GEOTHERMAL SILICA WASTE AS SUSTAINABLE AMORPHOUS SILICA SOURCE FOR THE SYNTHESIS OF SILICA XEROGELS

Abstract

Silica waste from the geothermal plant in Dieng-Indonesia can be utilized as amorphous silica source regarding the high content of silica and high productivity in the plant. However, in the presence of metal oxides, a series of purification steps need to be carried out. This paper describes silica xerogels preparation via acid leaching and sol gel method. Sulfuric acid was chosen in acid leaching due to corrosivity and safety factors. In the beginning, FTIR spectrophotometry and BET-BJH of geothermal silica revealed characteristic functional groups and physisorption of amorphous silica. Response data were collected based on XRF data to obtain silica content at optimum sulfuric acid concentration. To ensure the optimum data, it was confirmed by using XRF at prior and post leaching. The result informed that acid leaching attained optimum at 25% of acid concentration with R2 = 1 releasing more than 98% of silica. Leached silica was introduced a sol-gel method by using NaOH 2 N with a ratio of SiO2 to NaOH (1:6 (w/V)) followed 1 N of HCl addition. The product was aged for 18 h before washing and drying at 105 °C. The functional groups spectra such as hydroxyl (-OH), silanol (Si-OH), and siloxane (Si-O-Si) account for the molecular model that might be formed along with the polymerization process. Analysis of SEM and FTIR confirmed morphology, particle size, and disappearance of organic functional groups during the xerogel synthesis process from geothermal silica.