Effects of MnO and CaO/SiO₂Mass Ratio on Phase Formations of CaOAl₂O₃MgOSiO₂CrO_xSlag at 1673 K and PO2=10−10 atm

Abstract

The knowledge on distribution of mineralogical phase in slag is of vital importance to disposal and utilization of slag. Despite of certain amount (up to 5%) of MnO found in stainless steel slag, MnO distribution in phases of slag was not thoroughly investigated. In this work, phases of synthetic CaO–Al2O3–MgO–SiO2–CrOx–MnO slag with varied CaO/SiO2 and MnO content, which was soaked at 1673 K for 12 h, were determined by combining SEM‐EDS and XRD technique. Phases for samples with CaO/SiO2 ratio of 1.5 and 1.3 were composed of Ca2SiO4, merwinite, spinel, and liquid phase, while phases for samples with CaO/SiO2 ratio of 1.1 are composed of spinel and liquid phase. The calculated phases by FactSage were in good agreements with observed ones by SEM‐EDS and XRD. Manganese was found to be enriched in spinel and liquid, and chromium is enriched in spinel, and only negligible Cr could be found in merwinite and Ca2SiO4. The spinel increases in size with increasing of MnO and decreasing of CaO/SiO2 ratio. Disintegration was found in samples with increased MnO content and CaO/SiO2 ratio. The size of Ca2SiO4 crystal increases in size with increase of MnO content and CaO/SiO2 ratio, which could interpret the disintegration of slag. The present investigation indicates that MnO content has important effects on disintegration and spinel precipitation in stainless steel slag.

Immobilization of Chromium in Stainless Steel Slag Using Low Zinc Electric Arc Furnace Dusts

“…[9] Albertsson et al [10,11] indicated that slow cooling, low oxygen partial pressure and low slag basicity (1.0 to 1.4) can improve the spinel phase precipitation. Shu et al [12] found that the size of the spinel phase increased with increasing MnO content and decreasing CaO/SiO 2 ratio. However, disintegration was found in samples with a high MnO content and CaO/ SiO 2 ratio.…”

“…[6,7] Hence, the immobilization of chromium in stainless steel slag has been investigated by many researchers. [8][9][10][11][12][13][14][15] Romero-Serrano et al [8] reported that chromium leaching was suppressed by adding MgO to the CaO-SiO 2 -Cr 2 O 3 system, which was attributed to stable binding of chromium in the MgCr 2 O 4 phase. They also found that the addition of FeSO 4 and FeS 2 had positive effects on the immobilization of chromium.…”

Effect of B2O3 addition on mineralogical phases and leaching behavior of synthetic CaO–SiO2–MgO–Al2O3–CrOx slag

“…The mitigation of disintegration of slag could be achieved by some physical methods, such as rapid cooling to suppress the phase transition [3]. The modification of slag could be performed by additives to mitigate the disintegration of slag and immobilize chromium in slag [4][5][6][7][8][9]. It is well accepted that spinel phase is very stable during oxidation and leaching due to the strong bonding of chromium in spinel phase [2].…”

“…Modification with MgO could mitigate the precipitation of Ca 2 SiO 4 [4] and be beneficial to spinel formation during solidification of slag [5,6]. The additions of appropriate amounts of Al 2 O 3 [5,7], MnO [8], and FeO [9] were found to promote the spinel formation. Meanwhile, low basicity [6,8,10] and oxygen partial pressure [11] have a positive influence on spinel precipitation.…”

“…[19]. The basicity of synthetic slag (defined as the mass ratio of CaO to SiO 2 ) was maintained as 1.5, considering that the basicity of industrial stainless steel slag is generally in the range of 1.0 ~ 2.5 [5][6][7][8][9][10][11]. The contents of MgO, Al 2 O 3 , and Cr 2 O 3 in slags were fixed as 8.0, 6.0, and 6.0, respectively.…”