Thiol Collectors Research Articles

The role of copper and lead in the activation of pyrite in xanthate and non-xanthate systems

Lead and copper activation of pyrite in the presence of thiol collectors was examined by means of cyclic voltammetry and microflotation techniques. Di-isobutyl dithiophosphinate (Aerophine 3418A) and alkyl thionocarbamate (AERO 3894) were employed as collector of lead and copper, respectively. Otherwise, isopropyl xanthate (IPX) was also used as a collector of both: lead and copper. The results revealed that in the presence of non-conventional collectors, the increase in pyrite recovery due to the activation by copper and lead species, was noticeably smaller than that exhibited when xanthate (IPX) was used. The electrochemical response of pyrite indicates that lead activation favors the formation of dixanthogen. In non-xanthate systems, the voltammograms of pyrite remained unaffected regardless of the activation by lead or copper species.

The ability of static secondary ion mass spectrometry to discriminate submonolayer from multilayer adsorption of thiol collectors

Experiments have been carried out to establish whether static time-of-flight secondary ion mass spectrometry (ToF-SIMS) alone is able to differentiate monolayer and multilayer coverage of thiol collectors on sulfide minerals. The systems investigated were those for which X-ray photoelectron spectroscopy is able to provide an independent determination of the extent of coverage, and included diethyldithiophosphate (DTP) and 2-mercaptobenzothiazole (MBT) on chalcocite, DTP on Ag 2+ ∂ S, and iso-butyl xanthate (BX) and MBT on galena. For adsorption of a thiol collector (TC) on copper and silver sulfides, TC and metal(TC)H ions were detected for both monolayer and multilayer coverage. For multilayer coverage only, metal(TC) 2 ions were evident, notwithstanding the fact that other spectroscopic measurements had revealed the stoichiometry of the principal multilayer species to be metal(TC). For adsorption on galena, TC and metal(TC) ions were observed for both monolayer and multilayer coverage, whereas for multilayer coverage only, fragment ions from Pb(TC) 2 and (TC) 2 species were evident. Indeed, for all the systems studied, static ToF-SIMS was able to distinguish monolayer from multilayer coverage. However, differentiation was reliable only when both positive and negative secondary ion spectra were determined, and possible only because the multilayer species on copper and silver sulfides included a low concentration of metal dithiolate. In light of those findings, unequivocal differentiation by means of static SIMS is expected to be possible for all thiol collector/sulfide systems.

Adsorption of dithiophosphate and dithiophosphinate on chalcopyrite

Electrochemical behavior of chalcopyrite was investigated in the absence and presence of dithiophosphate (DTP) and dithiophosphinate (DTPI), selective thiols against Fe-sulfides in the flotation of sulfide ores, in potentiostatically controlled electrochemical condition. Diffuse reflectance Fourier transformation (DRIFT) spectroscopy was applied to determine the type of adsorbed collector species, and Hallimond tube flotation tests were performed to clarify the role of polarization potential and thiol collectors on the floatability of chalcopyrite. DRIFT spectroscopy study proposed that dithiolate of DTP, (DTP) 2, was the major surface compound formed under oxidizing potentials in slightly acidic and neutral conditions. However, DTP species formed on mineral surface in alkaline condition could not be determined possibly due to heavy surface coating of metal oxyhydroxides. DTPI species formed on chalcopyrite was found to be in the form of CuDTPI + (DTPI) 2. Additionally, presence of adsorbed DTPI, DTPI 0, was also detected. Self-induced floatability was significantly high particularly in slightly acidic condition and decreased by increasing pH due to surface coating of metal oxyhydroxides. Addition of both collectors improved the flotation performance at all pH values. However, the positive effect of DTP at high alkaline pH values was lower than that of DTPI. This was attributed to weak collecting property and lower hydrocarbon chain length of DTP compared to DTPI. Effect of pulp potential could not be observed in slightly acidic condition, but it became apparent at higher pHs. Although better flotation responses were obtained in mildly oxidizing potentials, both collectors enlarged the floatability potential range of chalcopyrite.

Reactivities of some thiol collectors and their interactions with Ag (+1) ion by molecular modeling

The most commonly used collectors for sulfide minerals in the mining industry are the thiol collectors for the recovery of these minerals from their associated gangues by froth flotation. For this reason, a great deal of attention has been paid to understand the attachment mechanism of thiol collectors to metal sulfide surfaces. The density functional theory (DFT) calculations at the B3LYP/3-21G* and B3LYP/6-31++G** levels were employed to propose the flotation responses of these thiol collectors, namely, diethyl dithiocarbamate, ethyl dithiocarbamate, ethyl dithiocarbonate, ethyl trithiocarbonate and ethyl dithiophosphate ions, and to study the interaction energies of these collectors with Ag (+1) ion in connection to acanthite (Ag2S) mineral. The calculated interaction energies, ΔE, were interpreted in terms of the highest occupied molecular orbital (HOMO) energies of the isolated collector ions. The results show that the HOMOs are strongly localized to the sulfur atoms and the HOMO energies can be used as a reactivity descriptor for the flotation ability of the thiol collectors. Using the HOMO and ΔE energies, the reactivity order of the collectors is found to be (C2H5)2NCS2− > C2H5NHCS2− > C2H5OCS2− > C2H5SCS2− > (C2H5O)(OH)PS2−. The theoretically obtained results are in good agreement with the experimental data reported.

Interaction of thiol collectors with pre-oxidised sulfide minerals

In order to determine whether pre-oxidation results in a change in the identity of the products of the interaction of sulfide minerals with flotation collectors, chalcocite or galena surfaces that had been exposed to air were treated with diethyl dithiophosphate (DTP) or iso-butyl xanthate (BX), respectively, in a borate buffer solution of pH 9.2. The resulting surfaces were studied by means of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The metal oxidation products formed on each mineral surface during the exposure to air were removed by immersion in water or the buffer solution alone and, to avoid this happening in collector solutions, most experiments were carried out with solutions saturated with the ion of the metal component of the mineral. Immersion of chalcocite surfaces in copper-saturated 10 −5 mol dm −3 dithiophosphate solution for 40 s, or of galena surfaces in lead-saturated 10 −4 mol dm −3 xanthate solution for 8 min, resulted in the formation of chemisorbed DTP or BX. Immersion of chalcocite or galena in similar DTP or BX solutions for longer periods gave rise to CuDTP or Pb(OH)BX, respectively, in addition to the chemisorbed collector. In each case, the products of interaction of the mineral with the collector were the same for freshly exposed and pre-oxidised surfaces. The results indicate that the mechanism for the formation of the chemisorbed layer on the pre-oxidised surfaces would have been ion exchange with copper–oxygen or lead–oxygen species followed by reorganisation adjacent to the mineral surface, rather than dissolution of the metal–oxygen species in the aqueous medium followed by chemisorption of the collector at the oxide-free surface.

Surface enhanced raman scattering spectroscopic studies of the adsorption of flotation collectors

Surface enhanced Raman scattering (SERS) spectroscopy at surfaces under electrochemical control has been applied to elucidate the adsorption of thiol collectors. Voltammetry has shown that charge transfer chemisorption of ethyl, isopropyl, isobutyl and isoamyl xanthates occurs on silver surfaces at potentials below the reversible value for the formation of the silver xanthate. SERS spectroscopy has identified the species formed at underpotentials to be xanthate bonded to silver atoms through the sulfur atoms. Application of this technique has also shown that the adsorption of O-isopropyl-N-ethylthionocarlpamate on copper involves a charge transfer process and rest potential measurements indicate that this adsorption occurs at underpotentials. SERS spectra also establish that 2-mercaptobenzothiazole undergoes charge transfer chemisorption on copper, silver and gold over a wide potential range by bonding through the exocyclic sulfur atom.

A SERS spectroelectrochemical investigation of the interaction of O-isopropyl- N-ethylthionocarbamate with copper surfaces

The interaction of the sulfide mineral flotation collector, O-isopropyl- N-ethylthionocarbamate (IPETC), with copper surfaces has been investigated by surface enhanced Raman scattering (SERS) spectroscopy. Adsorption of IPETC has been shown to involve a charge transfer process in which the sulfur atom in the organic species becomes bonded to a copper atom in the metal surface and the hydrogen is displaced from the nitrogen atom to form a hydrogen ion in solution. IPETC and copper IPETC compounds were characterised by 13C NMR and Raman spectroscopy to provide a basis for identifying surface species. The formal potential for the Cu ∣ IPETC system in acid and neutral solutions was found to be 0.131 V and the dependence of the reversible potential on IPETC concentration and on pH to be in agreement with the proposed mechanism. The SERS investigations showed that adsorption of IPETC commenced at a potential more than 0.31 V below the reversible value for the formation of the bulk copper compound; this behaviour is analogous to that previously found for the adsorption of other thiol collectors on metal and sulfide mineral surfaces. An estimate is made of the potential dependence of the interaction of IPETC with chalcocite.

Chemisorption—the thermodynamically favoured process in the interaction of thiol collectors with sulphide minerals

Abstract Voltammetric investigations show that chemisorption is the thermodynamically favoured process in the interaction of thiol collectors with sulphide minerals. The potential dependence of chemisorption coverage is in accordance with the Frumkin adsorption isotherm. Chemisorbed thiols render sulphide mineral surfaces hydrophobic and induce efficient flotation of mineral particles. UV-Visible, Fourier transform infrared, surface-enhanced Raman scattering, and electron spectroscopic studies provide complementary information on the nature of the adsorbed species. X-ray photoelectron spectroscopic (XPS) studies of xanthate on galena reveal sulphur environments associated with chemisorbed xanthate and lead xanthate but no oxidised sulphur derived from the galena substrate. This finding is explained by electrochemical studies that have shown the surface composition of oxidized galena to relax. Discrepancies between the results of conventional and synchrotron radiation excited XPS studies of the oxidation of galena are discussed.

Verification by surface-enhanced Raman spectroscopy of the integrity of xanthate chemisorbed on silver

The monolayer chemisorbed from ethyl xanthate solution at the surface of silver has been analysed ex situ by means of Fourier transform-Raman spectroscopy, and the results compared with the corresponding data for multilayer and bulk silver xanthate. The surface layer was deposited on the silver at a controlled potential in the chemisorption region, and the monolayer status of the adsorbate was verified by X-ray photoelectron spectroscopy. The Raman spectra confirmed that xanthate retained its structural integrity in the chemisorbed monolayer, even after the surface had been subjected to ultra high vacuum and soft X-ray irradiation without cooling in the electron spectrometer. Confirmation of the integrity of xanthate chemisorbed on the metallic substrate provides further evidence for the underpotential deposition of thiol collectors on sulphide minerals.

Selective flotation of pyrite and gold tellurides

The separation of tellurides from pyrite can be carried out by selective flotation. The selection and dosage of collectors and pulp pH are very important to produce one concentrate containing tellurides and free gold, and a further concentrate containing pyrite. A number of thiol collectors were tested to determine their effect on the rate and recovery of tellurides and sulphides. Mineralogical and chemical analysis were used to determine the time-recovery curves of the individual tellurides and sulphides. At natural pH, the tellurides floated readily with the addition of a frother only. This recovery could be enhanced by the further addition of an activator and xanthates while some dithiophosphate collectors decreased the natural floatability of the tellurides. The floatation rates and recoveries of the telluride minerals and tetrahedrite were similar making selective separation difficult. However there is sufficient difference in the floatation rates between tellurides and pyrite to make selective separation possible.

Electrochemical investigation of wettability of sulfide minerals under conditions of flotation. I. Galena and copper sulfides

1. The wettability of sulfide surfaces in the presence of thiol collectors depends not only on the length of the hydrocarbon radical of the collector and the amount of collector used, but also on the nature and redox state of the sulfide mineral; this finding does not support the conclusion of Wark to the effect that the surface wettability is independent of the nature of the mineral when using thiol collectors.

Identifying chemisorption in the interaction of thiol collectors with sulfide minerals by XPS: adsorption of xanthate on silver and silver sulfide

The adsorption of ethyl xanthate on silver and sulfidised silver surfaces at controlled potentials has been investigated by X-ray photoelectron spectroscopy (XPS). Silver/xanthate and silver sulfide/xanthate were chosen as model systems for investigating the identification of chemisorption of thiol collectors on sulfide minerals by means of core electron energy shifts. There was no discernible effect from submonolayer adsorption on either substrate on the corresponding Ag(MNN) spectrum, even when the presence of adsorbed xanthate was clearly evident from the S 2p spectrum. It was confirmed that the Ag(MNN) electron energies for multilayer silver xanthate were significantly different from those for silver and silver sulfide. The basis for the general proposition, that chemisorption of thiol collectors on sulfide mineral surfaces might not necessarily give rise to discernible substrate core electron energy shifts, was examined in the context of previously reported investigations of chemisorption of adsorbates from the vapour phase. It was concluded from this appraisal, and from the experimental results for the interaction of xanthate with silver and silver sulfide, that substrate core electron energy shifts on chemisorption are not always large enough to be detectable by conventional XPS. By contrast, core electron energy shifts for multilayer metal-collector compound formation are clearly discernible.

The flotation of pyrite using mixtures of dithiocarbamates and other thiol collectors

This paper presents results which show that when mixtures of dithiocarbamates are used to float pyrite each component has a synergistic effect on the performance of the others. In particular cyclo-hexyl dithiocarbamate which produced the lowest recovery when used as a pure collector had a significantly advantageous effect on recovery and grade when mixed in small quantities with another dithiocarbamate. Different molar ratios of cyclo-hexyl (oC6) and di-n-propyl (di-n-C3) dithiocarbamates (DTC) in the mixtures were tested. In all cases 90:10 and 10:90 mixtures produced higher recoveries and grades than did 50:50 mixtures or the pure components. Recoveries increased from 74.0% for pure oC6 DTC and 83.5% for pure di-n-C3 DTC to 89.5% for the 90:10 mixture. Grades increased from 14.5% for pure oC6 DTC and 18.5% for pure di-n-C3 DTC to 20.5% for the 50:50 mixture. The effect of mixtures was less marked at higher dosages indicating that for the same performance lower dosages of mixtures were required compared to those required by the pure components. The mixtures resulted in faster rates of flotation as well as a greater recovery of coarse particles. Increased recoveries and grades were obtained in the first minute due to an enhancement in the rate of flotation. When mixtures were used the p 50 of the concentrate increased showing that coarser material was collected. This effect was greater in the first concentrate than the final concentrate. Mixtures of dithiocarbamates and other thiol collectors, viz. xanthate, sodium mercaptobenzothiazole and dithiophosphate further enhanced recoveries and grades to a maximum recovery of 96.0% and grade of 21.0% for a mixture of 90% potassium n-butyl xanthate (PNBX) and 10% oC6 DTC. The method (premixing or separate) and sequence of collector addition had little effect on recoveries or grades. The effect of copper sulphate addition varied. In the case of cyclo-hexyl dithiocarbamate, the addition of copper sulphate dramatically reduced recoveries and grades but when other collectors were present this did not occur. Generally the addition of copper sulphate slightly enhanced recoveries and grades and greatly enhanced water recoveries probably due to a froth stabilization effect.

Underpotential deposition of dithiophosphate on chalcocite

An electrochemical and electron spectroscopy investigation of the interaction of diethyl dithiophosphate with chalcocite (Cu 2S) at pH 9 has been undertaken in order to explore differences between submonolayers of thiol collectors adsorbed on sulfide minerals and the corresponding metal thiol compounds. The chemisorption of the initial monolayer of dithiophosphate on chalcocite gives rise to a prewave on voltammograms at underpotentials to copper dithiophosphate formation. The equilibrium coverage of chemisorbed dithiophosphate was determined as a function of potential and found to obey a Frumkin isotherm. X-ray excited Cu(LMM) Auger electron spectra revealed that the copper atom environment in the submonolayer is similar to that in chalcocite, and significantly different from that in the readily formed subsequent layers of copper dithiophosphate.

Mineral solution-interface chemistry in minerals engineering

In the treatment of sulphide ores, the reactions occurring in several processes like wet grinding, flotation, collectorless flotation, leaching/bioleaching and in adsorption mechanisms, for example the interaction of thiol collectors with oxidation-reduction reactions, play a dominant role. To optimize the conditions for metallurgical yield (grinding, flotation, leaching) or to combat a problem (acid mine drainage) understanding of the mechanisms involved in the process is needed. In broad terms this is mineral/solution interface chemistry. These mechanisms are discussed in this paper with emphasis on galvanic interactions.

Sulphide collector mineral bonding and the mechanism of flotation

Preliminary concentration of sulphide minerals by froth flotation requires nascent bubble formation for particle capture, and sulphide collectors which chemisorb selectively on the mineral. The amount of collector adsorbed is such that at the optimum flotation conditions, bubble contact angle values are zero, or minimal, i.e., the mineral surface is not hydrophobic , which means that the mineral carrying capacity of the bubble should be calculated from bonding energy, and not from surface tension forces. Based on Linus Pauling's argononic sulphur atom theory, which postulates surplus electrons on the metal in sulphide mineral crystals, it can be shown that the collector bond is not sulphur-to-metal, but rather sulphur-to-sulphur. The use of bubble contact angle experiments, and Hallimond tube data, to interpret sulphydryl collector behaviour in sulphide mineral flotation systems is questionable in light of the lack of surface hydrophobicity, when normal amounts of collector are used. As most thiol collectors form six- and seven-coordination complexes with metal cations, it is unlikely that the spectroscopic data on surface compounds formed during sulphide flotation can be interpreted as dithiolate formation, and considering that the more common xanthates and dithiophosphates form insoluble solid dimers it is unlikely that dithiolates, per se, play a dominant role in sulphide ore flotation.

Calculations of Thermodynamic Equilibria in Lead Sulfide Surface–Thiol Collector Systems, Part I: Ethyl Xanthate Ion as Collector

The chemisorption of ethyl xanthate ion on lead sulfide surface is examined by means of thermodynamic calculations with special attention to the surface behavior. The calculations are based on balance equations written in terms of equilibrium constants and solved to determine the surface coverage and the concentrations of various species under different conditions. The calculations cover various ways of regulating the chemisorption such as the addition of oxygen, sodium sulfide, sulfuric acid, and sodium hydroxide, the evaporation of hydrogen sulfide, and change in the initial concentration of the collector. Résumé On étudie la chemisorption de l'ion éthyl xanthate sur la surface du sulfure de plomb par calculs thermodynamiques, en s'intéressant particulièrement au comportement de la surface. On base les calculs sur des équations de bilan fondées sur des constantes d'équilibre et résolues afin de déterminer le degré de recouvrement des surfaces et les concentrations des diverses espèces à différents conditions. Les calculs recouvrent plusieurs facns d'influencer la chemisorption, tels l'addition d'oxygène, de sulfure de sodium, d'acide sulfurique, d'hydroxyde de sodium, l'évaporation de sulfure d'hydrogène, et la variation de la concentration initiale de collecteur.

Calculations of Thermodynamic Equilibria in Lead Sulfide Surface–Thiol Collector Systems, Part I: Ethyl Xanthate Ion as Collector

The chemisorption of ethyl xanthate ion on lead sulfide surface is examined by means of thermodynamic calculations with special attention to the surface behavior. The calculations are based on balance equations written in terms of equilibrium constants and solved to determine the surface coverage and the concentrations of various species under different conditions. The calculations cover various ways of regulating the chemisorption such as the addition of oxygen, sodium sulfide, sulfuric acid, and sodium hydroxide, the evaporation of hydrogen sulfide, and change in the initial concentration of the collector. Résumé On étudie la chemisorption de l'ion éthyl xanthate sur la surface du sulfure de plomb par calculs thermodynamiques, en s'intéressant particulièrement au comportement de la surface. On base les calculs sur des équations de bilan fondées sur des constantes d'équilibre et résolues afin de déterminer le degré de recouvrement des surfaces et les concentrations des diverses espèces à différents conditions. Les calculs recouvrent plusieurs facns d'influencer la chemisorption, tels l'addition d'oxygène, de sulfure de sodium, d'acide sulfurique, d'hydroxyde de sodium, l'évaporation de sulfure d'hydrogène, et la variation de la concentration initiale de collecteur.

Thermodynamics of the system lead sulfide and thiol collector

The thermodynamics of the systems between lead sulfide and two thiol collectors, potassium ethyl xanthate and sodium diethyl dithiophosphate, have been examined in this work. It was found that the experimental data cannot be explained using the thermodynamics of bulk phases. Therefore, a mixed phase model was developed in which the concentrations of the components PbS and (PbX) 2S in the surface phase are taken into account. When the experimental results are compared with the theoretical ones it could be found that the system of ethyl xanthate and lead sulfide behaves as an ideal mixed phase, whereas the system of diethyl dithiophosphate behaves non-ideally, i.e. the activity coefficients of the components in the surface phase are unity in the former system but differ from unity in the latter case. This difference is probably due to the different sizes of the two thiol collector molecules.

Adsorption mechanism of thiol collectors on metal and sulfide surfaces

Adsorption mechanism of thiol collectors on metal and sulfide surfaces