Sustainable Approach of Mineral Dispersion Recovery from the Technological Wastewater Resulting from Porcelain Manufacturing

Porcelain manufacturing technological wastewater contains many mineral particles, like kaolinite 27%, quartz 29%, calcium feldspar 15%, and mullite 12%. These particulate matters are dispersed into the wastewater from all technological steps influencing the water parameters, such as pH, electrical conductivity, total dissolved solids (TDS) and turbidity. These properties were measured and correlated with the physicochemical investigation of the collected particles. The two sample types are as follows: particles collected directly from the wastewater dispersion (WWS) and the slurry (SLR) collected from the dump. The mineral distribution was assessed by XRD correlated with mineralogical optical microscopy, revealing the relative distribution of the finest kaolinite particles with respect to quartz and feldspar boulder-like particles. Mullite was observed as a rounded inclusion occurring due to the re-circulated grounded material. It results in the presence of sodium silicate, acting as a densification binder when the samples are completely dried. Particle morphology was correlated with their elemental composition through SEM–EDX investigation. Iron hydroxide was found at about 9%. It prevents re-circulation of this wastewater slurry in porcelain production. Thus, a sustainable approach is required for its utilization as a sub-product. Therefore, the samples were subjected to thermal analysis in order to reveal its sintering behavior. Thermal analysis revealed the dehydroxylation of kaolinite between 530 and 630 °C, and a high-temperature thermal event at 994 °C (WWS) and 997 °C (SLR), which was further confirmed by DSC and attributed to mullite formation. Particle consolidation through the dehydroxylated kaolinite matrix and further mullitized mass was assessed through SEM microscopy, indicating proper densification to ensure slurry utilization for less pretentious ceramic products, allowing them to be fired at relatively lower temperature than porcelain (e.g., 600–800 °C) and ensuring a significant energy consumption saving.