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The thermal behavior of green clay samples from the Arumetsa and Füzérradvány deposits (Hungary) and the influence of two new types of Estonian oil shale (OS) ashes and cement bypass dust (clinker dust) additives on it were the objectives of this study. Thermal and thermo-dilatometric analysis methods were applied using a Setaram Setsys 1750 thermoanalyzer coupled with a Pfeiffer Omnistar spectrometer and a Setaram Setsys 1750 CS Evolution dilatometer. The kinetic parameters were calculated based on the differential isoconversional method of Friedman. The results of the thermal analysis of clays and blends indicated the emission of physically bound water at 200–250 °C. At temperatures from 200–250 °C to 550–600 °C the release of water is caused by oxidation of organic matter and dehydroxylation of different clay minerals like illite, illite-smectite, mica and kaolin. From blends, in addition, also from the decomposition of portlandite. The emission of CO2 at these temperatures was a result of the oxidation of organic matter contained in the clays. In the temperature range from 550–600 °C to 800–900 °C, the mass loss was caused by ongoing dehydroxylation processes in clay minerals but was mainly due to the decomposition of the carbonates contained in the OS ashes and clinker dust. These processes were accompanied by contraction and expansion of the ceramic bodies with the corresponding changes in the SSA and porosity values of the samples. Therefore, the decomposition of the clays took place in one step which blends in two steps. At first, dehydroxylation of the clay minerals occurs, followed by decomposition of the carbonates. The value of the conversion-dependent activation energy E along the reaction progress α varied for the Arumetsa and illitic clay between 75–182 and 9–206 kJ mol−1, respectively. For the blends based on Arumetsa and illitic clay, the activation energy of the first step varied between 14–193 and 5–205 kJ mol−1, and for the second step, it was between 15–390 and 135–235 kJ mol−1, respectively, indicating the complex mechanism of the processes.

This work focuses on the local alkaline wastes of Estonia where different waste streams were studied for the performance testing of the fly ash based building blocks. Fly ash from oil shale direct combustion and wood fly ash from district heating plant were considered in the applications for utilizing both CO2 and combustion residues. These types of ashes contain Ca/Mg-oxides, silicates, or other metal oxides as candidate precursor materials for CO2 mineralization. Based on the results obtained from the performance testing of all compacted and carbonated (both with model flue gas and 100%CO2) samples, it can be concluded that flue gas curing can be an effective method for direct mineral carbonation of compacted fly ash blocks. The formation of carbonate phases in compact bodies lead to an increase in compressive strength. The rate limiting impact due to the low CO2 concentration in flue gas curing was negligible on the CO2 uptake level when elevated curing pressures were applied to the fly ash based compacts.

The increasing need for phosphorus and rare earth elements (REEs) has initiated the studies of new mineral deposits and new complex processing technologies. Estonian phosphate rock (EPR) resources, which are not in use, are estimated to be more than 3 billion metric tons or 800 million tons of P2O5. The experiments of dissolution of three different EPR samples in hydrochloric acid were carried out with the aim of studying the impact of the chemical and mineralogical composition of EPR on the leaching process. The leaching of P, Ca, Mg, and consumption of H+ ions depend on HCl concentration and dosage. The solubility of fluorine and REEs are also influenced by CaF2 and REEs-phosphates precipitation. Fe solubility depends on the mineralogical composition of EPR but also on particle size, acid dosage, pH, and phosphorus content in the solution. The dissolution of pyrite is much lower than the solubility of carbonate apatite. Dolomite dissolution depends on the acid dosage and the fractional composition of EPR. Dolomite dissolution also rests lower than that of apatite. For all the samples studied, the best regression models that describe P, Mg, and Ca solubility and the optimum concentration of HCl for phosphorus dissolution were found using mathematical modeling.

Graptolite–argillites (black shales) are studied as potential source of different metals. In the processing technologies of graptolite–argillites, a preceding thermal treatment is often applied. In this study, the thermal behavior of Estonian graptolite–argillite (GA) samples from Toolse, Sillamäe and Pakri areas were studied using a Setaram Labsys Evo 1600 thermoanalyzer coupled with the Pfeiffer OmniStar Mass Spectrometer. The products of thermal treatment were studied by XRD, FTIR, and SEM analytical methods. The experiments were carried out under non-isothermal conditions of up to 1200 °C at different heating rates in the atmosphere containing 79% Ar and 21% O2. The differential isoconversional Friedman method was applied for calculating the kinetic parameters. All studied GA samples are characterized with high content of orthoclase (between 38.0 and 57.3%) and quartz (between 23.8 and 35.5%), and with lower content of muscovite, jarosite, pyrite, etc. The content of organic carbon in GA samples studied varied between 7.3 and 14.2%. The results indicated that, up to 200 °C, the emission of hygroscopic and physically bound water takes place. Between 200 °C and 500–550 °C, this is followed by thermo-oxidative decomposition of organic matter. The first step of thermo-oxidation of pyrite with the emission of water, carbon and sulphur dioxide, nitrogen oxides, and different hydrocarbon fragments indicated the complicated composition of organic matter. At higher temperatures, between 550 °C and 900 °C, the transformations continued by dehydroxylation processes in clay minerals, and the decomposition of jarosite and carbonates took place. At temperatures above 1000–1050 °C, a slow increase in the emission of sulphur dioxide followed, indicating the beginning of the second step of thermo-oxidative decomposition of pyrite, which was not completed for temperatures of up to 1000 °C. Kinetic calculations prove the complicated mechanism of thermal decomposition of GA samples: for Pakri GA samples, it occurs in two steps, and for Silllamäe and Toolse GA samples, it occurs in three steps. Preliminary tests for the estimation of the influence of pre-roasting of GA samples on the solubility of different elements contained in GA at the following leaching in sulphuric acid is based on Toolse GA sample.

A circular economy becomes an object of actual discussions as a real alternative to the existing linear economy system. The problem is actually in Estonia also, first of all in the sector of heat and power production which based mainly on the combustion of local solid fossil fuel—Estonian oil shale (OS) resulting in the formation of ~5–6 million tons of OS ashes annually. The thermooxidative decomposition of OS samples from different deposits and estimation of the possibilities of utilization of OS ashes formed at both—pulverized firing (PF) and circulating fluidized bed combustion (CFBC) of Estonian OS were studied. The thermal analysis combined with evolved gas analysis (EGA) methods like Fourier transform infrared (FTIR) and mass-spectroscopy (MS) was exploited. It was established that the differences in the thermal behaviour of different OS samples are caused by the differences in the chemical matrix of organic matter, chemical and mineralogical composition of the inorganic part of OS, and morphology of samples. It was also found that moderate grinding of OS ashes with simultaneous moderate water treatment notably improved the SO2 binding efficiency of cyclone ash, and that the strength and leachability characteristics of granulated OS ashes strongly depend on the post-granulation treatment conditions allowing to increase the soil neutralizing ability of the granulated products. This overview was based on our investigations carried out during the last fifteen years.

In recent years, carbon sequestration into thermodynamically stable carbonates has been developed as a promising carbon capture, utilization and storage (CCUS) method, especially, when alkaline industrial wastes are used as sorbents. The use of industrial wastes to sequester CO2 plays a dual role in environment protection, creating opportunities not only for capture and disposal of CO2 but also for recycling of wastes and promoting the transition to circular economy. The CLEANKER project (Horizon 2020 Project Clean clinker production by Calcium looping process) aims to build a CO2 mineralization pilot incorporated into Ca-looping demo system in Vernasca cement plant and use the re-carbonated wastes in concrete applications. Different types of wastes such as burnt oil shale (BOS) from Eesti, Balti and Auvere power plants as well as from Enefit280 oil producing unit in Estonia, concrete demolition wastes (CDW), cement by-pass dust (CBD) from Robilante, Italy, blast furnace slag (NSF) from Bremen, Germany were tested first in laboratory scale via dry and wet direct carbonation routes under the conditions of CO2-rich model gas flow of 70 – 100% CO2, simulating the Ca-looping system. The results show that selected types of BOS and cement wastes could be used as efficient binders in both dry and wet CO2 mineralization systems with binding capacities up to 0.18 kg of CO2 per kg of BOS and up to 0.24 kg of CO2 per kg of CBD. The activating effect of hydration as a pre-treatment method showed that at lower operating temperatures, the same level of CO2 capture can be achieved, thereby rendering the carbonization processes of similar industrial wastes more energy efficient. Moreover, the CO2 mineralization tests with BOS in a 46 L concrete mixer confirmed the applicability of wet carbonization process also in larger scale. Based on the results, the most promising materials, BOS and CBD, were selected for in the proposed CO2-mineralization process in wet conditions at ambient temperature. The pilot (200 L) was designed based on a commercially available concrete mixer integrated into CLEANKER Ca-looping demo system and equipped with CO2 inlets and outlets, as well as CO2, temperature and moisture sensors to detect the reaction progress. The re-carbonated wastes will be tested via concrete casting in order to demonstrate the quality of the commercial product in the following stages of the project.

The ClimMIT project was funded by Estonian Research Council from National Programme for Addressing Socio-Economic Challenges through R&D (RITA), which is supported by the Estonian Government and European Regional Development Fund from April 2019 to April 2021. ClimMIT (https://www.taltech.ee/climmit) aims to assess the feasibility of investing in carbon capture infrastructure to minimise greenhouse gas emissions (GHG) from oil shale industry in Estonia. The main technological deliverables of the project include analysis and recommendations on measures for potential implementation of carbon capture technologies and utilisation of carbon dioxide in Estonia’s public and private sectors. Estonia’s economy has, per capita, one of the highest GHG emission rates and carbon-intensity levels in the European Union. To decrease GHG emissions, the best options for implementing carbon capture and utilization (CCU) technologies must be worked out. The main goal of the project is to assess the suitability of existing CCU technologies and to develop scenarios for adopting these technologies in Estonia’s oil shale sector. The project results in a multifaceted overview of the feasibility of investing in carbon capture infrastructure to help to minimize GHG emissions from the oil shale industry in Estonia.

Phosphorus is an essential and non-substitutable element for the cellular processes of all living organisms. The main source of phosphorus in the biosphere is phosphate rock. With more than 700 Mt phosphate rock, Estonia holds the largest sedimentary phosphate rock deposits in the European Union. Estonian phosphate rock is particularly outstanding due to its remarkably low content of hazardous heavy metals such as Cadmium (&lt, 5 ppm) and trace elements of Uranium (&lt, 50 ppm). It is also a reliable source of valuable elements such as rear earth elements (REEs). The aim of this study was to investigate the distribution of the main minerals (apatite and quartz) between slimes, tailings, and concentrates that formed at the froth flotation of Estonian phosphate rock with the up-to-date level of know-how and techniques. Subsequently, the relationship between the obtained grades and recovery levels in concentrates was determined based on the collector dosage and flotation duration. It was observed that the fine fraction of the tailings contains 17.9&ndash, 33.49 wt% P2O5 that can be added to the final product. Moreover, it was found that, with the lower dosage of the collector, the extended flotation time does not influence the phosphate grade and a high amount of quartz remains in the concentrates. It was also shown that, by raising the collector dosage and setting the flotation time, an adequate grade (&gt, 32 wt% P2O5) and recovery (up to 98%) can be gained. The results showed that Estonian phosphate rock can be beneficiated to produce a high-quality concentrate at high recovery levels by modifying the main flotation parameters depending on the properties of the ore.

The alkaline wastes such as burnt oil shale (BOS) and cement bypass dust (BPD) generally contain free lime and portlandite which make them suitable sorbent materials for CO2 trapping via mineral carbonation technique of carbon capture and sequestration. In order to study the reaction kinetics and effect of operating parameters on carbonation processes of such alkaline wastes for future industrial sized scale-ups, as well as to identify the effects on carbonation capacity when these sorbents undergo pre-treatment and are exposed to different temperatures, BOS and BPD as sorbents in CO2 mineralization process have been investigated with thermal analysis methods in the current work. Results indicate that selected types of BOS and BPD could be used as binders in the CO2 mineralization systems, binding reasonably good amount of CO2 already in the early stage of the carbonation process which later slows down as the rate of CaO carbonation becomes mainly diffusion controlled. Increased process temperature and hydration as pre-treatment improve the CO2 binding ability, while the effect of milling has been found to be staggering and not as significant as the effect of hydration and temperature rise. The appropriate kinetic mechanism functions were determined, and the kinetic parameters—activation energy (Ea) and pre-exponential factor (A) values were calculated for all the samples. The Ea values of hydrated samples are lower for BOS samples compared to non-hydrated samples. It was shown that activation by hydration enables to reach the same CO2 uptake levels at lower temperatures, thereby making the mineralization process more energy efficient and thus lowering the costs.

In this study, fly ash (FA) compacts were prepared by accelerated carbonation as a potential sustainable building material application with the locally available ashes (oil shale ash (OSA), wood ash (WA) and land filled oil shale ash (LFA)) of Estonia. The carbonation behaviour of FAs and the performance of 100% FA based compacts were evaluated based on the obtained values of CO2 uptake and compressive strength. The influence of different variables (compaction pressure, curing temperature, CO2 concentration, and pressure) on the CO2 uptake and strength development of FA compacts were investigated and the reaction kinetics of the carbonation process were tested by different reaction-order models. A reasonable relation was noted between the CO2 uptake and compressive strength of the compacts. The porous surface structure of the hydrated OSA and WA compacts was changed after carbonation due to the calcite formations (being the primary carbonation product), especially on portlandite crystals. The increase of temperature, gas pressure, and CO2 concentration improved the CO2 uptake levels of compacts. However, the positive effect of increasing compaction pressure was more apparent on the final strength of the compacts. The obtained compressive strength and CO2 uptake values of FA compacts were between 10 and 36 MPa and 11 and 13 wt%, respectively, under various operation conditions. Moreover, compacts with mixed design (OSA/LFA and WA/LFA) resulted in low-strength and density compared to the single behaviour of OSA and WA compacts, yet a higher CO2 uptake was achieved (approximately 15% mass) with mixed design. The conformity of Jander equation (3D-diffusion-limited reaction model) was higher compared to other tested reaction order models for the representation of the carbonation reaction mechanism of OSA and WA. The activation energy for OSA compact was calculated as 3.55 kJ/mol and for WA as 17.06 kJ/mol.

Estonia holds the largest unexploited sedimentary phosphate rock reserves in the EU. Compared to other sedimentary and also igneous phosphate rocks the Estonian phosphorite is particularly outstanding by its remarkably low Cd (1–5 ppm) and trace U content (~50 ppm) and also contains valuable elements such as rare earth elements (REEs), which could be used in important high-technologies in the future. In this paper beneficiation by reverse flotation of the silicates for three types of Estonian phosphorite ores was investigated. The apatite concentrates with grades of over 33 wt% P2O5 at recoveries of 84.8 to 89.2% were achieved. The concentrates had low MgO contents and grades of FeO ranged from 1.29 up to 2.54 wt%. The study gives an overview of the specifics of enrichment of Estonian shelly phosphorite ores, provides a ground for future in-depth and pilot-scale experiments to find proper solutions for the Estonian phosphorite processing and will be applied in the feasibility studies of the phosphorite industrialization.

The development of a Ca-based CO2 capture sorbent from a limestone-rich mine waste via aqueous mineral carbonation was first time evaluated. Aqueous carbonation of calcined oil shale mine waste rock was conducted at the laboratory scale at ambient temperature and atmospheric gas pressure using CO2 gas mixture simulated the average exhaust gas composition of a fossil fuel power generation plant. The dissolution and carbonation of calcium were found to be optimal at 2.5% pulp density and were found to proceed faster during the initial 5–10 min. The overall aqueous carbonation efficiency was estimated at ≥89%. The carbonation process resulted in the production of pure calcite, whereas a mixture of Ca and Mg carbonates was found in the reaction residue. The CO2 uptake capacity (∼80 wt%) of the developed Ca-based sorbent was promising and revealed that it can be used for direct CO2 capture.

A set of conditions was simulated with ASPEN PLUS software, including air and oxyfuel (OF) combustion of carbonate-rich unconventional fuels: Estonian oil shale (EOS) and Utah White River oil shale (UOS). For OF combustion cases, two different flue gas recycle (FGR) strategies were applied by controlling the O2 percentage in the flue gas on the basis of maintaining similar temperatures at the outlet of combustion reactor with those of air combustion. Differences between the fuels and simulated cases have been identified, focusing on the flue gas volumetric flow rates, heat capacities, flue gas compositions, and boiler efficiencies. The results show that it is possible to reach similar temperature levels in OF cases, as it was in air combustion by increasing the O2 concentration in the recycled flue gas (RFG) mixture for both fuels. When the O2 concentration is increased to almost 26% for wet recycle and 28% for dry recycle in the case of EOS combustion, the calculated temperatures are similar to the tempe...

The article CO2 mineralization by burnt oil shale and cement bypass dust: effect of operating temperature and pre-treatment, written by Can Rüstü Yörük, Mai Uibu, Mustafa Cem Usta, Tiit Kaljuvee, Andres Trikkel.

The EU Horizon 2020 project CLEANKER is aimed on Ca-looping capture of CO2 emissions produced by cement industry. For the first time capture-focused EU project includes the full CCUS value chain study. This study includes techno-economic modelling of CO2 transport, storage, and utilization scenarios; CCUS regulatory issues; definition of BUZZI and ITC-HCG cement plants suitable for first-of-a-kind CCS plant based on transport and storage opportunities; mineral trapping of CO2 from the demo system and testing the carbonated materials for reuse in concrete. Gaps in national regulations were analysed for Italy, Estonia, Latvia, Lithuania and Russia involved in two planned CCUS scenarios (Italian and Baltic). Russia is one of the largest emitters and Estonia has one of the highest CO2 emissions per capita in the world. Russia has not ratified yet Paris Climate Agreement. Latvia, Lithuania and Russia are not parties of the London Protocol. CO2 use options in these countries include CO2 use for EOR, Geothermal Energy Recovery and mineral carbonation using waste materials. Additional CCUS regulations and political incentives are needed in these countries. Estonian burnt oil shale could be used as an effective sorbent in the proposed CO2-mineralization process, binding up to 0.18 kg CO2 per kg of waste. The onshore CCUS scenario was proposed for CO2 emissions produced and captured by Kunda Nordic Cement plant (KNC), Eesti and Balti power plants, and Latvenergo TEC-2, the largest CO2 emitters in Estonia and Latvia. CCUS scenario includes mineral carbonation of 1.2 mln tonnes CO2 and transport and storage of about 10 mln tonnes annually into North- Blidene and Blidene structures in the western Latvia. The average optimistic capacity of the structures (297 Mt CO2) will allow to store these emissions for at least 29.5 years. The share of the Estonian emissions stored in Latvia will be about 92.6%, including 5.6% by KNC. Latvian stored emissions will compose 7.4%. Such scenario will support Estonia and Latvia to reach their climate strategic targets. Techno-economic modelling of this scenario will be the next step of this study. Utilizing of the re-carbonated wastes in concrete application supports closing the CO2 cycle of Vernasca cement plant by trapping the carbon dioxide into a concrete that contains the cement of the same plant.

In this work, non-isothermal thermal analysis (TA) methods combined with Fourier transform infrared (FTIR) spectroscopy were applied to investigate specifics of different stages of oxy-fuel (OF) combustion of Estonian oil shale (EOS) and its char. Kinetics of EOS and its char oxidation were analyzed in different atmospheres in order to understand the complex mechanism of oil shale (OS) OF combustion. Additionally, the OF combustion of OS in circulating fluidized bed (CFB) was simulated with the recently released Aspen Plus fluidized bed (FB) reactor which treats bottom zone and freeboard hydrodynamics. Particular attention was given to the determination of the required elutriated mass flows to maintain the heat balance of the system for OF combustion cases. Four case studies were simulated including: Case 1: Air combustion, Case 2: 21%O2/flue gas, Case 3: 23%O2/flue gas and Case 4: 30%O2/flue gas. The results of TA experiments show that the pyrolysis behavior is very similar in Ar and CO2 until 500°C and there is no visible char carbon and CO2 reaction under OF conditions. The emissions of CO2 from mineral part of OS can be diminished as decomposition of calcite takes place at higher temperatures in OF combustion. Activation energies calculated for oxidation of OS and its char in CO2/O2 are notably less than activation energies calculated for Ar/O2 atmosphere. Modeling results show that higher fuel mass flow rate and higher O2 concentration in the oxidizer have to be considered in the set of conditions for OF in order to extract the same amount of heat as in air combustion. The Case 3 with 23% inlet O2 concentration has a similar behavior as compared to air combustion in terms of temperature of the boiler and recirculation rate of the particles. The data obtained from experimental measurements and models is valuable for the possible implementation of OF combustion of EOS in CFB boilers.

The current research involves characteristics of pyrolysis and thermo-oxidation of Estonian oil shale (OS) and its char. Non-isothermal and isothermal thermal analysis methods were used to characterise and compare the specifics of these processes under air and oxy-combustion conditions using Ar, CO2, O2 and their mixtures. The study of reaction kinetics including pyrolysis and oxidation characteristics is crucial to understand the complex mechanism of OS oxy-fuel combustion. The experimental results showed that the pyrolysis behaviour is highly similar in Ar and CO2 until the end of decomposition of organic part. There is no visible char carbon and CO2 reaction during the char oxidation stage under oxy-fuel conditions. The release of CO related to the char carbon and CO2 reaction in 100 % CO2 atmosphere increases notably at temperatures above 650–700 °C. The role of inorganic minerals in the oxidation and gasification of char was described as well as the effect of oxy-fuel conditions on gaseous emissions. It was found that the rate constants for char oxidation in CO2/O2 are approximately 1.2–1.3 times higher as compared to Ar/O2 atmosphere and that char oxidation under oxy-fuel conditions takes place with lower activation energies as compared to Ar/O2.

International audience; Motivated by the role of copper ions in biological processes the aim of this study was to elucidate the impact of copper ions bound to hydroxyapatite on l-serine (l-Ser) and O-phospho-l-serine (O-Ph-l-Ser) adsorption at different acidity of aqueous solutions. The adsorption phenomenon was studied by FTIR, UV, and AA spectroscopy, XRD and thermal analysis methods together with the evolved gases analysis taking into consideration the ionic state of the amino acids as well as the apatite surface state, which are tightly correlated with the solution pH. In acidic solution, the main process involves apatite dissolution releasing calcium and copper ions. At pH > 5 the complexation of amino acids with Ca2+ or Cu2+ ions is more important leading also to the release of cations. The ability of copper ions to form water soluble complexes with l-Ser and O-Ph-l-Ser leads to an important loss of these ions, while calcium release is very low at this pH. Therefore, the use of copper ions substituting calcium in the apatite structure to enhance the ability of amino acids adsorption on the apatite surface seems problematic even at pH > 5.

A possible technology that can contribute reduction of carbon dioxide emission is oxy-fuel combustion of fossil fuels enabling to increase CO2 concentration in the exhaust gas by carrying out the combustion process with oxygen and replacing air nitrogen with recycling combustion products to obtain a capture-ready CO2 stream. The laboratory studies and pilot-scale experiments discussed during the last years have indicated that oxy-fuel combustion is a favorable option in retrofitting conventional coal firing. Estonian oil shale (OS) with its specific properties has never been studied as a fuel in oxy-fuel combustion, so, the aim of the present research was to compare thermo-oxidation of OS and some coal samples under air and oxy-fuel combustion conditions by means of thermal analysis methods. Experiments were carried out in Ar/O2 and CO2/O2 atmospheres with two oil shale and two coal samples under dynamic heating conditions. FTIR analysis was applied to characterize evolved gases and emission dynamics. Kinetic parameters of oxidation were calculated using a model-free kinetic analysis approach based on differential iso-conversional methods. Comparison of the oxidation characteristics of the samples was given in both atmospheres and it was shown that the oxidation process proceeds under oxy-fuel conditions by all studied fuels with lower activation energies, however, it can last longer as the same temperatures are compared.

Thermooxidative decomposition (TOD) of seven coal samples from different deposits (Bulgaria, Russia, Ukraine) was studied with the aim to determine characteristics of the process and the differences related to the origin of the coal samples studied. The experiments with a Setaram Setsys 1750 or Labsys Evo 1600 thermoanalyzers coupled to a Nicolet 380 FTIR spectrometer or Pfeiffer mass spectrometer, respectively, were carried out under non-isothermal heating conditions up to 1,000 °C at the heating rates of 1, 2, 5, 10, and 20 °C min−1 in an oxidizing atmosphere. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The combined TG-FTIR and TG-MS study of TOD of the coal samples made it possible to identify a number of gaseous species formed and evolved at that as well as to determine the differences in the thermal behavior of the coal samples and in the emission profiles of these species depending on their origin. The value of activation energy E along the reaction progress α varied more for the samples with higher content of organic matter and, especially, for the samples having at that also quite high content of mineral matter, indicating to the close association of mineral matter with organic matter and fixed carbon.

Urea is one of the main nitrogen fertilizers used in agriculture. But being well soluble in water, hardly 50% of its nitrogen is assimilated by plants. One possibility to eliminate this disadvantage is to use coating agents for modification of urea to obtain a controlled-realized fertilizer. The aim of this research was to study the influence of different lime-containing additives on the thermal behavior and decomposition kinetics of urea in oxidizing atmosphere. Commercial fertilizer-grade urea (46.4% N) and analytical-grade CaO, MgO, CaCO3, MgCO3 were used in the experiments. In addition, one Estonian limestone and one dolomite sample were used as additive or coating material. The experiments with a Setaram Setsys 1750 thermoanalyzer coupled to a Nicolet 380 FTIR Spectrometer by a heated transfer line were carried out under non-isothermal conditions up to 900 °C at the heating rate of 5 °C min−1 and to calculate kinetic parameters, additionally, at 1, 2, and 10 °C min−1 in the atmosphere containing 80% of Ar and 20% of O2. The differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results obtained indicate that thermooxidative decomposition of urea as well as the blends of urea with lime-containing materials and urea prills coated with limestone or dolomite powder follows a complex reaction mechanism.

In order to elucidate the influence of Ca and Mg carbonates with or without the presence of boron, manganese and copper compounds on the thermal stability of ammonium nitrate (AN), thermodynamic analysis of different reactions between AN and additives was carried out. Temperature dependency of Gibbs free energy changes ∆G T and equilibrium composition of reaction products were calculated for a set of reactions using the HSC software. Main solid compounds that can form in the systems of AN and carbonates, were Ca(NO3)2 and Mg(NO3)2, Ca(OH)2 and Mg(OH)2, CaO2 and MgO2, CaO and MgO, and N-containing gaseous compounds NO, N2O and NO2. As a result of H3BO3, MnO2 and CuSO4 addition, the content of CuO, Cu2O and MnO as solids and SO2, SO3 and HBO as gaseous reaction products reached the same level. Thereby, their equilibrium concentrations did not depend on the carbonate origin of CaCO3, MgCO3 or CaMg(CO3)2. Small amount of CuSO4, H3BO3 or MnO2 additive (0.01–0.05 mol) in the system, practically, did not influence the temperature dependencies of ∆G T of the reactions between AN and CaCO3 or CaMg(CO3)2. The influence of additives taken in the larger amount (0.5 mol) was evident and, depending on the additive and reaction, shifted their proceeding temperatures in either direction by more than 300–400 K.

The thermooxidative decomposition of four oil shale samples from Estonia, Jordan, Israel and Morocco and one sample of Estonian oil shale derivative, semicoke, was studied with the aim to determine the characteristics of the process and the differences of it related to the origin of oil shale. The experiments with a Setaram Setsys 1750 thermoanalyzer coupled to a Nicolet 380 FTIR Spectrom- eter were carried out under non-isothermal conditions up to 1000 C at the heating rates of 1, 2, 5, 10 and 20 C min -1 in an oxidizing atmosphere. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results of TG-DTA-FTIR analyses and the variation of activation energy E along the reaction progress a indi- cated the complex character of thermooxidative decom- position of oil shale and semicoke, being at that the most complicated for Estonian and Jordanian oil shale charac- terized by higher content of organic matter as compared to the other samples studied.

In the present research, CO2 and SO2 binding ability of different oil shale ashes and the effect of pre-treatment (grinding, preceding calcination) of these ashes on their binding properties and kinetics was studied using thermogravimetric, SEM, X-ray, and energy dispersive X-ray analysis methods. It was shown that at 700 °C, 0.03–0.28 mmol of CO2 or 0.16–0.47 mmol of SO2 was bound by 100 mg of ash in 30 min. Pre-treatment conditions influenced remarkably binding parameters. Grinding decreased CO2 binding capacities, but enhanced SO2 binding in the case of fluidized bed ashes. Grinding of pulverized firing ashes increased binding parameters with both gases. Calcination at higher temperatures decreased binding parameters of both types of ashes with both gases studied. Clarification of this phenomenon was given. Kinetic analysis of the binding process was carried out, mechanism of the reactions and respective kinetic constants were determined. It was shown that the binding process with both gases was controlled by diffusion. Activation energies in the temperature interval of 500–700 °C for CO2 binding with circulating fluidized bed combustion ashes were in the range of 48–82 kJ mol−1, for SO2 binding 43–107 kJ mol−1. The effect of pre-treatment on the kinetic parameters was estimated.

The thermal behaviour of ammonium nitrate (AN) and its prills coated with limestone and dolomite powder was studied on the basis of commercial fertilizer-grade AN and six Estonian limestone and dolomite samples. Coating of AN prills was carried out on a plate granulator and a saturated solution of AN was used as a binding agent. The mass of AN prills and coating material was calculated based on the mole ratio of AN/(CaO + MgO) = 2:1. Thermal behaviour of AN and its coated prills was studied using combined TG-DTA-FTIR equipment. The experiments were carried out under dynamic heating conditions up to 900 °C at the heating rate of 10 °C min−1 and for calculation of kinetic parameters, additionally, at 2, 5 and 20 °C min−1 in a stream of dry air. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results of TG-DTA-FTIR analyses and the variation of the value of activation energy E along the reaction progress α indicate the complex character of the decomposition of neat AN as well as of the interactions occurring at thermal treatment of AN prills coated with limestone and dolomite powder.

The effect of heating rate on the thermal behavior of ammonium nitrate (AN) and on the kinetic parameters of decomposition of AN and its blends with limestone and dolomite was studied on the basis of commercial fertilizer-grade AN and several Estonian limestone and dolomite samples. Experiments were carried out under dynamic heating conditions up to 900 °C at heating rates of 2, 5, 10 and 20 °C min−1 in a stream of dry air using Setaram Labsys 2000 equipment. For calculation of kinetic parameters, the TG data were processed by differential isoconversional method of Friedman. The variation of the value of activation energy E along the reaction progress α showed a complex character of decomposition of AN—interaction of AN with limestone and dolomite additives with the formation of nitrates as well as decomposition of these nitrates at higher temperatures.

High temperature behavior of spray-dried NiO-based oxygen carrier samples for Chemical Looping Combustion (CLC) under oxidizing and reducing conditions was studied using a ceramic fluidized bed furnace. Differently from the common CLC process, high enough temperatures were obtained by burning air and methane mixture directly in the bed of carriers, changing the stoichiometric air to fuel ratio in the range of 0.70 to 1.30 and using external electric heating. None of the five particle samples tested showed any sign of defluidization in oxidizing atmosphere at any of the temperatures tested, i.e. up to 1175–1185 ∘C. However, under reducing conditions or in the oxidizing-reducing sequences, shortly after changing the atmosphere from oxidative to reducing, some of the spray-dried samples agglomerated causing defluidization. To study the structure of the carrier particles and to clarify the agglomeration phenomena, SEM and EDX analysis of the initial and treated samples was carried out. It was shown that agglomerates are formed through small bridges between the particles which consist of pure Ni phase. Three samples which were produced using MgO as an additive were tested. For these no defluidization was observed at any of the temperatures tested, i.e. up to 1175–1185 ∘C, neither in oxidizing, nor in reducing atmosphere. So, addition of proper components to the carrier particles can significantly improve reliability of the CLC process at higher temperatures.

In thermal processing of oil shale in vertical retorts huge quantities of a solid waste — semicoke are formed. It has been shown that circulating fluidized bed combustion of semicoke could be a promising technology allowing utilization of its high residual energy potential. The main parameters of combustion process and the additional heat produced were calculated and verified by combustion tests in a fluidized bed device with a thermal capacity of 50 kWth. The experiments indicated that semicoke with low moisture content can be burnt directly in fluidized bed. For the combustion of semicoke with higher moisture content (over 10%) about 10% of oil shale must be added. In addition, possibilities for utilizing residual carbon present in semicoke by obtaining carbon-rich materials with further production, for example, activated carbon were discussed. A series of experiments accompanied by SEM and EDAX analysis was carried out in order to elucidate the distribution of carbon and mineral part in semicoke and to find possibilities for their separation and subsequent enrichment. Different separation methods — selective grinding and subsequent screening, pneumatic separation and triboelectroseparation method were analyzed. It was shown that due to close integration of mineral and organic part in semicoke, the separation of carbon-rich ingredients by these methods was not enough effective to obtain enriched products suitable for the production of activated carbon.

The results of investigation of MgO participation in the binding of SO2 with lime-containing materials as sorbents are presented. Experiments of SO2 binding into solid phase using model samples of reactive grade MgO and CaO varying the mole ratio of MgO/CaO from 9:1 to 1:9 were carried out. Besides, dolomite and limestone samples with different MgO/CaO mole ratio (from 1.24 to 0.13) and samples of ashes formed at combustion of Estonian oil shale (containing 35-40% of carbonates) and its semicoke were studied Initial samples, intermediate and final products were subjected to chemical, IR-spectroscopy, X-ray and BET specific surface area analyses. The results of the present study confirmed the active participation of MgO in the binding of SO2 into the solid phase. In addition to CaSO4 the formation of Ca,Mg-double sulphate CaMg3(SO4)4 and β-MgSO4 was observed. The presence of CaMg3(SO4)4 was fixed in a large temperature range 400-900°C and that of β-MgSO4 in between 500-700°C. The optimum temperature range for formation and durability of CaMg3(SO4)4 was 700-800°C.

Approximately one million tons of semicoke (SC) is formed and stored in open air dumps every year in the production of shale oil by processing Estonian oil shale (OS). The content of different harmful compounds as sulphides, PAH, phenols, etc. in SC make these dumps one of the most serious sources of environmental contamination. The aim of this work was to study the behaviour of sulphur compounds in OS and its SC, formation of SO2 and possibilities of binding it into the solid phase during thermooxidation of fuel blends based on SC. Blends modified with SC ash addition were studied as well. It was determined that SO2 emission in thermooxidation of SC samples started at 280-300°C and proceeded with a steady speed up to 580-600°C and the amount of sulphur evolved was 5-10% from the total content of sulphur in the sample. The amount of SO2 emitted decreased depending on the mass ratio of the composite fuels from 49-56 to 15-35% during thermooxidation of OS samples studied or their blends with SC, respectively, from 43-80% for coal samples to 13-60% for their blends with SC and to 2-13% during thermooxidation of these blends modified with SC ash addition. In the products of thermooxidation formed at 800-900°C the only sulphur containing phase was CaSO4, at 650°C also traces of CaS and CaMg3(SO4)4 were fixed.

The results obtained by studying decarbonization of different samples of Estonian limestone and dolomite and the following sulphation or carbonation of calcined products to estimate their SO2 and CO2 binding ability were presented. Experiments were carried out with thermogravimetric equipment(Q-Derivatograph, MOM and Labsys™, SETARAM) – calcination of the samples in the atmosphere of air with the heating rate 10 K per minute using multiplate crucibles, the following sulphation or carbonation of the calcined products after cooling to the fixed temperature (temperature range 400–900°C) under isothermal conditions in the flow of air-SO2 or air-CO2 mixture. Chemical, X-ray, BET nitrogen dynamic desorption, etc. methods for the characterization of the initial samples, intermediate and final products were used. In addition, the possibilities of recurrent use of oil shale ashes taken from different technological points at operating thermal power plants (Estonian and Baltic TTPs, Estonia) as sorbents for SO2 binding from gaseous phase were studied, as well as the possibilities of activation of these ashes towards SO2 binding. The results of these studies confirmed the high reactivity of Estonian limestone and dolomite towards SO2 and CO2. Dependence of SO2 binding mechanism on the SO2 concentration has been established. Modelling of SO2 capture of dolomite and limestone was carried out to establish the kinetic parameters of these processes. The possibilities of activation of oil shale ashes and their effective recurrent use for binding SO2 and CO2 from gaseous phase were confirmed.

Power production in Estonia is predominantly based on combustion of a local low-grade fossil fuel Estonian oil shale. Due to the high content of carbonaceous mineral matter in oil shale, its combustion is related to formation of lime-containing ashes (content of free CaO 10–30%) which could be utilized as sorbents for CO2. In the present research CO2 uptake by circulating fluidized bed and pulverized firing ashes from different technological devices (furnace, cyclones etc) of an operating power plant was studied and the effect of pre-treatment (grinding, calcination at different temperatures) of these ashes on their capture capacity was estimated using thermogravimetric, SEM, X-Ray and EDX analysis methods. It was found that capture capacities were determined mainly by free CaO content in the ashes, thereby, fluidized bed ashes showed higher CaO conversion levels (19.2–74.2%) as compared to pulverized firing ones (8.7–51.8%). Pre-treatment conditions influenced noticeably CO2 uptake. Grinding decreased CO2 capture capacity of fluidized bed ashes, calcination at higher temperatures decreased capture capacity of both types of ashes. Clarification of this phenomenon was given. Kinetic analysis of the process has been carried out, mechanism of the reactions and respective kinetic constants have been estimated.

The impact factors on Cd sorption and desorption in aqueous solution on apatite were studied. Batch experiments were carried out using synthetic hydroxyapatite with Ca/P 1.44, 1.66 and 1.94 in Cd(NO3)2 and Cd(NO3)2–EDTA equimolar complex solutions in the pH range from 4 to 7. It was established that Cd sorption on apatite depends not only on apatite specific surface area but also on Ca/P mole ratio in apatite as well as on the presence of chelating compounds. Presence of EDTA in the solution decreases the amount of Cd bound. [CdEDTA]2− prevents chemical sorption of Cd2+ ions on apatite. EDTA considerably decreases the sorption capacity of apatite with Ca excess. Impact of EDTA is smaller for the stoichiometric apatite and for the apatite with calcium deficiency. Cd bound due to adsorption is more easily removed from apatite. Ca2+ ions increase and presence of EDTA in a solution cause total Cd desorption from apatite.

The alkaline wastes such as burnt oil shale (BOS) and cement bypass dust (BPD) generally contain free lime and portlandite which make them suitable sorbent materials for CO2 trapping via mineral carbonation technique of carbon capture and sequestration. In order to study the reaction kinetics and effect of operating parameters on carbonation processes of such alkaline wastes for future industrial sized scale-ups, as well as to identify the effects on carbonation capacity when these sorbents undergo pre-treatment and are exposed to different temperatures, BOS and BPD as sorbents in CO2 mineralization process have been investigated with thermal analysis methods in the current work. Results indicate that selected types of BOS and BPD could be used as binders in the CO2 mineralization systems, binding reasonably good amount of CO2 already in the early stage of the carbonation process which later slows down as the rate of CaO carbonation becomes mainly diffusion controlled. Increased process temperature and hydration as pre-treatment improve the CO2 binding ability, while the effect of milling has been found to be staggering and not as significant as the effect of hydration and temperature rise. The appropriate kinetic mechanism functions were determined, and the kinetic parameters—activation energy (Ea) and pre-exponential factor (A) values were calculated for all the samples. The Ea values of hydrated samples are lower for BOS samples compared to non-hydrated samples. It was shown that activation by hydration enables to reach the same CO2 uptake levels at lower temperatures, thereby making the mineralization process more energy efficient and thus lowering the costs.