Studying the Pelletization of Rosseta Ilmenite Concentrate With Coke Breeze Using Molasses and Reduction Kinetics of Produced Pellets At 800-1150

Ilmenite ore fine and coke breeze as reduced material which were pelletized with different amounts of molasses were studied in this investigation. The produced pellets at optimum condition were reduced in nitrogen atmosphere at temperature range 80


Introduction
The reduction of iron titanium concentrate with anthracite as reducing agent was investigated at temperature 1000-1300 o C. The results indicated that the degree of reduction of FeO to Fe and TiO 2 to Ti 2 O 3 increased with time and temperature, also the reduction rate is directly proportional to time at 1000 o C, while at higher temperature the reduction becomes diffusion controlled [1].
Some investigators [2] studied the reduction of synthetic ilmenite with graphite.It was found that the reaction has been observed to initiate near 860 o C at the contact points between the reactants, while up to 1020 o C solid state reduction appears to be the main reaction mechanism.Above this temperature(1020 o C), it was observed a rate of reaction increased due to the change of mechanism to gaseous reduction of ilmenite by regenerated CO.
The reduction kinetics of mixtures of synthetic ilmenite and graphite powder in the temperature range 980 o C-1100 o C in N 2 and CO 2 atmospheres was studied and the results observed that the initial rate of reduction was explained in term of solid-solid reaction between graphite and ilmenite, while in the latter stage of the reduction is gas solid reaction [3] When the prepared pellets from mixtures of synthetic ilmenite and graphite were heated in argon at 1000 to 1100 o C, it was found that no measurable reaction was obtained at 1000 °C but the rate was high at 1100 °C.It was showed that an inflection in the reduction curve at about 2 pct weight loss at 1050 and 1100 o C was due to the difficulty in nucleating iron [4].
The carbothermic reduction of Panzhihua ilmenite (FeTiO 3 ) were studied extensively at temperature ranges from 900 o C to 1400 o C [5].The results indicated that the reduction degree of ilmenite increases with increasing temperature and the reaction initiates at 860 o C.
Ilmenite concentrate with graphite were reduced under argon gas at temperature between 1250 °C and 1350 °C.The results indicated that the reduction of Fe 3+ to Fe 2+ , Fe 2+ to Fe and Ti 4+ to Ti 3+ took place within 50% reduction during which a secondary oxide phase was formed and replaced the natural ilmenite.Also, the reduction of Ti 3+ to Ti 2+ took place after 50% reduction, which altered the composition of the secondary oxide phase by decreasing its oxygen content.Reduction of Ti 2+ took place while the oxygen deficient TiO (1−x) phase formed.Formation of any titanium carbide or oxycarbide phases depended on the completion of the reduction which was not possible at the specified temperatures [6] The results of experimental data on reduction of ilmenite with char coal in a rotary reactor showed that the rate controlling steps are solid-solid reaction during initial stages and diffusion of carbon monoxide through product layer during later stages of reaction.The activation energies for the two heterogeneous reactions are estimated to be 25 and 35 kcal/ mol for solid-solid and gas-solid reactions, respectively [7].
Some authors [8] indicated that the carbothermic reduction of ilmenite up to 1200 °C proceed through the formation of a series of oxides (Ti n O 2n−1 ) and iron metal.Also, the results showed that the metallization percentage reached up to 99% for a period of 6 h at 1200 °C using particle size a 200 mesh (−74 μm).
The reduction of Bama ilmenite concentrate by graphite under argon gas ambient from 850 to 1400 °C were studied [9].The results showed that the reduction degree of Bama ilmenite is enhanced with increasing temperature and the molar ratio of carbon to oxygen, and that the reaction rate varies with temperature and reduction time simultaneously.The high content of impurities in Bama ilmenite evidently bates the reduction of ilmenite.Forming the enrichment zone of manganese prevents complete reduction of Fe 2+ .The reduction products are mostly reduced iron, rutile, reduced rutiles, Ti 3 O 5 and pseudobrookite solid solution.The reduction kinetics shows that the reduction temperature is a key factor to control reaction rate.
The reduction of briquettes prepared mixtures of Rossetta ilmenite and coke breeze in nitrogen atmosphere at 800 -1200 ºC were studied [10].The results indicated that the reduction degree of the ilmenite increased with the increase stoichiometric ratio of carbon which required converting all FeO & Fe 2 O 3 to Fe and TiO 2 convert to Ti 3 O 5 .The reduction degree of the briquettes increased with temperature rise.The sample reduced at 1200 ºC illustrated that the product contain α Fe and Ti 3 O 5 , rutile (TiO 2 ) and pseudobrokite.At 800 ºC the products formed were ilmenite, rutile, anatase and traces of hematite.
The carbothermal reduction of ilmenite concentrate and graphite pellets was studied in hydrogen, argon, and helium [11].Reduction was studied in isothermal and temperatureprogrammed reduction experiments in a tube reactor with continuously flowing gas.CO, CO 2 , and CH 4 contents in the off-gas were measured online using infrared sensors.The main phases in the ilmenite concentrate were ilmenite and pseudorutile.The reaction started with the reduction of pseudorutile to ilmenite and titania , followed by the reduction of ilmenite to metallic iron and titania.Titania was reduced to Ti 3 O 5 and even more to Ti 2 O 3 , which was converted to titanium oxycarbide.Reduction was faster in hydrogen than in helium and argon, which was attributed to involvement of hydrogen in the reduction reactions.The formation of titanium oxycarbide in hydrogen started at 1000 °C and was completed in 300 minutes at 1200 °C, and 30 minutes at 1500 °C.The formation of titanium oxycarbide in argon and helium started at 1200 °C and was not completed after 300 minutes at 1300 °C.
This work aimed to study the reduction kinetic of Rosseta beach ilmenite concentrate in the form of pellets with coke breeze in nitrogen atmosphere.

Materials and Experiments 2.1. Materials 2.1.1. Ore Characterization
A representative sample of Rosetta beach ilmenite concentrate was provided by the black sands project of Nuclear Material Authority (NMA) used for all experiments during this work.The Rosetta ilmenite concentrate ore contains about 43.6% TiO 2 , 27.5% FeO and 20.9 %Fe 2 O 3 .The size of Rosetta ilmenite ore used in this investigation was less than 0.075 mm.
X-ray analysis of Rosetta ore concentrate (Fig. 1) indicated that the components of Rosetta ilmenite concentrate are ilmenite FeTiO 3 , pseudorutile Fe 2 Ti 3 O 9 , hematite Fe 2 O 3 and small quantity of rutile.

Coke Breeze
The chemical composition of used coke breeze used contain 90.6 % fixed carbon, 1.16% volatile matter, 8.24% ash and 0.75 humidity.The coke breeze fines used in this work have size less than 0.075 mm.

Experimental Procedures 2.2.1. Preparation of Sample
Preparation of samples for the briquette process was carried out by mixing of ilmenite ore concentrate with 1.5 stoichiometric ratio of carbon [10] to convert all FeO & Fe 2 O 3 to Fe and TiO 2 convert to Ti 3 O 5 according to the following reactions:

Production of the Pellets
The pellets were prepared in a disc pelletizer of diameter 400 mm, collar height 100 mm, angle of inclination 52 o , disc rotating speed 17 rpm and residence time 10-30 min.The 200 g of mixture of ilmenite with 1.5 stoichiometric coke breeze as shown in equation 4 were fed to the pelletizer.
The stoichiometric amount of coke breeze = X(100)/Y (4) Where X -stoichiometric amount of carbon, Y -Percentage of carbon in coke.) The predetermined amount of water (9%) with molasses (3-10%), were then sprayed onto the rolling bed of material in the disc pelletizer.At the end of the tests, a pellet sample was collected and screened to collect the (7-10 mm diameter) fraction which was taken as a measure of the productivity of the pellet as shown in equation number 5 P p =W 1 /W 2 * 100 (5) Where: P p is the productivity of the pellets (7 -10 mm size), %.W 1 is the weight of the pellets (7 -10 mm size), g W 2 is the weight of the charge fed to disc pelletizer, g The produced green pellets were dried in air for three days, to ensure the evaporation of water used during the pelletization process.The average compressive strength of pellets is measured by compressing at least 10 pellet samples (7-10 mm diameter) between parallel steel plates until they break.The mean value for the tested pellets gives their compressive strength.The dried granules were then subjected to use in sinter mix.

Reduction Procedures
The reduction of produced pellets was done on thermo gravimetric apparatus in nitrogen atmosphere (A schematic diagram of thermo gravimetric apparatus is shown in Fig. 2. It consisted of a vertical furnace, electronic balance for monitoring the weight change of reacting sample and temperature controller.The sample was placed in an Alumina crucible which was suspended under the electronic balance by Ni-Cr wire.The furnace temperature was raised to the required temperature and maintained constant to ± 5 ºC.Then samples were placed in hot zone.The weight of the sample was continuously recorded at the end of the run; the samples were withdrawn from the furnace and kept in the desiccators.

Fig. 2. Schematic diagram of the apparatus
The percentage of reduction was calculated according to the following equation number 6.
Percent of reduction =[ (W o -W t ) (100)(16)/28]/ Oxyge (mass) (6) Where W o the initial mass of sample after removal of moisture.W t mass of sample after each time, t.Oxygen (mass) indicates the mass of oxygen percent in ilmenite ore concentrate in form FeO & Fe 2 O 3 and oxygen loss due to convert TiO 2 to Ti 3 O 5 .

Results and Discussions 3.1. Effect of Molasses Addition on the Properties of Green and Dried Pellets
The effect of using different amount of molasses (2-10 % molasses), with constant amount of water (9 %), on the properties of produced green and dried pellets were studied where the following conditions were kept constant (residence time in the disc pelletizer 10 min, disc rotating speed 17 rpm, inclination angle of disc pelletizer 50°).Figs 3-7 indicated that as the amount of molasses increases up to 8% the productivity of the produced pellets increases.This is due to the viscosity of liquid sprayed on the pellets increased with increasing the amount of molasses.The increase of molasses from 8 to 10% the productivity of the pellets decreased, this may be due to the sticky of pellets together and formation of large pellets having size more than 10 mm.Also it is clear that increasing the percentage of molasses increases the drop damage resistance and compressive strength of the green and dried pellets as shown in Figs 4-7.This may be attributed to the fact that increasing molasses addition leads to an increase in the contact points between the particles of the ilmenite and coke breeze and a decrease in the distance between them [16].

Effect of Time of Pelletization on the Properties of Green and Dried Pellets
The effect of time of pelletization (5-25 min.), on the properties of produced green and dried pellets, were studied where the following conditions were kept constant (the amount of molasses=8% with 9% water, disc rotating speed 17 rpm, inclination angle of disc pelletizer 50°).Results illustrated in Figs.8-12, Fig. 8 indicated that as the residence time of pelletization increase to 20 min the productivity of the produced pellets increases to maximum value.The decrease in productivity at time more than 20 min may be due to the flushing away of some water during their growth.[12,17].Figs.11 and 12 shows the effect of time of pelletization on the drop damage resistance and crushing strength of the dried pellets, from which it is clear that the damage resistance approximately constant and = 100 as the time of pelletization increased, while the compressive resistance of dried pellets increased as the time of pelletization increased.

Effect of Temperature on the Reduction Degree
Experiments were performed in the temperatures ranges of 800 to 1150 ºC.Plots of the reduction percentage of ilmenite by coke breeze as a function of time are shown in Fig. 13.It is clear that the reduction rates increased with increasing temperature.At high reduction temperatures (more than 1000 ºC), with increasing temperature, the oxygen removal increased.Also, it is clear that the reduction rates was faster in the first period and then decreased at the end of period.

Kinetics of Reduction of Ilmenite Ore
Applied model of solid-solid reaction as shown in equation number 4 [19], on the reduction of ilmenite ore concentrate.
[1-(1-R) 0.333 ] 2 = kt (7) Where R is fractional reduction t-is time mint and k is rate constant.The results showed that this model gave straight line for all temperature as shown in Fig. 14.The slope of these straight lines gave the constant rate for each reduction temperature.
The logarithms (ln) of these constants were used to calculate the activation energies (Fig. 15).From the slope of this straight line, it was found that the activation energy of this reaction ≈ 159.4837Kj /mole.This value corresponds solid diffusion control.

X-Ray Diffraction of the Reduction by Carbon
X-ray diffraction of the reduction of Ilmenite pellets with carbon using molasses as binder material at 800°C, illustrated in Fig. (16).From which it is clear that the main phases are psedorutile, pseudobrookite, rutile, small amount of iron and ilmenite.This may be due to pseudorutile decomposes to pseudobrookite and rutile Fe 2 Fe 2 TiO 5 + TiO 2 + CO → 2 FeTiO 3 + CO 2 X-ray diffraction of the reduction of ilmenite with carbon, using molasses as a binder at 100-1100°C, is illustrated in Fig. (16), it is clear that the main phases are pseudobrookite, rutile and iron.This may be due to Fe 2 O 3 reduced to Fe and CO according to the following reaction Fe 2 O 3 +3 C → 2 Fe + 3CO And pseudorutile is decomposes to pseudobrookite and rutile.
Fe 2 Ti 3 O 9 → Fe 2 TiO 5 + 2 TiO 2 Also these results are consistent with the reaction of Ilmenite to metallic iron and rutile according to the general mechanism [20] FeTiO 3 + CO → Fe + TiO 2 + CO 2

Conclusions
1.The amount of molasses added to the mixture of ilmenite and coke breeze during the pelletization played a very important role on the quality of the green and dried pellets.The productivity of green pellets -10+7 mm increased as the amount of molasses increased up to 8 %. 2. As the time of pelletization increase to certain time the quality of the produced pellets improved.3. The reduction rates increased with increasing temperature.4. The activation energy of the carbothermic process of the pellets of ilmenite and coke breeze using molasses as a binder in nitrogen atmosphere ≈ 159.4837 kJ /mole .

Fig. 3 .
Fig.3.Effect of changing molasses percentage on the productivity percentage of green pellets.
molasses added.drop damage resistance.

Fig. 4 .
Fig. 4. Effect of changing molasses percentage on the drop damage of the green pellets (10 min.pelletization time.

Fig. 5 .
Fig. 5. Effect of changing molasses percentage on the crushing strength of the green pellets (10 min.pelletization time).

Fig. 6 .
Fig. 6.Effect of changing molasses percentage on the drop damage resistance of the dry pellets after 3 days (10 min.pelletization time).

Fig. 7 .
Fig. 7. Effect of changing molasses percentage on the drop damage resistance of the dry pellets after 3 days (10 min.pelletization time).

Fig. 8 .
Fig. 8. Effect of changing the time of pelletization on the productivity percentage of green pellets, (8% molasses added).

Fig. 9
Fig. 9 indicated that as increasing the time of pelletization more than 15 min.the drop damage resistance decreased this fact may be the flashing amount of water during the growth of pellets [18].

Fig. 9 .
Fig. 9. Effect of change the time of pelletization on the drop damage resistance of green pellets

Fig. 10 .
Fig. 10.Effect of change the time of pelletization on the crushing strength of green pellets.

Fig. 11 .
Fig. 11.Effect of change the time of pelletization on the drop damage resistance of dry pellets for 3 days.

Fig. 12 .
Fig. 12.Effect of change the time of pelletization on the crushing strength of dry pellets for 3 days

Fig. 13 .
Fig. 13.The relation between the time of reduction and reduction percentage for pellets containing 8% molasses after drying for 3 days.

Fig. 15 .
Fig. 15.Relationship between ln k and 1/T for pellets containing 8% molasses and drying for 3 days.

Fig. 16 .
Fig. 16.X-ray diffraction of the reduced ilmenite with coke breeze pellets at different temperature.
Ti 3 O 2 → Fe 2 TiO 5 + 2 TiO 2 And hematite Fe 2 O 3 reduce by carbon formed CO and iron Fe 2 O 3 + 3C → 2 Fe + 3 CO And then Ilmenite is then reformed by recombination reduction process involving rutile.