Zhongxi Sun

Surface reactions in aqueous metal sulfide systems: 2. Ion exchange and acid/base reactions at the ZnSH2O interface

Abstract The amphoteric properties of hydrous ZnS surfaces as well as an ion exchange reaction between surface coordinated Zn 2+ ions and H + ions of the aqueous phase have been established. The measurements were performed as potentiometric titrations in 0.1 M NaClO 4 medium at 25°C. Besides measuring −log[H + ] by using a glass electrode, −log[S 2− ] was recorded (Ag/Ag 2 S selective electrode). In addition, the total concentrations of H + , Zn 2+ , and S were analyzed as a function of −log[H + ] of the bulk solution. Synthetically prepared ZnS and the mineral sphalerite were studied. Bro¨nsted acidity constants pK 1 s = 6.91 and pK 2 s = 10.28 for synthetic ZnS, and pK 1 s = 7.14 and pK 2 s = 10.29 for sphalerite, were established, which implies −log[H + ] of zero proton condition equal to 8.60 and 8.72, respectively. Furthermore, the ion exchange reaction SZn + 2H + ⇆ SH 2 + Zn 2+ was characterized within the range 4 ⩽ −log[H + ] ⩽ 7, with log K = 9.59 and 9.65. Experimental data were evaluated on the basis of the constant capacitance model by using the computer program FITEQL. The “best” fit to experimental data was obtained by assuming no charge dependence of K 1 s and K 2 s .

The degradation kinetics of ethyl-xanthate as a function of pH in aqueous solution

Xanthate degradation kinetics plays an important role in sulfide mineral flotation and in the treatment of flotation tailings. Increasing environmental concern about consequences of flotation taili ...

Surface reactions in aqueous metal sulfide systems. 1 : Fundamental surface reactions of hydrous PbS and ZnS

Proton adsorption at hydrous sulfide mineral surfaces has been investigated. Potentiometric titrations and solubility studies of freshly precipitated PbS, commercially available PbS and ZnS as well ...

Shear-flocculation of quartz

Abstract The present work deals with the shear-flocculation of quartz in aqueous solutions of dodecylamine chloride. The variables studied include pH, concentration of the amine, size of the coarse particles, stirring speed and time. The zeta potentials were correlated with flocculation behaviour. It was observed that particle hydrophobicity and pH were most important since the dodecylamine chloride-solution reactions are pH- and concentration-dependent.

Use of surface complexation models in sulphide mineral flotation

Abstract Surface complexation modelling is introduced to investigate the surface reactions in a mixed galena and sphalerite flotation system. Computer-assisted calculations based on surface complexation modelling (SCM) are performed to obtain the mineral surface distribution of ethyl xanthate as well as carbonate and excess sulphide ions as a function of pH. The significance of pe is demonstrated by computing the mineral surface speciation in a flotation system with xanthate and excess of sulphide ions. The results are used to evaluate the influences of pH, pe, the concentration of xanthate, sulphide or carbonate ions to the mineral flotability. The flotation mechanisms in galena-sphalerite system are discussed based on SCM.

Complexations in illite-fulvic acid-Cu2+ systems

As part of an extended project to illustrate how heavy metals are complexed by natural aquatic particles, we conducted various experiments to study the adsorption of fulvic acid (FA) at aqueous ill ...

A flexible method of carbonate determination using an automatic gas analyzer equipped with an FTIR photoacoustic measurement chamber

A Fourier transform infrared spectrometer was employed to determine automatically the total inorganic carbonate (TIC) in solids and waters, based on active photoacoustic absorption of infrared light by carbon dioxide. A 2.0 l reactor, connected to the spectrometer, is immersed in water-bath at 20 °C. After purging with pure N2, 5 ml of 0.5 mol l–1 HClO4 are injected into 50 ml of solid suspension or solution with continuous stirring. The specific absorption of infrared light by the CO2 evolved induces corresponding fluctuations of temperature and pressure in a measurement chamber. Accordingly, photoacoustic signals, with frequencies dependent on the absorbed wavelengths, are generated and measured by the chamber microphones in the form of an absorption spectrum and concentration. For solids, the method exhibits a linear response up to 120 mg of CaCO3 with a detection limit of 0.02 mg; in the case of waters, these figures of merit are 36.4 mmol l–1 and 3 µmol l–1 NaHCO3, respectively. Since proton consumption by TIC in clay minerals may commonly influence the evaluation of surface acid–base properties, the methodology was applied to determine TIC in three natural illite samples of different origins. In addition, some potential interferences and modifications of this method are discussed.

Shear Flocculation and Flotation of Galena and Synthetic PbS

The present work deals with the shear flocculation and flotation of galena and synthetic PbS and emphasis is laid on the surface charge and the degree of hydrophobicity of the particles. The results are discussed based on the zeta potential measurements and the turbidity tests and supporting evidence is provided by the scanning electron micrographs.

Variables in the shear flocculation of galena

Like froth flotation the shear flocculation is governed by the physical, chemical and geometrical variables. Among the important factors which influence the particle aggregation are the particle size, hydrophobicity, charge and the intensity of agitation. The present paper investigates the effect of different variables on the shear flocculation of (1). galena and (2). synthetic PbS. Since flocculation is influenced both by the charge and the hydrophobicity of the particle the zeta potentials were measured for different experimental conditions. The reaction mechanisms of PbS surfaces in aqueous solutions are examined based on the results; of electrokinetic- and potentiometric titration- studies. In comparison to conventional flotation, higher recoveries were obtained with shear flocculated aggregates. The results are discussed.