Xanthate Adsorption Research Articles

Sulfidisation Promotion Effect of Ammonium Sulfate on Flotation of Copper Oxide Ore

This paper presents the sulfidisation promotion effect of ammonium sulfate on the sulfidisation flotation of both malachite and copper oxide ores. Copper oxide ores are commonly difficult-to-float due to its molecular structure, and adding sodium sulfide as activator is necessary; however, its dosage to the flotation pulp must be strictly controlled, as it is also a powerful depressant for copper sulfide minerals, and will, if in excess, depress the activated copper oxide minerals. This depression will be alleviated while ammonium sulfate is added, as it accelerates the speed of sulfidisation, and alleviates excessive sulfide ions on the depression of copper oxide minerals. Ammonium sulfate, therefore, may be a sulfidisation promoter, and plays a role of sulfidisation promotion effect; it makes the coating of sodium sulfide on the ore surface more dense and stable, which is ready for xanthate adsorption on the surface of copper oxide minerals. The results of experiments show that the flotation recovery is increased 12.28% while ammonium sulfate is added in the presence of excessive sodium sulfide in the pulp, and the highest recovery is obtainable when the ammonium sulfate and sodium sulfide are in the same dosages. The sulfidisation promotion effect of ammonium sulfate is confirmed by pure copper oxide mineral flotation test and copper oxide ores flotation test, as well as by SEM images of floated malachite.

The influence of the impurities on the flotation behaviors of synthetic ZnS

To investigate the effect of three typical impurities (iron, copper and cadmium) on the flotation behavior of sphalerite, we have synthesized impurity-doped ZnS using a coprecipitation method. In the absence of CuSO4, the flotation tests show that Cd and Cu impurities greatly improve the recovery of ZnS, while Fe impurities apparently decrease the floatability of ZnS. The spectral results show that both dixanthogen and the metal xanthate are observed on Cu- and Cd-doped ZnS surfaces, but only metal xanthate is observed on Fe-doped ZnS surface. Xanthate adsorption tests show that Cd and Cu impurities favor xanthate adsorption, while Fe impurities decrease the adsorption of xanthate.In the presence of CuSO4, Cd impurities not only greatly improve the recovery of ZnS but also enhance the adsorption of xanthate. Cu impurities can improve the flotation of ZnS but show little influence on xanthate adsorption. Fe impurities apparently decrease both ZnS flotation and xanthate adsorption.

Study of Adsorption of Sodium Isopropyl Xanthate on Galena

This paper deals with a study of the oxidation processes of the PbS-sodium isopropyl xanthate system in alkaline conditions (pH 8, similar to flotation circuits Pb-Cu) by using cyclic voltammetry and Electrochemical Impedance Spectroscopy (EIS). Three oxidation peaks are identified in the voltammograms that correspond to reactions previously reported in the literature. A plot of the differential capacitance of the double layer vs. potential gives a potential of zero charge (PZC) of -0.31 V vs. SCE for the system, that coincides with an oxidation peak attributed to the adsorption of xanthate. EIS at PZC for different xanthate concentrations evidence an adsorption processes via a charge transfer mechanism under diffusional control. EIS data at potentials more positive than PZC display an inductive loop that is related to a charge transfer processes involving the reaction of the adsorbed intermediates with the consequent modification of the PbS-sodium isopropyl xanthate interface.

Surface stoichiometry of zinc sulfide and its effect on the adsorption behaviors of xanthate

In this paper, the surface stoichiometry, acid-base properties as well as the adsorption of xanthate at ZnS surfaces were studied by means of potentiometric titration, adsorption and solution speciation modeling. The surface proton binding site was determined by using Gran plot to evaluate the potentiometric titration data. Testing results implied that for stoichiometric surfaces of zinc sulfide, the proton and hydroxide determine the surface charge. For the nonstoichiometric surfaces, the surface charge is controlled by proton, hydroxide, zinc and sulfide ions depending on specific conditions. The xanthate adsorption decreases with increasing solution pH, which indicates an ion exchange reaction at the surfaces. Based on experimental results, the surface protonation, deprotonation, stoichiometry and xanthate adsorption mechanism were discussed.

In situ kinetic study of zinc sulfide activation using a quartz crystal microbalance with dissipation (QCM-D)

We have studied the activation kinetics of zinc sulfide (ZnS) using silver as an activator by a quartz crystal microbalance with dissipation (QCM-D). The zinc sulfide coating on QCM-D sensor was shown to have similar crystallographic structure, composition, and surface properties as nature sphalerite through the characterization of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and xanthate adsorption measurement using QCM-D. The activation of ZnS sensor by silver was confirmed by the mass increase in ZnS sensor coupled with subsequent xanthate adsorption during QCM-D measurement, the change of surface wettability, and the presence of Ag2S on the surface. Two distinct stages on the silver uptake vs. time curve were identified and fitted well by a logarithmic function for the initial stage and a parabolic law in the later stage, which agrees with the two-stage zinc–silver reaction kinetics reported previously. Argon sputtering followed by XPS measurement on the ZnS surface demonstrated the penetration of silver into the bulk ZnS after activation. The present study is the first of its kind to apply the QCM-D technique to investigate sphalerite activation, which introduces a new in situ approach to investigate surface adsorption and activation in many mineral processes and surface modifications.

Effect of potential on characteristics of surface film on natural chalcopyrite

Electrochemical behavior of natural chalcopyrite in electrolyte solution containing 5×10 −4 mol/L ethyl xanthate, and the effect of potential on the composition and characteristics of surface film were studied by cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The adsorption of xanthate (X −) occurred on the mineral surface at open-circuit potential (OCP). In the potential range from −0.11 to 0.2 V, the electrochemical reaction related to the formation of the hydrorphobic film of dixanthogen (X 2) occurred on natural chalcopyrite surface. This surface film had high coverage and large thickness at the potential of 0 V, but it had low coverage and small thickness at the potentials of 0.1 V and 0.2 V. Electrochemical activation started to occur when the potential was higher than 0.2 V, and the film of X 2 transformed to plenty of Cu(II) and Fe(III) oxygen-containing species which had the porous and loose characteristics.

Study on Potassium iso-Propylxanthate and Its Decomposition Products: Experimental 13C CP/MAS NMR Combined with DFT Calculations

Solid-state (13)C NMR is believed to be a valuable tool for studying adsorption and speciation of xanthates on sulfide mineral surfaces, but to do that, model compounds of possible xanthate species need to be investigated. (13)C NMR chemical shift tensors for molecular fragments of potassium iso-propylxanthate and six of its decomposition products have been determined by combining DFT calculations and (13)C CP/MAS NMR experiments. DFT calculations were performed in NWChem using GIAO method for the NMR shielding tensor calculations. The results of the calculations are in good agreement with experimental data. In the -XCYZ moiety (X, Y, Z = O, S), the more sulfur atoms, the more deshielded the chemical shift becomes and the larger the span of the chemical shift tensor. The δ11 principal value has the largest influence on the span, decreasing when the number of sulfur atoms decreases and the number of oxygen atoms increases. The significant differences in chemical shifts make it possible to distinguish between different species and, hence, in future studies, interpret surface speciation. The tensor parameters can also aid in the interpretation.

Effect of sodium hexametaphosphate on separation of serpentine from pyrite

The effect of sodium hexametaphosphate (SHMP) on the separation of serpentine from pyrite and its mechanism were studied systematically through flotation tests, sedimentation tests, surface dissolution, ζ potential tests, adsorption measurements, and infrared spectroscopic analyses. The results show that the SHMP could significantly reduce the adverse effect of serpentine on the flotation of pyrite and make the mixed sample of pyrite and serpentine more disperse in the alkaline condition, thus improve the adsorption of xanthate on pyrite. The action mechanism of the SHMP is that it lowers the pH value at the isoelectric point of serpentine and enhances the negative charge through the dissolution of magnesium from the surface of serpentine and adsorbing on the surface of serpentine. It changes the total interaction energy between serpentine and pyrite from gravitational potential energy to repulse potential energy, according to the calculation of the EDLVO theory.

Cu–S flotation separation via the combination of sodium humate and lime in a low pH medium

The flotation separation of chalcopyrite and pyrite was studied in the presence of sodium humate. The results of flotation tests indicated that pyrite can be selectively depressed by sodium humate, and the activity of sodium humate was strongly affected by the pH of the pulp. At high pH values, pyrite was strongly depressed by sodium humate; however, the content of chalcopyrite was not affected. Ore flotation tests were successfully conducted in the laboratory and at the Dexing Copper Mine by applying sodium humate as a pyrite depressant. By adding 40–60 g/t of sodium humate to the pulp and adjusting the pH to 10–10.5 with CaO, a concentrate with a Cu content of 24% was obtained without reducing the Cu recovery rate. In addition, the dosage of CaO was reduced, and the recovery of Au, Ag and Mo in the copper concentrate was enhanced due to the reduced pH of the pulp. The zeta potential, adsorption of xanthate and contact angle of the mineral surface were measured, and the results from surface measurements indicated that there was a strong hydrophilic interaction between sodium humate and the surface of pyrite. Moreover, the results revealed that the interaction between sodium humate and chalcopyrite was weak. Infrared (IR) spectra of pyrite and sodium humate were obtained, and the results indicated that sodium humate was chemically adsorbed on the surface of pyrite.

An in situ ATR-FTIR investigation of adsorption and orientation of heptyl xanthate at the lead sulphide/aqueous solution interface

A lead sulphide film precipitated on a zinc sulphide layer of an ATR crystal has been used to study in situ surface reactions of heptyl xanthate adsorption. The lead sulphide film was made by the chemical bath deposition method and was analyzed by X-ray photoelectron spectroscopy. In turn deposited layers make it possible to study the PbS/aqueous solution interface in situ and open up interesting areas for attenuated total reflection spectroscopy. Monitoring the adsorption of heptyl xanthate from a 0.1 mM aqueous solution using the vibration band at 1200 cm −1 has shown the existence of adsorbed molecules on the lead sulphide surface as well as precipitated lead xanthate on the surface at bulk concentrations higher than 1 mM. At lower concentrations, the adsorbed species are dominant as is the precipitate at higher concentrations. The rate of adsorption is in accordance with pseudo first-order kinetics with a rate constant of 0.21 s −1. The Dichroic ratio for heptyl xanthate adsorbed on PbS indicates the hydrocarbon chain of the heptyl xanthate to be preferentially orientated perpendicular to the surface normal of the internal reflection element.

Mechanisms of trithiocarbonate adsorption: A flotation perspective

In recent years the use of trithiocarbonates (TTC) in combination with dithiocarbonates (xanthates) in the platinum industry has indicated increases in flotation grades and recoveries. A great number of studies performed on the mechanism of adsorption of xanthates onto substrates have indicated that xanthate adsorbs via charge transfer processes. It would appear from spectroscopic investigations that the TTC has two mechanisms of adsorption; one dominating in reducing conditions and the other in oxidising conditions. The TTC is thus able to be used in reducing or non-oxidising conditions – such as in the milling circuit – to render the target mineral hydrophobic before the possible oxidation of the target mineral. The current study indicated that the TTC is very unstable in solution. The TTC decomposition reaction follows a first-order reaction rate and the TTC decomposes to its corresponding thiol. Microflotation of pyrite indicated that the TTC significantly increases the rate of flotation compared to xanthate flotation. This would suggest that the TTC possible removes faster-floating minerals before xanthate targets the slower-floating minerals. This could account for the apparent synergism between xanthate and TTC when used simultaneously.

The effect of surface treatment and slime coatings on ZnS hydrophobicity

Hydrophobicity of ZnS particles in the 150–212 μm size fraction was examined using film flotation. It was revealed that hydrophobicity of studied ZnS particles was affected by slime coatings as well as prolonged conditioning in water. Conditioning in concentrated methanol solution resulted in increased hydrophobicity of ZnS particles, similar to the activation with CuSO 4. Copper activation with CuSO 4 is a common procedure to increase hydrophobicity of ZnS and to facilitate xanthate adsorption to form stable chemical compound. Conditioning ZnS with concentrated methanol was shown to have beneficial effect on the increase of hydrophobicty of ZnS particles. The atomic force microscopy (AFM) with tapping mode imaging technique, was used to examine ZnS surface before and after the methanol treatment. The nanobubbles were found on the ZnS surface after the methanol treatment and this led to an increased in hydrophobic force and an increase in the range of attraction between examined hydrophobic surfaces. The slime effects on hydrophobicity of ZnS surface were investigated using contact angle (captive bubble and sessile drop). The slime coatings before and after methanol treatment were observed with AFM. The methanol conditioning was shown to result in aggregation of slimes and eventually cleaning the surface of the mineral.

Dextrin as a Regulator for the Selective Flotation of Chalcopyrite, Galena and Pyrite

The adsorption of both dextrin and xanthate ions at the pyrite/aqueous solution and the galena/aqueous solution interfaces have been studied through batch adsorption tests. Batch flotation tests were also carried out on a chalcopyrite ore and a chalcopyrite-galena scavenger concentrate using dextrin. Dextrin adsorption isotherms on two types of surfaces of pyrite show that the greater the initial surface density of iron hydroxides, the higher the adsorption of dextrin is. These adsorption isotherms exhibit two plateaus suggesting that dextrin adsorbs on pyrite not only on ferric hydroxide sites, but also on ferrous hydroxide sites. Adsorption of xanthate ions gives rise to a partial desorption of dextrin lowering the surface hydrophilicity of pyrite. This desorption of dextrin is proposed to occur due to the dissolution of ferric hydroxide which is associated with the oxidation of xanthate ions to dixanthogen. It is shown that dextrin is an effective depressant for pyrite in flotation of copper in the chalcopyrite ore at pH 8, but the pulp needs to be aereated in order to promote the surface oxidation of pyrite and enhance the adsorption of dextrin. On galena, adsorption of xanthate ions also leads to the desorption of dextrin, but, dextrin can be an effective depressant only if the surface of galena is sufficiently oxidized to have dextrin left on the surface after xanthate adsorption. This surface oxidation of galena is more effective with pyrite than using air. Results are presented on the flotation of chalcopyrite from a chalcopyrite-galena bulk concentrate high in pyrite using dextrin as a depressant for galena and pyrite at pH 8.

An in situ ATR-FTIR study of the adsorption kinetics of xanthate on germanium

The in situ adsorption of n-heptyl xanthate on a germanium multiple internal reflection element was studied at constant ionic strength and X-ray photoelectron spectroscopy was used in the investigation of the germanium surface. The kinetics of heptyl xanthate adsorption was evaluated using the integrated absorbance of a sub-band under the vibration at 1200 cm −1. This vibration was assigned to the adsorbed xanthate molecule. It was shown that the adsorption of heptyl xanthate can be represented by a pseudo-first-order rate law and a monodentate binding of the xanthate to the germanium surface is proposed. During the adsorption of xanthate, the dimeric form of xanthate was simultaneously formed.

In situ total internal reflection Raman spectroscopy of surfactant adsorption at a mineral surface

We present the first attempt to characterise surfactant adsorption from solution onto a particle film using total internal reflection Raman spectroscopy. Three surfactant collectors of interest to the mineral processing industry were studied in their adsorption onto sphalerite: heptyl xanthate, 2-mercaptobenzothiazole (MBT), and O, O-dibutyldithiophosphate (DTP). All three surfactants adsorbed to the surface of the sphalerite. Adsorption of heptyl xanthate was monitored as a function of time and increasing concentration. The spectrum of heptyl xanthate indicated the presence of a small amount of dixanthogen on the surface of the sphalerite. MBT adsorption studies were complicated due to the fluorescence of the adsorbed layer. However, peaks due to the adsorbed MBT were observed on top of the fluorescent background, allowing the identification of the adsorbed species to be confirmed as the oxidised dimer species. Spectra obtained from MBT and DTP co-adsorption studies did not display the strong adsorbate layer fluorescence, indicating that the fluorescence spectrum of the adsorbed MBT is most likely affected by ring–ring interactions.

Ethyl xanthate adsorption and adsorption kinetics on lead-modified galena and sphalerite under flotation conditions

Infrared attenuated total reflection spectrophotometry, UV data, microelectrophoresis and a Hallimond tube flotation cell have been used to investigate the effect of Pb(II) on the galena and sphalerite surface properties (hydrophobicity and charge of the surface), ethyl xanthate adsorption and ethyl xanthate adsorption kinetics in alkaline medium. It has been found that lead adsorbed on the galena or sphalerite surface as Pb(OH) + and less as Pb 2+ reduced the collectorless galena floatability from pH 7 to 9.5, but had a strong activating effect on natural sphalerite floatability (in pH range 7.6–10.5). Collecting of Pb(II)-modified minerals with K-ethyl xanthate both forms of lead ethyl xanthate, monolayer, Pb EX (chemically adsorbed (EX) −), and multilayer, physically adsorbed Pb(EX) 2, were detected on the mineral surfaces. Sphalerite floated 90–100% in pH range from 7 to 9.5, but galena floated better only from pH 8 to 9.5 (85–95%). The main surface reaction in pH range 8–9.5 is probably the ion-exchange reaction M Pb OH + (EX) − = M Pb EX + (OH) − (M—mineral), which contributes to the chemical adsorption of (EX) − as monolayer Pb EX, on the surface of either mineral. The reaction between Pb(II)-treated mineral and (EX) − ion is a reaction of pseudo-first order with respect to ethyl xanthate (on Pb(II)-modified galena the rate constant is k 1 = 0.711 min −1; on Pb(II)-modified sphalerite k 1 = 0.1014 min −1).

Kinetics of collector adsorption on mineral surfaces

In the present study infrared attenuated total reflection (IR-ATR) was used to monitor the rate of in situ adsorption of heptyl xanthate on a layer of zinc sulphide synthesized on a germanium ATR crystal. The zinc sulphide surface was characterized using X-ray photoelectron spectroscopy (XPS). The absorbance of heptyl xanthate measured increased with increasing bulk concentration of the adsorbate up to an equilibrium plateau value corresponding to a fractional coverage of the surface sites of the substrate. For the adsorption from solutions of concentrations between 10 −3 and 10 −5 M, the rate of adsorption increased with increasing bulk concentration. At higher concentrations the measured absorbance should be corrected for the absorbance due to the concentration of xanthate in bulk solution. The present work provides a discussion of this correction. Assuming the adsorption stage to be rate-controlling and proportional both to the concentration of the adsorbing species in solution and unreacted surface area, a rate law governing this type of transient adsorption kinetics was derived. By means of absorbance data for the concentrations 0.1 and 0.01 mM, the rate constant of adsorption was calculated. From the initial part of a Langmuir adsorption isotherm, the absorbance at monolayer coverage and the equilibrium constant of adsorption could be estimated.

Correlation between copper-activated pyrite flotation and surface species: Effect of pulp oxidation potential

The effect of pulp oxidation potential, Eh, on the flotation of copper-activated pyrite at pH 9.0 in the presence of xanthate was investigated. It was found that pyrite recovery is at a maximum value when the Eh during conditioning is approximately 35 mV (SHE), but decreases at lower and higher Eh values. Solution and surface analytical techniques (EDTA extraction, and UV–visible and X-ray photoelectron spectroscopies) were used to explain the trends observed in the pyrite recovery with Eh. The increase in pyrite recovery with increasing Eh values has been attributed to an increase in xanthate adsorption at the pyrite surface while the decrease in recovery at high Eh values is the result of an increase in the proportion of surface iron oxidation species covering the hydrophobic species.

On the cathodic reaction coupled with the oxidation of xanthates at the pyrite/aqueous solution interface

The adsorption of ethyl, propyl and butyl xanthates on pyrite has been studied through electrokinetics, batch adsorption tests, and quantification of Fe 2+ ions in solution. Adsorption isotherms for the three alkyl xanthates indicate that their adsorption to dixanthogen produces Fe 2+ ions in solution and decreases the pyrite zeta potential negatively. It seems that the oxidation reaction of xanthates to dixanthogen on pyrite is coupled with the reduction reaction of surface-ferric hydroxide to ferrous ions, leading to the dissolution of hydrophilic ferric hydroxide and growth of hydrophobic dixanthogen on the surface of pyrite. Flotation of pyrite is presented as a function of pH using various ethyl xanthate concentrations. The floatability results are explained in terms of the surface coverage relationship between ferric hydroxide and dixanthogen, which is pH dependent.

N-Heptyl xanthate adsorption on a ZnS layer synthesized on germanium: An in situ attenuated total reflection IR study

Adsorption of n-heptyl xanthate on synthesized zinc sulfide was followed in situ by monitoring the methylene absorption band at 2925 cm −1. The zinc sulfide surface used in the adsorption experiments was synthesized on a germanium internal reflection element using the chemical bath deposition method. Characterization of the adsorbent surface was performed by X-ray photoelectron spectroscopy. The time needed to reach adsorption equilibrium varied with the initial concentration of the aqueous potassium heptyl xanthate solution. The amount of adsorbed xanthate ions increased with the concentration of the solution within the range studied (10 μM–50 mM). The experimental data are reasonably well described by the Langmuir adsorption isotherm. Polarized infrared attenuated total reflection (ATR) was used to determine the average orientation of the heptyl chains by measuring the absorbance of the infrared beam polarized perpendicularly and parallely to the plane of incidence. Measured absorbances were corrected for contribution from heptyl xanthate in bulk solution.