Synthesis of Mesoporous Silica Xerogel from Geothermal Sludge using Sulfuric Acid as Gelation Agent

A large amount of sludge is produced by the geothermal brine at the Dieng Geothermal power plant, exceeding ۱۶۵ tons per month. This sludge is generally not utilized, except for use in landfills. The precipitate (sludge) is primarily composed of silica. The aim of this research is to synthesis mesoporous silica (SiO۲) xerogel from geothermal sludge (GS) and to investigate the effects of pH as an effort to elevate the economic value of sludge through alkaline extraction followed by acidification. SiO۲ xerogel was prepared by extracting the GS to become sodium silicate (Na۲SiO۳) assisted by a base NaOH and precipitated using H۲SO۴ as a gelation agent. The FTIR analysis of the SiO۲ xerogel showed a group of silanol (Si-OH) and siloxane (Si-O-Si). The XRD analysis indicated that SiO۲ xerogel was amorphous. Furthermore, it was observed from nitrogen absorption-desorption using BET (Breneur-Emmet-Teller) method test that decreased pH tends to the specific surface area increase, and the pore size becomes decrease. The largest specific surface area observed at SiO۲ xerogel prepared at pH of ۵.۵ reached ۴۰۰.۱۰ m۲/g with a pore size of ۴.۵ nm. The pore sized for all cases was in the range of ۴ ~۱۲ nm, indicating that the SiO۲ xerogels were mesoporous. Pore size of the as-prepared silica affected the thermal stability property of the sample.

Keywords:

SiO۲ Mesoporous , Geothermal Sludge , Gelation Agent , Alkaline Extraction , High specific surface area