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Sequential extraction of calcium in lake sediments for investigating the cycle of phosphorus in water environment
He, J.; Liu, G. L.; Zhu, D. W.; Cai, J. B.; Zhou, W. B. & Guo, W. W.
Abstract
The role of calcium (Ca) in the cycle of phosphorus
in water environment depends on the speciation of
Ca in sediments, and reliable Ca sequential extraction
method is useful for obtaining information about Ca
transport processes from sediment to water. Experiments
have been carried out to develop a simple but robust Ca
sequential extraction method for identification of Ca portioning
in sediments. The sequential extraction protocol
was modified for extractants, extracting time, concentration
and pH of the reagents in the first three steps of Tessier
sequential procedure. With optimum conditions, there were
1:25 sediment to solution ratio and 3 h of extracting time
shaken with NH4AC (1 mol L-1, pH 7.0) (exchangeable
Ca fraction); 1:25 sediment to solution ratio and extracted
with NH4AC (1 mol L-1, pH 5.0) for 5 h (carbonate-bound
Ca fraction); and 1:30 sediment to solution ratio and
extracted with NH2OH HCl (0.5 mol L-1, pH 1.5) for 6 h
(Fe and Mn oxides bound Ca fraction). The recovery for
Tessier procedure ranged form 35.6 to 71.1 %, while the
recovery for the modified Tessier procedure ranged form
46.1 to 86.9 %. These results revealed that Tessier procedure
underestimated the proportion of Ca in exchangeable
fraction. In sediments, Ca was mainly exchangeable and
carbonate bound, which was considered as the most liable
fractions.
Keywords
Fraction protocol; Modified Tessier procedure; Condition selection; Recovery
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