Wyniki wyszukiwania - BazTech

Ograniczanie wyników

2 Dobrzyński D.

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: hydroxyaluminosilicates (HAS)

Sortuj według:

Ogranicz wyniki do:

Silica solubility in groundwater from Permian volcanogenic rocks (the Sudetes Mts., SW Poland) : the role of reversible aluminosilicate solids

Dobrzyński D.

Geological Quarterly

2006

Vol. 50, No. 4

407-417

The chemistry of groundwater in Permian volcanic rocks (rhyolitic tuffs, trachyandesites) in two small headwater catchments (the SudetesMts., SW Poland) has been investigated. The calculated transfer of silica released during weathering is greater than the real concentration in groundwater, and indicates that part of the silica is immobilized in secondary aluminosilicates. Silica solubility is interpreted in terms of the solubility of reversible secondary aluminosilicates (allophanes, hydroxyaluminosilicates). Partial chemical equilibrium of these phases is sometimes locally achieved. In groundwaters with pH above 6.7 from trachyandesites of the BukowiecMt. type, chemical equilibrium with respect to the hydroxyaluminosilicate HASB is probably maintained. Its solubility constant, calculated accordingly to the method given by Schneider et al. (2004), is lgK HASB = –44.74 (۪.52), and indicates that this "field" HASB has a solubility lower than the published experimental value (lgK HASB = –40.6 ۪.15) for synthetic HASB (op.cit.). Non-equilibrium with respect to aluminosilicates in groundwaters from rhyolitic tuffs and from trachyandesites of the Stożek Wielki Mt. type is caused by the short turn-over time of groundwater in the systemand by the poor neutralisation capacity of the bedrock. The silica concentration in these groundwaters results from steady-state conditions achieved between weathering release, hydrological removal and precipitation of secondary phases. The hydrogeochemical data are conducive to the presence of allophane minerals in the weathered rhyolitic tuffs.

Silica origin and solubility in groundwater from the weathered zone of sedimentary rocks of the Intra-Sudetic Basin, SW Poland

Dobrzyński D.

Acta Geologica Polonica

2005

Vol. 55, no. 4

445-462

The groundwaters studied in the Intra-Sudetic Basin, SW Poland, occur in the regolith and in the fissured bedrock. Silica concentration in groundwaters ranges from 0,7 to 24,1 mg/L SiO2. Mineral phases that are the source of silica solute were pointed out on bedrock mineralogy and saturation state analysis. Interpretation of aqueous chemistry in terms of mineral stability confirms that partial geochemical equilibrium is maintained. In groundwater with pH values below 4.8 from the fissured aquifer in Carboniferous siliciclastic rocks, kaolinite controls silica solubility. Congruent dissolution of the allophane phase and/or incongruent reaction between the Al(OH)3 form and kaolinite/ halloysite or allophane can be responsible for silica activity in groundwater, with pH values between 5,5 and 6,7, from the regolith on Carboniferous rocks and from the fissured aquifer in Cretaceous mudstones.Groundwaters with pH values above 6,7 occur in the Permian and Cretaceous fissured aquifers which contain calcite/dolomite minerals. Silica and aluminium concentrations in these aquifers are clearly maintained by equilibrium with the hydroxyaluminosilicate HASB. The solubility constant of HASB estimated on groundwater chemistry is lgK HASB = -44,88 (± 0,48), which is lower than the recently published experimental value (SCHNEIDER and al. 2004). In groundwater with pH values between 4,8 and 5,5 from the regolith sampled during snow melt, equilibrium, even with reversible secondary aluminosilicates, is not maintained. Silicon and aluminium concentrations result from kinetics or steady-state between weathering release and hydrological removal.