An experimental study on the phase equilibrium of the quaternary system KVO_3-NaVO_3-CO(NH_2)_2-H_2O at 298K

The solubility of vanadium in soil solution is effected by the kinds of co-exist ion in soil.The equilibrium solubilities and phase diagram of the quaternary system KVO3-NaVO3-CO(NH2)2-H2O at 298 K are studied by isothermal dissolution equilibrium method.The reciprocal reaction between potassium,sodium,urea and metavanadate ion is investigated.The solubility diagram of the quaternary system consists of three crystallization fields,three univariant curves and one invariant point.At the invariant point,the saturated solid salts are KVO3+NaVO3+CO(NH2)2.No double salt or solid solution is formed.Three crystallization fields correspond to salt KVO3,NaVO3,and CO(NH2)2,respectively.The crystallization area of KVO3 is the largest.This shows that the presence of potassium in soil may reduce the solubility of vanadium.The salting-out effect lies in the salt of the system.