Precipitation of magnesium hydroxide

Mg(OH)2 was precipitated from MgCl2 and NaOH solutions in a continuous agitated reactor and the effects of the solutions concentration, residence time of suspension in the reactor and stoichiometric ratio of the reacting components on the properties of Mg(OH)2 were studied. The properties of the resulting suspension were evaluated on the basis of its filtration resistance α as determined by a filtration test. The value of α is inversely proportional to mean residence time of the suspension in the reactor and it depends, at the same time, on the ratio of concentration of the precipitated solutions γ = [MgCl2]/[NaOH]. A critical value of γ can be assessed for a continuous reactor and when this value is exceeded a comparatively well filtering suspension with α ≦ 1012 m · kg−1 is always obtained. The relationship between α and the parameters of the precipitation process was expressed quantitatively within the framework of the exiting theories.