Phase composition and formation kinetics of polyvanadates in the KVO3-VOSO4-K2SO4-H2O system

Hydrolysis of KVO3 in a solution with pH 1.4-2 at 80 degreesC first yields the polyvanadate K2V12O31-delta. nH(2)O, which then converts to K2V6O16. nH (2)O via the intermediate compound KV5O13-delta. 2H(2)O, which is stabilize d by K2SO4. KVO3 solutions containing up to 10 mot % VOSO4 give a precipita te that consists of KxV12O31-delta. nH(2)O and K2V6O16. nH(2)O. Added VOSO4 favors the precipitation of KxV12O31-delta. nH(2)O (1.5 less than or equal to x less than or equal to 2.25, 0.4 less than or equal to delta < 1.15). Within the solution pH range 3-5, the precipitate is a mixture of KxV12O31- <delta>. nH(2)O and KxV3O8-delta. nH(2)O. A single-phase sample of the latt er with 1.02 less than or equal to x less than or equal to1.91 and 0 less t han or equal to delta less than or equal to 0.22 forms at pH 5 to 9. Polyva nadate precipitation from KVO3 solutions is characterized by a induction pe riod (nucleation), which is shorter in the presence of K2SO4 and is not obs erved at all in the presence of VOSO4. In these cases, the process is contr olled, respectively, by a second- and a third-order reaction on the polyvan adate surface.