The traditional method to prepare silica uses sodium silicate, silicon tetrachloride and metasilicic
acid as silicon materials; however, except for sodium silicate, the other two materials are very expensive, and the use of oil shale ash as a silicon material not only may greatly reduce the production cost of silica but also contribute to the comprehensive use of oil shale resources .
Certain trace constituents, such as free carbon dioxide (CO2), total soluble iron (TFe), nitrate-nitrogen (N[O.sub.3-]N), ammonia-nitrogen (N[H.sub.4-]N), nitrite-nitrogen (N[O.sub.2-]N), fluoride ([F.sup.-]), and metasilicic
acid ([H.sub.2]Si[O.sub.3]), were also analyzed.
The addition of one molecule of water to metasilicic
acid generates silicic acid in the intestinal tract.