A method for preparing
anhydrous magnesium carbonate through a
magnesium-containing mother solution includes the following steps of firstly, adjusting the pH value, wherein
ammonia gas is introduced into the
magnesium-containing mother solution till the pH value is 10.0-12.0 to obtain Mg(OH)2
slurry; secondly, conducting CO2 carbonizing, wherein CO2 is introduced till the pH value is 7.5-8.0 to obtain a carbonized mother solution; thirdly, conducting
pyrolysis separation, wherein the carbonized mother solution is heated and decomposed to separate
solid and liquid and obtain MgCO3.3H2O
solid salt and a
pyrolysis separation mother solution; fourthly, conducting calcining, wherein MgCO3.3H2O is calcined to obtain
anhydrous magnesium
carbonate. Calcining is further conducted to obtain magnesium
oxide. The MgCO3.3H2O obtained through
pyrolysis separation is large in
granularity, the filter separation performance is good, the carrying amount of the mother solution is small, the MgO content reaches up to 47.3%, and the total yield of magnesium ions reaches up to 92.8%; the purity of the MgO product is high, and inorganic
ammonium salt type by-products can be co-produced; the method is simple in process, beneficial to industrial production, low in cost, green and
environmentally friendly.