Magdalena Wdowin

Coal fly ash as a resource for rare earth elements

Rare earth elements (REE) have been recognised as critical raw materials, crucial for many clean technologies. As the gap between their global demand and supply increases, the search for their alternative resources becomes more and more important, especially for the countries which depend highly on their import. Coal fly ash (CFA), which when not utilised is considered waste, has been regarded as the possible source of many elements, including REE. Due to the increase in the energy demand, CFA production is expected to grow, making research into the use of this material a necessity. As Poland is the second biggest coal consumer in the European Union, the authors have studied different coal fly ashes from ten Polish power plants for their rare earth element content. All the fly ashes have a broadly similar distribution of rear earth elements, with light REE being dominant. Most of the samples have REE content relatively high and according to Seredin and Dai (Int J Coal Geol 94: 67–93, 2012) classification can be considered promising REE raw materials.

Investigation of the sorption of mercury vapour from exhaust gas by an Ag-X zeolite

Abstract The removal of gaseous mercury from flue gases from coal-fired power plants is currently an environmental challenge under investigation. Therefore, the main aim of this paper was to evaluate the suitability of faujasite group zeolites (Na-X) to adsorb mercury compounds. Previous, initial tests showed negligible Hg0 uptake by Na-X zeolite, but silver impregnation improved adsorption markedly. Therefore, the testing of mercury adsorption from flue gases into Ag+- impregnated Na-X synthetic zeolite (Ag-X zeolite) derived from coal fly ash was carried out. This material was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, X-ray fluorescence and nitrogen adsorption/desorption before being evaluated for mercury removal from exhaust gas. After preliminary mercury adsorption tests (fixed bed) under a nitrogen atmosphere, the adsorbent was examined with a simulated flue gas composition under various conditions, i.e. weight of zeolite, temperature of experiment and zeolite in powder and granulated forms. The removal of mercury was shown to depend on the sorbent texture (powder or granulate), exhaust gas flow rate and contact time, as well as the temperature of the experiment. The Ag-X zeolite tested reduced the level of mercury in the flue gas and, depending on the experimental conditions, long-time mercury breakthrough ranges from 15 to 40% were obtained. The best results for mercury capture were obtained for granulated material.

SEM Investigation of Microstructures in Hydration Products of Portland Cement

Portland cement is the one of the main ingredients in the manufacture of many building materials include concrete composites. The phase composition of hydration products is controlled by means of XRD and DTA/TG analysis. Observations of phase changes and microstructure of maturing cement pastes can also be observed using scanning electron microscopy (SEM) techniques combined with chemical analyzes in microareas (EDS analysis). Hydrating in time cement paste is composed mainly of hydrated silicates of calcium so called C–S–H-phase accompanied with a calcium hydroxide (portlandite) and hydration products of calcium aluminate i.e. ettringite. SEM analysis of changes in the morphology and microstructure of cement pastes allow to track the hydration progress observed mainly by changes in the C–S–H phase. The initial stages of hydration of this phase is characterized by radial concentration of fibers or needles, often narrowed at the ends. This fibers grow from the surface of the cement grains. The increase in the degree of C–S–H structure orientation is shown by formation of fibers lattice, sometimes three-dimensional plates so called “honeycomb”, which is transformed into the form of a closely-packed, isometric grains. In addition, besides C–S–H cement phase investigation, scanning electron microscopy can also be applied to observation of the crystals formation of tobermorite, ettringite and relicts of portlandite, that often can’t be detected by XRD and DTA/TG due to their small amount in mineral composition of concrete.

The Use of Scanning Electron Microscopy to Identify Zeolite Minerals

Zeolites are hydrated aluminosilicates of alkali elements and alkaline earth elements. The primary structural element is silicon-oxygen and aluminum-oxygen tetrahedrons, which are arranged in three dimension, form the spatial lattice about frame structure. The primary method of zeolite identification is the X-ray Diffraction. An alternative method for recognizing zeolites is a scanning electron microscopy (SEM) combined with chemical analysis in the microarea (SEM-EDS). Application of this method is justified because of the zeolites reach the crystal size in the range from a few microns to several millimeters about crystal habit: needle-like, cubic-like, plate-like. The one of needle-like zeolites is natrolite and carcinogenic erionite. Plate-like zeolites are represented by stilbite, heulandite, whether most commonly occurring clinoptilolite or synthetic zeolite type Na-P1. The zeolites with the cubic-like habits include philipsite, chabazite and harmotome and a number of synthetic zeolites such as Na-X and Linde-A. The use of SEM to observe the form of zeolite crystals confirmed by diffraction studies in full allows for the phase identification of these group minerals. Chemical analyzes in microarea additionally specify the nature of ion-exchange cations and the Si/Al ratio as well thermal stability and surface activity.

Changes in the Textural Parameters of Fly Ash-Derived Na-P1 Zeolite During Compaction Processes

Abstract This paper presents the possibility of receiving the granular forms of a zeolitic material of the Na-P1 type obtained from high-calcium fly ash in a semi-technical scale by means of three compacting techniques. The compaction process was carried out using cement, molasses and water glass as binders. Each of the proposed compacting methods affected the textural parameters of the obtained granular zeolite forms, as well as the binders used. In comparison to the other binders it was found that the cement binder had the smaller impact on the values of the textural parameters of the obtained compacted zeolite forms. The surface area for the zeolite Na-P1 was 98.49 m2·g-1, for the cement as a binder was 69.23 m2·g-1, for the molasses was 52.70 m2·g-1and for the water glass was 40.87 m2·g-1. For this reason, the briquetting and extruding tests were carried out using cement as a binder.

Fly Ash Derived Zeolites in the Removal of Toxic Compounds

The present paper describes the previous obtained results concerning purification of gases, water and sewages from toxic components such as mercury, radionuclides and petroleum substances. The tested materials constitute synthetic zeolites obtained in hydrothermal reaction, i.e., Na-X, Na-P1, and natural zeolite clinoptilolite. The zeolites (Na-X, Na-P1 and clinoptilolite) needed for mercury capture were activated by silver ions; however, for the removal of petroleum substances (Na-X and Na-P1) as well as radionuclides (Na-P1) raw zeolite materials were used. The review of the results have shown that zeolites used both for mercury capture and the removal of radionuclides, as well as petroleum substances, can be considered promising sorbent materials.

Determination of CO 2 -Brine-Rock Interactions for Carbon Dioxide Sequestration Using SEM-EDS Methods

The article constitutes a review of so far obtained results of the mineralogical changes occurs in reservoir and cap rocks due to the effect of carbon dioxide injection and storage in the presence of saline. The impact of CO2 was observed based on the determination of mineralogical changes by SEM-EDS method. In order to evaluate such interactions (changes) a numerous laboratory investigations were carried our using special designed devices for this purposes where samples of rocks were flooded in artificial brines and closed in autoclaves. Next the CO2 stream was driven. The investigations were performed at different conditions of pressure, temperature and period of time. To determine the changes in the individual minerals, via the scanning electron microscopy method, the results of mineralogical observations of the same sort of minerals in rock samples before and after the experiment were described. In all investigated cases the minerals precipitation and dissolution processes were observed as the result CO2-brine-rock interactions. The changes were detected on the following minerals: feldspars, micas, dolomite, calcite, anhydrite, kaolinite, pyrite.

SEM-EDS Observation of Structure Changes in Synthetic Zeolites Modified for CO2 Capture Needs

Carbon dioxide is the main greenhouse gas and its amount still increase in the atmosphere. Air pollution and greenhouse effect caused by CO2 emission have become a major threat to the environment on a global scale. Carbon dioxide sequestration (i.e. capture and consequently geological storage) is the key strategy within the portfolio of actions to reduce CO2 emission to the atmosphere. The most costly stage is capture of CO2, therefore there is a need to search new solutions of this technology. For this purpose it was examined Na–X synthetic zeolites, that were silver and PEI (polyethyleneimine) activated. SEM-EDS investigation enable to find a changes in structure of this materials after treatment. Where, as a result of silver activation from EDS analysis it is seen that Ag occur in Na–X structure, what indicate a substitution of Ag2+ for Na+ ions in crystal lattice. Analysing wt% the EDS analysis has shown that zeolite Na–X after silver impregnation becomes Ag–X zeolite. For Na–X–PEI activated it is observed a distinct organic compound in the form of coatings on Na–X crystals causing a sealing of pores in tested zeolite. Further examination of these materials concern determination of surface properties and experiments of CO2 sorption. But SEM-EDS analysis enable to determine the extent of activation, what is very important in determination of optimal conditions for such treatment in order to obtain better sorbent of CO2.