Pre-reduction Behaviour of Manganese Ores in H&lt;sub&gt;2&lt;/sub&gt; and CO Containing Gases

Ngoy, Didier; Sukhomlinov, Dmitry; Tangstad, Merete

doi:10.2355/isijinternational.isijint-2020-120

Cited by 14 publications

(16 citation statements)

References 17 publications

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“…In the hydrogen-containing gas mixtures, all experiments at 700 • C and 800 • C were fully reduced after 210 min (O/Mn = 1.00-1.01 by chemical analyses), and the reduction rate increased with decreasing pO 2 , which is consistent with previous results [15]. Addition of hydrogen was seen to increase the reduction rate less for the low pO 2 parallels (Figure 7a) compared to the high pO 2 parallels (Figure 7b).…”

Section: Resultssupporting

confidence: 91%

“…The correlation between reactivity and porosity suggests that a lower mass transfer resistance in the material improves the reduction rate. Ngoy et al found that addition of hydrogen to the reducing gas improved the reduction rate compared to CO-CO 2 mixtures with similar oxygen partial pressure [15]. Larssen et al (2021) investigated the reduction of different size fractions of Nchwaning ore in various CO/CO 2 gas mixtures [16] and found that the reduction rate was proportional to the inverse average particle size and to p CO to the power of 1.5 [17].…”

Section: Introductionmentioning

confidence: 99%

“…Hydrogen can be produced from renewable sources and, thus, has the potential to be carbon-neutral. With its additional advantage of improving the reduction kinetics [15], it is an excellent candidate for pretreatment.…”

Section: Introductionmentioning

confidence: 99%

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Prereduction of Nchwaning Ore in CO/CO2/H2 Gas Mixtures

Schanche

Tangstad

2021

Minerals

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Prereduction of Nchwaning manganese ore was investigated by isothermal reduction between 600 and 800 °C to optimize the conditions for industrial pretreatment of manganese ores. Experiments were conducted in CO/CO2 gas mixtures with and without hydrogen at two different oxygen partial pressures. Ore in the size fraction 9.52–15 mm was reduced in a thermogravimetric furnace, and the O/Mn ratio from the chemical analysis was used to determine the extent of prereduction. The samples were investigated by X-ray diffraction to investigate the evolution of phases under the course of reduction. The X-ray diffraction revealed that bixbyite and braunite (I and II) were reduced to manganosite with no or limited formation of hausmannite. Reduction of iron oxides subsided with wüstite, which is stabilized by manganese in the monoxide phase, and hydrogen was seen to improve the reduction of iron oxides. Modeling revealed that the reduction rate increased 2.8-fold upon increasing the CO content from 30% to 70% in a CO/CO2 gas mixture. The addition of hydrogen improved the reduction rate with factors of 1.3 and 2.6 for the low and the high oxygen partial pressures, respectively. Hence, the optimal conditions for pretreatment can be achieved by keeping the oxygen partial pressure as low as possible while adding hydrogen to the reducing gas and ensuring a high reduction temperature. Successful pretreatment limits the extent of the Boudouard reaction in the submerged arc furnace, reducing the amount of CO produced and, thus, reducing the CO available for pretreatment. Hydrogen is a useful addition to the pretreatment unit since it lowers the oxygen partial pressure and improves the kinetics of prereduction.

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Section: Resultssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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Prereduction of Nchwaning Ore in CO/CO2/H2 Gas Mixtures

Schanche

Tangstad

2021

Minerals

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“…In general, there is a positive correlation between porosity and reactivity, indicating that a lower mass transfer resistance within the materials improves the reduction rate. Ngoy et al, 2020 found that the addition of hydrogen to the reducing gas increased the reduction rate compared to CO/CO2 mixtures at similar oxygen partial pressures. Larssen, 2020, did Where k0 [cm/atm•min]is the frequency factor , Ea [J/mol] is the activation energy, R [J/mol•K] is the universal gas constant, T [K] is temperature, pCO [atm] is the CO partial pressure , rp [cm] is the average particle size, n and m are constants, X is the degree of reduction and dX/dt is the reduction rate [1/min].…”

Section: Pretreatment Unitmentioning

confidence: 95%

Isothermal Reduction of Nchwaning Manganese Ore in CO/CO2/H2 Atmospheres

Schanche

Tangstad

2021

SSRN Journal

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“…Typically, metallurgical grade ores contain more than 35 pct Mn and literature [8][9][10][11][12][13][14] covers properties of ores with Comilog, CVRD, Groote Eylandt, Wessels and Mamatwan type ores as examples. Several studies [10,11,[15][16][17][18][19][20][21][22] have been conducted on the prereduction of manganese ores by either CO gas or solid carbon.…”

Section: ½8mentioning

confidence: 99%

Prereduction Behavior of Manganese Ores With Solid Carbon and in CO/CO2 Gas Atmosphere

Mukono

Reiersen

Schanche

et al. 2022

Metall Mater Trans B

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The prereduction reactions in the submerged arc furnace (SAF) are highly decisive of the total carbon, and energy consumption of the ferromanganese process. Therefore, understanding the dependency of prereduction behavior on ore characteristics and furnace conditions is of paramount importance. Prereduction behavior of Comilog, Nchwaning and UMK ores with solid carbon was studied in an open 75 kVA induction furnace set up simulating the conditions of an industrial SAF. In addition, the ores were thermogravimetrically studied with non-isothermal heating to 1000 °C in a flowing 70/30 CO/CO2 atmosphere. Gasification of carbon according to Boudouard reaction was considered significant for carbonate ores in induction furnace setup. UMK had a greater extent of prereduction compared to Nchwaning which is low in carbonates and Comilog which is known to have a higher CO reactivity at similar CO contents. TGA rate curves shows that prereduction of UMK ore occurred with two major distinctive steps. The first one was a combination of prereduction reactions and decomposition of carbonates with a peak temperature of 700 °C, and the second peak was the decomposition of calcite at 900 °C. The O/Mn ratio for UMK shows that prereduction is already completed prior to the second decomposition peak at 900 °C. In addition to prereduction reactions, Nchwaning is also characterized by an endothermic step which is decomposition of carbonates at 900 °C. Comilog ore produced the most fines followed by Nchwaning and lastly UMK on decrepitation.

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Pre-reduction Behaviour of Manganese Ores in H<sub>2</sub> and CO Containing Gases

Cited by 14 publications

References 17 publications

Prereduction of Nchwaning Ore in CO/CO2/H2 Gas Mixtures

Prereduction of Nchwaning Ore in CO/CO2/H2 Gas Mixtures

Isothermal Reduction of Nchwaning Manganese Ore in CO/CO2/H2 Atmospheres

Prereduction Behavior of Manganese Ores With Solid Carbon and in CO/CO2 Gas Atmosphere

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