Solubility of kaolinite and beryl to 573 K

Compositions of aqueous solutions in equilibrium with quartz (SiO2), kaolinite (Al2Si2O5(OH)4) and beryl (Be3Al2Si6O18) in the system BeO-Al2O3-SiO2-H2O have been measured along the 5 phase subcritical curve for temperatures up to 573 K. The solubility data are consistent with the existence of mononuclear aqueous Si, Al, and Be hydroxy species from 363 to 573 K. Solutions at 473 and 573 K had pH adjusted between 3.5 and 5.5 by varying partial pressures of CO2 from 0 to 235 bars. Measured total aqueous Be exhibited no evidence of carbonate ion complexing. The significant mononuclear ionic species at equilibrium with quartz-kaolinite-beryl used in interpreting the results were H4SiO4°, Al3+, AlOH2+, Al(OH)2+, Al(OH)4°, Al(OH)4−, Be2+, Be(OH)+, Be(OH)2° and Be(OH)3−.The apparent Gibbs free energies of formation (cal/mol) calculated from this work for Be species to 573 K are:Temperature (K)Species298373473573Be2+−90 707−87 385−82 904−78 453BeOH+−140 049−139 051−137 809−136 722Be(OH)2°−185 464−185 958−187 121−188 821Be(OH)3−−229 052−229 716−230 200−227 590 These values are based on ΔG°(298) for Be2+ (−90707) and ΔG°(T) for Be2+ modelled after ΔG° (T) for Al3+. Hydrothermal transportation of Be as hydroxy-complexes appears adequate to explain the presence of beryl (emerald) deposits such as those found in the Muzo and Chivor districts of Colombia. Complexing by other ions such as chloride and fluoride has not been investigated but would presumably enhance the solubility. If transport is dominantly as hydroxy species in slightly acid waters, cooling cannot be a precipitating mechanism, but a pH shift caused by wall rock alteration, or by loss of CO2, would suffice.