Evaluation of the solubility constants of the hydrated solid phases in the H2O-Al2O3-SO3 ternary system

International audienceDuring the acid processing of aluminosilicate ores, theprecipitation of a solid phase principally consisting of hydratedaluminium hydroxysulfates may be observed. The experimentalstudy of the H2O-Al2O3-SO3 ternary system at 25◦C and 101 kPaenabled to describe the solid-liquid equilibria and to identify the nature,the composition and the solubility of the solid phases which mayform during the acid leaching. To predict the appearance of thesealuminium hydroxysulfates in more complex systems, their solubilityconstants were calculated by modelling the experimental solubilityresults, 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 concentrationrange. The solubility constants of three out of four solid phaseswere calculated: 104.08 for jurbanite (Al(SO4)(OH).5H2O), 1028.09for the solid T (Al8(SO4)5(OH)14.34H2O) and 1027.28 for the solidV (Al10(SO4)3(OH)24.20H2O). However the activity correction modelwas not suitable to determine the solubility constant of alunogen(Al2(SO4)3.15.8H2O), as the ion concentrations of the mixtures weretoo high and beyond the allowable limits of the model. Another ionicactivity correction model, based on the Pitzer equation for example,must be applied to calculate the solubility constant of alunogen