Sodium Aluminosilicate Research Articles

Iron ore tailings stabilization with alternative alkali-activated cement for dry stacking: mechanical and microstructural insights

Upstream tailings dams are high-risk structures that have experienced several failures worldwide, particularly with iron ore tailings (IOT). In this study, new disposal methods/techniques, such as cement-stabilized dry stacking, are discussed that provide enhanced mechanical behavior while reducing failure risks. Alkali-activated materials are used as cementing agents due to their mechanical and environmental advantages compared to ordinary Portland cement. This study evaluates the mechanical and microstructural behavior of IOT stabilized with an alkali-activated cement (AAC) composed of two by-products from the IOT beneficiation process, metakaolin and sodium silicate, tested under plane strain conditions. Simple shear tests and microstructural analysis were performed. Mixtures of IOT were produced with 0%, 1%, 3%, and 5% AAC to examine the influence of such variables on strength and deformability parameters under undrained conditions. The mixtures with 3% and 5% AAC showed the greatest impact on the strength; however, the addition of 1% AAC was able to reduce positive pore-pressure generation. Cementitious bounds were evidenced by forming a sodium aluminosilicate hydrate gel. The studied AAC was effective in stabilizing IOT, even at small contents.

Utilising Phosphogypsum and Biomass Fly Ash By-Products in Alkali-Activated Materials

Significant environmental issues are raised by the phosphogypsum (PG) waste that is being produced. In Lithuania, about 1,500,000 tons of PG waste is generated yearly, and about 300 Mt is generated yearly worldwide. A by-product of burning wood biomass in thermal power plants is biomass fly ash (BFA). By 2035, compared to 2008 levels, industrial biomass incineration for combined heat and power and, as a consequence, BFA, is expected to triple. This study revealed the possibility of using these difficult-to-utilise waste products, such as BFA and PG, in efficient alkali-activated materials (AAM). As the alkaline activator solution (AAS), less alkaline Na2CO3 solution and Na2SiO3 solution were used. The study compared the physical–mechanical properties of BFA-PG specimens mixed with water and the AAS. After 28 days of curing, the compressive strength of the BFA-PG-based, water-mixed samples increased from 3.02 to 6.38 MPa when the PG content was increased from 0 to 30 wt.%. In contrast, the compressive strength of the BFA-PG-based samples with AAS increased from 8.03 to 16.67 MPa when the PG content was increased from 0 to 30 wt.%. According to XRD analysis, gypsum crystallisation increased when the PG content in the BFA-PG-based samples with water increased. The presence of AAS in the BFA-PG-based samples significantly reduced gypsum crystallisation, but increased the crystallisation of the new phases kottenheimite and sodium aluminium silicate hydrate, which, due to the sodium ions’ participation in the reactions, created denser reaction products and improved the mechanical properties. The outcome of this investigation aids in producing sustainable AAM and applying high volume of hardly usable waste materials, such as BFA and PG.

Compressive reactive molecular dynamics on mechanical and structural behaviors of geopolymers: Imposing lateral constraints and varied temperatures

Geopolymer concrete offers superior mechanical properties and microstructure, yet micro-level compressive properties and structural evolutions remain insufficiently understood. This study employed molecular dynamics to simulate the uniaxial compressions of the sodium aluminosilicate hydrate (N-A-S-H) under UCZ, BCZ, and TCZ (z-axial compressions with zero, one, and two dimensions restrictions, respectively) conditions at 263 K, 300 K, and 800 K. The results provided valuable insights linking mechanical behavior with structural properties. Stress fluctuations in the yield stage were attributed to the continuous formation and fracture of Al-O-H bonds during micro-molecule processes. In the later compression stages, the rapid increase in Si-O-H groups suggested that water molecules equally attacked Al and Si tetrahedra due to limited voids. Under UCZ and BCZ conditions, slight bond contraction occurred, with the main structural resistance arising from bond angle bending within the skeleton. In contrast, TCZ experienced notable changes in both bond lengths and bond angles due to bilateral displacement constraints. The evolutionary molecular processes exhibited insensitive response to the temperature, especially under TCZ conditions. Additionally, varying trends were observed in different bond-angle styles (e.g., within or inside tetrahedra), providing a crucial insight for the design of N-A-S-H to determine optimal components.

Study on the mechanical properties and strength formation mechanism of high-volume graphite tailings concrete

Graphite tailings and coal gangue (CG) are solid wastes produced by mines. The large accumulation of surface materials poses great harm globally, and resource utilization is an urgent problem to be solved. In this paper, steel slag (SS), granulated blast furnace slag (GGBS), and fly ash (FA) are used as binder materials. Graphite tailings sand (GTS) is used as a fine aggregate. Using coal gangue and natural gravel as coarse aggregates, high-volume tailings aggregate concrete was prepared by the alkali excitation method. The strength formation mechanism of concrete was analyzed by combining scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry-differential scanning calorimetry (TG-DSC). The results showed that with increasing tailings replacement rate, the strength of concrete containing natural gravel and coal gangue as coarse aggregates gradually decreased. The strength of coal gangue aggregate concrete is 10-15 MPa lower than that of natural gravel aggregate concrete. The uniaxial compressive failure of GTS concrete is divided into three stages: quasielasticity, stable expansion, and critical stress. A small amount of steel scoria (less than 30 %) can provide a good calcium ion (Ca2+) environment for the hydration reaction. The concrete hydration products are mainly calcium silicate hydrate (C-S-H) gel, sodium aluminosilicate hydrate (N-(A)-S-H) gel, ettringite (AFt), etc., and the formation of calcium silicate hydrate C-S-H gel and N-(A)-S-H gel can inhibit the cracks that proceed by shrinkage deformation and improve the durability of concrete. GTS concrete can reduce carbon emissions and solidify some of the harmful substances of raw materials.

Densification of sodium and magnesium aluminosilicate glasses at ambient temperature: structural investigations by solid-state nuclear magnetic resonance and molecular dynamics simulations.

Sodium and magnesium aluminosilicate glasses with compositions 20Na2O-20Al2O3-60SiO2 (NAS) and 20MgO-20Al2O3-60SiO2 (MAS) were subjected to a 12 and 25 GPa compression and decompression at room temperature, resulting in density increases from 3.7% to 5.3% (NAS) and from 8.2 to 8.4% (MAS), respectively. The pressurization at 25 GPa was done on 17O-enriched glasses, to facilitate characterization by 17O NMR. The structural changes associated with this process have been investigated by solid state 29Si, 27Al, 23Na, 25Mg, and 17O magic-angle spinning NMR and compared with the situation in thermally relaxed glasses and/or glasses prepared at ambient pressure. While in the Na aluminosilicate glass only subtle structural changes were observed in a sample densified at 12 GPa, the average coordination number of Al 〈CN(Al)〉 increases moderately from 4.00 to 4.26 by pressurization at 25 GPa. In the Mg-based system, 〈CN(Al)〉 increases from 4.34 to 4.57 to 4.83 in the sequence 10-4 GPa → 12 GPa → 25 GPa. The experimental result at 25 GPa was qualitatively confirmed by molecular dynamics (MD) simulations. Overall, pressurization results in more positive 29Si and 17O chemical shifts, most likely reflecting a reduction in the Si-O-Si and Si-O-Al bonding angles in the pressurized glasses. Furthermore, the results are also consistent with either an increased number of non-bridging O-atoms upon pressurization, or a larger number of Si-O-Al or Al-O-Al linkages. The significantly higher sensitivity of MAS, compared to NAS glass, to an increase in 〈CN(Al)〉 upon pressurization, provides a good structural rationale for its significantly higher crack initiation resistance.

Understanding erosion resistance mechanisms of sodium aluminate silicate hydrate in erosion environments: a molecular dynamics study.

Sodium-aluminate-silicate-hydrate (NASH) gel, as the primary reaction product stimulated by alkali in silica-aluminum-rich minerals, influences the mechanical and durability properties of geopolymers. In erosion environments, NASH demonstrates superior compressive strength and erosion resistance compared to hydration products of ordinary Portland cement. However, the underlying erosion resistance mechanism of NASH under such conditions remains unclear. Therefore, this study employs molecular dynamics research methodology to investigate the alteration in performance and deterioration mechanism of NASH in erosive environments. The findings reveal that in Na2SO4 solution, the infiltration of H2O molecules and Na+ ions into the three-dimensional mesh structure of NASH results in slight expansion and reduced tensile strength. Although H2O intrusion induces hydrolysis of the three-dimensional skeleton, the adsorption sites within NASH possess the capability to capture externally introduced Na+ ions. During tensile loading, Na+ ions can interact with reactive oxygen species produced through stretching or H2O molecule-induced decomposition of the internal framework, facilitating the repair of fractured structures. Consequently, this process partially alleviates tensile rupture, modifies the fracture damage mode, enhances overall toughness, and improves resistance against sulfate attack.

HYDROGEN ABSORBERS BASED ON POROUS CERAMICS SYNTHESIZED IN A SOLAR FURNACE

In this study, we investigated the processes of hydrogen absorption in porous ceramic materials sythesized in a solar furnace. We used burning additives inserted into ceramic materials and melted in a solar furnace in a high-density stream of concentrated solar radiation (200 W/cm<sup>2</sup>). The melt was cooled by pouring it into water at a cooling rate of 10<sup>3</sup>-10<sup>4</sup> degree/s. The castings were characterized by a fine-grained microstructure (in which the grain size did not exceed 10 µm). The crushed and molded samples were fired at a temperature of 1150°C for 2 hours. Thr results obtained showed that the sodium aluminosilicate zeolite ceramic porous material based on a mixture of aluminum powder, quartz sand, and polyvinyl alcohol exhibited high hydrogen absorption-up to 13% (at temperature = 250°C and pressure = 13 atm).

Molecular insights into the microstructure, dynamics, wettability and mechanical properties of sodium aluminum silicate hydrate with saturated nanopores

Sodium aluminosilicate hydrate (NASH) serves as the primary binding phase governing the physical, mechanical, and durability characteristics of geopolymer binders. However, the intricate interactions at the water-nanopore interface and the inherent heterogeneity of geopolymer binders present formidable challenges in exploring the intrinsic microstructure and micromechanical properties of this pivotal binding phase. In response to these challenges, we conducted reliable molecular dynamics simulations aimed at unraveling the intricate molecular-level features of NASH within saturated nanopores. Using the state-of-the-art simulations, results reveal that the structural properties of NASH remain unaffected by variations in nanopore size. Nevertheless, a critical nanopore size is identified, impacting the distribution of water molecules within the nanopore, as evidenced by the convergence of the water molecule number density. In terms of dynamics, diffusion of water molecules within the nanopore exhibits quasi-two-dimensionality, while in NASH demonstrates characteristics of supercooled liquids due to constraints imposed by the aluminosilicate network. Notably, the mechanical properties of NASH within saturated nanopores exhibit a significant decline as nanopore size increases, with uniaxial tension tests indicating the absence of strain softening. Additionally, the presence of hydroxyl groups on the NASH surface influences the adhesion of water molecules through hydrogen bonding, resulting in a pronounced hydrophilicity with a contact angle of 12.2°. The findings offer valuable insights into the behavior of NASH with saturated nanopores, shedding light on the molecular-level details of its structure, dynamics, mechanical properties, and wettability.

Impact of interatomic structural characteristics of aluminosilicate hydrate on the mechanical properties of metakaolin-based geopolymer

This study explores the influence of the interatomic structure of sodium aluminosilicate hydrate (N-A-S-H) with varying silica contents on the mechanical properties of metakaolin-based geopolymer. Geopolymer pastes comprising Si/Al ratios between 2.0 and 3.0 were synthesized. A larger number of Si-O-Si linkages compared to Si-O-Al linkages and a higher atomic number density were found in the geopolymers with higher silica contents, which enhanced the compressive strength of the geopolymer pastes up to the optimal Si/Al ratio of 2.5. The paste with a Si/Al = 2.5 exhibited a greater portion of Q4(1Al and 2Al) and denser morphology compared to the other geopolymer pastes. Furthermore, in-situ high-energy synchrotron X-ray scattering experiments were conducted to assess the elastic modulus of the aluminosilicate structure at a local atomic scale. The modulus value in real space decreases with increasing silica contents up to Si/Al = 2.5 and increases with the presence of excessive unreacted silica fume. The modulus value in reciprocal space for the axial and lateral directions both presented a positive value at the geopolymer comprising a Si/Al ratio higher than 2.5, indicating that the load-bearing property of N-A-S-H changed at higher Si/Al ratios. Moreover, the smallest difference between the strains along the axial and lateral directions was detected for the geopolymer with Si/Al = 2.5 in both the real and reciprocal space, owing to the most interconnected and flexible nanostructure, which led to the highest mechanical strength.

Effects of retarders on the rheological properties of coal fly ash/superfine iron tailings-based 3D printing geopolymer: Insight into the early retarding mechanism

To increase the utilization rate of superfine iron tailings (SIT), a novel coal fly ash (CFA)/SIT-based three-dimensional printing geopolymers (CS-3DPG) were synthesized for high-value resource application of SIT. The optimal preparation parameters of CS-3DPG were sodium citrate of 0.4%, water-solid ratio of 38%, SiO2/Na2O molar ratio of 1 and alkali activator of 6%, with the compressive strength of 32.14 MPa. Besides, the yield stress and plastic viscosity (rheological properties) of CS-3DPG reached 284 Pa and 18.8 Pa·S, respectively. The sodium aluminum silicate hydrate (N-A-S-H) gels were identified as dominant hydration products by the selective chemical extractions. Microstructural analysis also successfully indicated that the retarder caused some CFA and SIT to be unreacted, resulting in the decrease of early compressive strength compared with CS-3DPG. Based on the full width at half-maximum (FWHM) values, kinetics of hydration and hydration kinetic contribution degree results, retarders effectually inhibited nucleation and growth (NG) and diffusion (D). The phase-boundary interaction (I) reaction played a major role after adding retarders. This work successfully reveals the early retarding mechanism of CS-3DPG, and provides the possibility of large-scale resource application of SIT-based 3DPG in 3D printing construction.

Recycling of phosphogypsum and clay by-products from phosphate mines for sustainable alkali-activated construction materials

This work investigated the recycling the large quantities of phosphogypsum, generated by phosphoric acid plants, by exploring its potential use as a precursor in alkali-activated materials. The alkali-activation involved using phosphogypsum and calcined clays as precursors and an alkaline activator. The compressive strength of elaborated materials was evaluated after 28 days of curing. Additionally, various techniques were used to characterize the diverse samples. The results demonstrated the effectiveness of the alkaline activation process to induce the formation of Calcium Aluminum Silicate Hydrate and Sodium Aluminum Silicate Hydrate gels in the elaborated samples. The samples with 22.4% phosphogypsum, 11.28 M NaOH, and a liquid/solid ratio of 0.86 presented the maximum compressive strength of 27.3 MPa as they presented a more dense and less porous structure. The Toxicity Characteristic Leaching Procedure test showed no release of harmful substances. These findings suggest that phosphogypsum could be recycled in alkali-activation technology in the construction industry.

Effects of Na/Al ratio on phonon sideband spectra and luminescent characteristics of Eu3+ doped sodium aluminosilicate glasses

In this work, sodium aluminosilicate (NAS) glass systems were fabricated via traditional melting technique with various Na/Al ratios. Structure and surface morphology of the fabricated glasses were investigated by X-ray diffractometer, Raman spectroscopy and SEM images. Optical characteristics of the fabricated glasses were inspected by photoluminescence (PL) and photoluminescence excitation (PLE) spectra, and the observations showed that intensity of the excitation peak of Eu3+ ions in the NAS glasses at 392 nm increases while one at 463 nm decreases with the increasing of Na/Al ratio. Analysis of the phonon sideband spectra shown a change of multiphonon relative rate (Wmp/W0) of the synthesized glasses relates to Na/Al ratio. By applying the Judd-Ofelt theory, Ωλ = 2,4,6 parameters were evaluated from the PL spectra and used these parameters to estimate the radiative parameters like calculated lifetime (τcal), effective line width (Δλeff), transition probability rate (A), emission cross-section (σp) and branching ratio (βR). Decay curves were measured to investigate luminescence quantum efficiency (η) of Eu3+ emission and η gets value in the 53%–65% region. The color coordinates (x, y) and correlated color temperature (CCT) were also estimated for the synthesized NAS glasses.

Formulation and properties of a new cleaner double liquid alkali-activated grouting material

Herein, a new cleaner double liquid alkali-activated grouting material (DLAG) was successfully developed, which could be applied similarly to cement by adding water. Desulphurisation gypsum (DG) was selected to activate ground granulated blast-furnace slag (GGBFS) and fly ash (FA) to completely replace cement. The optimum proportion of the basic materials and admixtures were determined by a series of orthogonal and single-factor controlled variable experiments. The mechanism for the strength enhancement of the materials was interpreted by microscopic experiments. The optimum proportion of the basic materials was determined that slurry A comprised of only GGBFS, whereas DG, FA, and metakaolin (MK), were present in a mass ratio of 6:3:1 in slurry B. The single slurry maintained good workability over a long period before mixing, and the fluidity of mixed slurry could be dynamically adjustable from 138 mm to 215mm. The strength of solidified specimens reached 45.7 MPa at 28 days curing time, which was 220% higher than that of Portland cement. Microscopic analyses showed that Al2O3 and SiO2 in the precursor materials were continuously dissolved and reorganised to produce hybridised phase gels (C, N)-A-S-H (calcium, sodium aluminium silicate hydrate), and also hydrated with Ca2+, SO42− provided by DG to produce ettringite and calcium silicate hydrate (C-S-H) in the alkaline environment. The size and content of hydration products gradually increased with increasing curing time and acted together to enhance the strength of solidified body. The proposed material can promote the development of alkali-activated technology in the field of special grouting materials.

Desiccant Beads: A Novel Tool for Managing Pulse Beetle in Stored Chickpea

Chickpea is the most dominant pulse having a major share under area shown 65 per cent and production 72 per cent followed by lentil and field pea. Pulse beetle, Callosobruchus chinensis L. is a primary pest of stored chickpea which causes 50-60 per cent loss in seed weight and 45.5-66.3 per cent loss in protein content of the seeds (Rustamani et al., 1985) and injudicious and indiscriminate use of hazardous synthetic chemicals for preventing storage losses in chickpea may lead to human and animal health issues due to residual hazards. Therefore, the biorational management of the pulse beetle in stored chickpea has been undertaken keeping biology in mind will prevent the loss as well as protect human health hazard.The experiments on non-chemical biorational approaches like effect of desiccant beadswhich control the pulse beetle efficiently but have lesser toxicity hazards to non-target organisms and the environment was studied in the Department of Entomology, College of Agriculture, OUAT, BBSR, Odisha during 2018-2021.The results showed that desiccant beads viz., zeolite and sodium aluminium silicate impregnated with chickpea seeds in the ratio of 1:1 proved effective in suppression of the pulse beetle in chickpeaduring six months of storage.

Effect of low-calcium and high-magnesium ferronickel slag on the microstructure and micromechanical properties of alkali-activated blended ground granulated blast furnace slag

In recent years, low-calcium and high-magnesium ferronickel slag (FNS) has been gradually used in the preparation of alkali-activated cements (AACs). An in-depth exploration of the microstructural characteristics is crucial for a thorough understanding and enhancement of the macroscopic behaviors of AACs. In this study, the microstructural composition and micromechanical properties of the alkali-activated ground granulated blast furnace slag (GGBS)-FNS cements (AASF) prepared with sodium silicate and sodium hydroxide as alkali activators were quantitatively studied. Backscattered electron image analysis (BSE-IA) and nanoindentation were selected to reveal the micromechanical properties of different phases in FNS particles and AASF pastes. The results show that the elastic modulus of sodium aluminosilicate hydrate (N-A-S-H) in alkali-activated FNS cement is about 17 GPa, which is similar to that of the gel phase in alkali-activated fly ash cement (AAFA) and alkali-activated metakaolin cement (AAMK), confirming that the micromechanical property of N-A-S-H gel is independent of the kind of precursor materials. The Ca/Si and Al/Si of the hydration products in AASF gradually decline as FNS is incorporated, whereas the Mg/Al steadily rises, increasing the elastic modulus of the inner hydration product (IP) phase in AASF. The reaction degree of GGBS is higher in the sodium silicate-activated AASF system, while more N-A-S-H gels are formed in the sodium hydroxide-activated AASF system. The incorporation of FNS is conducive to improving the reaction degree of GGBS, resulting in the increase of calcium silicoaluminate hydrate (C-A-S-H) content and a significant decrease in IP content in AASF.

Exploitation of ladle furnace iron slag for semiconductor borosilicate glass production

The supply consumption of ladle furnace slag (LFS) is a prominence of recent researches and is extensively considered. In this work LFS has the potential to be utilized as the main raw material for producing glass and glass-ceramics because of its chemical compositions similarities to the silicate glass materials. Three borosilicate glass samples were produced via melting – quenching technique. The three samples contained 10, 20, 30 wt % of slag waste materials, respectively. The second sample was heat treated at 625 °C, guiding by DTA studies, for 2, 6, 10, or 15 h. XRD studies showed traces precipitation of Ca(Mg,Al) (Si,Al)2O6 (diopside), Sodium Aluminum Silicate (NaAlSiO4), Sodium Aluminum Borate (Na2Al2B2O7) and Clinoenstatite (MgSiO3) phases. FTIR analysis demonstrated the same functional groups through glass and glass ceramics sample confirming that all prepared samples had the same structure. Ferrimagnetism property of a glass sample and its glass ceramic sample derivative was confirmed by vibrating sample magnetometer (VSM) analysis. Vickers microhardness and fracture toughness results indicated noticeable rising in toughness value and decreasing of hardness after using 100 g load by increasing slag percent in glass samples. The glass ceramic sample had little change, in hardness and toughness values, rather than its corresponding glass sample due to its lower crystallization behavior. The low dielectric constant values are very good indication for the availability of using these type of glass for electronic applications. X-ray photoelectron spectroscopy (XPS) studies indicate that manganese ions are found as MnO in both glass and glass ceramic samples.

The Effect of Superplasticizers on Eco-friendly Low-Energy One-Part Alkali-Activated Slag

One-part alkali-activated materials (OP-AAM) have become a promising binder with low carbon and energy requirements associated with superior mechanical and durability characteristics. This study aims to employ commercial superplasticizers (naphthalene-based “Nb-SP” and polycarboxylate-based “PCb-SP”), as well as laboratory-prepared one (phenol–formaldehyde sulfanilate “PFS-SP”) in enhancing the properties of OP-AAM. The main problem of superplasticizers (SPs) in the AAM is their hydrolysis in the alkaline activator (NaOH) used in the activation reactions. Therefore, the thermo-chemical treatment process was utilized to mitigate the high activator alkalinity by impeding the NaOH in the aluminosilicate precursor matrix. The OP-AAM was fabricated from thermo-chemical treatment powder (TCT-P) resulting from sintering blast furnace slag (GGBFS) with 10 wt% NaOH at 300 and 500 °C. The XRD-pattern showed that NaOH was impeded in the GGBFS via sodium aluminum silicate phase formation after sintering at 500 °C. The results showed that the admixed OP-AAM prepared from TCT-P at 500 °C greatly enhanced the workability and mechanical properties. The PFS-SP proved its efficiency in improving the properties of OP-AAM prepared TCT-P at 300 and 500 °C, referring to its high stability in an alkaline medium. While PCb-SP reinforced the properties of OP-AAM prepared from TCT-P at 500 °C only, proving that PCb-SP promotes high capability in TCT-P-500 as well as in Portland cement.

Influence of Blast Furnace Slag on Pore Structure and Transport Characteristics in Low-Calcium Fly-Ash-Based Geopolymer Concrete

Alkali-activated fly ash slag (AAFS) has emerged as a novel and environmentally sustainable construction material, garnering substantial attention due to its commendable mechanical attributes and minimal ecological footprint. This investigation delves into the influence of slag incorporation on the strength, pore structure, and transport characteristics of AAFS, encompassing various levels of fly ash replacement with slag. To assess the mechanical properties of AAFS concrete, unconfined compression and ultrasonic pulse velocity tests were conducted. Meanwhile, microstructural and mineralogical alterations were scrutinized through porosity, N2-adsorption/desorption, and SEM/EDX assessments. In addition, transport properties were gauged using electrical surface resistivity, water permeability, and water vapor permeability tests. According to the results, a remarkable refinement in the pore volume was found by increasing the slag content. The volume of the gel pores and surface area increased significantly associated with the increase in tortuosity. Accordingly, Ca inclusion in the cross-linked sodium aluminosilicate hydrate gel remarkably reduced the transport properties.

Isothermal foaming-nucleation-crystallization of glass ceramic foams with hierarchical pore structure: A sustainable approach for disposal of secondary aluminum ash

Secondary aluminum ash (SAA) is a hazardous solid waste generated in the process of recycling aluminum. The preparation of glass ceramic foams from high content of SAA, used as nucleating and foaming agent, was proposed to achieve green and comprehensive utilization of SAA. With the help of thermodynamic phase diagram and viscosity calculation, a mixture of SAA and waste glass (WG) were transformed, at 1200 °C for 30 min, into glass ceramic foams with porosity of 45.49%–59.45%, respectively. The mean pore size of the samples decreased from 2.89 to 1.53 mm with the decrease of SAA addition. Through the adjustment of temperature, it was found that the mixture had a microporous region at 1100 °C. The expansion region was observed at 1180 °C and 1200 °C, because of the oxidation of AlN in SAA. The porosity of the samples could be raised to 64.51%, with 5–9% B2O3 as a supplement, which contributed to the development of the liquid phase and a decrease in the melt's viscosity. The mechanism of in-situ isothermal foaming, nucleation, and crystallization of SAA and WG was clarified. The crystal intensity dropped and the amorphous phase became the primary phase at 800 °C. Al2O3, sodium silicate and sodium aluminum silicate precipitated at 1000 °C. Al2O3 and spinel with high melting point were wrapped by silicate. Silicate turned into the melt again as the temperature continued to rise. With the further reduction of viscosity, the gas diffused in crystalline and amorphous phases, and finally forms glass ceramic foams with hierarchical pore structure.

Utilization of municipal solid waste incineration fly ash with coal fly ash/metakaolin for geopolymer composites preparation

The geopolymer technique is a promising method for the solidification/stabilization (S/S) treatment of municipal solid waste incineration fly ash (MSWIFA). To investigate the feasibility of resource utilization in MSWIFA by geopolymerization process, the macroscopic and microscopic properties of the coal fly ash/metakaolin-based geopolymer composites containing MSWIFA were studied. The leaching test was conducted to evaluate the S/S effect of geopolymer. Results showed that CFA/MK-based geopolymer demonstrated effective stabilization of heavy metals in MSWIFA. The flowability of geopolymer composites increased with the MSWIFA content, where 40% replacement ratio of MSWIFA significantly improved the slump and consistency of geopolymer mortar by 86.3% and 80.4%. However, 40% content of MSWIFA reduced the compressive strength and splitting tensile strength of geopolymer composites by 80% and 62%. The strength development rate in early ages of geopolymer composites was accelerated by mixing less than 15% MSWIFA. Whereas, the strength development at 7–28 days was almost unaffected by MSWIFA. The addition of MSWIFA decreased the amount of sodium-(calcium) aluminosilicate hydrate and sodium aluminosilicate hydrate gels. Although the addition of MSWIFA refined the gel pores in geopolymer, the pore volume and porosity increased and the compactness of microstructure decreased with the increment of the MSWIFA content in geopolymer composites. Based on these results, it is feasible to realize resource utilization of MSWIFA using geopolymer composites with low content of MSWIFA (less than 15% was recommended in this study).