Ilmenite and the White Pigment - journal.elmdb.comjournal.elmdb.com/WebUsers/nargm/UploadFiles/OK/139607232214358… · Ilmenite and the White Pigment Fathi Habashi Department of

Novel Applied Researches in Geo-Science and Mining 2(2), 1-11

Novel Applied Researches in Geo-Science and Mining

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Ilmenite and the White Pigment

Fathi Habashi

Department of Mining, Metallurgical, and Materials Engineering Laval University, Quebec, Canada

E-mail address: [email protected]

Received 17 April 2016, Accepted 10 May 2016

K E Y W O R D S A B S T R A C T

Ilmenite

Hydrometallurgy

Rutile

TiO2

Ilmenite occurs in black sand at the mouth of great rivers as in India or as massive deposits like in Quebec, Canada. It is unsuitable for processing into pigment or for metal production because of its low grade. Electric furnace and hydrometallurgical methods have been developed to cope with this problem which resulted in the production of two commercial products that became known as titanium slag and synthetic rutile, respectively. The discovery that low grade ilmenite can be leached at 80oC with HCl from which synthetic rutile containing ~95% TiO2 can be precipitated renders questionable the electric furnace for treating high grade ilmenite to produce slag containing not more than 80% TiO2.

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Cite this Paper:

Habashi, F., 2016, Ilmenite and the White Pigment, novel applied researches in geo-science and mining, 2(2), 1-11.

1- Introduction

The major titanium minerals are shown in Tables 1 and 2. Rutile deposits contain about 85% TiO2, and are easy to process to titanium metal or TiO2 pigment by the chlorination method (Figure 1).

Table 1- The main titanium minerals

Mineral Formula

Rutile, anatase, brookite TiO2

Ilmenite FeTiO3

Leucoxene Fe2O3.TiO2

Perovskite CaTiO3

Sphene (titanite) CaTiSiO5

Titanomagnetite Fe(Ti)Fe2O4

On the other hand ilmenite, FeTiO3, is more complicated because of its high iron content (Table 3). Since the world reserves of titanium are 90% in the form of ilmenite and only 10 % in the form of rutile,

the treatment of ilmenite is evidently an important question in metallurgy [1-3].

Mg

Rutile TiCl4

Oxygen

Ti

TiO2

Chlorine

Chlorination

Oxidation

Reduction

Figure 1- Production of titanium or TiO2 pigment from rutile

Ilmenite deposits may be massive as in Quebec Province (Figure 2) or as black sands (Figure 3) associated with magnetite, monazite, and other valuable minerals which are separated by physical methods (Figure 4). In the first magnetic separation a weak magnet is used to separate magnetite while in the second magnetic separation a high intensity magnet is used to separate ilmenite.

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Table 2- Crystallographic data for TiO2 modifications

Phase Crystal system

Lattice constants,

nm Density,

g/cm3 a b c

Rutile tetragonal 0.4594 0.2958 4.21

Anatase tetragonal 0.3785 0.9514 4.06

Brookite rhombic 0.9184 0.5447 0.5145 4.13

Table 3- Typical analysis of ilmenite ores in %

Quebec Norway USA Russia Malaysia Australia India

TiO2 34.3 43.5 44.6 48.8 51.9 52.9 59.9

FeO 27.5 32.6 36.7 38.8 30.8 9.3

Fe2O3 25.2 13.8 8.2 5.3 11.9 25.2

SiO2 4.3 4.0 4.0 3.3 0.4 — 0.7

Al2O3 3.5 1.3 3.2 0.5 1.5 0.25 1.6

P2O5 0.015 0.03 0.04 — 0.2 — 0.18

MgO 3.1 3.9 2.6 1.3 0.08 0.54 0.95

CaO 0.9 0.6 0.8 1.1 0.1 — < 0.1

Nb2O5 — 0.01 0.01 — 0.22 — 0.17

MnO 0.16 0.4 0.32 — 0.8 1.77 0.48

Cr2O3 0.1 0.015 0.015 — 0.015 0.14 0.13

V2O5 0.27 0.23 0.12 — 0.03 0.16 0.25

S 0.3 — — — — —

Na2O + K2O 0.35 — — — — —

Figure 2- A sample of massive ilmenite of Quebec

Figure 3- Black beach sands as in India


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Figure 4- Beneficiation of black sands to recover its valuable components

2- Early Methods of Processing Ilmenite

In 1916, the Titanium Pigment Corporation of Niagara Falls, New York and the Titan Company of Norway simultaneously began commercial production of this new white pigment. Then, the principal white pigments used in paints were white lead, zinc white, and lithopone. In this method ilmenite was treated with concentrated H2SO4 at 110–120°C to form ferrous and titanyl sulfates:

FeTiO3 + 4H+ → Fe2+ + TiO2+ + 2H2O

The reaction is conducted in large concrete tanks lined with acid resisting brick (Figure 5), heated by direct injection of high pressure steam or in a pug mill (Figure 6). The solidified mass produced in the reactor at the end of the reaction was then discharged from the reactor by dissolution in water or dilute acid. After removing the insoluble residue by filtration, the solution containing 120–130 g/L TiO2 and 250–300 g/L FeSO4 was concentrated under vacuum at 10°C to crystallize FeSO4·7H2O which was then centrifuged. Titanium oxide is then precipitated from solution by dilution and seeding resulting in the formation of dilute H2SO4 for disposal (Figures 7) [4]. However, the largest producer of pigment in Salvador, Brazil still uses this technology because it disposes the waste products in the ocean which are removed by the tide.

Figure 5- Large concrete tanks lined with acid resisting brick

Because of the pollution problems associated with the disposal of dilute sulfuric acid and FeSO4, iron in the ore is now separated at an early stage. This is achieved in two ways: by electric furnace and by hydrometallurgical routes.


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Figure 6- Heated pug mill

Baking

Ilmenite

Residue

Conc.H SO2 4

Leaching

Filtration

Crystallization

Centrifuge

Hydrolysis

Filtration

Drying

Calcinat ion

H O2

H O2

Dilute

H SO2 4

Seed

TiO2

FeSO á 4H O4 2

Figure 7- Production of TiO2 pigment by the sulfuric acid process

3- Chlorination Process

DuPont in USA produces the pigment by direct chlorination of ilmenite ore, separation of products by fractional distillation, then oxidation of TiCl4 [5] (Figure 8):

2FeTiO3 + 7Cl2 + 3C → 2TiCl4 + 2FeCl3 + 3CO2

TiCl4 + O2 → TiO2 + 2Cl2

The problem of this process is recovering of chlorine from ferric chloride or marketing the large amounts of this co-product.

Cl2

Ilmenite

FeCl3, etc.

O2

TiO2

Chlorination

Purification

Oxidation

Figure 8- Simplified Du Pont process for pigment production from ilmenite

4- Separation of Iron in Electric Furnace

The electric furnace method was developed in 1950s [6]. The ore was mixed with a certain amount of anthracite which was just enough to reduce the iron oxide component of the ore, and then charged in an electric furnace at 1650°C where iron oxide is reduced to metal while titanium is separated as a slag (Figure 9). The reactions taking place during reduction are the following:

FeTiO3 + C → Fe + CO + TiO2 (slag)

Fe2O3 + 3C → 2Fe + 3CO

This method is used by the Rio Tinto QIT at its plant in Sorel near Montreal (Figure 10) and at Richards Bay in South Africa. It is also used in the Soviet Union at Zaporozhye (Ukraine) and in Japan.


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Figure 9- Electric furnace process for iron separation

Titanium slag is mainly iron magnesium titanate, (Fe,Mg)Ti4O10, and a small amount of silicates; typical analyses is given in Table 4. A small amount of TiO2 is reduced to Ti2O3; but both oxides are slagged. The

reduction of the iron oxides is not taken to completion so that some iron oxide is left in the slag to decrease its melting point. Melting point of TiO2 is 1840°C and ilmenite is 1435°C. The analysis of iron produced at Sorel is given in Table 5.

Figure 10- QIT Fer et Titane plant in Sorel, Quebec, for the selective reduction of ilmenite. The top left building houses the electric furnaces

Table 4- Analysis of typical titanium slags

Sorel, Quebec Richards Bays,

South Africa Ozaka Titanium Company, Japan

Total TiO2* 72.5 84.5 97.9

TiO2 58.8 53.1 58.6

Ti2O3 12.4 28.2 35.3

FeO 10.6 12.8 2.2

Fe2O3 0 0 0

Fe (metallic) 0.6 0.4 0

MgO 5.9 1.0 1.5

CaO 0.6 0.5 0.03

Cr2O3 0.3 0.2 —

V2O5 0.4 0.2 0.2

Al2O3 5.0 1.0 0.5

SiO2 4.2 1.5 1.0

MnO2 0.2 1.7 0.6

P2O5 0.03 0.03 0.04

C 0.02 0.01 0.2

S 0.06 0.05 0.02

Total 99.1 100.7 100.2 *Total TiO2 includes the Ti2O3 content calculated as TiO2


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Table 5- Analysis of iron produced from Quebec ilmenite in Sorel, known as Sorelmetal

%

C 1.8–2.5

S 0.11

P2O5 0.025

MnO trace

V2O5 0

Cr 0.05

Si 0.08

TiO2 trace

The slag is high in titanium and low in iron and is therefore preferable to ilmenite in manufacturing TiO2 pigment or titanium metal. However, the slag produced in Quebec is not suitable for chlorination because of its high impurity level — about 16.6% as compared to about 6% in other slags. These impurities will not only consume unnecessary amounts of chlorine but also will create a disposal problem. Furthermore, some of these impurities, e.g., calcium and magnesium will interfere with the chlorination process itself which is conducted at 800°C by forming a molten phase (CaCl2 m.p. 770°C, MgCl2 m.p. 708°C).

For these reasons, Sorelslag was used only for making pigment by the sulfuric acid process. The slag was treated in the same way as ilmenite with the exception that no separation of ferrous sulfate was necessary because the bulk of iron was already separated by reduction in the earlier step (Figure 11). The sulfuric acid treatment process of the slag, however, still suffered from the disposal problem of the waste acid and as a result it was abandoned in the 1980s and replaced by a new technology based on upgrading the slag to 94.5% TiO2 by leaching away most of the impurities by HCl under pressure to render it suitable for chlorination.

5- Separation of Iron by Hydrometallurgical Route

The hydrometallurgical route was developed in 1960s and involved leaching of iron from ilmenite and obtaining a residue rich in titanium (90–95% TiO2) known as “synthetic rutile”. In one case, the Altair process, a pigment grade TiO2 was obtained. All these processes use an oxyhydrolysis process for treating ferrous chloride to get HCl for recycle and Fe2O3 as a by-product.

Figure 11- Leaching of titanium slag for production of TiO2 pigment, now obsolete

5-1- Production of synthetic rutile

In this method, ilmenite is decomposed in autoclaves by 20% HCl at 120°C and 200 kPa; iron is solubilized as ferrous chloride leaving a solid containing about 93% TiO2 (Figure 12):

FeTiO3 + 2H+ → TiO2 [impure] + Fe2+ + H2O

Figure 12- Production of synthetic rutile from ilmenite


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The synthetic rutile is then treated by chlorine to prepare TiCl4 from which TiO2 or titanium metals are obtained without pollution problems. The process is used in the USA, England, Japan, Taiwan, and

Australia. Modifications for this technology were introduced as shown in Table 6.

Oxyhydrolysis could be conducted in a variety of ways as is discussed below.

Table 6- Production plants for synthetic rutile

Process Process steps By-products Producer and location

Benilite Corporation of America

Partial reduction to Fe(II), digestion with HCl solution, calcination

FeCl2 pyrolyzed to Fe2O3 and HCl

- Kerr McGee, Mobile, USA - Kerala, Minerals and Metals Ltd., Chavara, Kerala - Indian Rare Earths, Orissa, India

Western Titanium Oxidation to Fe(III), reduction to Fe, digestion with FeCl2, with air oxidation

Iron hydroxides - Associated Minerals Consolidated Cael, Australia - AMC, Narngulu, Australia

Lurgi

Reduction to Fe, digestion with air blowing, hydrocyclone separation, calcination

Iron hydroxides - Westralian Sand Ltd., Capel, Australia

Ishibara Sangyo Kaisha

Reduction to Fe(II), digestion with H2SO4, calcination

FeSO4 solution reacted with NH3 to form ammonium sulfate and iron hydroxide

- Ishibara, Yokkaichi, Japan

Dhrangadhra Chemical Works

Reduction to Fe(II)/Fe, digestion with HCl, calcination

Iron chloride solution - Dhrangadhra Chemical Works Ltd., Suhupuram, Tamil Nadu, India

5-2- Ortech-Argex process

The Ortech-Argex process [Ortech] is being developed in Canada and is based on leaching ilmenite with HCl [7]. After solid -liquid separation the solution is subjected to two solvent extraction steps (Figure 13). The first is to remove iron and the second to recover titanium. Vanadium is then precipitated from the residual solution. The solution containing iron is treated to recover Fe2O3 while the solution containing titanium is treated to recover pigment grade 99.8% TiO2. Hydrochloric acid generated during the recovery of Fe2O3 and TiO2 is collected for recycle. The solvent extraction process makes this process unattractive.

5-3- Production of pigment-grade TiO2 by the Altair process

The Altair process produces pigment grade TiO2 from ilmenite without chlorination [8]. It is based on leaching of ilmenite concentrate containing 52.2 % TiO2 and 32.8 % Fe in hydrochloric acid to solubilise titanium and iron while silicates and chromites remain in the residue. Iron in solution is then reduced to the ferrous state by addition of iron powder, the solution cooled and filtered to separate ferrous chloride. Titanium in solution is extracted by organic solvent then converted to TiO2 hydrate by spray hydrolysis at about 600°C, calcined, and milled.

Ilmenite

Residue

Raffinate

V2O5

Thermal pptn.

Strip solution

Precipitation

Fe2O3

Titanium extn.

Filtration

HCl

Calcination

99.8% TiO2

Leaching

Filtration

Iron extn.

Figure 13- Flow sheet of Ortech-Argex process as deduced from the patent


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Water vapour and HCl gas from the spray hydrolyser are condensed in absorption columns. Ferrous chloride crystals are re-dissolved in weak acid and subjected to pyrohydrolysis or spray hydrolysis to generate HCl. The major part of the chloride remains in solution and is recycled to the digestion operation. Soluble impurities accumulating in the circuit are kept at a tolerable level by bleeding. The bleed stream is combined with the iron chloride crystals and sent to pyrohydrolysis. This process however, did not receive commercial application.

5-4- Oxyhydrolysis

Ferrous chloride solution is regenerated to HCl and Fe2O3 by oxyhydrolysis:

2FeCl2 + 2H2O + 1/2O2 → Fe2O3 + HCl

It is the same technology that is used for treating pickle solution. Two methods are used

5-4-1- Fluidized bed oxyhydrolysis

In a fluidized bed reactor the ferrous chloride solution is introduced onto a large bed of hot ferric oxide where heating is provided by the hot fluidizing combustion gases (Figure 14). As the combustion gas flows through the well agitated bed of oxide it quickly reaches thermal equilibrium with the bed. The solution is fed on top of the bed of oxides. The liquid feed wets the outer layer of the hot oxide particles and is quickly evaporated to form an onion-like layer of new solid oxide on top of the existing oxide, thereby producing dense homogeneous particles.

Figure 14- Fluidized bed reactor for oxyhydrolysis of ferrous chloride [9]

5-4-2- Spray roaster oxyhydrolysis

In this type of oxyhydrolysis roaster, the ferrous chloride solution is sprayed into an empty cylindrical vessel, while the required energy is supplied by the up flow of hot gases generated in the bottom burners (Figures 15 and 16). Spray roasters have large diameters to keep the gas velocities low. If the gas velocity is high, too many particles are elutriated with the off-gas, and the product quality and the efficiency of the roaster drop. The off-gas and oxides leave the roaster counter-currently at about 400°C to 500°C. The residence time of the sprayed particles in the high-temperature reaction zone is very short; therefore, very small liquid droplets, which can be quickly heated, should be created by atomization. The fast heat-up results in the formation of a solid oxide crust on the surface of each droplet. As the bulk of the droplet heats, the water content vaporizes and breaks through the oxide shell. Therefore, the spray roasted oxide is composed of very fine “fluffy”, hollow spheres.

Figure 15- Regeneration of HCl from ferrous chloride solution by oxyhydrolysis in spray roaster


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Figure 16- Hydrochloric acid regeneration plant in synthetic rutile production using spray roaster

6- MAGPEI Process

In 2014 it was found by MAGPEI Incorporation in Canada that low grade ilmenite can be dissolved at 80°C with concentrated HCl at atmospheric pressure. After filtration to remove insoluble matter, the solution is distilled to recover HCl and to hydrolyse titanyl ion to TiO2. After filtration, the residue is calcined to produce synthetic rutile (Figure 17) [10]:

FeTiO3 + 4HCl → TiO2+ + Fe2+ + 4Cl- + 2H2O

TiO2+ + 2Cl- + H2O → TiO2 + 2HCl

A pilot plant (Figure 18) has confirmed this process. It is evident that the new leaching technology at ambient pressure is superior to the old electric furnace smelting - autoclave upgrading.

7- Summary

Figure 19 gives a general outline of the schemes presently used for the treatment of high-grade

ilmenite and rutile while Figures 20 to 24 shows the raw materials, semi-finished, and finished products. It is evident that leaching technology at ambient pressure is superior to the old electric furnace smelting - autoclave upgrading as well as other upgrading processes.

Ilmenite

Solids

Residue

Fe2O3

HCl

Oxyhydrolysis

HCl

Leaching

Filtration

Distillation

Solution

Filtration

Calcination

Synthetic rutile

Slurry

Figure 17- Direct production of 95% TiO2 from a low grade ilmenite [MAGPEI process]

Figure 18- Pilot plant in operation. Fathi Habashi(left) and Ernesto Bourricaudy. Photo by Fouad Kamaleddine


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Figure 19- Processing routes for high-grade ilmenite and rutile. Dotted lines represent special cases

Figure 20- Titanium white, ~ 100% TiO2

Figure 21- Museum sample of rutile, ~ 90 % TiO2

Figure 22- Museum sample of ilmenite, FeTiO2 (59.4 % TiO2)

Figure 23- Ground titanium slag, FeTi4O10 (70-80 % TiO2)

Figure 24- Synthetic rutile (~95% TiO2)

References

[1] J. Barksdale, Titanium, Its Occurrence, Chemistry and Technology, Ronald Press, New York 1966.

[2] H. Sibum et al., “Titanium”, pp. 1129- 1179 in Handbook of Extractive Metallurgy edited by F. Habashi, published by WILEY-VCH, Weinheim, Germany 1997

[3] F. Habashi, “Two Hundred Years Titanium. The Processing of Titanium Ores for Pigment and Metal Production,” Arab Min. J. 11(1, 2), 74–84 (1993)

[4] F. Habashi, Pollution Problems in the Mineral and Metallurgical Industries, Métallurgie Extractive Québec, Québec City, Canada 1996. Distributed by Laval University Bookstore www.zone.ul.ca

[5] DuPont™ Ti-Pure® titanium dioxide Titanium Dioxide for Coatings, brochure published by DuPont in 2007

http://www.zone.ul.ca/


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[6] F. Habashi, Textbook of Pyrometallurgy, Métallurgie Extractive Québec, Québec City, Canada 2002. Distributed by Laval University Bookstore www.zone.ul.ca

[7] Ortech process, http://en.wikipedia.org/wiki/Argex_Mining

[8] D. Verhulst, B. Sabacky, T. Spitler and J. Prochazka, “New Developments in the Altair Hydrochloride TiO2 Pigment Process”, pp 565-575 in Hydrometallurgy 2003, Fifth International Conference edited by C.A. Young et al., published by The Metallurgy and Materials Society, Warrendale, Pennsylvania 2003

[9] K. Adham, C. Lee and D. Small, “Energy Consumption for Iron Chloride Pyrohydrolysis: Comparison Between Fluidized Beds and Spray Roasters”, pp. 815-830 in Iron Control Technologies, edited by J.C. Dutrizac and P.A. Riveros, published by Canadian Institute of Mining, Metallurgy, and Petroleum, Montreal 2006

[10] F. Habashi, F. Kamaleddine, E. Bourricaudy, “A New Process to Upgrade Ilmenite to Synthetic Rutile”, Proceedings Conference of Metallurgists, Canadian Institute of Mining, Metallurgy, and Petroleum, Montreal 2014. Reprinted in Metall 69(1-2),27-30(2015)

http://www.zone.ul.ca/

http://en.wikipedia.org/wiki/Argex_Mining

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