| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- Wang, Xianghuai, et al.
(författare)
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Thermodynamic calculations on iron-containing sulphide mineral flotation systems, I. The stability of iron-xanthates
- 1989
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Ingår i: International Journal of Mineral Processing. - : Elsevier BV. - 0301-7516 .- 1879-3525. ; 27:1-2, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Thermodynamic calculations have been carried out for the Fe-EX-H2O system to study the stability of iron-xanthates. It has been shown that the formation and stability of insoluble iron-xanthate compounds depend critically on the xanthate concentration, the pH, and the redox potential of the solutions. Ferric xanthate is stable in acidic solutions, which may cause and improve the flotation of iron-sulphides under the corresponding conditions. Insoluble hydroxyl ferric xanthates, FeOH (EX)2 (s) and Fe(OH)2EX(s), are obtained in the weakly acidic to alkaline pH range. The formation of liquid dixanthogen is favoured at high xanthate concentrations and redox potentials. It has been found that under conditions where insoluble ferric-xanthate compounds are stable, the quantity of aqueous dixanthogen is relatively small and no liquid dixanthogen can be obtained. The "intermediate pH depression" phenomenon is then observed during the flotation of pyrite with xanthates.
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