Synthesis of the Vanadium Analogue of Potassium Jarosite

Abstract

The vanadium analogue of potassium jarosite was synthesized at 100 °C from VCl3 solutions containing an excess of K2SO4. The vanadium analogue (KV3(SO4)2(OH)6) has a minor hydronium ion content which substitutes for K and a slight deficiency of V; it has the R3m structure characteristic of jarosite-type compounds. The amount of precipitated KV3(SO4)2(OH)6 increases with increasing solution pH to about pH = 1.8, but levels off at higher pH values. Similarly, the amount of the vanadium analogue increases with increasing temperature (60 to 100 °C) and with increasing concentration of VCl3 (0.00 to 0.45 M). Regardless of the amount of precipitate, the composition of the vanadium analogue of potassium jarosite remains nearly constant under all the conditions evaluated. The addition of the KV3(SO4)2(OH)6 jarosite as seed to the synthesis solution accelerates the rate of precipitation and the initial rate of precipitation increases in a nearly linear manner with increasing seed additions. Although some V(III) substitutes for Fe(III), complete solid solubility does not exist, as demonstrated by the compositional and X-ray diffraction data. This behaviour is attributed to the rapid oxidation of trivalent vanadium by an excess of ferric ions and to the limited solubility of the tetravalent vanadium oxidation product in jarosite-type compounds.