• International Journal of Technology (IJTech)
  • Vol 12, No 1 (2021)

Valorization of Geothermal Silica and Natural Bentonite through Geopolymerization: A Characterization Study and Response Surface Design

Valorization of Geothermal Silica and Natural Bentonite through Geopolymerization: A Characterization Study and Response Surface Design

Title: Valorization of Geothermal Silica and Natural Bentonite through Geopolymerization: A Characterization Study and Response Surface Design
Himawan Tri Bayu Murti Petrus, Muhammad Olvianas, Widi Astuti, Muhammad Istiawan Nurpratama

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Cite this article as:
Petrus, H.T.B.M., Olvianas, M., Astuti, W., Nurpratama, M.I., 2021. Valorization of Geothermal Silica and Natural Bentonite through Geopolymerization: A Characterization Study and Response Surface Design. International Journal of Technology. Volume 12(1), pp. 195-206

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Himawan Tri Bayu Murti Petrus 1. Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika No. 2 Kampus UGM Bulaksumur, Yogyakarta 55281, Indone
Muhammad Olvianas Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika No. 2 Kampus UGM Bulaksumur, Yogyakarta 55281, Indonesia
Widi Astuti Research Unit for Mineral Technology, Indonesian Institute of Sciences (LIPI), Jl. Ir. Sutami Km. 15, Tanjung Bintang, Lampung Selatan, Indonesia
Muhammad Istiawan Nurpratama PT. Geo Dipa Energi (Persero) Unit Dieng, Jl. Dieng RT. 01/ RW. 01, Area Industri, Sikunang, Banjarnegara, Kabupaten Wonosobo, Jawa Tengah 56354, Indonesia
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Abstract
Valorization of Geothermal Silica and Natural Bentonite through Geopolymerization: A Characterization Study and Response Surface Design

Geothermal silica is a potential source of amorphous silica for producing geopolymer concrete. The valorization of geothermal silica as a geopolymer concrete provides an opportunity for an added value to the geothermal-based power industry. In this study, silica content, NaOH molarity, and curing temperature effect were investigated and optimized for compressive strength using response surface methodology. The effect of the single parameter on geopolymerization was qualitatively observed using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy-coupled with energy dispersive X-ray spectroscopy (SEM-EDS). The characterization of the geopolymer samples using FTIR and SEM-EDS revealed that the aluminosilicate structure was formed in all geopolymer samples. The geopolymerization rate can be accelerated using the lower level of geothermal silica and the high level of NaOH molarity and curing temperature. Based on optimization studies, the R-square value was 99.89%. The optimum formulation was found at a silica content of 130 g, NaOH molarity of 10 M, and curing temperature of 80°C with a desirability value of 0.99. At the optimum condition, the compressive strength was calculated as 7.73 MPa.

Bentonite; Geopolymer; Geothermal silica; Response surface design; Valorization.

Introduction

Geopolymers can be produced by combining various solid aluminosilicate materials with a mixture of high concentrations of alkaline hydroxide and silicate solution (Hajimohammadi et al., 2008). Geopolymer possesses a three-dimensional structure that consists of an amorphous polymeric Si-O-Al framework (Hajimohammadi et al., 2010). These materials can be categorized as eco-friendly in comparison with Portland cement in terms of CO2 emission during the production process (Duxson et al., 2007; Hajimohammadi et al., 2008). Geopolymers exhibit excellent physical properties, such as relatively high mechanical strength, resistance to an acid environment, and heat resistance (Nurjaya et al., 2015) and possesses low thermal conductivity (Skvara et al., 2005; Duxson et al., 2007). Having those excellent properties, geopolymer has been recognized as a promising technology to substitute conventional cement in the construction industry and as a new method to utilize industrial and radioactive waste (Xua and van Deventer, 2003). Raw materials for geopolymer synthesis are varied and include fly ash, bottom ash, natural clays, and minerals, as well as metal slags (Heath et al., 2014; Ashadi et al., 2015). Many studies have concentrated on fly ash-based geopolymer due to its chemical suitability and relative abundant availability (Zhang et al., 2012). Fly ash and metakaolinite, which are classified as calcined materials, have a faster dissolution and gelation and exhibit higher compressive strength (Xua and van Deventer, 2003; Skvara et al., 2005). Recently, there has been a new trend to use a different source of aluminosilicate precursors, instead of fly ash, for geopolymerization (Perná et al., 2014). Xua and van Deventer (2003) studied the geopolymerization process using different sources of material (kaolinite, albite, and fly ash). Mixing these source materials can produce geopolymers of a higher mechanical strength. Alshaaer (2013) showed that additional immersion of kaolinite-based geopolymer in 6 M of alkaline solution for 1 hour can modify the geopolymer surface and enhance its compressive strength. Red mud and bauxite have also been utilized as geopolymer materials (Hairi et al., 2015).

Moreover, geothermal silica can also potentially be used as a geopolymer precursor due to its reactivity. At the geothermal power plant operated by PT. Geodipa Energy in Dieng, Jawa Tengah, Indonesia, approximately 250 tons of geothermal silica (inset of Figure 1a) are removed from the process equipment, collected in sedimentation ponds, and then dumped into landfills. The study of geopolymerization using geothermal silica is still lacking. Previous studies have presented the effect of a single variable on geopolymerization using a mixture of geothermal silica-kaolinite and geothermal silica-bentonite (Olvianas et al., 2015; Petrus et al., 2016). However, the effect of combined variables and associated optimization studies have not been reported. To analyze the various factors of geopolymerization, this study adopted response surface methodology (RSM). RSM is a statistical technique for process evaluation and optimization used in industries and research fields to control process response or independent variables (Dhakal et al., 2014; Ferdana et al., 2018; Petrus et al., 2020; Januardi and Widodo, 2020). It has been used in the field of geopolymer and concrete to optimize various parameters (Dhakal et al., 2014; ?im?ek et al., 2015; Gao et al., 2016; Mohammed et al., 2018). To this end, the present work was conducted to optimize the compressive strength of geopolymer material from a mixture of geothermal silica and bentonite. The combined effect of silica content, NaOH molarity, and curing temperature were investigated using a full two-level factorial design in RSM. The effect of a single variable on the chemical bond and microstructure was also observed using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy-coupled with energy dispersive X-ray spectroscopy (SEM-EDS).

Conclusion

A geopolymer has been successfully produced by using geothermal silica and bentonite. Its characterization using FTIR and SEM-EDS showed that the aluminosilicate structure was formed in all prepared samples. The effects of combined variables have been studied and optimized using the RSM technique. The geopolymerization rate can be accelerated using the lower level of geothermal silica and the high level of NaOH molarity and curing temperature. Based on optimization studies, the coefficient of correlation (R2) obtained was 99.89%. The optimum formulation (desirability value = 0.99) for geopolymer production from geothermal silica and bentonite is using 136 g of silica content, 10 M of NaOH molarity, and 80°C of curing temperature. At the optimum condition, the compressive strength was 7.73 MPa.

Acknowledgement

This research was financially supported by AUN-SEED-Net JICA Common Regional Issues (CRC) 2016. The authors also acknowledge PT. Geodipa Energy, Dieng for providing geothermal silica, Unconventional Georesources Research Center, UGM and LIPI' Science Services for Research Laboratories for supporting this research.

Supplementary Material
FilenameDescription
R3-CE-3537-20200829120848.pdf ---
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