The dissolution behavior of Nb2O5, Ta2O5 and their mixture in highly concentrated KOH solution

The dissolution behavior of Nb2O5, Ta2O5 and their mixture in highly concentrated KOH solution (> 50% wt.) has been investigated. A 43 orthogonal design was used to study the effects of four leaching parameters, reaction temperature, KOH/Nb2O5, mole ratio, agitation speed and reaction time on the dissolution yield of Nb(V). It was found that the effect of reaction temperature on the dissolution yield of Nb(V) was much greater than that of the other three factors. The results of factorial experiments showed that a high KOH concentration was benefit to the formation of soluble potassium hexaniobate, but high temperature was benefit to the formation of insoluble potassium niobate, and almost all Ta2O5 was converted into insoluble potassium tantalate. The insoluble potassium niobate and potassium tantalate were analyzed by XRD, which were proved to be KNbO3 and KTaO3, respectively. The dissolution behavior of the mixture of Nb2O5 and Ta2O5 was similar with that of Nb2O5.