Crystallography of the High-Temperature Ca 2 SiO 4 -Ca 3 P 2 O 8 Solid Solutions
- PDF / 1,064,023 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 65 Downloads / 199 Views
I.
INTRODUCTION
THE high refining ability of high basicity slags saturated with CaO makes them well suited for use in the dephosphorization of steel. Recently, there has been a shift towards relatively lower basicity slag saturated with a Ca2SiO4-Ca3P2O8 solid solution ((C2S-C3P)ss) rather than CaO saturated slags for use as dephosphorization slags.[1–4] It has been revealed by the Electron-Probe Micro Analysis (EPMA) of relatively low basicity steelmaking slags that they consist of two main phases. One phase is a matrix phase containing FexO with a small amount of other slag components. The other phase is a solid solution phase consisting of Ca2SiO4-Ca3P2O8, referred to in this study as (C2S-C3P)ss.[5–9] Among the components containing phosphorus in slag, the phosphorus removed from the metal gets concentrated in
HUAFANG YU, TAKAHIRO MIKI, YASUSHI SASAKI, AND TETSUYA NAGASAKA are with the Graduate School of Engineering, Tohoku University, Sendai, Miyagi 980-8579, Japan. Contact e-mail: [email protected] Manuscript submitted May 3, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
(C2S-C3P)ss,[10–12] and in the research of Shimauchi et al. showed the concentration of P2O5 in (C2S-C3P)ss can be increased up to 100 pct of Ca3P2O8.[13] At low basicity, however, the (C2S-C3P)ss becomes thermodynamically unstable, the phosphorous transfers from the slag to liquid steel, reducing the efficiency of dephosphorization. Therefore, to optimize dephosphorization efficiency, detailed information on the instability of (C2S-C3P)ss with this decrease in basicity is essential. Due to the development of a highly effective dephosphorization process, about 100 kt/year of phosphorus is currently accumulated in steelmaking slags in Japan,[14,15] which is about two times more than that of sewage sludge.[16] Approximately 50 kt of phosphorus is contained in the phosphate ore imported into Japan annually.[17] That is, the amount of phosphorus in the steelmaking slags is approximately twice that in the imported phosphate ore. It is reasonable, therefore, to regard steelmaking slag as an important potential secondary resource of phosphorus. Not only is this true in terms of quantity, but also quality:[18,19] compared to other possible secondary phosphorus resources, such as sewage sludge and industrial waste, steelmaking slags contain a relatively low level of toxic heavy metal contaminants, such as lead, mercury, and cadmium. Due to this, many researchers have focussed their attention on developing techniques to recover phosphorus from steelmaking slags at the laboratory scale.[5,20–25]
Since phosphorus is mainly accumulated in (C2S-C3P)ss during the dephosphorization process, the thermodynamic and physicochemical properties of (C2S-C3P)ss need to be well understood to produce high-quality steel by improving the efficiency of the dephosphorization process and for the effective recovery of phosphorous for recycling. Despite the important role of (C2S-C3P)ss in the dephosphorization process, however, little is known about its properties
Data Loading...
