Total Silica Analysis Using a Double Beam Atomic Absorption Spectrophotometer

Abstract

Total silica in geothermal brine when diluted to concentrations less than 100 mg/l and acidified to pH 2.0 or less right after sampling will remain in solution as monomeric silica (Iler, 1978). Experimental runs using atomic absorption spectrophotometry (AAS) in analyzing total silica from geothermal brine was done at Southern Negros Geothermal Production Field (SNGPF) laboratory since 1998. The results were then compared with runs using UV-Visible spectroscopy, which is the standard method adopted by all PNOC-EDC laboratories. This study aims to obtain percent difference of less than 5% with the colorimetric method (UV-ViS) in terms of ppm result. Comparatively the alternative method is cheaper and faster compared with the traditional technique. Repeatable results can be obtained within several minutes to an hour upon sample receipt. Between 2002 to 2003 SNGPF laboratory have used the method of AAS for analyzing total silica. The method was also used in the 2003 IAEA water inter-lab consisting of medium and highly saline brine waters. The results passed for both water types. Optimum instrument settings and stable current is a must for attaining quality results.