Mineral Processing

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1 | Page Synopsis This report details an investigation made into the Ilmenite Smelting Process. The aim of this practical was the preparation and operation the 60 kW DC plasma-Arc Furnace and to obtain better understanding of the chemistry and thermodynamics of the ilmenite smelting process. This achieved by smelting the ilmenite at 1700°C with anthracite as a reductant in an electric furnace to produce high Titania slag as a major product. In the process, liquid iron and carbon monoxide were produced as by-products. The amount of off-gas and iron evolved is 72.092 g and 104.58 g respectively. The amounts of product formed are dependent on the starting conditions. The intensity of the arc is proportion to the arc length and current.

description

smelter

Transcript of Mineral Processing

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Synopsis

This report details an investigation made into the Ilmenite Smelting Process. The aim

of this practical was the preparation and operation the 60 kW DC plasma-Arc

Furnace and to obtain better understanding of the chemistry and thermodynamics of

the ilmenite smelting process. This achieved by smelting the ilmenite at 1700°C with

anthracite as a reductant in an electric furnace to produce high Titania slag as a

major product. In the process, liquid iron and carbon monoxide were produced as

by-products. The amount of off-gas and iron evolved is 72.092 g and 104.58 g

respectively. The amounts of product formed are dependent on the starting

conditions. The intensity of the arc is proportion to the arc length and current.

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Table of Contents Synopsis .................................................................................................................................................. 1

List of illustrations ................................................................................................................................... 3

Nomenclature ......................................................................................................................................... 4

Glossary ................................................................................................................................................... 5

1. Introduction ................................................................................................................................ 6

1.1. Subject of and motivation for report ...................................................................................... 6

1.2. Background to report .............................................................................................................. 6

1.3. Objectives of report ................................................................................................................ 7

1.4. Limitations and scope of investigation ................................................................................... 7

1.5. Plan of development ............................................................................................................... 7

2. Literature review ......................................................................................................................... 8

2.1. Extractive metallurgy .............................................................................................................. 8

2.1.1 Stages in Metal Extractions ..................................................................................................... 8

2.2. Ilmenite smelting ........................................................................................................................ 9

2.2.1. Solid state reduction ............................................................................................................. 10

2.2.2. Slag processing ...................................................................................................................... 10

2.2.3. Energy constraints ................................................................................................................ 11

2.3. Types of Furnaces ................................................................................................................. 12

2.3.1. DC Arc Furnace ..................................................................................................................... 12

2.3.2. Blast furnaces ....................................................................................................................... 13

3. Experimental ......................................................................................................................... 14

3.1. Apparatus .............................................................................................................................. 14

3.2. The experimental set-up ....................................................................................................... 14

3.3. Experimental procedure ....................................................................................................... 15

4. Results ....................................................................................................................................... 17

5. Discussion .................................................................................................................................. 21

6. Conclusions ............................................................................................................................... 22

7. Recommendations .................................................................................................................... 23

8. References ................................................................................................................................ 24

9. Appendices ................................................................................................................................ 25

9.1. Raw experimental data ......................................................................................................... 25

9.2. Sample calculations............................................................................................................... 27

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List of illustrations

Tables

Table 1 Overall mass balance around the furnace ......................................................... 17

Table 2 Analysis of the feed material Ilmenite used during the smelting practical .......... 17

Table 3 Ultimate analysis of anthracite used in the plasma furnace experiments ........... 17

Table 4 Ash analysis ....................................................................................................... 18

Table 5 Pig Iron formed .................................................................................................. 18

Table 6 Slag formed ....................................................................................................... 18

Table 7 Dust formed ....................................................................................................... 19

Table 8 Effect of arc length and current on the arc characteristics ................................ 20

Table 9 Overall element balance around the furnace ..................................................... 20

Table 10 Raw/Feed materials ......................................................................................... 25

Table 11 Data for analysis of anthracite used in the plasma furnace experiments ......... 25

Table 12 Elemental balance for Ilmenite ......................................................................... 25

Table 13 Elemental balance for Pig Iron product ............................................................ 26

Table 14 Elemental balance for Anthracite ..................................................................... 26

Table 15 Elemental balance for slag product .................................................................. 26

Table 16 Elemental balance for Dust product ................................................................. 27

Figures

Figure 1 Smelting mechanism for ilmenite in a DC arc furnace ........................................ 9

Figure 2 Calculated liquidus diagram of ilmenite smelter slags (Pistorius, 2007) .......... 11

Figure 3 Required carbon input and resulting (%FeO) in ilmenite smelting .................... 11

Figure 4 Typical DC arc Furnace .................................................................................... 12

Figure 5 Typical Blast Furnace ....................................................................................... 13

Figure 6 Schematic diagram of the DC plasma furnace ................................................. 14

Figure 7 Diagram showing major input and outputs of the process ................................ 19

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Nomenclature

List of symbols

List of abbreviations

Abbreviation Description

DC Direct current

SAIMM Southern African Institute of Mining and Metallurgy

C Elementary Carbon

AC Alternating current

LOL Mass gained or lost

Symbol Description Units

H Enthalpy J/mol

G Gibbs free energy J/mol

S Entropy J/mol.K

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Glossary

Ore Is a type of rock that contains minerals with important elements

including minerals.

Metallurgy The science and technology of extracting and refining metals. Pyrometallurgy Involves the extraction of metals through reactions conducted at

high temperatures.

Metamorphic rock Denoting rock that has undergone transformation by heat,

pressure, or other natural agencies.

Igneous rock Formed by the solidification of molten magma.

Arc An electrical conduction through a gas in an applied electric

field.

Furnace An enclosed chamber in which heat is produced to generate

steam, destroy refuse, smelt or refine ores.

Flux In metallurgy, a substance that promotes the fusing of minerals or metals or prevents the formation of oxides

. Mineral A naturally formed chemical element or compound having a

specific chemical composition and, most commonly, a characteristic crystal form.

Reduction A chemical process involving reactions that produce a decrease

in the oxidation state of elements such as iron or sulphur. Slag A glassy waste of the smelting of ores. A mixture of impurities

that separate from reduced metal during smelting. Concentrate The metal-rich product of the beneficiation process that is fed to

the smelter. Beneficiation The processing of ores for the purpose of regulating the size of

a desired product, removing unwanted constituents. Gangue The valueless minerals in an ore; that part of an ore that is

economically desirable but cannot be avoided in mining . Steady state A condition of a physical system or device that does not change

over time.

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1. Introduction

1.1. Subject of and motivation for report

This report details an investigation made into the Ilmenite Smelting Process. It is

believed that practical preparation and operation of the 60 kW Plama-Arc Furnace

will aid students to attain better understanding of the Ilmenite Smelting Process.

1.2. Background to report

On 22 August 2012 a smelting practical was performed at Stellenbosch, Western

Cape, attended by the directors and the students .Smelting is defined as the

chemical reduction of metal-bearing material such as ore, most commonly by a

process involving fusion, so that lighter and more fusible impurities can be readily

removed (Hudson et al, 1999). The process commonly involves addition of reagents

(fluxes) that facilitate chemical reactions and the separation of metals from

impurities. The process exploits heat and a chemically reducing agent to decompose

the ore, driving off all impurities as gasses or slag and retaining the pure elementary

metal behind. The reducing agent is commonly a source of carbon which removes

oxygen from the ore.

Ilmenite is a commonly accessory mineral found in metamorphic and igneous rocks.

During the 1950’s, ilmenite was mined at Umgubaba as feedstock for a sulphate

pigment plant located at Durban in KwaZulu-Natal In the late 1970’s Richard Bay

Minerals was founded on the east coast of South Africa. On the west coast of South

Africa, Namakwa Sands was founded in the early 1990’s to extract heavy metals

from deposits situated near Vredendal. Dong et al (2012) suggested that ilmenite

supplies about 90% of the world’s demand for titanium minerals and its production

reached 5.8 million metric tons in 2010.

Titanium is the ninth most plentiful element in the earth’s crust and the seventh most

plentiful metallic element (Xue et al, 2012). As a structural metal, titanium is the

fourth largest consumption after aluminium, iron and magnesium. Titanium is the

main raw material in the production of titanium slag, synthetic rutile, titanium dioxide

and spongy titanium. Titanium dioxide is an essential kind of white inorganic

pigment which is largely used in coating, paper, plastics, inks, foods, chemical fibre,

welding rod making, ceramics and metallurgical industries due to its brightness, high

refractive index and whiteness (Kotze, 2007).

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1.3. Objectives of report

The objectives of this report are therefore:

To obtain a better understanding of the thermodynamics of the ilmenite smelting

process.

To obtain a better understanding of the chemistry of the ilmenite smelting process.

To obtain a better understanding of mineral/phase characterisation and the

appropriate analytical techniques.

1.4. Limitations and scope of investigation

Although there are other types of furnaces available to be utilised in the smelting

process, the focus of this report is limited to the matters that affect the Ilmenite

smelting process operation using a 60 kW DC Plasma-Arc Furnace.

1.5. Plan of development

This report begins with a brief background of the smelting process before describing

the basics of extractive metallurgy. It then focuses on the fundamentals of the

Ilmenite smelting process and experimental methods. Attention is then paid in the

overall mass balance around the furnace. Conclusions are then drawn on the basis

of these results and finally, recommendations are made, based on these

conclusions.

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2. Literature review

2.1. Extractive metallurgy

Extractive metallurgy is the study of the processes used in the separation and

concentration of raw materials. It deals with extraction and refining of metals. More

than sixty elements are metals which are generally extracted from various forms of

natural occurrence in the earth’s crust (Ray and Ghosh, 1991). Chemical extraction

operations are attained by mixing of the material to be processed with other

chemically active species in a reactor. The reactor may be a furnace, a pressure

vessel or a mixer. Ray and Ghosh (1991) suggested that when ore deposits are

exploited in extractive metallurgy there is generally some waste product. This

product is composed of some minerals in the ore which are not valuable from point

of view of metal extraction and are denoted as gangue minerals.

2.1.1. Stages in Metal Extractions

Rarely can the desired extraction be achieved efficiently in one stage. Metal extract

ions, whether pyrometallurgical or hydrometallurgical in nature, require a series of

processing stages before a high recovery of metal at the required degree of purity

can be attained. The different stages of chemical processing can be group into four

categories as follows:

Preparation or pre-treatment stages.

Extraction stages.

Refining stages.

Metal-recovery stages.

Pyrometallurgy deals with chemical reactions at high temperatures. These reactions

are carried out involves numerous deferent solids, liquids, and gases, and are

carried out using many diverse types of furnaces (Erasmus, 2012).The metals are

extracted by converting sulphides into oxides and then reducing the oxides into

metals, using carbon or carbon monoxide.

Advantages of pyrometallurgical methods (Ray and Ghosh, 1991)

There is a greater ease of physical separation of the product metal from gangue

when the products can be melted or vaporised at high temperatures.

Pyrometallurgical methods of metal production are generally cheaper and

appropriate for large scale production.

Reaction rates are greatly accelerated at high temperatures hence small units

can attain high production rates.

Reactions which are not thermodynamically possible at low temperature become

possible at high temperature.

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The heat of reaction (H) determines the energy costs of the process (Zietsman,

2004). If the reaction is exothermic, then heat is given off by the reaction, and the

process will be partially self-heating. Contrary, if the reaction is endothermic, the

reaction absorbs heat, which will have to be supplied to the process. Most of the

reactions utilised in Pyrometallurgy are reversible but ilmenite smelting is

characterised by departure from equilibrium in several ways. The Gibbs free energy

(G) of a reaction is a measure of thermodynamic driving force that makes a

reaction to occur (Zietsman, 2004). The entropy change (S) is a measure of the

change in the possibilities for disorder in the products compared to the reactants.

2.2. Ilmenite smelting

Ilmenite has the nominal composition FeO.TiO2.South African beach-sand ilmenite

are close to this nominal composition (Pistorous, 2007).During the smelting process,

ilmenite is continuously fed with anthracite in a firmly controlled ratio through hollow

electrode into the operating furnace (Kotze, 2007). The primary product is titanium

oxide slag which contains approximately 85% of TiO2. In addition, the slag contains

approximately 10% FeO and impurities. The main impurities are MnO, MgO, SiO2,

and Al2O3 which add up to 3% of the mass of the ilmenite. During the ilmenite

smelting process, the iron content of the oxide is lowered by reduction to metallic

iron which takes place in the liquid phase at high temperatures (approximately 1650

to 1750°C). Kotze (2007) reported that both smelting and reduction processes are

conducted within a crucible of a solidified, high titanium content slag, conducted

within the furnace refractory walls. The slag has a lower density than the iron hence

separation of the two products occurs within the furnace.

Figure 1 Smelting mechanism for ilmenite in a DC arc furnace

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2.2.1. Solid state reduction

When the electric furnace operates, the electric arc generates at the bottom of the

electrode (Xue, et al, 2012). The temperature of the materials then rises due to the

heat from electric arc and electrode. When the temperature is high enough, ilmenite

reacts with carbon (reductant) and the main reactions are the following:

Reduction of FeO from the slag:

[1]

Partial reduction of TiO2 in the slag:

[2]

The main reaction in the furnace can be summarised as:

( ) ( ) ( ) [3]

Thermodynamically, the major gas product is CO when the system temperature is

lower or higher than the boudouard temperature. The CO gas produced by the

furnace passes through the gas-cleaning plants, where the gas is cooled, scrubbed,

and washed, to remove entrained dust from the furnace (Gous, 2006). The gas can

then be directed to the gas-holder for use in pre-heating of ilmenite and the drying of

anthracite. Gous (2006) further suggested that a portion of the ilmenite feed can be

pre-heated in the pre-heaters, thus lowering the specific energy requirement of the

process.

2.2.2. Slag processing

Xue et al (2012) reported that particles begin to melt when the temperature rises up

to the melting point of the titanium slag, metallic iron or the unreacted ilmenite. The

slag is made up of unreacted ilmenite, titanium oxides and other impurity oxides.

When the melting process has completed, the reduction of iron oxides from

unreduced ilmenite depends on the reaction with solid carbon reductant particle that

is suspended in the melt and CO bubble in the melt. Since the slag is less dense

than iron, the slag floats on iron inside the furnace.

Dong et al (2012) suggested that when the reduction process is complete, the

electrodes are typically lifted for rising system temperature in order to improve fluidity

and the separation of slag-iron. Slag and iron are then cooled naturally after being

discharged from the furnace.

The solidified slag is a largely single-phase (pseudobrookite-M3O5-phase), with only

small proportions of other phases, mainly rutile and silicates (Pistorous 2007).The

reactions are carried out at high temperatures since the melting point of the high-

titania slag is around 1650°C.

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Figure 2 Calculated liquidus diagram of ilmenite smelter slags (Pistorius, 2007)

Pistorous (2007) suggested that Figure illustrates that both FeO and TiO1.5 serve to

flux TiO2, thus lowering the liquidus temperature of the slag.

2.2.3. Energy constraints

Pistorous (2007) suggested that figure has an important implications for the way in

which inputs need to be changed relative to the existing set of points, if stable

operation is to be maintained.

Figure 3 Required carbon input and resulting (%FeO) in ilmenite smelting

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It is approximated that 5.3 kWh increased in electrical energy input, the carbon input

needs to be increased by 1 kg. The published enthalpy correlations show that

heating 1 ton of pure ilmenite and 100 kg of carbon to 1600 °C requires some 640

kWh per ton of ilmenite (Pistorius, 2007).

2.3. Types of Furnaces

2.3.1. DC Arc Furnace

The conventional alternating current arc furnace operates by means of electric

current flowing in three-phase operation from one electrode of three to another

through the scrap charge (CMP, 2005).Commonly used DC furnaces are single-

electrode units where the current flows down the carbon electrode, which serves as

a cathode, to an anode at the bottom of the furnace.

Figure 4 Typical DC arc Furnace

The furnace vessel shown in Figure 2 is used to contain the metallurgical process of

ilmenite smelting. Zietsman (2004) suggested that the furnace is divided into four

parts:

Hearth

The hearth of a DC furnace has two holes. The first is to act as the floor of the

furnace, containing metal bath present directly above. The second is to provide the

anode connection of the DC electrical circuit. Zietsman (2004) further suggested

that the hearth bricks are normally chosen to have high thermal conductivity, similar

to the side walls. Then air or water cooling is used to extract heat from the outer

surface of the hearth and cool it down.

Sidewalls

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The sidewalls of an ilmenite-smelting furnace must extract heat from the slag bath at

a high adequate rate to establish and maintain a freeze lining of the solidified slag on

the wall.

Roof

The roof of the furnace acts as a lid, closing the furnace so that no gas, fames or

dust escapes other than through the off-gas duct.

Tap holes

The tap holes are installed into the furnace sidewalls. They assemblies usually

include water cooling intended at preventing overheating and excessive wear of

refractory lining in the region of tap holes.

2.3.2. Blast furnaces

The function of a blast furnace is to produce pig iron. It is a furnace in which a blast

of preheated air is blown in through tuyeres at the bottom. The furnace is charged

with iron, pellets and coke. The resulting molten is tapped in the bottom of the

furnace so that it can flow.

Jones (2011) suggested that DC transferred-arc plasma technology is widely

preferred for metallurgical processing for the following reasons:

The electrical supply characteristics and geometry arrangement of the transferred-

arc are similar to those of conventional submerge arc-furnaces.

Scale-up to industrial operation, when a graphite electrode used.

Ability to sustain longer, more stable arcs than AC operation, with independent

current and voltage control

Figure 5 Typical Blast Furnace

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3. Experimental

3.1. Apparatus

60 kW DC Plasma-ARC Furnace

Ilmenite (TiO2Fe2O3)

Anthracite

Optical Pyrometer

Iron cubes

Weighing scale

Alumina bubble

Fiber-Frax (ceramic blanket insulator)

Sample containers

Hammer and chisel/diamond saw

3.2. The experimental set-up

Figure 6 Schematic diagram of the DC plasma furnace

The numbers in Figure 4 corresponds to the following:

1. Cathode Terminal

2. Cooling Water Channel

3. Feed Port

4. Graphite Electrode

5. Refractory Material

6. Graphite Crucible

7. Anode Terminal

8. Off gas Outlet

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3.3. Experimental procedure

Feed preparation

A mixture of ilmenite and anthracite was prepared for each furnace run. The

reductant (anthracite) was added in a ratio of 127 kg per ton of ilmenite to ensure a

carbon excess for maximum reduction. The total mass of ilmenite added was 241.60

g and the total mass of anthracite was 30.52 g.

Before commencing

The required amounts of anthracite and ilmenite were determined and mixed

together in a container. The alumina “fibrefrax” thermal insulation lining was

prepared for inside of the furnace to protect inner walls and to act as insulation. The

power supply was then turned off at the mains and the cooling water bypass valve

was opened (handle turned parallel to the pipe). The argon gas inlet pipes from sight

ports were removed on the roof of the furnace and the electrode was turned up so

that the tip of the electrode was above the bottom plane of the roof. The off gas

system was then removed from the main furnace body and cleared away from the

furnace. The stand was placed close to the furnace.

Operating procedure

The roof of the furnace was then removed and placed on the stand. It was checked

that the roof was not resting on any water pipes or electric cables before the alumina

insulation fiber was inserted into the furnace. It was ensured that there were no gabs

where the two ends off the fiber meet. Compressed air was then used to clean the

inside of the furnace, ensuring that there were no particles in the notch in the bottom

cathode. The bottom of the crucible was inserted into the notch of the bottom

cathode and checked to see that the crucible was securely in place.

A small amount of the ilmenite and anthracite was then placed into the bottom of the

crucible and positioned in the centre of the crucible to act as a starter to strike an

arc. The sight ports were removed from the furnace roof by removing the screws.

The roof was then placed back on the furnace and ensured that it was secured. The

off gas pipe was then aligned with off gas port on the roof of the furnace. The argon

gas supply was connected to the sight ports and turned on to begin flushing of the

furnace with argon gas. The cooling water bypass valve was then closed to allow the

water to the furnace and all the valves were switched to open positions (parallel to

the pipe). The extractor fan was turned on and it was ensured that the off gas outlet

was free of blockages and that the end of the pipe was securely fixed in the

excavator suction.

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Smelting

The feeding funnel was inserted in one of the open sight ports and the discharge end

of the vibrating feeder was then placed directly above it. It was insured that the end

of the funnel was able to discharge into the centre of the crucible. Before switching

on the power sources at the mains, it was ensured that the main power supply is off,

by turning the power knob to the left. The main power supply source was turned on

at the mains by flicking both switches upward and initial voltage 20V selected at a

height of 1950 mm. The main power supply was then turned on by turning the power

knob clockwise.

The electrode was then turned down the furnace until it was about 5 cm above the

bottom of the crucible. The electrode was carefully lowered further until the ark was

struck. Once the ark was struck, the crucible was allowed to heat up for two minutes

before feeding was started. After feeding was completed, the voltage and the

electrode position were set to 17V and 1980 mm respectively and left to allow mixing

to take place.

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Component Mass Moles

g mol Mass %

H2O 0.748 0.042 2.450

Ash 4.157 13.620

S 0.198 0.006 0.650

C 22.524 1.875 73.800

H 0.922 0.457 3.020

N 0.555 0.020 1.820

O 1.416 0.044 4.640

Total 30.520 2.444 100.000

Composition

Component Mass Moles Composition

g mol Mass %

Al2O3 0.918 0.009 0.380

CaO 0.145 0.003 0.060

Cr2O3 0.121 0.001 0.050

Fe2O3 118.697 0.743 49.130

K2O 0.169 0.002 0.070

MgO 1.208 0.030 0.500

MnO 2.609 0.037 1.080

Na2O 0.459 0.007 0.190

P2O5 0.072 0.001 0.030

SiO2 1.860 0.031 0.770

TiO2 105.530 1.321 43.680

LOL -7.538 -3.120

Total 224.251 2.184 92.820

Material Mass Fraction Material Mass Fraction

g Mass g Mass

Ilmenite 241.598 0.746 Slag 140.600 0.434

Antracite 30.520 0.094 Iron phase 45.300 0.140

Iron cubes 51.865 0.160 Dust 46.100 0.142

Unreacted material 17.800 0.055

Off gas 72.092 0.229

Total 323.984 1.000 321.892 1.000

IN OUT

4. Results

Table 1 Overall mass balance around the furnace

Table 2 Analysis of the feed material Ilmenite used during the smelting practical

Table 3 Ultimate analysis of anthracite used in the plasma furnace experiments

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Component Mass Moles

g Mol Mass %

Fe 45.02 0.81 99.37

C 0.28 0.02 0.63

Total 45.30 0.83 100.00

Composition

Component Mass Moles

g Mol Mass %

Al2O3 1.195 0.012 0.850

CaO 0.127 0.002 0.090

Cr2O3 0.197 0.001 0.140

Fe2O3 72.156 0.452 51.320

K2O 0.070 0.001 0.050

MgO 0.745 0.018 0.530

MnO 1.786 0.025 1.270

Na2O 0.056 0.001 0.040

P2O5 0.028 0.000 0.020

SiO2 2.348 0.039 1.670

TiO2 67.488 0.845 48.000

LOL -6.186 -4.400

Total 140.01 1.40 99.58

Composition

Component Mass Moles

g mol Mass %

SiO2 2.282 0.038 54.900

Al2O3 1.168 0.011 28.100

Fe2O3 0.326 0.002 7.850

P2O5 0.012 0.000 0.300

TiO2 0.083 0.001 2.000

CaO 0.049 0.001 1.190

MgO 0.041 0.001 0.990

K2O 0.096 0.001 2.310

Na2O 0.057 0.001 1.380

SO3 0.010 0.000 0.240

Total 4.126 0.057 99.260

Composition

Table 4 Ash analysis

Table 5 Pig Iron formed

Table 6 Slag formed

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Component Mass Moles

g Mol Mass %

Al2O3 0.535 0.005 1.160

CaO 0.134 0.002 0.290

Cr2O3 1.028 0.007 2.230

Fe2O3 12.991 0.081 28.180

K2O 0.023 0.000 0.050

MgO 0.373 0.009 0.810

MnO 0.221 0.003 0.480

Na2O 0.009 0.000 0.020

P2O5 0.009 0.000 0.020

SiO2 23.018 0.383 49.930

TiO2 7.454 0.093 16.170

LOL 2.125 4.610

Total 47.921 0.585 103.950

Composition

Titania rich slag

Ilmenite

Pig Iron

Dust

Antracite

Off gas

Iron tubes

Unreacted material

Furnace

Table 7 Dust formed

A mass balance for the furnace

General mass balance

At steady state there is no accumulation. The simplified mass balance becomes:

Figure 7 Diagram showing major input and outputs of the process

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Difference

Element Mass Moles Mass Moles

g mol g mol g

Al 1.104 0.041 0.915 0.034 0.189

Ca 0.139 0.003 0.186 0.005 -0.047

O 84.063 5.254 71.357 4.460 12.706

Cr 0.083 0.002 0.838 0.016 -0.755

Fe 135.120 2.419 104.579 1.872 30.541

K 0.220 0.006 0.077 0.002 0.143

Mg 0.753 0.031 0.675 0.028 0.079

Mn 2.021 0.037 1.554 0.028 0.467

Na 0.383 0.017 0.049 0.002 0.335

P 0.037 0.001 0.016 0.001 0.021

Si 1.937 0.069 11.860 0.422 -9.923

Ti 63.421 0.032 45.003 0.938 18.418

H 0.545 0.540 0.000 0.000 0.545

S 0.202 0.006 0.000 0.000 0.202

C 22.524 1.875 0.283 0.024 22.241

N 0.278 0.020 0.000 0.000 0.278

Total 312.831 10.353 237.394 7.832 75.437

IN OUT

Arc length Voltage Current Resistance

mm V A W

1950.00 20.00 2.00 10.00

1980.00 17.00 1.70 10.00

1990.00 19.00 1.90 10.00

Table 8 Effect of arc length and current on the arc characteristics

Table 9 Overall element balance around the furnace

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5. Discussion

Table 1 shows the results of the overall mass balance around the furnace. The total

mass fed and leaving the furnace is 323.98 g and 321.89 g respectively. The

resulting error is 0.64 %. The amount of off-gas formed is 72.09 g. Table 2 shows the

analysis of ilmenite used during the smelting process. The mass loss at 1000 °C is

7.54 g. This weight loss includes the total volatiles content at the rock (including the

water combined to the lattice of silica minerals) and gain on ignition related to the

oxidation of the rock (mostly due to Fe). The resulted error and weight loss might

have been due to the fact that the composition of Fe2O3 and TiO2 in the ilmenite

analysis fell outside the calibration range. Thus the values were extrapolated by

software and currently there are not adequate standards to correct this extra

extrapolation.

The other sources of error might be the assumptions made in the calculations. The

off-gas was assumed to be complete carbon monoxide (CO) from the reduction

reactions whereas the gas might contain other compounds like hydrogen from

volatiles in the reductant, carbon dioxide, moisture, nitrogen and sulphur dioxide. It

further assumed that the conversion of the moisture in the ash to hydrogen and

carbon monoxide was 100 %.

Table 3 shows the ultimate analysis of the anthracite. The mass of carbon

(reductant) is 22.52 g at purity 73.8 %. In table 5 it is observed that the mass of

metallic iron formed is 45.05 g at purity of 99.37 %. The mass of the TiO2 formed in

the Titania rich slag is 67.49 g at purity of 48 %. The corresponding mass loss is

6.19 g. the mass of TiO2 formed in the dust stream is 7.45 g at purity of 16.17 %.

The corresponding mass gained is 2.12 g.

Table 8 shows the effect of arc length and current on the arc characteristics. It is

observed that as the arc length is increased, the intensity of the arc decreased and

suddenly the arc will disappear. The separation of the anode and cathode becomes

longer. Raising the electrode made the furnace unstable and switched off the arc.

When the arc was started again a sparking sound was heard during the start up. The

electrode had a bright orange colour when the furnace was switched off. As the arch

length is increased the current increases and the resistance stays the same. Thus

more energy is generated and the arc intensity increases.

The operating temperature is approximately 1700 °C and this value was obtained

from literature.

22 | P a g e

6. Conclusions

Based on the forgoing information, the following conclusions have been made:

The amounts of product formed during the ilmenite smelting process are dependent

on the initial conditions namely the mass of ilmenite, anthracite and the iron cubes.

The arc intensity is directly proportional to the arc length.

The current affects the amount of energy evolved hence the intensity of the arc

formed.

The operating temperature of the furnace lies somewhere between 1600-1700 °C.

23 | P a g e

7. Recommendations

On the basis of the above conclusions, the following recommendations are made:

Find alternative software that will accurately predict the compositions of the

compounds reduce chances of weight loss.

The experiment should be repeated several times for error analysis.

Find an alternative device to measure the temperature during the smelting

process.

24 | P a g e

8. References

1. Pistorius, P.C., 2007, Ilmenite smelting: the basics, SAIMM, 75-84.

2. Kotze, H., 2007, Investigation into the effects of cooling conditions on the particle

size distribution titania slag, Metallurgical Engineering, 1-15.

3. Sun, H., Wang, T., Dong, X. and Xue, Q., 2012, A literature review of titanium

slag metallurgical processes, Metallurgical Engineering, 39-75.

4. Gous, M., 2006, An overview of the Nomakwa Sands Ilmenite Smelting

Operation, SAIMM, 1-14.

5. Pistorius, P.C., 2008, Ilmenite smelting: the basics, SAIMM, 108,

6. Kotze, H., Bessinger, D. and Beukes, J., 2006, Ilmenite Smelting at Ticor SA,

SAIMM, 1-12.

7. Coetzee, C., Lamont, P.H., Bessinger, D., Rabe, J., Zietsman, J. and Muller, J.,

2006, Application of UCAR Chill Kote to ilmenite smelting, Kumba resources, 1-

12.

8. Pistorous, P.C. and Zietsman, J.H., 2005, modelling an ilmenite-smelting DC arc

furnace process, Minerals Engineering, 1-18.

9. Hudson, T.L., Fox, F.D. and Plumlee, G.S., 1999, Metal Mining and the

Environment, AGI Environmental Awareness Series, 3, 60-68.

10. Ray, F. and Ghosh, A., 1991, Principles of Extractive Metallurgy, New Age

International, 50-100.

11. Zietsman, J.H., 2004, Interactions between freezing lining and slag bath in

Ilmenite Smelting, Metallurgical Engineering, 1-80.

12. Erasmus, M., 2012, Leaching of Nickel laterite with a solution of Ammonia and

Ammonium Carbonate utilising solids liquid separations under pressure,

Metallurgical Engineering, 21-22.

13. CMP, 2005, DC arc furnace, Melting Performance Analysis, 3, 1-2.

14. UCT, 2012, Mineral Processing Practical Manual, 33-41.

15. Jordan, P., 2011, Evaluation of reductants used for ilmenite smelting based on

CO2 reactivity (Boudouard reaction) measurement, SAIMM, 111, 1-8.

16. Jones, R.T., 2011, Plasma development in Africa, 1-2.

25 | P a g e

Proximate analysis % Ultimate analysis %

Moisture 2.45 Moisture 2.45

Ash 13.62 Ash 13.62

Volatile Combustible Matter 8.46 Sulphur 0.65

Fixed Carbon 74.47 Carbon 73.8

Hydrogen 3.02

Nitrogen 1.82

Oxygen 4.64

Total 99 100

Element Mass Moles Molar mass

g mol g/mol

Al 0.4859 0.0180 26.9800

Ca 0.1036 0.0026 40.0800

O 80.7197 5.0450 16.0000

Cr 0.0827 0.0016 52.0000

Fe 83.0262 1.4866 55.8500

K 0.1404 0.0036 39.1000

Mg 0.7286 0.0300 24.3100

Mn 2.0208 0.0368 54.9400

Na 0.3405 0.0148 22.9900

P 0.0316 0.0010 30.9700

Si 0.8698 0.0310 28.0900

Ti 63.3713 1.3213 47.9600

Total 231.9212 7.9922

Material Mass Fraction

g Mass

Ilmenite 241.598 0.746

Antracite 30.520 0.094

Iron cubes 51.865 0.160

Total 323.984 1.000

9. Appendices

9.1. Raw experimental data

Table 10 Raw/Feed materials

Table 11 Data for analysis of anthracite used in the plasma furnace experiments

Table 12 Elemental balance for Ilmenite

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Element Mass Moles Molar mass

g mol

H 0.5446 0.5402 1.0080

O 3.3436 0.2090 16.0000

S 0.2023 0.0063 32.0600

C 22.5245 1.8753 12.0110

N 0.2778 0.0198 14.0100

Si 1.0670 0.0380 28.0900

Al 0.6182 0.0229 26.9800

Fe 0.2283 0.0041 55.8500

P 0.0054 0.0002 30.9700

Ti 0.0499 0.0010 47.9600

Ca 0.0354 0.0009 40.0800

Mg 0.0248 0.0010 24.3100

K 0.0797 0.0020 39.1000

Na 0.0426 0.0019 22.9900

Total 29.0440 2.7227

Element Mass Moles Molar mass

g mol g/mol

Al 0.6325 0.0234 26.9800

Ca 0.0904 0.0023 40.0800

O 51.3817 3.2114 16.0000

Cr 0.1347 0.0026 52.0000

Fe 50.4716 0.9037 55.8500

K 0.0584 0.0015 39.1000

Mg 0.4495 0.0185 24.3100

Mn 1.3829 0.0252 54.9400

Na 0.0417 0.0018 22.9900

P 0.0123 0.0004 30.9700

Si 1.0978 0.0391 28.0900

Ti 40.5269 0.8450 47.9600

Total 146.2804 5.0748

Table 13 Elemental balance for Pig Iron product

Table 14 Elemental balance for Anthracite

Table 15 Elemental balance for slag product

27 | P a g e

Element Mass Moles Molar mass

g mol g/mol

Al 0.2830 0.0105 26.980

Ca 0.0956 0.0024 40.080

O 19.9756 1.2485 16.000

Cr 0.7034 0.0135 52.000

Fe 9.0869 0.1627 55.850

K 0.0191 0.0005 39.100

Mg 0.2252 0.0093 24.310

Mn 0.1714 0.0031 54.940

Na 0.0068 0.0003 22.990

P 0.0040 0.0001 30.970

Si 10.7618 0.3831 28.090

Ti 4.4764 0.0933 47.960

Total 45.8093 1.9273

Table 16 Elemental balance for Dust product

9.2. Sample calculations

Determining the amount of off gas

( )

Feout = 104.579 g

( )

(

)

Thus

and MCO =28.0 g/mol

Thus

( )

TiO2, in = 105.530 g and Molar mass of TiO2 = 79.866 g

Assume 100 % conversion, thus NCO,formed = 0.5×1.3213 = 0.6607 moles

Thus mass of Co formed = 0.6607 × 28 = 18.4987 g

( )

Assume 100 % conversion of H2O

Mass of H2O, in =0.7480 g, thus no of moles = 0.04155 mol

Thus no of moles of CO formed = 0.04155 mol

Thus mass of CO formed = 0.04155 × 28 = 1.1635 g

28 | P a g e

Hence total mass of CO formed = 52.4299 + 18.4987 + 1.1635 = 72.0921 g

2.