Mineralogical composition and particle size distribution as a key to understand the technological properties of Ukrainian ball clays

The ball clays from the Donetzk basin, Ukraine are widely utilized in the production of ceramic tiles. Their commercial success stems from unrivaled technological properties, whose link to mineralogical composition and particle size is not well understood yet. This work is an in-depth investigation of the mineralogical, chemical, and physical properties with the aim to disclose the reasons of the peculiar technological behavior of these clays. Five clay samples were studied by XRF, XRD (bulk and fractions <. 2. ?m and <. 0.2. ?m), SEM, TEM, rheological characterization, particle size distribution, BET, MBI, Pfefferkorn index, Atterberg plasticity limits, and laboratory simulation of the tilemaking process. The Ukrainian clays are very fine-grained and characterized by poorly ordered kaolinite (Kaol), interstratified illite/smectite (I-Sm) and a low quartz content. The Kaol-to-I-Sm ratio is lower than in conventional ball clays and two different I-Sm types are found to be predominant in the colloidal fraction. Morphologically, clay minerals appear to be mostly subhedral lamellae that curl and fold under pressure. These characteristics explain the outstanding technological properties of Ukrainian clays and particularly their high plasticity and suitable rheological behavior. These properties depend on the peculiar conjunction of mineralogical and grain size factors that are difficult to be reproduced by clay blending or mixing design.