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The solubility of selenate-AFt (3CaO dot Al2O 3 dot 3CaSeO4 dot 37.5H2O) and selenate-AFm (3CaO dot Al2O3 dot CaSeO 4 dot xH2O)
The Se(VI)-analogues of ettringite and monosulfate, selenate-AFt (3CaO dot Al2O3 dot 3CaSeO 4 dot 37.5H2O), and selenate-AFm (3CaO dot Al 2O3 dot CaSeO4 dot xH2O) were synthesised and characterised by bulk chemical analysis and X-ray diffraction. Their solubility products were determined from a series of batch and resuspension experiments conducted at 25 degree C. For selenate-AFt suspensions, the pH varied between 11.37 and 11.61, and a solubility product, log K so = 61.29 +/- 0.60 (I = 0 M), was determined for the reaction 3CaO dot Al2O3 dot 3CaSeO 4 dot 37.5H2O+12 H+ <==> 6Ca2+ + 2Al3+ + 3SeO4 2- + 43.5H2O. Selenate-AFm synthesis resulted in the uptake of Na, which was leached during equilibration and resuspension. For the pH range of 11.75 to 11.90, a solubility product, log Kso = 73.40 +/- 0.22 (I = 0 M), was determined for the reaction 3CaO dot Al2O 3 dot CaSeO4 dot xH2O + 12 H+ <==> 4Ca 2+ + 2Al3+ + SeO42- + (x + 6)H2O. Thermodynamic modelling suggested that both selenate-AFt and selenate-AFm are stable in the cementitious matrix; and that in a cement limited in sulfate, selenate concentration may be limited by selenate-AFm to below the millimolar range above pH 12.
The solubility of selenate-AFt (3CaO dot Al2O 3 dot 3CaSeO4 dot 37.5H2O) and selenate-AFm (3CaO dot Al2O3 dot CaSeO 4 dot xH2O)
The Se(VI)-analogues of ettringite and monosulfate, selenate-AFt (3CaO dot Al2O3 dot 3CaSeO 4 dot 37.5H2O), and selenate-AFm (3CaO dot Al 2O3 dot CaSeO4 dot xH2O) were synthesised and characterised by bulk chemical analysis and X-ray diffraction. Their solubility products were determined from a series of batch and resuspension experiments conducted at 25 degree C. For selenate-AFt suspensions, the pH varied between 11.37 and 11.61, and a solubility product, log K so = 61.29 +/- 0.60 (I = 0 M), was determined for the reaction 3CaO dot Al2O3 dot 3CaSeO 4 dot 37.5H2O+12 H+ <==> 6Ca2+ + 2Al3+ + 3SeO4 2- + 43.5H2O. Selenate-AFm synthesis resulted in the uptake of Na, which was leached during equilibration and resuspension. For the pH range of 11.75 to 11.90, a solubility product, log Kso = 73.40 +/- 0.22 (I = 0 M), was determined for the reaction 3CaO dot Al2O 3 dot CaSeO4 dot xH2O + 12 H+ <==> 4Ca 2+ + 2Al3+ + SeO42- + (x + 6)H2O. Thermodynamic modelling suggested that both selenate-AFt and selenate-AFm are stable in the cementitious matrix; and that in a cement limited in sulfate, selenate concentration may be limited by selenate-AFm to below the millimolar range above pH 12.
The solubility of selenate-AFt (3CaO dot Al2O 3 dot 3CaSeO4 dot 37.5H2O) and selenate-AFm (3CaO dot Al2O3 dot CaSeO 4 dot xH2O)
Baur, I. (author) / Johnson, C.A. (author)
Cement and Concrete Research ; 33 ; 1741-1748
2003
8 Seiten, 32 Quellen
Article (Journal)
English
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