After carbon, phosphorus is the most commonly detected element in archaeological iron. The typical phosphoric iron range is 0.1wt% to 1wt%P. The predominant source of phosphorus in iron is the ore smelted. Around 60% of economic UK rock iron ore formations contain over 0.2%P. Under fully reducing conditions, both in liquid-state (cast iron) and solid-state bloomery smelting (direct reduction) processes, such rock ores would be predicted to produce phosphoric iron, and bog iron ores even more so. Ore-metal-slag phosphorus ratios for bloomery iron are derived here, by means of: laboratory experiments; full-scale experimental bloomery smelting; and analysis of remains from three Medieval and two Late Roman-Iron Age iron production sites in England and the Netherlands. Archaeological ore, slag, metal residues (gromps), and iron artefacts were analysed by metallography, SEM-EDS, EPMA, and XRD. The effects of forging and carburising on phosphoric iron were studied by experiment and artefact analysis. The ore to slag %P ratio for solid-state reduction was determined to range from 1:1.2 to 1: 1.8. The ore to metal %P ratio varied from 1:0.2 to 1:0.7 ¿ 1.4, depending on furnace operating conditions. Archaeological phosphoric iron and steel microstructures resulting from non-equilibrium reduction, heat treatment, and mechanical processing are presented to define the technology of early phosphoric iron. Microstructures were identified by a combination of metallography and chemical analysis. The phosphoric iron artefacts examined appear to be fully functional objects, some cold-worked and carburised. Modern concepts of 'quality' and workability are shown to be inapplicable to the archaeological material.

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No description available.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: See item for full text / AFRIKAANSE OPSOMMING: Sien item vir volteks

Thesis (MScEng) –Stellenbosch University, 2010 / ENGLISH ABSTRACT: More mining houses are turning their attention to the processing of ore mined from the UG2 reef. This is mainly due to the depletion of the Merensky reef or the low availability of ore from the Platreef. With the higher UG2 ore concentration in the process feed, companies experience more problems with the processing of the ore due to its high chrome content. Although there are various possible solutions to the problems experienced in the processing of UG2 ore, very little of thise solutions are actually implemented in the industry. When smelting chrome-bearing ore, the chrome can go to any of three phases: matte phase, spinel phase or glass phase. If it reports to the furnace matte phase it can lead to problems in the down stream processing. When chrome forms part of the spinel phase it forms a solid, refractory-like material which, to an extent, is an unwanted material inside the furnace. Lastly the chrome can report to the glass phase (liquid phase) which is the more desireable phase to which chrome should report to since it will have little or no impact on downstream processing. There were four main objectives for this research project namely to conduct a literature review to understand the problem of chrome in the smelting process, to do an experimental simulation of a matte and slag phase in one crucible, to interpret the experimental results and compare the experimental results to thermodynamic predictions obtained using FactSageTM. From literature the following aspects were found to be important: Silica structures Research has shown that silica incorporates different metal ions into its structures. When the metal ions are incorporated into the silica structures they are seen as part of the glass phase. By incorporating cations such as chromium into the silica structure the structure is able to maintain its neutral electrical charge. Basicity of slag Oxides once melted will either donate or accept oxide ions. The group of oxides that are in excess will determine whether that specific slag is acidic or non acidic. This is important to our study since the basicity can determine the stability of the spinel phase. Partial pressures The partial pressure of the system is important since it forms part of the equilibrium constant calculations - meaning that partial pressures determine the stability of certain species. Currently different arguments exist as to how the sulphur pressure inside a molten bath is maintained. What is important, however, is that for the system in this research project a log oxygen partial pressure of -8 and a log sulphur partial pressure of -3.5 was chosen. These values were based on previous research done on PGM and copper smelting processes. Chrome deportment Previous research on chrome deportment shows a relationship between temperature and the amount of chromium dissolving into the glass phase as well as an increased chromium(II)oxide solubility (when compared to chromium(III)oxide) in a silicate melt. Regarding slag chemistry and chrome deportment very little work has been published for the system found in the PGM industry but it is mentioned that by adjusting certain slag additives (alumina, lime and silica) the chrome deportment can be manipulated. The scope of this project was to investigate the effect of chromium, lime and silica on chrome deportment. More specifically, the effect of lime. The reason being that lime was originally added as 10%wt of the feed stream in the processing of Merensky ore to act as a fluxing agent. With the new furnace design and higher power densities the slag are maintained at 200oC to 350oC higher than when Merensky ore was smelted. With these higher slag temperatures fluxing agents will play a smaller role meaning that lime additions become less important. Literature studies also showed that additional lime in a slag system can stabilize the spinel structure (which is an unwanted phase). Removing lime would be advantageous out of a chrome presepective as well as an economic point of view. The research was conducted in three sections namely the determination of the time required for this particular system to reach equilibrium, the investigation of different additives on chrome deportment using a controlled atmosphere and synthetic slags and, lastly, a comparison of the experimental results obtained to thermodynamic predictions. For the equilibration studies reaction time periods of 4,7,11 and 16 hours were used. From the results it was found that the alumina crucible dissolved into the glass phase continually. This indicated that equilibrium was not reached. However, a reaction time, rather than an equilibrium time, was chosen where the species and phases had enough time to react. This was based on literature, on observations of species diffusing between the matte and slag phase as well as on two-point analysis (diffusion gradients). A reaction time of nine hours was chosen With the reaction time fixed, the effect of different slag additives on chrome deportment was investigated. For the addition of chrome it was seen that an 1.5%wt increase in the starting material increased the chrome content of the slag phase by 0.025%wt. For the same increase in chromium in the starting materials the chrome content of the spinel phase increased by 2.1% indicating that chromium has a tendency to report to the spinel phase. The increase in chromium had a minor effect on the chrome content of the matte phase, however, since the chrome content only increased from 0.025%wt to 0.028%wt. Plotting the results showed that increasing the lime in the starting material decreases the chromium content in the glass phase. For the 39%wt silica system the chromium content in the glass phase decreased from 0.75%wt to 0.46%wt for an increase in the lime content from 1.7%wt to 7.3%wt. The same trend was seen for the 33%wt silica system. For the spinel phase an increase of 1.27%wt was seen when the lime content of the starting materials was increased from 1.7%wt to 10.1%wt for a 33%wt silica system. The same increase in lime increased the chrome content of the matte phase from 0.03%wt to 0.06%wt for a 33%wt silica system. Silica also proved to affect chrome deportment. Increasing the silica content of the starting materials from 25%wt to 39%wt increased the amount of chromium in the glass phase from 0%wt to 0.46%wt for a 10%wt lime system. The same effect is seen for a lower lime content except that more chromium were incorporated into the silica structure. A silica increase from 32.4%wt to 39%wt resulted in a chromium decrease from 5.2%wt to 0% in the spinel phase for a 10%wt lime system. The same trend was seen for the 1.5%wt lime system. An increase in the silica levels lead to an increase in the chrome level of the matte phase. When silica is increased from 32%wt to 39%wt the chrome content of the matte phase increased from 0.06%wt to 0.07%wt. The last part of the research project entailed the comparison of the trends observed with the experimental results to trends obtained from thermodynamic predictions. FactSageTM is a program that uses model equations to predict the Gibbs free energies for different phases. The program is therefore also able to predict the amount of different phases present at equilibrium. This is called thermodynamic ”optimization”. In section 6 trends that were observed from FactSageTM results are compared to the trends found in the experimental results. It is important to note that it is only trends that are evaluated and not actual values since FactSageTM calculations are for a system that is at equilibrium and (as explained above) this system is not at complete equilibrium. The comparison however was good. Several trends found in the experimental results were confirmed by the results from FactSageTM. These included the relationships of chromium fed versus chromium spinel, lime fed versus chromium spinel, lime fed versus chromium in glass, silica fed versus chromium in glass, silica fed versus chromium in spinel and silica fed versus chromium in matte. To conclude, slag additions can be used to manipulate chrome deportment to an extent. Secondly, FactSageTM can be used for thermodynamic predictions but a proper understanding as well as some form of validation of the specific system investigated is still needed. Due to time constraints and the difficulty of experimentally simulating this multi-phase system in the lab, only a few parameters were investigated. In order to obtain a more complete understanding of the system the effect of partial pressures and temperature should also be investigated.

Thesis (PhD)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: The growing need to improve accounting accuracy, precision and to standardise generally accepted measurement methods in the mining and processing industries has led to the joining of a number of organisations under the AMIRA International umbrella, with the purpose of fulfilling these objectives. As part of this venture, Anglo Platinum undertook a project on the material balancing around its largest smelter, the Waterval Smelter. The primary objective of the project was to perform a statistical material balance around the Waterval Smelter using the Maximum Likelihood method with respect to platinum, rhodium, nickel, sulphur and chrome (III) oxide. Pt, Rh and Ni were selected for their significant contribution to the company’s profit margin, whilst S was included because of its environmental importance. Cr2O3 was included for its importance in as far as the difficulties its presence poses in smelting of PGMs. The objective was achieved by performing a series of statistical computations. These include; quantification of total and analytical uncertainties, detection of outliers, estimation and modelling of daily and monthly measurement uncertainties, parameter estimation and data reconciliation. Comparisons were made between the Maximum Likelihood and Least Squares methods. Total uncertainties associated with the daily grades were determined by use of variographic studies. The estimated Pt standard deviations were within 10% relative to the respective average grades with a few exceptions. The total uncertainties were split into their respective components by determining analytical variances from analytical replicates. The results indicated that the sampling components of the total uncertainty were generally larger as compared to their analytical counterparts. WCM, the platinum rich Waterval smelter product, has an uncertainty that is worth ~R2 103 000 in its daily Pt grade. This estimated figure shows that the quality of measurements do not only affect the accuracy of metal accounting, but can have considerable implications if not quantified and managed. The daily uncertainties were estimated using Kriging and bootstrapped to obtain estimates for the monthly uncertainties. Distributions were fitted using MLE on the distribution fitting tool of the JMP6.0 programme and goodness of fit tests were performed. The data were fitted with normal and beta distributions, and there was a notable decrease in the skewness from the daily to the monthly data. The reconciliation of the data was performed using the Maximum Likelihood and comparing that with the widely used Least Squares. The Maximum Likelihood and Least Squares adjustments were performed on simulated data in order to conduct a test of accuracy and to determine the extent of error reduction after the reconciliation exercise. The test showed that the two methods had comparable accuracies and error reduction capabilities. However, it was shown that modelling of uncertainties with the unbounded normal distribution does lead to the estimation of adjustments so large that negative adjusted values are the result. The benefit of modelling the uncertainties with a bounded distribution, which is the beta distribution in this case, is that the possibility of obtaining negative adjusted values is annihilated. ML-adjusted values (beta) will always be non-negative, therefore feasible. In a further comparison of the ML(bounded model) and the LS methods in the material balancing of the Waterval smelter complex, it was found that for all those streams whose uncertainties were modelled with a beta distribution, i.e. those whose distribution possessed some degree of skewness, the ML adjustments were significantly smaller than the LS counterparts It is therefore concluded that the Maximum Likelihood (bounded models) is a rigorous alternative method of data reconciliation to the LS method with the benefits of; -- Better estimates due to the fact that the nature of the data (distribution) is not assumed, but determined through distribution fitting and parameter estimation -- Adjusted values can never be negative due to the bounded nature of the distribution The novel contributions made in this thesis are as follows; -- The Maximum Likelihood method was for the first time employed in the material balancing of non-normally distributed data and compared with the well-known Least Squares method -- This was an original integration of geostatistical methods with data reconciliation to quantify and predict measurement uncertainties. -- For the first time, measurement uncertainties were modeled with a distribution that was non-normal and bounded in nature, leading to smaller adjustments / AFRIKAANSE OPSOMMING: Die groeiende behoefte aan rekeningkundige akkuraatheid, en om presisie te verbeter, en te standardiseer op algemeen aanvaarde meetmetodes in die mynbou en prosesseringsnywerhede, het gelei tot die samwewerking van 'n aantal van organisasies onder die AMIRA International sambreel, met die doel om bogenoemde behoeftes aan te spreek. As deel van hierdie onderneming, het Anglo Platinum onderneem om 'n projek op die materiaal balansering rondom sy grootste smelter, die Waterval smelter. Die primêre doel van die projek was om 'n statistiese materiaal balans rondom die Waterval smelter uit te voer deur gebruik te maak van die sogenaamde maksimum waarskynlikheid metode met betrekking tot platinum, rodium, nikkel, swawel en chroom (iii) oxied. Pt, Rh en Ni was gekies vir hul beduidende bydrae tot die maatskappy se winsmarge, terwyl S ingesluit was weens sy belangrike omgewingsimpak. Cr2O3 was ingesluit weens sy impak op die smelting van Platinum groep minerale. Die doelstelling was bereik deur die uitvoering van 'n reeks van statistiese berekeninge. Hierdie sluit in: die kwantifisering van die totale en analitiese variansies, opsporing van uitskieters, beraming en modellering van daaglikse en maandelikse metingsvariansies, parameter beraming en data rekonsiliasie. Vergelykings was getref tussen die maksimum waarskynlikheid en kleinste kwadrate metodes. Totale onsekerhede of variansies geassosieer met die daaglikse grade was bepaal deur ’n Variografiese studie. Die beraamde Pt standaard afwykings was binne 10% relatief tot die onderskeie gemiddelde grade met sommige uitsonderings. Die totale onsekerhede was onderverdeel in hul onderskeie komponente deur bepaling van die ontledingsvariansies van duplikate. Die uitslae toon dat die monsternemings komponente van die totale onsekerheid oor die algemeen groter was as hul bypassende analitiese variansies. WCM, ‘n platinum-ryke Waterval Smelter produk, het 'n onsekerheid in die orde van ~twee miljoen rand in sy daagliks Pt graad. Hierdie beraamde waarde toon dat die kwaliteit van metings nie alleen die akkuraatheid van metaal rekeningkunde affekteer nie, maar aansienlike finansiële implikasies het indien nie die nie gekwantifiseer en bestuur word nie. Die daagliks onsekerhede was beraam deur gebruik te maak van “Kriging” en “Bootstrap” metodes om die maandelikse onsekerhede te beraam. Verspreidings was gepas deur gebruik te maak van hoogste waarskynlikheid beraming passings en goedheid–van-pas toetse was uitgevoer. Die data was gepas met Normaal en Beta verspreidings, en daar was 'n opmerklike vermindering in die skeefheid van die daaglikse tot die maandeliks data. Die rekonsiliasies van die massabalans data was uitgevoer deur die gebruik die maksimum waarskynlikheid metodes en vergelyk daardie met die algemeen gebruikde kleinste kwadrate metode. Die maksimum waarskynlikheid (ML) en kleinste kwadrate (LS) aanpassings was uitgevoer op gesimuleerde data ten einde die akkuraatheid te toets en om die mate van fout vermindering na die rekonsiliasie te bepaal. Die toets getoon dat die twee metodes het vergelykbare akkuraathede en foutverminderingsvermoëns. Dit was egter getoon dat modellering van die onsekerhede met die onbegrensde Normaal verdeling lei tot die beraming van aanpassings wat so groot is dat negatiewe verstelde waardes kan onstaan na rekosniliasie. Die voordeel om onsekerhede met 'n begrensde distribusie te modelleer, soos die beta distribusie in hierdie geval, is dat die moontlikheid om negatiewe verstelde waardes te verkry uitgelsuit word. ML-verstelde waardes (met die Beta distribusie funksie) sal altyd nie-negatief wees, en om hierdie rede uitvoerbaar. In 'n verdere vergelyking van die ML (begrensd) en die LS metodes in die materiaal balansering van die waterval smelter kompleks, is dit gevind dat vir almal daardie strome waarvan die onserkerhede gesimuleer was met 'n Beta distribusie, dus daardie strome waarvan die onsekerheidsdistribusie ‘n mate van skeefheid toon, die ML verstellings altyd beduidend kleiner was as die ooreenkomstige LS verstellings. Vervolgens word die Maksimum Waarskynlikheid metode (met begrensde modelle) gesien as 'n beter alternatiewe metode van data rekosiliasie in vergelyking met die kleinste kwadrate metode met die voordele van: • Beter beramings te danke aan die feit dat die aard van die onsekerheidsdistribusie nie aangeneem word nie, maar bepaal is deur die distribusie te pas en deur van parameter beraming gebruik te maak. • Die aangepaste waardes kan nooit negatief wees te danke aan die begrensde aard van die verdeling. Die volgende oorspronklike bydraes is gelewer in hierdie verhandeling: • Die Maksimum Waarskynlikheid metode was vir die eerste keer geëvalueer vir massa balans rekonsiliasie van nie-Normaal verspreide data en vergelyk met die bekendde kleinste kwadrate metode. • Dit is die eerste keer geostatistiese metodes geïntegreer is met data rekonsiliasie om onsekerhede te beraam waarbinne verstellings gemaak word. • Vir die eerste keer, is meetonsekerhede gemoddelleer met 'n distribusie wat nie- Normaal en begrensd van aard is, wat lei tot kleiner en meer realistiese verstellings.

Το ηλεκτροπαραγωγικό δυναμικό της ΔΕΗ περιλαμβάνει άνω των 40 πετρελαϊκών σταθμών συνολικής ισχύος 2100MW και οι μεγαλύτεροι είναι του διασυνδεδεμένου συστήματος και λειτουργούν στο Λαύριο και το Αλιβέρι. Οι υπόλοιποι λειτουργούν στο αυτόνομο σύστημα των νησιών του Αιγαίου και Κρήτης. Κατά τους καθαρισμούς των προθερμαντών αέρος και των δεξαμενών μαζούτ των μονάδων αυτών παράγονται σήμερα άνω των 500t στερεών καταλοίπων ετησίως με αυξητική τάση. Τα κατάλοιπα αυτά χαρακτηρίζονται σύμφωνα με την Ευρωπαϊκή οδηγία ως επικίνδυνα. Σύμφωνα με τους κανονισμούς της Ε.Ε. είναι υποχρεωτική η αδρανοποίησή τους και η διασφάλιση της ασφαλούς τους απόθεσης. Στα πλαίσια της παρούσας διατριβής πραγματοποιήθηκε πλήρης χαρακτηρισμός προεπεξεργασμένων και μη στερεών καταλοίπων. Προσδιορίστηκε ότι τα κατάλοιπα αυτά περιέχουν 1.6-13.4%V και 0.8-5.5%Ni, δηλαδή αποτελούν πολύ πλουσιότερες πρώτες ύλες από τα αντίστοιχα κοιτάσματα μεταλλευμάτων βαναδίου και νικελίου. Για παράδειγμα τα Ελληνικά νικελιούχα σιδηρομεταλλεύματα που καμινεύονται στη Λάρυμνα έχουν περιεκτικότητα μόλις 0.93-1.02% σε νικέλιο. Δεν ανιχνεύθηκε οργανικό φορτίο στα κατάλοιπα και το βανάδιο εντοπίστηκε σ’ αυτά στη μορφή VO2. Βασικός στόχος της διατριβής ήταν η ανάπτυξη μεθόδου, που να συνδυάζει την αδρανοποίηση των καταλοίπων με την ανάκτηση των περιεχόμενων μετάλλων. Η μέθοδος περιλαμβάνει και στάδιο πυροσυσσωμάτωσης των ανεπεξέργαστων καταλοίπων, στοχεύοντας στη συσσωμάτωση και εμπλουτισμό τους στα πολύτιμα κραματικά μέταλλα. Εξασφαλίζεται παράλληλη αποθείωση, απανθράκωση και ξήρανσή τους. Τα συσσωματώματα περιέχουν μέχρι και 6.0% Ni και 14.7% V, δηλαδή επιτυγχάνεται ο εμπλουτισμός τους κατά 8% σε Ni και κατά 10% σε V, με ταυτόχρονη απομάκρυνση θείου και άνθρακα σε ποσοστά 73 και 85% αντίστοιχα. Η πυροσυσσωμάτωση λειτουργεί ως αυτογενής διεργασία με την πλήρη ενεργειακή εκμετάλλευση της χημικής ενέργειας του άνθρακα και του θείου. Αποτελεί δε ταυτόχρονα το πρώτο βήμα για την ανάκτηση των περιεχόμενων μετάλλων. Συνακόλουθα, η εξασφάλιση ασφαλούς απόθεσης των αδρανοποιημένων και iii εμπλουτισμένων στα πολύτιμα μέταλλα καταλοίπων δίνει τη δυνατότητα δημιουργίας σοβαρού αποθέματος σωρεύοντας υλικό από το εσωτερικό αλλά και εισάγοντας παρόμοιου τύπου κατάλοιπα από ομοειδή εργοστάσια του εξωτερικού. Έτσι μια μεταλλουργική μονάδα ανάκτησης των μετάλλων θα μπορεί να εξασφαλίζει τη λειτουργία της με οικονομικότητα. Η εκτίμηση των επιπτώσεων της υπαίθριας απόθεσης των μελετούμενων στερεών αποβλήτων και των πυροσυσσωματωμάτων αποτελεί αδήριτο ανάγκη. Προς τούτο πραγματοποιήθηκε προσομοίωση της διεργασίας της έκπλυσής τους από τα όμβρια ύδατα. Το μοντέλο με την υπόθεση του μη αντιδρώντος πυρήνα, φαίνεται να περιγράφει με επαρκή ακρίβεια τη διεργασία. Οι σταθερές και ο πλήρης μηχανισμός του μοντέλου προσδιορίσθηκαν και επιβεβαιώθηκαν πειραματικά. Κατά την έναρξη της διεργασίας φαίνεται ότι η χημική αντίδραση αποτελεί το ρυθμορυθμιστικό βήμα για τη μεταφορά των μετάλλων στην υγρή φάση. Με την πρόοδό της έκπλυσης ελέγχεται από φαινόμενα διάχυσης. Την πρακτική εφαρμογή των μοντέλων που καταστρώθηκαν αποτέλεσε η πρόβλεψη των μακροχρόνιων επιπτώσεων της υπαίθριας απόθεσης των ανεπεξέργαστων και πυροσυσσωματωμένων καταλοίπων. Φάνηκε ότι απαιτείται μεγάλο χρονικό διάστημα, κατ’ ελάχιστο 10 έτη για την μείωση των συγκεντρώσεων των μετάλλων σε επιτρεπτά επίπεδα στον υδροφόρο ορίζοντα. Το τελευταίο στάδιο της προτεινόμενης μεθόδου περιλαμβάνει την αναγωγική τήξη των καταλοίπων. Πραγματοποιήθηκε σειρά πειραματικών χυτηρίων σε χωνευτήριο γραφίτη σε κάμινο Tammann. Μελετήθηκε η διεργασία αναγωγής των μεταλλοξειδίων καθώς και προσδιορίσθηκε η θερμοδυναμική ισορροπία των ετερογενών δράσεων μεταξύ ρευστής σκωρίας και μετάλλου σε θερμοκρασίες 1375-1600οC. Προσδιορίσθηκαν πειραματικά οι θερμοδυναμικές συναρτήσεις ισορροπίας για τα μεταλλοξείδια του βαναδίου, σιδήρου και νικελίου. Τα πειραματικά χυτήρια έδωσαν τελικούς βαθμούς ανάκτησης μετάλλων 85-98% για το Ni και 78-95% για το V, με παράλληλη παραγωγή αδρανοποιημένης σκωρίας κατάλληλης για απόθεση ή άλλες χρήσεις. Οι συνθήκες οι οποίες μεγιστοποιούν τις ανακτήσεις των Ni και V όπως έδειξαν οι πειραματικές δοκιμές είναι:  υψηλές θερμοκρασίες  χρήση χωνευτηρίου γραφίτη iv  προσθήκη σιδηροπυριτίου ως αναγωγικού μέσου Αντίθετα από την επικρατούσα άποψη, αποδείχθηκε, ότι επιτυγχάνονται υψηλοί βαθμοί ανάκτησης σε υψηλά επίπεδα βασικότητας CaO/SiO2>2, κάτι, που εξασφαλίζει την πυρίμαχη επένδυση της καμίνου και την περαιτέρω χρήση της παραγόμενης σκωρίας. Εναλλακτικά, μελετήθηκε και η απευθείας αναγωγική τήξη των φυσικοχημικά προεπεξεργασμένων καταλοίπων. Σημαντικό είναι το εύρημα, ότι η προσθήκη βωξίτη βοημιτικού τύπου σε μικρά ποσοστά προσθηκών μέχρι 10% δρα ενισχυτικά στις ανακτήσεις του νικελίου και του βαναδίου με βαθμούς ανάκτησης άνω του 98%. Διερευνήθηκαν επίσης η κινητική της αναγωγής των οξειδίων του σιδήρου και του βαναδίου από την σκωρία στο λουτρό σιδήρου και προσδιορίστηκαν οι αντίστοιχες σταθερές και τα ρυθμορυθμιστικά βήματα. Συνολικά, προτείνεται μια ολοκληρωμένη μέθοδος ανακύκλωσης των στερεών καταλοίπων πετρελαϊκών σταθμών παραγωγής ενέργειας σε συνδυασμό με υψηλότατους βαθμούς ανάκτησης των περιεχόμενων σε αυτά πολύτιμων κραματικών στοιχείων νικελίου και βαναδίου αποφεύγοντας την εξουδετέρωσή τους με ακριβές μεθόδους αδρανοποίησης. Με αυτόν τον τρόπο εξασφαλίζεται η εξουδετέρωση των επικίνδυνων αυτών υλικών με σημαντικά οικονομικά οφέλη από την ανάκτηση των μετάλλων. / The power generating installations of P.P.C. include m ore than 40 oil-fired power stations of about 2100MW total capacity. The mos t important stations are those of the interconnected system that ope rate in L avrio and Aliv e ri. The rest operate in the autonom ous system of the A eg e an islands and Cre te . M ore than 500t of solid w aste s are produce d annually during the w ashing proce sses of the air pre -he aters and the crude oil tanks of the aforementioned units w ith increasing te nden cy. These residue s are classifie d as hazardous according to the Europe an directive s. The ir neu tralizati on and safe de position is c om pulsory according to the E.U. re gulations. In the current the sis, complete characte rization of pretre ate d and untre ated re sidues was carried out. It w as found that the re sidues exa mined contained 1.6-13.4 %V and 0.8-5.5%Ni, being the refore a conside rably richer raw material than the vanadium and nickel ore deposits. For instance, the H elle nic nicke lferrous ore s, that are smelted in L arym na contain only 0.93-1.02% Ni. No organic compounds w ere de te cte d in the re sidues and the presence of vanadium was identified as VO 2. The fundam ental task of the thesis w as the de ve lopment of a method that com bine s the neutralization of the re sidue s with the recovery of the me tals containe d. The propose d me thod includes also a sinte ring stage of the untre ated residues, aiming at their agg lom e ration and e nrichm e nt in the pre cious alloying metals. The re sidues de sulphurization, de carburization and drying is achieved sim ultaneously. The sinter products contain up to 6.0% Ni and 14.7 % V, sugge sting that en richment of 8% in N i and 10 % in V w as achiev ed, with simultaneous loss of sulphur and carbon in the rates of 73 and 85% respe ctive ly. S inte ring, acts as an indigen ous process with total exploitati on of the che mical en e rgy of carbon and sulphur. It also rep re sents the first ste p for the re covery of the m etals containe d in the residues. Mo reov e r, provided the safe depo sition of the neutralize d and en riche d in valuable m e tals re sidue s, it is possible to ge ne rate a significant stock by piling m aterial from the indige nous sou rce s and imports of such residues. Thus a me tallurgical unit of m e tals re covery could operate at profit. The e valuation of the effects of the ground disposal of the investigate d solid re sidue s and sinte r produ cts is a mus t. The simulation of their le aching by rainfall wa s thus vii conducted. The hypothesis of the unreacted core mode l see ms to describe the proce ss ade que ntl y. The mode l constants and its complete m e chanism we re de te rmined and confirm ed expe rimentall y. Initially chem ical re action se ems to be the rate-de te rmining ste p for the transfe r of me tals in the liquid phase. W ith the e lution prog re ss the me chanism is controlled by diffusion phenomen a. The prediction of the long -te rm effects of the ground de position of the untre ate d and sinte red residue s w as att empted by applying the sugge sted models . It was shown that substantia l amount of time, 10 ye ars minim um, is ne e de d for the drop of the m e tals conce ntrations in the leachate to allowa ble lev e ls. The final stage of the proposed method contains the red uction smelting of the re sidues. A serie s of tests w as conducted in graphite crucibles in Tam mann furnace. The metal oxides re duction proce ss w as investi gated and the the rmod ynamic equilibrium of the hete rogen e ous actions betw e en liquid slag and me tal w as de te rmined in tempe ratures ranging from 1375 to 1600 oC. The therm od ynam ic equilibria functions conce rning the nickel, vanadium and iron oxides w ere exper ime ntally dete rmined. The e xpe rimental test heats yie lded final me tals recove ry rates of 85-98% for Ni and 78-95% for V , with simultaneous production of ne utralized slag suitable for deposition or othe r usage . The conditions that ma ximize the Ni and V re cove ries according to the expe rime ntal findi ngs we re:  the high tempe ratures  the use of graphite crucible  the Fe S i addi tions as re ductant In contrast to the dominating opinion, it w as shown that high rec ove ry rate s w e re achieved in high basicity rates of CaO/Si O 2>2, ensuring the re fractory lining of the furnace and the furthe r use of the produced slag. Alternatively, the direct re duction smelting of the physicochemic ally pretre ated re sidues was inve stigated. The finding that the small a dditions up to 10 % of boe hm itic type of bauxite improve the rec ove ries of nickel and in rate s highe r than 98% is ve ry important. The kinetics of the redu ction of iron and vanadium oxide s from the slag to the iron bath w ere also inve sti gate d and the corresponding constants and rate de te rmining ste ps we re de te rmined. viii A holisti c method of recycling the solid residue s of the oil-fire d stati ons is propose d The propose d me thod, in addition to high re cove ry rate s of the valuable alloying eleme nts containe d (nickel and vanadium) avoids the re sidue s treatment with expe nsive neutralization me thods. Mo reov e r, the ne utralization of these hazardous ma terials is achiev ed w ith substantial financial profit from the me tals re cove ry at the same time.

In this thesis I focus on mining and smelting in China during the Shang and Western Zhou periods (c. 2200-770 B.C.). The importance of bronze in Shang and Zhou society and the vast quantity of bronze artifacts recovered indicates that the acquisition of metal ore would have been a major occupation of the state. The Shang and Zhou governments controlled their own bronze foundries but did not control the mines. The mines are located in southern China where the Chu state flourished during the Eastern Zhou period, likely due partly to their possession of mineral resources, and in Inner Mongolia where the steppe cultures existed. The Zhou and the Shang were likely obtaining raw materials from southern and northern cultures, either through trade or raid. Provenance studies based on chemical composition of artifact and ore will help resolve the source of Shang and Zhou ore.

Mémoire(M.Eng.)-- Université du Québec à Chicoutimi, 2002. / Document électronique également accessible en format PDF. CaQCU

This study focused on the dynamic behaviour of the freeze lining and slag bath, and the interactions between these components in an ilmenite-smelting furnace process. The purpose of the work was to gain a better understanding of these issues and to ultimately contribute to an improved understanding of the ilmenite-smelting process in its entirety, and to future improvements in the design, operation and control of these processes. A mathematical model of the freeze lining and furnace sidewall was developed. This model was used in isolation for focused characterisation of the dynamic behaviour and interactions of the freeze lining and slag bath. The influences of net power input and slag composition were studied and various aspects of the freeze lining and slag bath were considered. These aspects included freeze lining thickness, temperature distribution through the freeze lining and furnace sidewall, composition distribution through the freeze lining, slag bath temperature and slag bath composition. The thermal response of thermocouples installed in the furnace sidewall to changing conditions on the inside of the furnace was also investigated. A mathematical model of the crust that forms on the slag bath surface was developed. This model was not used in isolation, and was only incorporated into a complete model of the process. A mathematical model of the entire ilmenite-smelting furnace process was constructed. This model incorporated the two models mentioned above and was able to describe the metal bath, slag bath, furnace atmosphere, freeze lining, furnace sidewall and the crust that is sometimes present on top of the slag bath. The model was used to study the influence of changes in operational parameters on the slag bath and freeze lining. The operational parameters that were studied included electrical power and reductant feed rate, both relative to ilmenite feed rate. The influence of severe operational errors and furnace down time were also investigated. Operational errors included loss of all feed while maintain electrical power input, and loss of reductant feed while maintaining power input and ilmenite feed. The above-mentioned studies were conducted by executing numerous experiments with two of the mathematical models. The experimental results were processed into sets of graphs displaying variations in the aspects that were considered. Many valuable insights resulted from the interpretation of these results. One specific aspect that formed part of the scope of this work was the origin of the compositional invariance of the slag close to the stoichiometric M3O5composition. This invariance was studied and a mechanism was proposed that explains the observed behaviour. The proposed mechanism created some questions about other mechanisms in the process. These mechanisms were also considered and elaborated on. The models and results produced in this study provide valuable insights into the behaviour of the ilmenite-smelting process. It also represents a useful foundation for future modelling work, and finally, it presents numerous opportunities for organisations operating ilmenite-smelting furnaces to improve their understanding and even the performance of their processes. / Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2004. / Materials Science and Metallurgical Engineering / unrestricted