High Purity Silica Nanoparticles from Geothermal Waste Brine as Reinforcing Filler in Rubber Composite Material

Abstract

Extraction of high purity silica nanoparticles from geothermal waste brine was studied as potential reinforcement for rubber. Properties of both as-received geothermal silica (AGS) and upgraded geothermal silica nanoparticles (UGS) were compared to the commercially-acquired precipitated silica (CPS). By X-ray fluorescence spectroscopy, AGS was found to have 58.19% Si content that was upgraded to 99.46% Si content (UGS). CPS, AGS and UGS were confirmed to be amorphous by X-ray diffraction analysis. Aggregate particles around ~100-300 nm were determined for CPS and UGS while AGS has around ~350-500 nm through Particle Size Analysis (PSA). Electron micrographs show that primary particles are around ~28-34 nm and ~40-65 nm in size for CPS and WGS, respectively. These differences resulted in the different properties of rubber filled with the three types of silica fillers. Mainly, due to the differences in particle sizes, the compound bearing AGS showed lower Mooney viscosity at (6 MU difference), faster curing at (0.4 min difference) and lower tensile modulus (about 1 MPa difference). Use of UGS showed improvements in the resulting rubber properties with the different parameters being comparable in value to those of the reference compound. Utilization of AGS and UGS will be beneficial both to the rubber and power industries – the former for its low-cost nature and potential as reinforcing filler in rubber compounds and the latter by resolving waste-handling problem in geothermal setting.