- Email: [email protected]
Preparation of nanosized synthetic rutile from ilmenite concentrate
Minerals Engineering 23 (2010) 587–589
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Technical Note
Preparation of nanosized synthetic rutile from ilmenite concentrate B.N. Akhgar a, M. Pazouki b,*, M. Ranjbar a, A. Hosseinnia b, M. Keyanpour-Rad b a b
Department of Mineral Processing, Engineering Faculty, Shahid Bahonar University, Kerman, Iran Materials and Energy Research Center, MeshkinDasht, Karaj, Iran
a r t i c l e
i n f o
Article history: Received 15 October 2009 Accepted 19 January 2010 Available online 12 February 2010 Keywords: Oxide ores Industrial minerals Mineral processing Particle size Leaching
a b s t r a c t In this paper, the preparation of nanosized synthetic rutile by reductive hydrochloric acid leaching of mechanically activated ilmenite concentrate (FeTiO3) is discussed. X-ray fluorescence analysis of the nanosized rutile which forms by rapid hydrolysis of dissolved titanium indicates that the powder contains 91.1% TiO2, 1.3% Fe2O3, 6.3% SiO2. The presence of the rutile phase is confirmed by X-ray diffractometry and the sizes of particles are measured by transmission electron microscopy to be less than 100 nm. The photocatalytic activity of nanosized rutile is observed by the decomposition of methylene blue. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Although TiO2 nanopowder is a useful photocatalyst, the search for new material in heterogeneous photocatalysis, Fe-doped TiO2 nanopowders and nanostructured TiO2 composites continues to be of interest (Javio et al., 1999). At present, rutile or titanium-rich slag is used mostly to make TiO2 pigments by the chlorination route. Several methods are used for the preparation of rutile from ilmenite concentrate (Li et al., 2008; Mahmoud et al., 2004). In recent years, the influence of mechanical activation on the dissolution of milled ilmenite has attracted the attention of many researchers (Li et al., 2007, 2008). The aim of this research was to prepare nanosized rutile as a final product from ilmenite concentrate using a process of mechanical activation and a reductive hydrochloric acid leach. 2. Experimental The ilmenite concentrate was screened and the 75 lm material retained for mechanical activation using a planetary ball mill with a rotation speed of 250 rpm and spin rate of 480 rpm. The milling cells were filled with 20 mm diameter steel balls and with an ore/ball mass ratio of 1:20. Leaching experiments were carried out under optimized conditions as determined from previous investigations (Mahmoud et al.,
* Corresponding author. Tel.: +98 261 6280036; fax: +98 261 6280030. E-mail addresses: [email protected], [email protected] (M. Pazouki). 0892-6875/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2010.01.007
2004; Li et al., 2008). The samples were leached in a 500 ml glass reactor equipped with a reflux condenser. A certain volume of 20% hydrochloric acid solution was heated to 110 °C in a thermostatically controlled paraffin bath. The milled powder was added to the reactor such that the ilmenite to hydrochloric acid mass ratio was 1:9.55. After 20 min, the iron powder was added to the reactor such that the ilmenite to iron powder mass ratio was 1:0.075. Mechanical agitation was carried out with a magnetic stirrer at a stirring speed of 400 rpm. The slurry was allowed to precipitate and the leach liquor was separated from the leach residue after 6 h. Benzene was employed for dehydration of the leached residue followed by calcination of the powder at 400 °C (Hosseinnia et al., 2009). A schematic route of the process is outlined in Fig. 1. The photocatalytic performance was evaluated by decomposition of an aqueous 0.03 M solution of methylene blue (C16HNSCl3H2O). A mass of 0.02 g of the rutile nanopowder was suspended into the methylene blue solution and sonicated for 10–15 min followed by irradiation. The chemical composition of the ilmenite concentrate and the product was studied by X-ray fluorescence (XRF) spectrometry (ARL 8410 SEQUENTIAL). Measurement of the surface area was carried out with a standard BET surface area analyzer (Micrometrics Gimini III 2375, USA). X-ray diffractograms (XRD) of the products were obtained using a Philips DW3710 instrument applying Cu Ka radiation at 50 kV and 250 mA in the range of 15–75. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were carried out using a Zeiss Em 10c and Stereoscan 5390 Cambridge 1990 instrument, respectively.
588
B.N. Akhgar et al. / Minerals Engineering 23 (2010) 587–589
ilmenite leaching efficiency (Li et al., 2007). Therefore, it was decided to carry out the milling in an argon atmosphere. The X-ray diffraction pattern of calcined product showed sharp bands, which confirmed the formation of the highly crystalline rutile phase (Fig. 2). The BET surface area of the nanosized rutile was found to be 53.25 m2 g 1, which was similar to that obtained from TEM microscopy. The photocatalytic property of the nanosized rutile was examined by decomposition of methylene blue which discolored completely when irradiated by sunlight within 205 min. Fig. 3a depicts the SEM micrograph of the nanosized rutile particles. It was noticed from the TEM micrograph in Fig. 3b that the rutile particles have different crystalline shapes. The maximum particle size of the calcined product at 400 °C is found to be less than 100 nm (see Table 1).
Ilmenite
Sieving - 75 µm Mechanical Activation
Reductive Leaching Leach residue
Dehydration/ Calcination
4. Conclusion
Nanosized Synthetic Rutile More than 30% of the ilmenite concentrate was converted to nanosized rutile. The nanosized rutile contained 91.1% TiO2, 1.3% Fe2O3, 6.3% SiO2 and trace amounts of impurities such as CaO, MgO, and Al2O3. The XRD trace of the calcined product confirmed the formation of rutile phase. In addition, TEM analysis indicated that the particle size of the nanosized rutile particles was less than 100 nm. The nanosized rutile displayed photocatalytic activity through its discoloration of methylene blue.
Fig. 1. A schematic flow sheet of techniques used.
3. Results and discussion The ilmenite concentrate BET surface area increased from 0.66 m2 g 1 to 4.85 m2 g 1 after 40 min of milling. Phase changes occurred during milling in atmospheric conditions reduced the
* = Rutile
*
*
*
* * 15
25
35
*
*
45
* *
55
2Theta/degree Fig. 2. The XRD pattern of nanosized synthetic rutile.
Fig. 3. (a) SEM micrograph and (b) TEM image of product.
65
*
75
589
B.N. Akhgar et al. / Minerals Engineering 23 (2010) 587–589 Table 1 Chemical compositions of the ilmenite concentrate and nanosized synthetic rutile produced.
Ilmenite concentrate Nanosized synthetic rutile
Fe2O3%
TiO2%
SiO2%
MgO%
CaO%
Al2O3%
MnO%
44.60 1.30
32.90 91.10
5.90 6.30
3.60 0.07
2.20 0.02
2.50 0.26
2.10 0.02
References Hosseinnia, A., Keyanpour-Rad, M., Kazemzad, M., Pazouki, M., 2009. A novel approach for preparation of high crystalline anatase TiO2 nanopowder from the agglomerates. Powder Technol. 190, 390–392. Javio, J.A., Colon, G., Macias, M., Real, C., 1999. Iron-doped titania semiconductor powders prepared by a sol–gel method. Part 1: synthesis and characterization. Appl. Catal. A: Gen. 177, 111–120.
Li, C., Liang, B., Guo, L.H., 2007. Dissolution of mechanically activated Panzhihua ilmenite in dilute solutions of sulphuric acid. Hydrometallurgy 89, 1–10. Li, C., Liang, B., Wang, H., 2008. Preparation of rutile by hydrochloric acid leaching of mechanically activated Panzhihua ilmenite. Hydrometallurgy 91, 121– 129. Mahmoud, M.H.H., Afifi, A.A.I., Ibrahim, I.A., 2004. Reductive leaching of ilmenite ore in hydrochloric acid for preparation of rutile. Hydrometallurgy 73, 99– 109.
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Technical Note
Preparation of nanosized synthetic rutile from ilmenite concentrate B.N. Akhgar a, M. Pazouki b,*, M. Ranjbar a, A. Hosseinnia b, M. Keyanpour-Rad b a b
Department of Mineral Processing, Engineering Faculty, Shahid Bahonar University, Kerman, Iran Materials and Energy Research Center, MeshkinDasht, Karaj, Iran
a r t i c l e
i n f o
Article history: Received 15 October 2009 Accepted 19 January 2010 Available online 12 February 2010 Keywords: Oxide ores Industrial minerals Mineral processing Particle size Leaching
a b s t r a c t In this paper, the preparation of nanosized synthetic rutile by reductive hydrochloric acid leaching of mechanically activated ilmenite concentrate (FeTiO3) is discussed. X-ray fluorescence analysis of the nanosized rutile which forms by rapid hydrolysis of dissolved titanium indicates that the powder contains 91.1% TiO2, 1.3% Fe2O3, 6.3% SiO2. The presence of the rutile phase is confirmed by X-ray diffractometry and the sizes of particles are measured by transmission electron microscopy to be less than 100 nm. The photocatalytic activity of nanosized rutile is observed by the decomposition of methylene blue. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Although TiO2 nanopowder is a useful photocatalyst, the search for new material in heterogeneous photocatalysis, Fe-doped TiO2 nanopowders and nanostructured TiO2 composites continues to be of interest (Javio et al., 1999). At present, rutile or titanium-rich slag is used mostly to make TiO2 pigments by the chlorination route. Several methods are used for the preparation of rutile from ilmenite concentrate (Li et al., 2008; Mahmoud et al., 2004). In recent years, the influence of mechanical activation on the dissolution of milled ilmenite has attracted the attention of many researchers (Li et al., 2007, 2008). The aim of this research was to prepare nanosized rutile as a final product from ilmenite concentrate using a process of mechanical activation and a reductive hydrochloric acid leach. 2. Experimental The ilmenite concentrate was screened and the 75 lm material retained for mechanical activation using a planetary ball mill with a rotation speed of 250 rpm and spin rate of 480 rpm. The milling cells were filled with 20 mm diameter steel balls and with an ore/ball mass ratio of 1:20. Leaching experiments were carried out under optimized conditions as determined from previous investigations (Mahmoud et al.,
* Corresponding author. Tel.: +98 261 6280036; fax: +98 261 6280030. E-mail addresses: [email protected], [email protected] (M. Pazouki). 0892-6875/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2010.01.007
2004; Li et al., 2008). The samples were leached in a 500 ml glass reactor equipped with a reflux condenser. A certain volume of 20% hydrochloric acid solution was heated to 110 °C in a thermostatically controlled paraffin bath. The milled powder was added to the reactor such that the ilmenite to hydrochloric acid mass ratio was 1:9.55. After 20 min, the iron powder was added to the reactor such that the ilmenite to iron powder mass ratio was 1:0.075. Mechanical agitation was carried out with a magnetic stirrer at a stirring speed of 400 rpm. The slurry was allowed to precipitate and the leach liquor was separated from the leach residue after 6 h. Benzene was employed for dehydration of the leached residue followed by calcination of the powder at 400 °C (Hosseinnia et al., 2009). A schematic route of the process is outlined in Fig. 1. The photocatalytic performance was evaluated by decomposition of an aqueous 0.03 M solution of methylene blue (C16HNSCl3H2O). A mass of 0.02 g of the rutile nanopowder was suspended into the methylene blue solution and sonicated for 10–15 min followed by irradiation. The chemical composition of the ilmenite concentrate and the product was studied by X-ray fluorescence (XRF) spectrometry (ARL 8410 SEQUENTIAL). Measurement of the surface area was carried out with a standard BET surface area analyzer (Micrometrics Gimini III 2375, USA). X-ray diffractograms (XRD) of the products were obtained using a Philips DW3710 instrument applying Cu Ka radiation at 50 kV and 250 mA in the range of 15–75. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were carried out using a Zeiss Em 10c and Stereoscan 5390 Cambridge 1990 instrument, respectively.
588
B.N. Akhgar et al. / Minerals Engineering 23 (2010) 587–589
ilmenite leaching efficiency (Li et al., 2007). Therefore, it was decided to carry out the milling in an argon atmosphere. The X-ray diffraction pattern of calcined product showed sharp bands, which confirmed the formation of the highly crystalline rutile phase (Fig. 2). The BET surface area of the nanosized rutile was found to be 53.25 m2 g 1, which was similar to that obtained from TEM microscopy. The photocatalytic property of the nanosized rutile was examined by decomposition of methylene blue which discolored completely when irradiated by sunlight within 205 min. Fig. 3a depicts the SEM micrograph of the nanosized rutile particles. It was noticed from the TEM micrograph in Fig. 3b that the rutile particles have different crystalline shapes. The maximum particle size of the calcined product at 400 °C is found to be less than 100 nm (see Table 1).
Ilmenite
Sieving - 75 µm Mechanical Activation
Reductive Leaching Leach residue
Dehydration/ Calcination
4. Conclusion
Nanosized Synthetic Rutile More than 30% of the ilmenite concentrate was converted to nanosized rutile. The nanosized rutile contained 91.1% TiO2, 1.3% Fe2O3, 6.3% SiO2 and trace amounts of impurities such as CaO, MgO, and Al2O3. The XRD trace of the calcined product confirmed the formation of rutile phase. In addition, TEM analysis indicated that the particle size of the nanosized rutile particles was less than 100 nm. The nanosized rutile displayed photocatalytic activity through its discoloration of methylene blue.
Fig. 1. A schematic flow sheet of techniques used.
3. Results and discussion The ilmenite concentrate BET surface area increased from 0.66 m2 g 1 to 4.85 m2 g 1 after 40 min of milling. Phase changes occurred during milling in atmospheric conditions reduced the
* = Rutile
*
*
*
* * 15
25
35
*
*
45
* *
55
2Theta/degree Fig. 2. The XRD pattern of nanosized synthetic rutile.
Fig. 3. (a) SEM micrograph and (b) TEM image of product.
65
*
75
589
B.N. Akhgar et al. / Minerals Engineering 23 (2010) 587–589 Table 1 Chemical compositions of the ilmenite concentrate and nanosized synthetic rutile produced.
Ilmenite concentrate Nanosized synthetic rutile
Fe2O3%
TiO2%
SiO2%
MgO%
CaO%
Al2O3%
MnO%
44.60 1.30
32.90 91.10
5.90 6.30
3.60 0.07
2.20 0.02
2.50 0.26
2.10 0.02
References Hosseinnia, A., Keyanpour-Rad, M., Kazemzad, M., Pazouki, M., 2009. A novel approach for preparation of high crystalline anatase TiO2 nanopowder from the agglomerates. Powder Technol. 190, 390–392. Javio, J.A., Colon, G., Macias, M., Real, C., 1999. Iron-doped titania semiconductor powders prepared by a sol–gel method. Part 1: synthesis and characterization. Appl. Catal. A: Gen. 177, 111–120.
Li, C., Liang, B., Guo, L.H., 2007. Dissolution of mechanically activated Panzhihua ilmenite in dilute solutions of sulphuric acid. Hydrometallurgy 89, 1–10. Li, C., Liang, B., Wang, H., 2008. Preparation of rutile by hydrochloric acid leaching of mechanically activated Panzhihua ilmenite. Hydrometallurgy 91, 121– 129. Mahmoud, M.H.H., Afifi, A.A.I., Ibrahim, I.A., 2004. Reductive leaching of ilmenite ore in hydrochloric acid for preparation of rutile. Hydrometallurgy 73, 99– 109.