# Utilisation of Mining Waste for Production of Ceramic Tiles
## 3 Results  
Studies have shown that the increase in the content of sludge causes a successive decrease in the shrinkage of the tile ceramic masses and is typical for the swelling of this material, especially at lower firing temperatures. The linear change is significant in terms of determining tile sizes. Figure 3 shows the results of the total shrinkage measurements of beams fired in a gradient furnace. At sludge content greater than 50% by weight,the linear swelling of the samples is intense and reaches about 3%. The mass sinters at higher firing temperatures, that is, above 1050 \({}^{\circ}\)C, partially eliminating the swelling phenomenon. Therefore, in these sets of samples, in the temperature range of 1100-1150 \({}^{\circ}\)C, the phenomenon finally weakens, or there is no change in the linear dimensions of the samples at all. It can be noticed that the kinetics of swelling and shrinkage associated with the sintering effect differ for the tested samples; hence, there are extremes of changes in linear dimensions in the tested temperature range. In particular, this can be seen in sets containing sludge in an amount of 70 to 90 %wt, in which, at a temperature of about 1130 \({}^{\circ}\)C, a porous alloy (expanded clay LECA) is already formed, while for samples with 50 %wt sludge content (as in set P5), the sample dimensions change to a small extent. This proves that the phenomena related to the sintering and decomposition of carbonates are comparable. At this temperature, with sludge contents below 50 %wt (P2 \(\div\) P5), as the temperature increases, there is a successive reduction in the linear dimensions of the samples as a result of the sintering process. On the other hand, at sludge contents greater than 50% (P6 to P10), there is a successive increase in linear swelling associated with the decomposition of carbonates. The temperature at the beginning of sintering decreases with the increase in the amount of sludge, as shown by the black dashed line (Figure 3). The change in water absorption and total porosity is directly related to the change in sample shrinkage (Figures 4 and 5). The \"Gilow\" post-flotation sludge introduced into the sets results in a noticeable increase in the water absorption of ceramics depending on its share, especially at low firing temperatures, that is, up to 1100 \({}^{\circ}\)C. The water absorption results (Figure 4) demonstrate distinct sintering behaviour patterns depending on sludge content. In sets containing more than 80 %wt of sludge, as the firing temperature increases above 1050 \({}^{\circ}\)C, there is a rapid increase in water absorption associated with the so-called melt gassing and the opening of closed pores. The open porosity results of compositions after firing as a function of temperature are presented at Figure 5 and will be discussed later. Figure 3: Shrinkage as a function of firing temperature. The increase in water absorption at higher temperatures can be attributed to several factors. First, both materials contain compounds that decompose at elevated temperatures, releasing gases during firing. The LOI (loss on ignition) values of both materials (10.5% in sludge and 13.8% in TG3 clay; Table 4) suggest the presence of volatile components that would contribute to gas evolution during firing. It can be assumed that the gases released create internal pressure within the ceramic body [40; 41; 42]. At temperatures below 1050 \({}^{\circ}\)C, this gas release likely occurs while the ceramic matrix still has sufficient viscosity to maintain its structural integrity. However, as temperatures exceed 1050 \({}^{\circ}\)C, particularly in high-sludge-content compositions, the increased flux content may lead to significant reduction in melt viscosity. The combination of continued gas evolution and reduced matrix viscosity would result in bloating, pore coalescence and, ultimately, an increase in both open porosity and water absorption. [PERSON] et al.