A Wet Purification Process for Diatomaceous Earth by Precipitation Method Using Nonaqueous Solvent

A wet silica purification method by precipitation in nonaqueous solvent is studied. This method can be applied in the treatment of resources containing alkali soluble silica. The process consists of three steps. At the first step, silica resource is leached in alkaline solution and filtrated. At the second step, the leach liquor is poured into nonaqueous solvent such as methanol or ethanol, and silica sediment is precipitated. At the third step, the sediment is washed with acid solution. The characteristic of this method is that alkali and nonaqueous solution used in the process can be easily recovered separately by heating at lower temperatures. In this study, diatomaceous earth was employed as the silica resource. It was leached in NaOH solution. By this method, Ba, Ca, Fe, K, Mg, Mn and Sr were removed effectively, but Al, Ti and Na had tendencies to remain in silica. The repeated treatment did not reduce Al and Ti contents effectively. In order to reduce the impurities, alkali leach liquor was pretreated with oxine etc. before the precipitation of silica by methanol. With this process Ti content was reduced effectively. The silica sediment formed in methanol method was the coagurate of spherical particles less than 1μm in diameter.