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- 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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- Wu, Liuming, et al.
(författare)
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Surface complexation of calcium minerals in aqueous solution : 1. Surface protonation at fluorapatite-water interfaces
- 1991
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 147:1, s. 178-185
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Tidskriftsartikel (refereegranskat)abstract
- The amphoteric properties of hydrous fluorapatite surfaces have been investigated. The measurements were performed as potentiometric titrations in 0.1M NaCl medium at 25°C using a glass electrode. The experimental data could be explained by a model that assumes the surface equilibria equivalent P-O- + H+ = equivalent P-OH log β101s(int.) = 6.6 ± 0.1 (3σ) equivalent Ca-OH2+ - H+ = equivalent Ca-OH log β-110s(int.) = -9.7 ± 0.1 (3σ). The equilibrium constants were evaluated using the computer program FITEQL by Westall (Report 82-01, Department of Chemistry. Oregon State University, Corvallis, 1982), assuming a constant capacitance model for the electric double layer. The acidity constants result in a value of log [H+]pzc = -8.15, which shifts to log [H+]pzc = -7.13 upon exposure to atmospheric carbon dioxide
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