Heat Treatment of Iron Ore Agglomerates with Microwave Energy

HEAT TREATMENT OF IRON ORE AGGLOMERATES WITH MICROWAVE ENERGY

A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY

ÇİĞ DEM ÇIRPAR

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MINING ENGINEERING

JANUARY 2005

Approval of the Graduate School of Natural and Applied Sciences

Prof. Dr. Canan Özgen Director

I certify that this thesis satisfies all the requirements as a thesis for the degree of Master of Science/Arts / Doctor of Philosophy.

Prof. Dr. Ümit Atalay Head of Department

This is to certify that we have read this thesis and that in our opinion it is fully adequate, in scope and quality, as a thesis for the degree of Master of Science.

Prof. Dr. Ali İhsan Arol Supervisor

Examining Committee Members

Prof. Dr.Gülhan Özbayo ğlu (METU,MINE)

Prof. Dr. Ali İhsan Arol (METU,MINE)

Prof. Dr. Ümit Atalay (METU,MINE)

Prof. Dr. Çetin Ho şten (METU,MINE)

Prof. Dr. Yavuz Topkaya (METU,METE)

I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work.

Name, Last name: Çi ğdem Çırpar

Signature :

ABSTRACT

HEAT TREATMENT OF IRON ORE AGGLOMERATES BY MICROWAVE ENERGY

Çırpar, Çi ğdem M.Sc., Department of Mining Engineering Supervisior: Prof.Dr. Ali İhsan Arol

January, 2005, 90 pages

Pelletizing is a size enlargement technique employed to process fine-grained iron-bearing concentrates and powder ores. Mechanical strength of fired pellets is important for handling. When the pellets undergo metallurgical processing, their mechanical strength is a measure of their resistance to degradation by breakage due to impacts and abrasion to which they are exposed in the upper part of the blast furnace.

In this study, heat treatment of iron ore agglomerates with microwave energy is investigated. First drying and then heat hardening tests were performed. Two main properties of pellets were taken into consideration: percent moisture and magnetite content for the dried pellets and compressive strength and also magnetite content for the fired pellets. The tests were conducted with different particle sized pellets, in different durations. In order to increase the oxidation rate in heat hardening tests, Na 2O2 is also added in different percentages.

The results of the study showed that, magnetite pellets can indeed be dried and heated with microwave energy. However, the attained compressive strength and

iv the oxidation of the fired pellets were not sufficient as compared to pellets produced by conventional heating

Keywords: microwaves, iron ore, magnetite, pelletizing, agglomerates

ÖZ

DEM İR CEVHER İ AGLOMERELER İNİN M İKRODALGA ENERJ İSİ İLE ISITILMASI

Çırpar, Çi ğdem Yüksek Lisans, Maden Mühendisli ği Bölümü Tez Yöneticisi: Prof.Dr. Ali İhsan Arol

Ocak, 2005, 90 pages

Peletleme, ince tane boyunda demir içeren konsantrelerin ve toz halindeki cevherlerin i şlenmesinde kullanılan bir boyut büyütme yöntemidir. Pi şirilmi ş peletlerin mekanik dayanımları ta şınma sırasında önemlidir. Peletler metalurjik işlemlere tabi tutulduklarında, mekanik dayanımları onların yüksek fırının üst kısımlarında maruz kaldıkları çarpmaların ve a şındırmaların sebep oldu ğu bozulma ve kırılmalara dayanımlarının ölçüsüdür.

Bu çalı şmada, demir cevheri aglomeratlarının mikrodalga enerjisi ile ısıtılması ara ştırılmı ştır. İlk olarak kurutma, daha sonra ısıyla sertle ştirme testleri yapılmı ştır. Kurutulmu ş peletler için nem yüzdesi ve manyetit oranı, pi şirilmi ş peletler için basma dayanımları ve yine manyetit oranı dikkate alınmı ştır. Deneyler farklı tane boyundaki peletlerle, farklı i şlem sürelerinde gerçekle ştirilmi ştir. Sertle ştirilme deneylerinde yükseltgenme oranının arttırılması için peletlere farklı oranlarda Na 2O2 eklenmi ştir.

Çalı şmanın sonuçları göstermi ştir ki, manyetit peletler mikrodalga enerjisi ile kurutulup, ısıtılabilmi ştir. Fakat pi şirilen peletlerde ula şılan sıkı şma dayanımı

vi ve yükseltgenme geleneksel ısıtma i şlemlerinle kar şıla ştırıldı ğında yeterli de ğildir.

Anahtar Kelimeler: Mikrodalga, demir cevheri, manyetit, peletleme, aglomerat.

vii

To My Parents, Who Always Support Me To Make My Dreams Come True…

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ACKNOWLEDGEMENTS

I want to express my sincerest and endless appreciation to my advisor Prof.Dr. Ali İhsan Arol for his kind supervision, guidance, suggestions, comments, help, and friendly attitude throughout this study. I also wish to express my appreciation to Prof. Dr. Ümit Atalay for his suggestions and comments.

I gratefully acknowledge Tuncer Gençtan, Süleymen Kırıcı, Mehmet Çakır, Tahsin I şıksal, İsmail Kaya for their kindness, friendly attitude, and technical support.

I would also like to express my thanks to my friends Burcu Ardıço ğlu who was always by my side these six years and being my dreamsharer, Tu ğcan Tuzcu, Filiz Toprak, Hamdaweh Suleymana, Sava ş Özün, Osman Sivrikaya, Mehtap Gülsün, Sinan İnal and Ömer Can Özcan for their help, comments, encouragement through the hard times during the study, and for their friendship…

Special thanks are also extended to my friend Ziya Ö ğütcü for being by my side during my trials and tribulations and assuring me, when I was most hopeless, that good days were yet to come.

Finally, my endless and profound thanks and love would go to my parents, my aunt for her role as the substitute mother, and my brother and his family with the new comer Ada. All the beauties, values and happiness they bring to my life and the love they give to me without any expectations make me the luckiest person in the world.

TABLE OF CONTENTS

PLAGIARISM…………………………………………………………… iii ABSTRACT……………………………………………………………… iv ÖZ………………………………………………………………………… vi DEDICATION…………………………………………………………… viii ACKNOWLEDGEMENTS……………………………………………... ix TABLE OF CONTENTS……………………………………………...... x LIST OF TABLES……………………………………………………..... xiii LIST OF FIGURES……………………………………………………... xv LIST OF ABREVIATIONS…………………………………………...... xviii CHAPTER 1. INTRODUCTION……………………………………………… 1 2. LITERATURE SURVEY……………………………………… 4 2.1 Pelletizing…………………………………………………... 4 2.1.1 General Principles of Pelletizing………………….… 4 2.1.1.1 Balling……………………………………… 4 2.1.1.2 Properties of Material for Balling…………... 4 2.1.1.3 Binders……………………………………… 7 2.1.1.4 Requirements for Ball Properties…………… 9 2.1.2 Hardening of Pellets………………………………… 11 2.1.2.1 Drying……………………………………… 11 2.1.2.2 Theory of Pellet Hardening………………… 12 2.1.2.3 Heat Hardening by Oxidation……………… 15 2.1.2.4 Hardening by Reduction…………………… 16 2.1.2.5 Low-Temperature Hardening Treatments… 17 2.1.3 Requirements for Pellet Properties………………… 17 2.1.4 Conventional Equipments Used to fire Pellets……... 18 2.1.4.1 Shaft Furnaces……………………………… 18 2.1.4.2 Horizontal Traveling Grate Process………… 19

x 2.1.4.3 The Grate-Kiln Process…………………… 19 2.2 Theory of Microwave Heating…………………………… 20 2.2.1 Basic Concept of Microwave Energy……………… 20 2.2.2 Working Principles of Microwave Oven………… 24 2.2.3 Early History of Microwave Oven………………… 26 2.2.4 Applications of Microwave Processing…………… 27 2.2.5 Advantages of Microwave Heating……………… 28 2.2.6 Microwave Energy for Mineral Treatment Processes...... 30 2.2.6.1 Microwave Heating of Minerals……………. 30 2.2.6.2 Microwave Assisted Ore Grinding…………. 39 2.2.6.3 Microwave Assisted Carbothermic Reduction of Metal Oxide………………….. 40 2.2.6.4 Microwave Assisted Drying and Anhydration 40 2.2.6.5 Microwave Assisted Mineral Leaching……. 41 2.2.6.6 Microwave Assisted Roasting and Smelting of Sulphide Concentrate……………………. 41 2.2.6.7 Microwave Assisted Pretreatment of Refractory Gold Concentrate……………….. 42 2.2.6.8 Microwave Assisted Coal Desulphurization... 42 2.2.6.9 Microwave Assisted Spent Carbon Regeneration………………………………... 43 2.2.6.10 Microwave Assisted Waste Management…. 43 2.3 Iron Ore…………………………………………………….. 43 3. MATERIALS AND METHODS………………………………. 45 3.1 Materials…………………………………………………… 45 3.2 Methods………………………………………………...... 45 3.2.1 Density Measurement………………………………. 45 3.2.2 Specific Area Measurement………………………… 46 3.2.3 Preparation of Magnetite Disk Pellets……………… 47 3.2.4 Drying and Hardening Tests………………………... 48

xi 4. RESULTS AND DISCUSSION………………………………... 52 4.1 Drying Characteristics of Magnetite Pellets with Microwave Oven………………………………………………. 52 4.2 Heating Characteristics of Magnetite Pellets with Microwave Oven……………………………………………… 58 4.2.1 Heating Characteristics of Magnetite Pellets with

Addition of Na 2O2...... 65 5. CONCLUSION…………………………………………………. 67 REFERENCES…………………………………………………………... 69 APPENDICES A. Air Permeability Apparatus Manual……………………………….. 73

B. Weight loss, %Fe 3O4 and Compressive Strength Tables………….. 80

xii

LIST OF TABLES TABLE 1. Moisture on balling various types of materials………………………… 6 2. Effect of mineralogical composition on particle shape………………… 7 3. Microwave heating of some oxides and sulphides compounds………... 31 4. Classification of some reagents grade materials based on microwave heating rate………………………………………………………………. 32 5. Mineral transparent to microwave irradiation (2450 MHz, 150 W, 5 min exposure)……………………………………………………………. 33 6. Results of microwave heating of ores (2450 MHz, 3-5 min exposure).. 34 7. Effect of microwave heating on the temperature of natural minerals…. 36 8. Effect of microwave heating on the temperature of reagent grade elements and compounds………………………………………………… 37 9. Effect of Microwave heating on the temperature of various minerals (500 W, 2450 MHz)……………………………………………………… 38 B1. % Moisture loss of 1297 Blaine pellets in 170 W…………………… 80 B2. % Moisture loss of 2180 Blaine pellets in 170 W…………………… 80 B3. % Moisture loss of 2549 Blaine pellets in 170 W…………………… 81 B4. % Moisture loss of 1297 Blaine pellets in 400 W…………………… 81 B5. % Moisture loss of 2180 Blaine pellets in 400 W…………………… 82 B6. % Moisture loss of 2549 Blaine pellets in 400 W…………………… 82 B7. % Moisture loss of 1297 Blaine pellets in 620 W…………………… 83 B8. % Moisture loss of 2180 Blaine pellets in 620 W…………………… 83 B9. % Moisture loss of 2549 Blaine pellets in 620 W…………………… 84

B10. % Fe 3O4 content of the dried samples in 170 W…………………… 84

B11. % Fe 3O4 content of the dried samples in 400 W…………………… 85

B12. % Fe 3O4 content of the dried samples in 620 W…………………… 85 B13. Compressive strength of microwave treated pellets………………… 86

B14. % Fe 3O4 content of microwave treated pellets……………………… 86

xiii B15. Compressive strength of metallurgical furnace treated pellets……... 86

B16. % Fe 3O4 content of metallurgical furnace treated pellets…………... 87 B17. Compressive strength of pellets prepared from 1297 cm 2/g Blaine treated in Metallurgical furnace and microwave oven…………………… 87 B18. Compressive strength of pellets prepared from 2180 cm 2/g Blaine treated in Metallurgical furnace and microwave oven…………………… 87 B19. Compressive strength of pellets prepared from 2549 cm 2/g Blaine treated in Metallurgical furnace and microwave oven…………………… 88 2 B20. % Fe 3O4 content of pellets prepared from 1297 cm /g Blaine treated in Metallurgical furnace and microwave oven…………………… 88 2 B21. % Fe 3O4 content of pellets prepared from 2180 cm /g Blaine treated in Metallurgical furnace and microwave oven…………………………… 88 2 B22. % Fe 3O4 content of pellets prepared from 2549 cm /g Blaine treated in Metallurgical furnace and microwave oven…………………………… 89

B23. Compressive strength of Na 2O2 added pellets……………………… 89

B24. % Fe 3O4 content of Na 2O2 added pellets…………………………… 89 B25. Compressive strength of pellets heated with Metallurgical furnace and heated with microwave oven in the presence of Na 2O2……………… 90

B26. % Fe 3O4 content of pellets heated with Metallurgical furnace and heated with microwave oven in the presence of Na 2O2………………… 90

xiv

LIST OF FIGURES

FIGURE 1. Structural elements of montmorillonite………………………………… 8 2. A general curve for strengthening of iron-ore balls, showing temperature dependence…………………………………………………… 13 3. Hematite recrystallization………………………………………………. 14 4. Compression strength of pellets depending on firing time……………... 14 5. Schematic view of shaft furnace………………………………………... 18 6. Feeding of balls onto a grate……………………………………………. 19 7. Functioning of grate-kiln process……………………………………….. 20 8. Electromagnetic spectrum………………………………………………. 21 9. Interaction of microwave with materials………………………………... 22 10. a Microwave Heating System. b Batch-type equipment. c Continuous- type equipment…………………………………………………………… 26 11. Blaine air permeability apparatus……………………………………… 47 12. Denison Testing Machine……………………………………………… 48 13. Moulinex domestic microwave oven………………………………….. 49 14. Tinus Olsen testing machine…………………………………………... 50 15. SATMAGAN (Saturation Magnetization Analyzer)………………….. 51 16. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 170 W power input………. 52 17. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 400 W power input………. 53 18. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 620 W power input………. 53 19. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 170 W power input in different durations……………………………...... 54 20. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine

xv magnetite concentrate in a microwave oven at 400 W power input in different durations………………………………...... 54 21. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 620 W power input in different durations………………………………………………………… 55 22. Drying pattern of pellets made of 1297 cm 2/g Blaine magnetite concentrate at 170, 400 and 620 W in different durations………………… 55 23. Drying pattern of pellets made of 2180 cm 2/g Blaine magnetite concentrate at 170, 400 and 620 W in different durations………………… 56 24. Drying pattern of pellets made of 2549cm 2/g Blaine magnetite concentrate at 170, 400 and 620 W in different durations………………… 56

25. % Fe 3O4 content of the dried samples in 170 W……………………… 57

26. % Fe 3O4 content of the dried samples in 400 W……………………… 58

27. % Fe 3O4 content of the dried samples in 620 W……………………… 58 28. Effect of duration of heat treatment on the compressive strength of pellets prepared from 1297, 2180 and 2549 cm 2/g Blaine pellets………… 59

29. Effect of duration of heat treatment on the %Fe 3O4 content of pellets prepared from 1297, 2180 and 2549 cm 2/g Blaine pellets………………… 59 30. Effect of heat treatment duration on the compressive strength of pellets prepared from 1297, 2180 and 2549 cm 2/g Blaine in metallurgical furnace at 1250 0C………………………………………………………… 60

31. Effect of heat treatment duration on the %Fe 3O4 content of pellets prepared from 1297, 2180 and 2549 cm 2/g Blaine in metallurgical furnace at 1250 0C………………………………………………………………….. 61 32. Comparison of compressive strength of pellets prepared from 1297 cm 2/g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620W……………………………………………………………… 61 33. Comparison of compressive strength of pellets prepared from 2180 cm 2/g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620W……………………………………………………………… 62 34. Comparison of compressive strength of pellets prepared from 2549

xvi cm 2/g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620W……………………………………………………………… 62 2 35. Comparison of % Fe 3O4 content of pellets prepared from 1297 cm /g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620W………………………………………………………………………. 63 2 36. Comparison of % Fe 3O4 content of pellets prepared from 2180 cm /g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620W………………………………………………………………………. 63 2 37. Comparison of % Fe 3O4 content of pellets prepared from 2549 cm /g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620W………………………………………………………………………. 64

38. Effect of addition of 1, 2, 3 % Na 2O2 on the compressive strength of pellets prepared from1297, 2180 and 2549 cm 2/g Blaine……...... 65

39. Effect of addition of 1, 2, 3 % Na 2O2 on the Fe 3O4 content of pellets prepared from1297, 2180 and 2549 cm 2/g Blaine………...... 65 40. Comparison of compressive strength of pellets heated in metallurgical furnace and in a microwave oven in the presence 1, 2, 3 % Na2O2……….. 66

41. Comparison of % Fe 3O4 of pellets heated in metallurgical furnace and in a microwave oven in the presence 1, 2, 3 % Na 2O2…………………….. 66

xvii

LIST OF ABREVIATIONS

ABREVIATIONS

P : Ball strength (N.m -2) x : Particle size ( µm) δ : Wetting angle (degrees) φ : Coefficient of pores filled with water ε : Porosity ρ : Density (g/cm 3) T : Temperature ( oC)

Ωo : Permittivity of free space (8.86E-12 F/m) Ω ' : Relative dielectric constant

'' Ω eff : Relative dielectric loss factor E : Internal electrical field (V/m) β : Loss tangent (Degrees) σ : Conductivity of the materials (S/m) f : Frequency of the incident wave (GHz) D : Penetration depth (mm)

λ0 : Incident or free-space wavelength (cm) ∆ : Power absorbed by a material per unit volume (W/cm 3) S : Specific surface area (cm 2/g) t : Measured time interval (sec)

xviii

CHAPTER 1

INTRODUCTION

The success of several technological and, in particular, metallurgical processes greatly depends on the particle size of all constituents included in the process. The size requirements differ and the sizes desired may range from tenths of millimeters to several tens of centimeters.

The desired size range can be obtained by crushing or grinding the input coarse material or, inversely, by agglomeration of loose masses. Larger particles are made in a process generally referred to as size enlargement; the terminology is specific for various technological applications and the terms express specific features of the production of bigger particles and the type of bonding in the agglomerate produced.

Sizing is a major factor in making metals from ores, especially in ferrous metallurgy. Pelletizing is a size enlargement technique employed to process fine grained iron- bearing concentrates, includes operations in which balls are formed under normal atmospheric conditions and hardened mainly by firing at 1200-1400 oC. First step is the preparation of the feed. The feed to a pelletizing plant is generally a wet concentrate. The concentrate slurry is then thickened and filtered to provide material with the desired moisture content (around 10%). At this stage a small quantity (0.5 - 1%) of bentonite is often mixed with the moist concentrate. Second step is balling where the moist material balled by passing it through a drum or disc which rotates at about 10-15 rev/min depending on its diameter, and inclined at about 5 – 10 o to the horizontal. The green balls are finally hardened which consists of three operations, namely; drying- firing and cooling. Three

1 different types of firing equipment are in general commercial use; the vertical shaft furnace, the traveling grate and the grate kiln.

The heat hardening by oxidation is a process commonly used in iron-ore pelletizing. The pellets are hardened owing to recrystallization of iron oxides, formation of slag phases and secondary components. These processes take place at high temperatures. (Smr ček and et.al., 1963).

In the pelletization of magnetite ores it is mainly oxidation of magnetite to hematite that occurs; the oxidation can be expressed as 1 2Fe 3O4 + O2 = 3Fe 2O3 + Q 2 where Q is equal to 264.55 kj/mol

The completeness of oxidation depends on the conditions under which the oxidizing firing takes place, and on the chemical composition of raw material being processed.

The firing time and temperature are decisive for structural changes of the pellets; the nature of the changes affects, in turn, the mechanical properties of the pellets. In addition to time and temperature, structural changes are affected by the composition of the iron-bearing, especially by the content of gangue constituents, or by addition of basic substances.

Following its inception in 1945 and an initial slow acceptance, the microwave oven is now extensively used for cooking all over the world. Although at the time little attention was devoted to the theory of microwave heating, early developers of the microwave oven recognized, in 1947 that “microwave heating of food produces the heat from within”. (Morse and et.al., 1947) Because microwave heating is volumetric, as distinct from conventional heating in which heat is transferred from the surface to the interior, microwave heating has been spreading successfully to the laboratory and industry in applications

2 such as heating and/or drying of food, paper, plastics, chemicals, textiles, building materials, fuels, medicine, etc. as well as in applications in ceramics, materials processing and metallurgy.

As early as 1967, Ford and Pei (1967) applied microwave energy to the heating of a number of reagents grade metal oxides and sulphides. The authors concluded that dark-colored compounds heated rapidly to high temperature (1000 oC), and the heating rates of dark colored compounds were much higher than those of light colored compounds. Magnetite reaches a temperature of 500 0C in 0.5 min. (Ford and Pei, 1967)

Further, microwave heating behavior of several metal oxides were reported (Wong,1975, Tinga, 1988-89). Materials are classified based on heating rate into hyperactive, active, difficult-to-heat and inactive. They demonstrated that microwave energy can be effective in the heating of minerals and inorganic compounds.

In this study, heat treatment of iron ore agglomerates by microwave energy was investigated. The effect of particle size, duration of treatment, power input and addition of Na 2O2 as oxidizing agent, on the mechanical strength and the rate of oxidation of magnetite to hematite were examined.

CHAPTER 2

LITERATURE SURVEY

2.1 Pelletizing

2.1.1 General Principles of Pelletizing

2.1.1.1 Balling

Balling is the basic technological process designed to transform fines into an agglomerate. The balls can be either a final product or, in pelletizing, they can serve as an input for further processing such as hardening by drying or firing. To produce such a product, the balls must be good quality to be acceptable for the requirements of the process technologies, and, in particular, to possess the properties required for the fired pellets when they are to be handled as a final product. Inferior-quality balls will not give good pellets because they can not be hardened in the manner needed for the pellets to match the subsequent handling and processing.

2.1.1.2 Properties of Material for Balling

The main property of the fines intended for balling will be the ballability, i.e. ability to produce balls with satisfactory compressive strength. Ballability is an outcome of a variety of properties, which include size of particles, and their distribution, with the intrinsic specific surface area and shape; wettability of particles and moisture content are other important properties. Mineralogical composition produces an effect if the material contains binding clayey constituents.

Granulometric composition of the raw material is essential for the balls to assume the required strength; this follows from the rules affecting the ball’s particle cohesion and the kinetics of ball formation. A generally valid rule says that finer the particles, the higher the ball strength; the particle fineness of a material must be at least below 0.2 mm to make it ballable to any extent. The fact is that particles well in excess of 0.2 mm can be balled to produce balls of satisfactory strength, if the raw material contains a sufficient amount of fines. The content of fines smaller than 0.04 mm is decisive for the ballability and green strength of balls; these properties increase with increasing ratio of fines.

Specific surface area is closely connected with the granulometric composition of the material being balled, or with the content of fines. The specific surface area is strongly indicative of the particle shape. The relationship of the two variables differs for various materials; to be well ballable; a material will generally have a Blaine specific surface area of 1600-2100 cm 2/g. The ball strength should increase with increasing specific surface area; however the strength is not always proportional to this value and the nature and type of material plays a part here.

The wettability of a material , combined with the surface tension of the liquid, is a property radically affecting the ballability and ball strength. As can be seen in Equation 1, the ball strength is governed by wettability, i.e the wetting angle, δ = 0o. Wettability greatly depends on the pre-balling processing of the material. Fine-grain concentrates from flotation process are made hydrophobic due to residual amounts of various agents, and this is why they are difficult to ball. Materials which have gone through different heat treatments are also difficult to wet because the surface of the particles had been affected by heat. To make them ballable, they must be made hydrophilic; this is done by means of a “restoration” of their surface by short regrinding or by adjusting the surface tension of the wetting liquid.

1− ε 1 P = ϕ f (δ ) f (x) (N.m -2)………...………………………...(1) ε x where P : Ball strength (N.m -2) x : particle size ( µm) δ: wetting angle (degrees) φ: coefficient of pores filled with water ε: Porosity

The moisture range of the material to be balled is particularly important, because each specific type of material has corresponding moisture, normally given beforehand, which is needed for the resultant balls to possess the highest possible strength. These relationships are given in Table 1.

Table 1. Moisture on balling various types of materials (Smr ček and et.al., 1963).

Raw material Moisture on balling (%) Magnetite 9.5 Synthetic magnetite 14.5 Hematite 8.0 Limonite 13.0 Siderite 7.5

Mineralogical composition especially that of iron ores, is also a factor decisive for the balling and ball strength. There is the action of clayey, sticky components, but more important are the effects of shape and nature of the surface of the ore particles. The nature of these differs with individual mineralogical types of mixes, as is documented in Table 2. Hematite-goethite ore, with platelike particles exhibits considerable differences in strength, depending upon the moisture content. Magnetite, with its sharp-edged and smooth-surface particles, is a perfect counterpart.

Table 2. Effect of mineralogical composition on particle shape (Smr ček and et.al., 1963).

Mineralogical composition Particle shape Hematite, goethite, quartz, kaolinite Platelike, fragmentary Hematite, goethite, quartz, calcite Platelike, rod, splintered Magnetite, hematite, goethite, Platelike, cubic quartz, Magnetite, pyrite, quartz cubic, spheroidal

2.1.1.3 Binders

Binders play a versatile role in pelletizing technologies; the role of binders is i- improve the ballability of the material; ii- affect the green and dry strength of balls and fired strength of pellets; iii- Adjust the chemical and mineralogical consistency and quality of fired pellets.

In a broader technological sense, the binders include bentonite, lime, soluble glass and cements. Binders used occasionally in balling include some organic substances like dextrin, sulphide waste liquor, tars or inorganic matter, and especially alkali compounds.

Bentonite is a clayey material consisting mainly of montmorillonite, which imparts specific properties to the bentonite. These properties make the bentonite important for balling. The montmorillonite structure is shown in Figure 1.

Montmorillonite has one exceptional property; it can take up water into the inter- layer space. This is connected with the typical swelling ability of bentonite, which is important for balling because it enhances the cohesion of particles in the ball.

Figure 1. Structural elements of montmorillonite (Si) 4++ ; (Al 3+ , Mg 2++ , Fe 3+ , 2+ 2- Fe ); (O) ; (OH); AC tetrahedron (SiO 4); B octahedron (MeO 6); DE layer of tetrahedrons (Grimm, 1968)

Dehydration by heat is important for drying and firing of pellets; the moisture removal takes place at two temperature intervals:

i) low-temperature dehydration at 20-300 oC; in this process the inter- layer moisture is liberated: ii) dehydration at 500-750 oC temperature interval: at these temperatures water bonded as (OH) - ions is removed.

The best pellet binder is the natural Na-bentonite, high in montmorillonite; for this material an addition of 0.5% bentonite is fully sufficient. Bentonite with artificially imparted Na is less efficient, making the additions of the binder correspondingly higher. In this way the contents of alkalis in the pellets rise and this behaviour is objectionable where ironmaking raw materials are concerned.

2.1.1.4 Requirements for Ball Properties

1- Mechanical Properties: Balls undergo considerable mechanical loading during shipping, storage, drying and high-temperature hardening. Therefore sufficient resistance to abrasion, good compressive strength, and shatter strength are essential. The requirements named above differ for balls which are a final product, and for balls intended for further processing. 2- Granulometric Composition: The ball size is tailored to further use of the product. Generally, there are three basic groups: i- Small balls, with a diameter of 3-8 mm, intended for sintering or hydrometallurgical processing; ii- Normal balls, with a diameter of 10-15 mm, which is a standard size for blast furnace pellets; iii- Large balls, with a diameter of 20-30 mm, intended for steel making pellets, fluorite pellets and raw material for cement manufacture. Close size tolerances and optimal globular shape of balls are required for each of the groups to make the balls properly permeable to drying and firing gases. 3- Porosity: Porosity is vital in green balls, which are intended for subsequent heat hardening. Basically, porosity is governed by the particle size of the feedstock, but may be affected by balling. Porosity plays an important role when the balls are heat-dried and fired; in these processes the moisture evaporates and phase transformations take place, the material recrystallizes. The best porosity is in a connection with the ball strength and an optimal value of porosity will be somewhere around 30%. 4- Resistance to Heat Shock: The resistance to heat shock is a technological property which gives the ball an ability to withstand a sharp temperature change. This type of resistance generally depends on a variety of factors acting at the same time, these factors include porosity, particle size of the input material and ball diameter. Resistance to heat shock is technologically vital at the firing stage, because the ball should

counteract, and accommodate, possible non-uniform heating so that the amount of decrepitated balls may reduce to minimum. Avoidance of ball decrepitation is essential for successful firing.

Methods for Ball Evaluating: i- Compressive strength: To measure the compressive strength of a ball, it is subjected to uniform loading between two parallel plates until the ball is ruptured. Balls with a mean granulometric composition range are taken as representative samples. ii- Drop strength: The drop strength is measured by means of letting a ball hit a steel plate repeatedly from a height of 18 inches. The resultant value is expressed as the drop number, which states the number of drops the ball is able to withstand without observable damage. iii- Resistance to abrasion: The resistance to abrasion is tested on dried balls, and is measured on vibratory or drum screen. The resistance to abrasion is stated in wt % of the undersizes smaller than 0.1 mm. iv- Resistance to heat shock: It is expressed as a temperature at which at least 80 % of the dried balls remain undamaged. The test is made in a preheated furnace. v- Moisture content: The moisture content of green balls is stated according to the content of water in percent, related to

the weight of moist balls, W rel , or as W S related to the materials’ dry matter. vi- Porosity: Total porosity of balls is expressed as a portion of pore volume out of the total volume of the input raw material, and is calculated using the difference between the true density and bulk density; thus

 ρ   P  ε total = 1− *100 (%) ……………………………………….(2)  ρt 

εtotal = total porosity 3 ρ P = bulk density (g/cm ) 3 ρt = true density (g/cm )

2.1.2 Hardening of Pellets

2.1.2.1 Drying

Drying is usually a part of the heat hardening treatment. Occasionally, drying is the final stage in cases where the pellets are not expected to withstand considerable mechanical stress. The basic process of drying green pellets include the following stages: i- Transformation of the moisture in the green pellets into gas ii- Withdrawal of the vapor, which is formed, from the material surface and discharge of this vapor into the environmental gas. Drying can be broken into three stages: i- Heating to a temperature which the moisture evaporates ii- Continued evaporation from the green pellet surface. The drying rate depends on the speed at which the moisture diffuses to the surface, the so –called critical point of drying is achieved and the moisture content of the pellet surface becomes zero. After this critical point has been achieved, iii- Drying continues inside the pellet, the moisture moves toward the internal evaporation zone thus created, and then proceeds, as vapor, through the dry, porous layers of the pellet toward the surface when it is taken away by the stream of the gaseous medium.

The drying rate depends on the heat conductivity of the material, conditions existing in the heat exchange pattern, and pellet porosity. Drying is a convenience

11 process occurring when pellets are being dried; the heat is supplied by a drying medium, i.e. a mixture of waste gases and air. To produce a completely dry product maximum porosity of the pellets is necessary to enable fast withdrawal of the vapor. The porosity value determines the resistance to heat shock (the possibility to heat the pellet rapidly without incurring the danger of damage to the pellet). Porosity and moisture content thus become the limiting factors during drying. This fact becomes most evident with the raw materials where the micro- porosity is very high, such as magnetite concentrates produced by roasting or partial reduction.

Drying also depends on the quantity and types of binders, which can absorb the moisture.

2.1.2.2 Theory of Pellet Hardening

The green strength of pellets is hardly adequate and may be increased by subjecting them to various treatments which depend on the starting material for the pellets, and further processing. Drying may sometimes prove sufficient, possibly in combination with the use of binders, or chemically hardening or heat hardening can be applied.

Heat hardening is the most common method employed, mainly in metallurgy. When iron-ore pellets are hardened by oxidizing firing, the ore particles are strengthened by recrystallization, or the gangue constituents fuse while a slag phase develops. The mechanism of hardening is governed by the initial chemical constitution of the input material.

Hematite and magnetite concentrates, low in gangue, are strengthened by recrystallization of hematite particles. Magnetite is oxidized to hematite before recrystallization, and the completeness of this reaction is ensured by a sufficient supply of oxygen reaching the magnetite particles. The recrystallization of hematite is expressed,

T α = V ………………………………………………………………..(3) Tt o TV = Firing temperature ( C) o Tt = Fusing temperature ( C)

Recrystallization takes place at the minimum value of α =0.33. Intensive diffusion during which recrystallization occurs, corresponds to α =0.66; fusion begins at α values exceeding 0.8-1.0 range.

The pellet hardening/firing temperature dependence is shown by the curve in Figure 2. The increase of strength is due to increasingly stronger bonding of ore particles, reaching a peak at temperatures between 1200-1300 oC. The strength begins to decrease above this level as is documented in Figure 3 where it can be seen that above 1200 oC the hematite grains begin to grow appreciably and the pellet strength decreases.

4000 3000 2000 1000 Strength (N) Strength 0 600 800 1000 1200 1400 Temperature ( oC)

Figure 2. A general curve for strengthening of iron-ore balls, showing temperature dependence (Smr ček and et.al., 1963).

500

m) 400 µ 300 200 100

Grain size ( 0 0 200 400 600 800 1000 1200 1400 1600 Temperature ( oC)

Figure 3. Hematite recrystallization (Smr ček and et.al., 1963).

In addition to temperature, time is important for the pellet strength. The strength/holding time dependence is shown in Figure 4. Obviously, a given strength can be achieved either by lower temperatures and longer firing, or higher temperature firing and shorter holding. Although suitable levels of strength are achieved, the mechanism of particle bonding is different and the pellets behave in a different manner during subsequent reduction. This fact is a basis for affecting the properties of pellets in addition to their strength.

3000

2000 1000°C 1100°C 1000 1200°C Strength (N) Strength 0 0 20 40 60 80 Residence time (min)

Figure 4. Compressive strength of pellets depending on firing time. (Smr ček and et.al., 1963).

A different mode of hardening obtains if ores higher in gangue or ores containing basic additives are processed. The pellets are hardened due to gangue fusion and

14 the formation of a slag binder between the ore particles. The chemical composition of the gangue, which is decisive for the temperature of softening or fusion of the slag phase, affects the degree to which magnetite is oxidized and hematite recrystallized. This method of bonding generally infers lower strength compared with the strength imparted by recrystallization.

The pellets are strengthened due to structural changes, whose nature is governed by the starting material. In a raw material lower in gangue the so-called recrystallization bonding develops as a result of recrystallization by oxidizing firing; raw materials higher in gangue develop the so-called slag bonding to the bonding of ore particles by the slag binder.

2.1.2.3 Heat Hardening by Oxidation

1 2Fe 3O4 + O2 = 3Fe 2O3 + Q………………...……………………….(4) 2 where Q is equal to 264.55 kj/mol

As there are two modifications of Fe 2O3, i.e. α-Fe 2O3 (hematite) and γ- Fe 2O3 (maghemite), the magnetite is oxidized gradually while several solid solutions of magnetite with maghemite, differing in composition, are being produced. This behavior is made possible because both have identical lattice structures. The oxidation of magnetite to hematite then proceeds according to equation (Smr ček and et al., 1963).

Fe 3O4→ Fe 3O4 . γ- Fe 2O3 → γ- Fe 2O3 . Fe 3O4 → γ- Fe 2O3 → α-Fe 2O3 …. .(5)

The completeness of oxidation depends on the conditions under which the oxidizing firing takes place, and on the chemical composition of raw material being processed. The firing time and temperature are decisive for structural changes of the pellets; the nature of the changes affects, in turn, the mechanical properties of the pellets. In addition to time and temperature, structural changes are affected by the composition of the iron-bearing, especially by the content of gangue constituents, or by addition of basic substances.

2.1.2.4 Hardening by Reduction

Ironmaking has seen a spectacular expansion of direct reduction process over the past decades; these processes include pre-reduction and metallization. The starting raw materials for the former are rich ores or a concentrate, and fired oxide pellets from which pre-reduced pellets are obtained. Green pellets can be pre-reduced in a rotary kiln. They may be pre-dried and partially hardened on a grate installed in front of the kiln. (Smr ček and et.al., 1963).

The pre-reduced pellets are hardened owing to the formation of sponge iron, which imparts considerable mechanical strength to the pellets. The slag phase plays only an insignificant role in the hardening, as the reduction processes are feasible mainly when applied to rich ores very low in gangue. Pre-reduced pellets made from iron-bearing materials exhibit a higher strength in reducing atmosphere at high temperatures than do oxide pellets. Pre-reduced pellets are hardened at temperatures around 1100-1150 0C, whereas temperatures of approximately 1300 0C are required to heat-hardened the pellets by oxidation.

2.1.2.5 Low-Temperature Hardening Treatments

These methods include processes affected at normal temperatures, or drying or baking at temperatures of 300-400 0C. The aim of such treatments is to create a strong skeleton from the binder added into the material, which would ensure cohesiveness of individual grains or which would react with the grains while producing stronger structures. The best structure is that in which each of the input charge is enveloped by the binder which clogs the pores of the pellet to be hardened. In low-temperature treatment the behavior of the binder is of primary importance, as it determines the whole technological sequence to be employed for the preparation of the charge for balling, pelletizing and hardening. (Smr ček and et.al., 1963).

2.1.3 Requirements for Pellet Properties

1. Consistent chemical composition: Iron within ±0.3 % and silica within ±0.2 % 2. Close size range: 90% -5/8+3/8in. (-16+9.5 mm); maximum of 5%. 3. High physical strength: a. A.S.T.M. index minimum 94% +1/4in., maximum 7% -30 mesh; b. Average compressive strength 250 kg 4. Reducibility:

a. minimum rate of reduction dR/dt 60 of 0.65 %/minute; b. minimum of 60 % reduction in the Gakushin test 5. Chiba low-temperature break-down index: Less than 3% -1 mm. 6. Burghardt Test: Pressure drop when 80% reduced not to exceed 20 mm water gauge. 7. Swelling: Maximum of 20 % increase in volume. 8. Porosity : 25-30%

2.1.4 Conventional Equipments Used to Fire the Pellets

2.1.4.1 Shaft Furnaces

The green balls are charged on top of the furnace opening. They move by gravity downwards through all thermal zones towards the discharge end. The pellets are in continuous movement and exposed to friction and increasing pressure (Figure 5). Control and influence of individual thermal steps from outside are practical impossible. The process gases flow at varying temperatures through the pellet bed, absorbing heat in the cooling zone and emitting heat in the burning and preheating zone (R ůžıčková and Srb, 1988)

Figure 5. Schematic view of shaft furnace. 1- shaft furnace, 2- combustion chamber, 3- chunk breaker, 4- to shaft, 5- fuel, 6- combustion air, 7- furnace gas

2.1.4.2 Horizontal Traveling Grate Process

The balls are first pre-dried by hot gases, are then hardened at high temperature and cooled at the end of the machine, to a temperature suitable for further handling. Indurated pellets are passed through a chunk breaker and are screened. Hardening of pellets on traveling grates gives a high output which makes these machines suitable for large capacity installations. Temperature control is also more flexible in these units. (Figure 6).

Figure 6. Feeding of balls onto a grate 1- feed belt, 2- swinging belt, 3- roller grate, 4- returns, 5- firing grate

2.1.4.3 The Grate-kiln Process

It differs from the rest of the units in which drying, hardening and cooling are carried out in a single device. The grate-kiln unit comprises three sections

i- preheat ii- rotary kiln iii- cooler

The system combines the advantages of the traveling grate as far as drying and preheating are concerned, and the pellets are hardened in a unit in which a close

19 control over the firing temperature can be exercised. The green balls are first dried and preheated on the traveling grate by gases discharge from the rotary kiln. They are then hardened in a counterflow manner in the rotary kiln, and air-cooled in the cooling section. The system of air and combustion gas circulation is designed so that the machine can operate with low heat requirements (Figure 7) (Meyer, 1980).

Figure 7. Functioning of grate-kiln process

2.2 Theory of Microwave Heating

2.2.1 Basic Concepts of Microwave Energy

Microwave energy is a nonionizing electromagnetic radiation with frequencies in the range of 300 MHz to 300 GHz. Microwave frequencies include three bands: the ultra high frequency (UHF; 300 MHz to 3GHZ), the superhigh frequency (SHF: 3GHz to 30GHz) and the extremely high frequency (EHF: 30 GHZ to 300 GHz) (Haque, 1999). The electromagnetic spectrum is given in Figure 8. Currently, 2450 MHz is the most commonly utilized frequency for the home

20 microwave oven which was invented by Percy L. Spencer almost 60 years ago (Peterson, 1993).

Figure 8. Electromagnetic spectrum (http://www.micrody.com/micro2.htm)

Microwave energy is derived from electrical energy with a conversion efficiency of approximately 50% for 2450 MHz and 85% for 915 MHz. Microwaves have longer wave lengths and lower available energy quanta than other forms of electromagnetic energy such as visible, ultraviolet or infrared light (Metaxas and Meredith, 1983).

Microwaves cause molecular motion by migration of ionic species and/or rotation of dipolar species. Microwave heating a material depends to a great extent on its ‘dissipation’ factor, which is the ratio of dielectric loss or ‘loss’ factor to dielectric constant of the material. The dielectric constant is a measure of the ability of the material to retard microwave energy as it passes through; the loss factor is a measure of the ability of the material to dissipate the energy. In other words, ‘loss’ factor represents the amount of input microwave energy that is lost in the material by being dissipated as heat. Therefore, a material with high ‘loss’ factor is easily heated by microwave energy. In fact, ionic conduction and dipolar

21 rotation are the two important mechanisms of microwave energy loss (i.e. energy dissipation in the material) (Kingston and Jassie, 1985). As shown in Figure 9, the extend to which a material absorbs microwave energy is primarily determined by its conductivity. Materials with low conductivities, such as insulators, are effectively transparent to incident waves and, thus, do not store any of the energy in the form of heat. Insulators are often used in microwave ovens to support the material to be heated. Materials with high conductivities, such as metals, reflect the microwaves which provide no significant heating effects and often used as conduits (waveguide) for microwaves. Materials, such as semiconductors, with medium conductivities, typically from 1 to 10 Sm -1, can be effectively heated from room temperature through the interaction of the materials with microwaves.

Material Type Penetration

TRANSPARENT Total transmission (no heat)

CONDUCTOR None (no heat)

ABSORBER Partial to total

(materials are heated) absorption

Figure 9. Interaction of microwave with materials.

However, as heating mechanisms are strongly temperature dependent, materials with low conductivities, such as insulators, begin to absorb and even couple more efficiently with microwave radiation when heated above a critical temperature

(T c). The microwave coupling properties of the material can be changed by adding conductive or magnetic phases in the form of fibers, particles, etc. As microwave heating is also dependent on the stage of the material, metals can be

22 heated through microarcing phenomena if they are in the form of a powder (Xia and Pickles, 1997). The degree to which any material will absorb microwaves is determined by the complex permittivity as follows (Roussy and Pearce, 1995; Sutton, 1989):

' '' ' '' Ω = Ω − jΩ = Ω0 (Ω r − Ω eff ) ………………………………….…….(6)

' where Ωo is the permittivity of free space (8.86E-12 F/m); Ω is the relative

'' dielectric constant; Ω eff is the relative dielectric loss factor and j = −1 .

When microwaves penetrate and propagate through a dielectric material, an internal electric field (E) is generated within a specific volume. Microwaves induce the transient motions of free or bound charges (e.g., electrons or ions) and also, rotating charge complexes such as dipoles are induced. The resistance to these induced motions causes losses and attenuates the electric field due to inertial, elastic, and frictional forces. As a result of these losses, volumetric heating occurs. For convenience, the loss mechanisms are combined in the loss

'' parameter, Ω eff . However, the loss tangent is commonly used to describe the losses as follows:

'' ' ' tan β = Ω eff Ω r = σ 2∏ fΩ 0 Ω r …………………………………. (7) where σ is the conductivity of the materials in S/m, and f is the frequency of the incident wave in GHz. This parameter can be related to the penetration depth (D), where this is defined as the depth at which the incident power is reduced by one half:

1 ' 2 D = 3λ0 ,8 868 ∏ tan β (Ω r Ω0 ) ……………………………………(8)

Where λ0 is the incident or free-space wavelength. It is clear that the penetration depth is inversely proportional to the frequency of the radiation. Although low frequencies result in greater penetration depths, the amount of heating may not significantly increase since the internal field, E, could be low. Again the effect is strongly dependent on the properties of the material.

The average power absorbed by a material per unit volume ∆ is defined as:

2 ' 2 ∆ = σ E = 2∏ fΩ0Ω r tan β E …………………………………….(9)

This equation shows that the power absorbed varies linearly with the frequency, and the relative dielectric constant, tan β, and varies with the square of the internal electric field.

In a non-homogenous material, the material may not heat uniformly. Thus, some parts of material heat faster than others even though some heat is conducted away. This effect is due to the increase in the dielectric loss factor and the loss tangent with increasing temperature. This phenomenon is referred to as thermal runaway and is one of the major problems with microwave heating (Roussy and Pearce, 1995; Sutton, 1989).

2.2.2 Working Principles of Microwave Oven

The microwave heating system is made up of four basic components: Power supply: Power supply drives the microwave tubes with an applied d-c voltage or even raw rectified voltage (50 or 60 Hz) Magnetron: Magnetron is the heart of the microwave oven. A magnetron converts electrical energy to microwave radiation. Inside the magnetron, electrons are emitted from a central terminal called a cathode. A positively charged anode surrounding the cathode attracts the electrons. Instead of traveling in a straight line, permanent magnets force the electrons to take a circular path.

As they pass by resonating cavities, they generate a continuous pulsating magneting field, or electromagnetic radiation. Applicator (i.e. oven): For heating of the target material. Waveguide: The microwaves are directed by an antenna at the top of the magnetron into a waveguide and travel down the length of the waveguide to the stirrer. The microwave stirrer is a fan-like, metal structure which rotates at the top of the oven cavity and disperses the microwaves around the oven’s interior. (http://www.eng2.uconn.edu/cse/Courses/CSE208/Microwave/34_Stirrer.html ). Fig. 10a shows a simplistic diagram of the microwave heating system. Fig. 10b and 10c represent industrial size batch and continuous operations microwave heating systems.

The batch-type microwave heating system is similar to a home microwave oven in that the work material is placed in a metal applicator (i.e. oven) for heating and removed when heating is complete. The microwave power is supplied from a self-contained microwave power supply unit that contains a magnetron tube, transformer, relay, choke and controls. The microwave energy is directed to the applicator by a waveguide.

The continuous-type microwave heating system is equipped with a conveyor belt to move the material through the oven for heating. Generally, the conveyor belt is made from an insulator.

Figure 10. a Microwave Heating System. b Batch-type equipment. c Continuous- type equipment.

2.2.3 Early History of Microwave Oven

Like many of today's great inventions, the microwave oven was a by-product of another technology. The field of “microwave heating” has followed the earlier applications of lower RF frequencies to induction and dielectric heating. It was during a radar-related research project around 1946 that Dr. Percy Spencer, a self-

26 taught engineer with the Raytheon Corporation, noticed something very unusual. He was testing a new vacuum tube called a magnetron when he discovered that the candy bar in his pocket had melted. This intrigued Dr. Spencer, so he tried another experiment. This time he placed some popcorn kernels near the tube and, perhaps standing a little farther away, he watched with an inventive sparkle in his eye as the popcorn sputtered, cracked and popped all over his lab. (http://www.gallawa.com/microtech/magnetron.html). From a commercial standpoint the microwave oven was first developed in 1951 when a large floor standing model was produced by Raytheon Company of America. For domestic purposes ovens became available in the early 1960’s and thus a mass market was initiated.

It was not longer after this, that industrial applications began to be considered and the first of these included rubber extrusion, plastic manufacture, and the treatment of foundary core ceramics. In the mid 1970’s the international oil and gas shortage led to an escalation in energy costs, this led to an increased research effort into the applications of microwave radiation (Kingsman and Rowson, 1998). A significant increase in microwave processing research began in the late 1980’s for ceramic and polymers. Since 1988, as a result of the increased interest among scientist and engineers, many advances have been made in dielectric property measurements, modeling and processing. A better understanding of microwave/material interactions and the economics of the microwave processing is beginning to evolve that will provide the basis for industrial applications (Clark and Sutton, 1996).

2.2.4 Applications of Microwave Processing

Heating: Almost any heat transfer problem can benefit technically from the use of microwaves because of their ability to heat in depth. There is an initial high capital cost but microwave components are tending to become less expensive.

Pasteurizing: Products are heated rapidly and uniformly to pasteurizing temperatures without the overheating associated with external, high temperature heating methods. Curing : Uniform, rapid heating throughout the product is ideal for polymerization reactions (ex: curing of rubber mouldings) Thawing and Tempering: The controlled deep penetration ability of microwaves makes rapid tempering of bulk items possible. Waste Control: Microwave applications have been identified for nuclear waste control, incineration of organic wastes and the recycling of rubber and asphalt. Denaturing Proteins : Enzymes are deactivated to reduce the decaying speed of fresh product. Deinfestation : Insect pests can be killed using microwaves.

2.2.5 Advantages of Microwave Heating

Microwave heating is unique and offers a number of advantages over conventional heating such as: i. Heat is generated rapidly and directly in the material being heated, thus eliminating the necessity of heating the entire thermal enclosure (oven) above the load temperature (energy transfer, not heat transfer) ii. Microwave energy uses power only when required and is instantly available, making the process most suitable for automatic control. iii. The microwave-generating equipment presents an economy of space and flexibility of adaptation. iv. Material selective heating v. Quick start-up and stopping vi. Environmentally friendly

In conventional thermal processing, energy is transferred to the material through convection, conduction, and radiation of heat from the surfaces of the material. In contrast, microwave energy is delivered directly to materials through molecular interaction with the electromagnetic field. In heat transfer, energy is transferred

28 due to thermal gradients, but microwave heating is the transfer of electromagnetic energy to thermal energy and is energy conversion, rather than heat transfer. This difference in the way energy is delivered can result in many potential advantages to using microwaves for processing of materials. Because microwaves can penetrate materials and deposit energy, heat can be generated throughout the volume of the material. The transfer of energy does not rely on diffusion of heat from the surfaces, and it is possible to achieve rapid and uniform heating of thick materials. In traditional heating, the cycle time is often dominated by slow heating rates that are chosen to minimize steep thermal gradients that result in process-induced stresses. For polymers and ceramics, which are materials with low thermal conductivities, this can result in significantly reduced processing times. Thus, there often is a balance between processing time and product quality in conventional processing. As microwaves can transfer energy throughout the volume of the material, the potential exists to reduce processing time and enhance overall quality. In addition to volumetric heating, energy transfer at a molecular level can have some additional advantages. Microwaves can be utilized for selective heating of materials. The molecular structure affects the ability of the microwaves to interact with materials and transfer energy. When materials in contact have different dielectric properties, microwaves will selectively couple with the higher loss material. This phenomenon of selective heating can be used for a number of purposes. In multiple phase materials, some phases may couple more readily with microwaves. Thus, it may be possible to process materials with new or unique microstructures by selectively heating distinct phases. Microwaves may also be able to initiate chemical reactions not possible in conventional processing through selective heating of reactants. Thus, new materials may be created.

2.2.6 Microwave Energy for Mineral Treatment Processes

Several studies demonstrate that microwave energy has potential in mineral treatment and metal recovery operations such as heating, drying, carbothermic reduction of oxide minerals, leaching, roasting and smelting, pretreatment of refractory gold ore and concentrate, spent carbon regeneration and waste management (Haque, 1999).

2.2.6.1 Microwave Heating of Minerals

As early as 1967, Ford and Pei (1967) applied microwave energy to the heating of a number of reagents grade metal oxides and sulphides. Microwaves of 2450 MHz were applied to the heating of a 10.0 g to 200.0 g powder sample per batch. Table 3 shows the test results. The authors concluded that dark-colored compounds were much higher than those of light colored compounds.

Further, microwave heating behavior of several metal oxides were reported (Wong, 1975, Tinga, 1989). These results were compared with published data; and classified based on heating rate into hyperactive, active, difficult-to-heat and inactive Table 4 represents the compilation results. They demonstrated that microwave energy can be effective in the heating of minerals and inorganic compounds.

Table 3. Microwave heating of some oxides and sulphides compounds (Ford and Pei, 1967)

Compound Heating Time (min) Max. Temp. ( oC) Al 2O3 24 1900 C 0.2 1000 CaO 40.0 200 a Co 2O3 3 900 CuO 4 800 CuS 5 600 Fe 2O3 6 1000 Fe 3O4 0.5 500 FeS 6.0 800 MgO 40 1300 a MnO 2 - MoO 3 46 750 MoS 2 0.1 900 a Ni 2O3 3.0 1300 PbO 13 900 UO 2 0.1 1100 a Indicates violent reaction; in the case of MnO 2 temperature could not be recorded

Table 4. Classification of some reagents grade materials based on microwave heating rate (Wong, 1975, Tinga, 1989)

Material Heating rate Max. Notes Classification reported Temp. ( oC) a. Hyperactive ~ o C/s Materials UO 2 200 1100 MoS 2 150 900 C 100 1000 a Fe 3O4 20 500/1000 Depend on the ratio of Fe 2O3 / Fe 3O4 in mixture probably > 20 o C/s FeS 2 20 500 CuCl 20 450 MnO 2 - - b. Active ~ o C/min Ni 2O3 400 1300 violent Co 2O3 300 900 violent CuO 200 800 Fe 2O3 170 1000 FeS 135 800 CuS 120 600 c. Difficult to heat ~ o C/min Al 2O3 80 1900 PbO 70 900 MgO 33 1300 ZnO 25 1100 MoO 3 15 750 d. Inactive ~ o C/min CaO 5 200 CaCo 3 5 130 SiO 2 2-5 70

In 1984, Chen et al. reported the results of heating 40 minerals individually with microwave energy (2450 MHz). As they had difficulty in recording accurate temperatures during microwave irradiation of the samples, they did not report temperature; instead they reported microwave power input. The mineral were characterized before and after microwave heating. The test results were divided into two groups:

(1) No or very little heat was generated and the mineral properties remained essentially unchanged, (Table 5) (2) Heat was generated, and the minerals were either thermally stable or decomposed / reacted rapidly into a different product. (Table 6)

The behavior of minerals to microwave heating depends on their composition; for example, when Fe substitutes for Zn in sphalerite the resulting high iron Sphalerite becomes microwave responsive. These test results indicate that microwave energy may find application in mineral treatment and metal recovery processes.

Table 5. Mineral transparent to microwave irradiation (2450 MHz, 150 W, 5 min exposure) (Chen et al., 1984)

Mineral Class Minerals / Compounds Carbonates Aragonite, calcite, dolomite, siderite Jarosite-type compounds Argentojarosite, synthetic natrojarosite, synthetic plumbojarosite Silicates Almandine, allanite, anorthite, gadolinite, muscovite, potassium feldspar, quartz, titanite, zircon Sulfates Barite, gypsum Others Fergusonite, monazite, sphalerite, stibnite

Table 6. Results of microwave heating of ores (2450 MHz, 3-5 min exposure) (Chen et al., 1984)

Mineral Power Heating response Product examination (W) Allanite >150 Does not heat No change; allanite Cassiterite 40 Heats readily No change; cassiterite Columbite (40 vol.%)- 60 Difficult to heat when Niobium minerals pyrochlore in silicates cold fused; most silicates (almanide 40%) unchanged Fergusonite >150 Does not heat No change; fergusonite Hematite 50 Heats readily; arcing at No change; hematite high temperature Magnetite 30 Heats readily No change; Magnetite Monazite >150 Does not heat No change; monazite Pitcblende (90 vol.%); 50 Heats readily Some fused to UO 2, contains chlorite, galena, U3O8, ThO 2 and Fe- calcite Al-Ca-SiO 2 glass; others unchanged Arsenopyrite 80 Heats, some sparking S and As fumes; some fusion. Pyrrhotite, As, Fe– arsenide and arsenopyrite Bomite 20 Heats readily Some changed to bornite–chalcopyrite– digenite; some unchanged Chalcopyrite 15 Heats readily with Two Cu–Fe-sulfides emission of sulfur fumes or pyrite and Cu–Fe- sulfide Covellite / anilite (60% vol.%) 100 Difficult to heat; sulfur Sintered to single fumes emitted composition of (Cu,Fe) 9S5 Galena 30 Heats readily with much Sintered mass of arcing galena

Nickeline / cobalite (3 vol.%) 100 Difficult to heat Some fused; most unaffected Pyrite 30 Heats readily; emission of Pyrrhotite and S sulfur fumes fumes

Pyrrhotite 50 Heats readily with arcing Some fused; most at high temperature unaffected Sphalerite (high Fe; Zn 58.9, 100 Difficult to heat when Converted to wurtzite Fe 7.4, S 33.7%) cold Sphalerite (low Fe; Zn 67.1, >100 Does not heat No change, sphalerite Fe 0.2, S 32.7%)

Table 6 (cont’d) Stibnite >100 Does not heat No change; stibnite Tennantine (Cu 42.8, Ag 0.1, 100 Difficult to heat when Fused mass of Fe 4.8, An 1.7, As 12.5, Sb cold tennantite-chalco- 10.6, S 27.5%)(90 vol.% pyrite; arsenic fumes tennantite, 6% chalcopyrite, emitted 4% quartz) Tetrahedrite (Cu 24.9, Ag 35 Heats readily Fused mass of Ag–Sb 18.0, Fe 1.9, Zn 4.8, Sb 25.6, alloy, PbS, As 1.3, S 23.4%) 85 vol.% tetrahedrite, Cu–Fe– tetrahedrite, 10% quartz, 5% Zn sulfide and Cu– pyrargyrite Fe–Pb sulfide

In 1999, the US Bureau of Mines reported test results of microwave heating a number of minerals with 2450 MHz (McGill and Walkiewicz, 1987; Walkiewicz et al.,1988). All heating tests were conducted on a 25.0 g powdered sample per batch. The temperatures of the samples were monitored by employing a type K thermocouple with an ungrounded tip sheathed in Inconel 702. Tables 7 and 8 show the test results.

The test results revealed that the highest temperatures were obtained with carbon and most of the metals oxides: NiO, MnO 2, Fe 3O4, Co 2O3, CuO and WO 3. Most metal sulphides heated well but without any consistent pattern. Metal powder and some heavy metal halides also heated well; gangue minerals such as quartz, calcite and feldspar did not heat. This study also revealed that rapid heating of ore minerals in a microwave transparent matrix generated thermal stress of sufficient magnitude to create microcracks along mineral boundaries. This kind of microcracking has the potential to improve grinding efficiency as well as leaching efficiency.

Table 7. Effect of microwave heating on the temperature of natural minerals (McGill and Walkiewicz, 1987; Walkiewicz et al.,1988).

Mineral Chemical Temp. ( oC) Time, min composition Albite NaAlSi 3O8 82 7 Arizonite Fe 2O3.TiO 2 290 10 Chalcocite Cu 2S 746 7 Chalcopyrite CuFeS 2 920 1 Chromite FeCr 2O4 155 7 Cinnabar HgS 144 8 Galena PbS 956 7 Hematite Fe 2O3 182 7 Magnetite Fe 3O4 1258 2.75 Marble CaCO 3 74 4.25 Molybdenite MoS 2 192 7 Orpiment As 2S3 92 4.5 Orthoclase KAlSi 3O8 67 7 Pyrite FeS 2 1019 6.76 Pyrrhotite Fe 1-xS 886 1.75 Quartz SiO 2 79 7 Sphalerite ZnS 87 7 Tetrahedrite Cu 12 Sb 4S13 151 7 Zircon ZrSiO 4 52 7 a Maximum temp. recorded in the indicated time.

Table 8. Effect of microwave heating on the temperature of reagent grade elements and compounds (McGill and Walkiewicz, 1987; Walkiewicz et al.,1988).

Chemical Temp. Time, min Chemical Temp. Time, min (oC) (oC) Al 577 6 Mo 660 4 AlCl 3 41 4 MoS 3 1106 7 C 1283 1 NaCl 83 7 CaCl 2 32 1.75 Nb 358 6 Co 697 3 NH 4Cl 31 3.5 Co 2O3 1290 3 Ni 384 1 CoS 158 7 NiCl 2 51 2.75 Cu 228 7 NiO 1305 6.25 CuCl 619 13 NiS 251 7 CuCl 2.2H 2O 171 2.75 Pb 277 7 CuO 1012 6.25 PbCl 2 51 2 CuS 440 4.76 S 163 6 Fe 768 7 Sb 390 1 FeCl 2 33 1.5 SbCl 3 224 1.75 FeCl 3 41 4 Sn 297 6 FeCl 3. 6H 2O 220 4.5 SnCl 2 476 2 Fe 2O3 134 7 SnCl 4 49 8 Fe 2(SO 4).9H 2O 154 6 Ta 177 7 Hg 40 6 TiCl 4 31 4 HgCl 2 112 7 V 557 1 HgS 105 7 YCl 3 40 1.75 KCl 31 1 W 690 6.25 Mg 120 7 WO 3 1270 6 MgCl 2.6H 2O 254 4 Zn 581 3 MnCl 2 53 1.75 ZnCl 2 609 7 MnO 2 1287 6 Zr 462 6 MnSO 4.H 2O 47 5 a Maximum temp. recorded in the indicated time.

Chunpeng et al. 1990 conducted microwave heating tests on several oxide, sulphides and carbonate minerals. All tests were conducted on a 50.0 g powder (- 200 mesh) sample per batch with an input microwave power of 500 W of 2450 MHz frequency and constant exposure time (4 min). Test results are shown in

Table 9. These results indicate that the majority of oxide and sulphide minerals heated well. Particle size was also an important but not necessarily consistent, factor in the heating of granular material. In the microwave heating of granular alumina and magnetite it was observed that fine Al 2O3 heated faster than coarse Al 2O3; whereas coarse Fe 3O4 heated faster than fine Fe 3O4 (Standish et al. 1991).

Table 9. Effect of Microwave heating on the temperature of various minerals (500 W, 2450 MHz) (Chunpeng et al., 1990)

Minerals Chemical Composition Time,min Temp.( oC). Jamesoite Pb 2Sb 2S2ZnS 2 >850 Titanomagnetite xTiO 2Fe 3O4 4 >1000 Galena PbS 4 >650 Chalcopyrite CuFeS 2 4 >400 Pentlantite (FeNi) 9-xS8 4 >440 Nickel pyrrhotite (FeNi) 1-xS 4 >800 Cu–Co sulphide Concentrate xCu 2S. yCoS 4 >800 Sphalerite ZnS 4 >160 Molybdenite MoS 2 4 >510 Stibnite Sb 2S3 4 room temp. Pyrrhotite Fe 1-xS 4 >380 Bornite Cu 3FeS 4 4 >700 Hematite Fe 2O3 4 >980 Magnetite Fe 3O4 4 >700

Table 9 (cont’d)

Minerals Chemical Composition Time,min Temp.( oC).

Limonite mFeO 2.nH O 4 >130 Cassiterite SnO 2 4 >900 Cobal hydrate CoO. nH2O 4 >800 Lead molybdenate PbMoO 4 4 >150 Iron titanite FeTiO 3 4 >1030 Rutile TiO 2 4 room temp. Lead carbonate PbCO 3 4 >180 Zinespar ZnCO 3 4 >48 Siderite FeCO 3 4 >160 Serpentine Mg(Si 4O10 )(OH) 3 4 >200 Melaconite (Cu 2,Al 3)H 2-x(Si 2O3)(OH) 4 4 >150 Antimony oxide Sb 2O3 4 >150

2.2.6.2 Microwave Assisted Ore Grinding

Walkiewicz et al. 1988, 1991 demonstrated that the rapid heating of ore containing microwave energy absorbing minerals in a non-absorbing gangue matrix generated thermal stress. This thermal stress caused microfracturing along the mineral grain boundaries; as a result, such an ore sample becomes more amendable to grinding. According to these authors the grinding operation comminution consumes 50%–70% of energy used in mineral processing operations. Again the energy efficiency of a conventional grinding operation is approximately 1%. They demonstrated that microwave preheating of an iron ore improved grinding efficiency by 9.9% to 23.9%. However, this improvement was

39 not enough to compensate for the energy consumption of the microwave preheating. It is reported that microwave heating a flotation mixture also improves the flotation rate, e.g., the flotation of CaF 2 (Roussy and Pearce, 1995).

2.2.6.3 Microwave Assisted Carbothermic Reduction of Metal Oxide

The vast majority of heavy metals oxides and carbon, as charcoal or coke, respond to microwave heating. Therefore, the microwave assisted carbothermic reduction of metal oxides is possible. If the metal oxide is low lossy i.e., poor receptor to microwave energy then added carbon plays the role of microwave heating accelerator. Various researchers have demonstrated that iron oxides hematite (Fe 2O3, magnetite Fe 3O4) mixed with carbon (charcoal or coke) could be reduced to metallic iron (Standish and Worner, 1991; Gomez and Aguilar, 1995)

Beside the carbothermic reduction of iron oxides the researchers used microwaves to smelt rare-earth magnet alloys, a high value product difficult to produce by conventional techniques. Although these alloys could be produced in a microwave furnace the furnace needed design changes to eliminate the formation of a gas plasma over the melt. Moreover, a suitable microwave transparent material was needed to contain the smelt at high temperature (Beard et al., 1992; Worner and Bradhurst, 1993) .

2.2.6.4 Microwave Assisted Drying and Anhydration

Microwave energy is finding increasing application to the drying of various kinds of materials and products such as agricultural, chemical and food product, textile, paper, lumber and many more (Cook, 1986; Schiffmann, 1987; Doelling et al., 1992). Generally, drying refers to the removal of physically adsorbed solvent such as water, acid or high vapor pressure organic substance (e.g., alcohol, acetone, ether, halogenated hydrocarbons, aromatics, etc.). Anhydration refers to the removal of water chemically bound to a substance present intermolecularly as

40 well as to the intramolecular elimination of water from hydroxyl or carboxylic compounds. The following reactions demonstrate typical anhydration.

CaSO 42H 2O → CaSO 4 + 2H 2O (gypsum) (anhydrite)

2HFeO 2 → Fe 2O3 + H 2O (goethite) (hematite)

2.2.6.5 Microwave Assisted Mineral Leaching

Kruesi and Frahm 1982 and Kruesi and Kruesi 1986 conducted microwave assisted leaching of lateritic ores containing oxides of nickel, cobalt, and iron. The metals of these mineral components were converted into their chlorides by microwave heating (1200 W, 2450 MHz, N 2 atmosphere) a mixture of the ore and ammonium chloride between 177 0C and 312 0C for 4–5 min, followed by water leaching at 80 0C for 30 min. Nickel and cobalt extractions were 70% and 85%, respectively, and are comparable with roasting at 300 0C in a conventional rotary kiln for 2 h. Similarly, copper ores or concentrates containing oxidic and/or sulphidic minerals were solubilized by microwave heating a mixture of the ore or concentrate and ferric or ferrous chloride between 350 0C and 700 0C, followed by hot brine leaching. Copper extraction was 96% (Kruesi and Frahm, 1982).

2.2.6.6 Microwave Assisted Roasting and Smelting of Sulphide Concentrate

Chunpeng and Jinhui 1993 reported tests result from roasting a nickel bearing pyrrhotite with microwave energy under a controlled supply of oxygen. Over 90% of the sulphur in the pyrrhotite was converted to elemental sulphur, and iron and nickel were oxidized into Fe 3O4, NiO, NiFe 2O4 and FeSiO 4.

2.2.6.7 Microwave Assisted Pretreatment of Refractory Gold Concentrate

Gold is considered to be refractory when it cannot be easily recovered by alkaline cyanide leaching. The vast majority of refractory gold occurs in sulphidic minerals such as pyrite (FeS 2), arsenopyrite (FeAsS) and pyrrhotite (FeS).

Generally, refractory gold concentrate or ore is pretreated by roasting, O 2 - pressure leaching or bacterial leaching, to render it amenable to gold recovery by alkaline cyanide leaching (Haque, 1987a,b).

Because sulphidic minerals are in general heated easily by microwaves, it should be possible to pretreat sulphidic refractory gold concentrate by microwave energy. Haque 1987 a,b conducted laboratory-scale microwave pretreatment tests in air on a typical arsenopyritic refractory gold concentrate. More than 80% of As and S were volatilized as As 2O3 and SO 2, whereas iron was oxidized into 0 hematite (Fe 2O3) at 550 C. Alkaline cyanide leaching of the calcine yielded 98% Au and 60% Ag extractions.

2.2.6.8 Microwave Assisted Coal Desulphurization

Environmental problems arise from the constituent high sulphur which, upon coal combustion, releases sulphur dioxide into the atmosphere. The removal of sulphur prior to combustion as a part of coal cleaning process offers a convenient and attractive way of reducing emissions of sulphur dioxide to the atmosphere (Özbayo ğlu,1999). Uslu 2002 reported test results of microwave heating characteristics of pyrite mineral and desulphurization of lignite, by using magnetic separation after the microwave heating. With 7.5 % magnetite addition as excellent microwave absorbing mineral, total sulphur and pyritic sulphur contents of pre-cleaned coal were reduced by 52.05 % and 58.20 % respectively, by magnetic separation after microwave heating.

2.2.6.9 Microwave Assisted Spent Carbon Regeneration

Currently, more and more gold ore processing industries are using activated carbon in CIP (carbon in pulp) or CIL (carbon in leach) operation. The carbon is regenerated after each cycle of adsorption and desorption of gold cyanocomplex. Usually, this spent carbon is regenerated by washing with a mineral acid followed by heating at high temperature 600 0C to 750 0C in an externally heated rotary kiln (Avraamides et al., 1987). Haque et al. (1993) conducted laboratory scale carbon regeneration tests by microwave 2450 MHz heating and confirmed the feasibility of spent carbon regeneration by microwave heating. Subsequent pilot scale carbon regeneration tests data 915 MHz demonstrated that microwave regenerated carbon performed well or better than conventionally regenerated carbon (Bradshaw et al., 1997).

2.2.6.10 Microwave Assisted Waste Management

Microwave energy is showing considerable potential in the management of a vast array of gaseous, liquid and solid wastes (Wan, 1993; Wicks et al., 1995). Mine milling operations generate large volumes of solid waste with acid generation potential, liquid waste containing acid, toxic heavy metals and non-metals, cyanide, ammonia, organics etc., and gaseous wastes such as, sulphur dioxide

(SO 2) , hydrogen sulphide (H 2S) , ammonia (NH 3) , oxides of nitrogen (NO x).

Cha (1993) demonstrated in laboratory scale tests that SO 2 and NO x in industrial off-gas can be decomposed into elemental nitrogen and sulphur, and a mixture of carbon dioxide and carbon monoxide.

2.3 Iron Ore

Iron is only found in the metallic state in certain types of meteorites but, in a combined form, it is one of the most common elements, comprising some 5 per cent of the earth’s crust. It is most usually found as an oxide, sometimes a

43 hydrated oxide, but it is also occurs as carbonate and sulphides and as a component of a wide range of complex minerals.

An iron-bearing mineral can only be considered to be an iron ore if the total cost of extracting iron from it is comparable with the cost of extracting iron from other ores. This will be governed by many factors, of which the iron content of the mineral, the nature of the impurities and the location of the deposit are of particular importance. (Ball, Dartnell, 1973)

The more economically important iron-bearing minerals are the following:

Hematite Fe 2O3

Magnetite Fe 3O4 Limonite, goethite and hydrogoethite Hydrated hematites

Siderite FeCO 3

Chamosite 3FeO.Al 2O3.2SiO 2.3H 2O

In addition, ore is recovered from a number of minerals from which other saleable products are also extracted: from pyrites (FeS 2) and pyrrhotite (FeS), in addition to sulphur; from ilmenite (FeTiO 3), in addition to titania, and from complex ores, in addition to such metals as nickel, copper and cobalt and vanadium.

CHAPTER 3

MATERIALS AND METHODS

3.1 Materials

Magnetite used in the experiment was obtained from Divhan-Divri ği Mine in the form of fire ore concentrate. The density of the concentrate was 4.3 g/cm 3 and the magnetite content was 98 %.

0.1 N NaOH first added to the as received concentrate and then concentrate was washed repeatedly with distilled water in order to remove impurities which would affect the pH, in other words balling behaviour of the concentrate. Bringing the pH near neutrality, the ore was dried at 100 oC for 8 hours and stored. Three different Blaine surface areas of the concentrate were prepared by grinding the representative sample of this concentrate; namely 1297 cm 2/g Blaine surface area (68% -325 mesh) with no grinding, 2180 cm 2/g Blaine surface area (80.88 % - 325 mesh) and 2549 cm 2/g Blaine surface area (85.46 % -325 mesh) with 30 and 60 min. of grinding, respectively.

3.2 Methods

3.2.1 Density Measurement

Samples with a specific gravity of 4.3 g/cm 3 in three different Blaine; 1297 (no grinding), 2180 and 2549 was used. Density measurement was performed by a pycnometer. First the pycnometer was weighed empty, then the sample was introduced in the pycnometer and the second weighing was made. The difference represents the weight of the sample. Secondly, the pycnometer was filled with acetone and again weighed. Therefore;

Wempty pycnometer +sample +acetone −Wempty pycnometer +sample = Wacetone

Wacetone Vacetone = ρacetone

Vsample = Vtotal −Vacetone

Wsample ρ sample = ...... ( 10 ) Vsample

3.2.2 Specific Surface Area Measurement

Specific surface area measurements were performed by a Blaine air permeability apparatus (Appendix A). The Blaine air permeability apparatus consists essentially of a means of drawing a definite quantity of air through a prepared bed of sample of definite porosity. The number and size of the pores in a prepared bed of definite porosity is a function of the size of the particles and determines the rate of airflow through the bed. The Blaine apparatus used in the experiments can be seen in Figure 11. Permeability test performed as described; first the permeability cell was attached to the manometer tube, making certain that an airtight connection is obtained. The air in the one arm of the manometer U-tube was slowly evacuated until the liquid reached the top mark, and then the valve was closed tightly. The timer was started when the bottom of the meniscus of the manometer liquid reached the second (next to top) mark and stopped when the bottom of the meniscus of liquid reached the third (next to the bottom) mark. The time interval measured and recorded in seconds. Specific surface area was calculated according to the following equation.

S ρ ()b − ε ε 3 t S = S S S S ………………………………….(11) 3 ρ ()b − ε ε S t S

S: Specific surface area of the test sample, cm 2/g, 2 SS: Specific surface of the test sample used in calibration of the apparatus, cm /g, t: Measured time interval, s, of the manometer drop for the test sample

46 tS: Measured time interval, s, of manometer drop for standard sample used in calibration of the apparatus, ε: Porosity of prepared bed of test sample

εS: Porosity of prepared bed of standard sample used in calibration of the apparatus, ρ: Density of test sample

ρS: Density of standard sample used in calibration of the apparatus, b: A constant specifically appropriate for the test sample (0.907), bS: 0.9, the appropriate constant for the standard sample.

Figure 11. Blaine air permeability apparatus

3.2.3 Preparation of Magnetite Disk Pellets

Disk pellets with a height of 9.3 and diameter of 18.8 mm and 20% porosity were prepared with addition of 1% binder (bentonite) and 10 % water for drying tests. For hardening tests in order to produce smooth pellets Denison Testing Machine

47 was used to squeeze the pellets with 100 kg load (Figure 12). Pellets with the same diameter and a height of 8.1 mm were prepared with same amount of binder and water.

Figure 12. Denison Testing Machine

3.2.4 Drying and Hardening Tests

All drying tests were performed with a 2450 MHz Moulinex domestic microwave oven (Figure 13). Pellets were placed in a ceramic crucible and weighted before drying in the oven. After the pellets exposed to microwave energy for 10, 30, 45, 60, 70, 90 seconds and weight losses were noted.

In microwave oven hardening tests as the true temperature can not be measured, power input levels were recorded for 5,10, 20 minutes. A clay bed was placed between the pellet and the glass plate of the microwave oven in order to avoid any cracking resulting from the excess heating of the pellet. In the conventional

48 hardening tests a Gebr. Ruhstrat 3401 Lenglern metallurgical furnace was used. Pellets were hardened at 1250 0C for 5, 10 and 20 minutes.

Figure 13. Moulinex domestic microwave oven

Mechanical strength of pellets is given in terms of compressive strength. Two different devices were used for measuring the compressive strength. For the pellets which were hardened by metallurgical furnace, Tinus Olsen testing machine (Figure 14) was used which has a wider load range (0-40000 kg) and Denison testing machine (0-980 kg) for more accurate measurement was used for the pellets which had a lower strength hardened by microwave oven

Figure 14. Tinus Olsen testing machine

Oxidation of the pellets is described in terms of % Fe 3O4 and measured by SATMAGAN (Figure 15). SATMAGAN (Saturation Magnetization Analyzer) is a balance in which the sample is weighed in gravitational and magnetic fields. If the field is strong enough to saturate the magnetic material in the sample, the ratio of the two weightings is linearly proportional to the amount of magnetic material present in the sample. First the sample cell was filled with the sample and closed with the plug and then inserted into the holder. The sample is weighed by bringing the balance into equilibrium with potentiometer. Then the magnet is turned with crank handle. The magnetic force acting on the sample was compensated by bringing the balance into equilibrium with potentiometer. The reading of the potentiometer is in the first approximation directly proportional to the weight fraction of the magnetic material in the sample. The weight percentage was read from the calibration curve.

Figure 15. SATMAGAN (Saturation Magnetization Analyzer)

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Drying Characteristics of Magnetite Pellets with Microwave Oven

The main purpose of this experiment was to determine the physical and chemical characteristics of magnetite pellets in different particle sizes treated with microwave energy. These tests were performed in a 2450 MHz microwave oven.

First, microwave assisted drying characteristics of 1297, 2180 and 2549 cm 2/g Blaine size fractions at 170, 400, and 620 W power input levels were investigated. Results are given in Table B1-9 and presented in Figures 16-18.

170 W

0.6

0.5

0.4 1297 0.3 2180

0.2 2549 weight loss (g) loss weight 0.1

0 0 20 40 60 80 100 time (sec)

Figure 16. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 170 W power input.

400 W

0.7 0.6 0.5 1297 0.4 2180 0.3 2549 0.2 weight loss (g) loss weight 0.1 0 0 20 40 60 80 100 time (sec)

Figure 17. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 400 W power input.

620 W

0.7 0.6 0.5 1297 0.4 2180 0.3 2549 0.2 weight loss (g) loss weight 0.1 0 0 20 40 60 80 100 time (sec)

Figure 18. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 620 W power input.

Moisture loss is slower in coarser particle sizes. But after a certain time pellets with different particle sizes reach the same level of moisture. Moreover, a fast evaporation occurs in 400 and 620 W input levels and after 60 seconds drying rate becomes nearly equal for three different input levels (Figure 19-24).

170 W

0.6

0.5 10' 0.4 30' 45' 0.3 60' 0.2 70' weight loss (g) loss weight 0.1 90'

0 1000 1500 2000 2500 3000

blaine (cm 2/g)

Figure 19. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 170 W power input in different durations.

400 W

0.7

0.6 10' 0.5 30' 0.4 45' 0.3 60' 0.2 70' weight loss (g) loss weight 0.1 90' 0 1000 1500 2000 2500 3000

blaine (cm 2/g)

Figure 20. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 400 W power input in different durations.

620 W

0.7

0.6 10' 0.5 30' 0.4 45' 0.3 60' 0.2 70' weight loss (g) loss weight 0.1 90' 0 1000 1500 2000 2500 3000

blaine (cm 2/g)

Figure 21. Drying pattern of pellets made of 1297, 2180 and 2549 cm 2/g Blaine magnetite concentrate in a microwave oven at 620 W power input in different durations.

1297 cm 2/g Blaine

0.7 0.6 10' 0.5 30' 0.4 45' 0.3 60' 0.2 70' weight(g) loss 0.1 0 90' 0 100 200 300 400 500 600 700 power (W)

Figure 22. Drying pattern of pellets made of 1297 cm 2/g Blaine magnetite concentrate at 170, 400 and 620 W in different durations.

2180 cm 2/g Blaine

0.7 10' 0.6 0.5 30' 0.4 45' 0.3 60' 0.2 70'

weight(g) loss 0.1 90' 0 0 200 400 600 800 pow er (W)

Figure 23. Drying pattern of pellets made of 2180 cm 2/g Blaine magnetite concentrate at 170, 400 and 620 W in different durations.

2549 cm 2/g Blaine

0.7 0.6 10' 0.5 30' 0.4 45' 0.3 60' 0.2 70' weight(g) loss 0.1 0 90' 0 100 200 300 400 500 600 700 power (W)

Figure 24. Drying pattern of pellets made of 2549cm2/g Blaine magnetite concentrate at 170, 400 and 620 W in different durations.

The increase of drying rates with increasing microwave power results from the increase in the absorption of microwave energy because the power absorbed increases with the square of the internal electric intensity (Xia and Pickles, 1997)

The weight loss of the pellets upon microwave heating did not reach the level at which complete moisture removal occurs. This was thought to be caused by the weight gain as result of the oxidation of magnetite to hematite as:

1 2Fe 3O4 + O2 = 3Fe 2O3 + Q 2

In order to substantiate this hypothesis, magnetite content of the dried pellet at different power levels as a function of time was determined. The results are given in Table B10-12 and Figure 25-27. As can be seen from the figures, magnetite content of the pellets start to decrease after 70 seconds for 170 W, 45 seconds for 400 W, and 10 seconds for 620 W.

170 W

100 90

4 1297 O

3 80 2180 70 %Fe 2549 60 50 0 20 40 60 80 100 Time (sec.)

Figure 25. % Fe 3O4 content of the dried samples in 170 W.

400 W

100 90

4 1297 O

3 80 2180 70 %Fe 2549 60 50 0 20 40 60 80 100 Time (sec.)

Figure 26. % Fe 3O4 content of the dried samples in 400 W.

620 W

100 90

4 1297 O

3 80 2180 70 % Fe % 2549 60 50 0 20 40 60 80 100 Time (sec.)

Figure 27. % Fe 3O4 content of the dried samples in 620 W.

4.2 Heating Characteristics of Magnetite Pellets with Microwave Oven

The second step in the heat treatment of pellets is the heat hardening. Pellets in three different particle sizes were heated at 900 W power input for 5, 10, and 20 minutes in 2450 MHz microwave oven. Compressive strength and the Fe 3O4 content of the samples were examined. Results are given in Table B13-14 and presented in Figures 28-29.

600

500

400 1297 300 2180 2549 200

100

Compressive(kg) Strength 0 0 5 10 15 20 25 Time (min.)

Figure 28. Effect of duration of heat treatment on the compressive strength of pellets prepared from 1297, 2180 and 2549 cm 2/g Blaine pellets

20 18 16 14 4 12 1297 O 3 10 2180 8 %Fe 2549 6 4 2 0 0 5 10 15 20 25 Time (min.)

Figure 29. Effect of duration of heat treatment on the %Fe 3O4 content of pellets prepared from 1297, 2180 and 2549 cm 2/g Blaine pellets

Magnetite grains are oxidized stepwise to hematite at first. As a result of vigorous recrystallization, hematite begins to form into sizeable agglomerates. The hematite grains, which are formed, agglomerate depending on time and temperature. Therefore, as the duration prolonged, due to increasing oxidation, the magnetite content decreases and the mechanical strength increases. Moreover,

59 with the increasing contact point in higher Blaines, strength of the pellets is also high.

To understand the efficiency of the microwave treatment of pellets, results are compared with the metallurgical furnace treatments. Same experiments were carried out with 1297, 2180 and 2549 cm 2/g Blaine pellets for 5, 10 and 20 minutes at 1250 0C. Results are given in Table B15-22 and Figure 30-37.

2500

2000

1500 1297 2180 1000 2549

500

CompressiveStrength (kg) 0 0 5 10 15 20 25 Time (min.)

Figure 30. Effect of heat treatment duration on the compressive strength of pellets prepared from 1297, 2180 and 2549 cm 2/g Blaine in metallurgical furnace at 1250 0C

2,5

4 1,5 1297 O 3 2180 1 % Fe 2549

0,5

0 0 5 10 15 20 25 Time (min.)

Figure 31. Effect of heat treatment duration on the %Fe 3O4 content of pellets prepared from 1297, 2180 and 2549 cm 2/g Blaine in metallurgical furnace at 1250 0C

1297 cm 2/g Blaine

1400 1200 1000 800 Regular Furnace

(kg) 600 Microw ave Oven 400 200

CompressiveStrength 0 0 10 20 30 Time (min.)

Figure 32. Comparison of compressive strength of pellets prepared from 1297 cm 2/g Blaine, treated in metallurgical furnace at 12500C and microwave oven at 620 W.

2180 cm 2/g Blaine

2500

2000

1500 Regular Furnace

(kg) 1000 Microw ave Oven

500

CompressiveStrength 0 0 10 20 30 Time (min.)

Figure 33. Comparison of compressive strength of pellets prepared from 2180 cm 2/g Blaine, treated in metallurgical furnace at 12500C and microwave oven at 620 W.

2549 cm 2/g

2500

2000

1500 Regular Furnace

(kg) 1000 Microw ave Oven

500

CompressiveStrength 0 0 10 20 30 Time (min.)

Figure 34. Comparison of compressive strength of pellets prepared from 2549 cm 2/g Blaine, treated in metallurgical furnace at 12500C and microwave oven at 620 W.

1297 cm 2/g Blaine

4 Regular Furnace O 3 10

Fe Microw ave Oven 5

0 0 5 10 15 20 25 Time (min.)

2 Figure 35. . Comparison of % Fe 3O4 content of pellets prepared from 1297 cm /g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620 W.

2180 cm 2/g Blaine

4 Regular Furnace O 3 10

Fe Microw ave Oven 5

0 0 5 10 15 20 25 Time (min.)

2 Figure 36. Comparison of % Fe 3O4 content of pellets prepared from 2180 cm /g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620 W.

2549 cm 2/g Blaine

4 Regular Furnace O

3 10

Fe Microw ave Oven 5

0 0 5 10 15 20 25 Time (min.)

2 Figure 37. Comparison of % Fe 3O4 content of pellets prepared from 2549 cm /g Blaine, treated in metallurgical furnace at 1250 0C and microwave oven at 620 W.

As can be seen from the graphs, same degree of oxidation and strength of pellets in metallurgical furnace treatment can not be attained with microwave oven. In firing, oxidation commences at the surface and then penetrates the pellets basically on a topochemical front, and the hematite crystal formed in the surface shell bond initially by oxide bonding. In the presence of a sufficient supply of oxygen, and as the temperature in increased, oxidation penetrates the pellets and stronger bonding is developed by the further crystallization and grain growth of hematite. This leads to the formation of a double structure, essentially a hematite shell and magnetite nucleus, and it is essential for oxygen to penetrate the hematite shell to oxidize this nucleus. The rate at which the firing temperature is increased is very important in maintaining a shell with adequate permeability. Too dense a shell not only slows down the rate of oxidation in the nucleus, but at temperatures above 900 0C magnetite can undergo recrystallization and grain growth, leading to magnetite bonding which further reduces the rate of oxidation.

This may be the reason of low strength and high Fe 3O4 content of the pellets treated in microwave oven.

4.2.1 Heating Characteristics of Magnetite Pellets with Addition of Na 2O2

In order to increase the oxidation rate 1, 2, and 3 % Na 2O2 were added to the pellets as oxidizing agents. Results are given in Table B23-24 and presented in Figure 38-39.

800 700 600 500 1 % NaO2 400 2% NaO2 3% NaO2 300 200 100 Compressive Strength (kg) Strength Compressive 0 0 1000 2000 3000 Particle Size (Blaine)

Figure 38. Effect of addition of 1, 2, 3 % Na 2O2 on the compressive strength of pellets prepared from1297, 2180 and 2549 cm 2/g Blaine.

8 7 6

4 5 1% NaO2 O 3 4 2% NaO2 3% NaO2

% % Fe 3 2 1 0 0 1000 2000 3000 Particle Size (Blaine)

Figure 39. Effect of addition of 1, 2, 3 % Na 2O2 on the Fe 3O4 content of pellets prepared from1297, 2180 and 2549 cm 2/g Blaine.

As presented in the figures, the compressive strength and the degree of oxidation increase with increasing Na 2O2 amount. However, the difference is not so

65 significant and there is still a big difference between the microwave and metallurgical furnace treatment (Table B25-26, Figure 40-41).

2500 2250 2000 1750 1 % NaO2 1500 2% NaO2 1250 3% NaO2 1000 Metallurgical 750 Furnace 500 Compressive Strength (kg) Strength Compressive 250 1000 2000 3000 Particle Size (Blaine)

Figure 40. Comparison of compressive strength of pellets heated in metallurgical furnace and in a microwave oven in the presence 1, 2, 3 % Na 2O2.

8 7 6 1% NaO2

4 5 O 3 4 2% NaO2

% Fe % 3 3% NaO2

2 Metallurgical 1 Furnace 0 1000 2000 3000 Particle Size (Blaine)

Figure 41. Comparison of % Fe 3O4 of pellets heated in metallurgical furnace and in a microwave oven in the presence 1, 2, 3 % Na 2O2.

CHAPTER 5

CONCLUSION

1. In microwave-assisted drying, until 60 seconds in 170 W and 30 seconds in 400 and 620 W, a fast evaporation was observed where the dry pellet attains an equilibrium with the drying gas determined by the temperature and humidity of the latter.

2. The increase of drying rates with increasing microwave power results from the increase in the absorption of microwave energy because the power absorbed increases with the square of the internal electric intensity.

3. Oxidation starts at 70 sec. in 170 W, 45 sec. in 400 W, and 10 sec. in 620

W where the Fe 3O4 content starts to decrease and heat hardening begins.

4. In the heat hardening with microwave energy, like conventional heat

hardening treatments, Fe 3O4 content decreases and the compressive strength of the pellets increases with increasing specific surface area of the material due to increasing contact point.

5. As the treatment duration is prolonged because of increasing oxidation, the magnetite content decreases and the mechanical strength increases.

6. Temperature increasing rate is higher in microwave oven than in metallurgical furnace. This causes a denser hematite shell which is less permeable and results in a slow oxidation in the nucleus. Additionally, at temperatures above 900 0C magnetite undergoes recrystallization and grain growth, leading to magnetite bonding which also reduces the rate of oxidation.

7. Addition of Na 2O2 which is an oxidizing agent increases the oxidation

rate and the mechanical strength of the pellets. Application of 1% Na 2O2

increases the compressive strength by 5%, 8%, and 10%, while 2% Na 2O2

performs at 17%, 18%, and 20%, and 3 % Na 2O2 at 20%, 30%, and 33 % for 1297, 2180 and 2549 cm 2/g Blaine pellets, respectively. . However, the difference is not so significant and there is still a big difference between the microwave and metallurgical furnace treatment.

REFERENCES

Advantages of Our Microwave Heating Plants. http://www.ncpower.com/ industrial/ etech03.html

Ball, D.F., Dartnell, J., Davison, J., Grieve, A., Wild, R., 1973. Agglomeration of Iron Ores., New York.

Chen, T.T., Dutrizac, J.E., Haque, K.E., Wyslouzil,W., and Kashyap, S., 1984. The relative transparency of minerals to microwave radiation . Canadian Metallurgical Quarterly, Vol.23, No.3, pp.349-351, 1984

Church, R.H., Webb, W.E., and Salsman, J.B., 1993. Dielectric Properties of Low-Loss Mineral. Bureau of Mines Report of Investigations 1994

Clark, D.E. and Sutton, W.H., 1996. Microwave processing of materials . Annu. Rev. Mater. Sci. 1996. 26. pp.291-331, 1996

Cook, N.P., 1986. Microwave Principles and System. Chapter 1. Prentice Hall, 1986

Haque, K.E., 1999. Microwave Energy for Mineral Treatment Processes, a brief review . International Journal of Mineral Processing, 57, pp.1-24

How Does a Microwave Oven Works? http://www.eng2uconn.edu/cse/Courses/CSE208W/Microwave /34_Stirrer.html

How Industrial Microwaves Heat? http://www.micrody.com/micro2.htm

Kingman, S.W. and Rowson, N.A., 1998. Microwave treatment of minerals-a review . Minerals Engineering, vol.11, No.11, pp.1081-1087

Kingston, H.M., Jassie, L.B., 1985. Introduction to Microwave Sample Preparation- Theory and Practice. Chapters 2 and 3, ACS professional reference book. Am. Chem. Soc.

Krusei, W.S., and Krusei, P.R., 1986. Microwave in laterite processing . Proceedings of CIM 25 th Conf. of Metallurgist, Toronto.

Metaxas, A.C., Meredith, R.J., 1983. Industrial Microwave Heating. Chapter 10, Peter Peregrinus, London, UK.

Meyer, K., 1980, Pelletizing of Iron Ores, Frankfurt, Germany.

Microwave Engineering. http://kauri.auck.irl.cri.nz/me_profile.html

Morse, P.W., and Rivercomb, H.E., Electronics , 20(1947), 85.

Osepchuk, J.M., 1984. A history of microwave heating applications . IEEE Transactions on Microwave Theory and Techniques. No:9, September 1984.

Özbayo ğlu, G., 1999. Coal Desulphurization Techniques: Their Drawbacks and Costs. VII. Balkan Mineral Processing Conference, Belgrade, Yugoslavia, Sept 13-18, 1999, pp.503-509

Peterson, E.R., 1993. Microwave Chemical Processing. Proceedings: Microwave- Induced Reactions Workshop, A-9-1-9-6. Pacific Grove, CA.

Roussy, G., and Pearce, J.A., 1995. Foundations and Industrial Applications of Microwave and Radiofrequency Fields, Physical and Chemical Processes. Chapter 10,11,12.

Růžıčková, Z., Srb, J., 1988. Pelletization of fines, Prague, Czechoslavakia.

Schiffmann,R.F.,1995. Commercialization microwave systems: path to success or failure. Microwaves: theory and application in Material Processing 111. In: Clark, D.E., Folz, D.C:, Oda, S.J., Silberglit, R., Ceramic Transc. Vol. 59.

Smr ček, K., Čejchar, O., J.Srb: Rudy, (1963), No.12, pp400-408.

Standish, N., and Worner, H., 1990. Microwave application in the reduction of metal oxides with carbon . Journal of Microwave Power and Electromagnetic Energy. Vol.25.No.3.1990.pp.177-180.

Tinga, W.R., 1988. Microwave Dielectric Constants of Metal Oxides, part 1 and part 2. Electromagnetic Energy Reviews 1 (5), 2-6

Tinga, W.R., 1989. Microwave Dielectric Constants of Metal Oxides, part 1 and part 2. Electromagnetic Energy Reviews 2 (1), 349-351

Uslu, T., 2002. Microwave heating characteristics of pyrite and microwave assisted coal desulphurization , PhD. Thesis, Middle East Technical University, Turkey.

Walkiewicz, J.W., Kazonich, G., and McGill, S.L., 1998. Microwave heating characteristics of selected minerals and compounds. Minerals and Metallurgical Processing, 39, (Feb.1998), pp.39-42

Walkiewicz, J.W., Kazonich, G., and McGill, S.L., 1991. Microwave assisted grinding . IEEE Transactions on Industry Applications. Vol.27, No.2, March- April 1991, pp.239-243

Wong, D.,1975. Microwave dielectric constants of metal oxides at high temperatures. MSc thesis. Univ. of Alberta, Canada

Xia, D.K., and Pickles, C.A., 1997. Application of Microwave Energy in Extractive Metallurgy, a review. CIM Bulletin, 90(1), pp.99-107.

APPENDIX A

APPENDIX B

Table B1. % Moisture loss of 1297 cm 2/g Blaine pellets in 170 W

% Moisture Time (sec.) Weight 1 (g) Weight 2 (g) Loss (gr) Loss 10 33.42 33.33 0.09 14.8 30 33.43 33.29 0.14 22.43 45 33.44 33.03 0.40 63.71 60 33.41 32.87 0.54 84.27 70 33.44 32.89 0.55 85.83 90 33.42 32.85 0.56 88.63

Table B2. % Moisture loss of 2180 cm 2/g Blaine pellets in 170 W

% Moisture Time (sec.) Weight 1 (g) Weight 2 (g) Loss (gr) Loss 10 33.46 33.33 0.12 19.48 30 33.44 33.26 0.17 27.26 45 33.44 33.04 0.4 62.31 60 33.45 32.95 0.50 78.51 70 33.44 32.89 0.55 86.14 90 33.41 32.84 0.57 88.79

Table B3. % Moisture loss of 2549 cm 2/g Blaine pellets in 170 W

% Moisture Time (sec.) Weight 1 (gr) Weight 2 (gr) Loss (gr) Loss 10 33.43 33.23 0.20 31.46 30 33.45 33.24 0.21 33.18 45 33.45 33.07 0.38 59.19 60 33.46 32.92 0.53 83.18 70 33.44 32.88 0.55 86.14 90 33.42 32.86 0.56 88.16

Table B4. % Moisture loss of 1297 cm 2/g Blaine pellets in 400 W

% Moisture Time (sec.) Weight 1 (g) Weight 2 (g) Loss (gr) Loss 10 33.47 33.39 0.08 12.93 30 33.44 32.93 0.50 78.82 45 33.45 32.91 0.54 84.42 60 33.44 32.88 0.56 87.38 70 33.42 32.86 0.5 87.69 90 33.42 32.86 0.56 88.32

Table B5. % Moisture loss of 2180 cm 2/g Blaine pellets in 400 W

% Moisture Time (sec.) Weight 1 (g) Weight 2 (g) Loss (gr) Loss 10 33.45 33.25 0.19 30.53 30 33.44 32.90 0.54 84.11 45 33.44 32.89 0.55 85.98 60 33.45 32.89 0.56 87.85 70 33.47 32.89 0.57 88.94 90 33.47 32.90 0.57 89.88

Table B6. % Moisture loss of 2549 cm 2/g Blaine pellets in 400 W

% Moisture Time (sec.) Weight 1 (g) Weight 2 (g) Loss (gr) Loss 10 33.45 33.19 0.26 41.28 30 33.44 32.89 0.54 84.58 45 33.45 32.88 0.56 88.47 60 33.44 32.86 0.58 90.97 70 33.43 32.84 0.58 91.59 90 33.46 32.89 0.57 89.41

Table B7. % Moisture loss of 1297 cm 2/g Blaine pellets in 620 W

% Moisture Time (sec.) Weight 1 (g) Weight 2 (g) Loss (gr) Loss 10 33.45 33.34 0.10 16.51 30 33.45 32.92 0.53 82.55 45 33.43 32.86 0.56 87.69 60 33.48 32.90 0.58 90.32 70 32.39 31.82 0.57 89.88 90 32.40 31.83 0.56 87.85

Table B8. % Moisture loss of 2180 cm 2/g Blaine pellets in 620 W

% Moisture Time (sec.) Weight 1 (g) Weight 2 (g) Loss (gr) Loss 10 33.45 33.27 0.17 27.57 30 33.45 32.90 0.54 85.05 45 33.44 32.86 0.57 89.41 60 33.44 32.86 0.58 91.12 70 33.45 32.84 0.60 94.55 90 33.46 32.90 0.55 86.14

Table B9. % Moisture loss of 2549 cm 2/g Blaine pellets in 620 W

% Moisture Time (sec.) Weight 1 (g) Weight 2 (g) Loss (gr) Loss 10 33.45 33.24 0.21 33.33 30 33.44 32.91 0.54 85.35 45 33.46 32.91 0.55 86.45 60 33.46 32.86 0.59 93.31 70 33.46 32.86 0.60 94.39 90 33.45 32.86 0.58 90.81

Table B10. % Fe 3O4 content of the dried samples in 170 W

Particle Size (cm 2/g Blaine) Time (sec.) 1297 2180 2549 10 95.6 93.6 94 30 91.6 94.2 93.6 45 94.4 92.2 94.5 60 94.7 94.8 93.8 70 92.9 95.5 91.7 90 93.4 86.1 76.2

Table B11. % Fe 3O4 content of the dried samples in 400 W

Particle Size (cm 2/g Blaine) Time (sec.) 1297 2180 2549 10 94 94.1 93 30 95 95.2 92 45 91.8 94.5 94.4 60 74 80.1 68.6 70 75.7 79.8 66.6 90 69.2 82 69.6

Table B12. % Fe 3O4 content of the dried samples in 620 W

Particle Size (cm 2/g Blaine) Time (sec.) 1297 2180 2549 10 97 97 93.3 30 88.4 78.3 86.9 45 73.6 72.4 76.3 60 72.7 64.3 66.6 70 71.7 62.5 63 90 66.6 60.2 61.8

Table B13. Compressive strength of microwave treated pellets

Particle Size (cm 2/g Blaine) Time (min.) 1297 2180 2549 5 296 330 415 10 330 425 450 20 356 449 533

Table B14. % Fe 3O4 content of microwave treated pellets

Particle Size (cm 2/g Blaine) Time (min.) 1297 2180 2549 5 19 17.1 15.25 10 12.25 10.12 9.75 20 7.8 7.2 5.8

Table B15. Compressive strength of Metallurgical furnace treated pellets

Particle Size (cm 2/g Blaine) Time (min.) 1297 2180 2549 5 850 1250 2250 10 1150 1670 2300 20 1300 2025 2375

Table B16. % Fe 3O4 content of Metallurgical furnace treated pellets

Particle Size (cm 2/g Blaine) Time (min.) 1297 2180 2549 5 2.25 2.2 1.8 10 2.1 1.9 1.7 20 1.95 1.8 1.7

Table B17. Compressive strength of pellets prepared from 1297 cm 2/g Blaine treated in Metallurgical furnace and microwave oven

Time (min.) Metallurgical Microwave Furnace Oven 5 850 296 10 1150 330 20 1300 356

Table B18. Compressive strength of pellets prepared from 2180 cm 2/g Blaine treated in Metallurgical furnace and microwave oven

Time (min.) Metallurgical Microwave Furnace Oven 5 1250 330 10 1670 425 20 2025 449

Table B19. Compressive strength of pellets prepared from 2549 cm 2/g Blaine treated in Metallurgical furnace and microwave oven

Time (min.) Metallurgical Microwave Furnace Oven 5 2250 415 10 2300 450 20 2375 533

2 Table B20. % Fe 3O4 content of pellets prepared from 1297 cm /g Blaine treated in Metallurgical furnace and microwave oven

Time (min.) Metallurgical Microwave Furnace Oven 5 2.25 19 10 2.1 12.25 20 1.95 7.8

2 Table B21. % Fe 3O4 content of pellets prepared from 2180 cm /g Blaine treated in Metallurgical furnace and microwave oven

Time (min.) Metallurgical Microwave Furnace Oven 5 2.2 17.1 10 1.9 10.12 20 1.8 7.2

2 Table B22. % Fe 3O4 content of pellets prepared from 2549 cm /g Blaine treated in Metallurgical furnace and microwave oven

Time (min.) Metallurgical Microwave Furnace Oven 5 1.8 15.25 10 1.7 9.75 20 1.7 5.8

Table B23. Compressive strength of Na 2O2 added pellets

Particle Size 2 (cm /g 1 % Na 2O2 2 % Na 2O2 3 % Na 2O2 Blaine) 1297 375 415 427 2180 485 529 582 2549 586 639 708

Table B24. % Fe 3O4 content of Na 2O2 added pellets

Particle Size 2 (cm /g 1 % Na 2O2 2 % Na 2O2 3 % Na 2O2 Blaine) 1297 7.58 6.48 5.65 2180 6.85 6.55 5.47 2549 5.8 5.6 4.19

Table B25. Compressive strength of pellets heated with metallurgical furnace and heated with microwave oven in the presence of Na2O2

Particle Size Metallurgical 2 (cm /g 1 % Na 2O2 2 % Na 2O2 3 % Na 2O2 Furnace Blaine) 1297 375 415 427 1300 2180 485 529 582 2025 2549 586 639 708 2375

Table B26. % Fe 3O4 content of pellets heated with Metallurgical furnace and heated with microwave oven in the presence of Na 2O2

Particle Size Metallurgical 2 (cm /g 1 % Na 2O2 2 % Na 2O2 3 % Na 2O2 Furnace Blaine) 1297 7.58 6.48 5.65 1.95 2180 6.85 6.55 5.47 1.8 2549 5.8 5.6 4.19 1.7