The conversion of Na3VO4 center dot nH(2)O to calcium vanadate is one of the key operation units of the vanadium cleaner production process. The solubility data for the Na2O-V2O5-CaO-H2O system at (40 and 80) degrees C therefore were studied in a wide alkali concentration range from (40 to 540) g.L-1 Na2O in order to optimize the conversion process. From the data, a method of producing calcium vanadate from Na3VO4 center dot nH(2)O and leaching calcium vanadate from vanadium slag and other calcium vanadate containing materials is proposed.