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Investigating the parameters that influence the behaviour of natural iron ores during the iron production process
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.ORCID iD: 0000-0002-5223-7857
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the iron production processes, sinters and pellets are mostly used as raw materials due to their consistency with respect to physical and chemical properties. However, natural iron ores, as mined, are rarely used directly as a feed material for iron processing. This is mainly due to the fact that they have small contents of iron and high concentration of impurities. Moreover, they swell and disintegrate during the descent in the furnace as well as due to low melting and softening temperatures. This work involves an investigation of the parameters that influence the use of natural iron ores as a direct feed material for iron production. Furthermore, it points out ways in which these can be mitigated so as to increase their direct use in iron production.

Natural iron ore from Muko deposits in south-western Uganda was used in this study. Initially, characterisation of the physical and chemical properties was performed, to understand the natural composition of the ore. In addition, investigations were done to study the low temperature strength of the ore and its behaviour in the direct reduction zone. Also, simulations were performed with three models using the experimental data from the direct reduction experiments in order to determine the best model for predicting the direct reduction kinetics of natural iron ores.

Chemical analyses showed that the Muko ore represents a high grade of hematite with an Fe content of 68% on average. The gangue content (SiO2+Al2O3) in 5 of the 6 investigated iron ore samples was < 4%, which is within the tolerable limits for the dominant iron production processes. The S and P contents were 0001-0.006% and 0.02-0.05% respectively. These can be reduced in the furnace without presenting major processing difficulties. With respect to the mechanical properties, the Muko ore was found to have a Tumble Index value of 88-93 wt%, an Abrasion Index value of 0.5-3.8 wt% and a Shatter Index value of 0.6-2.0 wt%. Therefore, the ore holds its form during the handling and charging processes.

Under low temperature investigations, new parameters were discovered that influence the low temperature strength of iron oxides. It was discovered that the positioning of the samples in the reduction furnace together with the original weight (W0) of the samples, have a big influence on the low temperature strength of iron oxide. Higher mechanical degradation (MD) values were obtained in the top furnace reaction zone samples (3-25% at 500oC and 10-21% at 600oC). These were the samples that had the first contact with the reducing gas, as it was flowing through the furnace from top to bottom. Then, the MD values decreased till 5-16% at a 500oC temperature and 6-20% at a 600oC temperature in the middle and bottom reaction zones samples. It was found that the obtained difference between the MD values in the top and other zones can be more than 2 times, particularly at 500oC temperature. Furthermore, the MD values for samples with W0 < 5 g varied from 7-21% well as they decreased to 5-10% on average for samples with W0 ≥ 5 g. Moreover, the MD values for samples taken from the top reaction zone were larger than those from the middle and bottom zones.

During direct reduction of the ores in a H2 and CO gas mixture with a ratio of 1.5 and a constant temperature, the reduction degree (RD) increased with a decreased flow rate until an optimum value was established. The RD also increased when the flow rate was kept constant and the temperature increased. An optimum range of 3-4g was found for natural iron ores, within which the highest RD values that are realised for all reduction conditions. In addition, the mechanical stability is greatly enhanced at RD values > 0.7. In the case of microstructure, it was observed that the original microstructure of the samples had no significant impact on the final RD value (only 2-4%). However, it significantly influenced the reduction rate and time of the DR process.

The thermo-gravimetric data obtained from the reduction experiments was used to calculate the solid conversion rate. Three models: the Grain Model (GM), the Volumetric Model (VM) and the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. The random pore model (RPM) provided the best agreement with the obtained experimental results (r2 = 0.993-0.998). Furthermore, it gave a better prediction of the natural iron oxide conversion and thereby the reduction kinetics. The RPM model was used for the estimation of the effect of original microstructure and porosity of iron ore lumps on the parameters of the reduction process.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , ix, 42 p.
Keyword [en]
natural iron ore, iron production, characterization, physical and metallurgical properties, sinter, pellet, direct reduction, low temperature degradation, sample weight, sample positioning, microstructure, reduction degree, solid conversion, Volumetric Model, Grain Model, Random Pore Model, Muko, Uganda
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-123063ISBN: 978-91-7501-750-1 (print)OAI: oai:DiVA.org:kth-123063DiVA: diva2:624400
Public defence
2013-06-13, B2, MSE Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Sustainable Technology Development in the Lake Victoria Region
Funder
Sida - Swedish International Development Cooperation Agency, 5410004501
Note

QC 20130531

Available from: 2013-05-31 Created: 2013-05-31 Last updated: 2017-03-07Bibliographically approved
List of papers
1. Characterization of chemical composition and microstructure of natural iron ore from Muko deposits
Open this publication in new window or tab >>Characterization of chemical composition and microstructure of natural iron ore from Muko deposits
2012 (English)In: ISRN Materials Science, ISSN 2090-6080, E-ISSN 2090-6099, Vol. 2012, 9- p.Article in journal (Refereed) Published
Abstract [en]

The study aimed at investigating the chemical composition and microstructure of raw iron ore from the deposits in Muko area (south-western Uganda). The quality of this iron ore was evaluated to establish its suitability to serve as a raw material for iron production. Samples were taken from the six hills of Muko ore deposits and tests carried out to establish their composition and properties. X-ray diffraction and scanning electron microscopy were employed in the investigation and chemical analysis performed to determine the compounds constituting the ore. The quality of this ore was compared to generalized world market standards and ores from other nations. It was found that Muko ore is a rich hematite grade with Fe content above 65%. It has little gangue (<6% SiO2 and 3-4% Al2O3) and low contents of the deleterious elements (P ~ 0.02% and S < 0.006%), which correspond to acceptable levels for commercial iron ores.

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2012
Keyword
raw iron ore; hematite; chemical composition; microstructural analysis; Uganda
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-123054 (URN)10.5402/2012/174803 (DOI)
Projects
Sustainable Technology Development in the Lake Victoria Region
Funder
Sida - Swedish International Development Cooperation Agency, 5410004501
Note

QC 20130531

Available from: 2013-05-31 Created: 2013-05-31 Last updated: 2017-12-06Bibliographically approved
2. Characterisation of the Physical and Metallurgical Propertiesof Natural Iron Ore for Iron Production
Open this publication in new window or tab >>Characterisation of the Physical and Metallurgical Propertiesof Natural Iron Ore for Iron Production
2012 (English)In: ISRN Materials Science, ISSN 2090-6080, E-ISSN 2090-6099, Vol. 2012, 9- p.Article in journal (Refereed) Published
Abstract [en]

The blast furnace is still the dominant form of iron production, but over the years, direct reduction methods have increased due to a number of reasons. Overall, iron production methods have optimal requirements with respect to the feed materials especially iron ore. In this study, tests were carried out on Muko iron ore from Uganda to analyse its suitability to meet the feed requirements of today's dominant iron production methods. More specifically, the Tumbler, Abrasion, and Shatter Indices of the ore were determined. In addition, porosity, thermoanalysis, and reducibility tests were performed. Overall, the Muko ore was found to have good mechanical properties exemplified with tumble and shatter index data >89.0 wt% and <2.5 wt%, respectively. Furthermore, its reducibility at 0.87%/min is within the acceptable range as a natural material feed for blast furnace and direct reduction furnaces. Also, the energy requirement for heating the ore to 1100°C was found to be higher in the samples containing a wider size range of irregular grains and the largest contaminations. In summary, it is concluded that the Muko iron ore has good physical and metallurgical properties to serve as a natural material for the blast furnace and direct reduction furnaces.

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2012
Keyword
physical and metallurgical properties, iron ore, iron, direct reduction, blast furnace
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-123058 (URN)10.5402/2012/147420 (DOI)
Projects
Sustainable Technology Development in the Lake Victoria Region
Funder
Sida - Swedish International Development Cooperation Agency, 5410004501
Note

QC 20130531

Available from: 2013-05-31 Created: 2013-05-31 Last updated: 2017-12-06Bibliographically approved
3. Effect of different factors on low temperature degradation of hematite iron ore during reduction
Open this publication in new window or tab >>Effect of different factors on low temperature degradation of hematite iron ore during reduction
2014 (English)In: Metallurgical Research and Technology, ISSN 2271-3646, Vol. 111, no 1, 57-66 p.Article in journal (Refereed) Published
Abstract [en]

Low temperature degradation (LTD) of iron oxides was investigated with the aim of understanding how natural iron ores degrade under different conditions. Minimisation of this degradation would increase the acceptance level of natural iron ores as feed materials without prior beneficiation. In addition to temperature and reduction gas composition, sample positioning in the reduction furnace and sample's original weight were also found to influence LTD. Samples placed in the top reaction zone of the furnace, which have the first contact with the reducing gas, were found to degrade 1.5 times more than those in the middle and bottom reaction zones. In addition, they presented a wide range of size in the disintegrated particles than those in the middle and bottom reaction zones. Furthermore, the samples with an original weight equal to or greater than 5 g, had a disintegration extent of less than 10%. Therefore, if the reduction gas comes into contact with a certain material first, before contacting the iron oxide, it may serve to reduce on LTD during reduction. Furthermore, in laboratory conditions, the occurrence of low temperature breakdown of the natural iron oxides can be minimised by using samples with an original weight equal to or greater than 5 g.

Keyword
Hematite iron ore, reduction degree, low temperature strength, reaction zones, size of lumps
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-123060 (URN)10.1051/metal/2014014 (DOI)000338512900008 ()2-s2.0-84904816193 (Scopus ID)
Projects
Sustainable Technology Development in the Lake Victoria Region
Funder
Sida - Swedish International Development Cooperation Agency, 5410004501
Note

QC 20130531. Updated from manuscript to article in journal.

Available from: 2013-05-31 Created: 2013-05-31 Last updated: 2017-03-07Bibliographically approved
4. Investigation of direct reduction of lumps from natural hematite iron ore
Open this publication in new window or tab >>Investigation of direct reduction of lumps from natural hematite iron ore
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effects of the main characteristics of hematite natural ore lumps such as weight and microstructure and the parameters of the direct reduction process (gas flow rate and temperature) on the reduction degree and thermo-mechanical degradation of iron ore lumps were investigated. Lumps from Muko deposit were used for direct reduction with H2/CO, ratio of 1.5. The temperature and gas flow rate ranged from 700-900°C and 0.25-1.0 L/min, respectively. The highest reduction degree (0.88-0.91) was obtained by direct reduction of 3-4 g samples at 900°C and 0.5 L/min. The effects of the flow rate of the reduction gas in the furnace and the carbon deposited on a sample surface on the accuracy of the weight measurement and the reduction degree by using the thermal gravimetric technique were estimated and discussed. It was further discovered that the natural microstructure of a lump iron ore has an effect on the reduction time.

Keyword
natural iron ore lumps, direct reduction, reduction behaviour, weight, microstructure, reduction degree
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-122456 (URN)
Note

QS 2013

Available from: 2013-05-22 Created: 2013-05-22 Last updated: 2013-05-31Bibliographically approved
5. Application of different models for the prediction of the kinetics of direct reduction of natural iron ores
Open this publication in new window or tab >>Application of different models for the prediction of the kinetics of direct reduction of natural iron ores
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Simulation of the direct reduction conditions was performed in a laboratory furnace. Lump samples from natural hematite iron ore were reduced by a gas mixture of H2 and CO (H2/CO =1.5) at temperatures 700, 800 and 900°C. The effect of reduction temperature on the reduction degree, reduction rate of samples and carbon deposition were investigated and discussed in this study. The thermo-gravimetric data obtained from the reduction experiments was run in a programme that calculates the solid conversion rate. Also, three models: i) Grain Model (GM), ii) Volumetric Model (VM) and iii) the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. It was found that the RPM model result agreed best with the obtained experimental results. Furthermore, it gave better predictions of the natural iron oxide conversion and thereby the reduction kinetics.

Keyword
natural iron ore, porosity, direct reduction kinetics, solid conversion, reduction rate
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-122457 (URN)
Note

QS 2013

Available from: 2013-05-22 Created: 2013-05-22 Last updated: 2013-05-31Bibliographically approved

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