High-Grade Silica Refined from Diatomaceous Earth for Solar-Grade Silicon Production

A refining processing of high-purity silica from biogenic diatomaceous earth is newly proposed to exploit the steady and stable resource to the solar-power generation industry. The specimens collected from various representative diatomaceous earth deposits, including both marine and freshwater origin, were chemically analyzed. Trace element distribution in diatomaceous earth was influenced by the biotope habitat of diatoms, when compared to that in quartz of igneous origin. Al, K, and Fe were mainly terrestrially derived, while Si and B were from diatom shells. B content in diatomaceous earth specimens from lacustrine sources was less than that in marine origin. Diatomaceous earth was then dissolved into caustic alkaline solution. With a decreasing pH value, amorphous silica precipitated with impurities. Al and Fe were concentrated in silica precipitated in the pH range of 12.5−10.5, while B was more soluble than silica at pH less than 9. Silica can be precipitated in the pH range of 10.5−9.0, followed by acid leaching to reduce Al and Fe content. A simple chemical operation consisting of extraction, precipitation, and acid leaching has been proposed. Repetition of chemical processing 3 times provides more than 5 N silica from diatomaceous earth samples from freshwater-source rocks.