GEOCHEMICAL MODELING OF ABANDONED SULFIDIC FLOTATION MILL TAILINGS: THE CASE OF KIRKI, NE GREECE

Το εργοστάσιο εμπλουτισμού της Κίρκης εντοπίζεται περίπου 5 km νότια του μεταλλείου του Αγίου Φιλίππου. Τα απορρίμματα της επεξεργασίας του μεταλλεύματος είναι εκτεθειμένα στις ατμοσφαιρικές συνθήκες, με αποτέλεσμα τη συσσώρευση μετεωρικού νερού στην επιφάνειά τους. Τα επιφανειακά ρευστά αλληλεπιδρούν με το λεπτόκοκκο υλικό με υψηλό φορτίο βαρέων μετάλλων, με τελικό αποτέλεσμα τη δημιουργία όξινων και οξειδωτικών διαλυμάτων με υψηλό φορτίο μετάλλων στην επιφάνεια των απορριμμάτων. Τα απορρίμματα της επεξεργασίας αποτελούνται κυρίως από σύνδρομα ορυκτά της μεταλλοφορίας (χαλαζίας, δικίτης/καολινίτης, πυροφυλλίτης και άστριοι), ενώ τα κυριότερα δευτερογενή ορυκτά που εντοπίζονται αφορούν ορυκτά της ομάδας του γιαροσίτη, γύψο και αγκλεσίτη. Μοναδική πρωτογενής φάση της μεταλλοφορίας που εντοπίζεται στα απορρίμματα είναι ο σιδηροπυρίτης. Ο λεπτόκοκκος χαρακτήρας των απορριμμάτων της επεξεργασίας ευνοεί ταχύτατες αντιδράσεις μεταξύ των επιφανειακών ρευστών με το υλικό των απορριμμάτων. Το γεωχημικό πρόγραμμα PHRΕEQC, με χρήση της βάσης δεδομένων MINTEQ, εφαρμόσθηκε για τη διερεύνηση της λειτουργίας του συστήματος «επιφανειακό διάλυμα - δευτερογενή ορυκτά», με την ανάπτυξη τριών διαφορετικών μοντέλων, «Άμεση Καθίζηση», «Ανάμιξη με Μετεωρικό Νερό» και «Εξάτμιση». Σε κάθε μοντέλο εξετάζεται ο μηχανισμός με τον οποίο βαρέα μέταλλα δεσμεύονται στο πλέγμα δευτερογενών ορυκτών, αλλά και αποδεσμεύονται/διαλυτοποιούνται μετά από διαλυτοποίηση μετασταθών φάσεων.The Kirki flotation plant is located approximately 5 km south of the Agios Filippos open pit mine (Thrace, NE Greece), and unconfined mill tailings are exposed to atmospheric conditions. Rain water accumulates on the surface of the tailings and interacts with the solids, resulting in highly acidic and oxidative surface solutions with increased heavy metal content. The tailings material is dominated by gangue minerals with very low acid buffering capacity, including quartz, kaolinite/dickite, pyrophyllite and minor orthoclase. Secondary phases identified include mainly species of the jarosite group, gypsum and anglesite. No primary ore minerals besides pyrite are identified. The finegrained character of the tailings material favors fast reactions between the surface waters and the solids. The speciation/mass transfer computer code PHREEQC-2 and the MINTEQ database were employed for geochemical modeling of the acidic surface waters of the tailings dams T1 and T2. Three different scenarios were employed, “Direct Precipitation”, “Mixing with Rainwater” and “Evaporation” to check the equilibrium between the developed surface solutions and the secondary minerals identified in the tailings. The purpose of this work is to understand the way heavy metals may be locked to the lattice of secondary minerals, or dispersed/dissolved after dissolution of unstable secondary phases

GEOCHEMICAL INVESTIGATION AND MODELLING OF AN ACID PIT LAKE FROM A HIGH SULFIDATION ORE DEPOSIT: KIRKI, NE GREECE

Open pit mining of a high sulfidation epithermal type deposit at Kirki (Thrace, NE Greece) resulted in the formation of an acid pit lake by infilling of the open cast by rain and drainage waters after mine closure. The acidic and oxidative pit lake waters show high concentrations of trace metals largely due to the high toxic metals content of the ore, the limited buffering capacity of host rocks and the direct exposure of the ore zone to weathering. The floor of the pit lake is covered by a finegrained mineral precipitate that comprises mainly detrital minerals, originating from erosion of the rocks exposed on the walls of the open pit. Secondary anglesite, several species of the jarosite-group, rozenite, melanterite, gypsum, bukovskyite, beaverite, scorodite and minor goethite are also detected. The mineral precipitate presents significant heavy metal content indicating effective removal of metals from the acidic waters. The speciation/mass transfer computer code PHREEQC-2 and the MINTEQ database were employed for geochemical modelling of the equilibrium between the acidic pit lake waters and the secondary phases of the mineral precipitate

Derivation of higher order gradient continuum theories in 2,3-d non-linear elasticity from periodic lattice models

localization of deformation (in the form of shear bands) at sufficiently high levels of strain, are frequently modeled by gradient type non-local constitutive laws, i.e. continuum theories that include higher order deformation gradients. These models incorporate a length scale for the localized deformation zone and are either postulated or justified from micromechanical considerations. Of interest here is the consistent derivation of such models from a given microstructure and the subsequent investigation of their localization and stability behavior under finite strains.In the interest of simplicity, the microscopic model is a discrete, periodic, non-linear elastic lattice structure in two or three dimensions. The corresponding macroscopic model is a continuum constitutive law involving displacement gradients of all orders. Attention is focused on the simplest such model, namely the one whose energy density includes gradients of the displacements only up to the second order. The relation between the ellipticity of the resulting first (local) and second (non-local) order gradient models at finite strains, the stability of uniform strain solutions and the possibility of localized deformation zones is discussed. The investigations of the resulting continuum are done for two different microstructures, the second one of which approximates the behavior of perfect monatomic crystals in plane strain. Localized strain solutions based on the continuum approximation are possible with the first microstructurc but not with the second. Implications for the stability of three-dimensional crystals using realistic interaction potentials are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31886/1/0000838.pd

Multi-sensor measurement of dynamic deflections and structural health monitoring of flexible and stiff bridges

We investigated the response of bridges of different types to controlled and to wind and traffic-induced excitations; the emphasis was on deflections,derived from recordings of geodetic sensors and accelerometers (output-only analysis). Our focus was to push the limits of the existing experimental techniques, in order to cover not only flexible, but also stiff structures, and to present independently validated results. Our study focused on a 700m long, thin-deck cable-stayed bridge, a stiff steel pedestrian bridge, a historic composite (masonry/steel) train bridge and a 30m long, gradually decaying, currently swaying pedestrian timber bridge. Our basic strategy was first to develop data measurement and processing techniques using controlled (supervised learning) experiments, and then, (1) use collocated, redundant and distributed geodetic sensors (GPS/GNSS and Robotic Total Stations, RTS), as well as accelerometers, in order to record bridge excitations, especially con-trolled excitations leading to free attenuating oscillations;(2) develop techniques to denoise recordings of various sensors based on structural/logical constraints and sensor fusion, compensating for the weaknesses inherent in each type of sensor), validate results and avoid pitfalls;(3) monitor the episodic and gradual decay of a pedestrian bridge, through repeated surveys under similar loading and environmental conditions and using similar instrumentation.The output of our studies is to confirm the potential of modern sensors to measure, under certain conditions, reliable mm-level dynamic deflections even of stiff structures (3-6Hz dominant frequencies) and to provide firm constraints for structural analysis, including evidence for changes of first modal frequencies produced by structural decay, even to identify dynamic effects such as foundations response to dynamic loading

Catalytic Fast Pyrolysis of Kraft Lignin With Conventional, Mesoporous and Nanosized ZSM-5 Zeolite for the Production of Alkyl-Phenols and Aromatics

The valorization of lignin that derives as by product in various biomass conversion processes has become a major research and technological objective. The potential of the production of valuable mono-aromatics (BTX and others) and (alkyl)phenols by catalytic fast pyrolysis of lignin is investigated in this work by the use of ZSM-5 zeolites with different acidic and porosity characteristics. More specifically, conventional microporous ZSM-5 (Si/Al = 11.5, 25, 40), nano-sized (≤20 nm, by direct synthesis) and mesoporous (9 nm, by mild alkaline treatment) ZSM-5 zeolites were tested in the fast pyrolysis of a softwood kraft lignin at 400–600°C on a Py/GC-MS system and a fixed-bed reactor unit. The composition of lignin (FT-IR, 2D HSQC NMR) was correlated with the composition of the thermal (non-catalytic) pyrolysis oil, while the effect of pyrolysis temperature and catalyst-to-lignin (C/L) ratio, as well as of the Si/Al ratio, acidity, micro/mesoporosity and nano-size of ZSM-5, on bio-oil composition was thoroughly investigated. It was shown that the conventional microporous ZSM-5 zeolites are more selective toward mono-aromatics while the nano-sized and mesoporous ZSM-5 exhibited also high selectivity for (alkyl)phenols. However, the nano-sized ZSM-5 zeolite exhibited the lowest yield of organic bio-oil and highest production of water, coke and non-condensable gases compared to the conventional microporous and mesoporous ZSM-5 zeolites

Membrane Spin Up in a Normal Gravity Field: Experiments and Simulations

Finite element simulations and experimental observations of the spin up in vacuum of a thin membrane loaded by gravity are presented. The numerical techniques take into account the run time of each simulation and energy convergence; it is shown that accurate results can be obtained quite quickly in a rotating reference frame, and that including stiffness-proportional material damping helps convergence of the integration. It is also found that a very fine finite element mesh around the hub of the membrane is required to obtain consistent results. The experimental setup allows spinning of the membrane in a vacuum box; a measurement technique that uses stereo Digital Image Correlation is presented. A comparison between experiments and simulations using characteristic parameters of the shape of a membrane, i.e. the number of rotational symmetric waves, the average deflection, and the elastic bending strain energy of the membrane, shows good agreement between experiments and simulations

Shape memory alloy honeycombs: experiments & simulation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76238/1/AIAA-2007-1739-156.pd