Utilising feldspathic overburden and basement rocks from the Vidnava kaolin deposit as secondary raw materials for the ceramic industry

The study describes the first comprehensive research focused on the overburden and bedrock of the Vidnava kaolin deposit as substitute raw materials for the ceramic industry in the dependence of the context of reducing the European Union on imports of critical feldspars. These materials, previously considered waste, were characterised in terms of their chemical and mineralogical composition and subsequently tested for the first time in model porcelain-type ceramic materials. Recipes containing kaolin KD (the trade name for a commercially available type of kaolin), Vidnava feldspar detritus, and waste feldspar powder from the Halamky I deposit (all sourced in the Czech Republic) were evaluated after firing at temperatures of 1260°C and 1360°C in oxidising and reducing atmospheres. The results showed that the selected materials meet the requirements of the CSN EN 60672-3 standard for basic physical properties even at lower firing temperatures, but their use is limited by their higher iron content and the colouration of the firing ceramic shard, making them suitable for producing technical ceramics. Practical tests of the behaviour of the raw ceramic body during the pressing process confirmed its technological suitability for wet pressing technology. The second part of the study focusses on the modification of feldspar kaolins and weathered granites from the bedrock of the deposit by magnetic separation. The results confirmed the promising melting properties of the products obtained and the potential of the overburden and subsoil of the Vidnava deposit as a source of secondary raw materials for the ceramic industry.