~(-8), 8.1 ×10~(-5), 2.9×10~(-3), 1.5×10~(-2), 1.1×10~(-1), or 6.6×10~3 Pa, by changing the CO/CO_2 ratio of environmental flowing gas. The Ca: Al: Fe atomic ratio of major cations of the slag (oxide) is 23 :9:13, and minor constituents are Mg (～3at%) and F (～0.3 at%). The phases and their distribution is characterized using SEM, EDS (point and mapping), Ri-etveld refinement of XRD. Increase of P_(O_2)( reduces fluorine dissolution, and the amounts of dissolution are higher than 1 mg/L when processed at P_(O_2)<10~(-2) Pa, but are about or less than 0.5 mg/L when processed at P_(O_2)>10~(-2) Pa. These results indicate that the low P_(O_2) processed slag has large fraction of low density Mayen-ite (Ca_(12)Al_(14)0_(33)) with most of fluorine in its sparse crystal structure, and liberates large amount of fluorine. On the contrary, the high P_(O_2) processed slag is mainly composed of high density Brownmillerite (Ca_2Al_xFe_(2-x)O_5), and the fluprine exists as CaF_2 particles not to liberate fluorine easily. It is concluded that the fluorine dissolution is strongly governed by the amount of phases, the density and empty space of each crystal structure to accommodate fluorine, and their distribution.