Electrochemical interactions of industrially important platinum-containing minerals

Vermaak, M.K.G.; Miller, J. D.; Lee, J.

doi:10.1016/j.mineng.2007.08.003

Cited by 5 publications

(4 citation statements)

References 7 publications

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“…While this makes for an attractive system size for computational modeling work, the issue of whether this is a realistic representation of surface coverage requires discussion. From electrochemical and surface-enhanced Raman spectroscopy (SERS) measurements it is generally accepted that ethyl xanthate monomers chemisorb to the surfaces of minerals and then undergo an oxidative dimerization reaction to form the dixanthogen species, which are thought to form physisorbed multilayers above the chemisorbed monomer. − The extent of surface coverage by the collector ligand appears not to be reported in the literature. However, since in this work we are interested in modeling the chemisorbed binding of the monomer state only, the number of available binding sites in the proposed models seems reasonable for the task at hand.…”

Section: Methodsmentioning

confidence: 99%

First-Principles Study on Ligand Binding and Positional Disorder in Pentlandite

et al. 2015

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Density functional theory, in conjunction with a cluster expansion model, has been used to study the structure and stability of the positionally disordered iron-nickel sulfide mineral pentlandite (Pn), (Fe, Ni)9S8, with results indicating heterogeneous nearest neighbour metal contacts are more energetically favourable than homogeneous contacts. The virtual crystal approximation was also explored as a means to address positional disorder, but while reliable results could be obtained for the bulk model, the same was not true for the surface, as local distortions which affected the surface model energies could not be reproduced. We also address the binding of ethyl xanthate (CH3CH2OCS2-), water and hydroxide to the [111] Pn surface to better understand the mode of action of industrial xanthate flotation agents. In order to model anionic ligands bound to a periodic boundary condition surface we propose applying a correction derived from the surface work function to remove the additional charge introduced by the ligand. The results obtained from the ligand binding studies indicate that while an ethyl xanthate collector could readily displace up to a full monolayer of water per unit cell, it is likely that Fe-enriched surfaces will bind xanthate in competition with the hydroxide anion, whilst a Nienriched surface will preferentially bind hydroxide anions over xanthate.

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Section: Methodsmentioning

confidence: 99%

First-Principles Study on Ligand Binding and Positional Disorder in Pentlandite

et al. 2015

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“…Raman and surface-enhanced Raman spectroscopy (SERS) measurements also confirmed that xanthate monomers chemisorb to metal and mineral surfaces and found evidence for the formation of metal complexes on surfaces. The appearance of dixanthogen at higher oxidation potentials through the appearance of the SS stretching mode was also reported. − The surface enhancement effect for dixanthogen bound to a gold surface was very weak, however, which led Woods et al to propose that dixanthogen species were more likely to form physisorbed multilayers above the chemisorbed monomer. Another work by Mermillod-Blondin et al for xanthate on pyrite (FeS 2 ) cited a combination of metal-xanthate species overlaid by multilayers of (EX) 2 as being the species involved in inducing flotation, which accords with the general findings of both the Woods and Vermaak groups.…”

Section: Introductionmentioning

confidence: 96%

“…The appearance of dixanthogen at higher oxidation potentials through the appearance of the S-S stretching mode was also reported. [6][7][8][9][10][11][12][13] The surface enhancement effect for dixanthogen bound to a gold surface was very weak, however, which led Woods et al 9 to propose that dixanthogen species were more likely to form physisorbed multilayers above the chemisorbed monomer.…”

Section: Introductionmentioning

confidence: 99%

“…Since the publication of Woods’ article, a number of others, , notably by Vermaak and co-workers, − also reported contact angle measurements to study the formation of air/nitrogen bubbles directly on the surface of xanthate-bound minerals (including PtAs 2 , PtTe 2 , PtBiTe, and PdBiTe) under electrochemically induced oxidizing conditions. Their data display a clear correlation between the dimerization of the xanthate collector ligands and contact angle, with the mineral surfaces displaying poor hydrophobicity at potentials below those required for dimerization and increasing hydrophobicity above.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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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 material. 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 sulphide mineral pentlandite, while all ligands showed strongest binding affinity to the [111] MI surface model of pure platinum. Calculations also support experimental observations that neutral ethyl xanthogen disulphide formed on 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 energies of comparable magnitude to the collector ligands on all surfaces. Cyclic voltammetry measurements performed on working electrodes constructed from sperrylite, pentlandite and platinum permitted measurement of the mixed oxidation potential associated with the surface dimerization reaction for all three collector ligands, although the data obtained for diisobutyl dithiophospinate was less clear cut than for the other ligands. Comparison of the relative ordering of the mixed potentials for the three ligands gave a favourable match with the predicted outcome of binding energy strengths obtained from the modelling study. This study demonstrates that first principles simulations can be used to predict the binding energies of collector ligands to mineral and metallic surfaces.

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