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Table 5 Total metal concentration of the humic acid fractions

From: Chemical and spectroscopic characterization of insoluble and soluble humic acid fractions at different pH values

Fraction

Ca

K

Mg

Na

(mol kg−1)

(mol kg−1)

(mol kg−1)

(mol kg−1)

pH 1

Insoluble

0.07ad

0.13ad

0.17ad

0.31a

Soluble

nd

nd

nd

nd

pH 3

Insoluble

0.11abcd

0.18a

0.22a

0.50a

Soluble

0.14abcd

0.06b

0.03b

1.69b

pH 5

Insoluble

0.12abcd

0.28c

0.55c

0.97c

Soluble

0.16bcd

0.07b

0.11d

2.32d

pH 7

Insoluble

0.09cd

0.33c

0.67e

1.00c

Soluble

0.14d

0.10bd

0.17ad

2.21d

  1. Within columns, values followed by the same letter are not significantly different (P < 0.05). nd, not determined because of the low amount of sample.