Iron ore sinter in the analytical transmission electron microscope

Abstract

Iron ore sinters prepared for the blast furnaces at Scunthorpe, Humberside, comprise iron oxides bound in a matrix of aluminium-and silicon-rich calcium ferrites with some calcium orthosilicate and a residual silicate glass. A super-silicon-deficient clinopyroxene with up to half of the Si in the chain replaced by Fe 3 + and A13 + precipitates from the glass in some areas. The iron oxides are principally magnetite and hematite with some w/istite in highly reduced areas. The calcium orthosilicate has been previously reported as the mineral larnite, fl-Ca2SiO4. This study found a range of Fe for Ca substitution and three polymorphs were recognised: the range Ca2SiO4 to Cal.ssFe0.15SiO4 has the structure of larnite; the range Cal.ssFe0.1sSiO 4 to Cal.6Fe0.4SiO4 has the structure of bredigite, e'-Ca2SiO4. Iron substitution beyond this, and up to a maximum of about Cal.sFe0.sSiO4, was not recognisable as a polymorph of CazSiO4, but an orthorhombic cell is tentatively proposed. The complex ferrite SFCA (silico-ferrite of Ca and A1) is variable in composition, but has a minimum of about 3 wt. ~o A1203 and contains 20 wt. ~ CaO and SiO 2 with a Ca: Si ion ratio of about 2 : 1. A C-face centred monoclinic cell has been deduced: a 15.70, b 9.70, c 8.48 A; fl 105o30 '. The A1 appears critical for the formation of SFCA in sinter; without it, a eutectic of magnetite and bredigite precipitates in preference.

A Review of the Chemistry, Structure and Formation Conditions of Silico-Ferrite of Calcium and Aluminum (‘SFCA’) Phases

“…CF 2 was also suggested to have the same crystal structure. In a similar study, Mulvaney 36) examined industrial and laboratory sinters by TEM and EPMA. He determined that the crystal structure of SFCA was not a magnetite superlattice but instead had a crystal structure identical to the CaSi 2 Fe 4 O 10 phase previously identified by Lister.…”

Evaluation of Iron Ore Concentrate and Micropellets as Potential Feed for Sinter Production

“…Based on the increasing SFCA-I as the micropellet content was increased, it can be argued that the degree of melt formation decreased. This can also be seen from the decrease in larnite which normally precipitates from silica rich parts of the melt (Mulvaney, 1987;Hapugoda et al, 2016). Since SFCA-I is mostly stable during the heating stage, those sinters containing high concentrations of SFCA-I suggest that not a large amount of melt remained.…”

Sintering Characteristics of Titanium Containing Iron Ores

“…Figure 8 shows the microstructure of a blend containing 1.0% TiO2 sintered at 1 290°C, indicating the presence of a large fraction of larnite phase. It has been shown 18) that larnite is thermodynamically unstable below 675°C and can invert to a stable phase of γ-Ca2SiO4. Then, it is expected that if larnite forms in the sinter melt, it can invert to γ-Ca2SiO4 (known as CalsioOlivine) during cooling of the sinter.…”