PURPOSE: To separate and recover high purity silica by treating an aqueous soln. of an alkali silicate with an ion exchange resin to remove impurities, neutralizing the remaining acidic silica sol with an aqueous soln. of ammonia, and adding an ammonium salt to precipitate SiO2 at a specified pH.
CONSTITUTION: A commercially available aqueous soln. of sodium silicate or potassium silicate contg. 20W35% SiO2 is diluted to prepare an aqueous soln. having 2W7% SiO2 content. This aqueous soln. is brought into contact with an ion exchange resin or the ion exchange resin and a chelate resin to separate and remove contained impurities such as alkali metals and alkaline earth metals. An aqueous soln. of ammonia is added to the remaining acidic silica sol of 1.8W3.0pH by ≤0.5mol per 1mol SiO2 to make the sol neutral or weakly alkaline. An ammonium salt such as NH4Cl or (NH4)2CO3 is then added to keep the sol at ≤10.5pH. High purity SiO2 is precipitated at ≤10.5pH, and it is separated by filtration and recovered.
MITA MUNEO
MORISHITA TOSHIHIKO
KOSHIMIZU HITOSHI
TORII KAZUYOSHI
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