| 1. |
- Du, Qing, et al.
(författare)
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Acid-base properties of aqueous illite surfaces
- 1997
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 187:1, s. 221-231
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the acid-base properties of illite/water suspensions are examined using the constant capacitance surface complexation model. On the basis of results of potentiometric titrations and solubility experiments, we conclude that the proton reactions in the supernatants of illite suspensions can be successfully represented by proton reactions of Al(H2O)63+and Si(OH)4in water solutions. For illustrating the acidic characteristics of aqueous illite surfaces, two surface protonation models are proposed: (1) one site-one pKamodel, ≡SOH ≡SO-+ H+, pKaint= 4.12-4.23; (2) two sites-two pKas model, ≡SIOH ≡SIO-+ H+, pKintaI= 4.17-4.44, and ≡SIIOH ≡SIIO-+ H+, [dipKintaII= 6.35-7.74. Evaluation of these two models indicates that both of them can give good descriptions of the experimental data of systems with different illite concentrations and ionic strengths and that the one site-one pKa model can be considered as a simplification of the two sites-two pKas model. Since both models assume only deprotonation reactions at the illite surfaces, they suggest that the surface behavior of the illite is similar to that of amorphous SiO2. Model assumptions, experimental procedures, and evaluative criteria are detailed in the paper.
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| 2. |
- Du, Qing, et al.
(författare)
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Adsorption of copper at aqueous illite surfaces
- 1997
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 187:1, s. 232-242
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we conducted potentiometric titrations, batch adsorption experiments and FT-IR analysis to study the uptake of copper in illite/water suspensions and then applied the constant capacitance surface complexation model to interpret the reaction mechanism at the aqueous illite surfaces. Our research shows that the copper adsorption at these surfaces is strongly dependent on pH and that the adsorption causes a deprotonation of surface groups. We propose that the uptake of copper in the carbonate-free illite suspensions can be explained by the formation of mononuclear surface complexes, ≡SOCu+ and ≡SOCuOH, and a multinuclear surface complex, ≡SOCu2(OH)2+, followed by the formation of a bulk precipitate, Cu(OH)2(s), or a surface precipitate, ≡SOCu2(OH)3(sp). For the illite suspensions containing carbonates, we propose that the copper-illite interaction can be depicted by the formation of mononuclear surface complexes, ≡SOCu+and ≡SOCuOH, followed by the formation of a copper hydroxylcarbonate precipitate, Cu2(OH)2CO3(s), rather than a copper hydroxide precipitate. The existence of Cu2(OH)2CO3(s) in the carbonate-containing illite suspensions was identified by FT-IR analysis.
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| 3. |
- Du, Qing, et al.
(författare)
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Complexations in illite–fulvic acid–Cu2+ systems
- 1999
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 33:3, s. 693-706
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Tidskriftsartikel (refereegranskat)abstract
- 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 illite surfaces and the complexation of heavy metal copper(II) in illite-FA bi-complexant systems. By analyzing batch adsorption and potentiometric titration data, we found that (i) the adsorption of FA by illite decreases with increases in pH values and its pH adsorption edge resembles those of SiO2-FA and montmorillonite-FA systems described by other researchers, (ii) it is possible to effectively simulate the complexation of Cu2+ ions in illite-FA bi-complexant systems by taking it to be an additive complexation of two mono-complexant systems (FA-Cu2+ and illite-Cu2+) and (iii) FA can inhibit the retention of heavy metals at solid surfaces by forming soluble complexes with metal ions. The above results and conclusions are supported by FT-IR analysis of various illite-FA-Cu2+ systems.
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| 4. |
- Liu, Wenxin, et al.
(författare)
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A flexible method of carbonate determination using an automatic gas analyzer equipped with an FTIR photoacoustic measurement chamber
- 1999
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Ingår i: The Analyst. - 0003-2654 .- 1364-5528. ; 124:3, s. 361-365
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Liu, Wenxin, et al.
(författare)
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Comparative study of surface acid-base characteristics of natural illites from different origins
- 1999
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 219:1, s. 48-61
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Tidskriftsartikel (refereegranskat)abstract
- The acid-base characteristics of naturally occurring illites, collected from different locations, were investigated by potentiometric titrations. The experimental data were interpreted using the constant capacitance surface complexation model. Considerable release of Al and Si from illite samples and subsequent complexation or precipitation of hydroxyl aluminosilicates generated during the acidimetric forward titration and the alkalimetric back titration, respectively, were observed. Therefore, the acidimetric supernatant, rather than the neutral one, was regarded as the system blank for each illite suspension to yield the surface site concentrations. In order to describe the acid-base chemistry of aqueous illite surfaces, two surface proton-reaction models, introducing the corresponding reactions between the dissolved aluminum species and silicic acid, as well as a surface Al-Si complex on homogeneous illite surface sites, were proposed as follows: (i) Model I, qq@SOH<=>qq@SO-+H+, pKinta = 3.76-4.09, qq@SOH+Al3++H4SiO4<=>qq@SOAl(OSi(OH)3 )+ +2H+, pKSC = 3.06-3.53; (ii) Model II, Al3++H4SiO4+2H2O<=>Al(OH)2(OSi( OH)3) +3H+, pKf2 = 9.85-10.71, qq@SOH<=>qq@SO-+H+, pKinta = 3.73-4.08, qq@SOH+Al3++H4SiO4<=>qq@SOAl (OSi(OH)3)++2H+, pKSC = 3.31-3.48. The Kf2 constant in Model II was obtained by simulating the complex formation between the dissolved aluminum species and silicic acid that occurred in acidimetric supernatant when the hydroxide was added. Additionally, the following cation exchange reaction was also considered for a special case, where a large amount of K+ is released during the corresponding acidimetric titration, in which a high concentration of protons are consumed. qq@XH+K+<=>qq@XK+H+, pKi = 8.24-8.52. Optimization results indicated that both models could provide a good description of the titration behavior for all aqueous illite systems in this study. The intrinsic acidity constants for the different illites were similar in Model I, showing some generalities in their acid-base properties. Model I may be considered as a simplification of Model II, evident in the similarities between the corresponding constants. In addition, the formation constant for surface Al-Si species (complexes or precipitates) is relatively stable in this study.
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| 6. |
- Rönngren, Lars, et al.
(författare)
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Surface reactions in aqueous metal sulfide systems : 2. Ion exchange and acid/base reactions at the ZnSH2O interface
- 1991
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 145:2, s. 396-404
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Tidskriftsartikel (refereegranskat)abstract
- The amphoteric properties of hydrous ZnS surfaces as well as an ion exchange reaction between surface coordinated Zn2+ ions and H+ ions of the aqueous phase have been established. The measurements were performed as potentiometric titrations in 0.1 M NaClO4 medium at 25°C. Besides measuring -log[H+] by using a glass electrode, -log[S2-] was recorded (Ag/Ag2S selective electrode). In addition, the total concentrations of H+, Zn2+, 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 pK1s = 6.91 and pK2s = 10.28 for synthetic ZnS, and pK1s = 7.14 and pK2s = 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+ ↔ ≡SH2 + Zn2+ 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 K1s and K2s.
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| 7. |
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| 8. |
- Sun, Zhongxi, et al.
(författare)
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Degradation kinetics of ethyl-xanthate as a function of pH in aqueous solution
- 1997
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Ingår i: Minerals Engineering. - 0892-6875 .- 1872-9444. ; 10:4, s. 389-400
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Tidskriftsartikel (refereegranskat)abstract
- 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 tailings makes this information even more important. In this paper, the degradation kinetics of xanthate in homogeneous solution as a function of pH at 5 °C, 20 °C and 40 °C is systematically studied by UV-Visible spectrophotometric measurements. The results indicate that the degradation of ethyl xanthate is rapidly increased with decreasing pH at pH<7. At pH 7-8, the maximum half-life of the xanthate appears. The degradation was faster at pH 9-10, but at pHgt;10 the half-lives of xanthate once again increase. The investigations are also extended to different media other than pure water, such as, 0.1 M NaClO4, 0.1 M NaNO3 0.1 M NaCl as well as in the supernatants of flotation tailings of sulfide minerals.The rate constants of xanthate degradation are calculated and presented together with half-lives and activation energies of xanthate degradation. The degradation products and reaction mechanisms are discussed based on experimental results.
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| 9. |
- Sun, Zhongxi
(författare)
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Surface reactions in aqueous metal sulfide systems
- 1991
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surface reactions in aqueous metal sulfide systems have been studied. The composition and stability of various complexes at the PbS-H20 the PbS/H20 and ZnS/H20 interface were evaluated. Experimental techniques widely used in solution chemistry such as potentiometric titrations and solubility measurements were applied in studying surface reactions in these systems, in conjunction with zeta potential and spectrophotometric determinations. Computer assisted analysis, using advanced computer programs like FITEQL and SOLGASWATER was used as a main method to treat data and to establish speciation models. Experimental data and theoretical values were compared and good agreement was achieved. Acid-base and ion exchange properties at the metal sulfide/water interface were discovered, which form basic reactions in metal sulfide suspensions. The complexation of sulfide and xanthate ions at the sulfide mineral surface was also quantitatively studied and a series of equilibrium constants for surface reactions are presented. The correlation between surface complexation by protons, hydroxide and crystal component ions, like metal and sulfide ions, and surface charge was qualitatively investigated, and furthermore the potential determining ions at the sulfide surface were identified. Special attention is paid to the applications of the surface reactions in flotation systems and some flotation mechanisms are discussed based on these surface reactions.
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| 10. |
- Sun, Zhongxi, et al.
(författare)
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Surface reactions in aqueous metal sulfide systems : 1. Fundamental surface reactions of hydrous PbS and ZnS
- 1991
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Ingår i: International Journal of Mineral Processing. - 0301-7516 .- 1879-3525. ; 33:1-4, s. 83-93
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Tidskriftsartikel (refereegranskat)abstract
- 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 as the natural minerals galena and sphalerite were performed. An experimental method for accurate determination of the concentration of reacted protons at the metal sulfide surface is presented. In slightly acidic solutions an ion exchange reaction between protons and surface metal ions was discovered leading to quite high metal ion concentrations in the bulk solution.
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| 11. |
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| 12. |
- Sun, Zhongxi, et al.
(författare)
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The SiO2 H2O interface and effects on quartz activation in flotation system
- 1992
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Ingår i: Transactions of Nonferrous Metals Society of China. - 1003-6326 .- 2210-3384. ; 2:2, s. 16-227
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Tidskriftsartikel (refereegranskat)abstract
- The correlation between surface complexation at the SiO2-H2O interface and quartz flotation behavior was studied. Computer assisted calculations, using the programs SOLGASWATER, were adapted to construct distribution diagrams of surface speciation in the SiO2-metal ion-H+ system in aqueous solutions. Equilibrium constants for both surface and solution reactions were introduced in the composition matrix. Surface complexation, surface change and flotation results were compared and a good agreement was obtained. Furthermore, flotation mechanisms of quartz activation by common metal ions like Ca2+ , Mg2+ , Fe3+ are quantitatively discussed based on the surface reaction equilibrium constants.
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| 13. |
- Yang, Xiaofang, et al.
(författare)
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Application of ATR-FTIR spectroscopy in the study of adsorption on environmental micro-interfaces
- 2010
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Ingår i: Huaxue jinzhan. - 1005-281X. ; 22:6, s. 1185-1194
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Tidskriftsartikel (refereegranskat)abstract
- Interfacial adsorption process is the initial step or key step for most of environmental micro-interface reactions. The online study of environmental micro-interfacial adsorption by in situ research methods provides direct information about interface reactions and reliable evidence for the detection of reaction mechanisms which are of great importance to understand the rule of transformation and distribution of pollutants in the environment. Because of its unique sampling principle, convenient sample pre-treatment and wide applicability, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) is becoming a powerful tool for investigating the interface reactions. Based on a brief introduction of the working principle of ATR-FTIR, the application of this technique in the investigation of adsorption on environmental interfaces, especially mineral-water interfaces, is summarized. Furthermore, the perspective of this method is discussed as well.
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| 14. |
- Yang, Xiaofang, et al.
(författare)
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Effect of phosphate on heterogeneous Fenton oxidation of catechol by nano-Fe3O4 : Inhibitor or stabilizer?
- 2016
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Ingår i: Journal of Environmental Sciences(China). - : Elsevier BV. - 1001-0742 .- 1878-7320. ; 39, s. 69-76
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Tidskriftsartikel (refereegranskat)abstract
- The effect of phosphate on adsorption and oxidation of catechol, 1,2-dihydroxybenzene, in a heterogeneous Fenton system was investigated. In situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) was used to monitor the surface speciation at the nano-Fe3O4 catalyst surface. The presence of phosphate decreased the removal rate of catechol and the abatement of dissolved organic compounds, as well as the decomposition of H2O2. This effect of phosphate was mainly due to its strong reaction with surface sites on the iron oxide catalyst. At neutral and acid pH, phosphate could displace the adsorbed catechol from the surface of catalyst and also could compete for surface sites with H2O2. In situ IR spectra indicated the formation of iron phosphate precipitation at the catalyst surface. The iron phosphate surface species may affect the amount of iron atoms taking part in the catalytic decomposition of H2O2 and formation of hydroxyl radicals, and inhibit the catalytic ability of Fe3O4 catalyst. Therefore, phosphate ions worked as stabilizer and inhibitor in a heterogeneous Fenton reaction at the same time, in effect leading to an increase in oxidation efficiency in this study. However, before use of phosphate as pH buffer or H2O2 stabilizer in a heterogeneous Fenton system, the possible inhibitory effect of phosphate on the actual removal of organic pollutants should be fully considered.
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| 15. |
- Yang, Xiaofang, et al.
(författare)
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Surface acid-base properties and hydration/dehydration mechanisms of aluminum (hydr)oxides
- 2007
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 308:2, s. 395-404
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, surface physiochemical properties of three typical aluminas, γ-Al(OH)3, γ-Al2O3, and α-Al2O3, were investigated by means of XRD, SEM, TEM, BET surface area, TG/DTA, and potentiometric titration techniques. Based on the titration data, surface protonation and deprotonation constants were determined using the constant capacitance model (CCM). The emphasis of this research was laid on the comparison of the crystal structure, surface hydration/dehydration and acid-base properties of these three typical alumina minerals. The calculation results revealed that the surface acidity of the aluminas is in the order of α-Al2O3>γ-Al(OH)3>γ-Al2O3 after being hydrated for 1 h. The correlation between the hydration/dehydration mechanisms of alumina and its acid/base properties is discussed.
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