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An investigation on the production of sodium metaborate dihydrate from ulexite by using trona and lime
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 5 8 3 3 e5 8 3 9
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An investigation on the production of sodium metaborate dihydrate from ulexite by using trona and lime Hakan Sert*, Hu¨seyin Yıldıran, Duygu Toscalı _ Department of Chemistry, Faculty of Science, Ege University, Bornova, 35100 Izmir, Turkey
article info
abstract
Article history:
In this study, it was investigated the optimum conditions (extraction temperature and
Received 16 August 2011
extraction period) for the production of sodium metaborate dihydrate (NaBO2.2H2O) by the
Received in revised form
reaction of ulexite (NaCaB5O9$8H2O) with trona (NaHCO3-Na2CO3$2H2O) and lime (CaO).
29 December 2011
The optimum extraction conditions were determined as 50 C and higher temperature; 6 h
Accepted 3 January 2012
and longer extraction time. The characterizations of the product (sodium metaborate
Available online 30 January 2012
dihydrate crystals) were performed by thermogravimetric (TG-DTG) and X-ray diffraction (XRD) analyses. In addition, the percent purity of the product was found to be 96% by using
Keywords:
a conductometric method.
Ulexite
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Trona Lime Extraction of boron Sodium metaborate dihydrate
1.
Introduction
Boron is one of the most important strategic elements. It is never found free in nature but invariably occurs as the oxide B2O3, in combination with the oxides of other elements, forming borates of greater or lesser complexity. Boron compounds, which are used in many branches of industry, are produced from boron-containing ores. There are lots of naturally occurring boron minerals in the earth. It was reported that Turkey has 72.20% of the world’s boron reserves based on 851 million tons of B2O3 content in terms of total reserve basis. In spite of Turkey’s large boron reserves, the desired level for the preparation of final products having commercial value has not been reached yet. Because of this reason, it is very significant to enhance number of researches and studies on the production of boron compounds [1e4].
The borates of sodium and their derivatives are the main materials for chemical and metallurgy industries and also the medical sector. One of the boron derivatives, having commercial importance, is sodium metaborate (NaBO2). Sodium metaborate is commonly used in commercial production of sodium perborate tetrahydrate (NaBO3$4H2O), photographic-textile chemicals, detergents, cleaners and adhesives [2]. NaBO2 compounds can be classified according to water content inside as 4-hydrate, 2-hydrate and anhydrous [5]. The solubility of NaBO2 in water at 25 C is 28 g/100 g water [6]. The use of anhydrous NaBO2 in the energy field and the importance of both commercial borates class are growing gradually. There are some literatures on the preparation of the NaBH4 by using anhydrous sodium metaborate (NaBO2) as a starting material. NaBH4 is stable compared to other chemical hydrides and has large theoretical hydrogen content (10.9
* Corresponding author. Tel./fax: þ90 276 224 48 72. E-mail address: [email protected] (H. Sert). 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.01.012
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wt.%). Since hydrogen is a crucial alternative energy sources for the future, when it is compared with traditional fossil fuels causing global warming [7,8]. Recent studies on the preparation of NaBH4 by using NaBO2 as a starting compound have revealed the commercial significance of sodium metaborate in hydrogen energy investigations. Therefore, scientists have paid particular attention to produce NaBO2 and to study on the methods how to use NaBO2 as a boron source in the synthesis of NaBH4. Nowadays, some methods based on the production of NaBH4 from anhydrous NaBO2, such as, ball-milling synthesis [9e12] and thermal synthesis [13e17] have been developed. For example, Cooper et al. [18] investigated the electrochemical conversion of NaBO2 to NaBH4 at room temperature and ambient pressure. Kojima and Haga [13] reported that NaBH4 could be synthesized by annealing a mixture of NaBO2 with MgH2 or NaBO2 with Mg2Si under high H2 pressure. The reaction between NaBO2 and MgH2 was performed at 550 C under 7 MPa of hydrogen pressure for 2 h. Li et al. [15] developed a method to obtain sodium borohydride by a reaction of saline hydride with metaborate through ball-milling at room temperature. Although the NaBH4 conversion rate showed a deviation from its theoretical value, almost 100% of NaBH4 conversion rate was achieved when an excessive amount of MgH2 (1.25 times more than stoichiometric amount) was added. Zhang et al. proposed a method for the production of NaBH4 based on the solid-state reaction by calcining the 4NaHeNaBO2e2SiO2 ternary mixture. They were successes to produce NaBH4 under Ar, instead of H2 atmosphere at approximately 480 C [19]. In literature, there are also some researches, focused on the preparation of NaBO2, carried out by Kanturk et al. [20], Figen and Piskin [21] and Yilmaz et al. [22]. Kanturk et al. [20] investigated the synthesis of sodium metaborate tetrahydrate (NaB(OH)4$2H2O) by using anhydrous borax (Na2O$2B2O3) and sodium hydroxide (NaOH) under conditions at 90 C for 150 min. The structure of the reaction product was determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and Thermogravimetric (TG) analyses. In addition, dehydration kinetics of NaB(OH)4$2H2O was performed under non-isothermal conditions and the CoatsRedfern equation was used to evaluate the TG data for calculation of activation energies (Ea) and pre-exponential factors (ko) for different heating rates. Figen and Piskin [21] investigated the synthesis of anhydrous sodium metaborate (NaBO2), an industrial and technologically important boron compound, from concentrated tincal. In the parametric investigation in order to determine the reaction mechanism, experimental studies were carried out at different temperatures and time. After analyzing the structure of metaborates products, they concluded that anhydrous NaBO2 synthesis from calcined tincal occurred at 400 C with 5 h of reaction conditions. They also expressed that anhydrous NaBO2 product could be used in many fields without the calcination steps. Yilmaz et al. [22] performed a study on the production of sodium metaborate tetrahydrate (NaB(OH)4$2H2O) by using borax (Na2B4O7$10H2O) and sodium hydroxide solution under ultrasonic irradiation. They investigated the effect of the
reaction parameters (amount of water, temperature, particle size, and time) on the synthesis of sodium metaborate tetrahydrate. They discovered that the reaction parameters (amount of water, temperature, and time) had great effect on the preparation of sodium metaborate tetrahydrate. Moreover, the concentration of characteristic BeO group in the reaction solution was quantitatively determined by Fourier Transform Infrared Spectroscopy (FTIR). As the result of this study, the optimum condition for the production process was determined as 26% water by weight, borax particles of size 250 þ 150 mm and irradiation time of 60 min at 80 C. The largest boron reserves in the world are found with an L-shaped area in western Turkey. Particularly, ulexite reserves, available in huge amounts in Turkey, are found at different borate deposits in the Marmara Region, Central Anatolia Region, and Aegean Region. The deposits have average ore grades of 29% B2O3 for the ulexite and appear to have been formed from a larger basin [2]. Furthermore, primary and secondary ulexite reserves are always found in association with reserves of borax and colemanite. Ulexite is a sodiumecalcium borate hydrate mineral (NaCaB5O9$8H2O) and is used for the production of commercially significant boron compounds, such as, boric acid, boron oxides and sodium perborate. Ulexite has complex structure, containing chains of sodium, water, and hydroxide octahedra. Due to these reasons, it is very significant and essential to investigate the formation of sodium metaborate from ulexite as a boron source [23]. In addition, there haven’t been found any studies regarding the production of sodium metaborate from ulexite in literature, yet. Therefore, in this study, it was aimed to extract boron as sodium metaborate dihydrate by the reaction of ulexite with trona and lime by determining the optimum extraction temperature and extraction period. We present an alternative route which has the advantage of producing sodium metaborate dihydrate with high purity and providing extraction energy from the sun.
2.
Experimental studies
2.1.
Reagents
All the chemicals (HCl, NaOH) used in this study were of the analytical grades. HCl and NaOH were purchased. 0.0981 M of NaOH (Smyras, 97%, d ¼ 0.8 g cm3) solution was prepared by dissolving 1.962 g of NaOH pellets in distilled water and then, the final solution diluted to 500 mL. To prepare 2.0 M of NaOH solution, 40.0 g of NaOH sample was dissolved in distilled water and then, this solution was diluted to 500 mL 2.0 M of HCl solution was prepared by taking 83.0 mL of HCl from the concentrated HCl reagent (Smyras, 37% pure, d ¼ 1.186 g cm3). Then, the resulting solution was diluted to 500 mL.
2.2.
Materials
Ulexite (NaCaB5O9$8H2O), trona (NaHCO3-Na2CO3$2H2O), lime (CaO), HCl (Smyras), NaOH (Smyras) and distilled water were used in the study. Ulexite and trona used in this study
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 5 8 3 3 e5 8 3 9
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Fig. 1 e The flow chart of the experimental studies.
were obtained from Eti Bor Facilities and Etibank Trona Facilities, Beypazarı, respectively. Ulexite and trona, separately, were crushed with Retsch Jaw Crusher and were ground with Denver Sala Stirred Ball Mill by putting crushed samples and porcelain balls in grinding chamber and then were sieved to a particle size 140 mesh (106 mm) with Endecotts ASTME11 in Dokuz Eylu¨l University Department of Mining Engineering Size Dropping and Classification Laboratory. All the plastic and glassware were cleaned by soaking in dilute HCl (10%) and were rinsed with distilled water prior to use.
2.3. Production of sodium metaborate dihydrate (NaBO2$2H2O) Before starting the experiments, the amount of boron contained in ulexite was determined by a conductometric method [24]. 1.0 g of ulexite was weighed and dissolved with 50 mL 2.0 M HCl and then filtered with a black band filter paper. A black band filter paper was washed with distilled water several times. Filtrate and water, gathered after washing filter paper, heated at about 80 C for a while in order to eliminate CO2. This solution was diluted to 250 mL with distilled water (Note: There was a mixture of strong acid HCl and weak acid H3BO3 in the solution). 25 mL of sample solution was taken from this solution and excess amount of HCl was neutralized with 2.0 M NaOH. Again 0.5 mL of 2.0 M HCl was added into the solution and then this solution was diluted to 250 mL with distilled water. The initial conductance value of the solution was measured before adding titrant NaOH. After that, this final solution was titrated with 0.0981 M NaOH by using WPA Linton Cambridge CMD750 conductometer. For the production of w1 M NaB(OH)4, according to reaction (1) below, calculated amount of 27.4 g (0.07 mol) of ulexite (NaCaB5O9$8H2O), 30.1 g (0.13 mol) of trona (Na3HCO3$CO3$2H2O) and 7.4 g (0.13 mol) of lime (CaO) were used.
3NaCaB5 O9 $8H2 OðaqÞ þ 4Na3 HCO3 $CO3 $2H2 OðaqÞ þ 5CaOðaqÞ #8CaCO3ðsÞ þ 15NaBðOHÞ4ðaqÞ þ 4H2 OðlÞ
(1)
Trona and lime were mixed with some amount (about 350 mL) of distilled water. The beaker was placed on a hot plate with a magnetic stirrer and the stirring speed was set. When the desired temperature of the mixture was reached, the amount of ulexite calculated before was added into this mixture. The final volume of mixture was completed to 400 mL with distilled water. At various reaction times of the experiment, the mixture was waited about 15 min in a water bath at desired temperature and then in order to determine extracted boron content by the conductometric method [24], 10 mL of sample was taken from transparent part of the mixture. After the remaining mixture was diluted to 400 mL
Fig. 2 e Conductometric titration curve used for determining the amount of total boron contained in ulexite.
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Table 1 e The amount of boron extracted from ulexite by using trona and lime at different temperatures and in different reaction periods (Expected amount of boron extraction from 32.4 g ulexite: 4.4 g). Reaction temperature ( C) 30 40 50 60 70 80
4th hour a
Extracted B (g) (X s) 3.2 3.4 4.5 4.3 4.3 4.2
0.9 0.4 0.5 0.5 0.5 0.3
6th hour
Extracted B (%)
a
8th hour
Extracted B (g) (X s)
Extracted B (%)
77 91 102 100 100 100
73 89 102 98 98 97
3.4 4.0 4.5 4.4 4.4 4.4
0.3 0.5 0.6 0.4 0.5 0.4
a
Extracted B (g) (X s)
Extracted B (%)
78 91 100 100 100 98
3.4 4.0 4.4 4.4 4.4 4.2
0.3 0.7 0.3 0.3 0.3 0.4
a The mean value, X, was obtained after five experiments.
with distilled water and was added about 1.0 g of ulexite, experiment was continued to desired period. Each experiment was repeated five times. After 8-h reaction period, in order to determine reaction yield, the mixture was waited about 15 min in a water bath at reaction temperature and then 200 mL of sample was taken from transparent part of the mixture and filtered through a black band filter paper fast. The water of filtrate was vaporized at about 100e110 C and sodium metaborate dihydrate crystals obtained was dried in an oven. The reaction taking place in the oven can be written as equation (2). Sodium metaborate dihydrate crystals were weighed. Thus, the amount of boron extracted was determined gravimetrically. Then, TG/DTG, XRD analyses and percent purity studies were performed. w100110 + C
NaBðOHÞ4 þ 2H2 O ! NaBO2 $2H2 O þ 2H2 O ðsodium orthoborateÞ ðsodium metaborate dihydrateÞ (2) The TG/DTG curves for the sample produced by the reaction of ulexite with trona, were obtained by using a Perkin Elmer TG/DTG instrument. 20 mg samples were weighed. The samples were heated under N2 atmosphere at a heating rate of 5 C min1. The samples were settled in standard aluminum crucibles and heated from 30 C up to 500 C. Crystalline structures were determined by X-ray diffraction. The X-ray analysis was carried out at an
Fig. 3 e The effect of reaction temperature and reaction periods on the extraction of the amount of boron from ulexite by using trona and lime.
ambient temperature by using a Philips Panalytical X’PertPro diffractometer with CuKa radiation (l ¼ 0.1506 nm) at operating parameters of 30 mA and 40 kV with step size 0.02 and speed of 2 C min1. Phase identification of solids was performed by inorganic crystal structure database (ICSD). The percent purity of the product, NaBO2$2H2O, was determined by the conductometric method [24]. The flow chart of the experimental studies was shown in Fig. 1.
Table 2 e The yield of the reaction was carried out by using ulexite, trona and lime at different temperatures for 8 h (Expected amount of NaBO2$2H2O production: 40.7 g; reaction period: 8 h). Reaction temperature, C 40 50 60 70 80
Weighed amount of aNaBO2 (g) (X s)
% yield
62 64 67 68 65
25.1 25.9 26.8 27.4 26.6
0.5 0.3 0.5 0.5 0.8
a The mean value, X, was obtained after five experiments.
Fig. 4 e TGA of NaBO2$2H2O after dried at 150, 250, 300, 350 C [25].
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Fig. 5 e TG-DTG curves for NaBO2.2H2O obtained by the reaction of ulexite with trona and lime.
3.
Results and discussion
3.1. Production of sodium metaborate dihydrate (NaBO2$2H2O) The amount of boron contained in ulexite used through this study was determined by conductometric titrations. Titration curve by graphically representing the conductivity values according to the volume of the titrant solution (NaOH) was shown in Fig. 2. The equivalence values were calculated by intersecting the curves. In Fig. 2, from the linear intersect points, the volume of NaOH consumed for H3BO3 was found. Then, boron content in ulexite was found to be 43.27% on the basis. The results based on optimum conditions for the boron extraction were obtained by following the same method as in the determination of boron content in ulexite and they are listed in Table 1. The results given in Table 1 and plotted in Fig. 3 show that 50 C and higher reaction temperature as well as 6-h and 8-h reaction periods meet our expectations according to level of boron extraction. Additionally, it was observed that 2-h extraction period was not enough to get satisfactory extraction result and that 10-h reaction period for boron extraction, on the other hand, was time-consuming.
In the production of NaBO2$2H2O by the reaction of ulexite with trona and lime at different temperatures for 8 h, the amount of product (NaBO2$2H2O) weighed and the reaction yield values calculated with the equation (3) and the data were given in Table 2. % Yield ¼
Weighed amount of NaBO2 $2H2 O 100 Expected amount of NaBO2 $2H2 O
(3)
The commercial borates lose all structural water through a series of dehydration steps. Dehydration is complete at temperatures below 400 C. The TGA of NaBO2$2H2O in Fig. 2 shows four dehydration steps. Fig. 4 shows TGA of three different samples of NaBO2$2H2O. The three curves in the graph show good reproducibility [25]. TG-DTG curves of the product obtained by the reaction of ulexite with trona and lime are shown in Fig. 5. TG-DTG curves indicated that the product (Fig. 5) had three dehydration steps at a heating rate of 5 C min1. In the first step, total weight loss of 11% was observed in the temperature ranges 36 Ce85 C. In the second step (85 Ce150 C) and in the third step (150 Ce240 C) weight losses 11% and 8% were observed, respectively. Consequently, total weight loss of 30% between 36 C and 240 C. This result proves that product obtained by the reaction of ulexite with trona and lime is NaBO2$2H2O if we compare the total weight loss of standard NaBO2$2H2O in Fig. 4 [25].
Table 3 e Crystallographic parameters of NaBO2.2H2O ICSD name ICSD reference code Empirical formula Chemical formula Crystal system Unit cell dimensions
Fig. 6 e XRD analysis of product obtained in the reaction of ulexite with trona and lime.
Calculated density (g cm3) Measured density (g cm3) Volume of cell (106 pm3) Z RIR
Sodium borate hydrate 00-006-0122 BH4NaO4 NaBO2.2H2O Anorthic ˚ ): 6.1400, Alpha ( ): 91.5000 a (A ˚ ): 10.5800, Beta ( ): 111.3700 b (A ˚ ): 5.8800, Gamma ( ): 89.6700 c (A 1.89 1.90 355.59 4 e
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purity (about 96%) in this study, can be used in different industrial applications especially, as a starting material for the preparation of sodium borohydride.
Table 4 e The results for the determination of percent purity of the product (NaBO2.2H2O) obtained by the reaction of ulexite with trona and lime. Percent Calculated Found amount purity, % amount of of B, (g) NaBO2.2H2O, (g) (X s) (X s)
Sample
Product (NaBO2.2H2O)
0.1020.2
0.960.2
96
The mean value, X, was obtained after five experiments.
XRD pattern of product is exhibited in Fig. 6 and crystallographic parameters are given in Table 3. The XRD pattern shows that the product contains high purity of sodium metaborate dihydrate (NaBO2.2H2O) and very small amount of sodium carbonate (Na2CO3). In order to determine percent purity of the product, the same method (conductometric method) as in the determination of boron content in ulexite was used. By using the amount NaOH consumed for H3BO3 in the sample, the amount of NaBO2.2H2O in 1.0 g of product was calculated with equations (4) and (5). Then, the percent purity of the product was computed by using equation (6)6. The results are listed in Table 4. nH3 BO3 ¼ MNaOH VNaOH
(4)
1 mole of boric acidðH3 BO3 Þh1 mole of boron h1 mole of NaBO2 $2H2 O % purity ¼
4.
Calculated amount of NaBO2 $2H2 O 100 Weighed amount of product
(5)
(6)
Conclusion
In the present experimental work, the optimum conditions for the production of purified sodium metaborate dihydrate by the reaction of ulexite with trona and lime at different temperatures (30 C, 40 C, 50 C 60 C, 70 C and 80 C) and various reaction times (2, 4, 6, 8 and 10 h) were investigated in detail. After these investigations, the following key points can be drawn: Sodium metaborate dihydrate yields increases with elevating reaction temperature and reaches at its maximum level when the reaction temperature is 50 C and higher. Optimum extraction conditions were determined as 50 C and higher temperature; 6 h and longer extraction time. It can be said that by the method used during this study, there will be no need for energy input since during the reaction, 50 C or 60 C of reaction temperature can be provided from the sun and crystallization temperature can be reached spontaneously at night in the region where the plant set up. We have suggested a method so as to produce sodium metaborate dihydrate very economically in the view of raw material since Turkey has approximately 72% of world’s boron reserves, and ranks the second in the world trona reserves after the U.S.A. Furthermore, we may conclude that after one dehydration step, anhydrous sodium metaborate, produced with a high
references
[1] Mining, Metallurgy, and Chemistry. ETI mine works general management, report 2001, http://www.etimaden.gov.tr/en; 2001 [accessed 02.12.08.]. [2] Garret DE. Borates, handbook of deposits, processing, properties and use. California: Academic Press; 1998. [3] Koca S, Savas M, Koca H. Flotation of colemanite from realgar. Minerals Eng 2003;16:479e82. [4] Helvacı C, Alonso RN. Borate deposits of Turkey and Argentina: a summary and geological comparison. Turkish J Earth Sci 2000;9:1e27. [5] Perry DL, Phillips SL. Handbook of inorganic compounds. New York: CRC Press; 1995. [6] Kojima Y, Suzuki K, Fukumoto K, Sasaki M, Yamamoto T, Kawai Y, et al. Hydrogen generation using sodium borohydride solution and metal catalyst coated on metal oxide. Int J Hydrogen Energy 2002;27:1029e34. [7] Schlesinger HI, Brown HC, Finholt AE, Gilbreath JR, Hoekstra HR, Hyde EK. Sodium borohydride, its hydrolysis and its use as a reducing agent and in the generation of hydrogen. J Am Chem Soc 1953;75:215e9. [8] Kim J-H, Lee H, Han S, Kim H-S, Song M-S, Lee J-Y. Production of hydrogen from sodium borohydride in alkaline solutiondevelopment of catalyst with high performance. Int J Hydrogen Energy 2004;29:263e7. [9] Li ZP, Liu BH, Morigasaki N, Suda S. Preparation of sodium borohydride by the reaction of MgH2 with dehydrated borax through ball milling at room temperature. J Alloys Compds 2003;349:232e6. [10] Li ZP, Liu BH, Arai K, Morigasaki N, Suda S. Protide compounds in hydrogen storage systems. J Alloys Compds 2003;356:469e74. [11] Kong L, Cui X, Jin H, Wu J, Du H, Xiong T. Mechanochemical synthesis of sodium borohydride by recycling sodium metaborate. Energy Fuels 2009;23:5049e52. [12] Huesh CL, Liu CH, Chen BH, Chen CY, Kuo YC, Hwang KJ, et al. Regeneration of spent-NaBH4 back to NaBH4 by using high-energy ball milling. Int J Hydrogen Energy 2009;4: 1717e25. [13] Kojima Y, Haga T. Recycling process of sodium metaborate to sodium borohydride. Int J Hydrogen Energy 2003;28: 989e93. [14] Suda S, Morigasaki N, Iwase Y, Li ZP. Production of sodium borohydride by using dynamic behaviors of protide at the extreme surface of magnesium particles. J Alloys Compds 2005;404:643e7. [15] Li ZP, Liu BH, Zhu JK, Morigasaki N, Suda S. NaBH4 formation mechanism by reaction of sodium borate with Mg and H2. J Alloys Compds 2007;437:311e6. [16] Liu BH, Li ZP, Morigasaki N, Suda S. Kinetic characteristics of sodium borohydride formation when sodium meta-borate reacts with magnesium and hydrogen. Int J Hydrogen Energy 2008;33:1323e8. [17] Liu BH, Li ZP, Morigasaki N, Suda S. Alkali oxide addition effects on borohydride formation during the reaction of Al, Si, and Ti with borate and hydrogen. Energy Fuels 2008;22:1894e6. [18] Cooper HBH. Electrolytic process for the production of alkali metal borohydrides. U.S. Patent, US 3,734,842;1973. [19] Zhang H, Zheng S, Fang F, Chen G, Sang G, Suna D. Synthesis of NaBH4 based on a solid-state reaction under Ar atmosphere. J Alloys Compds 2009;484:352e5.
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[20] Kanturk A, Sari M, Piskin S. Synthesis, crystal structure and dehydration kinetics of NaB(OH)4.2H2O. Korean J Chem Eng 2008;25:1331e7. [21] Figen AK, Piskin S. Parametric investigation on anhydrous sodium metaborate (NaBO2) synthesis from concentrated tincal. Adv Powder Technol 2010;21:513e20. [22] Yilmaz MS, Figen AK, Piskin S. Production of sodium metaborate tetrahydrate (NaB(OH)4$2H2O) using ultrasonic irradiation. Powder Technol 2012;215e216: 166e73.
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[23] Piskin MB. Investigation of sodium borohydride production process: ‘‘Ulexite mineral as a boron source’’. Int J Hydrogen Energy 2009;34:4773e9. [24] Sert H. An alternative method for the exctraction of boron _ from ulexite. MSc thesis. Izmir:EgeUniversity, Faculty of Science, Department of Chemistry; January 2005. [25] Eyma YMA, Joshua RG, Thomas AD, Michael AM. Minimizing water utilization in hydrolysis of sodium borohydride: the role of sodium metaborate hydrates. Int J Hydrogen Energy 2007;32:4723e30.
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
An investigation on the production of sodium metaborate dihydrate from ulexite by using trona and lime Hakan Sert*, Hu¨seyin Yıldıran, Duygu Toscalı _ Department of Chemistry, Faculty of Science, Ege University, Bornova, 35100 Izmir, Turkey
article info
abstract
Article history:
In this study, it was investigated the optimum conditions (extraction temperature and
Received 16 August 2011
extraction period) for the production of sodium metaborate dihydrate (NaBO2.2H2O) by the
Received in revised form
reaction of ulexite (NaCaB5O9$8H2O) with trona (NaHCO3-Na2CO3$2H2O) and lime (CaO).
29 December 2011
The optimum extraction conditions were determined as 50 C and higher temperature; 6 h
Accepted 3 January 2012
and longer extraction time. The characterizations of the product (sodium metaborate
Available online 30 January 2012
dihydrate crystals) were performed by thermogravimetric (TG-DTG) and X-ray diffraction (XRD) analyses. In addition, the percent purity of the product was found to be 96% by using
Keywords:
a conductometric method.
Ulexite
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Trona Lime Extraction of boron Sodium metaborate dihydrate
1.
Introduction
Boron is one of the most important strategic elements. It is never found free in nature but invariably occurs as the oxide B2O3, in combination with the oxides of other elements, forming borates of greater or lesser complexity. Boron compounds, which are used in many branches of industry, are produced from boron-containing ores. There are lots of naturally occurring boron minerals in the earth. It was reported that Turkey has 72.20% of the world’s boron reserves based on 851 million tons of B2O3 content in terms of total reserve basis. In spite of Turkey’s large boron reserves, the desired level for the preparation of final products having commercial value has not been reached yet. Because of this reason, it is very significant to enhance number of researches and studies on the production of boron compounds [1e4].
The borates of sodium and their derivatives are the main materials for chemical and metallurgy industries and also the medical sector. One of the boron derivatives, having commercial importance, is sodium metaborate (NaBO2). Sodium metaborate is commonly used in commercial production of sodium perborate tetrahydrate (NaBO3$4H2O), photographic-textile chemicals, detergents, cleaners and adhesives [2]. NaBO2 compounds can be classified according to water content inside as 4-hydrate, 2-hydrate and anhydrous [5]. The solubility of NaBO2 in water at 25 C is 28 g/100 g water [6]. The use of anhydrous NaBO2 in the energy field and the importance of both commercial borates class are growing gradually. There are some literatures on the preparation of the NaBH4 by using anhydrous sodium metaborate (NaBO2) as a starting material. NaBH4 is stable compared to other chemical hydrides and has large theoretical hydrogen content (10.9
* Corresponding author. Tel./fax: þ90 276 224 48 72. E-mail address: [email protected] (H. Sert). 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.01.012
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wt.%). Since hydrogen is a crucial alternative energy sources for the future, when it is compared with traditional fossil fuels causing global warming [7,8]. Recent studies on the preparation of NaBH4 by using NaBO2 as a starting compound have revealed the commercial significance of sodium metaborate in hydrogen energy investigations. Therefore, scientists have paid particular attention to produce NaBO2 and to study on the methods how to use NaBO2 as a boron source in the synthesis of NaBH4. Nowadays, some methods based on the production of NaBH4 from anhydrous NaBO2, such as, ball-milling synthesis [9e12] and thermal synthesis [13e17] have been developed. For example, Cooper et al. [18] investigated the electrochemical conversion of NaBO2 to NaBH4 at room temperature and ambient pressure. Kojima and Haga [13] reported that NaBH4 could be synthesized by annealing a mixture of NaBO2 with MgH2 or NaBO2 with Mg2Si under high H2 pressure. The reaction between NaBO2 and MgH2 was performed at 550 C under 7 MPa of hydrogen pressure for 2 h. Li et al. [15] developed a method to obtain sodium borohydride by a reaction of saline hydride with metaborate through ball-milling at room temperature. Although the NaBH4 conversion rate showed a deviation from its theoretical value, almost 100% of NaBH4 conversion rate was achieved when an excessive amount of MgH2 (1.25 times more than stoichiometric amount) was added. Zhang et al. proposed a method for the production of NaBH4 based on the solid-state reaction by calcining the 4NaHeNaBO2e2SiO2 ternary mixture. They were successes to produce NaBH4 under Ar, instead of H2 atmosphere at approximately 480 C [19]. In literature, there are also some researches, focused on the preparation of NaBO2, carried out by Kanturk et al. [20], Figen and Piskin [21] and Yilmaz et al. [22]. Kanturk et al. [20] investigated the synthesis of sodium metaborate tetrahydrate (NaB(OH)4$2H2O) by using anhydrous borax (Na2O$2B2O3) and sodium hydroxide (NaOH) under conditions at 90 C for 150 min. The structure of the reaction product was determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and Thermogravimetric (TG) analyses. In addition, dehydration kinetics of NaB(OH)4$2H2O was performed under non-isothermal conditions and the CoatsRedfern equation was used to evaluate the TG data for calculation of activation energies (Ea) and pre-exponential factors (ko) for different heating rates. Figen and Piskin [21] investigated the synthesis of anhydrous sodium metaborate (NaBO2), an industrial and technologically important boron compound, from concentrated tincal. In the parametric investigation in order to determine the reaction mechanism, experimental studies were carried out at different temperatures and time. After analyzing the structure of metaborates products, they concluded that anhydrous NaBO2 synthesis from calcined tincal occurred at 400 C with 5 h of reaction conditions. They also expressed that anhydrous NaBO2 product could be used in many fields without the calcination steps. Yilmaz et al. [22] performed a study on the production of sodium metaborate tetrahydrate (NaB(OH)4$2H2O) by using borax (Na2B4O7$10H2O) and sodium hydroxide solution under ultrasonic irradiation. They investigated the effect of the
reaction parameters (amount of water, temperature, particle size, and time) on the synthesis of sodium metaborate tetrahydrate. They discovered that the reaction parameters (amount of water, temperature, and time) had great effect on the preparation of sodium metaborate tetrahydrate. Moreover, the concentration of characteristic BeO group in the reaction solution was quantitatively determined by Fourier Transform Infrared Spectroscopy (FTIR). As the result of this study, the optimum condition for the production process was determined as 26% water by weight, borax particles of size 250 þ 150 mm and irradiation time of 60 min at 80 C. The largest boron reserves in the world are found with an L-shaped area in western Turkey. Particularly, ulexite reserves, available in huge amounts in Turkey, are found at different borate deposits in the Marmara Region, Central Anatolia Region, and Aegean Region. The deposits have average ore grades of 29% B2O3 for the ulexite and appear to have been formed from a larger basin [2]. Furthermore, primary and secondary ulexite reserves are always found in association with reserves of borax and colemanite. Ulexite is a sodiumecalcium borate hydrate mineral (NaCaB5O9$8H2O) and is used for the production of commercially significant boron compounds, such as, boric acid, boron oxides and sodium perborate. Ulexite has complex structure, containing chains of sodium, water, and hydroxide octahedra. Due to these reasons, it is very significant and essential to investigate the formation of sodium metaborate from ulexite as a boron source [23]. In addition, there haven’t been found any studies regarding the production of sodium metaborate from ulexite in literature, yet. Therefore, in this study, it was aimed to extract boron as sodium metaborate dihydrate by the reaction of ulexite with trona and lime by determining the optimum extraction temperature and extraction period. We present an alternative route which has the advantage of producing sodium metaborate dihydrate with high purity and providing extraction energy from the sun.
2.
Experimental studies
2.1.
Reagents
All the chemicals (HCl, NaOH) used in this study were of the analytical grades. HCl and NaOH were purchased. 0.0981 M of NaOH (Smyras, 97%, d ¼ 0.8 g cm3) solution was prepared by dissolving 1.962 g of NaOH pellets in distilled water and then, the final solution diluted to 500 mL. To prepare 2.0 M of NaOH solution, 40.0 g of NaOH sample was dissolved in distilled water and then, this solution was diluted to 500 mL 2.0 M of HCl solution was prepared by taking 83.0 mL of HCl from the concentrated HCl reagent (Smyras, 37% pure, d ¼ 1.186 g cm3). Then, the resulting solution was diluted to 500 mL.
2.2.
Materials
Ulexite (NaCaB5O9$8H2O), trona (NaHCO3-Na2CO3$2H2O), lime (CaO), HCl (Smyras), NaOH (Smyras) and distilled water were used in the study. Ulexite and trona used in this study
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Fig. 1 e The flow chart of the experimental studies.
were obtained from Eti Bor Facilities and Etibank Trona Facilities, Beypazarı, respectively. Ulexite and trona, separately, were crushed with Retsch Jaw Crusher and were ground with Denver Sala Stirred Ball Mill by putting crushed samples and porcelain balls in grinding chamber and then were sieved to a particle size 140 mesh (106 mm) with Endecotts ASTME11 in Dokuz Eylu¨l University Department of Mining Engineering Size Dropping and Classification Laboratory. All the plastic and glassware were cleaned by soaking in dilute HCl (10%) and were rinsed with distilled water prior to use.
2.3. Production of sodium metaborate dihydrate (NaBO2$2H2O) Before starting the experiments, the amount of boron contained in ulexite was determined by a conductometric method [24]. 1.0 g of ulexite was weighed and dissolved with 50 mL 2.0 M HCl and then filtered with a black band filter paper. A black band filter paper was washed with distilled water several times. Filtrate and water, gathered after washing filter paper, heated at about 80 C for a while in order to eliminate CO2. This solution was diluted to 250 mL with distilled water (Note: There was a mixture of strong acid HCl and weak acid H3BO3 in the solution). 25 mL of sample solution was taken from this solution and excess amount of HCl was neutralized with 2.0 M NaOH. Again 0.5 mL of 2.0 M HCl was added into the solution and then this solution was diluted to 250 mL with distilled water. The initial conductance value of the solution was measured before adding titrant NaOH. After that, this final solution was titrated with 0.0981 M NaOH by using WPA Linton Cambridge CMD750 conductometer. For the production of w1 M NaB(OH)4, according to reaction (1) below, calculated amount of 27.4 g (0.07 mol) of ulexite (NaCaB5O9$8H2O), 30.1 g (0.13 mol) of trona (Na3HCO3$CO3$2H2O) and 7.4 g (0.13 mol) of lime (CaO) were used.
3NaCaB5 O9 $8H2 OðaqÞ þ 4Na3 HCO3 $CO3 $2H2 OðaqÞ þ 5CaOðaqÞ #8CaCO3ðsÞ þ 15NaBðOHÞ4ðaqÞ þ 4H2 OðlÞ
(1)
Trona and lime were mixed with some amount (about 350 mL) of distilled water. The beaker was placed on a hot plate with a magnetic stirrer and the stirring speed was set. When the desired temperature of the mixture was reached, the amount of ulexite calculated before was added into this mixture. The final volume of mixture was completed to 400 mL with distilled water. At various reaction times of the experiment, the mixture was waited about 15 min in a water bath at desired temperature and then in order to determine extracted boron content by the conductometric method [24], 10 mL of sample was taken from transparent part of the mixture. After the remaining mixture was diluted to 400 mL
Fig. 2 e Conductometric titration curve used for determining the amount of total boron contained in ulexite.
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Table 1 e The amount of boron extracted from ulexite by using trona and lime at different temperatures and in different reaction periods (Expected amount of boron extraction from 32.4 g ulexite: 4.4 g). Reaction temperature ( C) 30 40 50 60 70 80
4th hour a
Extracted B (g) (X s) 3.2 3.4 4.5 4.3 4.3 4.2
0.9 0.4 0.5 0.5 0.5 0.3
6th hour
Extracted B (%)
a
8th hour
Extracted B (g) (X s)
Extracted B (%)
77 91 102 100 100 100
73 89 102 98 98 97
3.4 4.0 4.5 4.4 4.4 4.4
0.3 0.5 0.6 0.4 0.5 0.4
a
Extracted B (g) (X s)
Extracted B (%)
78 91 100 100 100 98
3.4 4.0 4.4 4.4 4.4 4.2
0.3 0.7 0.3 0.3 0.3 0.4
a The mean value, X, was obtained after five experiments.
with distilled water and was added about 1.0 g of ulexite, experiment was continued to desired period. Each experiment was repeated five times. After 8-h reaction period, in order to determine reaction yield, the mixture was waited about 15 min in a water bath at reaction temperature and then 200 mL of sample was taken from transparent part of the mixture and filtered through a black band filter paper fast. The water of filtrate was vaporized at about 100e110 C and sodium metaborate dihydrate crystals obtained was dried in an oven. The reaction taking place in the oven can be written as equation (2). Sodium metaborate dihydrate crystals were weighed. Thus, the amount of boron extracted was determined gravimetrically. Then, TG/DTG, XRD analyses and percent purity studies were performed. w100110 + C
NaBðOHÞ4 þ 2H2 O ! NaBO2 $2H2 O þ 2H2 O ðsodium orthoborateÞ ðsodium metaborate dihydrateÞ (2) The TG/DTG curves for the sample produced by the reaction of ulexite with trona, were obtained by using a Perkin Elmer TG/DTG instrument. 20 mg samples were weighed. The samples were heated under N2 atmosphere at a heating rate of 5 C min1. The samples were settled in standard aluminum crucibles and heated from 30 C up to 500 C. Crystalline structures were determined by X-ray diffraction. The X-ray analysis was carried out at an
Fig. 3 e The effect of reaction temperature and reaction periods on the extraction of the amount of boron from ulexite by using trona and lime.
ambient temperature by using a Philips Panalytical X’PertPro diffractometer with CuKa radiation (l ¼ 0.1506 nm) at operating parameters of 30 mA and 40 kV with step size 0.02 and speed of 2 C min1. Phase identification of solids was performed by inorganic crystal structure database (ICSD). The percent purity of the product, NaBO2$2H2O, was determined by the conductometric method [24]. The flow chart of the experimental studies was shown in Fig. 1.
Table 2 e The yield of the reaction was carried out by using ulexite, trona and lime at different temperatures for 8 h (Expected amount of NaBO2$2H2O production: 40.7 g; reaction period: 8 h). Reaction temperature, C 40 50 60 70 80
Weighed amount of aNaBO2 (g) (X s)
% yield
62 64 67 68 65
25.1 25.9 26.8 27.4 26.6
0.5 0.3 0.5 0.5 0.8
a The mean value, X, was obtained after five experiments.
Fig. 4 e TGA of NaBO2$2H2O after dried at 150, 250, 300, 350 C [25].
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Fig. 5 e TG-DTG curves for NaBO2.2H2O obtained by the reaction of ulexite with trona and lime.
3.
Results and discussion
3.1. Production of sodium metaborate dihydrate (NaBO2$2H2O) The amount of boron contained in ulexite used through this study was determined by conductometric titrations. Titration curve by graphically representing the conductivity values according to the volume of the titrant solution (NaOH) was shown in Fig. 2. The equivalence values were calculated by intersecting the curves. In Fig. 2, from the linear intersect points, the volume of NaOH consumed for H3BO3 was found. Then, boron content in ulexite was found to be 43.27% on the basis. The results based on optimum conditions for the boron extraction were obtained by following the same method as in the determination of boron content in ulexite and they are listed in Table 1. The results given in Table 1 and plotted in Fig. 3 show that 50 C and higher reaction temperature as well as 6-h and 8-h reaction periods meet our expectations according to level of boron extraction. Additionally, it was observed that 2-h extraction period was not enough to get satisfactory extraction result and that 10-h reaction period for boron extraction, on the other hand, was time-consuming.
In the production of NaBO2$2H2O by the reaction of ulexite with trona and lime at different temperatures for 8 h, the amount of product (NaBO2$2H2O) weighed and the reaction yield values calculated with the equation (3) and the data were given in Table 2. % Yield ¼
Weighed amount of NaBO2 $2H2 O 100 Expected amount of NaBO2 $2H2 O
(3)
The commercial borates lose all structural water through a series of dehydration steps. Dehydration is complete at temperatures below 400 C. The TGA of NaBO2$2H2O in Fig. 2 shows four dehydration steps. Fig. 4 shows TGA of three different samples of NaBO2$2H2O. The three curves in the graph show good reproducibility [25]. TG-DTG curves of the product obtained by the reaction of ulexite with trona and lime are shown in Fig. 5. TG-DTG curves indicated that the product (Fig. 5) had three dehydration steps at a heating rate of 5 C min1. In the first step, total weight loss of 11% was observed in the temperature ranges 36 Ce85 C. In the second step (85 Ce150 C) and in the third step (150 Ce240 C) weight losses 11% and 8% were observed, respectively. Consequently, total weight loss of 30% between 36 C and 240 C. This result proves that product obtained by the reaction of ulexite with trona and lime is NaBO2$2H2O if we compare the total weight loss of standard NaBO2$2H2O in Fig. 4 [25].
Table 3 e Crystallographic parameters of NaBO2.2H2O ICSD name ICSD reference code Empirical formula Chemical formula Crystal system Unit cell dimensions
Fig. 6 e XRD analysis of product obtained in the reaction of ulexite with trona and lime.
Calculated density (g cm3) Measured density (g cm3) Volume of cell (106 pm3) Z RIR
Sodium borate hydrate 00-006-0122 BH4NaO4 NaBO2.2H2O Anorthic ˚ ): 6.1400, Alpha ( ): 91.5000 a (A ˚ ): 10.5800, Beta ( ): 111.3700 b (A ˚ ): 5.8800, Gamma ( ): 89.6700 c (A 1.89 1.90 355.59 4 e
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purity (about 96%) in this study, can be used in different industrial applications especially, as a starting material for the preparation of sodium borohydride.
Table 4 e The results for the determination of percent purity of the product (NaBO2.2H2O) obtained by the reaction of ulexite with trona and lime. Percent Calculated Found amount purity, % amount of of B, (g) NaBO2.2H2O, (g) (X s) (X s)
Sample
Product (NaBO2.2H2O)
0.1020.2
0.960.2
96
The mean value, X, was obtained after five experiments.
XRD pattern of product is exhibited in Fig. 6 and crystallographic parameters are given in Table 3. The XRD pattern shows that the product contains high purity of sodium metaborate dihydrate (NaBO2.2H2O) and very small amount of sodium carbonate (Na2CO3). In order to determine percent purity of the product, the same method (conductometric method) as in the determination of boron content in ulexite was used. By using the amount NaOH consumed for H3BO3 in the sample, the amount of NaBO2.2H2O in 1.0 g of product was calculated with equations (4) and (5). Then, the percent purity of the product was computed by using equation (6)6. The results are listed in Table 4. nH3 BO3 ¼ MNaOH VNaOH
(4)
1 mole of boric acidðH3 BO3 Þh1 mole of boron h1 mole of NaBO2 $2H2 O % purity ¼
4.
Calculated amount of NaBO2 $2H2 O 100 Weighed amount of product
(5)
(6)
Conclusion
In the present experimental work, the optimum conditions for the production of purified sodium metaborate dihydrate by the reaction of ulexite with trona and lime at different temperatures (30 C, 40 C, 50 C 60 C, 70 C and 80 C) and various reaction times (2, 4, 6, 8 and 10 h) were investigated in detail. After these investigations, the following key points can be drawn: Sodium metaborate dihydrate yields increases with elevating reaction temperature and reaches at its maximum level when the reaction temperature is 50 C and higher. Optimum extraction conditions were determined as 50 C and higher temperature; 6 h and longer extraction time. It can be said that by the method used during this study, there will be no need for energy input since during the reaction, 50 C or 60 C of reaction temperature can be provided from the sun and crystallization temperature can be reached spontaneously at night in the region where the plant set up. We have suggested a method so as to produce sodium metaborate dihydrate very economically in the view of raw material since Turkey has approximately 72% of world’s boron reserves, and ranks the second in the world trona reserves after the U.S.A. Furthermore, we may conclude that after one dehydration step, anhydrous sodium metaborate, produced with a high
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