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.

<P> The occurrence of silver in galena, chalcopyrite, sphalerite, and pyrite as well as tailings from Cart Lake, Cobalt Ontario were investigated to compare with the undetectable ( <10^-11 g/g) Ag found in runoff water from the Cobalt area. </p> <p> Silver was detected at very low levels: 0.012 wt% ± 0.009 wt%, 0.015 wt% ± 0.01 wt%, and 0.0062 wt% ±0.02 wt% for pyrite, galena and chalcopyrite, respectively. </p> <p> Attempts to characterize the mineralogical associations of silver were not successful. The silver sequence of pyrite> galena> chalcopyrite is contrary to results from other studies. This may be due to the maximum thermal stabilities of the minerals in relation to the ions available for replacement. </p> / Thesis / Bachelor of Science (BSc)

The Mascot-Jefferson City zinc district of East Tennessee is the major source of zinc in the United States. Sphalerite mineralization which occurs as a breccia infilling in the Lower Ordovician Knox Group carbonates has been studied in detail at the Young Mine, located in the central portion of the district. The sphalerite occurs as fracture fillings and as rosettes between carbonate breccia blocks and displays well developed growth zoning characterized by variations in color, opacity, inclusions, and composition. Ore emplacement was preceded by two periods of solution brecciation. The first episode was related to a paleokarst terrain developed atop the Knox unconf orrni ty. The second episode was probably related to tectonic activity and expulsion of fluids from a sedimentary basin to the southeast. Episodic dolomitization in the vicinity of the ore bodies both predated and accompanied sphalerite deposition. Dolomite and other minor gangue phases deposited concurrently with sphalerite. Fluorite, calcite and quartz grew as postore, vug-filling phases. Sphalerite fluid inclusions reveal wide ranges in homogenization and freezing temperatures ( 81° to 199° C; -11.2° to -37.0° C) which may represent the mixing of two fluids--a hypersaline metal-rich brine with a less saline fluid resident in the host rocks. A geochemical model shows that Mg/Ca ratios and temperatures were such that dolomite was stable during ore deposition. Inclusions in post-ore gangue phases display an overall decrease in homogenization temperatures, are less saline, and show a narrower range of salinities. / M.S.

An atomic force microscope (AFM) has been used to conduct force measurements to better understand the role of hydrophobic forces in flotation. The force measurements were conducted between a flat mineral substrate and a hydrophobic glass sphere in aqueous solutions. It is assumed that the hydrophobic glass sphere may simulate the behavior of air bubbles during flotation. The results may provide information relevant to the bubble-particle interactions occurring during flotation. The glass sphere was hydrophobized by octadecyltrichlorosilane so that its water contact angle was 109 degrees. The mineral systems studied include covellite (CuS), sphalerite (ZnS) and hornblende (Ca₂(Mg, Fe)₅(Si₈O₂₂)(OH,F)₂). The collector used for all the mineral systems studied was potassium ethyl xanthate (KEX). For the covellite-xanthate system, a biopotentiostat was used in conjunction with the AFM to control the potential of the mineral surface during force measurements. This was necessary since the adsorption of xanthate is strongly dependent on the electrochemical potential (Eₕ) across the solid/liquid interface. The results show the presence of strong hydrophobic forces not accounted for by the DLVO (named after Derjaguin, Landau, Verwey and Overbeek) theory. Furthermore, the potential at which the strongest hydrophobic force was measured corresponds to the potential where the flotation recovery of covellite reaches a maximum, indicating a close relationship between the two. Direct force measurements were also conducted to study the mechanism of copper-activation of sphalerite. The force measurements conducted with unactivated sphalerite in 10⁻³ M KEX solutions did not show the presence of hydrophobic force while the results obtained with copper-activated sphalerite at pH 9.2 and 4.6 showed strong hydrophobic forces. However, at pH 6.8, no hydrophobic forces were observed, which explains why the flotation of sphalerite is depressed in the neutral pH regime. Direct force measurements were also conducted using hornblende in xanthate solutions to study the mechanism of inadvertent activation and flotation of rock minerals. The results show the presence of long-range hydrophobic forces when hornblende was activated by heavy metal cations such as Cu²⁺ and Ni²⁺ ions. The strong hydrophobic forces were observed at pHs above the precipitation pH of the activating cation. These results were confirmed by the XPS analysis of the activated hornblende samples. Force measurements were conducted between silanated silica surfaces to explore the relationship between hydrophobicity, advancing contact angle (CA), and the magnitude (K) of hydrophobic force. In general, K increases as Contact Angle increases and does so abruptly at Contact Angle=90°. At the same time, the acid-base component of the surface free energy decreases with increasing CA and K. At CA>90°, GammaS^AB approaches zero. Based on the results obtained in the present work a mathematical model for the origin of the hydrophobic force has been developed. It is based on the premise that hydrophobic force originates from the attraction between large dipoles on two opposing surfaces. The model has been used successfully to fit the measured hydrophobic forces using dipole moment as the only adjustable parameter. However, the hydrophobic forces measured at CA>90° cannot be fitted to the model, indicating that there may be an additional mechanism, possibly cavitation, contributing to the appearance of the long-range hydrophobic force. / Ph. D.

M. Tech. Metallurgical Engineering. / Investigate the dissolution behaviour of sphalerite minerals in sulphuric acid using ferric ions as oxidants. The specific objectives are to study the following: 1. the mineralogical characteristics of sphalerite ores ; 2. mineralogical effects on dissolution kinetics in sulphuric acid and 3. Effect of ferric ion concentration on the dissolution kinetics of sphalerite ores in sulphuric acid. Mineralogy is a critical area in mineral processing and has to be considered during process design stage, and during each processing stage. The type and concentration of oxidizing agent depend on the mineralogical composition of the ore. Many researchers investigations and test-works have been reported on leaching of sphalerite using both ferric sulphate and ferric chloride (Al-Harahsheh and Kingman, 2007; Rath et al., 1981). However, little or no studies have been reported on the combined oxidants.

The electronic spectra of sulfide minerals can be complex, and their features difficult to assign. Often, therefore, they are interpreted using electronic-structure models obtained from quantum-chemical calculations. The aim of this study is to provide such models for the minerals sphalerite, wurtzite, pyrite, marcasite, and chalcopyrite. All are important minerals within a mining context, either as a source for their component metals or as a gangue mineral. They are also semiconductors. Each is the structural archetype for a particular class of semiconductors, and so a knowledge of their electronic structures has wider applicability. / PhD Doctorate

Abstract Zinc production has been known since 200 BC. Fluidised bed roasting is the first process stage of the electrolytical zinc production process, was developed in the 1940s. The raw material for zinc is usually sphalerite concentrate. This sulphide concentrate is oxidised in a roaster. Oxidation reactions produce energy, which is removed as steam, and sulphur dioxide, which is used as the raw material of sulphuric acid. During recent decades sphalerite concentrates have contained more and more impurities and at the same time they have become more fine-grained. Impurities cause problems during fluidised bed roasting. As a consequence, production capacity decreases, there are breaks in production. Starting up and shutting down a process during production breaks cause the environmental emissions. In order to be able optimise production, the oxidation mechanisms of impure sphalerite and methods for controlling them have to be known. The hypothesis of this work was as follows: In addition to temperature, the impurity content and particle size of the feed and oxygen coefficient also have an effect on the stability of fluidised bed roasting. Diverse concentrates require different oxygen coefficients and temperatures. The basic target of this work was to develop a method to help find the required conditions and to control them in industrial roasters. This study was restricted to considering the effects of the iron, copper and lead contents in sphalerite concentrate. A review was made of earlier roasting studies and experiences. This study also evaluated the thermodynamic background of roasting. The oxidation mechanisms were also studied in the laboratory using a fluidised bed roaster and horizontal tube furnace. The results were validated in an industrial roaster. On the grounds of these studies the different sphalerite concentrates really do require diverse roasting temperatures and oxygen coefficients. Foremore, the same kinds of concentrates require a different roasting temperature and oxygen coefficient, if their particle size distributions are different. Controlling the concentrate feed particle size may help to control the stability of the roasting bed and the temperature of the upper part of the furnace. The impurities increase the forming of direct bond sintering and thus the forming of sulphide liquid phases. Oxides and sulphates may also form liquid phases. These kinds of liquid phases cause problems in the fluidised bed. Continuous control of the oxygen coefficient and bed temperature and the use of a unique oxygen coefficient and temperature range for every concentrate mixture would make it possible to minimise problems in the furnace. Laboratory and industrial scale tests have verified the variables and methods for controlling conditions in the roaster bed. / Tiivistelmä Sinkin valmistus on ollut tunnettua ajalta 200 eKr. Leijukerrospasutus, joka on ensimmäinen prosessivaihe elektrolyyttisessä sinkin valmistusprosessissa, otettiin sekin käyttöön jo 1940-luvulla. Sinkin raaka-aineena käytetään sfaleriittirikastetta, joka hapetetaan pasutuksessa. Hapetusreaktiot tuottavat energiaa, joka otetaan talteen höyrynä, ja rikkidioksidia, josta tuotetaan rikkihappoa. Viime vuosikymmeninä sfaleriittirikasteet ovat tulleet epäpuhtaammiksi ja samalla partikkelikooltaan hienommiksi. Epäpuhtaudet aiheuttavat ongelmia leijupetiin. Tämän seurauksena uunien kapasiteetti laskee, tulee tuotannon seisauksia. Näiden seisauksien yhteydessä tapahtuvat prosessin ylös- ja alasajot aiheuttavat päästöjä. Tuotannon optimoimiseksi täytyy tuntea epäpuhtaiden sfaleriittirikasteiden hapetusmekanismit ja tavat niiden hallitsemiseksi. Tämän työn hypoteesi oli: Leijukerrospasutuksen stabiilisuuteen vaikuttaa lämpötilan lisäksi epäpuhtauksien määrä syötteessä ja syötteen partikkelikokojakauma sekä happikerroin. Erilaiset rikasteet vaativat erilaisen happikerroin- ja lämpötila-alueen. Työn tavoite oli kehittää menetelmä,jolla saadaan vaaditut olosuhteet syntymään ja hallittua. Tutkimuksissa rajoituttiin tarkastelemaan sfaleriittirikasteiden sisältämän raudan, kuparin ja lyijyn vaikutusta. Työssä tutustuttiin epäpuhtaiden sfaleriittirikasteiden pasutuksen alueelta aiemmin tehtyihin tutkimuksiin ja eri pasutoilla saatuihin kokemuksiin sekä selvitettiin pasutuksen termodynaaminen tausta. Laboratoriotutkimuksilla selvitettiin hapettumismekanismeja leijukerrosreaktorissa ja pelleteillä kvartsilaivassa putkiuunissa. Tulosten todentaminen tehtiin koeajoilla teollisessa tuotantolaitoksessa. Johtopäätöksenä näistä tutkimuksista voidaan todeta, että erilaiset sfaleriittirikasteet edellyttävät kullekin rikasteelle ominaista pasutuslämpötilaa ja happikerrointa. Lisäksi samantyyppistenkin rikasteiden vaatima pasutuslämpötila ja happikerroin voivat vaihdella, jos rikasteen partikkelikokojakauma vaihtelee. Syötteen partikkelikokoa säätäen voidaan ohjata pedin stabiilisuutta ja uunin yläosan lämpötilaa. Epäpuhtaudet lisäävät suorasidossintrautumien syntyä ja siten sulfidisulafaasien muodostumista. Sulafaaseja voivat muodostaa myös tietyt oksidit ja sulfaatit. Tästä seuraa ongelmia leijupedissä. Happikertoimen jatkuva seuranta ja säätö kullekin rikasteelle ominaisella alueella, samoin kuin lämpötilan seuranta ja säätö, mahdollistavat ongelmien minimoinnin. Tähän työhön liittyvissä laboratoriotutkimuksissa ja teollisen mittakaavan tutkimuksissa todennettiin muuttujat ja keinot olosuhteiden hallitsemiseksi.

The aim of this study was to study the extraction of zinc from the mineral sphalerite, especially the leaching of concentrate recovered from the Rosh Pinah tailings by means of ferric chloride. To this end, the literature on zinc processing was surveyed and knowledgeable persons were consulted. The study also addressed the leaching kinetics of an upgrade Rosh Pinah tailings dam concentrate as well as those of a synthetic zinc sulphide in a ferric chloride medium. Valuable results were obtained, from the leaching of sphalerite concentrate in ferric chloride medium. An activation energy value of 45.82 kJ/mol was obtained, which compares well with what has been published in the literature. A chemical control model and a diffusion control model were applied to the data obtained. From neither of the models a straight-line relationship could be deduced over the leaching range. At t < 45 minutes it seems that the process is controlled by chemical reaction at the interface; at t > 45 minutes it seems that the process is controlled by diffusion through the product layer. If therefore seems that the rate-controlling step can be related to the process of diffusion through the product layer. The mixed control model proposed by Huang and Rowson, [1-(1-x)1/3+y/6[(1-x)1/3+1-2(1-x)2/3]=kMt, was applied to data obtained during this study. The resultant graphical fit was near perfect, indicating that sphalerite leached in ferric chloride follows a mixed control mechanism for the conditions reported in the study. An activation energy of 20.71 kJ/mol was determined for this model by using the following equation: / Dissertation (MSc)--University of Pretoria, 2006. / Chemistry / unrestricted

Les gisements de type Mississippi Valley Type (MVT) du centre et de l’est du Tennessee, respectivement MTM (Middle Tennessee Mine) et ETM (East Tennessee Mine), renferment des réserves importantes de zinc sous forme de sphalerite, mais aussi de germanium en substitution du zinc dans la sphalerite. Cependant seuls les gisements du district de MTM contiennent des teneurs économiquement exploitables de germanium. Ces deux districts miniers, observés dans les mêmes formations géologiques et de minéralogies comparables, sont comparés afin de comprendre la distribution du germanium et des autres éléments traces dans les MVT. Les analyses à l’échelle de l’atome par spectroscopie d’absorption X, XANES et EXAFS, ont mis en évidence plusieurs configurations de germanium dans la sphalerite : le germanium peut être en substitution du zinc dans ZnS sous forme 2+ ou 4+, mais il peut aussi être sous forme d’oxyde de germanium en inclusions nanométriques dans la sphalerite. Les analyses à l’échelle du minéral, par microsonde électronique, LA-ICP-MS et spectroscopie Raman, ont mis en évidence deux groupes d’éléments traces : i) le premier composé des éléments Fe et Cd, est préférentiellement incorporé suivant les faces (110) de la sphalerite, ii) le second composé des éléments Cu, Ga et Ge, est préférentiellement incorporé suivant les faces (010) de la sphalerite. Le couplage de la spectroscopie Raman avec l’ablation laser ICP-MS a permis de mettre en évidence un partitionnement des éléments traces entre la forme cubique et hexagonale de ZnS : les éléments Fe et Cd sont plus concentrés dans la forme cubique, alors que les éléments Cu, Ga et Ge sont plus concentrés dans la forme hexagonale de ZnS / Mississippi Valley-type Type deposits (MVT) in central and eastern Tennessee, respectively MTM (Middle Tennessee Mine) and ETM (East Tennessee Mine), contain large reserves of zinc in the form of sphalerite, but also germanium in substitution of zinc in sphalerite. However, only the deposits District MTM contain economic concentrations of germanium. These two mining districts hosted in the same geological formations and with a comparable mineralogy, are compared in order to understand the distribution of germanium and other trace elements in MVT. Analyses at atomic scale by atomic absorption spectroscopy X, XANES and EXAFS, revealed several of germanium configurations in sphalerites: germanium can substituted to zinc in ZnS under 2 + and 4+ form, but it can be under the form of nanoscale inclusions of germanium oxide associated with sphalerite. Analyses at mineral scale by electron microprobe, LA-ICP-MS and Raman spectroscopy showed two groups of trace elements: i) the first group composed by Fe and Cd is preferentially incorporated following (110) faces of sphalerite, ii) the second group composed by Cu, Ga and Ge, is preferably incorporated following (010) faces of sphalerite. The coupling of Raman spectroscopy with laser ablation ICP-MS revealed a partitioning of trace elements between the cubic and hexagonal forms of ZnS: the elements Cd and Fe are more concentrated in the cubic form, while Cu, Ga and Ge are more concentrated in the hexagonal ZnS

Sulfide minerals are a major source of metals; however, certain sulfide minerals, such as pyrite and pyrrhotite, are less desirable. Froth flotation is a commonly used separation technique, which requires the use of several reagents to float and depress different sulfide minerals. Xanthate, a thiol collector, has gained immense usage in sulfide minerals flotation. However, some sulfides are naturally hydrophobic and may float without a collector. Iron sulfides, such as pyrite and pyrrhotite, are few of the most abundant minerals, yet economically insignificant. Their existence with other sulfide minerals leads to an inefficient separation process as well as environmental problems, such as acid mine drainage during mining and processing and SO2 emissions during smelting process. A part of the present study is focused on understanding their behavior, which leads to undesired flotation and difficulties in separation. The major reasons for the undesired flotation are attributed to the collectorless hydrophobicity and the activation with heavy metal ions. To better understand the collectorless hydrophobicity of pyrite, Electrochemical Impedance Spectroscopy (EIS) of freshly fractured pyrite electrodes was used to study the oxidation and reduction of the mineral. The EIS results showed that the rate of reaction increases with oxidation and reduction. At moderate oxidizing potentials, the rate of reaction is too slow to replenish hydrophilic iron species leaving hydrophobic sulfur species on the surface. However, at higher potentials, iron species are replaced fast enough to depress its flotation. Effects of pH and polishing were also explored using EIS. Besides collectorless hydrophobicity, the activation of pyrrhotite with nickel ions and interaction with xanthate ions makes the separation more difficult. DETA and SO2 are commonly used as pyrrhotite depressants; however, the mechanism is not very well understood. Contact angle measurements, cyclic voltammetry and Tafel studies have been used to elucidate the depressing action of DETA and SO2. It was observed that DETA and SO2 complement each other in maintaining lower pulp potentials and removing polysulfides. DETA also helps in deactivating pyrrhotite. Therefore, the combined use of DETA and SO2 leads to the inhibition of both the collectorless flotation and the adsorption of xanthate. The adsorption of xanthate on sulfide minerals is a mixed-potential mechanism, i.e., the anodic oxidation of xanthate requires a cathodic counterpart. Normally, the cathodic reaction is provided by the reduction of oxygen. However, oxygen can be replaced by other oxidants. Ferric ions are normally present in the flotation pulp. Their source could be either iron from the grinding circuit or the ore itself. The galvanic studies were carried out to test the possibility of using ferric ions as oxidants and positive results were obtained. Tafel studies were carried out to measure the activation energies for the adsorption of ethylxanthate on several sulfide minerals. Pyrite, pyrrhotite (pure and nickel activated), chalcocite and covellite were studied in 10-4 M ethylxanthate solution at pH 6.8 at temperatures in the range of 22 – 30 0C. The Tafel studies showed that xanthate adsorbs as dixanthogen (X2) on pyrite and pyrrhotite, nickel dixanthate (NiX2) on nickel-activated pyrrhotite and cuprous xanthate (CuX) on both chalcocite and covellite. However, the mechanism for xanthate adsorption on each mineral is different. The free energy of reaction estimated from the activation energies are in good agreement with thermodynamically calculated ones. / Ph. D.