Pre-reduction of United Manganese of Kalahari Ore in CO/CO2, H2/H2O, and H2 Atmospheres

The incorporation of hydrogen, which is a relatively unexplored reductant used during ferromanganese (FeMn) production, is an attractive approach to lessen atmospheric gaseous carbon release. The influence of hydrogen on the pre-reduction of carbonate-rich United Manganese of Kalahari (UMK) ore from...

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Published in:Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 54; no. 2; pp. 515 - 535
Main Authors: Davies, J., Tangstad, M., Schanche, T. L., du Preez, S. P.
Format: Journal Article
Language:English
Published: New York Springer US 01.04.2023
Springer Nature B.V
Subjects:
Atmospheres
Carbon dioxide
Carbonates
Characterization and Evaluation of Materials
Chemistry and Materials Science
Decomposition
Electron probe microanalysis
Electron probes
Ferromanganese
Hydrogen
Iron
Magnesium
Manganese ores
Materials Science
Mathematical analysis
Metallic Materials
Metallizing
Nanotechnology
Original Research Article
Oxidation
Oxides
Phase stability
Reduced ores
Reducing agents
Structural Materials
Surfaces and Interfaces
Thin Films
Valence
Weight loss
ISSN:1073-5615, 1543-1916
Online Access:Get full text
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Summary:The incorporation of hydrogen, which is a relatively unexplored reductant used during ferromanganese (FeMn) production, is an attractive approach to lessen atmospheric gaseous carbon release. The influence of hydrogen on the pre-reduction of carbonate-rich United Manganese of Kalahari (UMK) ore from South Africa was investigated. Experiments were performed in 70 pct CO 30 pct CO 2 (reference), 70 pct H 2 30 pct H 2 O, and 100 pct H 2 gas atmospheres at 700 °C, 800 °C, and 900 °C. Calculated phase stability diagrams and experimental results showed good correlation. The pre-reduction process involved two reactions proceeding in parallel, i.e ., the pre-reduction of higher oxides and the decomposition of carbonates present in the ore. A thermogravimetric (TG) furnace was employed for the pre-reduction of the ore in various atmospheres. The calculated weight loss percentage was used to determine the degree and rate of pre-reduction. It was found that the oxidation state of higher Fe- and Mn-oxides was lowered when treated in 70 pct H 2 30 pct H 2 O and 70 pct CO 30 pct CO 2 , whereas FeO was metalized when using 100 pct H 2 . As for the intrinsic carbonates, the majority thereof were decomposed in the CO/CO 2 atmosphere at 900 °C, and ≥ 700 °C in the H 2 /H 2 O and H 2 atmospheres. Additionally, the degree and rate of reduction were accelerated by increasing the pre-reduction temperature and by employing a hydrogen-containing gas atmosphere (70 pct H 2 30 pct H 2 O, and 100 pct H 2 ). Scanning electron microscopy and electron microprobe analysis revealed the presence of three phases in the pre-reduced ore: (i) Mn- and Fe-rich, (ii) Mg- and Ca-rich, and (iii) Mg-, Si-, K-, and Na-rich. It was also found that there were no appreciable differences in porosity and decrepitation of the ores treated in the CO/CO 2 and hydrogen-containing atmospheres. The use of a hydrogen atmosphere showed potential for the pre-reduction of carbonate-containing manganese ores as it accelerated the decomposition of the carbonates as well as facilitated the metallization of Fe-oxides present in the ore.
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ISSN:1073-5615
1543-1916
DOI:10.1007/s11663-022-02705-0