Muhammad Olvianas

The study of geopolymers has become an interesting concern for many scientists, especially in the infrastructure sector, due to having inherently environmentally friendly properties and fewer energy requirements in production processes. Geopolymer attracts many scientists to develop practical synthesis methods, useful in industrial-scale applications as supplementary material for concrete. This study investigates the geopolymerization of fly ash and geothermal silica-based dry activator. The dry activator was synthesized between NaOH and silica geothermal sludge through the calcination process. Then, the geopolymer mortar was produced by mixing the fly ash and dry activator with a 4:1 (wt./wt.) ratio. After mixing homogeneously and forming a paste, the casted paste moved on to the drying process, with temperature variations of 30, 60, and 90 °C and curing times of 1, 3, 5, 7, 14, 21, 28 days. The compressive strength test was carried out at each curing time to determine the geopolymer’s strength evolution and simulate the reaction’s kinetics. In addition, ATR-FTIR spectroscopy was also used to observe aluminosilicate bonds’ formation. The higher the temperature, the higher the compressive strength value, reaching 22.7 MPa at 90 °C. A Third-order model was found to have the highest R² value of 0.92, with the collision frequency and activation energy values of 1.1171 day⁻¹ and 3.8336 kJ/mol, respectively. The utilization of coal fly ash and silica geothermal sludge as a dry activator is, indeed, an approach to realize the circular economy in electrical power generations.

Fly ash utilization is very urgent to be conducted alas contaminating the environment. One of the promising utilizations is geopolymer formation for material construction. In this study, geopolymer formation was studied using fly ash from PLTU Tanjung Jati Jepara. This study included kinetics prediction using solid state isoconversion kinetics that has been developed based on nucleation, geometric contraction, and diffusion models. Semi quantitative FTIR analysis (corr) has been applied to predict the kinetics of the fly ash geopolymerization in curing temperature of 30о and 90°C. In order to be able to verify the kinetics model time series data were taken in interval of 1,3,5,14,21, and 28 days. It is the diffusion model that represents the fly ash geopolymerization with R² of 0.9437.

Geothermal is one of the most reliable energy sources in Indonesia. The utilization of geothermal energy in the electricity generation provides green energy, as it can slow down the global warming and help control the climate change. However, the development of its capacity is still considerably slow. One of the most common problems encountered in geothermal power plants is silica scaling. This limits energy production by inhibiting the mass flow of the geothermal fluid and also adding resistance to the heat transfer. This study focuses on the silica precipitation of geothermal fluid using the addition of calcium hydroxide (Ca(OH)₂) in a continuous reactor. The experiment was conducted by varying the reaction times of 5.00 and 8.33 minutes; reaction temperatures of 30 and 70°C; and pH levels of 7 and 9. The silica concentration of the initial and processed fluids was analyzed using UV-Vis Spectrophotometry. The observed silica concentration of the initial fluid was 600 ppm, with the best concentration at 150 ppm (25%) under 5 minutes reaction time, 70°C of reaction temperature, and pH of 9. Significance analysis showed that the silica concentration in the fluid is decreased when pH is increased, but with a shorter time of reaction. In addition, pH has a significant effect on the silica precipitation, while temperature and reaction time are much less significant.

Suji (Pleomele angustifolia Roxb.) leaves are a prominent source of chlorophyll and well-known for their ability to produce green color for food ingredients. However, chlorophyll is suspectible to color degradation at high temperature. Color degradation occurred because porphyrin loses magnesium in its ring and it can be avoided by adding zinc. The aim of this work was to investigate the combined effect of independent variables on chlorophyll extraction process using ZnCl₂ as a stabilizer. Suji leaves were blanched with boiling water for 2 min, Zn-chlorophyll synthesis was done by varying concentration of ZnCl₂, Zn-chlorophyll extraction with ethanol, and UV–Vis spectrophotometry analysis of the final extracted solutions. A full three-level factorial design under response surface methodology was used to obtain the optimum condition of extraction process. The experimental data were analyzed by analysis of variance and fitted with second order polynomial equation. The coefficient of determination (R²) was found to be 81.99%. The optimum operating conditions were obtained at pH 7, ZnCl₂ concentration of 700 ppm and temperature of 85 °C with desirability value of 1.0000. At the optimum conditions, the total chlorophyll content (TCC) was found to be 47.2975 mg/100 g fresh weight.

The geopolymer structures are formed through polymerization of silicate and aluminate species. The resulted structure is predicted to be similar with zeolite. In this study, geopolymer samples were made from mix powder of geothermal silica and bentonite, then activated with sodium hydroxide and sodium silicate. The effect of silica content, NaOH molarity and curing temperature effect were investigated on geopolymer IR spectra and compared with 3A zeolite IR spectra. Pearson correlation value (r) and spectral similarity correlation (Corr) were used to assess spectra similarity between geopolymer samples and zeolite. The development of geopolymer bond and microstructure of samples were then investigated by FTIR technique. IR spectra of geopolymer samples show that Si-O-Al absorption bands are formed around 900-1300 cm^-1 and 400-800 cm^-1. The optimum of silica contents, NaOH molarity and curing temperature obtained from the experiment were 140 grams, 10 M and 80°C with Corr value of 922 and compressive strength of 7,59 MPa. Corr value is proven to have relation with material strength. Higher Corr value is identified to have higher aluminosilicate species which contributes to higher compressive strength.

Geothermal plant produces numerous kinds of possible side products. One of them is silica as a consequence of the existing silica scaling problem which causes geothermal power plant efficiency depletion. The silica recovery possesses a way to utilize it. Geopolymer concrete is a solution to utilize the abundance recovered geothermal silica with low energy consumption and green house gas emission. Thus, in this study, the geopolymerization of geothermal silica and kaolinite will be observed. Geopolymer was inorganic polymer consist of Si and Al atoms that formed through polymerization process. The raw materials being used are geothermal silica as amorphous silica source and kaolinite as alumina source, whereas the activator composed of sodium hydroxide and sodium silicate. Geothermal silica possesses amorphous structure which had been proven by X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) analysis with 96.09% silica (SiO₂) content and 18.92% alumina (Al₂O₃) content of kaolinite. The experiment conducted to determine geopolymerization rate of geothermal silica and kaolinite reaction in presence of alkali activator with certain composition and temperature variation ranged from 80°C up to 120°C. Study on geopolymerization rate was carried out by observing geopolymer bond along with the compressive strength as a function of curing time and temperature. As for geopolymer bonds for each sample with different curing temperatures, FTIR and SEM analysis were used to investigate.