A stabilized aqueous slurry of magnesium hydroxide and a method for preparing the same are provided. The method involves an aqueous magnesium hydroxide slurry prepared with a combination of (a) one or more polymeric dispersants and (b) one or more water-soluble alkali metal salts. Slurries prepared according to the invention are less susceptible to increases in viscosity upon standing and remain flowable after several days.

A method for producing a stabilized magnesium hydroxide slurry comprising physically deflocculating the magnesium hydroxide solids in a starting slurry to produce a stabilized magnesium hydroxide slurry. Depending on the chloride level of the starting slurry, a cationic polymer may be added to the slurry. Optionally a thickening agent may be added to the deflocculated slurry. Also disclosed is a stabilized magnesium hydroxide slurry produced by the method which may be transported and stored without substantial agglomeration of the magnesium hydroxide solids.

A treatment for reducing viscosity and inhibiting settling of an aqueous 30% or higher by weight magnesium hydroxide slurry which comprises adding to the slurry an amount, effective for the purpose of a combination of an alkyl sulfosuccinate surfactant, a xanthan gum and a clay.

A flame-retardant for a synthetic resin, which is obtained by surface-treating a magnesium hydroxide with an emulsion of a copolymer or polymer of the formula (1), ##STR1## wherein X is hydrogen, a phenyl group, etc., Y is an alkyl group, etc., each of R.sub.1 and R.sub.2 is hydrogen, an alkyl group, etc., m is 0 or a positive integer, n is a positive integer, and ".about." shows the polymerization state of a main chain, the formula (2), ##STR2## wherein X, Y, etc. are as defined in the formula (1), or the formula (3), ##STR3## wherein X and ".about." are as defined in the formula (1), each of Y.sub.1 and Y.sub.2 is hydrogen, an alkyl group, etc., each of R.sub.1, R.sub.2 and R.sub.3 is hydrogen or an alkyl group, and each of a, b and c is a positive integer, a resin composition containing said flame-retardant and a molded article thereof.

Magnesium hydroxide slurries and a method of producing same that can be shipped, without agitation, over a period of at least 28 days and can be readily removed from transport vehicles to customer storage. With respect to customer usage, such slurries can be readily handled without leaving significant residue in storage tanks and without fouling the customer's equipment. Also disclosed are magnesium hydroxide slurries containing a level of solids that is greater than what is commercially available and a method of producing same.