Gypsum Precipitation – A Medium to Control Sulphate Pollution of Freshwater Sediment Leachates |
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Authors: | Fajtl Jiří Tichý Richard Ledvina Rostislav |
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Affiliation: | 1.Faculty of Agriculture, University of South Bohemia, Studentská 13, 370 05, ?eské Budějovice, Czech Republic ;2.Faculty of Agriculture, University of South Bohemia, Studentská 13, 370 05, ?eské Budějovice, Czech Republic ; |
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Abstract: | To treat sulphate pollution resulting from freshwater sediments,an experimental study was done. This experimental study was carried out to determine the effects of pH values and calcium supplements (as CaCl2) on the formation of gypsum in a representative wetland sediment that was aerated. It was foundthat the differences between dissolved sulphate in untreatedcontrol and the other treatments with CaCl2 amendments canbe attributed to the precipitation of gypsum. At the same time, the system was highly affected by Ca adsorption/desorption thatwas controlled by pH values. ECOSAT equilibrium simulations showed that CaCl2 additions (0.2–0.3 mol L-1) to aerated freshwater sediment resulted in removal of 78–98% ofsulphate (from its total content) from the solution. It wascaused by favourable conditions for gypsum formation i.e. acidicpH values were not increased due to the neutral character of CaCl2. On the contrary to CaCl2 amendments, CaCO3supplements (in the same Ca doses as applied in CaCl2) caused the removal of only 5–25% of sulphate. The significantincrease of pH values after the application of CaCO3 limitedgypsum formation due to high saturation of the system with CO3 -2 and HCO3 -. It resulted in the prevalence of CaCO3 formation in this system. However, theaddition of Cl- can facilitate the mobilisation of cationicmetals like Cd and Pb in the form of Cl--complexes. Therefore, CaCl2 treatment should be used in the sites thatdo not contain elevated amounts of these metals. |
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