Mechanisms of phosphate sorption at alkaline pHKCl on ferralsol soil in central Vietnam
2010
Nguyen Ho Lam; Muehide Ishiguro; Hoang Thi Nguyen Hai; Nguyen Huu Ngu
There are several research the phosphate sorption on ferralsol soil in Vietnam. However, the mechanism of phosphate sorption at alkaline pH is not known well. The objectives of the study were to specify the capacity and mechanism of P sorption process of ferralsol soil at alkaline pH. P sorption isotherm were obtained by bath method at pH values of 7.0 and 8.5 in wide range of P concentration of 0.003 to 30mmol P/L at elapsed time of 3 hours and temperature 250C. P was added as form of Ca (H2PO4)2. H20 solution at 1mmolcCaCl2. 2H20. Ca(OH)2 was applied when the pH decreased after addition of P solution until the pH recovered to the initially prescribed pH. The results of experiment showed that: if the added P concentration 1.0 mmol/L at pH 7.0 and 0.3 mmol/L at pH 8.5, the P was removed from soil solution by adsorption reactions. If the added P concentration ¡Ý 1.0 mmol/L at pH 7.0 and ¡Ý 0.3 mmol/L at pH 8.5, the P was removed from soil solution by precipitation reactions. The mechanism of P sorption can be examined by ratio of amount of P sorption to net OH added and ratio of amount of P/Ca sorption.
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