Precipitation of magnesium hydroxide from hard coal mine brine, which contained 2.84 kg m(-3) Mg2+ and 68.06 kg m(-3) Cl-, by means of sodium hydroxide was tested. In order to increase the sedimentation and filtration rates of the acquired Mg(OH)(2) a so-called forming (of the precipitate) was applied which consisted in introduction of NaOH to a solution containing Mg2+ ions without stirring. The mixture was then left to stand for some time (called time of forming) and then stirred in order to get quantitative reaction. Within the time of forming, tau = 0-24 h, the sedimentation rate increased about 5 times and the filtration rate increased about 60 times. Humidity of the filter cake was also reduced. The microscopic observation showed an increase of particles, and X-ray structural analysis showed an increase in degree of order of Mg(OH)(2) crystal structure when the time of forming increased.