Effect of sludge from wastewater treatment processing of a tobacco agroindustry in ceramics matrix

The sludge of a wastewater treatment plant of a tobacco processing agroindustry is a waste material, and although it is not considered a hazardous waste, its disposal must occur in landfills, which causes high costs. Therefore, a thorough study to find a suitable destination for the sludge is necessary. In this work, this sludge and red clay were prepared in different formulations, uniaxial compacted and fired at 950, 1050 and 1150°C to evaluate the effects of the incorporation of sludge to obtain ceramic materials and to verify the potential application in the construction industry. Water absorption increases with sludge content (due the evolvement of gases related to the decomposition of hemicellulose and lignin present in tobacco) and decreases with higher firing temperatures, ranging from 9.55% to 20.10%. Values of mechanical resistance ranged from 7.23 to 1.84 MPa at a firing temperature of 950°C, 7.58 and 1.78 MPa at 1050°C and 6.94 and 3.97 MPa at 1150°C. The results show that ceramic materials obtained are promising in the production of masonry blocks. The use of the sludge reduces the environmental impacts that may be caused by waste and decreases the amount of raw material extracted from nature.     

New waste-based clinkers for the preparation of low-energy cements. A step forward toward circular economy

This paper describes the use of industrial wastes arising from different production processes of the ceramic and marble industries as raw materials for the design and formulation of new cement clinkers with a high content of dicalcium silicate (Belite). The aim was to reintroduce these wastes in the industrial sector and take advantage of them for a greater environmental benefit, as indicated by the principles of the circular economy. Formulations containing 2.5, 5 and 10 wt% of chamotte and marble sludge, respectively, and a waste-free formulation have been designed to obtain clinkers with a content of dicalcium silicate higher than 60 wt%. The different blends have been studied up to a maximum temperature of 1390°C by Thermal Analysis. Other techniques such as XRD, XRF, Modified Bogue Equation, Quality Indexes (LSF, AM, SM) and Optical Microscopy have been used for the study and characterization of industrial wastes, the raw materials and the high belite-type cement dosages. The results indicate that this type of cements can be designed using different types of wastes and in this way reduce the environmental impacts caused by the extraction of raw materials and the deposition of the wastes in landfills, improving the circular economy of the construction industry.     

The effects of fine fire clay sanitaryware wastes on ceramic wall tiles

In the last decade, environmental preservation has become an important issue. Specifically, recycling of sanitaryware fine fire clay (FFC) waste is important for reducing costs. In this study, the use of FFC waste as an alternative raw material in the production of ceramic wall tiles was investigated. Five ceramic wall tile bodies were prepared by substituting kaolin (max. 15 wt%) with FFC wastes. All formulations were mixed, pressed into pellets and sintered at 1145 °C. The sintering behaviour was evaluated using an optical dilatometer. Water absorption, linear shrinkage and bending strength were also measured. This study revealed that FFC wastes are good alternative raw materials, and the corresponding formulations were shown to be viable in the manufacturing of ceramic tiles. The most remarkable conclusion from this study was that the addition of FFC waste decreased moisture expansion.     

Synthesis and characterization of calcium silicate insulating material using avian eggshell waste

This work focuses on the synthesis of calcium silicate insulating material via solid state reaction using avian eggshell waste as alternative calcium source. The calcium silicate formulations were mixed in a molar ratio SiO₂:CaO (1:1) and fired at 1100 °C for 24 h. The calcium silicate formulations were characterized by XRD, TG-DTA, dilatometry, SEM/EDS, and thermophysical properties (thermal diffusivity, heat capacity per unit volume, and thermal conductivity). The synthesized calcium silicate materials are composed mainly of wollastonite with minor amounts of larnite and rankinite. It was found that a processing of the avian eggshell waste (raw eggshell waste and calcined eggshell waste) had an influence on the thermophysical properties. Calcium silicate pieces were prepared by uniaxial pressing at 82 MPa, curing, and then testing to determine their use as thermal insulating material. The microstructure was evaluated by SEM. The results showed that both raw and calcined avian eggshell wastes could be used as an alternative calcium source in the calcium silicate formulation. It was found that the calcium silicate pieces reached low thermal conductivity values (0.252–0.293 W/mK). Thus, the developed calcium silicate materials using avian eggshell waste act as a good thermal insulation ceramic material.     

Use of industrial wastes in the formulation of olivine green pigments

This work describes the formulation and synthesis of Ni-olivine green pigments from industrial wastes, namely foundry sand and a sludge resulting from the wastewater treatment of the Ni/Cr galvanising process. This second one is considered as hazardous waste since the leached levels of nickel and chromium are above legal concentrations. Pigments were prepared by the solid state reaction method and Ni₂SiO₄ is formed at only 1050 °C. SiO₂ (in excess) and NiCr₂O₄ are present as secondary phases. By using pure reagents and following similar processing conditions, the Ni-olivine phase is only observed at 1200 °C. The green colour of the pigments is due to spin-allowed transitions of Ni²⁺ in octahedral M1 and M2 positions. The sample prepared from wastes shows a stronger and darker green hue. The colouring performance of ceramic glazes and bodies is also optimal, confirming the potential of the use of such wastes for ceramic pigments production.     

Granite waste and coffee husk ash synergistic effect on clay-based ceramics

Brazil produces massive amounts of granite sawing waste and coffee husk ash and their inadequate and, often, illegal disposal causes enormous environmental problems. In the past decade, these and other industrial wastes have been intensively studied aiming at determining their potential as alternative raw materials, particularly for the ceramic industry. This work describes research carried out on the joint incorporation of those wastes in ceramic roof tile formulations. The results indicated that the simultaneous use of both materials translates into a very forgivable industrial working range, both composition- and temperature-wise, which, given the technological properties values observed after firing at 1100°C, enables industrial up-grade to wall tile production. As collateral benefits, the use of granite waste and coffee husk ash as alternative raw materials in the manufacture of clay-based products will relieve the stress on feldspars consumption and attenuate waste disposal concerns.     

Y-TZP,Ce-TZP and as-synthesized Ce-TZP/Al2O3 materials in the development of high loading rate digital light processing formulations

Y-TZP, Ce-TZP and Ce-TZP/Al₂O₃ materials are widely investigated in dentistry. Digital Light Processing (DLP) is considered as a breakthrough technology for the dental field to fine print Y-TZP green parts. High loading photocurable formulations (>45 vol%) with Y-TZP, Ce-TZP commercial powders and Ce-TZP/30 vol% Al₂O₃ as-synthesized powder suitable to DLP printing were achieved in this study. A low specific surface area (5–13 m²/g) of particles without any pores and 1 wt% to 2 wt% of steric dispersant are required to obtain high loading formulations. The as-synthesized composites provide these properties by increasing the calcination temperature from 800 °C to 1200 °C. The as-prepared ceramic formulations based on the same photocurable resin exhibit a curing behavior suitable to DLP process for Y-TZP formulations (thickness > 50 μm in few seconds with a high conversion rate) in comparison with ceria ceramic. The ceria is a strongly UV absorbing material and a specific formulation is developed to obtain 80% of conversion and a cured thickness of 75 μm in 0.5 s.     

Optimization of wastes content in ceramic tiles using statistical design of mixture experiments

Mineral extraction and processing industries have been cited as sources of environmental contamination and pollution. The inclusion of wastes into productive cycles represents an alternative form of restoration, which is interesting from both environmental and economic standpoints. In this work, the development of ceramic tile formulations containing kaolin processing and granite sawing wastes was investigated using the statistical design of mixture experiments methodology. Ten formulations using the raw materials, red clay, kaolin processing and granite sawing wastes, were selected and used in the mixture design. Test specimens were fired and characterized to determine their water absorption, linear firing shrinkage and modulus of rupture. Regression models were calculated, correlating the properties with the composition. The significance and validity of the models were confirmed by statistical analysis and verification experiments. The regression models were used to optimize the waste content in ceramic compositions. The results showed that formulations containing up to 62% of waste could be used in the production of ceramic tiles.     

Sugarcane Bagasse ash substituent feldspar for the production of porcelain electrical insulators

Sugarcane bagasse ash (SCBA) industrial waste was used to partially substitute feldspar in the production of porcelain electrical insulators from a mixture of locally available Bombawuha clay (BC), Chancho sand (CS), and mixture of Wolkite (WF) and Arerti feldspar (AF) (50:50%). The raw materials were characterized for their chemical composition, mineralogy, thermal behavior, and plasticity. The porcelain electrical insulator formulations containing various proportions of SCBA (0 wt%, 10 wt%, 15 wt%, and 20 wt%) were fired at different firing temperatures of 1200 °C, 1250 °C, and 1300 °C for 2.5 h. The fired bodies were evaluated for water absorption, apparent porosity, bulk density, flexural strength, dielectric strength, and microstructure. The results showed that SCBA had 65.06% silica (SiO₂) and had higher alkaline and iron oxide (Fe₂O₃) contents than the natural feldspars. Bombawuha clay contained kaolinite as a major mineral with a middle range plasticity index (PI = 11.2%) and the met the required purity necessary for mullite phase formation. The feldspars had a low alkali content of sodium oxide plus potassium oxide (Na₂O + K₂O) of < 6 wt %. The prepared porcelain insulator containing 10% SCBA, 50% BC, 30% mixed feldspars, and 10% CS, and fired at 1250 °C for 2.5 h exhibited a water absorption of 0.35%, flexural strength of 42.50 MPa, and a dielectric strength of 6.59 kV/mm, which satisfies the obligatory properties for quality porcelain insulators. Further, the partial replacement of feldspar by SCBA up to 10 w% lowered the firing temperature by 50 °C.     

Crystalline phases and physical properties of modified stoneware body with glaze sludge

Ceramic stoneware body has been modified with ceramic and glass industrial wastes by replacing 25–100% as flux in the formula. The effects of solid wastes added to the bodies were studied after firing in the temperature range 950–1280 °C. The physical properties of linear shrinkage, bulk density, apparent porosity, water absorption and 3-point bending strength were determined. A composition which related to the general stoneware properties was found when using soda-lime cullet and glaze sludge. It had a firing range lowered to 1050–1100 °C. SEM results demonstrated the sintered microstructure increased in density with increase in solid waste in the modified body. XRD results after firing showed the crystalline phases comprised of mullite, albite calcian and quartz. Thermal expansion was measured in the range 6.53–6.67 × 10^?6 K^?1 at 30–500 °C. The modified bodies were capable of forming prototype products by slip casting and jiggering.     

Assessment of recycling use of GFRP powder as replacement of fly ash in geopolymer paste and concrete at ambient and high temperatures

Environmental issues caused by glass fiber reinforced polymer (GFRP) waste have attracted much attention. The development of cost-effective recycling and reuse methods for GFRP composite wastes is therefore essential. In this study, the formulation of the GFRP waste powder replacement was set at 20–40 wt%. The geopolymer was formed by mixing GFRP powder, fly ash (FA), steel slag (SS) and ordinary Portland cement (OPC) with a sodium-based alkali activator. The effects of GFRP powder content, activator concentration, liquid to solid (L/S) ratio, and activator solution modulus on the physico-mechanical properties of geopolymer mixtures were identified. Based on the 28-day compressive strength, the optimal combination of the geopolymer mixture was determined to be 30 wt% GFRP powder content, an activator concentration of 85%, L/S of 0.65, and an activator solution modulus of 1.3. The ratios of compressive strength to flexural strength of the GFRP powder/FA-based geopolymers were considerably lower than those of the FA/steel slag-based geopolymers, which indicates that the incorporation of GFRP powder improved the geopolymer brittleness. The incorporation of 30% GFRP powder in geopolymer concrete to replace FA can enhance the compressive and flexural strengths of geopolymer concrete by 28%. After exposure to 600 °C, the flexural strength loss for geopolymer concretes containing 30 wt% GFRP powder was less than that of specimens without GFRP powder. After exposure to 900 °C, the compressive strength and flexural strength losses of geopolymer concretes containing 30 wt% GFRP powder were similar to those of specimens without GFRP powder. The developed GFRP powder/FA-based geopolymers exhibited comparable or superior physico-mechanical properties to those of the FA-based geopolymers, and thus offer a high application potential as building construction material.     

Preparing ceramic membranes for oil-in-water emulsions separation with oil-based drilling cutting pyrolysis residues (ODPRs) as raw material

Oil-based drilling cutting pyrolysis residues (ODPRs) are one of the solid wastes from pyrolysis of the oil-based drilling cuttings (OBDCs) that need to be recycled as raw materials to avoid the possible pollution. In this study, a facile low-cost ceramic membrane for oil-in-water emulsions separation was prepared with ODPRs incorporating with fly ash as raw material. CaCO₃ in ODPRs would decompose acting as pore-forming agent, and anorthite was formed in resultant membranes. The obtained membrane with 30 wt% ODPRs and 70 wt% fly ash fired at 1050 °C possessed apparent porosity of 38.2%, mean pore size of 0.4 μm, flexural strength of 13.1 MPa, and Darcy permeability of 1.06 × 10⁻¹³ m². Consequently, commendable filtration performance for oil-in-water emulsions was presented. In addition, the ceramic membrane showed favorable recyclability and corrosion resistance. Leaching test indicated that the membrane is safe for oil-in-water emulsion separation. Hereby, this paper confirmed the availability of ODPRs for preparing ceramic filtration membranes, and provided a new environmental conservation way to treat oil-in-water emulsions that was consistent with the sustainable development goals.     

Aluminum titanate based ceramics from aluminum sludge waste

This work aims at obtaining aluminum titanate-based ceramics (Al₂TiO₅: AT) composites from industrial wastes. Al-sludge waste and rutile ore were used as rich sources of alumina and titania instead of pure materials. Sludge-(0–40 wt%) rutile mixtures were mixed, formed and fired at 1350 °C for various times. Phase composition, microstructure, densification, mechanical and thermal behaviors of the obtained AT composites have been investigated. Complete conversion of the starting materials to AT with bulk density of 3.199 g/cm³, compressive strength and modulus of rupture of 326.425 MPa and 30.84 MPa, respectively and very low CTE (−0.927*10⁻⁶ K⁻¹) were achieved by firing the sludge-(30 wt%) rutile at 1350 °C for 4 h. These results suggest that the obtained AT-ceramics from Al-sludge waste-rutile ore are a promising and an ecofriendly route.     

A new eco-friendly mass formulation based on industrial mining residues for the manufacture of ceramic tiles

New eco-friendly mass formulations based on the scheelite and kaolin residues were developed to manufacture ceramic tiles. The start raw materials (scheelite residue, kaolin residue, feldspar and plastic clay) were characterized as to their chemical composition, main mineralogical phases, and particle size distribution. Three ceramic masses with 37 wt% of kaolin residues and different contents of the scheelite residues (2 wt%, 5 wt%, and 10 wt%) were formulated. The mass formulations were uniaxially pressed (19.6 MPa) to obtain samples with dimensions of 60 mm × 40 mm x 7 mm, which were dried at 110 °C/24 h, and sintered at different temperatures (1150 °C, 1200 °C, and 1250 °C). Dilatometric experiments measured thermal expansion coefficients. The results are in agreement with the literature, i.e., 6.0 μm/m°C^?1, 6.1 μm/m°C^?1 and 6.4 μm/m°C^?1 to samples with 2 wt%, 5 wt%, and 10 wt% of scheelite residues, respectively. The potential of the mass formulations studied was evaluated by linear shrinkage, water absorption, apparent density, apparent porosity, flexural strength, and mineralogical phase identification. The results were compared with the literature experimental data and International Technical Standards. It was concluded that the samples investigated have suitable properties for use as ceramic and porcelain tiles. Also, the pseudowollastonite and mullite phases were identified in the sample with the lowest concentration of scheelite residue. These phases are responsible for increasing flexural strength.     

Preliminary study of the use of spent diatomaceous earth from the brewing industry in clay matrix bricks

In this work the effect of spent diatomaceous earth (SDE), as pore forming or silica carrier, on the properties of clay ceramic bricks was investigated. Mixtures of clay and SDE waste were, compacted, dried and fired at 950°C during 6?h. The technological properties of waste-clay bricks were analysed to evaluate the influence of the waste incorporation. The SDE (1–5?wt-%) addition in the clay matrix causes a reduction between 6 and 12% of the bulk density compared with the control samples (only clay) which implies good insulating characteristics. In addition, the waste incorporation increases the water absorption within the range 4–31% and decreases the compressive strength between 12 and 26%. However, the incorporation of the waste is beneficial as no remarkable changes in the technological properties are observed. These results indicate that the waste has a predominant pore forming effect over a pore filling effect.     

Thermal behaviour of vitreous ceramic coatings obtained by electrophoretic deposition for furnace components

In this study, three different vitreous ceramic coatings have been designed to improve radiation heat transfer and thereby increase the thermal efficiency of fired heaters or furnaces working at high temperatures. The vitreous ceramic coatings were produced through Electrophoretic Deposition technique (EPD) of ceramic suspensions. These ceramic formulations were designed based on components which increase emissivity, such as SiO₂ and a Black dye (based on chromium, copper and iron oxides), added in 25 wt%. These coatings showed emissivity values around 0.89 at room temperature and around 0.82 at 550 °C in the middle infrared (MIR) spectral range, with slight differences between them. The SiO₂ and Black dye additions provide an important protective effect on the coatings’ thermal stability as it was proved by the absorbance level at long times, higher than 85% in the near infrared (NIR) spectral range. These results were also supported by microstructural characterisation, substrate-coatings adhesion strength and thermal stability tests.     

Compressive strength and microstructure of alkali-activated mortars with high ceramic waste content

The present work investigated alkali-activated mortars with high ceramic waste contents. Tile ceramic waste (TCW) was used as both a recycled aggregate (TCWA) and a precursor (TCWP) to obtain a binding matrix by the alkali-activation process. Mortars with natural siliceous (quartz) and calcareous (limestone) aggregates, and with other ceramic waste materials (red clay brick RCB and ceramic sanitaryware CSW waste), were also prepared for comparison purposes. Given the lower density and higher water absorption values of the ceramic aggregates, compared to the natural ones, it was necessary to adapt the preparation process of the recycled mortars by presaturating the aggregate with water before mixing with the TCWP alkali-activated paste. Aggregate type considerably determined the mechanical behaviour of the samples cured at 65 °C for 3 days. The mortars prepared with the siliceous aggregate presented poor mechanical properties, even when cured at 65 °C. The behaviour of the limestone aggregate mortars depended heavily on the applied curing temperature and, although they presented the best mechanical properties of all those cured at room temperature, their compressive strength reached a maximum when cured at 65 °C, and then decreased. The mechanical properties of the mortars prepared with TCWA progressively increased with curing time (53 MPa at 65 °C for 28 days). An optimum 50 wt% proportion was observed for the limestone/TCWA mortars (≈43 MPa, 3 days at 65 °C), whereas the mechanical properties of that prepared with siliceous particles (10 MPa) progressively increased with the TCWA content, up to 100 wt% substitution (23 MPa). Limestone particles interacted with the binding matrix, and played an interesting beneficial role at the 20 °C curing temperature, with a slight reduction when cured long term (28 days) at 65 °C. The results demonstrated a potential added value for these ceramic waste materials.     

Extrusion and property characterisation of waste-based ceramic formulations

This work describes the studies carried out with various industrial wastes and natural sub-products based on the SiO₂–Al₂O₃–CaO system, aimed at extruding all-waste ceramic products of industrial interest. Four waste materials were selected and characterised, namely, (i) Al-rich anodising sludge (A-sludge), (ii) sludge from the filtration/clarification of potable water (W-sludge), (iii) sludge generated in marble sawing processes (M-sludge), and (iv) foundry sand (F-sand).The plastic behaviour of two different all-waste formulations was first characterised by stress–strain curves and then, after prior adjustment of the plasticity level, the effect of the ram speed and extrusion pressure was evaluated using the Benbow–Bridgwater's model for paste extrusion. Using the waste-based formulations with additives and tube-dies of different die-land dimensions, a good agreement was demonstrated between predicted and measured values. The differences in the static friction coefficient give an effective indication of the surface quality of the extrudate.Extruded rods were then fired at several temperatures and characterised in terms of relevant functional properties (shrinkage, density and mechanical strength). Compositional evolution was assessed by X-ray diffraction. Since interesting performances were observed, the potential of the use of wastes in ceramic formulations of industrial interest was confirmed.     

Evaluation of solid wastes in the manufacture of ceramic tableware glazes

The recovery and reuse of industrial wastes are of great importance to the environment. Today, a large amount of waste is produced due to marble production, and it is extremely important to bring such wastes to the ceramic industry, to solve the pollution problem and to provide cost-efficient ceramic production. In this study, marble waste was used for ceramic earthenware glaze and body formulations. Marble waste was used in two different formulations as glaze and body. Chemical analysis, morphological features, crystallographic information of different formulations were made with XRF, SEM and XRD, respectively. When the hardness test results of the ceramic body and glazed samples were examined, the hardness values of the marble waste added samples increased by 1.9% compared to the standard samples. According to the results obtained, it has been seen that using marble waste in the ceramic industry is very important for both economic and environmental reasons.     

Use of industrial waste for the production of building materials

Results of using industrial waste, namely, spent forming mixtures after casting ferrous metals, for preparing fired ceramic and green silicate brick and steel-melting slag for preparing sinter blocks are presented.Translated from Ogneupory, No. 8, pp. 19–20, August, 1995.