Orimulsion fly ash in clay bricks—part 1: composition and thermal behaviour of ash

A bitumen-in-water emulsion (Orimulsion) is currently used as a fuel in several thermal power plants worldwide. Orimulsion combustion produces a fly ash rich in S, Mg, V and Ni, which is processed to recover metals. In order to assess the feasibility of a recycling in clay brick production, a characterization of the physico-chemical and thermal properties of ash was performed by ICP–OES, XRPD, SEM, BET and TGA–DTA techniques. Orimulsion ash resulted in fine-grained (aggregates of submicronic particles), highly hygroscopic, constituted mainly of magnesium sulphate, vanadyl sulphates and magnesium and nickel oxides, and thermally unstable in the usual brick firing conditions. These features can affect the brickmaking process, particularly the plasticity of the clay body and its drying and firing behaviour; furthermore, a mobilization of sulphates could occur, promoting the formation of efflorescence and/or the SO_x release during firing.     

Dry pressed ceramic tiles based on fly ash–clay body: Influence of fly ash granulometry and pentasodium triphosphate addition

Fly ash from brown coal (70 wt.%) and stoneware clay (30 wt.%) were used for the dry pressed ceramic tiles (according to EN 14411) raw materials mixture. The effects of fly ash milling and pentasodium triphosphate addition as a deflocculant and fluxing agent on the properties of green body (flexural strength, bulk density) and fired body (EN ISO 10545—water absorption, bulk density, true density, apparent porosity, flexural strength, frost resistance) were studied and explained as a function of the firing temperature (1000–1150 °C). Fly ash milling (corresponding to 5 wt.% residue of fly ash grains on 0.063 mm sieve) increased the sintering abilities of the fly ash–clay body. A similar effect was achieved by 1.3 wt.% pentasodium triphosphate (PST) addition with an increase in green body flexural strength and a decrease in water content of the granulate. Fly ash–clay bodies can be frost resistant with water absorption above 10% due to positive pore size distribution, which were examined using the high-pressure mercury porosimetry method.     

Slag-fly ash and slag-metakaolin binders: Part II—Properties of precursors and NMR study of poorly ordered phases

Sodium silicate-activated slag-fly ash binders (SFB) and slag-metakaolin binders (SMKB) are room-temperature hardening binders that have excellent mechanical properties and a significantly lower carbon footprint than ordinary Portland cement (OPC). The aim of this study was to use nuclear magnetic resonance (NMR) spectroscopy to study the nanostructure of poorly ordered phases in SFB by varying slag/fly ash ratio, curing time, and curing temperature. Fly ash was completely substituted with metakaolin and the effect of this substitution on the poorly ordered phases was studied. It was observed that the proportion of geopolymer was generally higher in SMKB when compared to SFB. Although C–N–A–S–H and geopolymer coexisted in SFB and SMKB, C–N–A–S–H was the major product phase formed. The mean chain length (MCL) and the structure of C–N–A–S–H gel were estimated as a function of time, temperature, and slag/fly ash ratio. The MCL was found to have a negative correlation with slag/fly ash ratio and Ca/(Si+Al) ratio, but positive correlation with curing temperature. The average Si/Al atom ratios for geopolymers were also estimated. Lastly, the increased proportion of five-coordinated aluminum (Al(V)) in metakaolin resulted in the decreased unreacted metakaolin in the hardened binder but did not increase the geopolymer content.     

Preparation and properties of porous SiC–Al2O3 ceramics using coal ash

In this paper, we first reported that porous SiC–Al₂O₃ ceramics were prepared from solid waste coal ash, activated carbon, and commercial SiC powder by a carbothermal reduction reaction (CRR) method under Ar atmosphere. The effects of addition amounts of SiC (0, 10, 15, and 20 wt%) on the postsintering properties of as-prepared porous SiC–Al₂O₃ ceramics, such as phase composition, microstructure, apparent porosity, bulk density, pore size distribution, compressive strength, thermal shock resistance, and thermal diffusivity have been investigated. It was found that the final products are β-SiC and α-Al₂O₃. Meanwhile, the SEM shows the pores distribute uniformly and the body gradually contacts closely in the porous SiC–Al₂O₃ ceramics. The properties of as-prepared porous SiC–Al₂O₃ ceramics were found to be remarkably improved by adding proper amounts of SiC (10, 15, and 20 wt%). However, further increasing the amount of SiC leads to a decrease in thermal shock resistance and mechanical properties. Porous SiC–Al₂O₃ ceramics doped with 10 wt% SiC and sintered at 1600°C for 5 hours with the median pore diameter of 4.24 μm, room-temperature compressive strength of 21.70 MPa, apparent porosity of 48%, and thermal diffusivity of 0.0194 cm²/s were successfully obtained.     

Orimulsion fly ash in clay bricks—part 2: technological behaviour of clay/ash mixtures

In order to appraise the technological feasibility of the Orimulsion ash recycling in clay bricks, a laboratory simulation of the brickmaking process was carried out with various clay/ash mixtures up to 6% waste. Two different clays were selected and mixes were characterized by XRF, XRPD, TGA–DTA, TDA and PSD analyses. Plasticity, extrusion and drying behaviour, and mechanical strength, were determined on unfired mixtures, while shrinkage, water absorption, bulk density, modulus of rupture, pore size distribution, microstructure and phase composition were measured on fired bricks. Orimulsion ash caused some detrimental changes of technological properties of both unfired and fired products, concerning particularly plasticity, drying rate and drying sensitivity, porosity and colour. These effects were slightly different on the two raw materials, the carbonate-rich clay being less sensitive to the presence of ash with respect to the carbonate-free clay. In all events, drawbacks appeared to be tolerable, in technological terms, for low waste additions, approximately 1–2% ash.     

Effect of fly ash–gypsum blend on porosity and pore size distribution of cement pastes

Abstract

Abstract

This paper reports results on the porosity and pore size distribution (PSD) of cement paste containing simulated desulphurised waste (SDW). The SDW was chosen due to the variability in chemical composition of real desulphurised waste. The SDW is a combination of fly ash and gypsum. The content of fly ash in the SDW changed from 0 to 100% by weight. The water to binder ratio was 0·5. The binder consists of cement and SDW. Cement in the pastes was partially replaced with 25 wt-% SDW. The porosity and PSD of cement pastes at 28 days of curing is reported. Increasing amount of gypsum does not seem to greatly change the pore volume; however, there is tendency of obtaining coarser pore structure in the presence of gypsum. The compressive strength increases with increasing amounts of gypsum. Correlation between strength and PSD is conducted.     

Sodium silicate activated slag-fly ash binders: Part III—Composition of soft gel and calorimetry

Sodium silicate activated, slag-fly ash binders are potential alternative binders to Portland cement. In this study, the early age properties of slag-fly ash binders namely, set time, and heats of reaction were investigated. Set time was investigated using a combination of two methods namely, the ASTM C403 penetration testing, and s-wave ultrasonic wave reflectometry (SUWR). The discrepancy in set time identified by these two methods suggested the presence of a soft gel which eventually hardened with time. The composition of this soft gel was analyzed by suspending the chemical reaction of the binder after the soft gel formed, but before it hardened. In order to analyze the composition of the soft gel, selective chemical extractions were performed on the binder. ²⁹Si Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR), and FTIR spectroscopy were performed on binders and extraction residues. The soft gel contained a modified calcium silicate hydrate gel (C–N–S–H where N=Na), with a short mean chain length and no observable Al incorporation. Orthosilicate units were also found to be present in relatively high proportions when compared to hardened binders at later ages.     

Zeolite P synthesis based on fly ash and its removal of Cu(Ⅱ) and Ni(Ⅱ) ions

Zeolite P was synthesized through hydrothermal method based on a kind of Class C fly ash(FA). X-ray diffraction(XRD), scanning electron microscopy(SEM), and Brunauer–Emmett–Teller(BET) were used to analyze and characterize the synthetic sample. The kinetics and thermodynamics of copper and nickel ions removed by the zeolite samples were experimentally explored in detail. The results of kinetic treatment showed the second-order exchange second-order saturation model(SESSM) can well describe the removal process of copper ions, while the first-order empirical kinetic model(FEKM) is the best kinetic model for nickel ions. Langmuir and Freundlich isotherms were used to fit the equilibrium concentration of Cu(Ⅱ) or Ni(Ⅱ) under certain conditions. Whether for copper or nickel ion, the Langmuir model is in good agreement with the experimental equilibrium concentration.The apparent theoretical removal capacities for Cu(Ⅱ) and Ni(Ⅱ) can reach to 138.1 mg·g~(-1) and 77.0 mg·g~(-1),respectively.     

Recycling bagasse and rice hulls ash as a pore-forming agent in the fabrication of cordierite–spinel porous ceramics

Bagasse and rice hulls ash are both waste materials. In recent years, in order to meet environmental protection, these materials have been recycled in the production of porous ceramics. A solid-state reaction mechanism of calcined alumina and talc was used to prepare cordierite–spinel porous ceramics. Talc was added from 30 to 60 wt.% at the expense of alumina and sintered at 1400°C for 2 h. The effect of bagasse and rice hulls ash (as a pore forming agent) on the densification parameters, cold crushing strength (CCS), and pore size distribution was also studied. The phase composition (X-ray diffraction) and microstructure (scanning electron microscopy) of sintered samples were investigated. The results showed that the main phases present in the samples are cordierite, corundum, spinel, and sapphirine. In the sample with a higher amount of talc additions (60 wt.%), only the formation of the cordierite and spinel phases was observed. The bulk density of the samples and the apparent porosity ranged from 1.77 to 2.26 g/cm³ and from 28.6% to 48.21%, respectively. The CCS of the samples ranges from 13.9 to 36.3 MPa. The microstructures of the sintered samples were observed for the formation of cordierite phase, alumina phase, and spinel phase in an excellent crystallization and phase arrangement.     

The effect of grinding process on mechanical properties and alkali–silica reaction resistance of fly ash incorporated cement mortars

The effect of fineness of fly ash on mechanical properties and alkali–silica reaction resistance of cement mortar mixtures incorporating fly ash has been investigated within the scope of this study. Blaine fineness of fly ash has been increased to 907 m²/kg from its original 290 m²/kg value by a ball mill. Test samples were prepared by replacing cement 20, 40 and 60%, with finer and coarser fly ashes and kept under standard and steam curing conditions until testing. Test results showed that grinding process improved the mechanical properties of all samples significantly. The beneficial effect of grinding fly ash, may increase utilization of this by-product in precast and ready-mix concrete industries. Incorporation of fly ash with different fineness values and ratios also decreased the expansions to harmless levels of cement mortars due to alkali–silica reaction.     

Utilization of bagasse fly ash for carbon–zeolite composite preparation

Bagasse fly ash (BFA), a solid waste from sugar cane industries, contains significant amount of carbon as well as silica. The coarse particles with high carbon content can be separated and further activated to produce BFA-based activated carbon, while silica content can be extracted from fine BFA particles to be used for zeolite crystallization. The zeolite crystal may be grown on a suitable solid surface to create a zeolitic composite. In this study, silicate extract from fine BFA particles were combined with pretreated carbon rich coarse BFA particles in a hydrothermal crystallization process to produce particular carbon–zeolite composites. The carbon rich particles could be subjected to any necessary activation or surface treatment before being used in the composite preparation. Meanwhile, a simple method based on thermogravimetry is proposed to evaluate the zeolite particles distribution on the carbon surface. Furthermore, the composite ability for treating mixed organic and inorganic pollutants in aqueous solution has been investigated.     

Properties of CNTs-modified lead-free BCTS ceramic–Portland fly ash cement composites

Fly ash (FA) is widely used as a supplementary cementitious material in the production of Portland cement concrete. The effect of addition of carbon nanotubes (CNTs) and FA on the properties of barium calcium stannate titanate (BCTS) ceramic–Portland FA cement composites was investigated. These composites have potential for use as sensors and transducers in the monitoring of structural health in concrete structures containing FA. CNTs were found to have filled the pores of the composites. All composites showed good compatibility with the concrete mix. The dielectric constant and electrical conductivity of composites were in the range 200–257 and 1.04 × 10^–6 to 1.66 × 10⁻⁶ S/m, respectively. The presence of FA in composites increased the piezoelectric voltage coefficient (g₃₃). Adding CNTs increased the piezoelectric charge coefficient (d₃₃), thickness electromechanical coupling coefficient (K_t), and also g₃₃ but decreased mechanical quality factor (Q_m), which is related to good for the receiving sensor and transducer application. CNTs can improve the properties of these composites and composite with FA content at 10 vol.%, and CNTs at 1 vol.% exhibited the highest compressive strength and piezoelectric values (d₃₃ = 44 pC/N, g₃₃ = 20.21×10^–3 V m/N, and K_t = 18.9%), along with higher g₃₃ values, than pure BCTS ceramic.     

Synthesis of geopolymers from volcanic ash via the alkaline fusion method: Effect of Al2O3/Na2O molar ratio of soda–volcanic ash

The alkaline fusion method was used to enhance the reactivity of volcanic ash for geopolymer synthesis. To that end, different mixtures of fused soda–volcanic ash (fused volcanic ash) were used to assess reactivity for geopolymer synthesis. The amount of amorphous phase was determined both in the volcanic ash and the fused volcanic ash and X-ray diffraction analysis was used to evaluate effect of the alkaline fusion method. Different geopolymer mortars were prepared by alkaline activation of mixtures of powders of fused volcanic ash and metakaolin and river sand using sodium silicate as activator. Metakaolin was considered as consumer of excess of alkali contained in the fused volcanic ash. The geopolymer mortars were characterized by determination of setting time, linear shrinkage, compressive strength and scanning electron microscopy. The amount of amorphous phase and excess of fused soda content of the fused volcanic ash depended on molar ratio of Al₂O₃/Na₂O and played a key role for geopolymer synthesis. The most convenient Al₂O₃/Na₂O molar ratio of fused volcanic ash to produce effective geopolymer mortars ranged between 0.13 and 0.18. This study showed that volcanic ash can be used successfully as an alternative raw material for production of geopolymers via alkaline activation of fused volcanic ash.     

Comparison of the fertilizing effects of ash from burnt secondary vegetation and of mineral fertilizers on upland rice in south-west C?te d'Ivoire

An important reason for burning the slashed vegetation in shifting cultivation systems is the release of nutrients. In an experiment in the Taï region, S.W. Côte d'Ivoire the fertilizing effects of ash and mineral fertilizers were compared. The ash was derived from a 20-year-old secondary forest which was slashed, dried, piled together and burned. The nutritional value of ash was compared with that of N, P, K fertilizers and lime in a field trial consisting of a fertilizer portion and an ash portion. The experimental design of the fertilizer portion was a 3⁴ factorial. The application rates per ha were 0, 50, 100 kg N (urea); 0, 12.5, 25 kg P (triple superphosphate); 0, 50, 100 kg K (KCl); 0, 400, 800 kg Ca(OH)₂. The 81 treatment combinations were divided into nine subblocks. To each of these subblocks three experimental units were added. In six of them ash was applied at rates of 0, 4000 and 8000 kg ash ha^–1. With 4000 kg ash ha^–1 31 kg P, 264 kg K, 915 kg Ca, 150 kg Mg, 10 kg Na, 10 kg Mn, 2.6 kg Zn and 32 kg S were applied. Upland rice (cultivar IDSA 6) was grown as test crop. The grain yields on individual experimental units varied from 1.2 to 3.2 t ha^–1. In the 3⁴ trial, N and P application significantly affected the yields of grain and straw. P application increased the uptakes of N, P, K, Ca and Mg significantly. N uptake was also significantly increased by N application and liming. There was a significant negative quadratic P effect on grain and straw yield, and uptake of nutrients, indicating that higher application rates did not result in higher yields and uptake of nutrients.Ash application significantly increased the yields of grain and straw and the uptakes of N, P, K and Mg, but not of Ca. It was concluded from the two trials that the response to ash application was mainly a P effect.The recovery fractions of P at about the same P applications rates were 7.4% and 11%, in the ash and 3⁴ trial, respectively. Hence, the relative effectiveness of ash-P was 0.67 or 67%, and the substitution rate 1.5. This implies that for the uptake of a unit of P about 1.5 times as much ash-P as fertilizer-P should be applied.The effectiveness of ash as liming material was 0.59 compared to Ca(OH)₂, hence 1.7 times as much ash as Ca(OH)₂ is needed to establish a same increase in pH. The CaO equivalent of ash proved to be 44% and the CaCO₃ equivalent 78%. In the ash trial a higher efficiency of utilization of absorbed P was found than in the 3⁴ trial. Several possible causes of this difference are discussed but no conclusive answers could be given.     

Characterization investigations of glass-ceramics developed from Seyitömer thermal power plant fly ash

Glass-ceramic materials were produced from fly ash samples obtained from the Seyitömer thermal power plant in Turkey. Glass samples were crystallized by suitable nucleation and crystal growth heat treatments on the basis of DTA results. The microstructural analysis of glass-ceramic samples were carried out using SEM and XRD techniques. SEM investigations clearly demonstrated the presence of a tiny crystallized phase dispersed in the microstructure. XRD results revealed that the main crystalline phase was diopside [Ca(Mg,Al)(Si,Al)₂O₆]. It was observed that the mechanical properties and the thermal expansion coefficient of the glass-ceramic samples depend only on the amount of the crystalline phase. Furthermore, chemical durability of the produced glass-ceramic samples were high.     

Changes of mineralogical–chemical composition,cation exchange capacity,and phosphate immobilization capacity during the hydrothermal conversion process of coal fly ash into zeolite

In the search for a technique to augment the nutrient removal capacity of zeolite synthesized from fly ash (ZFA), the present study investigated the changes of mineralogical–chemical composition, cation exchange capacity (CEC), and phosphate immobilization capacity (PIC) during the synthesis process. The ZFAs were obtained as a function of temperature (40–120 ^oC), liquid/solid ratio (1–18 ml/g), NaOH concentration (0.5–4 mol/L) and reaction time (2–72 h). The formation of low-silica zeolites (P1, hydroxysodalite, and chabazite) and the stability of mullite were observed, causing a marked decrease in SiO₂ content but roughly no change in Al₂O₃ content during the synthesis process. The decrease in K₂O, MgO content and the insignificant change in Fe₂O₃ and TiO₂ content were related to the solubility of the oxides while the increase in Na₂O and CaO was due to the increase in CEC. A high CEC was achieved under a high temperature, a high liquid/solid ratio, a long reaction time, and an appropriate NaOH concentration (2 mol/L), while a maximum PIC was achieved under relatively mild synthesis conditions instead (e.g., a reasonably short reaction time 10 h). This discrepancy was explained by the fact that different controlling factors/components in ZFA are responsible for CEC (content and kind of zeolite) and PIC (Ca component, specific surface area, and dissociated Fe₂O₃ and Al₂O₃).     

Orimulsion fly ash in clay bricks—part 3: chemical stability of ash-bearing products

The chemical stability of clay bricks containing Orimulsion ash (up to 6 wt.%) was assessed with a laboratory simulation of the brickmaking process. The development of efflorescence, the amount of water soluble salts and their elution, the fraction of S, V, Ni, Mg, Ca, Na and K immobilized in the ceramic matrix, and the amount of volatile elements potentially released during firing were determined by ICP–OES, XRPD, TGA, SEM and EMP analyses. The stabilizing mechanism acts through the capture of metals into the crystalline structure of silicates formed at high temperature. However, the firing conditions adopted in the brick industry (about 900 °C) do not permit the complete reaction of sulphates; there is considerable efflorescence and soluble salts are formed, even with 1.5% of ash added, producing a risk of sulphate attack to the mortars. On the other hand, the decompostion of sulphates during firing could bring about remarkable SO_x emissions, particularly in carbonate-free bodies. In conclusion, the disposal of Orimulsion ash in clay bricks must be practiced with caution and an amount of ash below 1 wt.% weight is strongly recommended.     

Fabrication of multifunctional TiO2–fly ash/polyurethane nanocomposite membrane via electrospinning

In this study, we demonstrate the fabrication of multifunctional composite polyurethane (PU) membrane from a sol gel system containing TiO₂ and fly ash (FA) nanoparticles (NPs). The adsorptive property of FA and photocatalytic property of TiO₂ can introduce different functionalities on PU mat for water purification. Different types of PU nanofiber mats were prepared by varying the composition of NPs in blend solution. FE-SEM, TEM, TGA, XRD, UV–visible spectra, and water contact angle measurement confirmed the incorporation of FA and TiO₂ NPs on/into PU nanofibrous mat. The influence of NPs on PU membrane was evaluated from the adsorption of heavy metals (Hg, Pb), removal of dyes (methylene blue), antibacterial activity, and water flux. The improvement of all these activities is attributed to the adsorptive property of FA and photocatalytic/hydrophilic property of TiO₂ NPs. Therefore, as-synthesized composite membrane can be utilized as an economically friendly filter media for water purification.     

Chemical correlates of α-tocopherol (Vitamin E) alteredMalacosoma disstria herbivory inFraxinus pennsylvanica var.Subintegerrinia,green ash

The antioxidant -tocopherol (vitamin E), applied in a basal trunk band to the green ash tree,Fraxinus pennsylvanica var.subintergerrinia, elicited an alteration of foliar feeding byMalacosoma disstria larvae (Lepidoptera: Lasiocampidae). The bioassayed effects were dependent on the dosage of elicitor, the time after elicitation, and the position in the tree. Leaves for chemical analysis were collected from trees receiving two dosages and at two intervals after elicitation. Compounds in the ethyl acetate extractables from the ash tree leaves were separated by TLC and HPLC. TLC separations showed differences in the nonhydrolyzed extractables attributable to elicitor dosage and time after elicitation. TLC-resolved differences were also evident among acid-hydrolyzed samples. HPLC-resolved profiles revealed eight peaks in the nonhydrolyzed extractables that were quantitatively negatively correlated with larval feeding preference between elicited versus control foliage on at least one of the two sampling dates. Results from this study and other investigations reported in the literature indicate that the antioxidant-tocopherol (vitamin E) can function as an environmental-stress elicitor of alterable defensive chemistry in green ash and other plants.     

Cr(Ⅲ) removal from simulated solution using hydrous magnesium oxide coated fly ash:Optimization by response surface methodology(RSM)

Hydrous magnesium oxide coated fly ash(MFA) has environmental remediation potential by providing a substrate for the adsorption of aqueous Cr(Ⅲ). Aqueous Cr(Ⅲ) adsorption onto MFA was examined as a function of MFA dosage, p H and initial Cr(Ⅲ) concentration with the Box–Behnken approach used for experimental design and optimization using response surface methodology(RSM). p H and dosage(dosage and concentration) have significant interactive effects on Cr(Ⅲ) adsorption efficiency. Analysis of variance shows that the response surface quadratic model is highly significant and can effectively predict the experimental outcomes. Cr(Ⅲ) removal efficiency of 98% was obtained using optimized conditions of MFA dosage, p H and initial Cr(Ⅲ) concentration of 1.57 g·L~(-1), 4.11 and 126 mg·L~(-1), respectively. Cr(Ⅲ) adsorption onto MFA is mainly attributed to the interaction between Cr(Ⅲ) and the functional group \\OH of the hydrous magnesium oxide, in all probability caused by chemisorptions. The results of this study can conduce to reveal the interactions between Cr(Ⅲ) pollutant and MFA characteristics, posing important implications for the cost-effective alternative adsorption technology in the treatment of heavy metal containing wastewater.