제강슬래그의 수용액중 불소용출에 대한 산소 포텐셜 영향

Abstract

This paper studies effect of oxygen partial pressure at molten flux state on the fluorine dissolution from synthetic steelmaking slag solidified from the flux. The Po2’s were set as 6.6x10-8, 8.1x10-5, 2.9x10-3, 1.5x10-2, 1.1x10-1, or 6.6x103 Pa, by changing the CO/CO2 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 (~3 at%) and F (~0.3 at%). The phases and their distribution is characterized using SEM, EDS (point and mapping), Rietveld refinement of XRD. Increase of Po2 reduces fluorine dissolution, and the amounts of dissolution are higher than 1 mg/l when processed at Po2 < 10-2 Pa, but are about or less than 0.5 mg/l when processed at Po2 > 10-2 Pa. These results indicate that the low Po2 processed slag has large fraction of low density Mayenite (Ca12Al14O33) with most of fluorine in its sparse crystal structure, and liberates large amount of fluorine. On the contrary, the high Po2 processed slag is mainly composed of high density Brownmillerite (Ca2AlxFe2-xO5), and the fluorine exists as CaF2 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. The effect of Al2O3/(Al2O3+Fe2O3) molar ratios in CaO-Al2O3-FeOx-CaF2 slag system on the dissolution of fluorine were investigated. Also, the effect of oxygen partial pressure in CaO-SiO2-(Al2O3)M.L-(FeOx)H.L-MgO-CaF2 slag system on the dissolution of fluorine was investigated by analyzing the O1s of slag crystal structure with XPS and the respective relationship of oxygen bonding state and oxygen partial pressure to the dissolution of fluorine was investigated. The results are as follows: 1) In the case of CaO-Al2O3-FeOx-CaF2 slag system, as A/(A+F) increased, T-F within slag decreased and the amount of dissolved fluorine decreased proportionally with T-F.2) In the case of CaO-SiO2-(Al2O3)M.L-(FeOx)H.L-MgO-CaF2 slag system, when the oxygen partial pressure is low (Po2<10-3.34 Pa), the Fe1-xMgxO phase increases and the brownmillerite decreases, hence, the amount of dissolved fluorine increased. When the oxygen partial pressure is high (Po2>10-1.83 Pa), brownmillerite(Ca2(AlxFe2-xO5) becomes closer to Ca2Fe2O5, due to the increase in Fe2O3. As the ability to stabilize fluorine decreased, the amount of dissolved fluorine increased.3) For the samples of CaO-SiO2-(Al2O3)M.L-(FeOx)H.L-MgO-CaF2 slag system,, O1s peak were deconvoluted into three peaks (530.6, 528.9 and 527.0eV) in the XPS analysis. When the oxygen partial pressure is low (Po2<10-3.34 Pa), Mg-O-Fe2+ increases and when the oxygen partial pressure is high (Po2>10-1.83 Pa), the chemical adsorptive oxygen increases, hence, the increase in amount of dissolved oxygen in both cases. When the oxygen partial pressure was in between the values mentioned above (Po2= 10-3.34 ~ 10-0.98 Pa ), the amount of dissolved fluorine was below 0.8mg/L.