| 摘要 |
PROBLEM TO BE SOLVED: To easily polymerize silica monomers in a short time while avoiding a trouble of gelation by adding and mixing an acidic aq. soln. of ferric salt to an alkaline aq. sodium silicate soln. under stirring to prepare an iron-contg. silica acidic aq. soln. having a specified Si/Fe ratio and pH. SOLUTION: While an alkaline sodium silicate aq. soln. having about 3 to 12 wt.% concn. and about 11 to 13 pH is stirred, an acidic aq. soln. of ferric salt having about 1.5 to 10% concn. and about 0 to 1 pH is added and mixed within about 3 minutes, preferably about 0.5 to 1 minute, and the mixture is reacted at about 8 to 100 deg.C without gelation. As for the acidic aq. soln. of ferric salt, an ferric chloride aq. soln., ferric sulfate aq. soln. and ferric polysulfate aq. soln. are preferably used. Thereby, activated silica having an excellent flocculation accelerating effect is obtd. as the iron-contg. silica acidic aq. soln. having >=0.3 Si/Fe molar ratio, preferably about 0.5 to 3.0, and having <=2.0 pH, preferably about 0 to 1.
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