P-sorption isotherms were determined for 37 Egyptian and Italian calcareous soils. The results were shown to be well described by the Freundlich, one-surface Langmuir and initial mass (IM) equations. Multiple regression equations of the soil properties related to P sorption parameters, showed that the regression coefficients were in the following order: active calcium carbonate equivalent (ACCE) >calcium carbonate equivalent (CCE) >citrate-bicarbonate-dithioniteextractable Fe (CBD-Fe) >clay. The Q parameter of the Langmuir isotherm resulted as the most suitable for providing direct evidence of the contribution of calcareous component in P sorption experiments carried out after removal of this component from soil. A phosphate sorption study on calcite, under varying ionic strength and dielectric constant of the P solutions, established that about 13% of the adsorption was caused by electrostatic attraction. Phosphate-treated calcite, after reaction times of 24h and 14d, was extracted sequentially with H2O (easily soluble Ca-P compounds) and 0.5 N NaHCO3 (slightly soluble Ca-P compounds). Only a small proportion of the added P was easily soluble, while with time an increase of sparingly and a decrease of slightly soluble Ca-P compounds were observed. X-ray diffraction of the P-calcite system after a contact of 14 days individuated only dicalcium phosphate anhydrate as reaction product.
|Autori:||Riffaldi R.; Saviozzi A.; Levi-Minzi R.;Wahba M.M.|
|Titolo:||Phosphate sorption by some Egyptian and Italian calcareous soils|
|Anno del prodotto:||2001|
|Appare nelle tipologie:||1.1 Articolo in rivista|