REUSING OF SODIUM SILICATE AS A RAW MATERIAL IN GLASS INDUSTRY: BY PRODUCT OF SODIUM BOROHYDRIDE PRODUCTION

Global energy and ecology problems continue to grow because of burning of fossil fuels, environmental pollution, decrease of energy sources and difficulties in storing electricity. Hydrogen has great potential to solve these problems as an environmentally clean energy carrier and as a way to reduce reliance on imported energy sources. Hydrogen can be stored and transported safely in the form of sodium borohydride (NaBH4) due to its high theoretical hydrogen yield by weight (10.6%) in applications where H2 gas is used, e.g., proton exchange membrane (PEM) fuel cells. NaBH4 is synthesized from boron minerals (borax, ulexite, colemanite ... ) by the thermal-chemical reactions. The main aim of this paper is the investigation of reusing of Na2SiO3, obtained from Na8H4 production based on the conversion reaction of borosilicate glass, as a raw material in glass industry. The by-product, was defined as Na2SiO3 (PDF number: 00-016 -0818) by XRD (X­ Ray Diffractometer) technique, was then vitrificated into a glass for utilization. The obtained glass was characterized by scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis and FT-IR (Fourier Transformer-Infrared spectroscopy) techniques. The results show that by-product Na2SiO3 can be reused as a raw material in glass industry.


I INTRODUCTION
Sodium borohydride (NaBH 4 ), which is known as sodium tetrahydroborate, has attracted attention due to its high theoretical hydrogen content of I 0.6 wt% and the excellent stability of its solution under high pH value at ambient temperature [I, 2]. Also, Na8H 4 is a selective specialty reducing agent used in the manufacture of pharmaceuticals and other organic compounds [3]. It is important to note that NaBH 4 can be produced by economical methods to be applied in practical use. According to the several publications, NaBH 4 was synthesized by reacting Na8O2 with MgH 2 or Mg 2 Si by annealing the mixture of these two compounds under high hydrogen pressure. Also, it was note that NaBH 4 can be produced by reaction of MgH2 with Na 2 8 4 O 7 through ball milling at room temperature [4,5].
In previous study of authors was expressed that process for producing NaBH4, which is based on the conversion reaction of borosilicate glass at temperatures between about 400-500 ° C under high hydrogen pressure. They defined the by-product as sodium silicate (Na 2 SiO 3 ) [6], In the present work, reusing of Na 2 SiO 3 , obtained from NaBH 4 production based on the conversion reaction of borosilicate glass, as a raw material in glass industry was investigated. The by-product, characterized as Na 2 SiO 3 (PDF number: 00-016-0818) by XRD (X-Ray Diffractometer) technique, was vitrificated into a glass for utilization. The obtained glass was detennined by SEM (Scanning Electron Microscopy) with EDS (Energy Dispersive Spectroscopy) analysis and FT-IR (Fourier Transformer-Infrared spectroscopy) techniques. The analysis results indicate that by-product Na 2 SiO 3 can be reused as a raw material in glass industry.

Material
The by-product (Na 2 SiO 3 ) which was obtained from NaBH 4 production is based on the conversion reaction of borosilicate glass at temperatures between about 400-500 ° C under high hydrogen pressure. The flow chart of NaBH 4 production process is given in Figure 1. After the conversion reaction of borosilicate glass, the resulting reaction product was analyzed by XRD technique for qualitative identification. It was detennined that resulting reaction product includes NaBH 4 (main product) and Na 2 SiO 3 (by product). It was extracted with suitable solution to separate NaBH 4 from Na 2 SiO 3 . Extraction solution was separated from the by product and remaining reactants by filter paper and was evaporated in the rotary dryer, By-product (see Figure 2) was dried for two hours before the XRD analysis and XRD pattern is given in Figure 5, Figure 2. image of by-product

Vitrification
In this study, the potentiality of by-product vitrification without any additives was examined for utilizing as a raw material in glass industry. The by-product was subject to a vitrification process to production of glass in a high temperature furnace. The mineralogical structure and the chemical properties of the obtained glass were carried out by SEM-EDS and FT-IR analysis. The images of obtained glass are shown in Figure 3.

Characterization
Crystalline structure of by-product obtained by the Na8H4 process was investigated by XRD technique that reveals detailed information about the chemical composition and crystallographic structure of materials. Analysis was made by using a Philips PAnalytical X'Pert Pro diffractometer using CuKa radiation (45 kV and 40 mA) and recorded at room temperature with a diffraction angle from 0 ° to 90 ° at 0.02 ° (20) step size. Phase identification was performed using the XRD library available on the data system. XRD pattern of by product is given in Figure 5.
Scanning electron microscope (JEOL JSM-59 I OLV) with a type of electron microscope capable of producing high-resolution images of a sample surface was used to determine the microstructure of obtained glass at the energy of the electron beam of 25 kV. Quantitative  Figure 3. The XRD pattern indicated that by product was defined as Na 2 SiO 3 , Also, XRD result showed that nonexistence of NaBH 4 in by product.   Figure 3 (a) and (b)) showed fonnation of amorphous phase. The EDS spectra in Figure 6 (b) and (c) were collected from the enclosed area I and 2 in Figure 6 (a), respectively. According to the EDS spectrums, the chemical composition of obtained glass is calculated as 48.12% 0, 51.88% Si in Figure 6 (b), while the chemical composition of obtained glass is calculated as 33.85% 0, 9.75% Na and 56.40% Si in Figure 6

CONCLUSION
This paper presents investigation of reusing of Na 2 SiO 3 , obtained by NaBH 4 production, as a raw material in glass industry, Na 2 SiO 3 was vitrified without any additives in high temperature furnace, Detailed morphological and chemical analyses of glass obtained were carried out by FT-IR and SEM-EDS analysis, In a conclusion, obtained glass can be used for decorative purpose because of greenish colour,