Thesis (M.Sc.)--Chulalongkorn University, 2002

The silicate extraction method was developed by using the principal of sequential extraction method. Five of silicate species, namely manganese bound silicates (Mn-Si), aluminum bound silicates (Al-Si), iron bound silicates (Fe-Si), biogenic silicates (B-Si) and residual silicates (Res-Si) were examined in sediments from Mae Klong, Bang Pakong and Chao Phraya estuaries. These sediments were divided into < 114 micrometre, >114 micrometre and non-sieved. The results indicated that residual silicates are the highest species in all three sediment samples, following by biogenic silicates, iron bound silicates, aluminum bound silicates and manganese bound silicates. Except in sediment size < 114 micrometre from Mae Klong and Chao Phraya, the aluminum bound silicates are higher than iron bound silicates. Total silicates hve been analyzed by X-ray fluorescence spectrometry (XRF) and acid digestion (HF-HCIO[subscript 4]-HNO[subscript 3]) in order to assess the accuracy of the sequential extraction method. Moreover, mineralogical analysis by X-ray diffractometry reveals minerals occurring in neoformation or neocrystalline group, which verify the existence of the silicate species in the sediments.