Abstract: The invention concerns a process for the precipitation of aluminium hydroxide by seeding in two phases, which is intended to produce at a high level of productivity alumina with large grains, referred to as `sandy coarse`, by precipitation in a succession of tanks in cascade relationship of a supersaturated solution of sodium aluminate coming from alkaline attack on bauxite in accordance with the BAYER process. The process comprises three stages:in the first agglomeration stage, the supersaturated aluminate liquor is introduce into the tank, with an equivalent amount of terms of Na.sub.2 O of between 110 and 175 g/liter, at a temperature of between 65.degree. and 80.degree. C.