Ceramic porcelain stoneware production with Spanish clays purified by means of the removal of iron compounds and organic matter using physical methods

Abstract As the production of ceramic porcelain stoneware in Spain is totally conditioned by the importation of ball clays, because of the lack of adequate Spanish ball clays, this work has focused on the formulation of ceramic porcelain body from Spanish clays purified by means of physical removal processes. This method was applied to three Spanish clays containing common clay impurities of iron (hematite and siderite) and organic matter. Iron removal was carried out using the wet sieve method, the hydrocycloning method and the electromagnetic filtering method, obtaining a reduction in iron content of up to 80 wt%, while the clay containing organic matter was treated thermally at 400 °C for 30 min so as to leave it almost completely purified. These treated clays, after being characterized (chemical and mineralogical composition, plasticity, organic carbon, thermal behaviour and colour), were used in the porcelain stoneware body composition instead of imported clays, the result being a composition capable of substituting the standard porcelain stoneware formulation in terms of sintering, morphology, colour, flexural strength and dilatometry.