On the Stabilization of Nb^V-Solutions by Zr^IV and Hf^IV

Niobium cannot be separated from zirconium or hafnium when these elements occur together in solution with common anions such as Cl- and SO4—. This is ascribed to the copolymerisation of Nbv and the hydrolyzed ionic species of ZrIVv and HfIV by which the colloidal particles are masked as Zr- and Hf-compounds.

In HCl the particles are positively charged as opposed to when they are in sulphate solution where the Zr- and Hf-sulphate complexes confer a negative charge. The two cases are considered separately.