Thesis (Ph.D.(Materials Science & Metallurgical Engineering))--University of Pretoria, 2009. / Abstract in English. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Pyrrhotite (Fe(1-x)S) is one of the most commonly occurring metal sulfide minerals and is recognised in a variety of types of ore deposits. Since the principal nickel ore mineral, pentlandite, almost ubiquitously occurs with pyrrhotite, the understanding of the behaviour of pyrrhotite during flotation is of fundamental interest. For many nickel processing operations, pyrrhotite is rejected to the tailings in order to control circuit throughput and concentrate grade and thereby reduce excess sulfur dioxide smelter emissions. For the platinum group element processing operations however, pyrrhotite recovery is targeted due to its association with the platinum group elements and minerals. Therefore, the ability to be able to manipulate pyrrhotite flotation performance is of importance. It can be best achieved if the mineralogical characteristics of the pyrrhotite being processed are known and their relationship to flotation performance is understood. Pyrrhotite is known to naturally occur in different forms that have varying physical and chemical attributes. These different pyrrhotite forms are commonly known as magnetic (Fe7S8) and non-magnetic pyrrhotite (Fe9S10, Fe10S11, Fe11S12) and as a result of their varying properties are expected to show some difference in their reactivity towards oxidation and flotation performance. Yet the accounts in the literature are inconsistent as to which of the pyrrhotite types is more reactive. Similarly, there appears to be little agreement in the literature as to which of the pyrrhotite types is more floatable. It is probable that this lack of agreement arises from the fact that previous studies have not given due consideration to the effect of the mineralogy of the samples examined. The success of the discipline of process mineralogy as a whole however, has been to gain an understanding of how the mineralogy of an ore affects its processing properties. The objective of this process mineralogy study was to develop the relationship between pyrrhotite mineralogy and flotation performance based on a thorough characterisation of pyrrhotite from selected nickel and platinum group element ore deposits in terms of their crystallography, mineral association, mineral chemistry and mineral reactivity. This was achieved through the characterisation of the mineralogy and mineral reactivity of pyrrhotite samples obtained from the Sudbury ore in Canada, Phoenix ore in Botswana and the Merensky Reef and Nkomati ores in South Africa. Based on the linkage of these characteristics to flotation performance, an understanding of the relationship and mechanisms that cause pyrrhotite mineralogy to influence pyrrhotite flotation performance has been gained. Mineralogical characterisation of the pyrrhotite samples in this study was performed using ore petrography, x-ray diffraction and mineral chemistry analysis. On the basis of these results pyrrhotite samples were classified as: single phase magnetic 4C Fe7S8 pyrrhotite, single phase non-magnetic 5C Fe9S10 pyrrhotite; two phase magnetic 4C Fe7S8 pyrrhotite intergrown with non-magnetic 5C Fe9S10 pyrrhotite and as two phase non-magnetic 6C Fe11S12 pyrrhotite intergrown with 2C FeS troilite. Nickel was identified as the main trace element impurity in the pyrrhotite structure and the amount of solid solution nickel in the pyrrhotite structure was correlated with whether the pyrrhotite was magnetic or non-magnetic, and whether it coexisted with another pyrrhotite phase. All pyrrhotite samples investigated showed a strong association to pentlandite that occurred in both granular and flame pentlandite forms. These key features of pyrrhotite mineralogy were in turn shown to be controlled by the bulk composition and cooling history of the monosulfide solid solution (MSS) from which pyrrhotite is derived. The reactivity of the different pyrrhotite samples towards oxidation was determined using open circuit potential, cyclic voltammetry and oxygen uptake measurements at both pH 7 and 10. Non-magnetic Sudbury Copper Cliff North pyrrhotite was the most unreactive of the samples examined, whereas magnetic Sudbury Gertrude West pyrrhotite was the most reactive. The magnetic Sudbury Gertrude West pyrrhotite was so reactive that open circuit potential and oxygen uptake measurements showed it was already passivated and likely covered with hydrophilic ferric hydroxides. The magnetic Phoenix pyrrhotite was slightly less reactive than the magnetic Sudbury Gertrude West pyrrhotite. The reactivity of the Nkomati Massive Sulfide Body (MSB) mixed pyrrhotite was in between that of the non-magnetic Sudbury Copper Cliff North and magnetic Phoenix pyrrhotite, due to the combined contribution of intergrown magnetic and non-magnetic pyrrhotite to its reactivity. The flotation performance of the different pyrrhotite samples was investigated at both pH 7 and 10 using microflotation tests. A variety of different reagent conditions was also investigated that included the use of different chain length xanthate collectors (sodium isobutyl xanthate (SIBX), sodium normal propyl xanthate (SNPX)) and the use of copper activation. The collectorless flotation of the non-magnetic Sudbury Copper Cliff North pyrrhotite was the greatest of the samples investigated. Only with the addition of flotation reagents were differences in the floatability of the other pyrrhotite samples identified. Magnetic Phoenix pyrrhotite showed good flotation performance whereas the flotation performance of the magnetic Sudbury Gertrude and Gertrude West pyrrhotite was very poor. The Nkomati MSB mixed pyrrhotite only showed good flotation performance at pH 7. All pyrrhotite samples generally showed improved flotation performance with the use of the longer chain length SIBX collector than the shorter chain length SNPX, whereas the efficiency of copper activation was influenced by pyrrhotite mineralogy, pH and collector chain length. Differences in the flotation performance of the pyrrhotite samples investigated were linked to their reactivity towards oxidation. Although not directly measured, the formation of hydrophilic ferric hydroxides on pyrrhotite surfaces due to oxidation was inferred as the reason for the poor flotation performance of some of the pyrrhotite samples. Key features interpreted to influence both pyrrhotite reactivity and flotation performance were pyrrhotite crystallography, mineral chemistry and mineral association. It has been proposed that differences in the amount of vacancies in the pyrrhotite crystal structure influence the oxidation rate and similarly the greater proportion of ferric iron in the magnetic pyrrhotite structure was argued to account for its greater reactivity relative to non-magnetic pyrrhotite. Differences in the solid solution nickel content and trace oxygen in the pyrrhotite structure were also proposed as additional characteristics influencing pyrrhotite oxidation rate and flotation performance. Depending on the degree of association of pyrrhotite to pentlandite, its flotation performance could be affected by the liberation characteristics and flotation of composite particles containing abundant locked flame pentlandite, although this could be manipulated by changing the grind size. The presence of nickel ions derived from the flame pentlandite in these composite particles could also assist in the activation of pyrrhotite and further improvement of its flotation performance. Some guidelines are also presented as to which simple mineralogical and mineral reactivity measurements have been of the most use in developing the relationship between mineralogy and flotation performance. / Thesis (DPhil)--University of Pretoria, 2009. / Materials Science and Metallurgical Engineering / unrestricted

M.Sc. (Chemistry) / Please refer to full text to view abstract

16 samples of increasing metamorphic grade from the Ballachulish Igneous Complex and Aureole, located in the west of Scotland, were studied in order to analyze the sulfide mineralogy and to what extent they were affected by contact metamorphism. The samples were collected from two lithologies, the Creran Succession and the Ballachulish Slate lithology, as well as from the igneous complex. The sulfides of main interest in the samples are pyrite and pyrrhotite. At the onset of contact metamorphism, pyrite disappears while pyrrhotite gets more abundant as metamorphic grade increases. Pyrrhotite also undergoes multiple changes such as 1) elongation and thinning of the grains, 2) development of 120° grain-boundaries, 3) development of pyrite-zones within the pyrrhotite and 4) the decomposition of pyrrhotite and alignment of pyrite along its grain-boundaries at high temperature. The elongation of the grains occurs in both the Creran Succession and the Ballachulish Slate. The rest of the textures, however, can only be found in the Creran Succession. The two lithologies differ by the high graphite content in the Ballachulish Slate. The elongated grains as well as the pyrite inclusions in the pyrrhotite both are strong evidence of recrystallization. The absence of pyrite in the Ballachulish Slate was most probably caused by the buffering properties of the graphite-rich fluid in these rocks, causing more reducing conditions. There is evidence against a heavy, pervasive fluid flow through the aureole. However, the inner contact zone seems to have been affected by a more pronounced fluid flow. This could have been caused by the metamorphic fluid working in conjunction with fluids released from the intrusion. Regarding the mobility of S in the aureole, no strong evidence could be found, other than the decomposition of pyrrhotite grain-boundaries in the high-grade metamorphic samples.

M.Sc. (Geology) / Please refer to full text to view abstract

Zinkgruvan is a stratiform Zn-Pb-Ag deposit located in the Bergslagen ore district in south central Sweden. Elevated concentrations of cobalt have been detected in zinc ore from the mine. Cobalt is one of EU’s critical raw materials, since cobalt is mainly mined in politically unstable countries like Congo and is an important metal needed in batteries for modern technology, e.g., electrical cars. However, elevated contents of cobalt can also cause problems during smelting of zinc ore and lower the value of zinc concentrates. Knowledge of the mineralogical deportment of cobalt is in this context critical, since accessory cobalt minerals could potentially be separated from zinc concentrates, whereas lattice-bound cobalt in sphalerite will follow the latter throughout the processing chain. In this study, the mineralogical distribution in zinc ore from three different main areas of Zinkgruvan (Knalla, Nygruvan and Westfield) has been investigated using optical microscopy, whole rock lithogeochemistry, Scanning Electron Microscope (SEM), Electron Microprobe Analysis (EMPA), Quantitative Target Mineralogy (QanTmin) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The different datasets have been integrated in order to provide quantitative data on cobalt deportment in the samples, and for defining geochemical proxies that can be used to predict the cobalt deportment using only whole rock assay data. For the majority of the samples of this study, the cobalt content in sphalerite is higher than what has been reported in earlier studies of Zinkgruvan and are among the highest globally. In addition, this study provides the first account of high levels of lattice-bound cobalt in pyrrhotite at Zinkgruvan, for some samples being even higher than in sphalerite. Thus, the pyrrhotite could also potentially be separated from the zinc concentrate in order to dispose of some of the cobalt in the samples.  However, for the samples on which cobalt deportment calculations have been made, the results of the calculations suggest that for 50% of the samples most of the whole rock cobalt is lattice-bound to sphalerite, which is by far the predominant mineral in the zinc ore. For the remaining 50% of the samples most of the whole rock cobalt is bound to the cobalt mineral safflorite, which locally forms an important accessory mineral. No sample has the majority of the whole rock cobalt in pyrrhotite, reflecting the generally minor contents of this mineral in the zinc ore. In general, there is more lattice-bound cobalt in pyrrhotite and sphalerite in samples from Westfield and more cobalt bound to cobalt minerals in samples from Knalla. Samples from Nygruvan have very low whole rock cobalt contents altogether and contain no cobalt minerals. These spatial variations support ore genetic zonation models presented by earlier studies, with increasing Zn/Pb ratios and decreasing cobalt content in zinc ore from proximal to distal, in relation to an old hydrothermal vent zone at Knalla. However, the high cobalt and cadmium contents found at Westfield could imply that the vent zone might be more widespread than assumed by earlier studies. / Zinkgruvan är en stratiform Zn-Pb-Ag-malmförekomst som ligger i malmdistriktet Bergslagen i södra Sverige. Förhöjda koncentrationer av kobolt har upptäckts i zinkmalmen från gruvan. Kobolt är en av EU:s kritiska råmaterial eftersom kobolt främst bryts i politiskt instabila länder som t.ex. Kongo och eftersom det är en viktig metall som behövs i batterier för modern teknik, exempelvis elbilar. Förhöjda halter av kobolt kan dock också orsaka extra kostnader och försämrat utbyte vid zinkframställning från zinkmalm, och kan därmed sänka en zinkmalms värde. Kunskap om den mineralogiska fördelningen av kobolt i zinkmalmen är i detta fall avgörande, eftersom accessoriska koboltmineral potentiellt skulle kunna avlägsnas innan smältprocessen, till skillnad från gitterbunden kobolt i zinkblände som följer med zinken i hela utvinningsprocessen. I denna studie har den mineralogiska distributionen i zinkmalm från tre olika huvudområden i Zinkgruvan (Knalla, Nygruvan och Västra fältet) undersökts genom användning av optisk mikroskopering, geokemisk analys av bulkprover, svepelektronmikroskopi (SEM), elektronmikrosondanalys (EMPA), kvantitativ mineralogi (QanTmin) och laserablation-induktivt kopplad plasma-masspektrometri (LA-ICP-MS). De olika dataseten har integrerats för att tillhandahålla kvantitativa data för koboltfördelning i proverna och för att kunna definiera geokemiska kriterier som kan användas för att förutsäga koboltfördelningen med hjälp av endast litogeokemisk analysdata. För majoriteten av proverna i denna studie är koboltinnehållet i zinkblände högre än vad som har rapporterats i tidigare studier av Zinkgruvan, och är bland de högsta globalt. Dessutom tillhandahåller denna studie den första redogörelsen för höga nivåer av gitterbunden kobolt i magnetkis. För vissa prover är det sistnämnda till och med högre än i zinkblände. Således skulle även magnetkisen potentiellt kunna separeras från zinkkoncentratet för att bli av med en del av kobolten i proverna. För de prover där beräkningar på koboltfördelningen har gjorts visar dock resultaten av beräkningarna att för 50% av proverna förekommer merparten av bulkinnehållet av kobolt i malmen som gitterbundet i zinkblände, vilket är det överlägset dominerande mineralet i zinkmalmen. För de resterande 50% av bulkproverna är det mesta av kobolten bundet till koboltmineralet safflorit, som lokalt är ett viktigt accessoriskt mineral. Inget bulkprov har merparten av koboltinnehållet i magnetkis, vilket reflekterar det generellt lägre innehållet av detta mineral i zinkmalmen. I allmänhet finns det mer gitterbunden kobolt i magnetkis och zinkblände i bulkprover från Västra fältet och mer kobolt bundet till koboltmineral i bulkprover från Knalla. Bulkproverna från Nygruvan har väldigt lågt koboltinnehåll överlag, och innehåller inga koboltmineral. Dessa spatiala variationer stödjer malmgenetiska zoneringsmodeller presenterade i tidigare studier, med ökande Zn/Pb kvoter och minskande koboltinnehåll i zinkmalmen från proximal till distal, i relation till en fossil hydrotermal tillförselkanal i Knalla.  Det höga kobolt- och kadmiuminnehållet som detekterats i Västra fältet kan dock antyda att den hydrotermala tillförselkanalen skulle kunna vara mer utbredd än vad som antagits av tidigare studier.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 95-99. / by Simon Muir Peacock. / M.S.

Ce travail concerne l’évaluation par méthodes non destructives (ND) de l’endommagement du béton associé à l’oxydation des sulfures de fer présents dans les granulats. Plus spécifiquement, ce projet a été réalisé dans le cadre des problèmes de dégradation précoce de fondations résidentielles relevés dans la région de Trois-Rivières. Ce projet de maîtrise vise à valider les essais ND réalisés pour la caractérisation des phénomènes de dégradation, ce qui va permettre de donner une nouvelle approche à la caractérisation ND du béton endommagé par l’oxydation des sulfures de fer. Quatre méthodes ND ont été évaluées afin de quantifier le niveau d’endommagement et faire un suivi de l’évolution de la réaction d’oxydation : vitesses ultrasonores en mesure directe, vitesses ultrasonores en mesure indirecte, impact-écho, acoustique non linéaire (technique du saut temporel). Le programme expérimental a été effectué en trois volets. Le premier volet consiste à réaliser un suivi sur des blocs prélevés à partir de murs de fondation (4 séries de S blocs) et de murs mitoyens (1 série de 5 blocs) de maisons affectées par le problème et ayant des niveaux visuels de dégradation variant entre 0 (faible) et 3 (très élevé), respectivement. Ces blocs ont été placés sur un site d’exposition extérieure à Trois-Rivières. Dans le deuxième volet, un programme de carottage consistait à retirer cinq carottes de chaque série de blocs/année, de même que trois carottes de trois niveaux différents (de la base au sommet de la fondation) dans deux maisons sélectionnées. Des essais de résonance (non linéaire), mesure directe (UPV) et mesure indirecte (linéaire) ont été réalisés sur toutes les carottes. Le troisième volet, en collaboration avec l’IREQ, consistait à réaliser des essais ND sur des blocs de béton fabriqués à l’IREQ. Ces blocs sont caractérisés par différentes formulations (dosage en ciment, e/c) et l’utilisation de granulats réactifs (type Trois-Rivières) et non réactif (contrôle). Les résultats obtenus au cours de cette recherche ont montré une diminution significative des vitesses de propagation au cours de la période d’essai (mai 2011 - 2012) sur les blocs prélevés des murs de fondation à Trois-Rivières (blocs B, C, D et E). Cependant, aucun changement n’a été détecté au niveau de la série de blocs prélevés du mur mitoyen (blocs A) puisque ces derniers n’avaient pas commencé à se détériorer. Les résultats obtenus sur les carottes prélevées à partir des blocs de fondation indiquent des degrés de dégradation similaires à ceux des blocs. Les carottes prélevées d’une des maisons présentent un gradient de dégradation, (i.e. dégradation plus élevée dans la partie supérieure exposée aux intempéries des murs de fondation). Cet écart entre les 2 maisons n’a pu être expliqué à ce jour. De même, les essais destructifs sur les carottes (résistance à la compression uniaxiale et traction indirecte) ont montré une bonne corrélation avec les essais ND sur site. Aucun changement n’a été enregistré dans la vitesse de propagation des blocs de l’IREQ sur une période de 6 mois, ce qui est logique compte tenu de leur jeune âge. Cette étude par caractérisation ND, menée sur des bétons endommagés par l’oxydation sulfures de fer, a permis de porter un éclairage sur l’efficacité des méthodes ND au chantier et au laboratoire, en démontrant une différence de sensibilité de ces méthodes face au degré d’endommagement du béton.

Hydrometallurgical processing of sulphide concentrates is an attractive method for the selective extraction of valuable metals. The dissolution of minerals in a leaching process involves several electrochemical parameters that need to be investigated• to ensure the development and growth of the base metal industry in South Africa. A study has been carried out to elucidate the leaching mechanism of a nickel-coppercobalt sulphide concentrate in an oxidative pressure-acid medium. The sulphide concentrate studied in this research, comprises mainly of the minerals pyrrhotite, (Fe1_xS) with x = 0 to 0.2, pentlandite, (Ni,Fe)9S8 and chalcopyrite, (CuFeS2). The leaching behaviour of these minerals was successfully studied by means of Atomic Absorption (AA) measurements, Scanning '•Electron Microscopy (SEM) and Moss bauer spectroscopy, after leaching took place in an oxidative pressure-acid medium. The dissolution of the valuable metals was achieved effectively with recoveries of well over 90% for nickel, copper and cobalt under the specific conditions studied. Mechanical activation by means of ultra fine milling improved metal extraction with an average of approximately 40%, after a leaching period of 150 minutes. The most suitable conditions for the oxidative pressure-acid leaching of the mechanically treated nickel-copper-cobalt sulphide concentrate in a dilute sulphuric acid medium were found to be: particle size 80% - 10J.Lm; temperature l10°C; oxygen partial pressure 10 bar; sulphuric acid concentration 30 kg/ton; solids content 15% by mass and an impeller agitation rate of 800 r/min. The values of the apparent activation energies of nickel, copper and cobalt, extracted from the sulphide concentrate, were found to be 20.6 (± 4.4) kJ/mol K, 33.6 (± 4.2) kJ/mol K and 17.4 (± 3.5) kJ/mol K respectively. / Thesis (MIng (Chemical Engineering))--Potchefstroom University for Christian Higher Education, 2001