Silicon and aluminium in groundwater of the Kłodzko Region (the Sudetes, SW Poland) -- partial geochemical equilibrium with secondary solid phases

Abstract

The chemistry of shallow, cold groundwater in the eastern part of the Kłodzko Region (the Sudetes, SW Poland) was investigated. Groundwaters occur in the short turn-over time zone of the hydrogeological systems. The aquifers are composed of various bedrock types (metamorphic, igneous and sedimentary). Silicon and aluminium concentrations in the waters of particular aquifers are documented. The aqueous chemistry is interpreted in terms of the solubility of solid phases to indicate phases that are responsible for silicon and/or aluminium solubility control. Locally and/or periodically (seasonally) partial geochemical equilibrium between the groundwater and the secondary solid phases might be reached and maintained. In groundwater with a pH below 6.7, aluminium activity is usually controlled by the reversible congruent dissolution of Al(OH)3 forms, whereas silicon activity is probably controlled by the solubility the SiO2 form (chalcedony). At pHs above 6.7, the incongruent reaction between the hydroxyaluminosilicate colloid (HASB) and forms of Al(OH)3 controls both silicon and aluminium activities.