Magnesium oxide suitable for the use in basic refractories was prepared from dolomite (CaMg(CO₃)₂) by hydrochloric acid leaching, precipitation with CO₂ and thermal hydrolysis. Leaching of the dolomite ore in aqueous hydrochloric acid solution was investigated with respect to the effects of time on dissolution of the dolomite sample. The dependence of the observed dissolution rate on pH was established. In the carbonation experiments changes in pH, Ca₂₊ and Mg₂₊ concentrations versus time in the effluent solution were determined. Effects of the temperature on the precipitation rate of Ca²⁺ ions as solid CaCO₃ were studied. Experiments were conducted to determine the kinetics of thermal decomposition of MgCl₂^.6H₂O during pyrohydrolysis process. From high purity magnesium chloride brine magnesium oxide containing 98.86 % MgO was obtained with the thermal decomposition recovery of 98.10 %.