Several analytical techniques were used to identify and optimize the main variables affecting the separation of magnesium and calcium carbonates from dolomite using partial thermal decomposition followed by hydration and recarbonation processes, It is shown that by careful control of these variables, the MgO content in the calcium carbonate residue can be reduced to less than 3.3% in a single processing cycle, resulting in a suitable raw material for the production of portland cement, High purity hydromagnesite, having less than 1% total impurities, was obtained from the aqueous residue.