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The high demand for raw materials has increased interest in mining in the northern latitudes. However, mining and mineral processing may pose risks to the environment, which is especially vulnerable in the Arctic region. Xanthates are a group of chemicals used in mineral processing that have recently raised concern. They can be toxic to aquatic environments, even at low concentrations. The toxicity of xanthates is mostly related to their decomposition products, such as carbon disulfide. The amounts of xanthates that are at risk of being discharged into the environment are so low that few methods are capable of reliably determining these concentrations. The first aim of this dissertation was to develop new, selective methods for the determination of low xanthate concentrations in process and environmental waters. The second aim was to study the effect of cold climates on the decomposition of xanthates. The studies were conducted at laboratory scale using artificial samples and samples collected from a mine site located in Finland. In this study, two analysis methods were developed. Both methods were based on the determination of xanthate derivatives by high-performance liquid chromatography tandem mass spectrometry (HPLC-ICP-MS/MS). The sample preparation procedures developed were based on oxidation and the complex formation reactions of xanthates; the former was applied when the decomposition of xanthates was studied in artificial and real samples. The results showed that the HPLC-ICP-MS/MS technique enables the selective determination of low xanthate concentrations. However, the complexity of the chemical reactions of xanthates required careful optimization of the sample preparation procedures to improve their reliability. Additionally, decomposition studies showed that low temperatures significantly decrease the decomposition rate of xanthates. This study presents a pioneering step to improve the analysis methods for the determination of xanthates. It als, Tiivistelmä Tarve uusien raaka-aineiden louhintaan on lisännyt kiinnostusta pohjoisten alueiden kaivostoimintaan. Kaivostoiminta ja malmin rikastaminen kuitenkin aiheuttavat riskejä ympäristölle, ja pohjoiset ympäristöt ovat usein tavallista herkempiä ympäristöhaitoille. Ksantaatit ovat rikastusprosessissa tavallisesti käytettävä kemikaaliryhmä, joiden ympäristövaikutukset ovat nousseet keskusteluun viime vuosina. Ksantaatit ja erityisesti niiden hajoamistuotteet ovat vesieliöille myrkyllisiä jo alhaisissa pitoisuuksissa. Mahdolliset ympäristöön päätyvät ksantaattipitoisuudet ovat kuitenkin niin pieniä, että niiden luotettava määrittäminen nykyisillä analyysimenetelmillä on vaikeaa. Väitöskirjatutkimuksen tavoitteena oli kehittää uusia, selektiivisiä analyysimenetelmiä alhaisten ksantaattipitoisuuksien määrittämiseksi prosessi- ja ympäristövesistä. Lisäksi tavoitteena oli tutkia arktisten ilmasto-olosuhteiden vaikutusta ksantaattien hajoamiseen. Tutkimukset on tehty laboratoriomittakaavassa käyttäen sekä synteettisiä että kaivosalueelta kerättyjä vesinäytteitä. Tutkimuksessa kehitettiin kaksi analyysimenetelmää, joissa ksantaattipitoisuudet määritetään esikäsittelyn jälkeen korkean erotuskyvyn nestekromatografi – induktiivisesti kytketty plasma tandem massaspektrometrisesti (HPLC-ICP-MS/MS). Määritystä varten ksantaatit esikäsiteltiin muodostamalla niiden johdannaisia joko hapettamalla tai kompleksoimalla. Näistä ensin mainittua hyödynnettiin, kun tutkittiin erityisesti lämpötilan vaikutusta ksantaattien hajoamiseen. Tutkimuksen tuloksena todettiin, että HPLC-ICP-MS/MS tekniikkaa voidaan hyödyntää pienten ksantaattipitoisuuksien selektiivisessä määrityksessä. Havaittiin myös, että olosuhteet esikäsittelyn aikana on optimoitava huolellisesti, sillä ksantaattien monimutkaiset reaktiot vaikeuttavat luotettavien kvantitatiivisten menetelmien kehittämistä. Lisäksi todettiin, että alhaisissa lämpötiloissa ksantaattien hajoaminen hidastuu merkittävästi. Tämä väitöstutkimus

Because of their widespread use as reagents in the flotation processing of sulphide ores, xanthates are largely found in tailings as residues. Regrettably, it is known that xanthates are not stable compounds and their decomposition generates carbon disulfide (CS2), a substance that is considered toxic. In this study, the chemical stability of xanthate was evaluated by UV/Vis spectroscopy, as a function of pH and time. The zero charge point of modified waste slag was also determined. The obtained results showed that the lowest degree of xanthate degradation is for the pH=10 and was 24.72%. For different concentrations of the KNO3 (0.1, 0.01, and 0.001 mol/dm3 ) the point of zero charge of the modified waste slag was 7.28, respectively

Xanthates are considered to be the most widely used reagents in the flotation processing of sulphide ores, and therefore are largely present in flotation tailings as residuals. Since xanthates posses a certain toxicity and numerous negative effects from an ecological point of view, it is very important to find a suitable solution for their removal from aqueous solutions. In this study, the removal of xanthate from aqueous solutions was investigated using modified waste slag as promising adsorbent. For that purpose, two different starting concentrations of xanthates were selected, -20, and 90 mg/l. The obtained results showed that over 90% of residual xanthate from the aqueous solution can be removed in a period of 24 hours by using modified waste slag when its initial concentration is 20 mg/dm3 .

The rising concern over the environmental impact of xanthates, especially in the arctic region, has increased the need to study these traditional flotation reagents in greater detail. The environmental concern relates mostly to the formation of carbon disulfide (CS₂) and the heavy metal complexes of xanthates. Due to the unstable nature and multiple reaction mechanisms of xanthates, their reliable determination at low concentration levels is difficult. In this study, a xanthate pretreatment method was optimized and applied for the determination of ethyl xanthate (EX⁻) by high performance liquid chromatography–inductively coupled plasma tandem mass spectrometry (HPLC–ICP-MS/MS). Ethyl xanthate was oxidized to diethyl dixanthogen ((EX)₂) by triiodide (I₃⁻) in aqueous solution and the formed (EX)₂ was extracted into n-hexane. Important experimental parameters, including pH, I₃⁻ amount, and oxidation time, were optimized and the detection limit of 0.29 mg L⁻¹ for potassium ethyl xanthate was obtained. During the optimization experiments, it was found that the oxidation reaction resulted in multiple products, decreasing the efficiency of (EX)₂ formation and, therefore, the sensitivity of the method. The proposed method was applied to wastewater samples with recoveries of 105–106%. This study provides a selective method for the determination of ethyl xanthate and introduces novel information on the parameters affecting the oxidation of xanthates.

Xanthates are commonly used collectors in flotation processes but are highly toxic to the aquatic environment. However, there are few methods for reliable determination of low xanthate concentrations in water samples. In this work, a sensitive, selective, and fast method is presented for the determination of potassium ethyl xanthate (KEX). KEX was determined by high-performance liquid chromatography–inductively coupled plasma–mass spectrometry (HPLC-ICP-MS/MS) directly and as diethyl dixanthogen [(EX)₂] after oxidation with triiodide. The HPLC method was optimized for (EX)₂ and the separated compounds were detected by ICP-MS/MS. The ICP-MS/MS was used in mass-shift mode using O₂ as the cell gas and S⁺ was measured as SO⁺ to reduce spectral interferences. Detection limits of 88 µg L⁻¹ for KEX and 20 µg L⁻¹ for (EX)₂ calculated from the peak area were obtained using mass-shift ³²S⁺ → ³²S¹⁶O⁺. No significant matrix effects were present when spiking experiments of (EX)₂ were done to a sample collected from the tailings of a flotation process. The developed method demonstrates the potential of the HPLC-ICP-MS/MS for the determination of ethyl xanthate. This method may be extended to analyzing other xanthates and similarly structured sulfur containing collectors.

Atomic force microscopy (AFM) has been applied to study the adsorption morphology of various collectors, i.e., potassium ethyl xanthate (KEX) and potassium amyl xanthate (PAX) and Cytec Aerofloat 238 (sodium dibutyl dithiophosphate), on chalcocite in situ in aqueous solutions. The AFM images show that all these collectors adsorb strongly on chalcocite. Xanthate adsorbs mainly in the form of insoluble cuprous xanthate (CuX), which binds strongly with the mineral surface without being removed by flushing with ethanol alcohol. This xanthate/chalcocite adsorption mechanism is very similar to the one obtained with the xanthate/bornite system; while it is different from the one of the xanthate/chalcopyrite systems, for which oily dixanthogen is the main adsorption product on chalcopyrite surface. On the other hand, dibutyl dithiophosphate adsorbs on chalcocite in the form of hydrophobic patches, which can be removed by rinsing with ethanol alcohol. AFM images show that the adsorption of collectors increases with increasing adsorption time and collectors’ concentration. In addition, increasing the solution pH to 10 does not prevent the adsorption of xanthate and Aerofloat 238 on chalcocite and the result is in line with the fact that chalcocite floats well in a wide pH range up to 12 with xanthate and dialkyl dithiophosphate being used as collectors. The blending collectors study shows that xanthate and dialkyl dithiophosphate can co-adsorb with both insoluble cuprous xanthate and oily Cu(DTP)2 (Cu dibutyl dithiophosphate) on a chalcocite surface. The present study helps to clarify the flotation mechanism of chalcocite in industry practice using xanthate and dialkyl dithiophosphate as collectors.

Thermodynamic and kinetic control of a chemical process is the key to access desired products and states. Changes are made when a desired product is not accessible; one may manipulate the reaction with additional reagents, catalysts and/or protecting groups. Here we report the use of carbon dioxide to accelerate cyanohydrin synthesis under neutral conditions with an insoluble cyanide source (KCN) without generating toxic HCN. Under inert atmosphere, the reaction is essentially not operative due to the unfavored equilibrium. The utility of CO2-mediated selective cyanohydrin synthesis was further showcased by broadening Kiliani?Fischer synthesis under neutral conditions. This protocol offers an easy access to a variety of polyols, cyanohydrins, linear alkylnitriles, by simply starting from alkyl- and arylaldehydes, KCN and an atmospheric pressure of CO2.

In view of the difficulty in sulphidation of hemimorphite, lead ions were used to pre-activate it. The flotation behaviour and strengthening sulphidation mechanism in the xanthate system were studied. The results show that, compared with conventional sulphidation (sulphidation + activation by heavy metal), the pretreatment of appropriate amount of Pb2+ can strengthen the sulphidation of hemimorphite, which not only improves the recovery, but also reduces the dosages of sodium sulphide, while the gangue mineral (quartz) is almost unaffected. The activation mechanism of lead ions is as follows: lead ions can be adsorbed on the surface of hemimorphite to increase the sulphidation active sites. When sodium sulphide is added, lead sulphide can be rapidly generated which has the effect of induced crystallisation for the subsequent formation of lead sulphide. Thus more PbS crystals can be formed on the surface, so as to achieve the purpose of strengthening sulphidation. (Authors.), In view of the difficulty in sulphidation of hemimorphite, lead ions were used to pre-activate it. The flotation behaviour and strengthening sulphidation mechanism in the xanthate system were studied. The results show that, compared with conventional sulphidation (sulphidation + activation by heavy metal), the pretreatment of appropriate amount of Pb2+ can strengthen the sulphidation of hemimorphite, which not only improves the recovery, but also reduces the dosages of sodium sulphide, while the gangue mineral (quartz) is almost unaffected. The activation mechanism of lead ions is as follows: lead ions can be adsorbed on the surface of hemimorphite to increase the sulphidation active sites. When sodium sulphide is added, lead sulphide can be rapidly generated which has the effect of induced crystallisation for the subsequent formation of lead sulphide. Thus more PbS crystals can be formed on the surface, so as to achieve the purpose of strengthening sulphidation. (Authors.)

Base metals (and any associated PGMs and/or PMs) are generally recovered from sulphide concentrates in the initial stage using pyrometallurgical processing. However, as the grade and quality of sulphide resources continue to decline, it is becoming harder to generate feed materials that are suitable for smelting without incurring penalties. Apart from being employed for sulphide mattes, hydrometallurgical processes provide options for materials that are not amenable to smelting due to their low grade and/or impurity levels. The metal extraction step is typically characterised by approaches that range from pressure to atmospheric leaching in reactors, to leaching in vats or heaps (both chemical and biological) to in situ recovery. This Special Issue includes the following 6 articles: High temperature pressure oxidation of a low-grade nickel sulphide concentrate with control of the residue composition, by R.G. McDonald, Jian Li, P.J. Austin, 55 refs.; Research on behaviour of iron in the zinc sulphide pressure leaching process, by Shu-Chen Qin, Kai Xi Jiang, Hai-Bei Wang, Bang-Sheng Zhang, Yu-Fang Wang, Xue-Dong Zhang, 22 refs.; Effect of a small amount of iron impurity in sphalerite on xanthate adsorption and flotation behaviour, by Jiang Yu, Xiqun Wu, Zhiqiang Zhao, Yangge Zhu, Sigang Luo, 32 refs.; Cupric and chloride ions: leaching of chalcopyrite concentrate with low chloride concentration media, by C.M. Torres, Y. Ghourbani, P.C. Hernandez, F.J. Justel, M.I. Aravena, O.O. Herreros, 63 refs.; Zeta potential of pyrite articles in concentrated solutions of monovalent seawater electrolytes and amyl xanthate, by A. Paredes, S.M. Acuna, L. Gutierrez, P.G. Toledo, 36 refs.; The effect of sodium alginate and serpentine in chalcopyrite flotation, by Guangjiu Pan, Guofan Zhang, Qing Shi, Wei Chen, 51 refs.., Base metals (and any associated PGMs and/or PMs) are generally recovered from sulphide concentrates in the initial stage using pyrometallurgical processing. However, as the grade and quality of sulphide resources continue to decline, it is becoming harder to generate feed materials that are suitable for smelting without incurring penalties. Apart from being employed for sulphide mattes, hydrometallurgical processes provide options for materials that are not amenable to smelting due to their low grade and/or impurity levels. The metal extraction step is typically characterised by approaches that range from pressure to atmospheric leaching in reactors, to leaching in vats or heaps (both chemical and biological) to in situ recovery. This Special Issue includes the following 6 articles: High temperature pressure oxidation of a low-grade nickel sulphide concentrate with control of the residue composition, by R.G. McDonald, Jian Li, P.J. Austin, 55 refs.; Research on behaviour of iron in the zinc sulphide pressure leaching process, by Shu-Chen Qin, Kai Xi Jiang, Hai-Bei Wang, Bang-Sheng Zhang, Yu-Fang Wang, Xue-Dong Zhang, 22 refs.; Effect of a small amount of iron impurity in sphalerite on xanthate adsorption and flotation behaviour, by Jiang Yu, Xiqun Wu, Zhiqiang Zhao, Yangge Zhu, Sigang Luo, 32 refs.; Cupric and chloride ions: leaching of chalcopyrite concentrate with low chloride concentration media, by C.M. Torres, Y. Ghourbani, P.C. Hernandez, F.J. Justel, M.I. Aravena, O.O. Herreros, 63 refs.; Zeta potential of pyrite articles in concentrated solutions of monovalent seawater electrolytes and amyl xanthate, by A. Paredes, S.M. Acuna, L. Gutierrez, P.G. Toledo, 36 refs.; The effect of sodium alginate and serpentine in chalcopyrite flotation, by Guangjiu Pan, Guofan Zhang, Qing Shi, Wei Chen, 51 refs..

This study investigated the effects of H2O2 treatment on xanthate interaction and flotation separation of chalcopyrite and pyrite by making use of a series of laboratory flotation experiments and surface analysis techniques. Flotation test results showed that H2O2 treatment influenced the flotation behaviours of the two minerals; however, flotation of pyrite was depressed more significantly than that of the chalcopyrite. Under well-controlled H2O2 concentration, the selective separation of chalcopyrite from pyrite was realised at pH 9.0, at which the recovery of chalcopyrite was over 84% and that of pyrite was less than 24%. Zeta potential, UV-visible and IR spectrum measurements revealed that the collector interacted differently with the two minerals after H2O2 treatment, and the surface of chalcopyrite adsorbed a much greater amount of xanthate than that of the pyrite. IR and XPS analyses showed that the H2O2 treatment significantly changed the surface properties of pyrite to a very hydrophilic species that inhibited the adsorption of collector and thus depressed the floatability of pyrite. While, the surface of chalcopyrite remained mildly inert to H2O2, as a result, the adsorption of xanthate and its oxidation to dixanthogen were very effective, which enhanced the flotation of chalcopyrite., This study investigated the effects of H2O2 treatment on xanthate interaction and flotation separation of chalcopyrite and pyrite by making use of a series of laboratory flotation experiments and surface analysis techniques. Flotation test results showed that H2O2 treatment influenced the flotation behaviours of the two minerals; however, flotation of pyrite was depressed more significantly than that of the chalcopyrite. Under well-controlled H2O2 concentration, the selective separation of chalcopyrite from pyrite was realised at pH 9.0, at which the recovery of chalcopyrite was over 84% and that of pyrite was less than 24%. Zeta potential, UV-visible and IR spectrum measurements revealed that the collector interacted differently with the two minerals after H2O2 treatment, and the surface of chalcopyrite adsorbed a much greater amount of xanthate than that of the pyrite. IR and XPS analyses showed that the H2O2 treatment significantly changed the surface properties of pyrite to a very hydrophilic species that inhibited the adsorption of collector and thus depressed the floatability of pyrite. While, the surface of chalcopyrite remained mildly inert to H2O2, as a result, the adsorption of xanthate and its oxidation to dixanthogen were very effective, which enhanced the flotation of chalcopyrite.

Microwave-assisted tertiary carbon radical reaction was developed. The reaction of tertiary xanthates with electron deficient alkenes was prompted by microwave irradiation, and various coupling products possessing quaternary carbon centers were obtained in good yields. The reaction was conducted under simple and common radical condition except for microwave irradiation, and the reaction completes within 5 min.

L’industrie minière génère d’importantes quantités de rejets miniers, qui peuvent impacter l’environnement quand ils contiennent des sulfures de métaux capables de s’oxyder. Parmi ces rejets, les résidus de concentrateur sont composés de phases minérales sans valeur économique avérée, soit les sulfures et la gangue silicatée, finement broyées pour faciliter la libération des minéraux de valeurs. Les sulfures, dont la pyrite est le minéral prédominant, peuvent entraîner un drainage minier acide ou neutre sous l’action de l’oxygène en milieux aqueux. Une technique de gestion intégrée de ces résidus, appelée désulfuration environnementale, consiste à séparer les sulfures par flottation, produisant un rejet décontaminé et un concentré de sulfures plus apte à être géré de par son faible volume. La concentration des sulfures est possible grâce aux collecteurs de flottation, qui sont des composés organiques s’adsorbant sélectivement aux surfaces minérales pour les rendre hydrophobes. Le xanthate est le collecteur le plus utilisé pour la flottation des sulfures. Cependant, son utilisation devient restreinte pour des raisons toxicologique, écologique et de santé et sécurité. Des alternatives au xanthate, dont les composés de dithiophosphate, dithiocarbamate et benzothiazole, sont notamment étudiés comme collecteurs non sélectifs des sulfures lors de la désulfuration environnementale. Durant la phase fondamentale du travail, l’interaction entre la pyrite, deux collecteurs alternatifs de sulfures fournis par le groupe SOLVAY-CYTEC et le xanthate comme référence, a été caractérisée. Ces deux collecteurs, l’AERO 404 de la famille des dithiophosphates (DTP) et l’AERO 3739 de la famille des dithiocarbamates (DTC), sont des mélanges contenant du mercaptobenzothiazole (MBT). L’affinité des collecteurs pour le minéral a dans un premier temps été étudiée par UV-Visible, après conditionnement de la pyrite à pH naturel (pH 4-4,5) et pH alcalin (pH 10,5) avec ajout de NaOH ou de CaO, pou

Cryogenic XPS of wet particulate samples separated via centrifugation and fast-frozen allows quasi in situ examination of solid surfaces, adsorbates, and reaction products, largely preventing the loss both of volatiles and hydrated species at mineral/water interfaces. Here, the cryo-XPS has been applied to characterize the surfaces and interfacial layers of natural pyrite (FeS2), chalcopyrite (CuFeS2), and galena (PbS) in solutions of a common flotation collector, potassium n-butyl xanthate (KBX), in conjunction with zeta-potential measurement. It was found, in particular, that dibutyl dixanthogen was the major adsorbate at pyrite in 0.1 mM KBX and 10 mM KBX solutions; dixanthogen and cuprous xanthate in the next stage were formed on chalcopyrite, and predominant chemisorbed butyl xanthate was present at galena, including in 10 mM KBX solution. The results may suggest that the production of dixanthogens at the interface has been underestimated while the quantities of surface metal xanthates could be over evaluated in previous studies. Pronounced differential charging effects were observed in the XPS experiment for the samples moderately hydrophobized by the xanthate treatment; we proposed that the effect was due to electrically isolated mineral particles with hydrophobic and ice-repellent surfaces, which retained, however, some frozen water islets.

Hydrophobic interaction plays an important role in biology, daily lives, and a variety of industrial processes such as flotation. While the mechanisms of hydrophobic interactions at molecular scale, as in self-assembly and micellization, is relatively well understood, the mechanisms of macroscopic hydrophobic interactions have been controversial. It is, therefore, the objective of the present work to study the mechanisms of interactions between macroscopic hydrophobic surfaces in H-bonding liquids, including water, ethanol, and water-ethanol mixtures. The first part of the present study involves the measurement of the hydrophobic forces in the thin liquid films (TLFs) confined between two identical hydrophobic surfaces of contact angle 95.3o using an atomic force microscope (AFM). The measurements are conducted in pure water, pure ethanol, and ethanol-water mixtures of varying mole fractions. The results show that strong attractive forces, not considered in the classical DLVO theory, are present in the colloid films formed with all of the H-bonding liquids tested. When an H-bonding liquid is confined between two hydrophobic surfaces, the vicinal liquid molecules form clusters in the TLFs and give rise to an attractive force. The cluster formation is a way to minimize free energy for the molecules denied of H-bonding with the substrates. Thus, solvophobic forces are the result of the antipathy between the CH2- and CH3-coated surface and H-bonding liquid confined in the film. A thermodynamic analysis of the solvophobic forces measured at different temperatures support this mechanism, in which solvophobic interactions entail decreases in the excess film enthalpy and entropy. The former represents the energy gained by building clusters, while the latter represents loss of entropy due to structure building. Thus, hydrophobic interaction may be a subset of solvophobic interaction. The solvophobic forces are strongest in pure water and pure ethanol, and decrease when one i

Radical-initiated support: Xanthates were used as chemical reagents for the sidewall covalent functionalization of carbon nanotubes (see figure). The best grafting yields were obtained with stoichiometric ratios of xanthate and the radical initiator lauroyl peroxide. One grafted function was used as a tether for bimetallic cluster compounds, which were converted into very small (1-2nm) supported nanoparticles upon heating. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radical-initiated support: Xanthates were used as chemical reagents for the sidewall covalent functionalization of carbon nanotubes (see figure). The best grafting yields were obtained with stoichiometric ratios of xanthate and the radical initiator lauroyl peroxide. One grafted function was used as a tether for bimetallic cluster compounds, which were converted into very small (1-2nm) supported nanoparticles upon heating. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

It is illustrated using test data on liquid-phase Pb(NO3)2 and ROCSSK reactions that dixanthogen originates in the solution, and the origination mechanism is suggested. The said reaction can happen at galena surface in the course of galena oxidation in flotation. © Pleiades Publishing, Ltd., 2012.

La désulfuration environnementale, utilisant la flottation, est une méthode de gestion intégrée des rejets miniers dont l'efficacité a été démontrée de nombreuses fois sur des résidus de concentrateur dans le cadre de la prévention du drainage minier acide. La flottation est une technique de séparation minéralurgique fréquemment utilisée pour la concentration des sulfures en traitement du minerai. Elle est basée sur la différenciation des surfaces par ajout de composés organiques (collecteurs) qui, par adsorption à la surface des particules, les recouvrent d'un film hydrophobe. La capacité de fixation du collecteur à la surface des particules dépend principalement des paramètres physico-chimiques de la solution et de l'état de surface des particules au moment du conditionnement de la pulpe. Les objectifs principaux de ce doctorat résident en l'application de la désulfuration à des problématiques environnementales spécifiques telles que la diminution de SO2 dans le cadre du grillage de minerai sulfureux (cas du minerai d'hémo-ilménite de la mine Tio de Rio Tinto Fer et Titane; ou la flottation de la pyrite grossière est visée) et la prévention du drainage neutre contaminé à l'arsenic et à l'antimoine (cas du minerai de la mine Lapa d'Agnico-Eagle Mines Ltd., où la flottation de l'arsénopyrite est ciblée). Ce projet vise également à étudier les mécanismes fondamentaux à la base de la constitution d'un film hydrophobes permettant la concentration des sulfures, pyrite de taille grossière notamment et arsénopyrite dans le but de diminuer le potentiel polluant des produits miniers étudiés. Pour répondre à ces objectifs, l'étude s'est penchée sur la caractérisation surfacique de poudres de pyrite pure (3 fractions : 3 2-63 µm; 63-150 µm; 150-425 µm) et d'arsénopyrite pure de taille standard (32-63 µm). L'évolution de la surface (analyses XPS et FTIR) de ces 2 minéraux a été étudiée après un broyage, suivi d'un conditionnement à différents pH, une activation au sulfate de c

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 measurement

This paper presents results of a laboratory study designed to look into the effect of calcium on sphalerite hydrophobisation with xanthate making use of zeta potential, contact angle, microflotation and UV/vis spectrometry techniques. The experimental results show that xanthate adsorbs onto the mineral surface at neutral and slightly acid pH as reflected by contact angle, floatability (by microflotation) and xanthate adsorption (by UV/vis spectrometry) measurements. Apparently, xanthate adsorption is due to both the less negative surface charge of the mineral and to the presence of Zn in equilibrium with the mineral, rather than Zn(OH)2, which is the product of the mineral oxidation with dissolved oxygen at pH above 8. When calcium is present in the aqueous solution at concentrations similar to that of saturation for gypsum precipitation (e.g. about 0.017 mol/l), calcium apparently adsorbs on the sphalerite surface decreasing its negative charge (e.g. zeta potential) and promoting xanthate adsorption and hydrophobisation, as reflected by contact angle and floatability measurements (around 30 degrees and 33% recovery, respectively). Calcium adsorption appears to be favoured by the increase in pH, as reflected by the increased xanthate adsorption, thus suggesting that the calcium hydroxo-complex (CaOH+) is the adsorbing species. At pH 10 and 11, precipitation of calcium hydroxide (observed by SEM-EDS measurements at pH 11) appears to counteract xanthate adsorption, substantially decreasing mineral hydrophobicity. Calcium and xanthate appear to display some type of chemical interaction while calcium and dithiophosphinate do not. (Authors.)., This paper presents results of a laboratory study designed to look into the effect of calcium on sphalerite hydrophobisation with xanthate making use of zeta potential, contact angle, microflotation and UV/vis spectrometry techniques. The experimental results show that xanthate adsorbs onto the mineral surface at neutral and slightly acid pH as reflected by contact angle, floatability (by microflotation) and xanthate adsorption (by UV/vis spectrometry) measurements. Apparently, xanthate adsorption is due to both the less negative surface charge of the mineral and to the presence of Zn in equilibrium with the mineral, rather than Zn(OH)2, which is the product of the mineral oxidation with dissolved oxygen at pH above 8. When calcium is present in the aqueous solution at concentrations similar to that of saturation for gypsum precipitation (e.g. about 0.017 mol/l), calcium apparently adsorbs on the sphalerite surface decreasing its negative charge (e.g. zeta potential) and promoting xanthate adsorption and hydrophobisation, as reflected by contact angle and floatability measurements (around 30 degrees and 33% recovery, respectively). Calcium adsorption appears to be favoured by the increase in pH, as reflected by the increased xanthate adsorption, thus suggesting that the calcium hydroxo-complex (CaOH+) is the adsorbing species. At pH 10 and 11, precipitation of calcium hydroxide (observed by SEM-EDS measurements at pH 11) appears to counteract xanthate adsorption, substantially decreasing mineral hydrophobicity. Calcium and xanthate appear to display some type of chemical interaction while calcium and dithiophosphinate do not. (Authors.).