Abstract: A flocculant for water treatment containing a highly polymerized silicic acid solution having a high concentration of SiO.sub.2 and an extremely low concentration of alkali metal substance, and a method for producing such flocculant. The silicic acid solution is prepared by treating an aqueous solution of an alkali metal silicate such as water glass to remove alkali metal and allowing the solution to liquefy after once gelling. The flocculant may further contain a water soluble metal salt such as ferric chloride or ferric nitrate.

Abstract: A flocculant for water treatment containing a highly polymerized silicic acid solution having a high concentration of SiO.sub.2 and an extremely low concentration of alkali metal substance, and a method for producing such flocculant. The silicic acid solution is prepared by treating an aqueous solution of an alkali metal silicate such as water glass to remove alkali metal and allowing the solution to liquefy after once gelling. The flocculant may further contain a water soluble metal salt such as ferric chloride or ferric nitrate.

Abstract: A method and flocculant for water treatment in which the highly polymerized silicic acid and a water-soluble salt of a metal capable of forming a hydroxide in water such as aluminum are added to the water to be treated. The highly polymerized silicic acid can be prepared by polymerizing water glass. In the case where the highly polymerized silicic acid and the water-soluble metal salt are prepared as a flocculant in the form of aqueous solution before adding to the water to be treated, the flocculant is maintained at a pH value of not less than about 2 or not lower than about 11. The flocculant may be a silicic acid solution of which the gel time is prolonged by being added with a substance capable to generate ferrice ion in the solution so that the flocculant can maintain high aggregation ability after being stored for a long time. The silicic acid solution may be polymerized before being added with such ferric ion generating substance.

Abstract: The present invention provides a process for separating floc in a liquid and for accomplishing the sedimentation of the floc, and provides an apparatus for carrying out the same. In the present invention, a plurality of partition chambers having a narrow gap and being constructed in a square and tubular shape is formed by a plurality of separate plates in the settling tank and a plurality of fins to hit the floc against the fin thereby catching effectively the floc suspended in the mother liquid and separating smoothly and accomplishing the sedimentation of the floc.