basic zirconium carbonate and especially if the basic zirconium carbonate is to be converted into the oxide the use of the corresponding ammonium carbonate or ammonium hydrogen carbonate is recommended particularly good yields and a product which can be filtered especially well are obtained when ammonium hydrogen carbonate is used it is therefore preferable when using ammonium carbonate to introduce co 2 during the precipitation reaction in order to obtain the hydrogen carbonate in situ in this manner the amount of the purification effect achieved by the process of the present invention is seen from the following comparison of crude and purified products ______________________________________ end productstarting material basic zirconiumzr so sub 4 sub 2 4h sub 2 o carbonatein each case the data refers to thezro sub 2 content______________________________________fe sub 2 o sub 3 0 25 u2266 0 02 sio sub 2 0 15 u2266 0 05 tio sub 2 0 10 u2266 0 04 cao 0 20 u2266 0 02 ______________________________________ technically pure zirconium sulfate 356 6 g is dissolved with stirring in 1 5 l of water and filtered until clear after the addition of 50 g of sodium chloride the solution is stirred vigorously treated portionwise with a total of 148 4 g of sodium.