EXPERIMENTAL STUDY OF THE STABILITY OF ALUMINATE-BORATE COMPLEXES IN HYDROTHERMAL SOLUTIONS
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dc.contributor.author | Tagirov B. | |
dc.contributor.author | Schott J. | |
dc.contributor.author | Harrichoury J.-C. | |
dc.contributor.author | Escalier J. | |
dc.date.accessioned | 2022-04-17T09:21:30Z | |
dc.date.available | 2022-04-17T09:21:30Z | |
dc.date.issued | 2004 | |
dc.identifier | https://www.elibrary.ru/item.asp?id=14466042 | |
dc.identifier.citation | Geochimica et Cosmochimica Acta, 2004, 68, 6, 1333-1345 | |
dc.identifier.issn | 0016-7037 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/37199 | |
dc.description.abstract | Formation of aqueous aluminate-borate complexes was characterized at 25°C using 27Al NMR spectroscopy, and at 50–200°C via measurements of gibbsite and boehmite solubility in the presence of boric acid. 27Al spectra performed at pH = 9 in Al-B solution with m(B) = 0.02 show the presence of two peaks at 80.5 and 74.5 ppm which correspond to Al(OH)4− and a single Al-substituted Q1Al dimer, Al(OH)3OB(OH)2−, respectively. In 0.08 m and 0.2 m borate solution, a third peak appears at 68.5 ppm which can be assigned to the Q2Al trimer Al(OH)2O2(B(OH)2)2−. These chemical shifts are close to those measured for Al(OH)3OSi(OH)3− and Al(OH)2O2(Si(OH)3)2− (74 and 69.5 ppm, respectively; Pokrovski et al., Min. Mag.62a (1998), 1194) which demonstrates the similar structure of Al-B and Al-Si complexes formed in alkaline solutions. Gibbsite and boehmite solubility were measured in weakly basic solutions as a function of boric acid concentration at 50°C and 78 to 200°C, respectively. Equilibrium was reached within several days at m(B) = 0.01–0.1, but more slowly at higher boron concentrations, and at 50°C and m(B) = 0.2, Al concentration increased continuously during at least 3 months as a result of the sluggish formation of Al-polyborates. The equilibrium constant of the reaction Al(OH)4− + B(OH)30(aq) = Al(OH)3OB(OH)2− + H2O decreases very slowly with increasing temperature to 200°C. The log K values are 1.58 ± 0.10, 1.46 ± 0.10, 1.52 ± 0.15, and 1.25 ± 0.15 at 50, 78, 150 and 200°C, respectively, which result in the following values of the standard thermodynamic properties for this reaction: ΔrG0 = −9.22 ± 3.25 kJ/mol, ΔrH0 = −4.6 ± 2.5 kJ/mol, ΔrS0 = 15.5 ± 6.9 J/mol K. The thermodynamic data generated in this study indicate that Al-B complexes can dominate aqueous aluminum speciation in solutions containing ≥0.7 g/L of boron at temperature to at least 400°C. | |
dc.title | EXPERIMENTAL STUDY OF THE STABILITY OF ALUMINATE-BORATE COMPLEXES IN HYDROTHERMAL SOLUTIONS | |
dc.type | Статья |
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