Ind ian Journal of Engineering & Materi als Sciences Vol. 9, August 2002, pp. 275-28 I

Studies on the upgrading of Indian ilmenites to synthetic rutile

D Y Baubande, P R Menon & J M Juneja

Materia ls Processing Division, Bhabha Atomic Research Centre, T rombay, Mumbai 400085, India

Received 18 October 2001 .. accepted 19 April 2002

A process based on solid state reductio n of iron ox ide content of ilmeni te w ith carbon in presence of alka li carbonate catalysts fo llowed by removal o f iron content of reduced ilmenite by ru sting in NH 4C1 so luti on has been investi gated fo r up­grading the Indi an ilmenites (Qui Ion and Ori ssa grades) to synthetic rutile. The process vari ables such as the te mperature of reducti on, presence of cata lyti c agents during reducti on and rusting condi tio ns etc. were examined to obtain an upgraded product contai ning ~ 92% Ti 0 2. Whereas Quilon ilmenite could be reduced with carbon at 950°C for 2 h in presence of 5% Na2CO), the reductio n of Ori ssa ilmenite required a pre-ox idation treatment in air at 850°C fo llowed by reduction with car­bon at 1025°C for 4 h in presence of 5% K2CO) catalyst. The upgraded rutile product containing 92-93% Ti02 was obtai ned when reduced ilmenite was rusted in 1% NH4C1 soluti on at a p H of 4 .5 and a temperature o f 65°C.

Titanium is mainly used in the form of Ti02 in the pigment industry and as a coating materi al for weld­ing electrodes. These applications account for almost 90% of titanium consumption in the industry . Tita­nium metal and its alloys also find applications in aerospace, power engineering and chemical process industries.

Ilmenite (FeTi03) and rutile (Ti02) are the two chief minerals of titanium. Natural weathering results in the beneficiation of ilmenite to rutile. This process involves ox idation of ferrous iron to ferric and pro­gressive removal of iron by leaching, leaving rutile as the final product. Whereas the world reserves of il­menite are quite extensive, the quantity of rutile avail­able in nature is very limited. A major proportion of . ilmenite mined is therefore used for the production of synthetic ru tile which in turn is used to produce pig­ment grade Ti02 and titanium metal. India has large reserves of ilmenite in the beach sand deposits at Manavalakurichi (MK) in Tamil Nadu and at Chavara in Quilon (Q) in Kerala State and as huge dune de­posits in Chatrapur coast in Orissa state.

A number of methods have been proposed for up­grading ilmenite to a rutile substitute l.2. These can be di vided into four main groups-reduction, selecti ve chlorination, selecti ve leaching and miscellaneous. The reduction processes, which involve reduction of iron oxide content of the ore either partially to ferrous (+2) or completely to metallic state, have proved more successful procedures for upgrading the ilmenite.

Solid state parti al reduction of iron oxide to the ferrous (+2) state followed by acid leaching has been practiced in a number of cases3-5 fo r the preparati on of synthetic rutile. A number of reports are also available on the solid state reduction of iron oxide content of ilmenite to the metallic state6-16. Walsh et ai.6 reported that hydrogen reduction of ilmenite at 800°C yields metallic iron , rutile and pseudobrookite but no reduction of ilmenite is possible with coke at 800°e. Shomate et al. 7 carried out a thermodynami c study of reduction of ilmenite by carbon, carbon monox ide and hydrogen. Yij ay et ai.8 studied pre-oxidation and hydrogen reduction of ilmenite in a fluidi zed bed reactor. In a kinetic study on the reduction of ilmenite with graphite, Guindy and Davenport9 observed that the reduction initi ates at 860°C and accelerates only after 1020°e. Annie George et ai. 10 carried out studi es on the reduction of Quilon ilmenite with pith as reductant and observed that the reduction takes place at about IOSO°e. They obtained a rutile product containing about 2% iron by leaching the reduced ilmenite with 20% HCI at 80°C fo r 1 h. Grey and Reid II used X-ray di ffraction to study the reacti on sequence during solid state reduction of ilmenite with coke and observed that the reaction started around IOOO°C and was complete at 11 90°e. Galgali et ai.12

used a pl asma reactor to study the carbothermic reduction of ilmenite ore.

Pre-oxidation of ilmenite has been reported 13. 17-22 to increase its reducibility with hydrogen and carbon-

276 INDIAN J ENG MATER SCI, AUGUST 2002

carbon monoxide. Becher et al.17 found that pre­oxidi sed Australian Capel ilmenite was more easily reducible with carbon than raw ilmenite at tempera­tures between 950-1 WO°c. Pre-oxidation of ilmenite in oxidising atmosphere produces pseudobrookite (Fe2Ti05) and rutile (Ti02) phases l3 in the tempera­ture range 750-1000°C.

Reduction of pure iron oxide with coke has been reported23. 24 to be accelerated by the presence of salts of alkali and alkaline earth metals. Mohanty and Smith25 studied selec tive reduction of iron oxide con­tent of sy nthetic ilmenite, i.e, a mixture of iron oxide and Ti02 by graphite in presence of catalysts in the temperature range 850-1200°C using thermogra­vimetric analysis. They found that in case of uncata­lysed reduction, the reaction initiates at 860°C but the maximum rate is observed only at 1150°C. No meas­urable weight loss was observed below 1020°C. Above 1020°C reduction was effected mainly by gaseous CO. The gasification reaction: CO2 + C = 2CO (Boudouard reaction) constitutes the main rate limiting step. However in case of catalysed reduction, Mohanty et al. 25 observed that the rate of reaction was significantly enhanced by the addition of 5% of alkali carbonates to the mixture of ilmenite and carbon. The temperature at whicb measurable weight loss occurs, drops from about J()20°C with graphite alone to be­tween 900-920°C when alkali carbonates such as Na2C03 and K2C03 i3lJ'e present. However, these stud­ies have not been applied to the processing of natu­rally occurring ilmenite ores.

The reduction of ilmenite with carbon yields Ti02 and metallic iron. The metallic iron content of re­duced ilmenite can be removed by leaching with HCl or FeCh solution l4 (Summit process) or by rusting in presence of NH4CI solution I5.17 (Becher process). The Becher process, which has been applied to the proc­essing of Australian ilmenites I3, appears to be eco­nomically advantageous as it generates solid iron ox­ide by-product, which is less polluting and not harm­ful to the environment. Mohan Das et al. 16 studied the removal of iron content of reduced Manavalakurichy ilmenite by rusting in aqueous medium.

The present investigation involves preparation of synthetic rutile by solid state reduction of two types of Indian ilmenites - Chavara or Q-grade and Orissa­grade with carbon using alkali carbonates as catalytic agents. The purpose of using catalytic agents was to see if the reduction of naturally occurring ilmenites could be carried out at lower temperatures by the use

of such agents. Ori ssa ilmenite contains a high ratio of 2.924 of FeO/Fe20 3 as compared to a value of 0.368 for Q-grade ore. Thus Orissa grade ore has a lower degree of oxidation as compared to the Q-grade . Pre­oxidation of Orissa ore converts FeO in to Fe203 and results in the formation of pseudobrookite and rutile phases . This hel ps to make subsequent reduction with carbon easier. So natural as well as pre-oxidised Ori ssa ilmenite ores were used in the present investi­gations. The removal of metallic iron con tent of re­duced ilmenite was studied by rusting in presence of NH4CI solution. Process variables including tem­perature of reduction, presence of catalytic agents during reduction and rusting conditions such as (a) amount of NH4CI in solution, (b) pH of solution, (c) temperature of rusting and (d) period of rusting etc. were examined.

Experimental Procedure Two types of domestic ilmenites were evaluated in

this investigation . One of the ilmenite concentrates was derived from Chavara beach sands of Kerala (Q­grade) and the other was an alluvial sand deposit from Chatrapur coast in Orissa state. Chemical composi­tions of these titaniferous materials are presented in Table 1. Carbon having composition given in Table 2

Table I -- Chemical analysis of Indian iimenites

Element Q-grade Orissa grade (%) (%)

Ti02 60.60 50.80 Fe20 ) 26.10 11.80 FeO 9.60 34.50

AI2O) 0.50 0.35 MnO 0.40 0.54 Cr20 ) 0.12 0.06 V20 S 0.15 0.23 MgO 0.50 0.57 P20 S 0.15 0.03 Zr02 0.40 0.12 Si02 0.80 0.93

FeO/Fe20) 0.368 2.924

Table 2 - Chemical analysis of carbon

Moisture Ash Volatile matter Fixed carbon Sulphur Partical size

%

7.6 6.9 12.4 73.1 1.2 - 100 mesh (ASTM)

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BAUBANDE et al.: STUDIES ON THE UPGRADING OF INDIAN ILMENITES TO SYNTHETIC RUTILE 277

was used as the reducing agent. Other chemicals used such as Na2C03, K2C03, HCI, NH4CI were of techni­cal grade.

The pre-oxidation of Orissa ilmenite was carried out by heating the ore in air at 850°C in a fluidized bed reactor. The reactor (5cm dia. x 75 cm long) was made up of INCONEL 600 and was fitted with a multi-hole-type distributor. The upper portion of the reactor was provided with an outlet for gas and thermo-well port. The ore was fluidized using a cur­rent of compressed air. The reactor was heated by a nichrome wire resistance furnace. The pre-oxidation runs were carried out in batches of 200 gore.

Reduction experiments were conducted in a one end closed INCONEL retort (10 cm dia. x 50 cm long). The charge consisting of ilmenite, carbon and catalyst was mixed thoroughly and reduced in argon atmosphere at 800-1025°C in a Kanthal wire resis­tance furnace. The extent of reduction was examined by X-ray diffraction as well as chemical analysis.

The metallic iron content of reduced ilmenite was removed by rusting in a solution containing NH4Cl. The reduced ilmenite (50 g) was treated with 300 mL of NH4C1 solution. The ilmenite particles were agi­tated by passing compressed air through the solution. The pH of the solution was adjusted - 4.5 using dil. HC!. After rusting for the required period, the floating iron hydroxide precipitates were removed and col­lected on a filter paper, dried at - 110°C under Infra red lamp and weighed. The beneficiated ilmenite was

finally leached with 10% HCI, washed, dried and analysed.

Results and Discussion The studies on the upgrading of Indian ilmenites

were carried out in two stages . The first stage in­volved selective reduction of iron oxide content of ilmenite with carbon in presence of catalytic agents like Na2C0 3 & K2C03. The second stage consisted of separation of metallic iron from Ti02 by rusting in presence of NH4CI solution. Two types of Indian il­menites - Chavara or Q-grade and Orissa-grade were used in the present study.

Reduction of Quilon ilmenite The solid state reduction of Quilon grade ilmenite

with carbon was investigated in presence of 5% Na2C03 as catalyst in the temperature range 800-1000°e. The progress of the reduction reaction was observed by X-ray examination of the products . Re­sults of these studies are presented in Table 3. It was observed that when Quilon ilmenite was reduced with carbon in presence of 5% Na2C0 3 for 2 h, the reduc­tion started at 900°C and it was complete at 950°e. No reduction was observed at 800°e. Further reduction of ilmenite at 950°C without the use of Na2C03 resulted in a product that contained some unreduced ilmenite. A soaking period of 2 h at 950°C was found to be adequate for complete reduction of ilmenite.

A 94% metallisation of iron values of Quilon il­menite was achieved when a charge containing 100 g

Table 3 - Results of X-ray examination of products obtained by carbothermic reduction of ilmenite

Duration of reduction: 2 h

Sr. Tempera- Charge comlZosition (g) Phase analysis of Remarks No lUre of Ilmenite Oxidised C Na2C03 K2COJ product

reduction Ilmenite Major Minor (ac) (850aC) Phase Phase

Quilon Ilmenite

I. 800 100 10 5 Ilmenite No reduction 2. 900 100 10 5 a-Fe, Ti02 Ilmenite Partial reduction 3. 950 100 10 5 a-Fe, Ti02 Complete reduction 4. 950 100 10 a-Fe, Ti02 Ilmenite Partial reduction

Orissa Ilmenite

5. 950 100 10 5 a-Fe, Ti02 Ilmenite Partial reduction 6. 1000 100 10 5 7. 1025 100 10 5 8. 1025 100 10 5 9. 1025 100 10 5 a-Fe, Ti02 Complete reduction

278 INDIAN J ENG MATER SCI, AUGUST 2002

ilmenite, 10 9 C and 5 g Na2CO) was heated at 950°C for 2 h. The reduced charge on analysis was found to conta in 61 .3% Ti02, 32.46% Fe and 3.32% C. Leaching of reduced ilmenite (50 g) with 500 mL of 20% HCI at 80-90°C for 2 h gave a product analyzing 91 .8% Ti02. The upgraded product on X-ray exami­nation was found to contain rutile.

Thus the present study has shown that natural Quilon ilmenite can be reduced with carbon around 950°C in presence of 5% Na2CO). Similar results have been reported by Mohanty et al.25

. The chemical re­actions that can occur in the temperature range 900-1025°C during the reduction of ilmenite with carbon are :

I . Solid-Solid reduction:

Fe TiO) + C = CO + Fe + Ti02 ... (l)

2. Gaseous reduction:

FeTi02 + CO = CO2 + Fe + Ti02 .. . (2)

3. CO generation (Boudouard reaction):

CO2 + C = 2CO ... (3) In case of uncatalysed reduction25, the reaction

proceeds at an insignificantly slow rate between 860 and 1020°C. During this early stage of reduction solid-solid interaction at the contact points between ilmenite and carbon particles, i.e, reaction 1 appears to be the main contributor to the process. With in­crease in time and temperature, the contribution of reaction 1 diminishes owing to decrease in the contact area caused by the accumulation of product at the in­terface. Meanwhile, the rate of regeneration of CO via reaction 3 and consequently the rate of gaseous re­duction via reaction 2, increase. There is, therefore, a significant increase in the overall rate of reduction. At higher temperatures (>1020°C) the relative contribu­tion of gaseous reduction would be expected to in­crease and that of solid-solid reduction to decrease. The overall reduction rate however, is controlled by the availability of CO, i.e., by the Boudouard reaction. In the presence of catalysts (the alkali carbonates), the reaction involving CO generation takes place at a faster rate at relatively lower temperatures. As a re­sult, gaseous reduction takes over from solid-solid reduction at signific2.:ntly lower temperatures of 850-

1000°C.

Reduction of Orissa i1melllite The reduction products of Orissa ilmenite obtained

under conditions similar to those adopted for Quilon

ilmenite (i .e . at 950°C for 2 h in presence of 5% Na2CO)) were found to contain some unreduced il­menite (Table 3). Increasing the temperature of re­duction upto 1025°C did not help in achieving com­plete reduction. This shows that it is di fficult to re­duce Orissa ilmenite with carbon as compared to the Quilon ilmenite. Further studies wete carried out with Orissa ilmenite pre-oxidised in air at 850°C for 4 h. However, reduction of oxidized ilmenite with carbon at temperatures upto 1025°C showed presence of some unreduced ilmenite (Table 3). The reduction experiments were repeated in presence of 5% Na2C03 as well as K2CO). Whereas the use of Na2CO) as catalyst helped to improve the degree of reduction of ilmenite, near complete reduction could be achieved in presence of K2CO) as catalyst, when reduction was carried out at 1025°C. Thus, K2CO) was found to be a better catalyst as compared to Na2CO). Similar results have been reported by Mohanty et al.25

. They have reported that the activation energy value for a process catalysed by K2CO) is lower at 57.7 kcallmol as com­pared to a value of 68.2 kcallmol for a Na2CO) cata­lysed process and 78-84 kcallmol for the uncatalysed process . XRD analysis of reaction products25 showed presence of small amounts of Na2TiO), Na2Ti)0 7, Na2Ti5011 and K2TiO).

Separation of metallic iron f:rom reduced ilmenite Reduced ilmenite contains Ti02 and metallic iron

(a-Fe). Such a product is suitable for use as such in the coating of welding rods. However for use in pig­ment industry or in titanium metal preparation, it is necessary to separate metallic iron from Ti02. The products of reduced ilmenite cannot be separated by physical means such as froth floatation or magnetic separation. Even reoxidation and grinding, followed by froth floatation cannot separate Ti02 and iron ox­ide particles as surfaces of Ti02 and iron oxide be­have almost similarly under the flotation conditions 16. The simplest chemical method available for separa­tion is to leach out the metallic iron content by treat­ment with di!. HC!. Two stage leaching of reduced ilmenite with 20% HCI at 80-90°C for 2 h each gave a product analyzing 9l.8% Ti02. However the leaching process involves consumption of HCI and generation of a dilute solution containing FeCI3, which poses disposal problems 1o.14. As an alternative to the acid leaching process, studies were carried out on the re­moval of iron content of reduced ilmenite by rusting in aqueous medium using NH4C1 catalyst. The ad­vantages of such an aeration process are low require-

-t

BAUBANDE et af.: STUDIES ON THE UPGRADING OF INDIAN ILMENITES TO SYNTHETIC RUTILE 279

ment of chemicals and generation of solid Fe203 waste, which is easy to dispose off.

The removal of iron from reduced ilmenite by aqueous oxidation is an accelerated corrosion process. The iron-oxygen reaction being a redox process in­volves two half reactions:

Oxidation of iron: Fe ---7 Fe+2 + 2e-

Reduction of oxygen: O2 + 2 H20 + 4e' ---7 4 OR

Initially, the ferrous ions are formed in the vicinity of metallic iron particles of reduced ilmenite. These ions are transported to the solution and subsequently oxi­dised. The concentration of dissolved oxygen in the bulk of the aeration liquor and the solution pH deter­mine the final iron oxide species formed. The poten­tial- pH diagram of iron-air- water system26 at 25°C shows that the stable phases within the pH - potential ranges used in the aeration process are the hydrated forms of Fe304 and Fe203.

NH4Cl acts as a catalyst during the aeration proc­ess. Studies were carried out to investigate the effect of various parameters such as concentration of NH4Cl, temperature of rusting reaction, pH of the solution and period of rusting on the rusting process and optimum conditions determined.

Results of rusting of reduced ilmenite in solutions containing different amounts of NH4Cl are indicated in Table 4 . The concentration of NH4Cl in the solution was varied from 0.2 to 1.2% and the rusting was car­ried out at a pH of 4.5 for 5 h each, maintaining tem­perature of the solution at 65°C. It is seen from the data in table that the rate of removal of iron increases with increase in concentration of NH4Cl from 0 .2 to 1 %. Further increase in concentration of NH4Cl to 1.2% results in almost the same rate of rusting. Hence, a concentration of -I % NH4Cl appears to be optimum for the rusting reaction. NH4Cl plays three important roles in the aeration process:

(i) the ammonium ion acts as a buffer for hydroxyl ions and prevents the precipitation of iron hydroxide at the surface of the particle.

(ii) the ammonia formed as a result of the buffering action forms a complex with iron ions and removes them from the surface.

(iii) the chloride ion helps to break down any pas­sive oxide layer formed on the surface.

The rate of the reaction between reduced ilmenite and oxygen is determined by the speed with which oxygen diffuses to the reduced ilmenite surface. Hence, the availability of sufficient oxygen and proper suspension of the ilmenite particles in the

Table 4-Results of rusting experiments [Amount of reduced product taken: 50 g]

Sr. Concentration of NH4C1 in Temperature of pH of solution Period of rusting Amount of rust No solution rusting (0C) (h) formed (g)

(%)

I. 0.2 65 4.5 5 3.50 2. 0.4 65 4.5 5 3.80 3. 0.6 65 4.5 5 4.90 4. 0.8 65 4.5 5 7.02 5. 1.0 65 4.5 5 7.33 6. 1.2 65 4.5 5 7.10 7. 1.0 65 2 5 1.40 8. 1.0 65 3 5 3.75 9. 1.0 65 4.5 5 7.33 10. 1.0 65 5 5 6.55 11. 1.0 65 5.5 5 5.10 12. 1.0 40 4.5 5 2.45 13. 1.0 50 4.5 5 3.33 14. 1.0 60 4.5 5 4.06 15. 1.0 65 4.5 5 7.33 16. 1.0 70 4.5 5 7.05 17. 1.0 65 4.5 2 0.09 18. 1.0 65 4.5 3 2.30 19. 1.0 65 4.5 4 5.67 20. 1.0 65 4.5 5 7.33 21. 1.0 65 4.5 6 6.80

280 INDIAN J ENG MATER SCI, AUGUST 2002

Table 5-Results o f upgrading o f Ori ssa ilmenite by carbothermi c reduction of preox idi sed ore fo llowed by rusting

Temperature of pre-oxidation o f Ilmenite: 850°C Period o f pre-oxidation : 4 h Rusting conditi ons: Concentration of NH4Ci : 1% pH of solution : 4.5 Temperature o f solution : 65°C Period o f rusting : 10- 12 h

Sr. No. Red uction temperatu re Duration of reduction (h) Anal ys is o f upgraded product

I 2 3 4 5

(OC)

950 1000 1025 1025 1025

2 2 2 4 5

system for maximum diffusion are required for effi­cient rusting. This was achieved by passing com­pressed air through the solution at the rate of 4 .5 to 5.0 liters per minute. .

The rate of rusting is dependent on the initial pH of the system. The initial pH o f the system is influenced by the amount of gangue and other impurities present in reduced ilmenite. Hence, experiments were carried out to determine the e ffec t of initia l pH of the solution on iron removal. The initial pH of the solution was varied from 2 to 5.5 and it was maintained constant during the period o f rusti ng by addition of required amounts of dilute HCI ( I :9). The results of these studies are also presented in Table 4. It is evident from the data in Table 4 that max imum amount of rust was formed when the initial pH was maintained at 4.5 and the rusting was carried out for 5 h in a solutio n

conta ining 1% NH4C1 at a temperature of 65°C. In order to study the effec t of temperature on rust­

ing of reduced ilmenite, experiments were carri ed out

at temperatures of SO, 60, 65 and 70°C for a fixed du­ration of 5 h. The results of these studies (Table 4) show that maximum amount of rust is formed at

higher temperature of 65-70°C, i.e, the removal of iron is more efficie.nt at higher temperatures. How­ever, as pointed out above, the reaction rate is de­pendent on the availability of dissolved oxygen in the system. As the solubility of oxygen decreases at higher temperatures, temperature beyond an upper

limit will not be favourable. So 65°C was taken as the optimum temperatu.re for rusting. In the case of Aus­

tra lian ilmenite'3, a temperature of 70°C has been used for rusting.

Ti02

(%)

83 .3 83 .8 1 89.65 92.97 93.05

16.70 13.03 6.64 4 .27 1.98

The effect of period of rusting was s tudied by car­rying out rusting experiments for di ffere nt periods vary ing from 2 to 6 h . The data in Table 4 shows that maximum rust was formed when rusting was carried

out for 5 h at 65°C in a solution conta ining 1% m4CI at a pH of 4.5.

Thus, the iron content of reduced ilmenite can be effic iently removed by rusting in an aqueous solution

containing 1% NH4CI at a pH of 4.5 for 5 h at 65°C. Rusting of reduced ilmenite under these conditio ns followed by washing wi th 10% HCI solution gave a rutile product containing 92.97% T i0 2.

Upgrading of Orissa ilmenite

The orissa ilmenite pre-oxidised at 850°C fo r 4 h was reduced with carbon in presence of 5 % K2C0 3 at

different temperatures (950 to 1025°C) and the re­duced product was subjec ted to rusting under the op­timum conditions established above, viz, 1% NH4C1

solutio n at a pH of 4.5 at 65°C. The results of up­grading at different temperatures are shown in T a­ble 5. Studies on the influence of temperature of re­duction of preoxidised Orissa ilmeni te in presence of 5% K2C03 (Table 5) showed that Ti02 content of up­graded product inc reased from 83.3% to 89.65% as

the temperature was varied from 950 to 1025°C with a soaking period of 2 h. Increas ing the soaking period

from 2 to 4 h at 1025°C yielded a product anlaysing 92.97% Ti02. However, increasing the soaking period beyond 4 h did not help much in further improving the Ti02 content of the upgraded product.

Thus, a synthetic rutile product conta ining around 93 % Ti02 was obtained from Ori ssa ilmenite when

+

BAUBANDE et al.: STUDIES ON THE UPGRADING OF INDIAN ILMENITES TO SYNTHETIC RUTILE 28 1

ore preoxidi sed at 850°C was reduced with coke at 1025°C for 4 h in presence of 5% K2CO) and the iron content of reduced product was removed by rusting in a solution containing 1 % NH4CI at a pH of 4.5 and a temperature of 65°C.

Conclusions The solid state reduction of ilmenite with carbon in

presence of alkali carbonate followed by rusting in NH4CI solution can be employed for upgrading of Indian ilmenites to sy nthetic rutile. The use of alkali carbonate catalyst during reduction helps in carrying out reduction at lower temperatures of 950-1025°C. as compared to the reported temperatures of 1100-1190°C for uncatalysed reductions II . The Orissa il­menite is more difficult to reduce as compared to the Quilon ilmenite as it requires a pre-oxidation treat­ment followed by reduction at a higher temperature (l025°C).

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