Hydrometallurgy 139 (2013) 88–94

Contents lists available at ScienceDirect

Hydrometallurgy

j ourna l homepage: www.e lsev ie r .com/ locate /hydromet

Hydrolysis of TiOCl2 leached and purified from low-gradeilmenite mineral

Nasser Y. Mostafa a,b,⁎, M.H.H. Mahmoud a,c, Z.K. Heiba a,d

a Faculty of Science, Taif University, P.O.Box:888 Al-Haweiah, Taif, Saudi Arabiab Chemistry Department, Faculty of Science, Suez Canal University, Ismailia 41522, Egyptc Central Metallurgical R&D Institute (CMRDI), P.O. Box: 87 Helwan, Cairo, Egyptd Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt

⁎ Corresponding author at: Chemistry Department, FUniversity, Ismailia 41522, Egypt. Tel.: +20 64 382216; fa

E-mail address: nmost69@yahoo.com (N.Y. Mostafa).

0304-386X/$ – see front matter. Crown Copyright © 2013http://dx.doi.org/10.1016/j.hydromet.2013.08.002

a b s t r a c t

a r t i c l e i n f o

Article history:Received 11 December 2012Received in revised form 26 June 2013Accepted 4 August 2013Available online 15 August 2013

Keywords:ExtractionPowder metallurgyChemical techniquesIlmenite

Low grade ilmenite (FeTiO3) is not suitable for the production of titaniummetal or TiO2 due to its high iron con-tent. An economic process is devised for extraction and purification of titaniumas TiOCl2 solution from low-gradeilmenite. The extracted TiOCl2 solution could be transformed to rutile, anatase or amixture of them by hydrolysisunder different conditions. Themicrostructuremorphology of the obtained productswas investigated using SEMand TEM. Hydrolysis under open atmosphere at 100 °C for 6 h gives a very stable suspension of anatase withnano-leaf morphology. On the other hand, hydrolysis under closed hydrothermal condition at 100 °C and120 °C gives mainly rutile. A mixture of rutile and anatase was obtained by hydrothermal hydrolysis at 150 °C,while at 180 °C the main phase was anatase.

Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.

1. Introduction

Titanium dioxide exists in three main polymorphic forms: rutile,anatase and brookite (Khataee and Mansoori, 2012). Rutile and ana-tase are the most commonly synthesized phases; rutile is a whitepigment used in paints and cosmetic products, while anatase is gen-erally used as a photocatalyst in solar cells and in the production ofhydrogen and as a sensor (Gambogi, 2009; Khataee and Mansoori,2012). The growth use of TiO2 in many technological applicationswill strongly influence the titanium metal demand for the foresee-able future (Gambogi, 2009, 2010). Based on the announced capacityexpansion plans by 2015, world-wide capacities would be expectedto reach 350,000 t/yr (Gambogi, 2010).

As the sources of high-grade titanic minerals decrease worldwide,many investigators have investigated extractionof titanium from ilmenite(Akhgar et al., 2012; Manhique et al., 2011; Zhang et al., 2011a,b).The extraction methods can be summarized into two categories; py-rometallurgical and hydrometallurgical routes. In the pyrometallur-gical route, ilmenite is partially reduced by anthracite at elevatedtemperature to obtain slag with high titanium (Akhgar et al., 2012;Mahmoud and Georges, 1997; Manhique et al., 2011; Mohanty and

aculty of Science, Suez Canalx: +20 64 322381.

Published by Elsevier B.V. All rights

Smith, 1993; Zhang et al., 2011a). In the hydrometallurgical process,sulfuric acid (Liang et al., 2005; Sasikumar et al., 2004) or hydrochloricacid (Ogasawara and Veloso de Araiyo, 2000; Van Dyk et al., 2002) isused as a leachant. The leaching reactions can be carried out under nor-mal atmosphere or under pressure (Ogasawara and Veloso de Araiyo,2000). The titanium acidic solution resulting from the hydrometallurgi-cal process is further purified and hydrolyzed to produce pure TiO2 (Haoet al., 2012; Mahmoud, 2012; Wu et al., 2011a).

In recent years, hydrometallurgical process has been activated andbecomemore commercially important due to its low energy require-ment compared to the conventional thermo- and electro-chemicalprocesses (Liu et al., 2006; van Vuuren, 2009). The main fascinatedadvantage of hydrothermal synthesis is the significant improvementin the chemical activity of the reactants (Mostafa et al., 2009a,b). Theparticle shape, size distribution and crystallinity of the final productcan be precisely controlled through adjusting the reaction parameterssuch as temperature, time, solvent and surfactant type (Mostafa et al.,2009a,b, 2012; van Vuuren, 2009). In Egypt, most of the titanium-bearing minerals belong to the low-grade ilmenite minerals. There aremany difficulties in utilizing such minerals due to the high content ofimpurities, especially iron. Therefore, it is important to develop a pro-duction process for upgrading the low titanium ilmenite.

In the present work, we utilize inexpensive available high iron con-tent ilmenite as a source of titanium for preparing titania by hydrother-mal method. Also, the effect of hydrolysis conditions on the formationand properties of TiO2 phases was also investigated.

The present investigation relates to a process for producing differentphases of titanium dioxide from low-grade ilmenite ore. The process

reserved.

TiOCl2+FeCl3

Ilmenite concentrate

Titanium Leaching HCl (20% V/V)

Solvent extraction with trioctylamine (TOA)

89N.Y. Mostafa et al. / Hydrometallurgy 139 (2013) 88–94

includes a novel combination of HCl leaching, solvent extraction ofiron and hydrothermal treatment to economically produce a highpurity grade titanium dioxide.

2. Materials and methods

2.1. Materials

A representative sample of 10 kg ilmenite ore from Abu Ghalagaregion, Red Sea, Egypt, was thoroughly mixed, crushed and ground to100%—75 μm. The material was obtained from a massive deposit ofprimary ilmenite–magnetite mineral rock. The chemical analysis ofthe ilmenite sample, as determined using X-ray fluorescence (XRF),is given in Table 1.

Chemicals of analytical grade were used for the extraction andpurification (hydrochloric acid HCl; 37% and nitric acid HNO3;98%). Trioctylamine (Merck) was used after dilution with kerosenefor solvent extraction of iron from ilmenite leachant. Double distilledwater was used during the work.

2.2. Titanium leaching and purification from raw ilmenite ore

The acid leaching process of ilmenite was carried out using a250 cm3 three necked glass reactor provided with a reflux condenserand a mechanical agitator. First, a 200 cm3 of 20% v/v hydrochloricacid was heated to 70 °C in the reactor using a thermostatically con-trolled glycerol/water bath. Then, 20 g from ilmenite concentratewas added and themixture was stirred at 400 rpm for 3 h. The slurrywas filtered off and the un-dissolved solids was thoroughly washedwith 10 ml 3% HCl; then the wash liquor was added to the first fil-trate. The percent of titanium extraction was calculated by the fol-lowing formula:

TFC %ð Þ ¼ V � CTi

Gt � PTi

� �� 100

where TFC(%) is the titanium fractional conversion, CTi is the titani-um concentration in the extract (g/l), V is the volume of extract (li-ters), Gt is the total mass of the ore (g) and PTi is the titanium massfraction in the ore.

The ilmenite leachant was diluted with distilled water and 20 cm3

nitric acid was added. The solution was boiled for 15 min to achievethe oxidation of Fe2+ to Fe3+ ions. The iron was then separated by sol-vent extraction using trioctylamine (TOA) (Abdel-Aal et al., 2010).Equal volumes (250 cm3 each) of 30% v/v TOA in kerosene and ilmeniteleachant were mixed at room temperature using a magnetic stirrer at400 rpm for 30 min. The loaded organic phase in the mixture wasthen separated by settling and the contained iron was stripped byadding slightly acidified water. The fresh organic solution was usedagain for purification of the ilmenite leachant. This purificationprocedure was repeated three times.

Table 1Chemical composition of concentrated ilmenite concentrate.

Component Wt.%

TiO2 41.95Fe (total) 37.68Fe2O3 (equivalent) 53.83FeO 37.71Fe2O3 11.92SiO2 2.18CaO 0.06MgO 0.83Al2O3 1.07MnO 0.27V2O5 0.025

2.3. Hydrolysis and synthetic TiO2

The above concentrated titanyl chloride solution obtained after puri-fication was used in the hydrolysis process. A 60 ml titanium leachantwas heated at different temperatures in 80 ml stainless steel autoclavevessel with Teflon inner container for 6 h. The white product was sepa-rated by centrifugation and washed with distilled water and dried at100 °C for 24 h. For the open hydrolysis process, 40 ml of the purifiedilmenite leachant was added to 200 ml boiling water and the mixturewas stirred at boiling condition for 6 h. The contained titaniumwas pre-cipitated as finewhite particles of hydrated TiO2 suspended in the solu-tion. This TiO2 suspension was found to be stable over several months.The percent of titania hydrolysis yield was calculated by the followingformula:

Y %ð Þ ¼ WtCTi � 1:669 � V

� �� 100

where Y(%) is the hydrolysis yield of titania, Wt is the weight ofobtained titania (TiO2), CTi is the titanium concentration in the extract(g/l), and V is the volume of the extract (liters). Fig. 1 shows a schematicflow sheet of ilmenite ore leaching with hydrochloric acid and purifica-tion with solvent extraction and hydrolysis to produce pure TiO2.

2.4. Characterization

Chemical analysis of the ore was carried out by X-ray fluorescence(XRF) using AXIOS, Wavelength Dispersive-XRF Sequential Spec-trometer. Chemical analysis of Fe ions in aqueous solutions was car-ried out using Atomic Absorption Spectrometer Model Perken-Elmer3100. Titanium was determined spectrophotometrically by the hy-drogen peroxide method at wavelength 410 nm (Vogel, 1978). X-ray diffraction (XRD) patterns was obtained using an automated dif-fractometer (Philips type: PW1840), at a step size of 0.02°, scanningrate of 2° in 2θ/min, and a 2θ range from 4° to 80°. Semi-quantitativephase analysis was performed applying X'Pert HighScore Plus software.

TiOCl2

HydrothermalHydrolysis

AtmosphericHydrolysis

TiO2 TiO2

100ºC100ºC 120ºC 150ºC 180ºC

Fig. 1. A schematic flowsheet of the process for titanium dioxide (TiO2) production fromlow-grade ilmenite concentrate.

20 30 40 50 60 700

10

20

30

40

50

60

70

2θ (degree)

Inte

nsity

(cp

u)

I- Ilmenite, FeTiO3 (JCPDS # 71-1140)H-Hematite, Fe2O3 (JCPDS # 72-0469)

I

I

I II

I

I

I I II

HH

H H I H

Fig. 2. XRD pattern of ilmenite concentrate.

Table 3Open atmospheric and hydrothermal hydrolysis products of TiOCl2 solutions at differenttemperatures.

Temperature (°C) Time (hours) Yield (%) Main phase

100 (open atmosphere) 6 73 Anatase100 6 82 Rutile120 6 91 Rutile150 6 95 Anatase (41%) + rutile (59%)180 6 97 Anatase (81%) + rutile (19%)

90 N.Y. Mostafa et al. / Hydrometallurgy 139 (2013) 88–94

The morphology of the obtained titania was investigated usingscanning electron microscopy (SEM; JEOL, Model: JSM-5600, Japan.)equipped with secondary electron detector and energy dispersive X-ray analysis system (EDX). All samples were coated with gold. Theshape and particle size distribution were studied using transmissionelectron microscope (TEM) operated at 200 kV accelerating voltage(JTEM-1230, Japan, JEOL). The samples were prepared by making asuspension from the powder in distilled water using ultrasonic waterbath. Then a drop of the suspension was put into the carbon grid andleft to dry before examination.

RRA Hydrolysis at 150oC

R

R

R AAAA

R

AA= anataseR= rutile

Hydrolysis at 180oC

3. Results

3.1. Characterization of the ilmenite ore

The X-ray powder diffraction pattern of ilmenite ore is shown inFig. 2. As can seen from Fig. 2, XRD spectra of both ilmenite and he-matite are present. Although the major phase is ilmenite, chemicalanalysis showed that FeO concentration is 37.71 wt.% and Fe2O3 is11.92 wt.%, as shown in Table 1. Since the concentration of FeO is37.71 wt.%, it can be predicted that 82 wt.% of the ore is ilmenite.Semiquantitave phase analysis using X-ray diffraction (XRD) con-firmed the above results.

RHydrolysis at 100oC

R

RRR

RR

R

Hydrolysis at 120oC

R

R

RAAAA RR

R

3.2. Extraction and purification

The chemical analysis of the acidic solution produced from extrac-tion of 20 g ilmenite ore with 20% (V/V) HCl is given in Table 2. Analysisshowed that leachant contains 23.0 g/l titanium and 36.4 g/l iron.According to this, about 94.6% of titaniumpresent in the orewas succes-sively extracted after 3 h extraction at 70 °C.

After dilution and oxidation of Fe2+ to Fe3+, iron was separated bysolvent extraction for three times. The final purified ilmenite leachantis found to contain 12 g/l titanium and 0.02 g/l iron, as given inTable 3. The solvent extraction process successively removed nearly allof the iron.

Table 2Chemical analysis of leachant before and after purification.

Metal Conc. before purification (g/l) Conc. after purification (g/l)

Titanium 23 12Iron 36.4 0.02

3.3. Hydrolysis under hydrothermal conditions

Fig. 3 shows the XRD patterns of titanium dioxide produced byhydrothermal treatments for 6 h at 100 °C, 120 °C, 150 °C and 180 °C.All the hydrothermal hydrolysis products were crystalline, irrespectiveof the reaction temperature. Either rutile, anatase or a mixture ofthem is produced, depending on the reaction temperature. For sampleshydrolyzed hydrothermally at 100 °C and 120 °C, pure rutile phasewasobtained. It is interesting to note that raising the reaction temperaturefrom 100 °C to 120 °C increases both the crystallinity of rutile and thehydrolysis yield from 82% to 91%, as given in Table 3. On the otherhand, increasing the reaction temperature from 120 °C through 180 °Cresults in an increase in the relative amount of anatase to rutile. At150 °C, the presence of anatase became significant (Fig. 3), and at180 °C, anatase was the main phase with a trace amount of rutile.Table 3 shows the results obtained under different reaction conditionsand the corresponding hydrolysis yields. Under hydrothermal hydroly-sis, almost complete crystallization of TiO2 occurred at 180 °C after 6 hreaction time.

10 20 30 40 50 60 702Θ

RRR

R

RRR

R

Fig. 3. Powder XRD patterns of TiO2 prepared by hydrothermal treatments for 6 h at:(a) 100 °C, (b) 120 °C, 150 °C and (c) 180 °C (A = anatase; R = rutile).

91N.Y. Mostafa et al. / Hydrometallurgy 139 (2013) 88–94

Fig. 4 shows SEM micrographs and the corresponding EDX patternsof titania produced by hydrothermally hydrolysis at 100 °C and 150 °C.SEM micrographs reveal agglomerated particles of quasi-spheres andquite uniform in their overall morphology. The average particle size ofthe produced TiO2 is the largest at 100 °C. From EDX patterns, we cannotice that the hydrolyzed titanium residue contains no iron or chlorideas impurities.

Fig. 5 shows TEM micrographs of titania hydrothermally hydro-lyzed at different temperatures. Inspecting the micrograph at100 °C, the obtained TiO2 consists predominantly of densely packedaggregates of nanocrystals without any defined shape (Fig. 5a). At120 °C the aggregates take the rod-like morphology (Fig. 5b). By in-creasing the hydrolysis temperature to 150 °C (Fig. 5c) and to 180 °C(Fig. 5d) the rod-like morphology became clear with an increase incrystallite size. From Fig. 5c and d, an average rod length of 100 nmcould be estimated with an average diameter of about 20 nm.

3.4. Hydrolysis under open atmosphere

Fig. 6 shows XRD pattern of titanium dioxide prepared by hydro-lysis of the purified ilmenite leachant under open atmospheric pres-sure at 100 °C. Under this condition only anatase was detected as themain hydrolysis products. However, the hydrolysis yield was verylow (75%) in comparison with those of hydrothermal hydrolysis(82–97%), as given in Table 3. Fig. 7 shows the SEM and EDX of titanium

(a) (b

(c) (d

Cou

nts

Fig. 4. SEM and EDX of TiO2 produced from hydrothermal hydrolysis of TiOCl2 sol

dioxide prepared by hydrolysis of the purified ilmenite leachant at openatmospheric pressure at 100 °C. The SEM micrograph reveals cotton-like morphology consisting of nanoparticle aggregates. EDX analysisshowed that the hydrolysis products contain traces of chloride duethe adsorption of some TiOCl2 on titanium nanoparticles. The corre-sponding TEM andHRTEMmicrographs of the same sample are givenin Fig. 8. Inspecting these micrographs revealed that anatase nano-structures form distinct leaf-like morphology nanocrystals. At highmagnification it is possible to see the ‘leafy’ morphology. These‘leaves’ dispersing evenly in solution so that it is stable more than6 months at room temperature. In order to separate TiO2 we centri-fuged at 13000 rpm for 20 min.

4. Discussion

Low-grade ilmenite is becoming increasingly important due tothe rapid depletion of natural rutile (Zhang et al., 2011a,b). Manyprocesses are commercially used or proposed to upgrade ilmeniteto synthetic TiO2 phases (Lakshmanan and Sridhar, 2002; Lakshmananet al., 2004, 2005). Hydrometallurgical leach processes in combinationwith solvent extraction and hydrothermal hydrolysis are advantageousin processing abundant low-grade ilmenite ores (Lakshmanan et al.,2004). These processes could be controlled to produce sufficientlyhigh purity TiO2 products for awide range of applications. In the presentinvestigation titanium was extracted from low-grade ilmenite ore

)

)

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

keV

001

0

100

200

300

400

500

600

700

800

900

1000

OK

aT

iLl

TiL

a

TiK

a

TiK

b

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

keV

003

0

100

200

300

400

500

600

700

800

900

1000

Cou

nts

OK

aT

iLl

TiL

a

TiK

a

TiK

b

ution at different temperatures; (a) and (b); 100 °C, and (c) and (d); 150 °C.

Fig. 5. TEM of TiO2 produced from hydrothermal hydrolysis of TiOCl2 solution at (a) 100 °C, (b) 120 °C, (c) 150 °C and (d) 180 °C.

92 N.Y. Mostafa et al. / Hydrometallurgy 139 (2013) 88–94

utilizing concentrated hydrochloric acid. Titanium, as well as the ironcontained in ilmenite ore, was dissolved. The ilmenite leaching reactioncould be described by the following chemical reaction (Zhang et al.,2011a):

FeTiO3 þ 2HCl→Fe2þ þ TiO

2þ þ 2Cl− þ 2OH

−:

ConcentratedHCl extracted at least 94% of the titanium in the ilmen-ite ore. After dilution and oxidation of Fe2+ to Fe3+, iron was separatedby solvent extraction. This step prevented the contamination of the fi-nally produced TiO2 (Berkovich, 1975). Direct hydrolysis of the purified

A= anatase

AAAA

A

10 20 30 40 50 60 702Θ

Fig. 6.Powder XRDpattern of TiO2 prepared by openhydrolysis at atmospheric pressure at100 °C.

acidic TiOCl2 solution allows recovering TiO2, according to the followingreaction (Zhang et al., 2011a):

TiOCl2 þ H2O→TiO2 þ 2HCl:

Rutile and anatase are the most commonly used polymorphs ofTiO2. Anatase and rutile are well known photocatalysts with anatasegenerally showing much higher photocatalytic activity (Kominamiet al., 2002; Schuisky et al., 2000). Rutile is commonly used as awhite pigment in paints (Braun et al., 1992). At ambient temperatureand pressure, rutile has higher thermodynamic stability as comparedto anatase (Coronado et al., 2008; Reddy et al., 2004). However, atrelatively low temperatures, nanocrystalline form of anatase TiO2 hashigher kinetic stability (Coronado et al., 2008). Anatase is transformedinto rutile phase upon either increasing the particle size or heating toa high temperature (Reddy et al., 2004). In sol–gel and precipitationprocess, amorphous titanium precursors are formed as intermediatephase (Zhang et al., 2000). The transformation of the amorphous to an-atase or rutile phase under hydrothermal condition is influenced by thesynthesis conditions, such as temperature, pressure and impurities(Akhgar et al., 2012; Jagtap et al., 2005). Some additives such as alumi-na, zirconia and sulfate ions stabilized the anatase phase (Calleja et al.,2008; Cheng et al., 2003; Xiong et al., 1998). Chloride ions have an accel-erating effect on the anatase to rutile phase transformation (Coronadoet al., 2008).

In the present study, ultrafine nanoparticles of anatase were pro-duced by homogeneous hydrolysis of acidic TiOCl2 solution underopen atmospheric pressure at 100 °C. The EDX pattern of TiO2 pro-duced from open hydrolysis contains Cl as impurity. This is becausethe precipitated nano-TiO2 with leafy morphology in this case has a

(a) (b)

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00keV

0

80

160

240

320

400

480

560

640

720

800

Cou

nts

CK

aO

Ka

ClK

aC

lKb

TiL

lT

iLa

TiK

a

TiK

b

Fig. 7. (a); SEM and (b); EDX of TiO2 produced from open hydrolysis of TiOCl2 solution at 100 °C.

93N.Y. Mostafa et al. / Hydrometallurgy 139 (2013) 88–94

hydrated surface which can adsorb Cl− ions (Wu et al., 2011b; Xionget al., 2013; Yasir et al., 2001). Hwu et al. (1997) found that anatasewas thermodynamically stable for sizes b11 nm, and rutile was sta-ble for sizes N35 nm. This may explain the stability of nano-leafy an-atase formed at open hydrolysis. The stability of nano-sized anatasemay be due to the large distortions existed in samples with smallerparticle size (Hwu et al., 1997).

The possibility of controlling the crystalline structure and morphol-ogy of TiO2 nanoparticles is a current topic of great interest (Testinoet al., 2007). The hydrothermal method is widely used in the synthesis

Fig. 8. (a); TEM and (b); HRTEM of TiO2 produced from open hydrolysis of TiOCl2 solutionat 100 °C.

of nanostructure materials (Heiba et al., 2013; Mostafa et al., 2012,2013; Xie and Shang, 2007,). The hydrothermal synthesis is performedunder relatively low temperatures, compared to those methods involv-ing calcination and sintering (Mostafa et al., 2012, 2013). During hydro-thermal processing the particles remain in solution throughout theprocess. This prevents aggregation and agglomeration of the particles(Heiba et al., 2013). The shape, size distribution and crystallinity of thefinal product can be precisely controlled through adjusting the reactionparameters such as temperature, time, solvent type, surfactant type andprecursor type (Mostafa et al., 2013; Testino et al., 2007). Therefore theuse of hydrothermal synthesis to produce a tailored TiO2 form leachedand purified TiOCl2 is advantageous.

In the present study, a variety of TiO2 particles with different phasecompositions, sizes, and shapes have been obtained from acidic TiOCl2solutions by systematically changing the temperature of the hydrother-mal hydrolysis. For samples hydrothermally hydrolyzed at 100 °C and120 °C, pure rutile phase was formed. Many investigators (Gribb andBanfield, 1997; Testino et al., 2007; Zhang and Banfield, 1998) reportedthat strong acidic conditions and crystal growth favor rutile formation.Zhang and Banfield (1998) found that the prepared TiO2 nanoparticleshad anatase and/or brookite structures, which transformed to rutileafter reaching a certain particle size. Once rutile was formed, it grewmuch faster than anatase. Andersson et al. (2002) found in hydrother-mal synthesis of TiO2 the acid type plays a great role. If hydrochloricacid was used, the rutile formed, and if nitric acid was used, anataseformed (Andersson et al., 2002).

Increasing the reaction temperature from 120 °C through 180 °Cresults in an increase in the relative amount of anatase to rutile. At150 °C, the presence of anatase became significant, and at 180 °C, ana-tase was themain phase. Synthesis of anatase nanoparticles by solutionprocessingmethod has been reported for a large variety of experimentalconditions (Oskam et al., 2003; Wu et al., 2002; Zaban et al., 2000).Phase-pure anatase nanoparticles with diameters ranging from 6 to30 nm are generally prepared from titanium (IV) isopropoxide andacetic acid (Zaban et al., 2000). Wu et al. (2002) reported that largeranatase particles are difficult to synthesize due to transformation torutile upon increasing treatment times and/or temperature. However,in the present investigation, anatase rods were obtained by hydrother-mal treatments at 150 and 180 °C. These rods were over 100 nm inlength and 20 nm in diameter.

5. Conclusions

A method is proposed for titanium extraction from low-grade il-menite ore utilizing concentrated hydrochloric acid combined with

94 N.Y. Mostafa et al. / Hydrometallurgy 139 (2013) 88–94

solvent extraction process for Fe3+separation. The extracted and pu-rified acidic TiOCl2 solution was hydrolyzed to produce differentphases of TiO2. The hydrolysis under open atmosphere at 100 °C pro-duces nanosized, well-dispersed particles of anatase phase, while,under hydrothermal conditions at the same temperature producesrutile phase. Generally a mixture of anatase and rutile results fromthe hydrolysis, with the percent of the former phase increased byraising the hydrolysis temperature. The hydrothermal hydrolysis at180 °C was almost complete after 6 h curing without adding anymineralizer. Hydrothermal process has proven to be effective to con-trol the phase of the obtained TiO2. The advantage to this process isthat ilmenite may be used as the starting ore, which is relativelyplentiful, particularly when compared to the diminishing reservesof rutile.

References

Abdel-Aal, E.A., Mahmoud, M.H.H., Sanad, M.M.S., Criscuoli, A., Figoli, A., Drioli, E., 2010.Membrane contactor as a novel technique for separation of iron ions from ilmeniteleachant. Int. J. Miner. Process. 96, 62–69.

Akhgar, B.N., Pazouki, M., Ranjbar, M., Hosseinnia, A., Salarian, R., 2012. Application ofTaguchi method for optimization of synthetic rutile nano powder preparation fromilmenite concentrate. Chem. Eng. Res. Des. 90, 220–228.

Andersson, M., Osterlund, l., Ljungstrom, S., Palmqvist, A., 2002. Preparation ofnanosize anatase and rutile TiO2 by hydrothermal treatment of microemulsionsand their activity for photocatalytic wet oxidation of phenol. J. Phys. Chem. B106, 10674–10679.

Berkovich, S.A., 1975. Recovery of titanium from ores. US Patent, 3903239.Braun, J.H., Baidins, A., Marganski, R.E., 1992. TiO2 pigment technology: a review. Prog.

Org. Coat. 20, 105–138.Calleja, G., Serrano, D.P., Sanz, R., Pizarro, P., 2008. Mesostructured SiO2-doped TiO2 with

enhanced thermal stability prepared by a soft-templating sol–gel route. Micropor.Mesopor. Mater. 111, 429–440.

Cheng, P., Zheng, M., Jin, Y., Huang, Q., Gu, M., 2003. Preparation and characteriza-tion of silica-doped titania photocatalyst through sol–gel method. Mater. Lett.57, 2989–2994.

Coronado, D.R., Gattorno, G.R., Espinosa-Pesqueira, M.E., Cab, C., De Coss, R., Oskam, G.,2008. Phase-pure TiO2 nanoparticles: anatase, brookite and rutile. Nanotechnology19, 145605.

Gambogi, J., 2009. Titanium mineral concentrates. US Geological Survery 172–173.Gambogi, J., 2010. Titanium and titanium dioxide, mineral commodity summaries. US

Geological Surv. 176–178.Gribb, A.A., Banfield, J.F., 1997. Particle size effects on transformation kinetics and phase

stability in nanocrystalline. TiO2. Am. Mineral. 82, 717–728.Hao, X., Lü, l., Liang, B., Li, C., Wu, P., Wang, J., 2012. Solvent extraction of titanium from

the simulated ilmenite sulfuric acid leachate by trialkylphosphine oxide. Hydromet-allurgy 113–114, 185–191.

Heiba, Z.K., Mostafa, N.Y., Mohamed, M.B., El-Harthy, H., 2013. Structural and magneticproperties of ferromagnetic nano-sized (Ni1 − xCox)0.85Se prepared by simple hydro-thermal method. Mater. Lett. 93, 15–117.

Hwu, Y., Yao, Y.D., Cheng, N.F., Tung, C.Y., Lin, H.M., 1997. X-ray absorption of nanocrystalTiO2. Nanostruct. Mater. 9, 355–358.

Jagtap, N., Bhagwat, M., Awati, P., Ramaswamy, V., 2005. Characterization of nano-crystalline anatase titania: an in situ HTXRD study. Thermochem. Acta 427,37–41.

Khataee, A., Mansoori, G.A., 2012. Nanostructured Titanium Dioxide MaterialsProperties, Preparation and Applications. World Scientific Publishing Co.,Pte. LtD.

Kominami, H., Murukami, S.Y., Kato, J.I., Ohtani, B., 2002. Correlation between some phys-ical properties of titanium dioxide particles and their photocatalytic activity for someprobe reactions in aqueous systems. J. Phys. Chem. B 106, 10501–10507.

Lakshmanan, V.I., Sridhar, R., 2002.Methods for separation of titanium from ore, Canadianpatent 2289967.

Lakshmanan, V.I., Sridhar, R., Hains, D.H., 2004. A novel hydrometallurgical process forvery high purity TiO2 production. Proceedings of 17th Industrial Minerals Interna-tional Congress. Cambrian Printer, Aberystwyth, UK, pp. 92–95.

Lakshmanan, V.I., Sridhar, R., Harris, B.G., Puvvada, G., 2005. Process for the recovery of ti-tanium in mixed chloride media. US patent 0142051 A1.

Liang, B., Li, C., Zhang, C.G., Zhang, Y.K., 2005. Leaching kinetics of Panzhihua ilmenite insulfuric acid. Hydrometallurgy 76, 173–179.

Liu, Y.M., Qi, T., Chu, J.l., Tong, Q., Zhang, Y., 2006. Decomposition of ilmenite by con-centrated KOH solution under atmospheric pressure. Int. J. Miner. Process. 81,79–84.

Mahmoud, M.H.H., 2012. Effective separation of iron from titanium by transport throughTOA supported liquid membrane. Sep. Purif. Technol. 84, 63–71.

Mahmoud, Y.D., Georges, J.K., 1997. Processing titanium and lithium for reduced-cost ap-plication. JOM 49, 20–27.

Manhique, A.J., Focke, W.W., Madivate, C., 2011. Titania recovery from low-gradetitanoferrous minerals. Hydrometallurgy 109, 230–236.

Mohanty, S.P., Smith, K.A., 1993. Alkali metal catalysis of carbothermic reaction of ilmen-ite. Trans. Inst. Min. Metall. 102, C163–C173.

Mostafa, N.Y., Kishar, E.A., Abo-El-Enein, S.A., 2009a. FTIR study and cation exchange ca-pacity of Fe3+- and Mg2+-substituted calcium silicate hydrates. J. Alloys Compd.473, 538–542.

Mostafa, N.Y., Shaltout, A.A., Omar, H., Abo-El-Enein, S.A., 2009b. Hydrothermal synthesisand characterization of aluminium and sulfate substituted 1.1 nm tobermorites.J. Alloys Compd. 467, 332–337.

Mostafa, N.Y., Hessien, M.M., Shaltout, A.A., 2012. Hydrothermal synthesis and character-izations of Ti substituted Mn-ferrites. J. Alloys Compd. 529, 29–33.

Mostafa, N.Y., Zaki, Z.I., Heiba, Z.K., 2013. Structural and magnetic properties of cad-mium substituted manganese ferrites prepared by hydrothermal route. J. Magn.Magn. Mater. 329, 71–76.

Ogasawara, T., Veloso de Araiyo, R.V., 2000. Hydrochloric acid leaching of a pre-reducedBrazilian ilmenite concentrate in an autoclave. Hydrometallurgy 56, 203–219.

Oskam, G., Nellore, A., Penn, R.l., Searson, P., 2003. The growth kinetics of TiO2

nanoparticles from titanium (IV) alkoxide at high water/titanium ratio. J. Phys.Chem. B 107, 1734–1738.

Reddy, K.M., Guin, D., Manorama, S.V., 2004. Selective synthesis of nanosized TiO2 by hy-drothermal route: characterization, structure property relation, and photochemicalapplication. J. Mater. Res. 19, 2567–2575.

Sasikumar, C., Rao, D.S., Srikanth, S., Ravikumar, B., Mukhopadhyay, N.K., Mehrotra, S.P.,2004. Effect of mechanical activation on the kinetics of sulfuric acid leaching ofbeach sand ilmenite from Orissa, India. Hydrometallurgy 75, 19–204.

Schuisky, M., Harsta, A., Aidla, A., Kukli, K., Keisler, A., 2000. Atomic layer chemical vapordeposition of TiO2 low temperature epitaxy of rutile and anatase. J. Electrochem. Soc.147, 3319–3325.

Testino, A., Bellobono, I.R., Buscaglia, V., Canevali, C., D'Arienzo, M., Polizzi, S., Scotti, R.,Morazzoni, F., 2007. Optimizing the photocatalytic properties of hydrothermal TiO2

by the control of phase composition and particlemorphology. A Systematic approach.J. Am. Chem. Soc. 129, 3564–3575.

Van Dyk, J.P., Vegter, N.M., Chris Pistorius, P., 2002. Kinetics of ilmenite dissolution inhydrochloric acid. Hydrometallurgy 65, 31–36.

van Vuuren, D.S., 2009. A critical evaluation of processes to produce primary titanium.J.The Southern African Institute Mining Metallurgy 109, 455–461.

Vogel, A.I., 1978. A Textbook of Quantitative Inorganic Analysis, 4th ed. Longman, London.Wu, M., Lin, G., Chen, D., Wang, G., He, D., Feng, S., Xu, R., 2002. Sol hydrothermal synthe-

sis and hydrothermally structural evolution of nanocrystal titanium dioxide. Chem.Mater. 14, 1974–1980.

Wu, F., Li, X., Wang, Z., Wu, l., Guo, H., Xiong, X., Zhang, X., Wang, X., 2011a. Hydrogenperoxide leaching of hydrolyzed titania residue prepared from mechanically ac-tivated Panzhihua ilmenite leached by hydrochloric acid. Int. J. Miner. Process.98, 106–112.

Wu, F.X., Wang, Z.X., Li, X.H.,Wu, l., Wang, X.J., Zhang, X.P., Wang, Z.G., 2011b. Preparationand characterization of spinel Li4Ti5O12 anode material from industrial titanyl sulfatesolution. J. Alloys Compd. 509, 596–601.

Xie, R., Shang, J.K., 2007. Morphological control in solvothermal synthesis of titaniumoxide. J. Mater. Sci. 42, 6583–6589.

Xiong, G., Wang, X., Lu, l., Yang, X., Xu, Y., 1998. Preparation and characterization ofAl2O3–TiO2 composite oxide nanocrystals. J. Solid State Chem. 141, 70–77.

Xiong, X.,Wang, Z.,Wu, F., Li, X., Guo,H., 2013. Preparation of TiO2 from ilmenite using sul-furic acid decomposition of the titania residue combinedwith separation of Fe3+withEDTA during hydrolysis. Adv. Powder Technol. 24, 60–67.

Yasir, V.A., Das, P.N.M., Yusuff, K.K.M., 2001. Preparation of high surface area TiO2

(anatase) by thermal hydrolysis of titanyl sulphate solution. Int. J. Inorg. Mater. 3,593–596.

Zaban, A., Aruna, S.T., Tirosh, B.A., Gregg, B.A., Mastai, Y., 2000. The effect of the preparationcondition of TiO2 colloids on their surface structures. J. Phys. Chem. B 104, 4130–4133.

Zhang, H., Banfield, J.F., 1998. Thermodynamic analysis of phase stability of nanocrystal-line titania. J. Mater. Chem. 8, 2073–2076.

Zhang, Q., Gao, l., Guo, J., 2000. Effect of hydrolysis conditions on morphology and crystal-lization of nanosized TiO2 powder. J. Eur. Ceram. Soc. 20, 2153–2158.

Zhang, l., Hu, H., Liao, Z., Chen, Q., Tan, J., 2011a. Hydrochloric acid leaching behav-ior of different treated Panxi ilmenite concentrations. Hydrometallurgy 107,40–47.

Zhang, W., Zhu, Z., Cheng, C.Y., 2011b. A literature review of titanium metallurgical pro-cesses. Hydrometallurgy 108, 177–188.