Evaluation of the solubility constants of the hydrated solid phases in the H2O-Al2O3-SO3 ternary system
Résumé
During the acid processing of aluminosilicate ores, the
precipitation of a solid phase principally consisting of hydrated
aluminium hydroxysulfates may be observed. The experimental
study of the H2O-Al2O3-SO3 ternary system at 25
◦
C and 101 kPa
enabled to describe the solid-liquid equilibria and to identify the nature,
the composition and the solubility of the solid phases which may
form during the acid leaching. To predict the appearance of these
aluminium hydroxysulfates in more complex systems, their solubility
constants were calculated by modelling the experimental solubility
results, using a geochemical reaction modelling software, CHESS.
A model for non-ideality correction, based on the B-dot equation,
was used as it was suitable for the considered ion concentration
range. The solubility constants of three out of four solid phases
were calculated: 104.08 for jurbanite (Al(SO4)(OH).5H2O), 1028.09
for the solid T (Al8(SO4)5(OH)14.34H2O) and 1027.28 for the solid
V (Al10(SO4)3(OH)24.20H2O). However the activity correction model
was not suitable to determine the solubility constant of alunogen
(Al2(SO4)3.15.8H2O), as the ion concentrations of the mixtures were
too high and beyond the allowable limits of the model. Another ionic
activity correction model, based on the Pitzer equation for example,
must be applied to calculate the solubility constant of alunogen.