The corrosion behaviour of cast Al-Mg alloy A535 and its composites containing 10 wt.% and 15 wt.% fly ash, and 10 wt.% hybrid reinforcement (5 wt.% fly ash + 5 wt.% SiC) was investigated using weight-loss and electrochemical corrosion tests, optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The tests were conducted in fresh water collected from the South Saskatchewan River and 3.5 wt.% NaCl solution at room temperature. The pH of the salt solution varied from 3 to 9. For comparison, two other aluminum alloys, AA2618 and AA5083-H116, were tested in the same electrolytes. The results of the weight-loss corrosion test showed that unreinforced A535 alloy had a lower corrosion rate in fresh water and seawater environments than the composites at all the tested pH values. The corrosion rate of the composites increased with increasing fly ash content. As expected, the corrosion rates of A535 alloy and the composites tested in fresh water were lower than those in salt solution. The results of the potentiodynamic and cyclic polarization electrochemical tests showed that the corrosion potential (Ecorr) and pitting potential (Epit) of the alloy were more positive than those of the composites. The corrosion and pitting potentials of the composites became more negative (active) with increasing fly ash content. The composites showed more positive (noble) repassivation or protection potential (Erp) than the matrix alloy, with the positivity increasing with fly ash content. Analysis of the electrochemical noise data showed that pitting corrosion was the dominant mode of corrosion for the alloy in 3.5 wt.% NaCl solution. Optical microscopy and SEM revealed that Mg2Si phase and Al-Mg intermetallics corroded preferentially to the matrix. The EDS data indicated that the protective oxide film formed on A535 contained Al2O3 and MgO.

Sub-surface soil pollution by various processes with high concentration of contaminants can significantly alter geotechnical properties of soils causing unexpected failures of structures founded on them. The changes can occur due to alteration in soil water interaction processes and/or by intense chemical interactions leading to mineralogical and microstructural changes. Behaviour of soil upon contamination with alkali pollutant is one of the major concerns faced by the geotechnical researchers in recent years. In the present study an attempt has been made to understand the role of mineralogical and morphological changes on the volume change (swelling and compressibility) behaviour of soils by prolonged interaction with caustic alkali pollutant. Based on the results it has been proposed to develop remedial measures to nullify and/or control the detrimental effects. A comprehensive experimental program has been planned to achieve these objectives. The experimental investigations carried out and results obtained are presented in eight chapters as follows. The broad outline of thesis is given in Chapter 1. A detailed review of literature on the type of phyllosilicate minerals present in various soils is presented in Chapter 2 with a view to select most common soils for the study. Various sources of contaminants and their effect on the properties of soils have been summarised. Present understanding on the mechanisms leading to changes in the soil properties has been elucidated. The occurrence of alkali contamination has been reviewed in this chapter which enabled to select the ranges of alkali concentration for the study. Based on the review of various methods employed to improve the soil behaviour, the use of salt solutions such as potassium chloride (KCl) and magnesium chloride (MgClB2B) and pozzolanic fly ash has been considered to counteract the alkali effects. Based on this detailed survey, the scope of the present investigation has been elaborated at the end of the chapter. Chapter 3 presents different materials used and various methods adapted in the current study. Three soils having different mineralogy have been used in this study to bring out the effect of alkali solutions on their volume change behaviour. While two soils were classified as CH, the third one was of CL. The CH soils used in this study are called Black Cotton Soils in India. One soil contained predominantly mixed layer illite-smectite mineral (BCS I) and the other contained predominantly montmorillonite mineral (BCS M). The locally available CL soil used is referred as red earth (RE) whose predominant mineral is kaolinite. Alkali solutions of concentration ranging from 1N to 4N are prepared using sodium hydroxide pellets (NaOH). Slat solutions viz. potassium chloride and magnesium chloride and pozzolanic fly ash obtained from Neyveli thermal power plant (NFA) are used as additives. Procedures to determine the geotechnical properties of the soils such as Atterberg limits, specific gravity, grain size distribution and compaction characteristics are given in this chapter. Procedures for identifying the mineral and microstructure of the soils such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) are also presented in this chapter. Standard oedometer tests with fixed ring apparatus were performed to study the volume change behaviour of soils under various conditions. Volume change behaviour of soils in the presence of alkali solutions is presented in Chapter 4. In order to assess the effect of alkali solution on the volume change behaviour of soils it is necessary to study their behaviour in water. Relatively very high swell was observed in BCS M, whereas the swell in RE and BCS I soil specimens was very low and moderate respectively. Adsorption of water to form diffuse double layer near the negative surface of clay mineral particles leads to swelling in soils. The thickness of the double layer depends on the cation exchange capacity of soil. Higher cation exchange capacity leads to development of higher thickness of double layer thereby inducing swell. The higher is the swell the higher would be the compression. The effect of different concentrations (1N, 2N and 4N) of alkali solutions on volume change behaviour of three types of soil is presented in this chapter. All the three soils studied, irrespective of their mineralogical composition, exhibited high swell when contaminated with alkali solution compared to water. However, the extent and nature of swell varied both with the type of mineral present in the soil and concentration of sodium hydroxide solution. The swell in BCS I increases with increase in the concentration of the alkali solution. In 1N alkali solution the high swell occurred is due to the breaking up of interstratified mineral into constituent minerals initiated by the leaching of potassium from soil due to high pH. In 2N and 4N alkali solutions, the observed high swell occurs in two stages: the first stage of swelling is due to breaking up of interstratified mineral into constituent minerals initiated by the leaching of potassium from soil due to high pH, and the second stage of swelling is due to the formation of new minerals (Zeolite P in case of 2N NaOH and Sodalite in case of 4N NaOH). The nature of swell is influenced by the formation of minerals depending on the concentration of alkali solution. Thus the studies clearly indicate that the swelling is due to the release of potassium from soil at higher pH and due to mineralogical changes depending upon the concentration of alkali solution. Confirmative tests were conducted to support the release of potassium during first stage of swelling and mineralogical alteration after second stage of swelling. The high swell in BCS M becomes higher in 1N alkali solution. The increased swell in the soil with 1N alkali solution is due to increase in the ion exchange capacity of soil at higher pH. The swell which is very high with 1N alkali solution decreases with 2N alkali solution. With increase in concentration of alkali solution to 2N, the increase in the negative charges due to alkalinity becomes less and the swell decreases due to dominant influence of electrolyte effect. With increase in the concentration of alkali solution to 4N, both these influences become less and the amount of swell remains the same. Significant increase in the amount of swell is observed with alkali solution even in non-swelling red earth. The nature of swell as well as the formation of minerals is not altered by the change in the concentration of alkali solution. At any concentrations of alkali solution the observed swell is noticed in two stages – very small first stage of swell due to lower ion exchange capacity and considerable second stage of swell due to the formation of new mineral (Sodalite) with any concentration of alkali solution. It has been observed that the normal hyperbolic swell – compression relationship does not apply for the alkali contaminated soils. The higher swell does not result in higher compression, as the swollen soil remains fairly incompressible. Analysis of the results and detailed studies on micro-structure and mineralogy of soils bring out mechanism of alkali effects. Comparing the swell behaviour of soils with alkali solutions brings out the relative importance of various mechanisms proposed for induced heave. The effect of salt solutions used viz., potassium chloride and magnesium chloride to restrict the influence of alkali solution on the volume change behaviour of BCS I is presented in Chapter 5. These salts react with alkali solution to form partly soluble potassium hydroxide (KOH) and sparingly soluble magnesium hydroxide (Mg(OH)B2B) respectively. Presence of ionic potassium can bring out potassium linkages, by bridging potassium ion between the unit layers of expansive minerals reducing the swell. Magnesium ions can restrict swell, by replacing the monovalent exchangeable ions present in soil and/or by formation of magnesium hydroxide which is a weak cementing agent. The effect of potassium hydroxide on the volume change behaviour of soil has been studied and the results clearly indicate that fixation of potassium is facilitated by high pH of KOH solution. Addition of potassium chloride has partially controlled the alkali induced heave in soil. Of the two stages of swelling observed in soil in the presence of 4N alkali solution, only the first phase of swelling is reduced which may be due to electrolyte effect and/or due to fixation of potassium. The second phase of swelling that occurs in soil due to mineralogical changes can not be controlled with the use of potassium chloride. Addition of magnesium chloride salt solution also reduced the effect of alkali solution mostly due to suppression of thickness of diffuse double layer that develops near clay surface. The nature of reduction in the swell of alkali solution during the two stages by magnesium chloride is similar to that of potassium chloride. The partial reduction in swell of soil in the presence of salt solutions leads to reduction in the compressibility of soil. Detailed data and analysis, presented in this chapter, bring out the role of microstructure and mineralogy on soil behaviour. The abnormal volume changes due to mineralogical changes affected by high concentration of sodium hydroxide could not be controlled with salt solutions, attempts are made to utilize fly ash to control the alkali induced heave. The pozzolanic compounds produced by hydration of compounds presented and/or produced by lime silica reactions can bind the soil particles controlling the swelling. The results on the effectiveness of fly ash on BCS I soil are presented in Chapter 6. The physical and chemical properties of fly ash along with the mineralogical composition and the microstructure of the fly ash are also presented in this chapter. Before studying the effect of fly ash to control the volume change behaviour of soils in presence of alkali solutions, the effect of alkali solutions on the volume change behaviour of fly ash itself has been studied. The results showed no noticeable changes in swell and compressibility of fly ash, encouraging its use for controlling the alkali induced swell. The ability of different percentages (10%, 20% and 50%) of fly ash to control alkali induced volume changes in soil with varying concentrations of alkali solutions, viz., 1N, 2N and 4N has been studied. The results indicate that the addition of fly ash effectively reduces alkali induced swell in BCS I. The effectiveness of fly ash increases with increase in its content. The reduction in swelling of soil is partially due to replacement of soil with fly ash and mainly due to cementation of soil particles by pozzolanic compounds produced. More than 25% of fly ash is generally required to significantly reduce the swell in alkali solutions. The reduction in swell with addition of fly ash also leads to lower compressibility of soil. The role of microstructure and mineralogy in controlling the volume change behaviour are also presented in this chapter. The effectiveness of fly ash in controlling the volume changes in RE and BCS M due to alkali solutions are studied in Chapter 7. The addition of fly ash completely eliminates the swelling in both the soils. The reduction in swelling up on addition of fly ash is essentially due to efficient binding of particles by pozzolanic reaction compounds. Addition of even 10% of fly ash is sufficient in completely arresting the swelling of RE and BCS M by alkali solution. Detailed data and analysis of the results to bring out the role of microstructure and mineralogy on the behaviour of soils are presented. It is clear that relatively higher amounts of fly ash is required to control the alkali induced heave in BCS I than in other soils at higher concentrations of alkali solution. The major conclusions from the study are presented in Chapter 8. The thesis demonstrates that alkali contamination alters mineralogy and morphology of soils affecting the volume change behaviour significantly. The study also brings out that fly ash can control the undesirable swell that occurs in most types of soils by cementing the soil particles to resist swelling. Though the amount of fly ash required to control the alkali induced heave varies, 25% of fly ash is often sufficient.

In South Africa, being the second largest global coal exporter, coal mining plays a pivotal role in the growth of our economy, as well as supplying our nation’s ever increasing electricity needs; while also accounting for more than 10% of the 20 x 109 m3 water used annually in the country. Coal mining may thus be classified as a large-scale water user; known to inevitably generate wastewater [acid mine drainage (AMD)] and other waste material, including fly ash (FA). Current and conventional AMD treatment technologies include precipitation–aggregation (coagulation/flocculation) – settling as hydroxides or insoluble salts. The process stream resulting from these precipitation processes is still highly saline, therefore has to undergo secondary treatment. The best available desalination techniques include reverse osmosis (RO), electro dialysis (ED), ion exchange and evaporation. All available treatment methods associated with raw AMD and its derived process stream fall prey to numerous drawbacks. The result is that treatment is just as costly as the actual coal extraction. In addition, remediation only slows the problem down, while also having a short lifespan. Research conducted into converting fly ash, an otherwise waste material, into a marketable commodity has shown that direct mixing of known ratios of FA with AMD to a pre-determined pH, erves a dual purpose: the two wastes (AMD and FA) could be neutralized and produced a much cleaner water (secondary co-disposal [FA/AMD]-process water), broadly comparable to the process water derived from precipitation-aggregation treated AMD. The collected post process solid residues on the other hand, could be used for production of high capacity ion exchange material (e.g. zeolite A, faujasite, zeolite P, etc.). The produced ion exchange material can subsequently be utilized for the attenuation of metal species in neutralized FA/AMDprocess waters. / Magister Scientiae - MSc

Μία από τις σημαντικότερες αποθέσεις λιγνίτη της Δυτικής Τουρκίας εντοπίζεται στην λεκάνη της Mugla. Η λεκάνη της Mugla αποτελείται από δύο τάφρους ΒΔ-ΝΑ διεύθυνσης, οι οποίες χωρίζονται από μία πλατιά έξαρση του υποβάθρου, δημιουργώντας τις υπολεκάνες του Yatağan και του Milas. Η εμφάνιση του υποβάθρου αποτελείται στα νότια από τα Λυκκιακά καλύμματα, τα οποία περιλαμβάνουν ένα σύμπλεγμα πετρωμάτων ωκεάνιας και ηπειρωτικής προέλευσης και στα βόρεια από μεταμορφωμένα πετρώματα, όπως σχιστόλιθοι, γνεύσιοι, αμφιβολίτες, και μάρμαρα της Μάζας Menderes. Η παρούσα εργασία εστιάζει στο λιγνίτη της περιοχής Milas και τα στερεά παραπροϊόντα καύσης του (ιπτάμενη τέφρα και τέφρα εστίας) από τις περιοχές Yeniköy, Yatağan και Kemerköy της Τουρκίας. Σκοπός της μελέτης είναι η εκτίμηση της κινητικότητας των ιχνοστοιχείων κατά την εκμετάλλευση του λιγνίτη για ηλεκτροπαραγωγή και κατά την αποθήκευση και διάθεση των στερεών παραπροϊόντων της καύσης του στην περιοχή Mugla της Τουρκίας. Αντικείμενο της εργασίας αποτέλεσε η γεωχημική μελέτη του λιγνίτη και των παραπροϊόντων του, καθώς και η χημική μελέτη των διαλυμάτων που προέκυψαν κατά την απόπλυσή τους σε συνθήκες pH 5 και 8,5. Επιπρόσθετα, πραγματοποιήθηκε μία σειρά εργαστηριακών αναλύσεων, που περιλαμβάνουν την προσεγγιστική και στοιχειακή ανάλυση, την ανθρακοπετρογραφική εξέταση, καθώς και τις ορυκτολογικές αναλύσεις όλων των δειγμάτων. Στα πλαίσια των εργαστηριακών αναλύσεων, προσδιορίστηκε η υγρασία, η τέφρα, η περιεκτικότητα σε πτητικά συστατικά, καθώς και η περιεκτικότητα των C, H, N και S του λιγνίτη και των παραπροϊόντων του, ο μόνιμος άνθρακας, η θερμαντική ικανότητα και η ανακλαστικότητα του λιγνίτη. Οι συγκεντρώσεις των ιχνοστοιχείων στον λιγνίτη, την ιπτάμενη τέφρα και την τέφρα εστίας προσδιορίστηκαν με τη χρήση του οργάνου ELAN 6100 Perkin Elmer®. Τα στοιχεία, που προσδιορίστηκαν είναι τα Αg, As, B, Ba, Be, Co, Cr, Cu, Fe, Ga, Hf, Hg, Li, Mn, Mo, Ni, Pb, Se, Sr, U, V και Zn. Σύμφωνα με τις περιεκτικότητες των ιχνοστοιχείων του λιγνίτη και των παραπροϊόντων της καύσης του εκτιμήθηκε η κινητικότητά τους κατά την καύση με τον υπολογισμό του συντελεστή εμπλουτισμού (R.E.). Πολύ μικρό συντελεστή εμπλουτισμού και κατά συνέπεια έντονη πτητικότητα παρουσιάζουν τα στοιχεία As, Cd, Mo, Pb και Sr. Μέτρια πτητικότητα εμφανίζουν τα Ag, B, Cr, Ni, U, V, Zn, ενώ όλα τα υπόλοιπα έχουν μικρή πτητικότητα, καθώς συμμετέχουν στο τμήμα των παραπροϊόντων που παραμένει στην τέφρα των ατμοηλεκτρικών σταθμών. Ακολούθως, έλαβαν χώρα πειράματα έκπλυσης των ιχνοστοιχείων από το λιγνίτη και τα παραπροϊόντα του σε συνθήκες pH 5 και 8,5, ούτως ώστε να προσδιοριστεί η κινητικότητα τους, με τη βοήθεια του Ποσοστού Σχετικής Έκπλυσης (RML) και της Έντασης έκπλυσης (Ιl). Τα αποτελέσματα των παραπάνω έδειξαν ως πιο κινητικά ιχνοστοιχεία σε συνθήκες pH 5 και 8,5, στο λιγνίτη τα As, B, Mn, Sr, στην ιπτάμενη τέφρα τα Cr, Li, Mo και Sr, και στην τέφρα εστίας τα Li, Mo, Sr. Προκειμένου να προσδιοριστεί η γεωχημική συγγένεια των ιχνοστοιχείων στα «ως έχει» δείγματα του λιγνίτη και των παραπροϊόντων καύσης του, αλλά και να περιγραφεί η συμπεριφορά τους κατά τη διάρκεια της έκπλυσής τους σε διαφορετικές τιμές pH, πραγματοποιήθηκε στατιστική επεξεργασία των αποτελεσμάτων της στοιχειακής ανάλυσης. Ειδικότερα, στα αποτελέσματα των στοιχειακών αναλύσεων και των τιμών έκπλυσης των ιχνοστοιχείων όλων των δειγμάτων ξεχωριστά για pH 5 και pH 8,5, καθώς και των ορυκτών της ιπτάμενης τέφρας και της τέφρας εστίας εφαρμόστηκε η μέθοδος της παραγοντικής ανάλυσης R-τύπου. / One of the most important lignite deposits of Western Turkey is located in the basin of Mugla. The Mugla basin consists of two NW-SE direction grabens, which are separated by a wide rise of the basement that creates the sub-basins of Yatağan and Milas. Southern, the basement is consisted of the Lyccian nappes, which contain a cluster of ocean and continental origin rocks, while northern is consisted of metamorphic rocks, such as schists, gneiss, amphibolites and marbles of the Menderes Mass. The present study focuses on the lignite of Milas region and its combustion solid by-products (fly ash and bottom ash) from Yeniköy, Yatağan and Kemerköy areas in Turkey. The purpose of this study is to estimate the mobility of elements and trace elements in the exploitation of the lignite deposits for generating power in the region of Mugla in Turkey. The object of the present study lies in the geochemical study of lignite and its combustion products and in the determination of the mobility of trace elements during the combustion of lignite and the leaching of lignite and its by-products, under pH 5 and 8.5 conditions. In addition, several laboratory analyses are performed, including the proximate and the elemental analysis, the coal-petrographical examination and the mineralogical analysis of all samples. During these laboratory analyses are determined the moisture, the ash, the content of volatile components and the content of C, H, N and S of lignite and lignite combustion products the permanent carbon, the calorific value and the reflectivity of lignite. The contents of trace elements in lignite, in fly ash and in bottom ash are determined using an ELAN 6100 Perkin Elmer ® instrument. The elements, which were identified, are Ag, As, B, Ba, Be, Co, Cr, Cu, Fe, Ga, Hf, Hg, Li, Mn, Mo, Ni, Pb, Sr, U, V and Zn. According to the trace elements contents of lignite and its combustion products, the mobility during combustion was determined using the Enrichment Factor (RE). Very low rate of enrichment and thus, strong volatility, have the elements As, Cd, Mo, Pb and Sr. Medium volatility is being observed in the elements Ag, B, Cr, Ni, U, V, Zn, while all the rest have low volatility due to their existence in the part of the lignite co-products that remain in the ash of the Thermal Power Plants. Furthermore, leaching experiments under pH 5 and 8.5 conditions took place to estimate the mobility of trace elements from lignite and its by-products using the Relative Mass Leached (RML) and Leaching Intensity (Ιl). The above results, under pH 5 and 8.5 conditions, indicate as more mobile trace elements in the lignite the elements As, B, Mn, Sr, in the fly ash the elements Cr, Li, Mo and Sr, and in the bottom ash the elements Li, Mo, Sr. In order to determine the geochemical affinity and the mode of occurrence of trace elements in the samples of lignite and its combustion by-products and to describe their behavior during the leaching at different pH conditions, a statistical process of the elemental analysis results is performed. In particular, the methodology of factor analysis R-type is used in the elemental analysis results, in the leaching values of trace elements of all samples, separately for pH 5 and pH 8,5 and in the fly ash and the bottom ash minerals.

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2017-08-08T18:02:30Z No. of bitstreams: 1 CACURO_Thiago_2016.pdf: 32188052 bytes, checksum: 4ea1d6b1518db8bbf23e24ea2e2a94d7 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-08-08T18:03:10Z (GMT) No. of bitstreams: 1 CACURO_Thiago_2016.pdf: 32188052 bytes, checksum: 4ea1d6b1518db8bbf23e24ea2e2a94d7 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-08-08T18:03:16Z (GMT) No. of bitstreams: 1 CACURO_Thiago_2016.pdf: 32188052 bytes, checksum: 4ea1d6b1518db8bbf23e24ea2e2a94d7 (MD5) / Made available in DSpace on 2017-08-08T18:03:21Z (GMT). No. of bitstreams: 1 CACURO_Thiago_2016.pdf: 32188052 bytes, checksum: 4ea1d6b1518db8bbf23e24ea2e2a94d7 (MD5) Previous issue date: 2016-03-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / The ashes resulting from the burning of sugarcane bagasse is a heterogeneous material and has various applications as an adsorbent. To enhance and assist in prospecting new applications is critical to better understand the properties of the material. In this work, its morphological, spectroscopic and elemental characterization of the ashes of sugarcane bagasse from three different plants and two different harvests and the prospect of its use as an adsorbent. The particles of the ash were separated according to their density and in order to characterize, FTIR was used in the investigation of chemical groups present in the samples, additionally to the SEM and EDS elemental and morphological characterization of the particles present in the samples. Cenospheres, spherical particles present in ash, were identified as coreshell structure, where the core is a mixed metal oxide and the shell is a layer of silicon dioxide. The correlation between the ratio of the relative abundance between the carbonyl and hydroxyl groups and the mass distribution of the granulometric extracts were used as indirect measure of the level of oxidation of the samples. The ashes’ adsorption capacity showed affinity for the methylene blue dye with an adsorption capacity of 39 mg of dye per gram of ash used, in contrast to the low adsorption of potassium chromate solution, 1.2 mg per gram of ash. / As cinzas oriundas do processo de queima do bagaço de cana-de-açúcar são um material heterogêneo e com diversas aplicações, como a adsorção. Para potencializar e auxiliar na prospecção de novas aplicações é fundamental conhecer melhor as propriedades do material. Neste trabalho foi feita esta caracterização morfológica, espectroscópica e elementar das cinzas do bagaço da cana-de-açúcar provenientes de três diferentes usinas e duas diferentes safras e a prospecção de seu uso como adsorvente. As partículas das cinzas foram separadas de acordo com sua densidade e para a caracterização foi utilizada a técnica de FTIR na investigação dos grupos químicos presentes nas amostras e MEV juntamente com o EDS para a caracterização morfológica e elementar. As cenosferas, partículas esféricas presentes nas cinzas, foram identificadas como estruturas coreshell onde o core é composto por um misto de óxidos metálicos e o shell composto por dióxido de silício. A correlação entre a razão da abundância relativa entre os grupos de carbonila e hidroxila e a distribuição mássica dos extratos granulométricos, foi usada como medida indireta do nível de oxidação das diferentes amostras. Quanto à sua capacidade de adsorção, as cinzas mostraram afinidade na adsorção do corante azul de metileno com uma capacidade de adsorção de 39mg de corante por grama de cinza usada em contraste com a baixa adsorção apresentada para a solução de cromato de potássio com 1,2 mg por grama de cinza.

Made available in DSpace on 2014-10-09T12:42:11Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:08Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Dissertation submitted in fulfilment of requirements for the degree Master of Technology: Chemical Engineering In the FACULTY OF ENGINEERING 2014 / In South Africa only 5% of the coal fly ash produced annually by power stations finds use. Due to the high quantities of Si and Al in the coal fly ash researchers have explored the opportunity to use the fly ash as a feedstock in zeolite synthesis. Two principal methods have been successfully employed on a micro scale namely the 2-step method and fusion assisted method. However, in order to scale-up these processes some fundamental process design changes are required. Fly ash contains various elements including highly toxic elements such as As, Pb and Hg. The fate of these elements during the synthesis processes is not known. Both these processes generate large quantities of liquid supernatant waste. Disposal of these wastes would be expensive and environmentally harmful, thus making these processes industrially unfeasible. The well known fusion assisted process, contains an energy intensive fusion step operating at 550 C. Construction and operation of a furnace to implement fusion would be too expensive on an industrial scale. The 2-step method has a time consuming pre-hydrothermal treatment step (aging step). In order to improve the feasibility of the 2-step process the processing time of the aging step needs to be reduced. In order to breach the scale gap between micro and pilot plant scale a principal reactor design has been suggested. However, to date, no consideration has been given to the safety and operational reliability of this design. A HAZOP study is required to prevent costly incidents from occurring during the operation of this reactor. The aim of this study formed part of the overall initiative to scale-up the synthesis of zeolites to pilot and ultimately do at industrial scale. The aim of this study specifically was to perform some principal process design activities in order to prepare these processes for scale-up. The objectives were to perform material balances on the two principals synthesis approaches in order to determine the distributional fate of elements. Secondly, to make critical process design changes and develop protocols whereby the supernatant waste resulting from these processes can be minimised. Thirdly, to replace the fusion step (used in the fusion assisted process) and the aging step (used in the 2-step process) with a short high intensity sonochemical treatment step. Lastly, to perform a HAZOP study on the principal bench scale reactor design, and make design changes based on the outcome of the study. Material balances illustrated that most of the elements originating from the coal fly ash (Fe, Mn, Mg, Ca, Ti, Ba, Ce, Co, Cu, Nb, Ni, Pb, Rb, Sr, Y and Zn) do not leach out into solution during either of the two synthesis approaches. This was due to the CaO content in the ash retarding the mobility of these elements. This meant that during the 2-step process these elements reported to the overall zeolite product but did not form part of the zeolite crystal structure. On the other hand, during the fusion assisted process these elements reported to the solid residue waste. The yield efficiency of the fusion assisted process was found to be poor with only 19.6% of the Si and 21.6% Al reporting to the zeolite A product. The 2-step process on the other hand incorporated 72.2% of the Si and 81.5% Al into the zeolite product. However, the 2-step process produced a mixed phase zeolite product while the fusion assisted process produced a pure phase zeolite A product. Therefore there is a trade-off between yield efficiency and product purity. It was found that the liquid supernatant waste produced during both the synthesis processes contained toxic elements such as As, Pb, Hg, Al and Nb. This highlighted the importance to minimise the liquid supernatant waste generated. The waste minimisation studies illustrated that the liquid supernatant waste can be recycled while still producing highly crystalline zeolite products, in both the synthesis approaches. During the 2-step process the supernatant waste was recycled as a source of NaOH. By recycling the waste it was found that 40% of the supernatant could be recycled. However, by making a minor process design change a protocol was developed whereby 100% of the supernatant waste could be recycled. Also, by recycling the liquid waste, zeolite analcime became the dominant phase due to the accumulation of Si in the waste. In the fusion assisted process, protocols were developed whereby the liquid supernatant waste was recycled as a source of water. It was found that 100% of the supernatant could be recycled without compromising the relative crystallinity and purity of the zeolite A product. Both the fusion step (used in the fusion assisted approach) and the 48 hr aging step (used in the 2-step process) could be replaced with 10 min of sonochemical treatment. It was found in both cases that the introduction of ultrasound, during the pre-hydrothermal stage, increased the rate of crystal formation during the hydrothermal treatment step. It was also found that by replacing the high temperature fusion step, in the fusion assisted process, the required hydrothermal treatment temperature could be reduced to 90 C. By introducing sonochemical treatment in these two synthesis approaches their synthesis time and energy demands could be reduced successfully. A HAZOP study on the principal bench scale reactor design enabled design changes to be made preventing future loss during operation. A final optimised reactor design was proposed based on the outcome of the HAZOP study. This study effectively prepared both zeolite synthesis approaches for up-scale operation. Scale-up of this process will reduce disposal of coal fly ash offering relief to the financial and environmental strain caused to the country.

Made available in DSpace on 2014-10-09T12:42:11Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:08Z (GMT). No. of bitstreams: 0 / No presente estudo obteve-se com sucesso o compósito zeólita:magnetita usando-se como material de partida sulfato ferroso para síntese da magnetita e cinzas leves de carvão para síntese da fase zeolítica. A zeólita foi sintetizada por tratamento hidrotérmico alcalino e as nanopartículas de magnetita foram obtidas pela precipitação de íons Fe2+ em uma solução alcalina. Uma reprodutibilidade foi alcançada na preparação de diferentes amostras do nanocompósito zeolítico. O material foi caracterizado pelas técnicas de espectrometria de Infravermelho, difratometria de raios-X de pó, fluorescência de raios-X, microscopia eletrônica de varredura com a técnica de EDS, massa especifícia e área específica e por outras propriedades físico-químicas. O compósito era constituído pelas fases zeolíticas hidroxisodalita e NaP1, magnetita, quartzo e mulita das cinzas remanescentes do tratamento alcalino e magnetita incorporada na sua estrutura. A capacidade de remoção de U(VI) de soluções aquosas sobre o compósito zeólita:magnetita foi avaliada pela técnica descontínua. Os efeitos do tempo de contato e da concentração inicial do adsorbato sobre a adsorção foram avaliados. Determinou-se o tempo de equilíbrio do sistema e foram avaliados os modelos cinéticos de pseudo-primeira ordem, pseudo-segunda ordem e o modelo de difusão intrapartícula. Um tempo de contato de 120 min foi suficiente para a adsorção do íon uranilo alcançar o equilíbrio. A velocidade de adsorção seguiu o modelo cinético de pseudo-segunda-ordem, sendo que a difusão intrapartícula não era a etapa determinante do processo. Dois modelos de isotermas de adsorção, os modelos de Langmuir e de Freundlich, também foram avaliados. O modelo de Langmuir foi o que melhor se ajustou aos dados experimentais. A partir do modelo cinético e da isoterma que melhor descreveram o comportamento do sistema foi possível calcular os valores teóricos para a capacidade máxima de adsorção do U(VI) sobre o compósito zeólita:magnetita. As capacidades máximas de remoção calculadas foram de 20,7 mg.g-1 pela isoterma de Langmuir e de 23,4 mg.g-1 pelo modelo cinético de pseudo-segunda ordem. O valor experimental obtido foi 23,3 mg.g-1. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

D’après les limites d’acceptation pour la mise en décharge des déchets, les REFIOM (Résidus d’Epuration des Fumées d’Incinération d’Ordures Ménagères) sont considérés comme déchets dangereux, car ils libèrent des quantités importantes de chlorures et de métaux lourds lorsqu’ils entrent en contact avec de l’eau. Ces solides doivent par conséquent être traités avant leur mise en décharge. A côté des traitements visant l’acceptabilité des REFIOM en décharge, quelques recherches entrevoient la possibilité de valoriser ces résidus, notamment dans des matériaux cimentaires. <p>Les recherches présentées ici s’inscrivent dans cette tendance nouvelle et visent l’élaboration d’un procédé combinant traitement et valorisation des REFIOM. <p>Les REFIOM représentent en fait différents types de résidus provenant des installations que rencontrent les fumées issues de l’incinération des déchets. La composition des résidus diffère selon leur origine. Il est dès lors apparu essentiel de considérer chaque type de résidu séparément et de poursuivre l’élaboration d’un traitement sur un seul type de REFIOM. Nous avons choisi de concentrer les recherches sur les Cendres Volantes de Chaudière (CVC), ces résidus se retrouvant dans tout incinérateur. <p>Le traitement des CVC est basé sur l’extraction de fractions valorisables et la séparation de fractions contaminées, permettant d’obtenir des résidus acceptables en décharge ou, idéalement eux-mêmes valorisables. <p>Une séparation magnétique permet d’extraire environ 10% en poids des CVC mais ne semble pas exploitable dans le cadre du traitement des CVC car les particules magnétiques contiennent des impuretés (composés non magnétiques) et que le résidu final reste contaminé. <p>Une étude de la répartition des éléments en fonction de la taille des particules (granulochimie) est effectuée sur les CVC. Il apparaît intéressant de séparer la fraction inférieure à 38 µm obtenue lors d’une séparation granulométrique, effectuée en voie humide en utilisant une solution dense. En effet, cette fraction semble être nettement plus contaminée en Pb (soluble) que le reste des CVC. Une telle séparation constitue dès lors la première étape du traitement des CVC. Elle est suivie par des étapes de lavage des fractions obtenues, visant à extraire les sels solubles (chlorures et métaux). Les lavages sont envisagés à contre-courant afin d’utiliser au mieux l’eau de lavage. Une recirculation interne des solutions est également prévue, de sorte que, théoriquement, le procédé ne génère pas d’effluents liquides. Une étape de précipitation de composés métalliques (PbS dans ce cas-ci) est prévue après le lavage des boues. <p>Le procédé de traitement des CVC produirait ainsi des boues et des granulats décontaminés, des sels et des précipités métalliques. Seules certaines étapes du procédé ont été investiguées en laboratoire ;des essais supplémentaires sont encore nécessaires pour optimiser chaque étape, comprendre les phénomènes physico-chimiques qui se produisent et assurer des filières de valorisation. <p>/<p>Municipal Solid Waste Incineration (MSWI) fly ashes and Air Pollution Control (APC) residues are considered as hazardous waste according to the limits for the acceptance of waste at landfills, because high amounts of chlorides and heavy metals leach from the solids when those are in contact with water. These residues have thus to be treated before they can be accepted in landfill. Several treatments aim to limit the leaching of the residues. Beside these treatments, some research works go further the treatment and consider the valorisation of MSWI fly ashes and APC residues, e.a. in cementitious materials. <p>The present work follows the new trend and aims to build up a process that combines treatment and valorisation of MSWI fly ashes and APC residues. <p>MSWI fly ashes and APC residues come from the devices encountered by the flue gases from waste incineration. The residues composition differs according to their origin. It seems thus essential to consider each type of residues separately and to develop the treatment only on one sort of residue. Boiler Fly Ashes (BFA) were chosen because they exist in every modern MSWI plant. <p>The BFA treatment is based on the extraction of valorisable fractions and on the separation of contaminated fractions, which makes the final residues less hazardous; these final residues would then be acceptable in landfill, or, even better, be valorisable. <p>A magnetic sorting extracts ~10% (wt.) of BFA; however, such a separation would not be useful in a treatment process because the magnetic particles contain some impurities (non magnetic particles) and the final residue is still hazardous. <p>The repartition of the elements according to the particles size has been studied on BFA. It seems interesting to separate the BFA at 38 µm by a wet sieving process using a dense solution. The lower fraction presents a higher contamination in Pb (soluble) than the larger. Consequently, the first step of the BFA treatment consists of a wet sieving. Washing steps follow the sieving and aim to extract soluble salts (chlorides, heavy metals). These washings work in a counter-current way to optimise the use of water. The solutions are recycled in the process, which implies the absence of liquid effluents. A precipitation step of some metallic compounds (PbS in this case) is foreseen after the washing of the lower fraction. <p>The BFA treatment process would produce decontaminated sludge and coarse fractions, salts and metallic compounds. Some steps of the process have been investigated at lab-scale; further studies are necessary to optimise each step, to understand the observed reactions and to guarantee valorisation channels. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Dans un site de stockage profond de déchets radioactifs, l’utilisation de matériaux à base de ciment Portland en association avec de l’argile pourrait se révéler inadaptée en raison de leur forte alcalinité. Une alternative serait de mettre en œuvre des ciments générant des solutions interstitielles de pH réduit (de l’ordre de 11 au lieu de 13,5 pour un CEM I). Les formulations étudiées dans cette thèse font appel à des ciments composés (également appelés « liant bas pH ») élaborés à partir de mélanges binaires (CEM I / fumée de silice) ou ternaires (CEM I / fumée de silice / cendres volantes ou laitier), avec de forts taux de substitution du CEM I (de 30% à 80%). Le travail réalisé répond à un double objectif : (i) étudier l’évolution chimique des liants bas pH à 50°C ou 80°C, températures qui pourraient être rencontrées dans certaines zones du stockage, et (ii) préciser les mécanismes à l’origine de la bonne rétention des alcalins par ces liants hydratés. (i) Le suivi sur une période d’un an de pâtes de liant bas pH montre que l’accroissement de la température de 20 à 80°C accélère l’hydratation des liants et favorise la consommation de la portlandite. L’allongement et la réticulation des chaînes de silicates des C-A-S-H est mise en évidence par RMN de l’27Al et du 29Si. L’ettringite observée dans les pâtes conservées à 20°C est par ailleurs déstabilisée. Les sulfates ainsi relâchés sont pour partie adsorbés sur les C-A-S-H et dissous dans la solution interstitielle. Le pH de cette dernière est réduit de 1,7 à 2,2 unités selon les formulations. En revanche, les fractions solubles d’alcalins n’évoluent pas de façon importante. Le liant ternaire T1 composé de 37,5% de CEM I, 32,5% de fumée de silice et 30% de cendres volantes est le seul des ciments étudiés à conduire à un pH de solution interstitielle inférieur à 11 aux trois températures considérées (20, 50 et 80°C - échéances 6 mois et 1 an). Son évolution à plus long terme a pu être simulée à l’aide de systèmes modèles reproduisant sa composition chimique à partir d’oxydes réactifs. A l’équilibre thermodynamique, l’assemblage minéralogique est constitué de C-A-S-H (rapports Ca/Si et Al/Si de 0,75 et 0,15 respectivement) ainsi que d’hydroxyde d’aluminium et de silice amorphes, et il impose un pH de 10,3 à 20°C. (ii) Ce sont les C-A-S-H qui jouent le rôle essentiel dans la rétention des alcalins. Le mécanisme mis en jeu est celui d’une compensation des charges négatives des C-A-S-H par interaction électrostatique. Il existe une sélectivité de sorption : le potassium est mieux retenu que le sodium. Celle-ci pourrait être attribuée en première approche à la différence de rayon solvaté entre ces ions. Une modélisation Monte Carlo des interactions électrostatiques entre des particules de C-S-H et un électrolyte contenant des ions sodium et potassium montre cependant que cette hypothèse ne suffit pas à elle seule à expliquer la sélectivité observée expérimentalement. / Because of their high alkalinity, Portland cement (OPC)-based materials may have deleterious effects in an underground waste repository. A solution would be to use low-alkalinity cements (also referred as low-pH cements) generating interstitial solutions with a reduced pH (11 instead of 13.5 for OPC), and thus showing an improved chemical compatibility with the repository environment. In this work, the investigated formulations were based on binary (OPC / silica fume) or ternary (OPC / silica fume / slag or fly ash) blends, with high substitution levels of CEM I (from 30% to 80%). This research project met two main objectives: (i) study the chemical evolution of low-pH cements at 50°C or 80°C, since such temperatures could be encoutered in certain zones of the waste repositories, and (ii) determine the mechanisms of alkali retention by hydrated low-pH cements. (i) Investigation of low-pH cement pastes with ongoing hydration over one year showed that increasing the temperature from 20°C to 80°C accelerated cement hydration and favoured the depletion of portlandite. A lengthening of the C-A-S-H silicate chains was also detected by 27Al and 29Si NMR analyses. Besides, ettringite precipitated at 20°C, but was destabilised at higher temperature. The released sulphates were partly adsorbed on the C-A-S-H and dissolved in the interstitial solution. The pH of this solution was reduced from 1.7 to 2.2 units depending on the formulations. The soluble fractions of alkalis did not significantly change with temperature. Among the five investigated blends, ternary binder T1 (37.5% CEM I, 32.5% silica fume, 30% fly ash) was the only one giving a pore solution pH lower than 11 at 20, 50 and 80°C (curing time of 6 months and 1 year). Its long-term evolution was simulated by model systems reproducing its chemical composition with reactive oxides. At equilibrium, the hydrate assemblage comprised C-A-S-H (Ca/Si and Al/Si ratios of 0.75 and 0.15 respectively), amorphous silica and aluminium hydroxide. It led to a pH of 10.3 at 20°C. (ii) C-A-S-H hydrates played a major role in the retention of alkalis. Sorption of potassium was higher than that of sodium and mainly resulted from electrostatic interactions with C-A-S-H. Monte Carlo modelling of these interactions showed that the difference of solvated radii between these ions could not explain by itself the sorption selectivity experimentally observed.