Investigation of volcanic ash based geopolymers as potential building materials

Volcanic ash powders from Etna (Italy) and Cameroon were used as the principal source of aluminosilicate to produce geopolymers with the potential for making building products. The volcanic ash was ball milled and reacted with concentrated alkaline solutions for polymerisation and subsequent curing at 75-400 °C for 12-48 h. It was found that the gel was more viscous than a similar gel formed from metakaolin. Geopolymers made from both ashes had bulk densities of 1.7-2.0 g/cm3 and water absorption values of 20-25 %. Their compressive strength values were 25-35 MPa and the bi-axial four-point flexura! strength values ranged from 14-20 MPa. These values increased by 20 % when cured for 21 d after 90 d storage. It was also found that by curing at 200-400 °C the mechanical properties increased. Scanning electron micrographs showed that with thermal curing microcrystalline phases were present along with undissolved crystalline phases. These phases remained bound to the matrix and acted as a filler for strengthening the materials. The Ca, Mg and Fe present as impurities in the volcanic ash formed some of these crystalline phases and did not form any deleterious hydroxide or carbonate phases

Modeling the compressive strength of geopolymeric binders by gene expression programming-GEP

GEP has been employed in this work to model the compressive strength of different types of geopolymers through six different schemes. The differences between the models were in their linking functions, number of genes, chromosomes and head sizes. The curing time, Ca(OH)2 content, the amount of superplasticizer, NaOH concentration, mold type, aluminosilicate source and H2O/Na2O molar ratio were the seven input parameters considered in the construction of the models to evaluate the compressive strength of geopolymers. A total number of 399 input-target pairs were collected from the literature, randomly divided into 299 and 100 sets and were trained and tested, respectively. The best performance model had 6 genes, 14 head size, 40 chromosomes and multiplication as linking function. This was shown by the absolute fraction of variance, the absolute percentage error and the root mean square error. These were of 0.9556, 2.4601 and 3.4716 for training phase, respectively and 0.9483, 2.8456 and 3.7959 for testing phase, respectively. However, another model with 7 genes, 12 head size, 30 chromosomes and addition as linking function showed suitable results with the absolute fraction of variance, the absolute percentage error and the root mean square of 0.9547, 2.5665 and 3.4360 for training phase, respectively and 0.9466, 2.8020 and 3.8047 for testing phase, respectively. These models showed that gene expression programming has a strong potential for predicting the compressive strength of different types of geopolymers in the considered range

Recycling high volume Fe-rich fayalite slag in blended alkali-activated materials : Effect of ladle and blast furnace slags on the fresh and hardened state properties

AbstractThe valorization of Fe-rich fayalite slag (FS) as a precursor for alkali-activated materials (AAMs) is hampered by its low reactivity at ambient temperature. Here, FS was blended with waste-based reactive co-binders such as ladle slag (LS) and blast furnace slag (BFS) to improve the fresh and hardened state properties of the AAMs for potential construction applications. The results showed that the incorporation of LS and BFS as an additional source of Ca and Al accelerated the reaction kinetics and influenced the binder gel type and formation mechanism. In all the mixes, Fe, Si and Na are present in the evolving binder gel. In addition to these elements, the binder gel of the blended formulations is also rich in higher quantities of Ca and Al and showed possible formation of C-A-S-H and C-(N)-A-S-H together with the development of andradite, a calcium ferrosilicate hydrate phase formed from chemical interaction between FS and co-binders; it indicates that both FS and co-binder participated in the binder gel formation. Furthermore, the nucleating and filling effects of co-binders improved the workability, ultrasonic pulse velocity and mechanical properties; this also densified the structure and lowered the water absorption and permeable porosity of the blended mortars. The compressive strength of blended mortars was above 20 MPa, thus satisfying the strength requirements of building materials according to ASTM C62. The results of this study emphasize the reuse potential of FS with other waste streams in producing eco-friendly AAMs, which can have a wide range of construction applications.Abstract The valorization of Fe-rich fayalite slag (FS) as a precursor for alkali-activated materials (AAMs) is hampered by its low reactivity at ambient temperature. Here, FS was blended with waste-based reactive co-binders such as ladle slag (LS) and blast furnace slag (BFS) to improve the fresh and hardened state properties of the AAMs for potential construction applications. The results showed that the incorporation of LS and BFS as an additional source of Ca and Al accelerated the reaction kinetics and influenced the binder gel type and formation mechanism. In all the mixes, Fe, Si and Na are present in the evolving binder gel. In addition to these elements, the binder gel of the blended formulations is also rich in higher quantities of Ca and Al and showed possible formation of C-A-S-H and C-(N)-A-S-H together with the development of andradite, a calcium ferrosilicate hydrate phase formed from chemical interaction between FS and co-binders; it indicates that both FS and co-binder participated in the binder gel formation. Furthermore, the nucleating and filling effects of co-binders improved the workability, ultrasonic pulse velocity and mechanical properties; this also densified the structure and lowered the water absorption and permeable porosity of the blended mortars. The compressive strength of blended mortars was above 20 MPa, thus satisfying the strength requirements of building materials according to ASTM C62. The results of this study emphasize the reuse potential of FS with other waste streams in producing eco-friendly AAMs, which can have a wide range of construction applications

Spodumene tailings for porcelain and structural materials : Effect of temperature (1050–1200 °C) on the sintering and properties

AbstractThe use of industrial by-products as substitute to conventional natural resources in ceramic production is of interest from an environment preservation and solid wastes management. This paper deals with the recycling of tailings from spodumene concentration during lithium production (Quartz Feldspar Sand; QFS), for the production of porcelain and structural materials. The QFS obtained from spodumene processing consisted mainly of quartz, albite, microcline with traces of muscovite. Mixtures of QFS and standard porcelain ingredients were sintered at 1050–1200 °C at 50 °C intervals and their properties were compared with a conventional porcelain composition prepared under the same conditions. Phase composition was assessed by XRD analysis using Rietveld refinement. Tests such as water absorption, apparent density, sintering shrinkage, compressive and flexural strength were used for physical comparison. The results showed that higher densification was achieved at 1200 °C, with a drastic reduction of water absorption below 1%. A compressive strength of 40 MPa was obtained at 1050 °C in the composition made of 50 wt% QFS and 50 wt% kaolin, increasing to 85 MPa at 1100 °C. The strength increase was attributed to better glassy phase formation and mullite growth. The QFS was found to contain no hazardous elements and showed promising sintering results, indicating its high suitability to substitute conventional resources in the production of ceramic materials.Abstract The use of industrial by-products as substitute to conventional natural resources in ceramic production is of interest from an environment preservation and solid wastes management. This paper deals with the recycling of tailings from spodumene concentration during lithium production (Quartz Feldspar Sand; QFS), for the production of porcelain and structural materials. The QFS obtained from spodumene processing consisted mainly of quartz, albite, microcline with traces of muscovite. Mixtures of QFS and standard porcelain ingredients were sintered at 1050–1200 °C at 50 °C intervals and their properties were compared with a conventional porcelain composition prepared under the same conditions. Phase composition was assessed by XRD analysis using Rietveld refinement. Tests such as water absorption, apparent density, sintering shrinkage, compressive and flexural strength were used for physical comparison. The results showed that higher densification was achieved at 1200 °C, with a drastic reduction of water absorption below 1%. A compressive strength of 40 MPa was obtained at 1050 °C in the composition made of 50 wt% QFS and 50 wt% kaolin, increasing to 85 MPa at 1100 °C. The strength increase was attributed to better glassy phase formation and mullite growth. The QFS was found to contain no hazardous elements and showed promising sintering results, indicating its high suitability to substitute conventional resources in the production of ceramic materials

Reuse of copper slag in high-strength building ceramics containing spodumene tailings as fluxing agent

AbstractThe recycling of industrial side streams is of interest for a sustainable use of resources and from an environmental perspective. This paper deals with the reuse of copper slag and spodumene tailings in the development of ceramic materials for potential application in construction. Copper slag included fayalite and magnetite as crystalline phases while spodumene tailings (quartz-felspar sand, QFS) mainly consisted of albite, quartz and microcline. Kaolin (10 wt%) was added as green strength increasing agent in some compositions and the prepared formulations were sintered between 950 and 1150 °C at 50 °C intervals. The phase composition was studied by scanning electron microscopy and X-ray diffraction using Rietveld refinement. Tests such as compressive and flexural strength, water absorption, apparent density and freeze thaw cycles were used to assess the material performances. The results showed that densification and strength development were mainly due to partial melting of QFS particles at 1050–1100 °C, leading to water absorption in the range 0.5–7 %. At 1100 °C, a high-performance compressive strength of 140 MPa was achieved with the formulation made fully of recycled materials (50 wt% copper slag and 50 wt% QFS) suggesting its suitability for high strength demanding materials such as load bearing bricks; values of ultrasonic pulse velocity and compressive strength of these ceramics remained stable after 200 freeze thaw cycles, demonstrating their potential suitability as construction materials in severe weathering environments. Additionally, the leaching test proved a good encapsulation of heavy metals in these ceramics. These results are of interest for waste management and efficient use of resources.Abstract The recycling of industrial side streams is of interest for a sustainable use of resources and from an environmental perspective. This paper deals with the reuse of copper slag and spodumene tailings in the development of ceramic materials for potential application in construction. Copper slag included fayalite and magnetite as crystalline phases while spodumene tailings (quartz-felspar sand, QFS) mainly consisted of albite, quartz and microcline. Kaolin (10 wt%) was added as green strength increasing agent in some compositions and the prepared formulations were sintered between 950 and 1150 °C at 50 °C intervals. The phase composition was studied by scanning electron microscopy and X-ray diffraction using Rietveld refinement. Tests such as compressive and flexural strength, water absorption, apparent density and freeze thaw cycles were used to assess the material performances. The results showed that densification and strength development were mainly due to partial melting of QFS particles at 1050–1100 °C, leading to water absorption in the range 0.5–7 %. At 1100 °C, a high-performance compressive strength of 140 MPa was achieved with the formulation made fully of recycled materials (50 wt% copper slag and 50 wt% QFS) suggesting its suitability for high strength demanding materials such as load bearing bricks; values of ultrasonic pulse velocity and compressive strength of these ceramics remained stable after 200 freeze thaw cycles, demonstrating their potential suitability as construction materials in severe weathering environments. Additionally, the leaching test proved a good encapsulation of heavy metals in these ceramics. These results are of interest for waste management and efficient use of resources

Synthesis and characterization of porous ceramics from spodumene tailings and waste glass wool

AbstractGlass wool waste remains a challenging waste fraction with relatively little utilization prospects. The present study investigated the development of porous ceramic materials from glass wool waste and spodumene tailings mainly made of quartz feldspar sand (QFS), with 0.05–0.5% silica carbide (SiC) as a pore-forming agent. The formulated compositions were sintered at 950 °C and analyzed in terms of mechanical properties, phase composition, and microstructure using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray micro-computed tomography. The results showed that a synergetic effect of glass wool and SiC started to be significant from 15 wt% glass wool and 0.05 wt% SiC, the strength reducing and the porosity increasing with the increase of SiC. The porous ceramics were largely amorphous, with compressive strength ranging from 5 to 30 MPa while the water absorption and apparent density ranged from 2 to 10% and 0.7–1.2 g/cm³, respectively. The total porosity varied between 20 and 75%, and the wall thickness between 62 and 68 μm; besides, most of the prepared materials floated in water. These results are of interest for the repurposing of glass wool waste in the development of non-flammable lightweight materials for potential filtering or high-rise building applications.Abstract Glass wool waste remains a challenging waste fraction with relatively little utilization prospects. The present study investigated the development of porous ceramic materials from glass wool waste and spodumene tailings mainly made of quartz feldspar sand (QFS), with 0.05–0.5% silica carbide (SiC) as a pore-forming agent. The formulated compositions were sintered at 950 °C and analyzed in terms of mechanical properties, phase composition, and microstructure using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray micro-computed tomography. The results showed that a synergetic effect of glass wool and SiC started to be significant from 15 wt% glass wool and 0.05 wt% SiC, the strength reducing and the porosity increasing with the increase of SiC. The porous ceramics were largely amorphous, with compressive strength ranging from 5 to 30 MPa while the water absorption and apparent density ranged from 2 to 10% and 0.7–1.2 g/cm³, respectively. The total porosity varied between 20 and 75%, and the wall thickness between 62 and 68 μm; besides, most of the prepared materials floated in water. These results are of interest for the repurposing of glass wool waste in the development of non-flammable lightweight materials for potential filtering or high-rise building applications

Recycling glass wool as a fluxing agent in the production of clay- and waste-based ceramics

AbstractConcerns about the management of glass wool waste, approximately 800,000 tons of which are generated annually in Europe, are increasing. To test the feasibility of incorporating this waste into ceramic materials, this study examined the reuse of glass wool as a fluxing agent in the production of clay- and waste-based building ceramics. Commercial kaolin clay and two industrial residues, namely quartz-feldspar sand (QFS) and copper slag (CS), were selected as the precursors. Six compositions were prepared, three samples containing glass wool and three counterparts without glass wool, and then sintered at 750, 850, and 950 °C. The materials and prepared ceramics were characterized by employing x-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy (EDS), differential scanning calorimetry (DSC), water absorption, apparent density, and compressive and flexural strength tests. Interestingly, the results indicated that incorporating 10 wt% of glass wool into the QFS, CS, and kaolin mixtures created ceramics with better physical, mechanical, and microstructural properties. This was ascribed to the glass wool melting reactions observed from approximately 700 °C. The QFS samples with glass wool and sintered at 950 °C achieved compressive strength values as high as 117 MPa and water absorption percentages as low as 2%. However, the fluxing effect of glass wool was less significant in the CS- and kaolin-based ceramics, likely due to differences in their chemical composition, mineralogy, and particle-size distribution. The results of this study emphasize the reuse potential of glass wool and other waste streams in building ceramics and could contribute to improving the management of glass wool waste in line with social sustainability objectives.Abstract Concerns about the management of glass wool waste, approximately 800,000 tons of which are generated annually in Europe, are increasing. To test the feasibility of incorporating this waste into ceramic materials, this study examined the reuse of glass wool as a fluxing agent in the production of clay- and waste-based building ceramics. Commercial kaolin clay and two industrial residues, namely quartz-feldspar sand (QFS) and copper slag (CS), were selected as the precursors. Six compositions were prepared, three samples containing glass wool and three counterparts without glass wool, and then sintered at 750, 850, and 950 °C. The materials and prepared ceramics were characterized by employing x-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy (EDS), differential scanning calorimetry (DSC), water absorption, apparent density, and compressive and flexural strength tests. Interestingly, the results indicated that incorporating 10 wt% of glass wool into the QFS, CS, and kaolin mixtures created ceramics with better physical, mechanical, and microstructural properties. This was ascribed to the glass wool melting reactions observed from approximately 700 °C. The QFS samples with glass wool and sintered at 950 °C achieved compressive strength values as high as 117 MPa and water absorption percentages as low as 2%. However, the fluxing effect of glass wool was less significant in the CS- and kaolin-based ceramics, likely due to differences in their chemical composition, mineralogy, and particle-size distribution. The results of this study emphasize the reuse potential of glass wool and other waste streams in building ceramics and could contribute to improving the management of glass wool waste in line with social sustainability objectives

Upcycling spodumene tailings in the preparation of high alumina porcelain composition sintered at 1200––1400 ˚C

Abstract Concentration of spodumene from lithium pegmatite ore generates large amounts of tailings that need to be recycled for sustainability and circular economy concerns. This study investigated the preparation of high-alumina porcelain compositions incorporating spodumene tailings, i.e., quartz feldspar silt (QFS). The mix design closely matched the theoretical composition of 60.51-wt.% Al2O3, 34.34-wt.% SiO2, 2.98-wt.% K2O, 0.66-wt.% Na2O, and 0.33-wt.% CaO. For comparison, a reference composition free of QFS, composed of commercial materials, was also prepared. Both compositions were thermally treated at 1200℃, 1300℃, and 1400℃. The prepared samples were characterised using several techniques, including X-ray diffraction, scanning electron microscopy–energy-dispersive X-ray spectroscopy, thermogravimetry/differential scanning calorimetry, compressive and flexural strength tests, water absorption, apparent density, and dilatometry at high temperatures up to 1400℃. The results show that corundum and mullite are the primary crystalline phases formed at high temperatures in addition to an amorphous glassy phase. The compressive and flexural strengths were 25–60 and 6–10 MPa, respectively. QFS milling favoured phase densification, resulting in greater sintering shrinkage. However, all samples were relatively stabilised after the first heating cycle and exhibited less than 1% dimensional changes during the second heating cycle at 1400℃. The reference and 26.4-wt.% QFS samples exhibited comparable results, indicating the potential for upcycling spodumene tailings as feldspar substitutes in the development of corundum-mullite based-ceramics for possible high temperature applications.Abstract Concentration of spodumene from lithium pegmatite ore generates large amounts of tailings that need to be recycled for sustainability and circular economy concerns. This study investigated the preparation of high-alumina porcelain compositions incorporating spodumene tailings, i.e., quartz feldspar silt (QFS). The mix design closely matched the theoretical composition of 60.51-wt.% Al2O3, 34.34-wt.% SiO2, 2.98-wt.% K2O, 0.66-wt.% Na2O, and 0.33-wt.% CaO. For comparison, a reference composition free of QFS, composed of commercial materials, was also prepared. Both compositions were thermally treated at 1200℃, 1300℃, and 1400℃. The prepared samples were characterised using several techniques, including X-ray diffraction, scanning electron microscopy–energy-dispersive X-ray spectroscopy, thermogravimetry/differential scanning calorimetry, compressive and flexural strength tests, water absorption, apparent density, and dilatometry at high temperatures up to 1400℃. The results show that corundum and mullite are the primary crystalline phases formed at high temperatures in addition to an amorphous glassy phase. The compressive and flexural strengths were 25–60 and 6–10 MPa, respectively. QFS milling favoured phase densification, resulting in greater sintering shrinkage. However, all samples were relatively stabilised after the first heating cycle and exhibited less than 1% dimensional changes during the second heating cycle at 1400℃. The reference and 26.4-wt.% QFS samples exhibited comparable results, indicating the potential for upcycling spodumene tailings as feldspar substitutes in the development of corundum-mullite based-ceramics for possible high temperature applications

Recycling lithium mine tailings in the production of low temperature (700–900 °C) ceramics : Effect of ladle slag and sodium compounds on the processing and final properties

AbstractThis paper deals with the valorization of quartz and felspar rich lithium mine tailings (QFS) in the development of construction materials. Ladle slag was used as green strength increasing agent. Sodium hydroxide and carbonate were used as fluxing agents to allow sintering at 700–900 °C. Of these, sodium hydroxide was found to be the more efficient. The sintered ceramics were characterized by X-ray diffraction, scanning electron microscopy, compressive test, water absorption, apparent density and dilatometry; the results were found to comply with ASTM C62–99 specifications for building brick, and interesting for a sustainable use of resources.Abstract This paper deals with the valorization of quartz and felspar rich lithium mine tailings (QFS) in the development of construction materials. Ladle slag was used as green strength increasing agent. Sodium hydroxide and carbonate were used as fluxing agents to allow sintering at 700–900 °C. Of these, sodium hydroxide was found to be the more efficient. The sintered ceramics were characterized by X-ray diffraction, scanning electron microscopy, compressive test, water absorption, apparent density and dilatometry; the results were found to comply with ASTM C62–99 specifications for building brick, and interesting for a sustainable use of resources

Utilisation of glass wool waste and mine tailings in high performance building ceramics

AbstractThe generation of glass wool waste and mine tailings has raised increasing concerns. This paper deals with the reuse of glass wool waste and lithium mine tailings from spodumene ore (quartz feldspar sand; QFS) in the development of building ceramic materials. The effect of glass wool particle size and sintering temperatures (750, 850 and 950 °C) were investigated. Phase composition and sintering reactions were studied using several techniques including X-ray diffraction with Rietveld refinement, differential scanning calorimetry, scanning electron microscopy, density, water absorption and mechanical tests. The results showed that glass wool acted as fluxing agent, with melting reactions observed from about 700 °C. Grinding glass wool improved its reactivity, enhancing densification and strength development at lower temperatures. The properties of the prepared building ceramics satisfied the requirement of building materials according to ASTM C62, achieving high performance values of 90 MPa and 25 MPa for compressive and flexural strength respectively. These results are of interest for the reuse of glass wool waste, QFS and similar waste streams in building ceramics.Abstract The generation of glass wool waste and mine tailings has raised increasing concerns. This paper deals with the reuse of glass wool waste and lithium mine tailings from spodumene ore (quartz feldspar sand; QFS) in the development of building ceramic materials. The effect of glass wool particle size and sintering temperatures (750, 850 and 950 °C) were investigated. Phase composition and sintering reactions were studied using several techniques including X-ray diffraction with Rietveld refinement, differential scanning calorimetry, scanning electron microscopy, density, water absorption and mechanical tests. The results showed that glass wool acted as fluxing agent, with melting reactions observed from about 700 °C. Grinding glass wool improved its reactivity, enhancing densification and strength development at lower temperatures. The properties of the prepared building ceramics satisfied the requirement of building materials according to ASTM C62, achieving high performance values of 90 MPa and 25 MPa for compressive and flexural strength respectively. These results are of interest for the reuse of glass wool waste, QFS and similar waste streams in building ceramics