dDissoin of K, Na, and NH4 vanadates in aq. urea was described in terms of the layer dissoin. model, which was oversimplified dc/dt = k'AD((c(sat)-c)/l) e k(c(sat)-c)(n), and integrated to give (c(sat)-c)(1-n) = c(sat)(1-n) + (n-1)kt. where c(sat) saturation concn., D diffusion coeff., c bulk conc., I - limiting layer thickness. In the KVO3 + CO(NH2)(2) + H2O, NaVO3 + CO(NH2)(2) + H2O, and NH4VO3 + CO(NH2)(2) + H2O systems, 293 K, the expti. dissoin. data gave n, 2.788, 1.944y 1.410; k, 1.415y 1.374, and 0.500 mol/(1(.)hr), c(sat), 0.556, 0.911, and 0.116 vs. the calcd. 599, 0.921. and 0.116 mol/l, resp.