Prevention of electrofilter ash toxic leaching by embedding in composite materials

Disposal of the fly ash may pose a significant risk to the environment due to the leaching of hazardous pollutants. The only sustainable solution for the pollution-prevention is the reapplication of fly ash as one of the components in construction material composites. There is a risk of leaching even when fly ash is built-in the construction composites and the goal of this investigation was to prove that leaching concentrations of toxic elements is in range assigned by actual regulations. Fly ash was applied in several composits: mortar, concrete and asphalt. The leachability of the potentially toxic elements from the fly ash based products was investigated. The leaching behavior and potential environmental impact of the 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 is included. The overall results showed that most of the elements are more readily leachable from the fly ash in comparison with the fly ash based composites

Thermal treatment of kaolin clay to obtain metakaolin

U radu su prikazani rezultati istraživanja dobijanja metakaolina termičkim tretmanom domaće kaolinske gline. Polazna sirovina je bila kaolinska glina sa ležišta Vrbica (Aranđelovački basen), čiji je sadržaj kaolinita oko 80% i gubitak žarenjem 12,33%. Diferencijalnom termičkom analizom (DTA/TGA) utvrđeno je da do dehidroksilacije i transformacije kaolinita u metakaolinit dolazi u opsegu temperature 450-700°C. Proces kalcinacije je praćen termičkim tretmanom kaolinske gline u laboratorijskim uslovima na temperaturama 550, 600, 650 i 700°C, različito vreme: 15, 30, 60, 90, 120, 150 i 180 min. Kao glavni kvantitativni kriterijum za ocenu ponašanja kaolinita u procesu kalcinacije, korišćen je stepen dehidroksilacije materijala, Dtg. Optimalni parametri procesa kalcinacije, pri kojima je postignut stepen dehidroksilacije 0,97, jesu: temperatura 650°C i vreme zagrevanja 90 min. Transformacije kaolinita u metakaolinit potvrđene su rendgenskom strukturnom analizom i IR spektroskopijom polazne gline i termički tretiranih glina. Na difraktogramima termički tretiranih glina nisu uočeni karakteristični pikovi kaolinita, dok IR spektri pokazuju odsustvo karakterističnih veza kaolinita. Pucolanska aktivnost metakaolina, određena direktnom metodom, pri optimalnim uslovima kalcinacije iznosi 0,65 g Ca(OH)2 / g metakaolina. Na osnovu ovih istraživanja može se zaključiti da je kaolinska glina sa nalazišta Vrbica pogodna za proizvodnju metakaolina, odgovarajuće pucolanske aktivnosti, a koji se može primenjivati u svojstvu dopunskog cementnog materijala u sistemima na bazi cementa.The metakaolin was produced by thermal treatment (calcination) of the starting high-quality kaolin clay from Serbia. The optimal calcination parameters, for which nearly complete dehydroxylation of the material was achieved, are: temperature 650°C and heating time of 90 min. The conversion of the kaolinite to metakaolinite was confirmed by XRD and IR analyses of the starting and thermally treated kaolin samples. The pozzolanic activity was determined by Chapelle test. The obtained value 0.65 g Ca(OH)2/g of metakaolin indicates that produced metakaolin may be used as supplementary cementitious material

Mineralogical and chemical composition of the mineral admixtures which use Serbian cement factories

Najveći deo proizvodnje cementa u Srbiji, približno 95%, su standardizovani mešani cementi na bazi Portland cementnog klinkera kome se dodaju mineralni dodaci: granulisana zgura visoke peći, prirodni i industrijski pucolani krečnjak i gips. Cilj ispitivanja je bio da se odredi mineraloški i hemijski sastav mineralnih dodataka koje domaće fabrike cementa koriste u svojoj redovnoj proizvodnji, jer oni mogu značajno doprineti kvalitetu i osobinama proizvedenih cemenata.The most of the cements production in Serbia, approximately 95 per cent, are standardized blended Portland cements based on Portland cement clinker mixed with mineral admixtures such as granulated blast furnace slag, natural and industrial pozzolana, limestone and gypsum. The aim of investigation were to determines mineral and chemical composition of the mineral admixtures which domestic cement factories uses in their regular production as their quality can great contribute to the quality of the cements produced

Compressive strength and microstructure of ordinary cured and autoclaved cement-based composites with mechanically activated kaolins

The effects of two different mechanically activated kaolins, AKV (61% kaolinite, 14% quartz and 16% mica) and AKG (51.6% kaolinite and 40.6% quartz) on the compressive strength of cement composites and microstructure of pastes were investigated. Composite mixtures, in which 10, 20, 30, 40 and 50% of ordinary Portland cement (OPC) was replaced by AKV or AKG, were prepared with w/b of 0.5, and exposed to different curing conditions (ordinary curing for 28 days and autoclaving). Factors affecting microstructure were investigated on pastes by X-ray diffraction (XRD), Differential thermal analysis/thermal gravimetry (DTA/TG) analyses, Mercury intrusion porosimetry (MIP) and Scanning electron microscopy with Energy-dispersive spectroscopy (SEM-EDS). AKG composites exhibited higher compressive strengths under both curing conditions. Positive autoclaving effects on strengths were predominantly pronounced at the higher cement replacement levels. Comparison of the autoclaved and ordinary cured paste microstructure, revealed more intensive pozzolanic reaction during autoclaving conditions (CH content near zero) and higher total porosity. The negative effect of hydrogarnet on the strength was compensated by the formation of the crystalline tobermorite. Obtained results revealed that mechanically activated kaolin, with high content of quartz, could be a promising pozzolanic addition, even at high cement replacement levels (30–50%), especially when autoclaving curing conditions were applied. © 2018 Elsevier Lt

Investigation of the mortar and concrete resistance in aggressive solutions

U radu je prikazan utjecaj dva agresivna rastvora – sulfata i nitrata na žbuku i beton. U eksperimentalnom radu ispitivane su prizme od žbuke s 5 % specijalnog dodatka. Četiri vrste betona su također izložene agresivnim rastvorima. Kemijska otpornost ispitivana je prema metodi Koch-Steinegger. Kako je uvjet za otpornost kod agresivnih rastvora da zatezna čvrstoća žbuke nije niža od 70 % u odnosu na referentne prizme njegovane u vodi, može se zaključiti da žbuka i beton izrađeni s kombinacijom cementa i dodataka, prikazani u ovom istraživanju, nisu otporni na rastvor amonijak nitrata ali jesu na sulfatnu koroziju.Testing the influence of two aggressive solutions - sulphate and nitrate on mortar and concrete was presented in this paper. Experimental work included testing of mortar prisms with 5 % special admixture. Also, four types of concrete were exposed to aggressive solutions. The chemical resistance was tested according to the Koch-Steinegger method. As a condition for resistance in aggressive solution means that flexural strength of mortar prisms is no less than 70 % of referent prisms cured in water it can be concluded that mortar and concrete made with combination of cement and admixture presented in this investigation are not resistant to ammonium nitrate solution, but are resistant to sulphate corrosion

Corundum and Bauxite Refractory Shotcretes based on Activated Waste Coal Ash: Investigation of Thermally Induced Properties Change

The necessity for application of activated secondary raw materials in refractory industry is caused by a growing demand for refractory castables with advanced properties and continuous technological evolution of high-temperature materials. In this investigation, refractory shotcretes with the same matrix composition were prepared from 15 wt.% of high aluminate cement and 45 wt.% of bauxite aggregate + 30 wt.% of chamotte filler, i.e. 75% of corundum aggregate. The request for obtaining a low-cement castable is fulfilled by application of 10 wt.% of mechanically activated coal ash as the cement substitution in the shotcretes. The ash was activated by means of various high energy mechano-activators. Results were compared in order to choose the most efficient activation procedure. The properties have been studied at temperatures ranging from room temperature to adopted maximal temperature 1400°C. Mechanisms of hydration and sintering were investigated by means of differential thermal analysis at three different heating rates. The measurements showed different activation energies for ordinary shotcretes and shotcretes with activated ash. The evolution of the refractory shotcretes properties was investigated and correlated to microstructural changes induced by temperature and microfiller addition. The combination of advantages in investigated refractory shotcretes makes them suitable for use in severe conditions at high temperature applications especially in refractory industries

Effective removal of the heavy metal ion Cd2+ from the structure of cementitious materials with mineral additives

Natural zeolite and bentonite were used as mineral addi-tions to create cement-based building materials that are safe for the environment. This research focuses on the adsorptive qualities of these two clay raw materials, i.e., their propen-sity to immobilize heavy metal ions like Cd2+. The acquired results were examined using kinetic models of pseudo-first and pseudo-second order. The isotherms of Langmuir and Freundlich were examined. Zeolite and bentonite had differ-ent adsorption affinities for Cd2+ cations. Seven cement binders with various mineral additions (fly ash, zeolite, bentonite) underwent a leaching test. The adsorption and hydration mechanisms that immobilized heavy metals within cementitious composites caused leachates obtained on cement samples with the addition of fly ash and clay (either zeolite or bentonite) to contain lower concentrations of Cd2+ ions than leachates obtained on cement samples with fly ash alone

Performances of Vermiculite and Perlite Based Thermal Insulation Lightweight Concretes

This experimental study was conducted with an aim to investigate the effect of the elevated temperature on the mineral phase composition, microstructure and mechanical properties of the thermal insulation lightweight concretes. The first group of experimental concretes was based on the expanded vermiculite and expanded perlite used as lightweight aggregates (in 65 wt%) in combination with either ordinary Portland cement or refractory calcium aluminate cement. The mix-design of the second group of concretes comprised standard quartz aggregate, vermiculite or perlite as aggregate replacement (25 wt%) and binder (PC or CAC). A total of 10 concrete mix-designs were fabricated in form of 40x40x160 mm samples which were submitted to heat-treatment at 400 degrees, 600 degrees, 800 degrees and 1000 degrees C upon standard 28-days period of curing and hardening. The changes in crystallinity and mineral phase composition induced by temperature were monitored by X-ray diffraction technique. Microstructural visualizations of the non-fired and fired concrete samples were conducted by scanning electron microscopy accompanied with EDX analysis. The results indicated that despite the decrease in compressive strengths upon firing, investigated lightweight concretes can be categorized both as thermal insulators and structural materials

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

A preliminary evaluation of normative and realistic needs for prosthetic treatment among frail elderly patients in Serbia

Background/purpose: Common to all frail elderly patients in Serbia is the fact that only little or no attention is given to their dental care. A normative need for prosthetic treatment exists for all partially edentulous and edentulous patients who lack adequate prosthetic devices. The realistic need for treatment means the opportunity to perform the treatment that will be beneficial for each patient individually. The goal of this study was to determine the normative and realistic needs for prosthetic treatment among frail elderly patients in Serbia. Materials and methods: The study involved 117 elderly and frail patients provided service at the Geriatrics Institute in Belgrade, and among families in suburban municipalities. We determined the patients' dental status, cognitive status, general health condition, and desire for treatment. Results: Results showed that 82.9% of patients had normative need for prosthetic treatment. Realistic need for prosthetic treatment was significantly lower-that is 19.7% to 28.2% of patients can be provided appropriate prosthetic treatment in order to improve their oral functionality and quality of life. Conclusion: Although realistic need for prosthetic treatment is significantly lower than normative need, treatment shouldn't be denied to patients who can receive it, especially when the treatment recommended is less invasive