Environmental advantages of oil shale ash as a secondary raw material: a focus on dioxin levels

The main idea of this research is to explore the prospective of ashes accumulated during the energy production to be used as a filler for thermoplastics. The return of waste for processing into secondary raw materials is cost reducing and nature protective. In this study, low‐density polyethylene filled with CaCO3, burnt coal, and oil shale ash were produced and scrutinized. The optimal extrusion compounding and injection molding parameters are discussed. The effect of different filler load up to 30 wt% on the mechanical properties, structure, and morphology is investigated. It was found that the processing conditions for ash‐filled compounds are similar to CaCO3 filled. Mechanical properties such as tensile and impact strength of ash‐filled composites are also close to CaCo3 filled.

This study determined the elastic properties of composites and concretes reinforced with oil shale ash (OSA) particles, a byproduct of oil shale combustion in an electric power plant in Estonia (Auvere). Since 2018, OSA has no longer been classified as hazardous waste in the EU, enabling its reuse in sustainable materials. The present research examined the effect of OSA on the elastic properties of epoxy–OSA and concrete–OSA composites. The experimental results show that the elastic modulus of epoxy resin increases with an increase in the ash concentration, while it decreases in concrete with a higher OSA content. Theoretical models, including the rule of mixtures, finite element method (FEM), Mori–Tanaka method, and Halpin–Tsai method, were used to predict these properties numerically. The rule of mixtures and FEM generally overestimated the modulus for epoxy–OSA, whereas the Mori–Tanaka and Halpin–Tsai methods provided closer predictions. For concrete–OSA, the compressive strength tests followed the LVS EN 12390-3:2019 standards, with elastic modulus conversions being made via IS 456:2000 Clause 6.2.3.1, which showed a variable decrease across different strength classes. The findings highlight the potential of OSA as a reinforcing filler in construction materials, promoting environmental sustainability by repurposing industrial waste while offering mechanical benefits.

The European Union (EU) presented a uniform List of Waste (LoW) in 2000 and last updated the technical guidance in 2018. The respective local regulations for the classification of waste in Estonia were set in 2015. Due to the changes in the regulations, it was necessary to review the properties of solid wastes generated in Estonian oil shale industry in light of hazardous properties. Therefore, the properties of the produced ash streams were analysed and the obtained results were compared to those for coal for being in accordance with common practices. The main objective of the paper was to answer the question whether the properties of oil shale (OS) are comparable to those of coal as coal and its combustion residues were not considered hazardous waste in Europe, but the respective counterparts of oil shale were. The EU guidelines suggest the use of calculations based on trace element concentrations for the classification of hazardous property (HP) 14 – ecotoxic. Therefore, an extensive study was conducted to investigate the hazardous properties of all the solid residues from power plants operating on oil shale and shale oil production facilities. This paper describes one part of it – the trace element compositions of the major ash streams produced in the Estonian oil shale industry and focuses on their comparison with data available for coal ash samples. The findings of the study showed that, similarly to coal, oil shale ash (OSA) should not be considered as ecotoxic due to the low concentrations of trace elements. It was found that the investigated oil shale ash samples exhibited a very similar composition and properties to those of coal, and as a result of a larger study, from the beginning of 2020, oil shale ash and other oil shale thermal treatment residues are not classified as hazardous waste in Estonia, thereby initiating policy changes that affect most areas of the economy.

In Estonian oil shale power plants, ash is transported to disposal sites using a wet transport method. Due to regional climatic conditions, where annual precipitation exceeds evaporation, part of the recirculated ash transport water has to be periodically discharged into natural surface waters. This discharge practice raises concerns about the potential environmental impact of the discharged water. This paper investigates the leaching behavior of several trace elements from oil shale ash, demolition wood ash, and their mixtures, with a focus on chromium. In particular, the occurrence, mobility, and oxidation state of chromium in the leachate are considered using the example of the mentioned ashes. The possible effect of ash content, influenced by fuel type and the liquid-to-solid (L/S) ratio, on trace element concentrations in the discharged water was studied. In leaching tests with 100% oil shale ash, the chromium concentration in the circulating water increases only slightly when circulating water from the oil shale ash field is used as the leaching medium. On the one hand, the amount of chromium and other trace elements leached from oil shale ash depends on the L/S ratio. At the same time, it is known from the literature that oil shale ash is also capable of binding chromium. The release and concentration of chromium in the leachate increase significantly as the proportion of waste wood ash rises, compared to tests using 100% oil shale ash. Consequently, the concentration of chromium in surface water, depending on the specific ratio of oil shale to waste wood used in co-combustion, can easily exceed the nationally permitted limit value.

Oil shale is a rock that contains organic matter in aconcentrationthat allows it to be used as an energy source. As a result of theshale combustion process, large amounts of two types of ash are formed:fly ash (∼10%) and bottom ash (∼90%). At present, inIsrael, only fly oil shale ash is used, which constitutes a minorityof the oil shale burn products, whereas bottom oil shale ash is accumulatedas waste. Bottom ash contains a high percentage of calcium in theform of anhydrite (CaSO4) and calcite (CaCO3). Thus, it can be used to neutralize acidic waste and to fix traceelements. This study examined the process of scrubbing the acid wasteby the ash, its characterization pre- and post-upgrade treatment,to test its suitability as a partial substitute for aggregates, naturalsand, and cement in concrete mixtures. In the current study, we comparedthe chemical and physical characterization of oil shale bottom ashbefore and after upgrading the ash via chemical treatment. In addition,its utilization as a scrubbing reagent for acidic wastes from thephosphate industry was studied.

ABSTRACTThe present study attempted to prepare modified oil shale ash and oil shale ash zeolite from oil shale ash, which were characterized by X-ray diffraction, scanning electron microscopy, and N2 adsorption–desorption. Detailed kinetics and isotherm studies of Cd2+ adsorption onto modified oil shale ash and oil shale ash zeolite were examined. The adsorption capacity was determined as a function for the adsorption system. The results showed that the adsorption capacity of oil shale ash zeolite was higher compared to modified oil shale ash and that the time required to reach equilibrium was shorter. The kinetics studies showed that Cd2+ adsorption was well fit by the pseudo-second-order kinetics model. Both the Langmuir and the Freundlich isotherms described the adsorption data well. And the maximum monolayer adsorption capacity determined by the Langmuir adsorption isotherm was found to be 108.70 and 169.49 mg/g for Cd2+ adsorption onto modified oil shale ash and oil shale ash zeolite, respectively. It was concluded that Cd2+ in aqueous solutions was more efficiently removed by oil shale ash zeolite, which could be employed as a low-cost and effective alternative adsorbent for wastewater treatment than modified oil shale ash.

Over 90% of the Estonian basic power supply is covered by oil shale-fired thermal power plants. Every year about 11 million tons of oil shale (ash content 45-47%) is fired. The old pulverised firing (PF) and the new circulated fluidised bed (CFB) technologies are used. The PF boilers were commissioned between 1959 and 1973. Due to their age and problems relating to environmental and economical performance, two old blocks were replaced using the CFB technology. The new CFB units (2x215 MWel) delivered by Foster Wheeler started operation in 2003-2004 and are meeting the EU LCP Directive limits of gaseous emissions without any additional flue gas cleaning equipment. The most serious problem today is ash handling. Power plants (PP) using big amounts of water for ash handling are not known in Europe and are environmentally hazardous. In compliance with the EU directives the oil shale power plants must be switched over to a technology which minimises high alkaline liquid waste (dry, semidry or dense slurry technology) from July 2009. Before taking a final decision, it has to be found out what might be involved in adopting the new technology and what problems might emerge. Whatever technology we use for ash removal, ash fields come into contact with millions of cubic metres of rainwater a year which becomes polluted. The question of how to neutralise free lime in oil shale ash as one of the most hazardous components seems to be a particularly important question. This paper describes the problems relating to the chemical-mineralogical composition of oil shale ash. The conditions at hydro (wet), dry, or semidry ash removal are analysed.

Combustion of low calorific fuel – oil shale – in industrial-scale pulverized firing and circulating fluidized bed combustion boilers produces large amounts of ash. Estonian oil shale ash is characterized by a high content of free CaO as compared to those listed in the European Standard EN 450. The main alternatives to oil shale ash utilization include its use as a lime replacement in mineral binders or as a constituent of Portland cement. The pulverized firing ash formed at 1400 °C has been effectively used as a second main constituent of Portland cement during the last fifty years. Further utilization of the low-temperature circulating fluidized bed ash (formed at 800 °C) depends on its composition and properties. Dust collect­ing systems of both boiler types consist of bottom dusters, cyclones and electro­static precipitators. The corresponding ash types differ in specific sur­face area, grain size and mineral composition. The structure and composition of the dry ash and ash based stone were studied using chemical, XRD and SEM analysis. The results indicated that hydration type, as well as the setting and hardening course of the selected ash type are determined by the firing temperature of oil shale.

During the industrial processing of fish raw materials, problems arise with the disposal of waste, such as caviar from small fish species (carp, silver carp, catfish, catfish). Caviar secondary raw materials are chemically comparable to the main semi-finished fish product. The isolation of biologically active compounds from secondary materials is promising. The study of the component composition of phospholipid and protein complexes of raw materials will make it possible to substantiate the biological effectiveness of final food additives. For the organization of rational industrial processing of fish secondary raw materials, information on its amino acid composition and complex of lipid acids is necessary. The purpose of this study was the experimental determination of the amino acid composition of the protein fraction, as well as the proportion of fatty acids and phospholipid fractions in the secondary caviar raw materials of freshwater fish. The eggs of silver carp, carp, catfish, and catfish, corresponding to the morphological parameters of the IV stage of maturity, were studied. Analysis of the data on the amino acid composition of the raw material showed that the amount of essential amino acids in it exceeds that in an ideal protein by 20–25%, taking into account the type of fish. The main predominant components are threonine and leucine. Palmitic acid predominates among the polyunsaturated fatty acids in the studied caviar raw materials. Among the main unsaturated fatty acids in the objects of study, linoleic acid was isolated. The ratio of phospholipid fractions for the studied caviar samples was revealed. The prevalence of phosphatidylcholine is determined by its mass concentration in the range from 80% to 90%, taking into account the type of fish. The high proportions of the phospholipid complex in the composition of caviar secondary raw materials determine the high emulsifying characteristics of the objects of study. The use of recycled secondary raw materials for the production of fractionated lecithin is proposed.

This paper presents an experimental study on mechanical and thermal properties of concrete made from oil shale ash, cement and sand and/or aggregate mixtures. The properties determined were compressive strength and thermal conductivity of the concrete mixtures. The used ash was obtained by direct combustion of Sultani oil shale. The composition of ash is close to that of Estonian oil shale ash. Thirty-two cubes and twelve cylindrical samples were prepared to conduct compression and thermal conductivity tests, respectively. The cure duration for the cubes was 1, 7, 14, and 28 days, for the cylinders – 28 days. The content of ash in binder was 10, 20, and 30% for compression and 10, 20, 30, 60, and 70% for thermal tests. The weight ratios of cement:aggregate, cement:sand and water:binder were 1:4.5, 1:3 and 1:2.5, respectively, kept constant for each sample. The results are compared with the corresponding data for concrete made without oil shale ash. The results show that compressive strength decreases with increasing proportion of ash in the mixtures and increases with increasing curing time for all cases. Thermal conductivity of concrete samples decreases with increasing content of ash in the mixtures.

Oil shale ash (OSA) as a binder has air, pozzolanic or latent hydraulic properties depending on the combustion temperature and type of ash collection equipment. This paper focuses on the use of OSA as the main binder for low strength concrete. Impact of hardening conditions on the strength development and soundness of various concrete mixes made with two main types of OSA and their mixes was tested. Crushed limestone was used as aggregate. Concrete mixes were designed at an OSA:aggregate ratio of 3:1 and 1:1, using fresh concretes with the same workability. The results revealed differences in the strength development, 28-day compressive strength and durability properties between hardened concretes made with various OSA binders. The compressive strength of concretes made with various OSA was tested in different curing conditions. The durability properties of OSA based hardened concrete such as water absorption and resistance were tested. The results of expansion and water resistance tests indicated that by increasing the content of CFB ash in OSA binders, water resistance was improved and expansion diminished.

Dioxin contents in fly ash from large-scale MSW incinerators in Taiwan

Oil shale rocks represent one of the most available sources of energy. Jordan land contains about 50 billion tons of oil shale, which makes Jordan the third in the world of the reserve of this material. Oil shale ash is a byproduct of the oil shale manufacturing process and considered a waste material and may cause hazards for human health. In this study, the effect of oil shale ash on asphalt binder rheological properties at higher temperatures was investigated. Five oil shale ash to asphalt (OSA/A) percentages by volume (0, 5, 10, 15, and 20 %) were used. The complex shear modulus (G*) and phase angle (δ) of asphalt binders were investigated using the Superpave Dynamic Shear Rheometer and the rotational viscosity (RV). It was found that increasing the OSA/A percentage increased the G* value and the RV of asphalt binders, and improved the Superpave rutting parameter, but did not affect significantly the phase angle. Thus, adding oil shale ash (the waste material) to asphalt binder enhanced its rheological properties and performance at high temperatures.

The present study focuses on the fate of polycyclic aromatic hydrocarbons (PAHs) in soils amended with oil shale ash (OSA). Leachability studies to assess the release of PAHs to the environment are essential before the application of OSA in agriculture. A quantitative estimation of the leaching of PAHs from two types of soil and two types of OSA was undertaken in this study. Two leaching approaches were chosen: (1) a traditional one step leaching scheme and (2) a leaching scheme with pretreatment, i.e.., incubation of the material in wet conditions imitating the field conditions, followed by a traditional leaching procedure keeping the total amount of water constant. The total amount of PAHs leached from soil/OSA mixtures was in the range of 15 to 48μg/kg. The amount of total PAHs leached was higher for the incubation method, compared to the traditional leaching method, particularly for Podzolic Gleysols soil. This suggests that for the incubation method, the content of organic matter and clay minerals of the soil influence the fate of PAHs more strongly compared to the traditional leaching scheme. The amount of PAHs leached from OSA samples is higher than from soil/OSA mixtures, which suggests soils to inhibit the release of PAHs. Calculated amount of PAHs from experimental soil and OSA leaching experiments differed considerably from real values. Thus, it is not possible to estimate the amount of PAHs leached from soil/OSA mixtures based on the knowledge of the amount of PAHs leached from soil and OSA samples separately.

This study determined the elastic properties of “green” concrete with cement partially replaced by oil shale ash (OSA) and reinforced with short basalt integral fibers (BIFs). Commercially available Deutsche Basalt Faser (DBF) GmbH Turbobuild Integral basalt fibers were used. There is currently a high demand both for strengthening concrete and applying ecological approaches with respect to circular economy. Oil shale ash is the byproduct of oil shale combustion. Basalt fiber is produced by melting basalt rock. Both BIF and OSA are used as additives in concrete. Cement replacement by OSA non-linearly changes the concrete’s strength properties, and the addition of BIF improves them. An experimental investigation was conducted using four-point bending tests and cube sample compression tests. Theoretical methods such as Voigt and Reuss boundaries, the Halpin–Tsai method, and the Mori–Tanaka method were used to predict the elastic properties of the fabricated samples. The theoretical models can provide useful information, although they may not fully capture the real properties observed experimentally. The results show that BIFs protect against instant brittle destruction. The experiments demonstrated an optimal OSA concentration for a fixed amount of BIF, resulting in the highest load-bearing capacity of the concrete. The addition of either 15% OSA only or 20% OSA and CBF can increase the stiffness of the concrete. This article provides guidance to the construction sector on using OSA and CBF together.