Abstract
In this paper the stabilization of Cr4+ in new ceramic matrices as willemite Zn2SiO4 and galium-gadolinium garnet GGG (Gd3Ga5O12) is studied and compared with the chromium-sphene ceramic pigment using the traditional solid reaction and an unconventional coprecipitation method.The chromate amount etched from the powders using CrIII and CrVI precursors on ceramic and coprecipitation routes are analysed in order to evaluate the environmental impact on the waste water. Cr-willemite and codoped Ca, Cr-GGG produces solid solutions of Cr4+ ion occupying tetrahedral and dodecahedral sites, respectively, while Cr4+ into sphene lattice occupies octahedral sites. Cr-willemite are stable when used as ceramic pigment in habitual tile glazes but Cr-GGG unstabilses and produces green colour associated to Cr3+ solved in the glaze. Coprecipitate powders are more reactive than ceramic powders but in Cr-GGG stabilizes the metastable Ca3Cr2O8 oxide. Chromate amount in washing hot water are not dependent of the chromium precursor but depends of the allowed reactivity level and the reaction media.
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