Leaching of the potentially toxic pollutants from composites based on waste raw material

Odlaganje letećeg pepela dobijenog u procesu sagorevanja uglja u termo-elektranama predstavlja veliki rizik za prirodnu sredinu zbog mogućnosti luženja opasnih čestica kao što su toksični metali. Takođe, opasnost od izluživanja je prisutna čak i kada je leteći pepeo ugrađen u konstukcioni kompozit. Leteći pepeli sa različitih deponija su upotrebljeni za spravljanje uzoraka različitih kompozita (malter, beton ili opeka) pri čemu na pepelu nije sproveden nikakav fizički ili termički pred-tretman. Ispitivano je luženje potencijalno toksičnih elemenata prisutnih u proizvodima na bazi letećeg pepela. Praćeno je izluživanje i mogući uticaj na prirodnu sredinu 11 potencijalno opasnih elemenata: Pb, Cd, Zn, Cu, Ni, Cr, Hg, As, Ba, Sb i Se. Sprovedeno je detaljno istraživanje fizičko-hemijskih svojstava letećeg pepela, sa posebnim naglaskom na ispitivanju hemijskog sastava i prisutnosti elemenata u tragovima. Fizičko-hemijska svojstva pepela su ispitivana sledećim metodama: X-ray fluorescenicija, difrakciona termička analiza i X-ray difrakciona metoda. Skenirajući elektronski mikroskop je primenjen u mikrostukturnoj analizi. Rezultati su pokazali da se većina elemenata lakše izlužuje iz pepela nego kompozita spravljenih na bazi pepela. Izluživanje svih ispitivanih toksičnih elemenata je bilo u dozvoljenim granicama što znači da se ispitivani leteći pepeo može upotrebiti u proizvodnji konstrukcionih materijala.The disposal of fly ash generated in coal based power-plants may pose a significant risk to the environment due to the possible leaching of hazardous pollutants, such as toxic metals. Also, there is a risk of leaching even when fly ash is built in the construction composites. Fly ashes from various landfills were applied in several composite samples (mortar, concrete and brick) without any physical or thermal pre-treatment. The leachability of the potentially toxic pollutants from the fly ash based products was investigated. The leaching behaviour and potential environmental impact of 11 potentially hazardous elements was tracked: Pb, Cd, Zn, Cu, Ni, Cr, Hg, As, Ba, Sb and Se. A detailed study of physico-chemical characteristics of the fly ash, with an accent on trace elements and the chemical composition investigation is included. Physicochemical properties of fly ash were investigated by means of X-ray fluorescence, differential thermal analysis and X-ray diffraction methods. Scanning electron microscopy was used in microstructure analysis. The results show that most of the elements are more easily leachable from the fly ash in comparison to the fly ash based composites. The leaching of investigated pollutants is within allowed range thus investigated fly ashes can be reused in construction materials production

Evaluation of Fly Ash Pysico-chemical Characteristics as Component for Eco-ceramic and Sintered Materials

The aim of the presented study is to evaluate utilization potential of the fly ash which is the main residue from the coal combustion thermal-plants. Decades long high production of fly ash represents extreme hazard for the environment. The storage problem of this waste material is also alerting. Thus, recycling and reapplication of fly ash in construction materials industry is the only economic solution. The well-known examples of fly-ash reapplication as a component in cement, mortar, concrete, bricks and tiles are not enough in means of reusing extreme amounts of this waste material. Therefore, new applications in ash-based composites have to be developed: eco-ceramic materials and sintered materials for refractory performances. In this investigation, characterization of three different fly ash capacities was used as base for further fly ash utilization possibilities analysis. Accent was on the investigation of the fly ash mineralogical and chemical composition. Thermal stability of crystalline phases was investigated with DTA. Macro-performance was correlated with the microstructure of fly ash studied by means of XRD and SEM analysis. Furthermore, content of trace elements, physico-chemical characteristics and leaching toxicity tests were carried out. Comparing the properties of investigated fly ashes with standard values, it could be presumed that fly ash originating from Serbian power plants can be potentially useful for high value products - eco-ceramic and refractory/sintered materials manufacturing. Key words: fly ash, microstructure, potential reusing, eco-ceramic, sintering. Acknowledgements: This investigation was supported by Serbian Ministry of Science and Education and it was conducted under following projects: 172057 and 45008

Synthesizing a new type of mullite lining

Various possibilities for developing new mullite-based refractory linings that can be applied in a casting process were investigated and are presented in this paper. An optimization of the refractory-lining composition design with the controlled rheological properties was achieved by applying different lining components and altering the lining-production procedure. Mullite was used as a high-temperature filler. A mullite sample was tested with the following methods: X-ray diffraction analysis, differential thermal analysis and scanning-electron microscopy. The particle shape and particle size were analyzed with the program package for an image analysis called OZARIA 2.5. It was proved that an application of this type of lining has a positive effect on the surface quality, structural and mechanical properties of the castings of Fe-C alloys obtained by casting into sand molds, according to the method of expandable patterns (the EPC casting process)

Properties of refractory bonding agent based on waste material

Leteći pepeo koji je deponovan na otvorenom predstavlja veliki rizik za prirodno okruženje. Održivo rešenje za sprečavanje zagađenja jeste primena letećeg pepela u građevinskim materijalima. Građevinski kompoziti - visokotemperaturna veziva, u kojima je leteći pepeo kombinovan s vatrostalnim komponentama, jesu nova mogućnost za reaplikaciju ovog otpadnog materijala. U ovom istraživanju, ispitivano vezivo dobijeno je na bazi letećeg pepela u kombinaciji s visokoaluminatnim cementom. Leteći pepeo je prethodno bio podvrgnut mehaničkoj aktivaciji. Analiza mineralnih faza pomoću XRD metode naglašena je zbog promena koje u materijalu nastaju s povećanjem temperature. Procesi koji se dešavaju u kompozitu u toku termičkog tretmana od 20 do 1100 oC identifikovani su DTA metodom. Analizirano je luženje i potencijalni uticaj na prirodnu sredinu. Ispitivani kompozit na bazi pepela i cementa pokazao je visoke fizičko-mehaničke performanse i dobra termoizolaciona svojstva. Sveukupni rezultati pokazali su da primena letećeg pepela za dobijanje visokotemperaturnih veziva predstavlja održivo rešenje za problem odlaganja i reciklaže ovog opasnog otpadnog materijala.The fly ash disposal on open landfills poses significant risk to the environment. Sustainable solution for the pollution-prevention is reuse of fly ash in building materials. Building composites - high temperature bonding agents, in which fly ash is combined with refractory components is new option for reapplication of this waste material. In this study, investigated bonding agent was based on fly ash mixed with high-aluminate cement. Fly ash previously underwent mechanical activation. Mineral phase analysis of the composite by means of XRD was accented due to the changes occurring with increasing temperature. Processes taking place during composite thermal treatment from 20 up to 1100 oC were identified by means of DTA method. The leaching behaviour and potential environmental impact of hazardous elements were analyzed. Investigated fly ash-cement composite proved to have high physical and mechanical performances, but also good thermoinsulation characteristics. The overall results showed that application of the fly ash in high-temperature bonding agents is sustainable solution for managing this environmentally hazardous waste material

The flaws of aluminium-magnesium alloy elements: Influence of inclusions

Rezultati ispitivanja uticaja uklanjanja gasa iz tečnog metala na kvalitet livenih elemenata od aluminijum-magnezijum legure, a na bazi recikliranih materijala su dati ovom radu. Dobijeni rezultati praktično definišu proceduru livenja kojom se može umanjiti prisustvo uključaka i gasova u livenim elementima, što je osnovni preduslov za postizanje projektovanog kvaliteta livenog materijala i krajnjih proizvoda. Ispitivani su kinetika i mehanizmi procesa degasifikacije, zatim su definisani parametri procesa degasifikacije, i na posletku primenjeni novi agensi za degasifikaciju legura. Rezultati ovog ispitivanja su značajni sa ekološkog aspekta i sa aspekta održivog razvoja proizvodnje livenih elemenata od aluminijumskih legura.The investigation results of gas removal from smelted metal and the effect on performances of aluminium-magnesium alloy cast elements are presented in this paper. The investigated alloy is based on recycled material. The obtained results define the specific procedure which is used for removal and reduction the presence of inclusions of various types in the cast elements, which is the basic step in achieving the designed quality of cast material and quality final products. Kinetics and mechanisms of degasification process were investigated, parameters of degasification procedures were defined, and the new agents for degasification of alloy cast were implemented. The results of this investigation are significant from the aspect of sustainable development the production of cast elements of aluminium alloys

Quality menagment of protective coating based on zirconium silicate

The composition and production procedures of refractory coatings based on zirconium silicate for the protection of metal structures in conditions of wear, cavitation and corrosion were investigated in the paper. The composition of the coating was defined with a filler based on zirconium silicate, a binder based on epoxy resin, organic additives and an organic solvent. A method for quality control of obtained coatings was investigated using the ultrasonic vibration method with a stationary sample according to the ASTM G 32 standard. The following methods were used to characterize the obtained filler samples: X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The change in the mass of the samples as a function of the cavitation time was monitored and the cavitation rate was determined. The formation and development of damage to the coating surface was monitored using a scanning electron microscope. The obtained test results showed a satisfactory resistance of the protective coatings to the effect of cavitation, with small damage to the coating surface and a cavitation rate of 0.6 mg/min. Tests have shown that the application of the ultrasonic vibration method is suitable for a quick assessment of the quality of protective coatings during synthesis and a forecast of their resistance and stability during exploitation in the protection of equipment parts in mining and metallurgy

Evaluation of Fly Ash Pysico-chemical Characteristics as Component for Eco-ceramic and Sintered Materials

The aim of the presented study is to evaluate utilization potential of the fly ash which is the main residue from the coal combustion thermal-plants. Decades long high production of fly ash represents extreme hazard for the environment. The storage problem of this waste material is also alerting. Thus, recycling and reapplication of fly ash in construction materials industry is the only economic solution. The well-known examples of fly-ash reapplication as a component in cement, mortar, concrete, bricks and tiles are not enough in means of reusing extreme amounts of this waste material. Therefore, new applications in ash-based composites have to be developed: eco-ceramic materials and sintered materials for refractory performances. In this investigation, characterization of three different fly ash capacities was used as base for further fly ash utilization possibilities analysis. Accent was on the investigation of the fly ash mineralogical and chemical composition. Thermal stability of crystalline phases was investigated with DTA. Macro-performance was correlated with the microstructure of fly ash studied by means of XRD and SEM analysis. Furthermore, content of trace elements, physico-chemical characteristics and leaching toxicity tests were carried out. Comparing the properties of investigated fly ashes with standard values, it could be presumed that fly ash originating from Serbian power plants can be potentially useful for high value products - eco-ceramic and refractory/sintered materials manufacturing. Key words: fly ash, microstructure, potential reusing, eco-ceramic, sintering.\ud Acknowledgements: This investigation was supported by Serbian Ministry of Science and Education and it was conducted under following projects: 172057 and 45008.\u

Zircon-based coating for the applications in Lost Foam casting process

U ovom radu je istraživana mogućnost dobijanja novih vatrostalnih premaza na bazi cirkona koji bi imali primenu u livarstvu. Optimizacija sastava premaza kontrolisana reološkim svojstvima postignuta je primenom različitih komponenata premaza, naročito primenom novog veziva na bazi suspenzije i variranjem načina spravljanja premaza. Čestice cirkonskoh praha veličine 25×10-6 m su korišćene kao ispuna. Uzorak cirkona ispitivan je pomoću sledećih metoda: difrakcija X-zraka, diferencijalna termalna analiza i mikroskopija. Oblik i veličina zrna su analizirani pomoću računarskog programa za analizu slike OZARIA 2.5. Pokazano je da primena ovih premaza na bazi vode i alkohola ima pozitivan uticaj na kvalitet površine, tj. na strukturne i mehaničke karakteristike odlivaka livenog gvožđa koji su dobijeni metodom livenja u peščane kalupe i pomoću isparljivih modela (Lost Foam metoda livenja).In this work, a possibility to develop a new zircon-based refractory coating for casting applications was investigated. Optimization of the coating composition with controlled rheological properties was attained by application of different coating components, particularly by application of a new suspension agent and by alteration of coating production procedure. Zircon powder with particle size of 25×10-6 m was used as filler. The zircon sample was investigated by means of X-ray diffraction analysis, diffraction thermal analysis and polarized microscopy. The shape and grain size were analyzed using OZARIA 2.5 software. It was shown that application of this type of water-alcohol-based coating had a positive influence on surface quality, structural and mechanical properties of the castings of cast iron obtained by pouring into sand molds by means of the expandable patterns method (Lost Foam casting process)

QUALLITY MANAGEMENT OF PROCETIVE COATINGS BASED ON ZIRCONIUM SILICATE

The composition and production procedures of refractory coatings based on zirconium silicate for the protection of metal structures in conditions of wear, cavitation and corrosion were investigated in the paper. The composition of the coating was defined with a filler based on zirconium silicate, a binder based on epoxy resin, organic additives and an organic solvent. A method for quality control of obtained coatings was investigated using the ultrasonic vibration method with a stationary sample according to the ASTM G 32 standard. The following methods were used to characterize the obtained filler samples: X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The change in the mass of the samples as a function of the cavitation time was monitored and the cavitation rate was determined. The formation and development of damage to the coating surface was monitored using a scanning electron microscope. The obtained test results showed a satisfactory resistance of the protective coatings to the effect of cavitation, with small damage to the coating surface and a cavitation rate of 0.6 mg/min. Tests have shown that the application of the ultrasonic vibration method is suitable for a quick assessment of the quality of protective coatings during synthesis and a forecast of their resistance and stability during exploitation in the protection of equipment parts in mining and metallurgy