Environmental and colour optimisation of mineraliser addition in synthesis of iron zircon ceramic pigment

The traditional synthesis of iron zircon or 'coral pink' ceramic pigment, Fe-ZrSiO4, has been optimised with the aim of diminishing atmospheric emissions (SO2, F, Cl, NOx, ...) and Fe3+ or SO42- leachates in washing waters, while also maintaining a good colour yield. The employment of two different Fe precursors (sulphate and goethite) and the addition of several mineralising agents (alkaline or alkaline earth halides, KNO3, etc.) have been analysed. Goethite (FeO(OH) appears to be optimum environmentally (SO2 emissions and SO42- leaching are avoided), though the reddish colour obtained was poorer than with FeSO4. The results allow classification of the mineralisers studied into two major groups. One, primary or zircon forming mineralisers, which promote zircon formation with good occlusion of hematite in the zircon matrix (NaF, NaCl, and BaF2 when using FeSO4, Na2SiF6, and NaAl3F6 with goethite), and two secondary or modifying mineralisers, that have a collateral effect on the pigment synthesis regulating both hematite crystallisation and occlusion (KNO3, Na2SiF6, and NaAl3F6 with FeSO4, KI, and KNO3 with goethite). Environmentally, Two compositions mineralised with the binary systems NaF-NaAl3F6 and NaF-BaF2 have been found to minimise iron and sulphate leaching and also give a good colour yield.