Oxidation Of Xanthate Research Articles

Removal of Sodium Isopropyl Xanthate by Capacitive Deionization Process

This study investigated the removal of sodium isopropyl xanthate (SIPX) by capacitive deionization using ion exchange resin/PVDF electrode. The electrode was prepared by coating a layer of ion exchange resin (Amberlite FPA54) and polyvinylidene fluoride (PVDF) on the carbon electrode. Batch experiments showed that 96% of SIPX was removed via the electrosorption and electrochemical advanced oxidation processes at 1 V. Carbon disulfide (CS2) was generated as a by-product of the xanthate oxidation. Adsorption/desorption cycle tests revealed that the ion exchange resin/PVDF electrode has high adsorption capacity, and the maximum adsorption could not be achieved within 60 min of adsorption times. The total xanthate removed in the final adsorption stage of eight cycles was 323 mg/m2, corresponding to 34.1% of xanthate from a 20 mg/L xanthate solution that flowed 0.4 mL per min at 1 V for 60 min of adsorption. In the desorption stage, some of the adsorbed xanthate was released back into the solution and oxidized to CS2, which was adsorbed by the electrodes in the following adsorption stage.

Activation flotation of lime-depressed pyrite with carbon dioxide: Performances, mechanism and pilot-scale application

Activation flotation of lime-depressed pyrite by sulfuric acid (H2SO4) is usually accompanied by safety hazards and environmental pollution. Exploring eco-friendly, economical and effective activator to replace H2SO4 holds great significance for the sustainable development of mining industry. In this study, carbon dioxide (CO2) as a potential activator was applied in activation flotation of lime-depressed pyrite. Micro-flotation experiments results showed CO2 significantly improved the floatability of pyrite, and a maximum recovery of 93.94% was achieved under optimal operating conditions. The activation mechanism was investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Results indicated the depression of pyrite by lime was attributed to the formation of iron oxide/hydroxide species and calcium film, and CO2 effectively eliminated these hydrophilic compounds from the surface of pyrite, thus promoted the adsorption of xanthate onto the pyrite surface. Moreover, the anodic oxidation of xanthate on pyrite and the influence of CO2 on this process were investigated by cyclic voltammetry measurements. It was found that xanthate oxidation to form dixanthogen was more likely to occur in the presence of CO2, and this reaction replaced pyrite surface oxidation as the dominant anodic process. Finally, pilot-scale experiments were successfully conducted and the recovery of pyrite reached 93.18%, surpassing the ore dressing index of using H2SO4 as activator in actual production at the same period. Moreover, the concentration of sulfate ions in mineral processing wastewater was significantly reduced, and the annual cost of activator can be saved by 0.52 million RMB. The new process of activation flotation pyrite with CO2 has prospects for large-scale application in terms of activation performance, cost-effectiveness and environmental impact.

Novel TiO2 nanoparticle-based sensor for xanthate quantification in mineral flotation samples

A voltammetric method for xanthate quantification was developed by fabricating a new electrode based on TiO2 nanoparticles (TiO2 NPs). The nanomaterial in the anatase phase was synthesized by a simple sol-gel method followed by a thermal treatment (9 h at 500 °C). The nanoparticles have a spheroidal morphology with an average size of 20.61 ± 6.01 nm. The band gap energy (3.7 eV) was determined by means of UV–visible spectroscopy from the absorption band at 335 nm. The TiO2 based sensor was employed as working electrode (electroactive area: 0.02248 cm2) in a cyclic voltammetry study, and a greater peak current was observed for the electrooxidation of isopropyl xanthate at pH 10 as compared to the unmodified electrode. The electrode optimization showed that the percentage of TiO2 and the amount of mineral oil in the electrode have a significant influence on the electrochemical response, with 18.4 % of TiO2 NPs, 0.74 mL of mineral oil, and 18 h of electrode rest before the first use as optimal conditions. In the polarization studies, the charge transfer reaction occurred through a lower overpotential with respect to the open circuit potential. The exchange current density was three times higher for the modified electrode. Electrochemical impedance spectroscopy indicated the detection of xanthate with lower charge transfer resistance than when the unmodified electrode was used. The electrochemical sensor allows the quantification of xanthate from 5 μmol/L to 10 mmol/L by cyclic voltammetry and the square wave technique. For the cyclic voltammetry calibration, the limits of detection and quantification were 40.6 μmol/L and 135 μmol/L, respectively. The limit of detection by square wave voltammetry was 2.4 μmol/L, and the limit of quantification was 7.9 μmol/L. The repeatability of the method showed a relative dispersion of 3.1 % at 0.51 mmol/L. The electroanalytical response of the sensor was reproducible up to 30 days. The recoveries of xanthate in real flotation samples were 91.9 % and 94.6 % for concentrations of 0.55 and 1.1 mmol/L, respectively. No statistically significant differences were found between the quantification using the sensor and the UV spectrophotometric method. Dicresyl dithiophosphate showed statistically significant interference with the xanthate oxidation signal.

In-situ hydrothermal synthesis of Fe-doped hydroxyapatite photocatalyst derived from converter slag toward xanthate photodegradation and Cr(VI) reduction under visible-light irradiation

In this work, the salicylic acid-pretreated artificial converter slag—an end product of the steel-making process containing rich Fe and Ca—was successfully utilized for in-situ fabrication of Fe(III)-doped HAp (Fe(III)-HAp) using a modified hydrothermal reaction. Structure, morphology, chemical composition, and photo-electrochemical properties were investigated experimentally and theoretically. The experimental results showed that the successful in-situ Fe(III) doping, along with the formation of oxygen vacancies (OVs), narrowed the bandgap of HAp and broadened its light response range, thus improving its photocatalytic activity. In simulated mineral flotation effluents, 18 % Fe(III)-HAp showed superior performance in xanthate photooxidation under visible light irradiation, giving a 99.4 % removal rate and 87 % mineralization rate within 180 min. While Fe(III)-HAp_CS showed optimum activity in Cr(VI) photoreduction (∼100 %) in the presence of a hole scavenger within 30 min. To understand the mechanism, we thus concentrated on the synergistic effects of the Fe(III) dopants and OVs on Fe(III)-HAp. DFT calculation revealed that Fe(III) occupying the Ca atom locations adjacent to the OV could form bandgaps close to experimental results. Intermediary energy levels generated by OVs and Fe(III) doping were responsible for greater visible-light absorption and excellent separation of photogenerated carriers. Scavenger tests and EPR results demonstrated that superoxide radicals (•O2–) and holes (h+) were dominant photoactive species in xanthate oxidation. Photo-produced electrons effectively reduced Cr(VI) in the presence of a hole scavenger. This work enabled Fe(III)-HAp with OVs to be synthesized from Fe and Ca-enriched converter slag via a viable approach and applied to the treatment of emulated floatation wastewater, which had significant potential in both solid waste recycling and actual industrial wastewater treatment.

Dual Role of Fe2+ in the Galena Flotation and Influence on Selective Separation

Fe ions, as one of the unavoidable metal ions, are present in flotation pulp as ferric and ferrous species, and the effect of ferric species on the flotation behavior of sulfide minerals has been widely discussed in the above literatures. However, the effect of ferrous species has rarely been noticed. In this paper, the effect of ferrous species on the flotation behavior and surface characteristics of galena was investigated by using microflotation, zeta potential measurements, X-ray photoelectron spectrometer (XPS) analysis, and density functional theory (DFT) calculations. Microflotation tests indicated that the flotation recovery of galena with potassium butyl xanthate (KBX) as collector was significantly decreased with the addition of Fe2+ in the pulp, and the recovery was further decreased with increasing dosage of Fe2+. In addition, the finer the galena particles, the greater the decrease in flotation recovery. Zeta potential analysis illustrated that the isoelectric point (IEP) was shifted from 4.4 to 5.8 due to the adsorption of ferrous hydroxyl complexes on the galena surface and the zeta potential. XPS surface analysis suggested that the surface oxidation of galena was alleviated by the consumption of O2 in the pulp, which reduced the adsorption of the collector KBX on and the oxidation of xanthates to dixanthogens. Density functional theory (DFT) calculations confirmed that the ferrous hydroxyl complex FeOH+ could be adsorbed on the galena surface by interactions between Fe and S atoms.

Degradation of potassium alkyl xanthogenate in wet air oxidation: Enhancement method, degradation mechanism and structure impact

Wet air oxidation (WAO) is suitable for high concentration organic wastewater treatment, but the oxidation efficiency still needs to be improved and the reaction mechanism is not clear. This work explored the enhancement of different chemicals to the WAO of typical pollutants in metallurgical wastewater and found that persulfate promoted WAO (PWAO) is very efficient in mineralization of potassium ethyl xanthate. The degradation rate and COD removal rate was over 99% and 96% after 30 min reaction, respectively. The oxidation of alkyl xanthate followed the pseudo first-order kinetics, with the constant order of potassium amyl xanthate > potassium ethyl xanthate > potassium butyl xanthate > potassium isopropyl xanthate. The EPR result confirmed that hydroxyl radicals (·OH) was the dominant active species in the WAO and PWAO processes, and persulfate significantly increased the production of ·OH. It was found that the electrophilic reactivity s-(1S) of the S atom in the -CS and the lipophilic coefficient ClgP of xanthate were the main factors affecting the degradation of xanthate, by constructing a quantitative structure–activity relationship model. The results reveal that PWAO can be used in efficient degradation of flotation reagents, based on which a green metal leaching process and simultaneous organics degradation can be possibly developed in future.

The Mechanism of the Effect of Pre-Magnetized Butyl Xanthate on Chalcopyrite Flotation

In this work, we applied the technology of magnetic treatment to the flotation of chalcopyrite. The mechanism of the effect of pre-magnetized butyl xanthate on chalcopyrite flotation was studied using monomineral flotation tests, adsorption tests, conductivity tests, Fourier transform infrared spectroscopy (FTIR), etc. The monomineral flotation test results showed that, after the magnetization pretreatment of butyl xanthate solution, the chalcopyrite flotation recovery was increased by nearly two percentage points, and the dosage was reduced by 4–10 mg/L at the same recovery. The adsorption, FTIR, dissolved oxygen, and conductivity test results all showed that the magnetization pretreatment increased the dissolved oxygen content and promoted the oxidation of butyl xanthate to double xanthate with better selectivity to chalcopyrite. An electrochemical analysis showed that the magnetization pretreatment of butyl xanthate reduced the corrosion potential and corrosion current density of chalcopyrite surface and inhibited the self-corrosion process of chalcopyrite surface. The flotation test results of actual copper sulfide ore showed that pre-magnetized butyl xanthate could increase the copper recovery of copper concentrate by 3.06 percentage points and the sulfur recovery of sulfur concentrate by nearly 3 percentage points, and effectively reduce the mutual content of copper and sulfur concentrates.

The interaction of grinding media and collector in pyrite flotation at alkaline pH

A significant proportion of invisible gold is hosted by pyrite and the successful recovery of this gold requires a high recovery of pyrite in flotation. In the industry, the flotation of gold-bearing pyrite is operated in a broad range of pH and collector concentration with different types of grinding media. Following the previous study at pH 5.0 and 7.0, the current study investigated the interaction of grinding media with collector and its effect on pyrite flotation at pH 8.5. It was interesting to find that at the same xanthate dosage the highest pyrite flotation was achieved when forged steel, instead of 30% chrome steel, was used as the grinding media although it produced the highest quantity of iron contamination. Pulp chemistry measurement, surface analysis and electrochemical study revealed that pyrite oxidation prevailed over xanthate oxidation at pH 8.5 and pulp potential played a dominant role in pyrite flotation. At this pH, the high pulp potential generated by high chrome steel grinding media facilitated pyrite oxidation instead of xanthate oxidation, but the low pulp potential generated by forged steel grinding media still allowed xanthate oxidation, thus promoting pyrite flotation.

The interaction between grinding media and collector in pyrite flotation at neutral and slightly acidic pH

Gold often coexists with pyrite as micron and submicron-inclusions and pyrite is therefore floated to maximize gold recovery in gold processing plants. In practice, different types of grinding media and a great range of pH and collector concentrations are used for pyrite flotation without scientific guidance. In this study, the effect of three different types of grinding media including forged steel, 15% chromium steel and 30% chromium steel on pyrite flotation at a range of collector (potassium amyl xanthate) concentration was investigated at pH 5.0 and 7.0, and the underpinning mechanism was determined through pulp chemistry measurement, X-Ray Photoelectron Spectroscopy (XPS) surface analysis and electrochemical measurement. It was found that grinding media had a different effect on pyrite flotation at pH 5.0 and 7.0. At pH 5.0, both iron contamination originating from grinding media and xanthate oxidation played an important role in pyrite flotation. While iron contamination on the pyrite surface depressed pyrite flotation, it might be reduced by xanthate oxidation. This explains higher pyrite flotation after grinding with chromium steel than forged steel and at a higher collector concentration. At pH 7.0, pyrite flotation was mainly controlled by xanthate concentration. At a low xanthate concentration, pyrite oxidation was the predominant anodic reaction and pyrite flotation was poor due to the inability to form dixanthogen. At a high xanthate concentration, the formation of dixanthogen became predominant, which facilitated pyrite flotation.

Surface properties of fractured and polished pyrite in relation to flotation

This research was designed to answer the question: can conventionally polished mineral surfaces be used in electrochemical studies in relation to flotation where minerals are fractured? Pyrite surfaces were prepared by fracturing and polishing, separately, and then subjected to electrochemical studies including open circuit potential (OCP), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements as well as X-ray photoelectron spectroscopy (XPS) analyses. Differences on polished and fractured pyrite surfaces were observed in the initial stage of electrochemical measurements, but became minor after conditioning in solution for a short time as the surfaces tended to reach an equilibrium quickly. In the presence of xanthate, dixanthogen formed on both the fractured and polished pyrite surfaces through xanthate oxidation. Immediately after fracturing, pyrite surfaces displayed the stoichiometry nearly in accordance with FeS2, while polished pyrite surfaces showed an iron loss and the formation of polysulfide. However, the surface composition of the fractured pyrite and polished pyrite became similar after conditioning in buffer solution. It was also similar to that on samples directly taken from flotation. It is concluded that polished pyrite surfaces can be used in electrochemical studies representing fractured pyrite surfaces in relation to flotation.

A Computational and Experimental Study on the Binding of Dithio Ligands to Sperrylite, Pentlandite, and Platinum

This benchmark study documents a combined computational and experimental investigation into the binding of three commercial dithio collector ligands used in industrial froth flotation processes to separate high-value minerals from lower-value materials. First-principles condensed-matter simulations showed that ethyl xanthate, N,N-diethyl dithiocarbamate, and diisobutyl dithiophospinate anions all bind least strongly to the [100] Miller index plane of the platinum-containing mineral sperrylite, followed by the [111] MI surface of the mixed nickel/iron sulfide mineral pentlandite, whereas all ligands showed the strongest binding affinity to the [111] MI surface model of pure platinum. Calculations also support experimental observations that neutral ethyl xanthogen disulfide formed upon oxidation of ethyl xanthate binds much more weakly than the monomer. A monolayer of water molecules would easily be displaced from all surfaces by any of the collector ligands. The hydroxide anion was found to have binding en...

Interaction of sphalerite with potassium n-butyl xanthate and copper sulfate solutions studied by XPS of fast-frozen samples and zeta-potential measurement

We acquired low-temperature X-ray photoelectron spectra of fast-frozen wet pastes prepared by centrifugation of the natural sphalerite slurries containing potassium n-butyl xanthate (KBX), without washing or any additional treatment, before and after the mineral activation in 0.1 mM CuSO4 solution. Zeta potentials of the slurry particles were also measured. The method allowed characterizing the mineral surfaces and adsorbates, volatile substances and hydrated species within the interfacial layers under more realistic flotation-related conditions. The uptake of xanthate by unactivated mineral was low even in 10 mM KBX, while the surface became metal-deficient (enriched in sulfur), more hydrophobic and contaminated with carbonaceous matter. Dibutyl dixanthogen was the major interfacial product of the interaction of Cu-activated sphalerite having the surface atomic Zn/Cu ratio of 3 and excess of sulfur with the KBX solutions. The spectra revealed only minor quantities of Zn and Cu xanthates and oxyhydroxides at all the samples; some hydrated K+ counter-ions were detected at the negatively charged surfaces after the xanthate treatment. The dixanthogen was concluded to form via oxidation of xanthate at the interface, probably catalyzed by surface cuprous species but not direct interaction with cupric ions.

The Poisoning of Pyrite Surface upon Xanthate Adsorption by Cyanide in Mildly Acidic Media

AbstractXanthate adsorbs on pyrite surface at mildly acidic pH, rendering mineral surface hydrophobic. By far, the electrochemical behavior of pyrite exposed to cyanide‐bearing solution has been reported in alkaline media. The impact of cyanide on the chemisorption of xanthate on pyrite in mildly acidic media is unclear. The present study clearly pictured the interfacial processes in pyrite‐xanthate‐cyanide system at pH 5 via methods of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It is determined that cyanide blocks the formation of xanthate layer on pyrite surface over a broad range of potential, although the oxidation of xanthate in solution almost remains unaffected. The pyrite surface upon xanthate adsorption is poisoned by cyanide with the formation of iron cyanide complex.

Influence of Ag, Sb, Bi and Zn impurities on electrochemical and flotation behaviour of galena

The influences of Ag, Bi, Sb and Zn impurities on the electrochemical adsorption of butyl xanthate on a galena surface were investigated. The impurity-doped and pure galena samples were synthesised by chemical precipitation and tested by X-ray diffraction (XRD) analyses. The flotation results suggest that the Ag and Bi impurities can promote the flotation of galena, while the Zn and Sb inhibit it. Both the lead- and impurity-xanthate are observed on the galena surface by infrared spectra, which suggests that the impurities on galena surface also interact with xanthate. However, Ag-xanthate and Bi-xanthate at the galena surface doped Ag or Bi may need to be further verified. The cyclic voltammetric measurements on galena microelectrodes reveal two oxidation peaks for both the pure and impurity-doped PbS, while no obvious reduction peaks are observed. It is found that the presence of Ag and Bi enhances the oxidation of xanthate on the galena surface, while the Zn and Sb impurities inhibit the oxidation of xanthate on the galena surface. The amount of electrochemically adsorbed xanthate on the galena surface varies based on the type of impurity and has a positive correlation with the flotation recovery of galena.

Decomposition of sodium butyl xanthate (SBX) in aqueous solution by means of OCF: Ozonator combined with flotator

In this study, ozonator combined with flotator (OCF) have been applied to treat the mineral processing wastewater. The process efficiency has been evaluated in the bench scale. Removing xanthate from aqueous solution was conducted by OCF. In all cases, the butyl xanthate concentration in the treated water was found to be negligible (<0.42mgL−1). The experiments were preceded under different reaction conditions to study the ozonation time and pH on the oxidation of butyl xanthate. The concentration of butyl xanthate and sulfide are analyzed at special time intervals to elucidate the decomposition of butyl xanthate. In addition, oxidation reduction potential and pH are continuously measured in the course of experiments. Chemical oxygen demand is chosen as a mineralization index of the ozonation of butyl xanthate. The degradation mechanism between butyl xanthate and ozone has been discussed. The OCF technology showed to be an efficient process, which requires ozone and flotator, and the treated water ended up with a very low residual concentration of xanthate and COD. It can be inferred from ultraviolet spectrum, HPLC-MS and COD measurement that SO42− is produced. The COD of butyl xanthate solution declined dramatically, the removal rate of COD reached 72.21% when ozonation time is 60min. And the biodegradability (BOD/COD) of butyl xanthate solution increased markedly and shifted from 0.251 to 0.361. It is believed that this ozonation–flotation technique, here named OCF, using ozonator and flotator has a high potential as a alternative method for pollutants removal (flotation reagents, such as butyl xanthate) form waste mining effluents.

Degradation of n-butyl xanthate using fly ash as heterogeneous Fenton-like catalyst

Heterogeneous Fenton-like process using fly ash as a catalyst was studied to degrade n-butyl xanthate form aqueous solution. The different reaction parameters on the degradation efficiency of the process were investigated. The fly ash/H2O2 catalyst possesses a high oxidation activity for n-butyl xanthate degradation in aqueous solution. It is found that both the dosage of catalyst and initial solution pH significantly affect the n-butyl xanthate conversion efficient. The results indicate that by using 1.176 mmol/L H2O2 and 1.0 g/L fly ash catalyst with mass fraction of 4.14% Fe(III) oxide at pH 3.0, almost 96.90% n-butyl xanthate conversion and over 96.66% COD removal can be achieved within 120 min with heterogeneous catalysis by fly ash. CS2 as an intermediate of n-butyl xanthate oxidation. Finally, it is demonstrated that the fly ash/H2O2 catalytic oxidation process can be an efficient method for the treatment of n-butyl xanthate containing wastewater.

A DFT Study of the Effect of Natural Impurities on the Electronic Structure of Sphalerite

The electronic and reaction properties of natural sphalerite containing seven typical kinds of impurities is studied by the density-functional theory (DFT). Mn and Ga impurities result in the Mulliken charge of the Zn atom reduced and consequently might decrease the ionicity of sphalerite; while Fe, Cd, In, Ge and Tl impurities lead to the increase in the Mulliken charge of the Zn atom. The frontier orbital calculations show that Mn impurities might lead to the over-oxidization of sphalerite, which may cause the further oxidation of lead xanthate, and thus are unfavorable for the flotation of sphalerite.

Effect of lattice defects on the electronic structures and floatability of pyrites

The electronic structures of three types of lattice defects in pyrites (i.e., As-substituted, Co-substituted, and intercrystalline Au pyrites) were calculated using the density functional theory (DFT). In addition, their band structures, density of states, and difference charge density were studied. The effect of the three types of lattice defects on the pyrite floatability was explored. The calculated results showed that the band-gaps of pyrites with Co-substitution and intercrystalline Au decreased significantly, which favors the oxidation of xanthate to dixanthogen and the adsorption of dixanthogen during pyrite flotation. The stability of the pyrites increased in the following order: As-substituted < perfect < Co-substituted < intercrystalline Au. Therefore, As-substituted pyrite is easier to be depressed by intensive oxidization compared to perfect pyrite in a strongly alkaline medium. However, Co-substituted and intercrystalline Au pyrites are more difficult to be depressed compared to perfect pyrite. The analysis of the Mulliken bond population and the electron density difference indicates that the covalence characteristic of the S-Fe bond is larger compared to the S-S bond in perfect pyrite. In addition, the presence of the three types of lattice defects in the pyrite bulk results in an increase in the covalence level of the S-Fe bond and a decrease in the covalence level of the S-S bond, which affect the natural floatability of the pyrites.

Comparison of the depressant action of sulfite and metabisulfite for Cu-activated sphalerite

The depressant action of sulfite and metabisulfite (MBS) for copper-activated sphalerite has been studied in the absence and presence of sodium isopropyl xanthate (SIPX) under both air and nitrogen atmospheres by using the contact angle technique. Results obtained indicate that MBS is a better depressant of sphalerite in the presence and absence of SIPX under both air and nitrogen atmospheres. The simultaneous presence of dissolved oxygen and bisulfate presumably promotes their synergetic action on sphalerite depression. Results corroborate the beneficial effect of using an aeration stage before collector addition in order to maximize the depressant action over the hydrophobizing species present on the sphalerite surface and to avoid xanthate oxidation.

Electrochemical kinetics of galena — sulphydryl collector interaction as the basis to develop ion models of sorption-layer formation on the surface of sulphide minerals

Electrochemical analysis of a galena electrode in alkaline xanthate-bearing solutions has revealed the order of reaction and yielded the reaction rate equation. The IR-spectroscopic analysis has shown that lead xanthate and galena oxidation products, namely, lead sulphate, lead thiosulphate and lead hydroxide, formed on the surface of the polarizable galena electrode in the xanthate-bearing solutions with varied concentrations and pH values.