A Short Review of the Effect of Iron Ore Selection on Mineral Phases of Iron Ore Sinter

The sintering process is a thermal agglomeration process, and it is accompanied by chemical reactions. In this process, a mixture of iron ore fines, flux, and coal particles is heated to about 1300 °C–1480 °C in a sinter bed. The strength and reducibility properties of iron ore sinter are obtained by liquid phase sintering. The silico-ferrite of calcium and aluminum (SFCA) is the main bonding phase found in modern iron ore sinters. Since the physicochemical and crystallographic properties of the SFCA are affected by the chemical composition and mineral phases of iron ores, a crystallographic understanding of iron ores and sintered ore is important to enhance the quality of iron ore sinter. Scrap and by-products from steel mills are expected to be used in the iron ore sintering process as recyclable resources, and in such a case, the crystallographic properties of iron ore sinter will be affected using these materials. The objective of this paper is to present a short review on research related to mineral phases and structural properties of iron ore and sintered ore.

Automated Optical Image Analysis of Iron Ore Sinter

Sinter quality is a key element for stable blast furnace operation. Sinter strength and reducibility depend considerably on the mineral composition and associated textural features. During sinter optical image analysis (OIA), it is important to distinguish different morphologies of the same mineral such as primary/secondary hematite, and types of silico-ferrite of calcium and aluminum (SFCA). Standard red, green and blue (RGB) thresholding cannot effectively segment such morphologies one from another. The Commonwealth Scientific Industrial Research Organization’s (CSIRO) OIA software Mineral4/Recognition4 incorporates a unique textural identification module allowing various textures/morphologies of the same mineral to be discriminated. Together with other capabilities of the software, this feature was used for the examination of iron ore sinters where the ability to segment different types of hematite (primary versus secondary), different morphological sub-types of SFCA (platy and prismatic), and other common sinter phases such as magnetite, larnite, glass and remnant aluminosilicates is crucial for quantifying sinter petrology. Three different sinter samples were examined. Visual comparison showed very high correlation between manual and automated phase identification. The OIA results also gave high correlations with manual point counting, X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) analysis results. Sinter textural classification performed by Recognition4 showed a high potential for deep understanding of sinter properties and the changes of such properties under different sintering conditions.

Characterization and abatement of SOx, NOx and PCDD/Fs in iron ore sinter machine wind legs

It was observed that SOx and NOx, in large concentrations, are getting released from certain wind boxes below the sinter machine. The particulates released from specific wind legs were characterized using Quantitative Evaluation of Materials by Scanning Electron Microscopy (QEMSCAN). Particulates with spherical, cubical, needle and bar-like morphologies containing K, Na, Cl were found. Nitrogen-based solids were found in clutter-like morphology. Some particles had a mixture of the above, SOx and NOx. A method of dissolving SOx, NOx and breaking them down into harmless substances was explored in this research. The deposits in the wind legs were dissolved in demineralized water and solutions of sodium bicarbonate, urea, and di-sodium borate deca-hydrate (borax) to estimate the absorbance of K, Na, Cl, Ca, Mg, S, and N based compounds present. Demineralized water and sodium bicarbonate were found to be the most effective sorbents of SOx and NOx. The filtrates were examined under QEMSCAN and found that SOx and NOx are not present. Based on the above finding, a solution of sodium bicarbonate and water 0.01% v/v was sprayed into a wind box and found that SOx and NOx have got reduced by about 55%. To maximize the capture of SOx and NOx, the solution was optimized at 0.02% v/v. With this novel technique, capital intensive Desulphurization (De-SOx) and Denitrification (De-NOx) installation can be avoided. Additionally, an economical solution to the Polychlorinated dibenzo para-dioxins and polychlorinated dibenzofurans (PCDD/Fs) emission was explored in this research. Various physicochemical mechanisms of forming harmful substances are described in this paper.

SFCA-II type Ca2.46Fe3+8.57 Fe2+0.52Al5.45O24 – an improved structural model for an iron-ore sinter phase

Single crystals of SFCA-II with composition Ca2.46Fe3+8.57Fe2+0.52Al5.45O24 have been obtained from synthesis experiments in the temperature range between 1300 and 1200 °C. Diffraction experiments at ambient conditions yielded the following basic crystallographic data: space group P$$ \overline{1} $$ 1 ¯ , a = 10.3016(4) Å, b = 10.4656(4) Å, c = 17.9553(6) Å, α = 90.062(3), β = 89.977(3)°, γ = 109.510(3)°, V = 1824.66(12) Å3, Z = 4. Structure determination and subsequent least-squares refinements resulted in a residual of R(|F|) = 0.0349 for 7406 independent reflections and 773 parameters. Site occupancy refinements on the 35 octahedral (M) and tetrahedral (T) positions in the asymmetric unit were aided by crystallochemical considerations and the assumption of charge balance between the cations and anions. The derived formula compares well with the outcome of electron microprobe studies. The crystal structure of SFCA-II shows the typical features of the SFCA-family. It can be built from an alternating sequence of two different types of fundamental layers. For SFCA-II, they are oriented parallel to (100). Layer-type I is solely based on [MO6]-octahedra (M: Ca, Fe3+, Al) forming individual five polyhedra wide bands. Within a single band, the octahedra share common edges. Layer-type II, on the other hand, contains [MO6]-octahedra as well as [TO4]-tetrahedra (T: Al, Fe3+, Fe2+). By corner sharing each [MO6]-group is linked to two adjacent tetrahedra into [MT2O12]-clusters or “winged octahedra”. Linkage between neighboring strips of these moieties is provided by additional [TO4]-tetrahedra arranged in vierer single-chains. Our investigation rectifies previous studies on SFCA-II where wrong atomic coordinates have been published.