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Abstract

A method is proposed for performing precipitation reactions which yields precipitate particles in the form of flakes. The precipitate particles are coarse, having cross-measurements in the order of 10 to 400 microns. According to this method, a suitable precipitant is one which will react with the ionic species to be precipitated and which is sparingly soluble, such as lime, and therefore capable of forming a slurry as opposed to a solution. Prior to adding the precipitant to the solution containing ions to be precipitated, the precipitant is slurried, normally in aqueous medium, and flocculated such that discrete floccules having diameters in the order of 1 to 6 mm are formed. Upon addition of the flocculated precipitant to the solution containing ions to be precipitated, a layer of precipitate forms on the surface of the precipitant floccules, encapsulating or partially encapsulating the floccule. Under agitation, the coated floccule breaks down releasing flakes of precipitate and exposing fresh surfaces of the precipitant floccule to allow continuation of the reaction. Liquid/solids separation and recovery of the precipitate by sedimentation, filtration or exfiltration is rapid and easy because of the relatively coarse size of the precipitate particles.

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