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

Abstract

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.

Keywords

• bentonite
• geopolymer
• geothermal silica
• response surface design
• valorization.