GB640348A - Improvements in processes for producing magnesium hydroxide from magnesium salts in aqueous solutions - Google Patents

Abstract

In making magnesium hydroxide by reacting calcium hydroxide with magnesium salts convertible by lime, e.g. sea water, calcium hydroxide made from calcined lime or calcined dolomite is made into a milk and mixed with the magnesium salt solution, the reaction being effected under normal conditions in the presence of agitated seeding magnesium hydroxide, and either the solid products are separated from the mother lyes and the separated magnesium hydroxide returned to the reaction as new seeding material, or the liquid is returned without separation of the magnesium hydroxide, the returning of the magnesium hydroxide from a previous reaction for seeding material in a following reaction being continued repeatedly until the final precipitate has acquired the desired physical properties. When this state is reached a fraction of the final precipitate is returned for seeding and the remainder is taken away as normal product. The calcium hydroxide milks, freed from coarse impurities, may be made and, if desired, diluted with the mother lyes or a fraction of the non-separated mixture of magnesium hydroxide and mother lye. The seeding precipitate may be injected into the magnesium salt solution or into the milk or into both prior to mixing. In one embodiment, the products flow continuously through a series of successive tanks provided with agitators, the reagent milk, seeding precipitate from the separating device and, if desired, diluting liquid taken from the last tank, being admitted into the first tank while magnesium salt solution is admitted into the following tanks from the second to the last from which the overflow is returned partially to the first tank and partially to the separating device. The Specification as open to inspection under Sect. 91 comprises also the addition of the reagent in powdered form or, as a thick wash, to the brine, and the use of a channel tank, the reagent milk, seeding precipitate and diluting liquid being admitted at the head or intake of the channel, magnesium brines being added in fractions along the channel and the overflow from the end being returned partially to the intake and partially to a separating device. This subject-matter does not appear in the Specification as accepted.