Used water treatment is one of the most important aspects of environmental protection regarding industrial processes. Particulate matter dispersions affect water parameters; for example, increased pH values such as 10.21 are found for used floor tile water, and values of 10.84 are found for used wall tile water. However, pH decreases to about 9.42 after the sediment filtration process. This influences water turbidity, which is higher for used wall tile water due to its finer suspensions, and it is considerably decreased after the filtration process. Thus, the main aim of the present research is to investigate particulate matter dispersion into the water flows that are involved in ceramic tile technological processes before and after treatment at used water treatment facilities. X-ray diffraction (XRD) coupled with mineralogical optical microscopy (MOM) reveals that waters from wall tiles and floor tiles have similar mineral dispersions, containing mineral particles of quartz (5–50 μm), kaolinite (1–30 μm), and mullite (5–125 μm). Glass particles (having a dark appearance at MOM investigation) were also found in both samples in a size range of 20–55 μm. High-resolution SEM imaging coupled with the EDS elemental analysis confirms the XRD and MOM observations. Water samples collected after treatment at the treatment facility reveal a significant reduction in the particulate matter MOM, evidencing only small traces of quartz, kaolinite, and mullite in a size range of 1–15 μm, with most of the particles being attached to the filters, as confirmed by XRD. Atomic force microscopy (AFM) effectuated on this sample reveals the presence of kaolinite nanoparticles with a tabular–lamellar aspect and sizes ranging from 40 to 90 nm. The obtained results prove the efficacy of the filtering system regarding targeted particulate matters, ensuring water recirculation into the technological processes. The sludge resulting from the filtration process presents with a dense grainy structure of sediment particles containing quartz, mullite, and kaolinite, along with traces of iron hydroxide crystallized as goethite. Therefore, it cannot be reused in the technological flux, as the iron causes glaze staining; but the observed microstructure, along with the mineralogical composition, indicates that it could be used for other applications, such as ecological bricks or plasters, which will be further investigated.

Ceramic slurry wastes have a significant hazardous potential when dumped. Their recycling as raw material is a sustainable approach for the development of nature-friendly applications. The microstructure and mechanical properties play a key role in the success of this sustainable recycling. Ceramic slurry samples resulting from the wall and floor tiles production facility were analyzed. The mineral composition was investigated by XRD combined with mineralogical microscopy and the microstructure was investigated by SEM microscopy coupled with EDX spectroscopy and elemental mapping. The ceramic slurry contains: quartz, kaolinite, mullite and small amounts of lepidocrocite. Quartz and mullite particles have sizes in the range of 5–100 μm and kaolinite has small particles of around 1 to 30 μm. Iron hydroxide crystallized as lepidocrocite is finely distributed among kaolinite aggregates. It makes the slurry unable to be reused in the technological process because of the glaze staining risk, but it does not affect the material cohesion. Thus, the cylindrical samples were prepared at progressive compactions rates as follows: 1808.55; 1853.46; 1930.79 and 2181.24 kg/m³ and dried. Thereafter, were subjected to a compression test with a lower compression strength of 0.75 MPa for lower density and a higher strength of 1.36 MPa for the higher density. Thus, slurry compaction enhances the kaolinite binding ability. The Young’s Modulus slightly decreases with the compaction increasing due to local microstructure rigidizing. This proves the binding ability of kaolinite, which properly embeds quartz and mullite particles into a coherent and resistant structure. The fractography analysis reveals that fracture starts on the internal pores at low compaction rates and throughout the kaolinite layer in the samples with high compactness. The observed properties indicate that the investigated ceramic slurry is proper as a clay-based binder for sustainable ecological buildings, avoiding the exploitation of new clay quarries. Also, it might be utilized for ecological brick production.

Kaolinite is able to assure the high binding affinity of the filler particles of raw ceramic bodies. It acts as a matrix that strongly holds the other constituents’ particles in a compact structure. The slurry samples were characterized by XRD, mineralogical microscopy and SEM coupled with an EDX elemental analysis. The slurry collected from the ceramic tile production wastewaters had a significant amount of kaolinite (36%), mostly fine particles of 3 µm, less surrounding quartz (37%) and mullite (19%) particles of 5–100 µm in diameter and traces of lepidocrocite (8%). It is a dense paste with a relative moisture of 25%. The square bar of the slurry as received, pressed at a load of 350 N, had a flexural strength of 0.61 MPa. Increasing the moisture to 33% using regular water, followed by mechanical attrition at 2000 rpm for 5 min, resulted in a porous bar with a flexural strength of 0.09 MPa; by increasing the attrition speed to 6000 rpm, the microstructural homogenization was improved and the flexural strength was about 0.68 MPa. It seems that regular water does not assure an optimal moisture for the kaolinite matrix conditioning. Therefore, we used technological water at pH = 10, a moisture of 33% and attrition at 6000 rpm for 5 min, and the bar pressed at a load of 350 N had a flexural strength of 1.17 MPa. The results demonstrate that the bar moistened with technological water and an attrition regime assured a proper conditioning for the kaolinite matrix, achieving the optimal binding of the quartz and mullite particles under the pressing load. Bars with the optimal mixture were pressed at several loads, including 70, 140, 210 and 350 N, and the flexural strength was progressively increased from 0.56 MPa to 1.17 MPa. SEM fractography coupled with atomic force microscopy (AFM) revealed that the optimal moisture facilitated a proper kaolinite particle disposal regarding the quartz and mullite filler particles, and the progressive load assured the strong binding of the finest kaolinite platelets onto their surface.

Background: ceramic tile wastewater slurry contains a large amount of fine kaolinite particles acting as a matrix for mineral filler particles of quartz and mullite. Reinforcing it with natural fibers increases its compression strength. A novel approach is using Stipa pennata fibers because of their local availability, good mechanical properties, and feathery aspect, making them able to reinforce ceramic slurry compacts. Preparation and investigation methods: Slurry conditioned at 33% humidity and milled at 6000 rpm for 5 min contains 39% quartz, 37% kaolinite, 16% mullite and 8% lepidocrocite (observed via XRD correlated with mineralogical microscopy). Kaolinite particles ensure optimal binding of the mineral filler and the Stipa pennata fibers into a dense composite structure, as observed via SEM. EDS maps reveal a local increase in C content, along with the natural fibers being associated with significant levels of Al and Si, indicating the microstructural compactness of the reinforcement layer. An additional compaction load enhances microstructural cohesion. Results: The sample without reinforcement has a compressive strength of 1.29 MPa. This increases to 2.89 MPa by adding a median reinforcing layer and reaches 3.13 MPa by adding a compaction load of 20 N. A median crossed fiber-reinforcing layer combined with the compaction load of 20 N ensures a compressive strength of 4.78 MPa. Introducing two reinforcing layers oriented perpendicular to one another ensures a compressive strength of 2.48 MPa. Lateral placement of the two reinforcing layers regarding the sample median plan causes a slight decrease in the compressive strength. SEM fractography reveals that the feather-like structure of Stipa pennata fiber acts as an anchor for the median site of the samples, slowing crack initiation under compressive efforts, creating a novel approach compared to natural fiber without lateral flakes. Conclusions: The optimal place for the reinforcement layer is the median site of the sample, and interlaced reinforcement ensures the best compressive resistance. Ceramic slurry reinforced with Stipa pennata is useful as an intermediary layer on the modular walls of ecologic buildings.

The slurry collected from the waste water resulting from ceramic tile processing contains significant amounts of quartz, kaolinite, and mullite, along with traces of iron hydroxides as observed using XRD analysis coupled with mineralogical optical microscopy (MOM). Such an admixture would be ideal for the development of ecologic building materials. Microstructural conditioning enhances the binding properties of kaolinite. Therefore, the influence of the vibration compaction of the moistened slurry at 30% humidity on the compressive strength was assessed. The compressive strength of the unvibrated sample is about 0.8 MPa with failure promoted by the microstructural unevenness. Several vibration amplitudes were tested from 20 to 40 mm. The optimal vibration mode was obtained at an amplitude of 25 mm for 10 min, ensuring a compressive strength of 2.37 MPa with a smooth and uniform failure surface involved within the binding layer as observed using SEM microscopy. The samples prepared under optimal conditions were thermally consolidated at 700, 800, and 900 °C below the mullitization temperature to ensure a low carbon footprint. XRD results reveal kaolinite dehydration in all fired samples, inducing its densification, which increases with increasing heating temperature. SEM coupled with EDS elemental investigations reveal that the dehydrated kaolinite better embeds quartz and mullite particles, ensuring a compact microstructure. The binding strength increases with the firing temperature. The mullite particles within the samples fired at 900 °C induce the partial mullitization of the dehydrated kaolinite matrix, increasing their homogeneity. The compression strength of the fired samples is temperature dependent: 4.44 MPa at 700 °C; 5.88 MPa at 800 °C, and 16.87 MPa at 900 °C. SEM fractography shows that failure occurs due to the dehydrated kaolinite matrix cracks and the quartz particles. The failure is rather plastic at low temperatures and becomes brittle at 900 °C. Reducing the firing temperature and treatment time reduces the carbon footprint of the consolidated ceramic parts. Samples fired at 700 °C exhibit a compressive strength comparable to low quality bricks, those fired at 800 °C exhibit a strength comparable to regular bricks, and those fired at 900 °C exhibit a superior strength comparable to high-quality bricks.