Microstructural Investigations Regarding Sustainable Recycling of Ceramic Slurry Collected from Industrial Waste Waters

Abstract

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.

Conditioning Influence of Kaolinite Matrices on Flexural Strength of Raw Pressed Slurry Collected from Ceramic Tile Production Wastewater

“…This additional reinforcement might be useful for developing ecological bricks using low thermal treatment or for chemical activation via geopolymer consolidation. The flexural strength obtained for S4 is compatible with the compressive strength achieved at the same compaction load observed in our previous study [16] that makes our composite material suitable as a plaster for ecological houses that are desired to minimize the carbon footprint. This is the path for our further research regarding the rich kaolinite matrix composite containing quartz and mullite particles as filler.…”

“…Some local appreciation of the kaolinite amount regarding the quartz proportion was noticed [19]. The general microstructural aspects and compression strength of the raw pressed samples were also discussed in another one of our previous studies [16], revealing a better consistency of the mineral composition of the slurry in the solid state (e.g., dense paste with relative low humidity), the dominant mineral being quartz followed by kaolinite and mullite and a low amount of lepidocrocite. Our preliminary results show that kaolinite presents both bigger particles and very small ones, even nanoparticles in the range of 40-60 nm [16,19], that are responsible for the microstructural cohesion.…”

“…The general microstructural aspects and compression strength of the raw pressed samples were also discussed in another one of our previous studies [16], revealing a better consistency of the mineral composition of the slurry in the solid state (e.g., dense paste with relative low humidity), the dominant mineral being quartz followed by kaolinite and mullite and a low amount of lepidocrocite. Our preliminary results show that kaolinite presents both bigger particles and very small ones, even nanoparticles in the range of 40-60 nm [16,19], that are responsible for the microstructural cohesion. Thus, we wonder if such a mixture might be conditioned as a composite matrix to enhance the filler particles of quartz and mullite and to follow the conditioning effect on the flexural behavior of the raw pressed samples.…”

“…When kaolinite particles are under intensive movement, admixture with other, harder, mineral particles like quartz might act as milling bodies generating very small fractions. Such a mechanism was observed in the quartz-kaolinite interaction in environmental street dust [11,12], but it is currently used in raw material preparation in the ceramic industry for porcelain pottery [13,14] and ceramic tiles [15,16]. The mineral admixture is milled under a wet condition at a very well-controlled humidity level to obtain ceramic paste, which is further molded into dies.…”

Investigation of Used Water Sediments from Ceramic Tile Fabrication

“…lepidocrocite does not affect the utilization. Some of our preliminary studies proved that the compressive strength of the pressed slurry can be increased by a proper compaction of the microstructure [37]. The study must be continued, and an investigation of the effect of the conditioning of the kaolinite matrix on the flexural strength of the pressed samples would be valuable.…”