| 1. |
- Ahlberg, E., et al.
(författare)
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The surface oxidation of pyrite in alkaline solution
- 1990
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Ingår i: Journal of Applied Electrochemistry. - 0021-891X .- 1572-8838. ; 20:6, s. 1033-1039
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Tidskriftsartikel (refereegranskat)abstract
- The collector-less flotation of pyrite has been studied by conventional techniques and is correlated to the electrochemical behaviour of pyrite in alkaline solution (1m NaClO4, pH 11). It was concluded that the initial oxidation of pyrite produces a hydrophobic sulphur rich surface together with hydrophilic iron hydroxide species. Also upon grinding, the surface is covered by hydrophilic species and therefore no significant flotation was obtained in the absence of a collector. However, collectorless flotation was readily obtained in an iron complexing solution like EDTA. This indicates that the remaining sulphur-rich layer is responsible for the floatability of pyrite under these conditions.
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| 2. |
- Lockard, Jenny V, et al.
(författare)
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Triplet Excited State Distortions in a Pyrazolate Bridged Platinum Dimer Measured by X-ray Transient Absorption Spectroscopy.
- 2010
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Ingår i: Journal of physical chemistry. A. - : American Chemical Society (ACS). - 1520-5215 .- 1089-5639. ; 114:48, s. 12780-12787
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Tidskriftsartikel (refereegranskat)abstract
- The excited-state structure of a dinuclear platinum(II) complex with tert-butyl substituted pyrazolate bridging units, [Pt(ppy)(μ-(t)Bu(2)pz)](2) (ppy = 2-phenylpyridine; (t)Bu(2)pz = 3,5-di-tert-butylpyrazolate) is studied by X-ray transient absorption (XTA) spectroscopy to reveal the transient electronic and nuclear geometry. DFT calculations predict that the lowest energy triplet excited state, assigned to a metal-metal-to-ligand charge transfer (MMLCT) transition, has a contraction in the Pt-Pt distance. The Pt-Pt bond length and other structural parameters extracted from fitting the experimental XTA difference spectra from full multiple scattering (FMS) and multidimensional interpolation calculations indicates a metal-metal distance decrease by approximately 0.2 Å in the triplet excited state. The advantages and challenges of this approach in resolving dynamic transient structures of nonbonding or weak-bonding dinuclear metal complexes in solution are discussed.
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| 3. |
- Wang, Xianghuai, et al.
(författare)
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A study of the natural and induced hydrophobicity of some sulphide minerals by collectorless flotation
- 1989
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Ingår i: Processing of complex ores. - New York : Pergamon Press. - 008037283X ; , s. 3-17
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Konferensbidrag (refereegranskat)abstract
- The native and induced surface hydrophobicity of a number of natural sulfide minerals (galena, pyrite) were investigated by flotation tests in the absence and presence of EDTA. The dissolution behaviour of the minerals in EDTA solutions was studied as a function of pH and EDTA concentration. With the exception of sphalerite, the flotation and dissolution of the tested minerals in EDTA solutions depend strongly on the pH values and EDTA concentration. In general, at a proper EDTA concentration, low flotation and small amount of released metal species were observed up to pH 5 and > 10. In the range of pH 6-10, both flotation recovery and the dissolution of the minerals exhibited a plateau, and the amount of released metal species increased with increasing EDTA concentration. The floatability first increases with an increase in EDTA concentration; however, a further increase in concentration ( > 10 exp --3 M ) leads to a significant decrease in flotation recovery. Zeta-potential measurements show that, in the presence of EDTA, the iep of the sulfide minerals is shifted considerably to lower pH values. These results are used to discuss the surface hydrophobicity of the sulfide minerals.
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| 4. |
- Wang, Xianghuai, et al.
(författare)
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Activation of arsenopyrites by copper(II) ions
- 1989
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Ingår i: Scandinavian journal of metallurgy. - 0371-0459 .- 1600-0692. ; 18:6, s. 288-294
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Tidskriftsartikel (refereegranskat)abstract
- Copper adsorption on arsenopyrite minerals has been investigated. The effect of solution pH, Cu(II) concentration, oxygen, and oxidation on Cu(II) adsorption were examined. The results indicate that activation of arsenopyrite by Cu(II) in acidic media proceeds according to an ion exchange mechanism. Quantities describing the adsorption processes and reaction time are related either parabolically or logarithmically, depending on the initial copper (II) concentration and solution pH. Oxygen inhibits the adsorption of Cu(II) on arsenopyrite in acidic media, but copper initially adsorbed on an arsenopyrite surface does not undergo desorption upon prolonged oxidation. Increasing the solution pH can reduce the effect of oxygen on copper adsorption. The principles underlying the processes are discussed.
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| 5. |
- Wang, Xianghuai, et al.
(författare)
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Adsorption of copper(II) by pyrite in acidic to neutral pH media
- 1989
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Ingår i: Scandinavian journal of metallurgy. - 0371-0459 .- 1600-0692. ; 18:6, s. 262-270
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that no iron is liberated from the pyrite during the adsorption of Cu(II) by pyrite. The mass of Cu(II) removed by pyrite in an acidic neutral proceeds at an exceedingly slow rate. In the presence of iron-complexing agents, the removal of Cu(II) by pyrite in the initial step is very rapid, but then follows the same relationship exhibited in the absence of such complexing agents. The rate of Cu(II) adsorption depends on the solution pH and the Cu(II) concentration in solution. The adsorption rate increases with an increase in the solution pH. The influence of oxygen on the adsorption of Cu(II) by the pyrite is critical. In solutions with lower pH, copper initially adsorbed on pyrite surface undergoes desorption from the surface upon prolonged reaction with oxygen. The possible mechanism involved in the processes and the practical implications of the findings are discussed.
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| 6. |
- Wang, Xianghuai, et al.
(författare)
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EDTA-induced flotation of sulfide minerals
- 1990
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 140:1, s. 217-226
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Tidskriftsartikel (refereegranskat)abstract
- The native and induced floatabilities of pyrite, galena, arsenopyrite, and glaucodot were investigated by flotation tests in the absence and in the presence of EDTA. The dissolution and electrokinetic behavior of the minerals in EDTA solutions was studied as a function of pH and of EDTA concentration. It was found that the flotation and dissolution of these minerals in EDTA solutions depend strongly on the pH values and on EDTA concentration. At a moderate EDTA concentration, the floatabilities and the released metal concentration are low or absent at pH below 5 and above 10. In the range of pH 6–10, both the flotation recovery and the dissolution of these minerals exhibit a plateau. The amount of released metal species increases with increasing EDTA concentration. The floatabilities of these sulfides first increase with an increase in EDTA concentration. However, a further increase in EDTA concentration to above 10−3M leads to a significant decrease in flotation recovery. ζ-Potential measurements show that in the presence of EDTA the IEP of the sulfide minerals is shifted considerably to lower pH values. The principles underlying the phenomena are discussed in terms of the results obtained from electrochemical studies of these sulfides and the instabilities of iron hydroxides in EDTA solutions.
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| 7. |
- Wang, Xianghuai, et al.
(författare)
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Effect of oxygen on Cu(II) adsorption by sphalerite in acidic to neutral pH media
- 1989
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Ingår i: Scandinavian journal of metallurgy. - 0371-0459 .- 1600-0692. ; 18:5, s. 243-250
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Tidskriftsartikel (refereegranskat)abstract
- Sphalerite activation with Cu(II) ions in acidic and neutral pH media was investigated. Special attention was paid to the short-time adsorption characteristics and the effect of oxygen on the activation. In acidic media, the adsorption of Cu(II) ions on sphalerite in the initial stage is controlled by a surface dissolution + surface nucleation process. Oxygen inhibits the adsorption of Cu(II) on sphalerite. In neutral pH media, the process of sphalerite activation by Cu(II) ions can be described by a three-step model, and the effect of oxygen on Cu(II) adsorption is negligible.
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| 8. |
- Wang, Xianghuai, et al.
(författare)
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Pyrrhotite activation by Cu(II) in acidic to neutral pH media
- 1989
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Ingår i: Scandinavian journal of metallurgy. - 0371-0459 .- 1600-0692. ; 18:6, s. 271-279
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of the activation of two natural pyrrhotite minerals by Cu(II) is described. The activation of pyrrhotite by Cu(II) ions involves a stoichiometric replacement of iron in the lattice by Cu(II) from the solution. The solubility of pyrrhotite, defined as the liberation of iron, decreases in the presence of Cu(II), presumably due to the formation of copper sulphides on the pyrrhotite surface. Copper adsorption increases with an increase in the solution pH. Oxygen inhibits the adsorption of copper on pyrrhotite, but the effect of oxygen decreases with an increase in solution pH. study shows that contrary to prevailing opinions, oxygen together with a high pulp pH cannot prevent copper adsorption on pyrrhotite.
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| 9. |
- Wang, Xianghuai, et al.
(författare)
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The chemistry of cyanide : metal complexes in relation to hydrometallurgical processes of precious metals
- 1990
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Ingår i: Gold. - New York : Gordon and Breach Science Publishers. - 2881243975 ; , s. 81-125
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Thermodynamic stability diagrams have been constructed for the cyanide--metal--sulphide/telluride/selenide systems. These were used to study the solution chemistry of the various metal--cyanide complexes in connection with cyanide leaching of Au and Ag from complex sulphide, arsenosulphide, telluride and selenide ores. The results show that the formation of the metal--cyanide complexes and their stability relative to the metal oxides and sulphides depend critically on the total concentration of the cyanide and metal ions. At lower concentration ratios of Tc(CN)/Tc(Me), Ag, Cu, Ni, and Zn all form insoluble metal cyanide precipitates. At higher concentration ratios, the precipitates are dissolved to form soluble cyano-metal complexes. The formation of gold and silver sulphides does not affect the stability region of aurocyanide and silver-cyanide complexes. Gold and silver telluride and selenide are stable in the presence of cyanide. These results suggest that direct leaching of gold and silver tellurides and selenides with cyanide is probably ineffective. The metal sulphides are classified into two groups according to their stability relative to the cyano-metal complexes. The application of these results to the cyanide leaching of Au and Ag is discussed.
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| 10. |
- Wang, Xianghuai
(författare)
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The chemistry of flotation activation and depression of iron-containing sulphide minerals
- 1989
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermodynamic calculations, electrochemical techniques, flotation and adsorption tests were used to study the physico-chemical principles involved in the flotation, activation and depression of the common ironcontaining sulphide minerals. Thermodynamic calculations on iron-xanthate-sulphur-water systems indicate that insoluble ferric hydroxo- xanthates can be obtained at a very low xanthate concentration in the neutral to weakly alkaline pH range, in which no liquid dixanthogen is formed. Dixanthogen is not the sole species for the flotation of iron-sulphides. Ferric (hydroxo-) xanthates play an important role in the flotation of the minerals. Good flotation of pyrite and other iron-containing sulphides occurs only when a monolayer of xanthate ion and/or dixanthogen is co-adsorbed on the ferric (di)hydroxo xanthate sites. Cyclic voltammetric investigations show that the initial oxidation of pyrite occurs simultaneously with the oxidation of hydroxyl ions. This facilitates the formation of iron hydroxide on the pyrite surface. The surface of pyrite oxidized at lower overpotentials is a sulphur-rich, surface but is covered with hydrophilic ferric hydroxide. The oxidation of pyrite at high overpotentials involves mainly sulphur and sulphide and is nearly independent of the previous history of the pyrite electrode surface. The initial oxidation of arsenopyrite surface produces ferric hydroxide and a realgar-like compound on the surface. At higher potentials, the oxidation of arsenopyrite results in elemental sulphur, arsenate and ferric hydroxide. Arsenate is adsorbed on the surface. The oxidation of arsenopyrite commences at lower potentials than that of pyrite. The separation of arsenopyrite from pyrite can therefore be achieved by selective oxidation of arsenopyrite. Flotation studies demonstrated that freshly ground arsenopyrite and pyrite are non-floatable in the absence of xanthate as a collector or strong iron-complexing agent: EDTA (hydrophilic). Good flotation was observed for both minerals with EDTA or ethyl xanthate. The floatability depends strongly on the pH value and concentration. With EDTA the minerals show good floatabilities in the pH range 6-10 for a concentrations <10-3M. Flotation is completely depressed for concentrations ≥10-2M. The principles for rendering the minerals hydrophobic by EDTA and xanthates are also discussed in this thesis. Studies of the activation of sphalerite, arsenopyrite, pyrite and pyrrhotite by Cu(II) ions by using adsorption tests and cyclic voltammetry showed that the activation reactions between the sulphides and copper(II) depend on the solution pH. The activation process in acidic media is essentially an electrochemical one. Sulphide activation by Cu(II) results in a sulphur-rich copper sulphide surface. In alkaline media, activation proceeds by a surface precipitation. The quantity of copper(II) adsorbed by the sulphides depends on the solution pH, Cu(II) concentration and oxygen content. In general, oxygen decreases the adsorption rate and the quantity of Cu(II) on the sulphide surface. The effect of oxygen on the activation of sulphide by Cu(II) decreases with an increase in pH value. Results from thermodynamic calculations for the cyanide-metalxanthate-sulphur systems and the literature show that the mechanisms of sulphide depression and deactivation by cyanide are extremely complex. Sulphide minerals are rendered hydrophilic and depressed by any of the following processes: the use of cyanide through adsorption of cyanometal complexes, dissolving metalxanthates and metal-sulphides, reducing the pulp potential to prevent chemical adsorption of xanthate ion and the formation and adsorption of dixanthogen, removal of heavy metal ions (activators) by forming cyano-metal complexes, and removal of elemental sulphur from the mineral surfaces.
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