characterization of sodium silicate prepared from

CHARACTERIZATION OF SODIUM SILICATE PREPARED FROM KANKARA KAOLIN NURUDEEN, S.* AND ABDULKARIM, S.A. Department of Chemical Engineering, Ahmadu Bello University, Zaria, Nigeria

ABSTRACT This study presents the characterization of sodium silicate prepared from Kankara kaolin. Mineralogical, chemical and thermogravimetrical characterizations were carried out using XRD, UV/VIS Spectroscopy, FTIR and TGA/DTG. Amorphous silica obtained from kaolin was used to prepare sodium silicate. The prepared sodium silicate had SiO2 and Na2O concentrations of 28.12 and 12.74 wt% respectively, and SiO2/Na2O ratio of 2.21. The SiO2 and Na2O concentrations were 94% and 106% of commercial sodium silicate respectively. The SiO2/Na2O ratio was 88% of commercial sodium silicate. The prepared sodium silicate showed close physicochemical resemblance to the commercial sodium silicate and it was thermally stable below 200˚C.

Keywords: Sodium silicate, Kankara kaolin, characterization. *Correspondence: [email protected]

INTRODUCTION

MATERIALS AND METHODS

Sodium silicate, which is also known as water glass or liquid glass forms, is a highly miscible colourless solution in water. The solution contains dissolved glass which has some water like properties. Its chemical formula is Na2SiO3. The chemical also exists in solid state; the solid form is called sodium metasilicate. Liquid sodium silicate is used for a broad spectrum of industrial applications such as: usage as sealants, binders, deflocculants, emulsifiers and buffers. Its common applications are in the pulp and paper industry, and the detergent industry- in which it improves the action of the detergent and lower the viscosity of liquid soaps. Sodium silicate is used in the production of composite bipolar plates for proton exchange membrane fuel cells (PEMFC), [1]. It is used as an ingredient in cement production [2]and in the synthesis of advanced gas adsorbents such as silica xerogel used to capture CO2 [3]. It is used in the solgel synthesis of various microporous materials such as zeolites and metallic organic framework (MOF) materials [4]. It is also used in production of various aerogels used for applications like radiation detectors, catalysis, acoustic and thermal insulation, filtration, windows, space research, electronics applications [5]. Other uses of sodium silicate include application in production of materials for optical fibers, LEDs and wave guides [6]. This work presents characterization of sodiumsilicate prepared from kaolin and compares it with that of a commercial sodium silicate.

Material

Nigerian Journal of Scientific Research, 13(1): 2014

Laboratory grade sodium hydroxide pellets (≥98%) and concentrated sulphuric acid (≥98%) were purchased from Lobal Chemie, India. Raw kaolinite clay was mined from Kankara Local Government Area of Katsina State, Nigeria.

Methodology Raw kaolin was wet beneficiated as presented in Ahmed et al. [7] and Salahudeen et al. [8]. The beneficiated clay was calcined at 750°C for 2 hr in an electric chamber furnace (Nabertherm) for processing into metakaolin. The metakaolin was dealuminated using 60 wt% concentrated sulphuric acid [9, 10]. The Silica obtained from the dealumination was processed to produce sodium silicate by leaching in a caustic solution [11, 12]. The SiO2 was characterized using the American Public Health Association (APHA) 4500-SiO2 C. Molybdosilicate Method [13]. Standard solutions of silica of variable concentrations; 5-25 ppm were prepared from silica stock solution. UV/VIS Spectrometer scan (Perkin Elmer UV/VIS Spectrometer Lambda 25) of the standards were run and the absorbance measurements at 410 nm were used to prepare the calibration curve. The prepared sodium silicate solution was diluted to 2.5 µl in 50 ml distilled water (2.5 mg in 50 g solution: dilution factor; 5 x 10-5). The diluted solution of sodium silicate was mixed with ammonium molybdate. The pH of the resulting mixture was adjusted to 1.2 by adding 1 ml of 1 + 1 hydrochloric acid [13]. The mixture was allowed to stand for 10 min then 2.0 ml of oxalic acid was added. UV-VIS absorbance at

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Nurudeen and Abdulkarim, 2014; Characterization of sodium silicate prepared from Kankara kaolin

wavelength of 410 nm was taken and the concentration of the sodium silicate was determined. The corresponding concentration of the silicate, in ppm, was determined using the calibration curve in Figure 1.The actual concentration of the silicate, in wt%, was determined using the equation below. Actual conc. (wt) = (conc. (ppm) x dilution factor)/ (1 x 10-4). The Na2O was characterized using Flame Photometer analysis (TIMPL µp Flame Photometer TMF-45). Firstly, variable concentrations of standard solutions of Na2O were prepared; 5-25 ppm from Na2O stock solution. The standard solutions were introduced into the flame photometer for inbuilt calibration. The sodium silicate solution was diluted to 2.5 µl in 100 ml distilled water (2.5 mg in 100 g solution: dilution factor; 2.5 x 10-5) and introduced into the flame photometer. FTIR analysis was carried out using Perkin Elmer Frontier FTIR Spectrometer. Wafer of the sodium silicate consisting of 1% sodium silicate and 99% KBr window was prepared using press pressure of 12 MPa. Thermogravimetry analyses were carried out using Perkin Elmer simultaneous thermal analyzer, STA 6000. The method used was thermal scan from 30 to 900˚C at heating rate of 10˚C/min and cooling at 20˚C/ from 900 to 30˚C. Nitrogen was used as the purge gas at flow rate of 20 ml/min.

RESULTS AND DISCUSSION Figure 1 shows the silica calibration curve using different concentrations of standard silica solution. Table 1 presents the UV absorbance of the prepared sodium silicate and the commercial sodium silicate at variable concentration. It was observed that the SiO2 concentration of the prepared sodium silicate was 28.12 wt% whereas that of the commercial sodium silicate was 30.02 wt%. Table 2 presents the concentrations of the Na2O in ppm for the sodium silicate prepared and that of the commercial sodium silicate. The actual Na2O concentrations of the samples in wt% were determined using Equation 1. It could be observed that the Na2O concentration of the prepared sodium silicate was 12.74 wt% whereas that of the commercial sodium silicate was 12.00 wt%. Table 2 also presented the SiO2/Na2O of the prepared and commercial sodium silicate. It could be observed that the SiO2/Na2O ratio of the prepared sodium silicate was 2.21whereas the commercial sodium silicate had SiO2/Na2O ratio of 2.50; 13% higher than the prepared sodium silicate.


Table 1: Concentration of silica (SiO2) using UV/V is spectroscopy analysis Sodium silicate

Conc. (ppm)

Actual wt%

Prepared

56.246

28.123

Commercial

60.033

30.016

Table 2: Na2O concentration using flame photometer analysis and the SiO2/Na2O Sodium silicate

Conc. (ppm)

Actual wt%

SiO2/Na2O

Prepared

50.976

12.744

2.21

Commercial

48.00

12.000

2.50

The FTIR spectra of the commercial and the prepared sodium silicate is shown in Figure 2. As could be observed, both spectra possessed similar patterns having infrared wave bands at 1000, 1500, 1700 and 3500 cm-1. However it could be observed that the commercial sample had relatively very low band intensity (high percentage transmittance) at wave length of 1500 cm-1 while the prepared sample had relatively very high band intensity (low percentage transmittance) at the same wave, the intensity ratio was 1:7. Similarly the band at 1700 cm-1 followed the same pattern and the intensity ratio was 1:3. However, for the commercial sample, the band at 3500 cm-1 was steep, while for the prepared sample, the band was broad extending between 2900 and 3500 cm-1. Although, the band at 3500 cm-1 was due to –OH stretching [14], the broadness of this band in the prepared sample was likely due to the chemical nature environment and the interactions there. Figure 3 shows the TGA/DTG curves of the prepared sodium silicate for thermal scan between 30 to 300˚C. It could be observed that total mass depletion resulting from the thermal treatment was about 53%. The DTG curve showed that the actual temperature responsible for the thermogravimetric mass depletion was around 200˚C. Therefore, it could be deduced that the sodium silicate was thermally stable up to about 200˚C, the DTG curve showed that further heating above 200˚C would denature the material. It was also observed that the material became solid after the thermal scan, the possible explanation for this was that the liquid sodium silicate could have transformed to solid metasilicate after heating above 200˚C.

CONCLUSIONS Characterization of the sodium silicate prepared showed close resemlance to the commercial sodium silicate. The sodium silicate prepared had SiO2 and

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Na2O concentrations of 28.12 and 12.74 wt% respectively, and SiO2/Na2O ratio of 2.21. Whereas the commercial sodium silicate had SiO2 and Na2O concentrations of 30.02 and 12.00 wt% respectively, and SiO2/Na2O ratio of 2.5, both the commercial and the prepared sodium silicate possessed similar FTIR spectra having infrared wave bands at 1000, 1500, 1700 and 3500 cm-1. The prepared sodium silicate was thermally stable up to temperature of about 200˚C, the DTG curve showed that further heating above 200˚C could result to transformation into metasilicate.

ACKNOWLEDGMENTS The authors gratefully acknowledge the financial and technical supports of Petroleum Technology Development Fund (PTDF), Abuja and Department of Chemical Engineering, Ahmadu Bello University, Zaria.

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Fig. 1: Calibration curve for silica using UV/Vis spectroscopy

Fig. 2: FTIR spectra of commercial and prepared sodium silicate.

Fig. 3: TGA/DTG curves for the prepared sodium silicate


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