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

Abstract

The traditional synthesis of iron zircon or ‘coral pink'ceramic pigment, Fe–ZrS_iO₄, has been optimised with the aim of diminishing atmospheric emissions (SO₂, F, Cl, NO_x,...) and Fe³⁺or SO₂2-⁴ 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 SO₂-⁴ 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, Na₂ SiF₆, and NaAl₃ F₆ with goethite), and two, secondary or modifying miner alisers, that have a collateral effect on the pigment synthesis regulating both hematite crystallisation and occlusion (KNO₃, Na₂ SiF₆, and NaAl₃ F₆ with FeSO₄, KI, and KNO₃ with goethite). Environmentally, two compositions mineralised with the binary systems NaF–NaAl₃ F₆ and NaF–BaF₂ have been found to minimise iron and sulphate leaching and also give a good colour yield.