Process for the manufacture of coarse aluminum hydroxide

Claim 1

A process for the manufacture of coarse aluminum hydroxide having a maximum of 15 weight percent of particles with a diameter less than 45 micrometers by a two stage decomposition of a supersaturated alkaline aluminate solution, by the addition of aluminum hydroxide seed material of different quality to said aluminate solution in each of said two stages, which comprises (a) distributing the quantity of aluminum hydroxide seed material as follows: adding to said aluminate solution a first addition of fine seed material (primary seed material) in a first stage of the decomposition, where the quantity thereof is so calculated that the ratio between the supersaturation in grams of Al 2 O 3 per liter of aluminate liquor and the surface area of said seed material expressed in square meters per liter of aluminate liquor lies between 7 and 25 grams per square meter; and adding to said aluminate solution a second addition of coarse seed material (secondary seed material) in a second stage of the decomposition after an interval of approximately two hours after the first addition such that the total amount of seed material (primary and secondary seed material) is at least 130 grams Al(OH) 3 per liter of aluminate liquor; and (b) regulating the temperature of the decomposition in the following manner: conducting said first stage of the decomposition in a temperature range of 77 degrees Celsius to 66 degrees Celsius; and conducting said second stage of the decomposition at a reduced temperature which can be down to approximately 40 degrees Celsius.