Συμβολή στη διερεύνηση των μηχανισμών γεωπολυμερισμού μεταλλουργικών αποβλήτων με έμφαση στις σκωρίες ηλεκτροκαμίνων

Development of new environmentally friendly technologies is required in order to improve the management of mining and metallurgical wastes and to moderate various environmental impacts, as well as, to minimise the disposal cost. Geopolymerisation is an emerging technology that may contribute to the utilisation of various wastes and the development of new materials withadvanced properties. Geopolymer synthesis using low calcium ferronickel slag is a novel researchtopic. Limited research has been carried out, specifically in Australia, France and Ukraine. Most of these efforts involve utilization of alumino-silicate materials, fly ash or high calcium slags (>40%) in order to develop new products and immobilize hazardous elements. The present PhD thesis aims to investigate the mechanisms of the reactions taking place when geopolymers are synthesised from mining and metallurgical wastes, with emphasis on ferronickel slag. The effect of various factors is examined when slag-based geopolymers are subjected to compressive strength testing, in order to optimise synthesis conditions. The factors examined include the use of alkaline activating solutionof various concentrations; the addition of kaolinite, metakaolinite, pozzolan, CaO, fly ash from Megalopolis or Ptolemais thermal power stations, red mud and silica sand; the water content, the pre-curing time, the heating temperature and the heating and aging period. Each of the above-mentioned factors plays a decisive role in the compressive strength of the final products. The excess of Al and Si provided from the raw materials does not fully react during geopolymerisation and, therefore, results in decreased compressive strength. The addition of an activating solution using the optimum concentrations (about 8 Μ ΚΟΗ or 6 Μ NaOH and 8 % w/w Na2SiO3) improves strength substantially. Optimum water content improves workability of the paste and prevents the development of pores and cracks. However, in order to develop new materials with desired mechanical properties for specific applications, appropriate pre-curing (2 days), heating (80 oC for 48 hours) and aging time (28 days) should be considered. Structural stability and durability of geopolymers, as well as dissolution of hazardous components were studied by immersing them in various corrosive and acidic solutions. Slag-based geopolymers show a better behaviour compared with slag-kaolinite geopolymers. The strength of geopolymers decreases substantially only when they are immersed in corrosive solutions, such as simulated acid rain, HCl 0.5 Ν or 0.05 Ν. Addition of heavy metals (Pb, Cu, Ni or Cr) as nitrate or sulfate salts in high percentages affects negatively the compressive strength. However, the application of TCLP test shows that Pb, Cu, Ni or Cr are stabilized effectively in slag-based geopolymers. In order to elucidate the microstructure of geopolymers mineralogical studies using XRD, optical microscopy with reflected light, SEM, FTIR and TG, were carried out. Despite the amorphous nature of geopolymers, these techniques when combined assist in the elucidation of several geopolymerisation mechanisms.Το πρόβληµα της διαχείρισης των µεταλλευτικών και µεταλλουργικών αποβλήτων ώστε να περιοριστούν οι διάφορες περιβαλλοντικές επιπτώσεις και να ελαχιστοποιηθεί το κόστος διάθεσης, οδηγεί στην αναζήτηση νέων φιλικών προς το περιβάλλον τεχνολογιών. Ο γεωπολυµερισµός αναδύεται ως µια πιθανή τεχνολογία που συµβάλλει στην αξιοποίηση µερικών αποβλήτων δηµιουργώντας νέα υλικά µε χαρακτηριστικές ιδιότητες και σηµαντικό εύρος εφαρµογών. Η σύνθεση γεωπολυµερών από σκωρίες σιδηρονικελίου µε χαµηλή περιεκτικότητα σε ασβέστιο, αποτελεί ένα πρωτότυπο ερευνητικό αντικείµενο. Αντίστοιχες προσπάθειες έχουν γίνει σε µερικά ερευνητικά ιδρύµατα του εξωτερικού, όπως της Αυστραλίας, Γαλλίας και Ουκρανίας. Οι περισσότερες έρευνες αφορούν στη χρήση αργιλο-πυριτικών υλικών, ιπτάµενης τέφρας ή σκωριών µε υψηλή περιεκτικότητα σε ασβέστιο (>40%) για την παραγωγή νέων προϊόντων και τη σταθεροποίηση επικίνδυνων συστατικών. Στόχος της παρούσας διδακτορικής διατριβής είναι να διερευνηθούν οιµηχανισµοί των γεωπολυµερικών αντιδράσεων που λαµβάνουν χώρα όταν χρησιµοποιούνται µεταλλευτικά και µεταλλουργικά απόβλητα και κυρίως σκωρία σιδηρονικελίου. Η επίδραση των διαφόρων παραγόντων ερευνάται µέσω δοκιµών αντοχής των γεωπολυµερών σε θλίψη, ώστε να βελτιστοποιηθεί η διαδικασία σύνθεσης. Οι παράγοντες που µελετήθηκαν είναι η χρήση αλκαλικού διαλύµατος ενεργοποίησης σε διάφορες συγκεντρώσεις, η προσθήκη καολινίτη, µετακαολινίτη,ποζολάνης, CaO, ιπτάµενης τέφρας Μεγαλόπολης/Πτολεµαΐδας, ερυθράς ιλύος και χαλαζιακής άµµου σε γεωπολυµερή σκωρίας, η περιεκτικότητα σε νερό, ο χρόνος ωρίµανσης, η θερµοκρασία θέρµανσης καθώς και η περίοδος θέρµανσης και γήρανσης. Κάθε ένας από τους παραπάνω παράγοντες παίζει καθοριστικό ρόλο στην αντοχή των τελικών προϊόντων. Η περίσσεια Al και Si που παρέχεται στο σύστηµα από τα προσθετικά υλικά δεν αντιδρά πλήρως µε αποτέλεσµα να µη συµµετέχει στις αντιδράσεις γεωπολυµερισµού µειώνοντας σηµαντικά την τελική αντοχή. Ηπροσθήκη διαλύµατος ενεργοποίησης στις κατάλληλες αναλογίες (περίπου 8 Μ ΚΟΗ ή 6 Μ NaOH και 8 % κ.β. Na2SiO3) ενισχύει την αντοχή των γεωπολυµερών. Το προστιθέµενο νερό βελτιώνει την πλαστικότητα του µίγµατος και περιορίζει την ανάπτυξη πόρων και ρωγµών. Ωστόσο, προκειµένου να αποκτήσουν τα γεωπολυµερή σκωρίας ικανοποιητικές αντοχές και να παραχθούν δευτερογένη προϊόντα µε επιθυµητές εφαρµογές, θα πρέπει να χρησιµοποιηθούν οι βέλτιστες συνθήκες ωρίµανσης (2 ηµέρες), θέρµανσης (48 ώρες στους 80 οC) και γήρανσης (28 ηµέρες). Η ανθεκτικότητα των γεωπολυµερών µελετήθηκε µέσω εµβάπτισής τους σε διαβρωτικά και όξινα περιβάλλοντα και προσδιορισµού των επικίνδυνων στοιχείων που διαλυτοποιούνται. Τα γεωπολυµερή σκωρίας εµφανίζουν γενικότερα καλύτερη συµπεριφορά από τα γεωπολυµερή σκωρίας-καολινίτη. Η αντοχή τους µειώνεται σηµαντικά µόνο όταν εµβαπτίζονται σε διαβρωτικά διαλύµατα όπως προσοµοιωµένης όξινης βροχής, HCl 0,5 Ν ή 0,05 Ν. Η προσθήκη βαρέων µετάλλων (Pb, Cu, Ni ή Cr) σε µορφή νιτρικών ή θειϊκών αλάτων επηρεάζει αρνητικά την τελική αντοχή των γεωπολυµερών όσο αυξάνεται το ποσοστό προσθήκης. Ωστόσο µέσω της δοκιµής τοξικότητας (TCLP) αποδεικνύεται ότι τα παραπάνω µέταλλα σταθεροποιούνται σε ικανοποιητικό βαθµό στα γεωπολυµερή σκωρίας. Για τη διερεύνηση της µορφολογίας των γεωπολυµερών χρησιµοποιήθηκαν οι µέθοδοι ορυκτολογικής ανάλυσης XRD, οπτική µικροσκοπία ανακλωµένου φωτός, SEM, FTIR και TG. Παρά τη χαρακτηριστική άµορφη φύση των γεωπολυµερών, οιτεχνικές αυτές συµβάλλουν σε κάποιο βαθµό, στην κατανόηση των πολύπλοκων µηχανισµών των αντιδράσεων που λαµβάνουν χώρα

Adsorption of Scandium and Neodymium on Biochar Derived after Low-Temperature Pyrolysis of Sawdust

The objective of this study was to investigate the adsorption of two rare earth elements (REEs), namely scandium (Sc) and neodymium (Nd), on biochar produced after low temperature pyrolysis (350 °C) of wood sawdust. The biochar was characterized with the use of several analytical techniques, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis, while the pH at point of zero charge (pHPZC) was also determined. The experimental conditions were: absorbent concentration 1–10 g·L−1, REE concentration in solution 20 mg·L−1, contact time for equilibrium 24 h, temperature 25 °C and stirring speed 350 rpm. The efficiency of biochar was compared to that of a commercial activated carbon. Geochemical modelling was carried out to determine speciation of Nd and Sc species in aqueous solutions using PHREEQC-3 equipped with the llnl database. The experimental results indicated the potential of low temperature produced biochar, even though inferior to that of activated carbon, to adsorb efficiently both REEs. The equilibrium adsorption data were very well fitted into the Freundlich isotherm model, while kinetic data suggested that the removal of both REEs follows the pseudo-second order kinetic reaction. Finally, the most probable adsorption mechanisms are discussed

Assessment of groundwater contamination risk in an agricultural area in north Italy

In the present study a specific approach is followed, considering the Pesticide DRASTIC and Susceptibility index (SI) methods and a GIS framework, to assess groundwater vulnerability in the agricultural area of Albenga, in north Italy. The results indicate “high” to “very high” vulnerability to groundwater contamination along the coastline and the middle part of the Albenga plain, for almost 49% and 56% of the total study area for Pesticide DRASTIC and SI methods, respectively. These sensitive regions depict characteristics such as shallow depth to groundwater, extensive deposits of alluvial silty clays, flat topography and intensive agricultural activities. The distribution of nitrates concentration in groundwater in the study area is slightly better correlated with the SI (0.728) compared to Pesticide DRASTIC (0.693), thus indicating that both methods are characterized by quite good accuracy. Sensitivity analysis was also performed to acknowledge statistical uncertainty in the estimation of each parameter used, assess its impact and thus identify the most critical parameters that require further investigation in the future. Depth to water is the parameter that exhibited the largest impact on the Pesticide DRASTIC vulnerability index followed by the impact of the vadose zone and topography. On the other hand, the SI method is more sensitive to the removal of the topography parameter followed by the aquifer media and the depth to water parameters

Pre-treatment of olive mill wastewaters at laboratory and mill scale and subsequent use in agriculture: Legislative framework and proposed soil quality indicators

Δημοσίευση σε επιστημονικό περιοδικόSummarization: The present study investigates the potential of pre-treatment of olive mill wastewaters (OMW) at laboratory and mill scale and their subsequent use in agriculture to satisfy irrigation and fertilisation needs for widely cultivated crops. The ultimate objective of this approach is the development of a feasible decentralized treatment scheme in parts of the Mediterranean region where most olive mills are small family businesses, soils have low organic matter and the risk of desertification is high. Tests carried out both at lab and pilot scale involving mainly the use of low cost and readily available industrial/agricultural wastes/by-products such as saw dust, lime, iron fillings and goat manure. The aim of pre-treatment was two-fold (a) to produce OMW suitable for land application and (b) to allow its safe disposal in unprotected evaporation ponds, thus minimizing the risk for soil, surface- and groundwater contamination. Trials investigating the effect of pre-treated OMW on the growth of spinach and beetroot, using application rates 4, 10 and 20 L/m2 (40, 100 and 200 m3/ha), were also carried out in 0.5 × 0.5 × 0.2 m containers. The parameters studied include emergence from soil, plant height, root length, aerial biomass, soil pH and conductivity as well as content of phenols, K, N and P in soils. Furthermore, in order to assess the long term impacts of OMW application on soil, soil quality data are provided from a field where occasional disposal of OMW from an operating evaporation pond takes place for a period of more than ten years. Furthermore, an overview of the existing EU legislation is provided to identify gaps and address important issues related to the management of OMW, its application/disposal on land and the potential risk for soil and water bodies. Finally, a set of indicators is proposed to define a code of good practice for OMW application on soils, safeguard soil quality in disposal areas and improve the overall sustainability of the olive oil sector.Παρουσιάστηκε στο: Resources, Conservation and Recyclin

Assessment of human and ecosystem risk due to agricultural waste compost application on soils: A review

Δημοσίευση σε επιστημονικό περιοδικόSummarization: Agricultural wastes (AW) are often characterized by varying pH and substantial contamination potential, which are mainly related to their high organic load, thus affecting—when improperly disposed of—soils, living organisms, and water bodies. Composting of AW is the most commonly used management option and results in the production of soil improver that enhances crop growth and contributes to agricultural sustainability. This study aims to present the framework for assessing human and ecosystem risk when compost produced from AW is applied on soil. In order to develop this framework, issues such as origin, composition and pre-treatment of AW, application rates on soils, bioavailability and mobility of contaminants present in compost, exposure routes and rates as well as determination of the fate of contaminants in soil, air, and water, should be taken into consideration.Παρουσιάστηκε στο: Environmental Forensic

Effect of sulphate and nitrate anions on heavy metal immobilisation in ferronickel slag geopolymers

Δημοσίευση σε επιστημονικό περιοδικόSummarization: Industrial wastes need to be valorised and new techniques need to be developed for the production of secondary materials or immobilisation of hazardous elements in order to improve sustainability of the respective industrial sector. In the present experimental study the effect of monovalent and divalent anions, such as sulphate and nitrate, on heavy metal immobilisation in ferronickel slag geopolymers was investigated. Low calcium electric arc ferronickel slag was geopolymerised using KOH and Na2SiO3 as activators, in the presence of limited quantities of sulphate and nitrate salts of Pb, Cu, Cr or Ni. Gel properties, final strength of the specimens produced and immobilisation of heavy metals were determined, in order to explore the potential of geopolymerisation in developing a hazardous waste encapsulation matrix. In addition, the Toxicity Characteristics Leaching Procedure was used to assess the potential toxicity of the produced geopolymers. The experimental results indicate that even limited quantities of sulphates and nitrates in the starting mixture affect adversely geopolymerisation of ferronickel slag. XRD (X-ray diffraction), SEM (scanning electron microscopy) and FTIR (Fourier transform infrared spectroscopy) studies were carried out to identify new phases, reactions taking place and thus elucidate the main mechanisms involved.Παρουσιάστηκε στο: Applied Clay Scienc

Assessment of reactivity of sulphidic tailings and river sludges

Δημοσίευση σε επιστημονικό περιοδικόSummarization: The aims of this work were: to assess the long-term reactivity of sulphidic wastes disposed of in a tailings dam at Bor, Serbia; to assess the reactivity of the sludges formed in a stream receiving acidic effluents; and to estimate the risk for the wider ecosystem. The laboratory assessment was carried out according to a slightly modified AMIRA protocol, using conventional free-draining leach columns. Deionized water and simulated acid rain were used as leaching media. The experimental results over a period of c. 70 weeks show increased solubilization for a number of metals and subsequently high risk for contamination of surface- and groundwater. Finally, feasible and effective remediation measures are proposed.Presented on: Geochemistry: Exploration, Environment, Analysi

Effect of synthesis parameters on the compressive strength of low-calcium ferronickel slag inorganic polymers

Δημοσίευση σε επιστημονικό περιοδικόSummarization: The wide range of physical and chemical properties of inorganic polymers, also known as geopolymers, commonly formed by alkali activation of aluminosilicates, makes these materials useful for a variety of applications. In the present experimental study inorganic polymers are synthesised from low-Ca electric arc ferronickel slag. The effect of experimental conditions on the compressive strength of the final products is assessed. A number of techniques, namely XRD, FTIR and TG–DTG were used to identify new phases and subsequently elucidate to some degree the mechanisms involved. Finally, the paper discusses briefly the potential of inorganic polymer technology as a feasible option for the utilisation of certain potentially hazardous mining and metallurgical wastes towards an increased sustainability of the wider minerals sector.Παρουσιάστηκε στο: Journal of Hazardous Material

Microstructural characteristics and adsorption potential of a zeolitic tuff–metakaolin geopolymer

Δημοσίευση σε επιστημονικό περιοδικόSummarization: The aim of this work is to investigate the microstructural characteristics and the adsorption potential of zeolitic tuff–metakaolin (ZM) geopolymers. For the identification of microstructure, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses were used. XRD showed that mordenite, a major zeolite mineral, disappeared upon geopolymerization, while SEM showed that ZM-geopolymers exhibit a uniform porous matrix consisting of nanoparticles (~40 nm). The adsorption efficiency of ZM-geopolymers was assessed using solutions containing 250 mg/L copper. The experimental results show that the maximum adsorption efficiency (7.8 mg Cu2+/g of adsorbent) is observed at an initial zeolitic tuff/metakaolin ratio of 0.5 which indicates that ZM-geopolymers can be used in environmental applications including the clean-up of industrial effluents and wastewaters.Παρουσιάστηκε στο: Desalination and Water Treatmen