Chemistry for Sustainable Development 15 (2007) 329-342 Processes of Chemical Weathering of Minerals in Sulphide-Containing Tailing Dumps: Modeling of the Composition of Vadose Water and Secondary Phases

Abstract Thermodynamic model of the oxidative leaching of sulphide-rich tailings from dressing of gold-containing ores (Berikul settlement, West Siberia) is investigated. When calculating the water-rock interactions, we applied some special approaches allowing one to determine the effect of the degree of reaction progress and change of the parameters of the medium (E h , pH) on the composition of the formed secondary minerals that restrain the development of acid drainage at the objects of this kind. Substantiation of several stages of the formation of a technogenic system in time and space is presented, depicting the approach of the system to equilibrium with the environment. The distinguished stages correspond to the zoning of mineral associations described at the object. These associations were formed during 50 years of storing the tailing mounds from the lowest weakly oxidized sulphide parageneses with gypsum and covellite to the capping jarosite-quartz-gypsum zones. The results of modelling provide evidence that an increase in rock affection by atmospheric water brings about the conditions favourable for the formation of the "final" association (goethite and quartz); however, this association is not stable even on the surface of the Berikul tailing dump. It is concluded on the basis of preliminary evaluation that hypergenesis processes in the objects of this kind may proceed hundreds of years till complete depletion of the acid-producing and toxic potential of industry-related wastes