Lignite Ash Research Articles

Size fraction characterisation of highly-calcareous and siliceous fly ashes

The properties of coal fly ash vary significantly depending on factors such as coal type, combustion conditions, and flue gas emission reduction methods. This study investigates the influence of particle size fractionation on the chemical composition, mineralogical structure, and thermal behaviour of two types of fly ash: high calcium ash derived from lignite (S1) and silica-rich ash from bituminous coal (S2). Dry aerodynamic separation was used to obtain distinct size fractions, which were then subjected to a comprehensive characterisation including X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and thermal analysis. The results reveal notable differences between the S1 and S2 ashes and between their size fractions. The finer fractions (< 20 μm) of S1 showed an increased calcium and sulphur content, while the coarser fractions (> 100 μm) contained more silica and alumina. The S2 ash exhibited a higher overall silica content, with alkali metals concentrated in finer fractions. Thermal analysis demonstrated distinct behaviours for each type and fraction of ash. Fine fractions of S1 ash showed SO2 emission at elevated temperatures, while S2 ash exhibited greater CO2 gas emission. After thermal treatment, the recrystallisation of the glassy phase was observed for S1, while the S2 ashes were more prone to melting and agglomeration. The study highlights the potential for the customised utilisation of specific ash fractions in various applications, such as geopolymer synthesis, adsorbent materials, and refractory products. This comprehensive characterisation contributes to a better understanding of fly ash properties and their dependence on particle size, providing valuable insights to optimise fly ash utilisation in various industries. The findings suggest strategies for a more efficient use of fly ash resources, particularly relevant in the context of decreasing fly ash availability due to the phase-out of coal power plants.

Thermal Studies of Fractionated Lignite and Brown Coal Fly Ashes.

Coal fly ash (CFA), a by-product of coal combustion, is a valuable raw material for various applications. However, the heterogeneous nature of the composition and properties of CFA provides challenges to its effective usage and utilisation. This study investigates the thermal behaviour of the fly ashes of lignite (FA1) and brown coal (FA2) and their fractions obtained by dry aerodynamic separation. Thermal analysis techniques, including thermogravimetry (TG), differential scanning calorimetry (DSC), and evolved gas analysis (EGA), were used to characterise the behaviour of the fly ash fractions while heating up to 1250 °C. The results reveal distinct differences in the thermal behaviour between ash types and among their different size fractions. For the FA1 ashes, the concentration of calcium-rich compounds and the level of recrystallisation at 950 °C increased with the decrease in particle size. The most abundant detected newly formed minerals were anhydrite, gehlenite, and anorthite, while coarser fractions were rich in quartz and mullite. For the FA2 ashes, the temperature of the onset of melting and agglomeration decreased with decreasing particle size and was already observed at 995 °C. Coarser fractions mostly remain unchanged, with a slight increase in quartz, mullite, and hematite content. Recrystallisation takes place in less extension compared to the FA1 ashes. The findings demonstrate that the aerodynamic separation of fly ashes into different size fractions can produce materials with varied thermal properties and reactivity, which can be used for specific applications. This study highlights the importance of thermal analysis in characterising fly ash properties and understanding their potential for utilisation in various applications involving thermal treatment or exposure to high-temperature conditions. Further research on advanced separation techniques and the in-depth characterisation of fly ash fractions is necessary to obtain materials with desired thermal properties and identify their most beneficial applications.

Kill two birds with one stone: Efficient leaching of germanium and recovery of lignite from germanium-rich lignite by thionyl chloride

Germanium, a critical metal, is predominantly located in lignite and lead–zinc ore. The germanium was commonly extracted from the fly ash of germanium-rich lignite (GRL), however, facing the challenges of specific combustion conditions, low lignite’s thermal efficiency and value, high CO2 emissions, and waste acid treatment. Therefore, in this work, a novel method for directly leaching germanium from the GRL was proposed, facilitating low-carbon extraction under mild conditions, and reducing lignite loss during leaching process. Results showed that leaching germanium from the GRL using thionyl chloride achieved the goals of “kill two birds with one stone”, i.e., leaching efficiency of germanium above 95 wt% and recovery yield of lignite over 95 wt%. Specifically, the theoretical leaching efficiency of germanium reached 99.60 wt% while the recovery yield of lignite reached 86.35 wt%, at the temperature of 20 °C, liquid–solid ratio of 4 mL/g, and leaching time of 6 h. Most of the leached germanium was remained in the aqueous phase after the leaching solution was quenched, facilitating the subsequent separation of germanium. In this study, efficient extraction of germanium from the GRL was achieved with a high recovery yield of lignite, preserving the matrix structure and main composition of lignite. Therefore, this method provides a feasible way for efficient extraction of germanium from lignite with low-carbon emission under mild condition.

Radioactivity of Technosols on thermal power station ash disposal sites: Assessment of potential radiological human‐health risk

AbstractSoil radioactivity is a poorly recognized form of land degradation; however, there are regions all around the world where it can be dangerous to the environment and human health. The aim of the study was to analyze the radioactivity of Technosols developed on thermal power station (TPS) ash disposal sites. Total concentration of uranium (U), thorium (Th), and cesium (Cs), as well as the radioactivity of select radionuclides in Technosols were determined to recognize the level of radioactivity and to assess the potential radiological health risk. Total U, Th and Cs concentrations in Technosols were in ranges 1.5 to 11.3, 4 to 22.9, and 0.2 to 21.3 mg·kg−1, respectively. The radioisotope activities in Technosols (in Bq·kg−1) were in the 1.6–25.5 (137Cs); 29.2–1265 (40K); 26.2–99.9 (228Th); 27.9–100 (228Ra); 20.5–134. (226Ra); 32.8–177 (210Pb); 23.9–144 (238U); 1.2–7.0 (235U) ranges. The activity concentrations were slightly higher than the activities of non‐contaminated soils. Technosols developed from bituminous coal ash had higher 40K, 228Th, and 228Ra activity concentrations than soils developed from lignite ash. Artificial 137Cs occurred in surface horizons of Technosols due to fall of atmospheric dust enriched in 137Cs. Annual effective dose (AED) in Technosols amounted 0.07–0.16 mSv·a−1 and was somewhat higher than the global and Polish average (0.06 and 0.07 mSv·a−1, respectively) for outdoor external terrestrial radiation. The radioactivity of the investigated Technosols is slightly above the average radioactivity of native soils. The radiological human‐health risk related to the analyzed soils is low.

Mechanical Synthesis of Nano Carrier Based Bio-formulation of Trichoderma harzianum and Their Bio-efficacy against Fusarium Wilt of Chick Pea

The terms "nano science" and "nanotechnology" have grown in popularity in comparison to micron-sized particles because they are more durable, efficient and have a high surface-to-volume ratio. In this regard, an experiment was conducted to assess the efficiency of a nano carrier-based formulation of Trichoderma harzianum against the chickpea wilt pathogen Fusarium oxysporum f. sp. ciceris. Carrier materials such as talc, lignite and fly ash were reduced to nano size using a high-speed cryo ball mill and particle sizes were determined using a particle size analyzer, scanning electron microscope and x-ray diffraction. The results revealed all of the concentrations of nano carrier formulated (talc, lignite and fly ash) T. harzianum viz.,100, 200, 300, 400 and 500 ppm concentrations were found to effective in inhibiting the growth of the F. oxysporum f. sp. ciceris with 100 per cent mean mycelial inhibition except nano talc formulated Trichoderma which shows mycelial inhibition of 2.56 per cent at 50 ppm concentration.

FORMING AND PROPERTIES OF GLASSES MADE FROM TWO THAI BOTTOM ASHES

Industrial wastes are often an under-utilized source of raw materials. Bottom ashes resulting from incineration processes can contain various metal oxides, including many commonly used in glass making. This research studied the forming and properties of glasses made from two bottom ashes. Lignite bottom ash (BL) from Lampang, Thailand and a municipal solid waste incinerator bottom ash (BP) from Phuket, Thailand. Both bottom ashes were found to contain significant amounts of SiO2, CaO, Al2O3, and Fe2O3. After ball milling, the ashes were melted without additions, at temperatures from 1300 to 1500°C. The resulting glasses, as confirmed by XRD, were black and fully opaque, a result of the high Fe2O3 content. It was found that the BP glasses were slightly more refractory, had a greater average thermal conductivity of 1.52 W/m·K and a lower coefficient of thermal expansion (CTE) of 6.97x10-6/°C, compared to the BP glasses, which had an average thermal conductivity of 1.39 W/m·K and a CTE of 7.98x10-6/°C. The BL glasses also had a higher average density of 2.88 g/cm3 and a Vickers hardness of 6.29 GPa, compared to the BP glasses, with average values of 2.74 g/cm3 and 6.06 GPa, respectively. The increase of glass melting temperature up to 1450°C tended to improve the observed properties, followed by a decrease at 1500°C. Despite the atypical glass chemistry of the two bottom ashes, they were successfully melted to produce glasses and the measured properties demonstrated suitable potential to warrant further study.

ENRICHMENT OF SİVAS/GEMEREK LIGNITE COAL BY OIL AGGLOMERATION USING DIFFERENT VEGETABLE OILS

The aim of this study was to investigate the use of various vegetable oils (almond oil, hazelnut oil, poppy oil, soybean (soya) oil, sunflower oil) for Sivas/Gemerek (in Turkey) lignite coal by oil agglomeration. The study examined the effect of bridging liquid type and dosage on oil agglomeration. Vegetable oil dosages of 2%, 5%, 10% and 20% were investigated in oil agglomeration experiments. The agglomeration of lignite coal with these bridging liquids was evaluated based on yield, combustible recovery and ash rejection. The agglomeration performances of these vegetable oils were compared. The highest ash rejection (70.30%) was observed by using soybean (soya) at 20% of the bridging liquid dosage. The yield and combustible recovery of lignite coal were achieved 36.46% yield and 38.05% combustible recovery in this soybean (soya) oil dosage, respectively. The lignite coal ash content was reduced from 19.08% to 15.54% under these optimum conditions.

Histopathology of chironomids exposed to fly ash and microplastics as a new biomarker of ecotoxicological assessment

In the last few decades, industrial pollution has gained extensive attention in terms of its effect on the aquatic environment. This imposes the need to develop sensitive biomarkers for early detection of pollutant toxicity in ecotoxicological assessment. The advantages of histopathological biomarkers are many, including quick reaction to the presence of contaminants, and the small number of individuals needed for efficient analysis. The present study analyzed the negative effect of lignite coal fly ash (LCFA) and microplastic particles (MPs) on Chironomus riparius, a suggested model organism by the Organization for Economic Cooperation and Development (OECD). This study aimed to perform histological analyses of larval tissues and target potential changes in treated groups that could serve as promising histopathological biomarkers of the contaminant's negative effects. Following that, other known sensitive sub-organismal biomarkers were analyzed and paired with the histopathological ones. Histological analysis of larvae showed a significantly decreased length of microvilli in midgut regions II and III in both treatments. Treatments with MPs affected oxidative stress parameters: thiobarbituric acid reactive substances (TBARS), advanced oxidation protein products (AOPP), superoxide dismutase (SOD), and hemoglobin levels, while LCFA significantly affected all tested sub-organismal biomarkers (DNA damage, levels of AOPP, SOD, and hemoglobin), except catalase (CAT) and TBARS. When observing histological slides, a significant shortage of brush border length in the posterior parts of the midgut was detected in all treatments. In the case of LCFA, the appearance of intensive vacuolization of digestive cells with inclusions resembling apoptotic bodies, in mentioned regions was also detected. This study demonstrated high sensitivity of brush border length to the MPs and LCFA exposure, complementary to other tested sub-organismal biomarkers. Revealing the great potential of this histopathological biomarker in ecotoxicological studies contributes to the international standard ecotoxicology assessment of emerging pollutants.

Improving the slurryability of high ash coal by blending anthracite of different particle size range

ABSTRACT Hydraulic transportation of lignite and high ash coal (HAC) is economically unviable due to their poor slurryability and stability. The study suggests and shows how the proper selection of appropriate size range and proportion of anthracite for blending can aid in the economical preparation of highly concentrated HAC slurry. Fine (+0–53 µm), coarse (+53–106 µm), and coarser (+106–150 µm) anthracite particles were added to the HAC sample. The proportion of anthracite particles was varied in the range of 10–40% (by weight), to obtain 12 blended tetra-modal samples. To determine the optimum size range and proportion of anthracite, the stability and rheological characteristics of both tri-modal HAC and blended tetra-modal coal samples were assessed. The addition of a fine anthracite sample (+0–53 µm) has an adverse impact on the rheological characteristics. The optimum size range and proportion of anthracite particles for enhanced slurryability and low apparent viscosity are found to be +106–150 µm and 30%, respectively. Optimal blending yields a 68% maximum solid concentration slurry. By taking advantage of both the tetra-modal particle size distribution and anthracite’s high slurryability characteristics, the maximum achievable solid concentration of HAC slurry increases by 17%.

Characterization of lignite deposits of Barmer Basin, Rajasthan: insights from mineralogical and elemental analysis.

The geochemistry of fly ash produced from the combustion of coal at thermal power plants presents a significant challenge for disposal and environmental impact due to its complex mineralogical and elemental composition. The objective of this study was to investigate the mineralogical and elemental distribution of thirty lignite samples from the Barmer Basin using advanced techniques such as X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analysis revealed the presence of minerals such as haematite (Fe2O3), nepheline, anhydrite, magnesite, andalusite, spinel and anatase. Other minor minerals included albite, siderite, periclase, calcite, mayenite, hauyne, pyrite, cristobalite, quartz, nosean and kaolinite. XRF analysis demonstrated that the most abundant elements in the Barmer Basin lignite ash were iron oxide (Fe2O3), sulphur oxide (SO3), calcium oxide (CaO), and quartz (SiO2) followed by minor traces of toxic oxides (SrO, V2O5, NiO, Cr2O3, Co2O3, CuO) that are known to have adverse effects on human health and the environment. The rare earth element (REE) composition showed higher concentrations of Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc at the Giral and lower concentrations at Sonari mine. The Barmer lignites recorded higher concentration of trace elements such as V, Cr, Co, Ni, Cu and Sr while lower concentration of Rb, Cs, Ba, Pb, As, Th and U were observed within optimal range. The study findings revealed the predominant mineral concentration, elemental makeup, trace elements and rare earth elements associated with lignite reserves in the Barmer Basin.

Advanced high-iron coal fly ash zeolites for low-carbon emission catalytic combustion of VOCs

Coal fly ash zeolites (CFAZs) with increased iron oxide content were prepared by double-stage alkaline conversion of high-iron lignite coal ash. Catalysts were modified by applying radiofrequency plasma treatment with trifluoromethane (RF CHF3) to increase their surface activity. Textural, compositional, and structural characterization of the parent and plasma-modified zeolites were performed by N2-physisorption, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FT-IR) spectroscopy. Oxidation state and coordination of iron species were studied by Mössbauer spectroscopy, UV-Vis spectroscopy and temperature-programmed reduction method (TPR). Acidic properties were investigated by FT-IR spectroscopy of adsorbed pyridine. The initial and plasma-modified samples were studied under toluene oxidation, where toluene was used as a model VOC. The plasma-modified iron-enriched zeolite was found to exhibit high catalytic activity for VOC oxidation, reaching a 98% toluene conversion rate at 500 °C. Despite some structural degradation effects, the plasma-treated catalysts outperformed the untreated ones in catalytic activity. Furthermore, CO2 adsorption capacity of the plasma-modified zeolite was investigated under dynamic conditions. Although plasma-treated iron-enriched zeolite showed relatively low specific surface area (194 m2/g), high dynamic carbon capture capacity of 3.8 mmol/g was measured. It significantly exceeded the capacity of CFAZs with higher specific surface area, not to mention the pure zeolite phase.

The Effect of Sludge-Ash Granulates on the Content and Uptake of Heavy Metals by Winter Rape Seeds and Triticale

Four granulates were prepared from waste, including lignite ash, industrial sludge, sawdust, ammonium nitrate and potassium salt (60% K2O). The produced granulates were chemically tested. They contained significant Ca and C organic contents and slightly less S, P, K and Mg. The concentration of Cd, Cr, Cu, Ni, Pb and Zn did not exceed the applicable standards. Then, they were tested in a experiment with 2 plants: spring rape, Larissa cv., and spring triticale, Milikaro cv. The content of the tested heavy metals in rape seed and triticale grain largely depended on the chemical properties and the amount of components used to produce granulates. As a rule, a higher share of industrial sludge and a lower share of lignite ash (granulates II with industrial sludge 40% and IV with industrial sludge 50%) in the granulates increased the content of heavy metals in the test plants. Applying the 2nd and 3rd doses of granulates increased the contents of cadmium, copper, chromium, nickel, lead, and zinc. Increasing doses of granulates significantly increased the uptake of heavy metals by rape seed and triticale grain. Under the influence of applied fertilizer granulates, the content of heavy metals in rape seeds and triticale grain was significantly positively correlated with their uptake.

Adsorption and catalytic oxidation of residual NH3 on coal ash after selective non-catalytic reduction in coal-fired boilers

Selective non-catalytic reduction (SNCR) with NH3 as the reducing agent is widely used for the denitrification of flue gas in coal-fired boilers, where fly ash significantly influences the conversion of the residual NH3 that does not participate in denitrification. However, there have been few studies on the exact nature of this influence, particularly the adsorption and reaction mechanisms of NH3 on fly ash. In this study, temperature-programmed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used to study the mechanisms of NH3 adsorption and reactions over coal ash. In the absence of oxygen, in the temperature range of 50–450 °C, NH3 was adsorbed on the surface of the coal ash. The adsorption capacity of lignite ash was higher than that of anthracite ash. This difference was attributed to the large specific surface area and surface acidity of the lignite ash. However, between 450–850 °C, coal ash had a catalytic effect on NH3 decomposition and oxidation. Due to the high surface lattice oxygen content of lignite ash, its catalytic oxidative ability was superior to anthracite ash. Moreover, NH3 was first adsorbed over Lewis and Brønsted acid sites on the surface of coal ash and later underwent hydrogen abstraction to produce either the NH2 or the NH intermediate. The intermediates further reacted with the surface lattice oxygen of coal ash to produce NO and N2O. These results might be helpful for the management of NH3 residues from SNCR processes and the utilization of amino reducing agents in coal-fired boilers.

Validation of numerical models for prediction of pressure drop in high capacity long distance lignite fly ash pneumatic conveying

This paper will validate two basic concepts of numerical models for prediction of pressure change along the transport pipeline in the case of long distance and high capacity lignite ash pneumatic conveying. Application of various friction factor correlations and variation of given parameter, led to the total of fourteen different numerical models and program codes in FORTRAN. The input data for numerical models are based on comprehensive experimental research of high capacity and long distance Kolubara lignite fly ash pneumatic conveying system within 620 MWe thermal power plant unit under operating conditions. Numerical simulation results are validated against experimental data and subjected to statistical analysis methods. The functional dependence obtained by the least squares method was evaluated using mean squared deviation and correlation ratio. The predicted pressure changes show the best agreement, with the measured decrease of pressure amplitudes along the transport pipelines, for the model based on the momentum balance of air-ash mixture flow and friction factor cor-relation given by Dogin and Lebedev for the parameter A = 1.4?10-6. This model achieved the best correlation ratio of 93.99% for Pipeline 1 and 91.33% for Pipeline 2, as well as the best mean squared deviation of 9.58% for Pipeline 1 and 13.66% for Pipeline 2. Also, the fanning friction factor values are fully consistent with previously examined cases available in the literature. Numerical simulation model can be used for prediction of the ash pneumatic conveying capacity and pressure drop for the specified transport pipeline.

Utilization of lignite coal ash and steel slag in fly ash brick manufacturing: A review

Brick plays an important role in the construction industry due their excellent properties like compressive strength and durability. From the earliest times they were considered an important factor in the purpose of the building. Considering the different types of bricks, fly bricks are the best in recent times because they are resource intensive and cost effective. This article provides an up-to-date review of current studies of bricks, categorizing these publications according to the materials used and the methods used for the production of invention bricks. In addition, this article makes an important note about coal ash, which may be the focus of future brick products as an alternative to fly-gray bricks with some amount of steel slug, and the main challenge is to go one step further in the properties of the bricks by implementing the respective requirements.

Shelf-Life Assessment Of Carrier Based Formulations Of Trichoderma Mutants

In present study six different substrates (talcum powder, lignite, charcoal, sawdust, compost and fly ash) were used to test the shelf life of the most virulent isolates of Trichoderma harzianum (AkTr 2GM5) and Trichoderma hamatum (AkTm1GM5) mutant’s upto 180 days. Maximum cfu/g 154.50 x 106 and 45.50 x 106 were obtained at 30 and 180 days after storage in the Trichoderma harzianum talc-based formulation respectively, and the lowest (16.25 x 106) in fly ash formulation. Furthermore, Trichoderma hamatum talc based formulations exhibit maximum cfu/g values of 156.75 x 106 and 41.50 x 106 at 30 and 180 days after storage, respectively.

A sustainable bottom ash-based alkali-activated materials and geopolymers synthesized by using activator solutions from industrial wastes

This research focused on a 100% using of industrial wastes to produce alkali-activated materials (AAMs) and geopolymers which are sustainable environmentally friendly materials having properties like a cement. Two different sources of lignite and bituminous coal-fired bottom ashes were used as starting materials. Two types of alkaline solutions from wastes, namely, NaOH solution waste discharged from anodize process in aluminum industry (AS1) and alkaline solution prepared from boiling rice husk ash in that NaOH solution waste (AS2), were used instead of commercial alkaline activator solution. Solid/liquid ratios of the samples were studied between 75:25, 70:30, 65:35, and 60:40. Forming by casting method, after curing 28 days, mechanical and physical properties, including XRF, XRD and SEM analysis were investigated. AAMs and geopolymers from wastes with low-cost of raw materials showed good enough properties to use for construction materials such as bricks, tiles, or cement substitution. The best properties were found from the sample using lignite bottom ash as precursor synthesized with AS1 solution at 75:25 solid/liquid ratio, it showed compressive strength of 28.91 ± 2.16 MPa, bulk density 1.77 ± 0.03 g/cm3, water absorption 17.23 ± 0.13%, and apparent porosity 30.46 ± 0.19%. The samples synthesized from lignite bottom ash exhibited better properties than bituminous bottom ash. Depending on SiO2 and Al2O3 contents in raw materials, the lignite bottom ash with lower Si/Al ratio resulted in the better compressive strength. In addition, the higher calcium content in lignite bottom ash significantly affecting increased compressive strength of the samples.

Study on particle radiative properties of lignite, hard coal and biomass fly ashes in the infrared wavelength range

Fly ash, which is a by-product of combustion in furnaces or boilers, is used in certain materials as an additive for waste recycling. The optical properties of fly ash and the effects on the heat transfer phenomena of materials used in engineering applications differ and depend on the kind of solid fuel and the combustion conditions. The morphological and the radiative properties of fly ash samples of Turkish lignite, biomass, and hard coal that are burned in different thermal power plants were studied herein. The samples, which were collected from cyclones, were morphologically examined using scanning electron microscopy (SEM) images, and their chemical compositions were analysed by energy dispersive x-ray spectroscopy (EDX). Absorbance measurements were made in the wavelength range from 2.5 to 25 μm, and the discrete dipole approximation (DDA) was applied for a numerical assessment of the radiative properties of the samples. The measured absorbance values of all samples for particle diameters of 25 and 75 μm displayed significant differences in the related wavelength range. The most prominent change was observed in the biomass sample, and the hard coal fly ash had the lowest absorbance values in the related spectrum range. Although the particle shapes of lignite and biomass fly ashes are not same, the changes in the measured absorbance values were similar. The effects of the k index of the complex refractive index (CRI) on the radiative properties were examined for values of 0.01, 0.1, 0.3, 0.5 and 1.0. According to the measured absorption values and the calculated absorption efficiency results, the k index may be between 0.3 and 1.0 at the related wavelength range. It was concluded that the effects of the particle size and absorption index of fly ash on the heat transfer properties are important in the specified wavelength range.

Determining physico-chemical parameters for high strength ambient cured fly ash-based alkali-activated cements

High strength ambient cured alkali-activated cement was developed from original Class-F (ASTM) fly ash using 1:2.5 mass ratio of 16 molar sodium hydroxide and sodium silicate liquid activator with solution to solid binder ratio of 0.36 for in-situ cast application. Graded strength of high, medium and low in the range of 60–103, 30–56 and ≤ 20 MPa were obtained using mono-component original fine, medium and coarse sized fly ashes respectively. The inclusion of 35 wt% GGBS in the medium sized Class-F fly ash improved the strength from 45 MPa to 60 MPa while 100% GGBS showed higher strength of 81 MPa. Chemically, CaO/SiO2 ratio in the composition influenced the fresh and hardened properties of alkali-activated fly ash/GGBS cements. For instance, in the Class-F fly ash (Si/Al=1.55-1.99) based compacts with CaO/SiO2 ratio ≤ 0.03, the strength improved with increasing atomic Al/(Na + K) ratio. Conversely strength decreased with increasing Al/(Na + K) ratio in bi-component fly ash and GGBS based alkali-activated cements where CaO/SiO2 ratio is higher in between 0.17-0.75. Interestingly Si-dissolution from subcrystalline silica or fine quartz from mechanically activated Class-C fly ash did not improve strength. Lignite ash with high specific surface area as obtained in low temperature combustion did not react with high pH alkaline solution indicating need for vitreous aluminosilicate glass. X-ray diffraction and attenuated total reflectance Fourier transform infrared spectroscopic analyses show that plagioclase and C-S-H were the reaction products responsible for strength gain in ambient cured alkali-activated fly ash/GGBS cements.

Self-Immobilizing Metals Binder for Construction Made of Activated Metallurgical Slag, Slag from Lignite Coal Combustion and Ash from Biomass Combustion.

Research on the effective use of secondary products is gaining more and more importance in Poland due to the intensively implementing idea of the circular economy. The solution used in this work are one of many tests useful in construction. The subject of this work was therefore the formation and testing of a new ecological construction binder, in particular for mortars or prefabricated elements working in the environment with high humidity. The binder was made of alkaline activated ground granular blast furnace slag (AAS), fly ash from biomass combustion (BFA) and furnace slag from brown coal combustion (LFS). The mixture was modified by introducing the zeolite to check the degree of metals immobilization contained in the ingredients of the mixture. A series of three mixtures were prepared: without and with zeolite soaked in distilled water or calcium nitrate. The strength of binders in time in dry and wet curing were tested and compared with the microstructure. The maximum compressive strength values at the eighth week were about 30 MPa. The strength values after 4 weeks of dry and wet curing were also compared. It was shown that 28-day wet curing increased the bending strength of the beams more than twice, but slightly decreased the compressive strength. The microstructure of the mixture with the highest values of compressive strength was the densest and the one with the lowest values of compressive strength, the most loosened with the most differentiated topographically fracture. The impregnation of zeolite with calcium nitrate decreased the compressive strength of the binder significantly. The bending strength of samples curing in dry conditions decreased during hardening. The results of the metals leaching test showed that the mixtures were safe for the environment, and due to the impregnation of zeolite with calcium nitrate, the binding effect of copper and zinc in the first weeks was greater than in the other mixtures.