|
|||||
|
|
Thermodynamic and kinetic aspects of formation of bauxites |
|
| Authors: | Mwakio P Tole |
| Institution: | Department of Geology, University of Nairobi, Nairobi, Kenya |
| Abstract: | Experiments in which cleavage nepheline samples were reacted with aqueous solutions at fixed pH's and temperature were carried out in the laboratory. The chemistry of the solution as a function of time was monitored, as well as the chemistry of the nepheline surfaces. At 25°C, Al derived from the nepheline stays in solution due to slow precipitation kinetics of Al(OH)3. At 60° and 80°C, precipitation of Al(OH)3 is so rapid that Al concentration in solution is below 0.05 ppm. This indicates that precipitation kinetics favour the formation of bauxite deposits in tropical regions (i.e. T Precipitation products on the surface of the nepheline fragments at 60° and 80°C depend on the pH. At pH 3.0, an amorphous aluminium silicate (proto-kaolinite?) is formed. At pH>7.0, the precipitated phase contains, in addition to Al and Si, high amounts of Na and K (proto-muscovite?). The optimum pH for the formation of bauxite is in the range 5–7. These results are in agreement with thermodynamic calculations. |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ | |
25°C), but not in temperate regions.