Environmental Engineering Reference
In-Depth Information
400
90
soil A
soil B
citric a cid
oxa lic a cid
ma lic a cid
a cetic a cid
320
citric a cid
oxa lic a cid
ma lic a cid
a cetic a cid
60
240
160
30
80
0
0
0
0.05
0.1
0.5
1
2
5
10
20
0
0.05
0.1
0.5
1
2
5
10
20
orga nic a cid concentra tion (mmol / L)
orga nic a cid concentra tion (mmol / L)
Figure 1. The amount of P extracted by different concentrations of four organic acids in the two soil
solution. Symbols represent mean ± SEM (Standard Error of Mean).
3.2. P Desorption Influenced by Reaction Time
As reaction time extended, the releases of P extracted by organic acid were dynamic
changes for both soils (Figure 2). However, compared to soil A, the changes was more
obvious in soil B, especially influenced by reaction time of citric acid, oxalic acid and malic
acid. Within 5 h, a marked decrease of P concentration for citric acid, malic acid and oxalic
acid ( p <0.01), and a slightly decrease for acetic acid in two soils were observed.
Nevertheless, after 10 h, the curves presented in soil A was more smooth than that in soil B
which presented an increase trend except for oxalic acid extraction. In soil A, oxalic acid
activation capacity was more stable than citric acid and malic acids, and stronger than the
others after 5 h; in soil B, that capacity changed greatly.
3.3. P Desorption Influenced by pH of Organic Acids
The P extraction capacity of organic acids in different acidity-alkalinity in soil A was
shown in Figure 3. Organic acids without pH adjusted extracted more P from soil than those
adjusted by NaOH.
25
soil A
8
soil B
citric a cid
ma lic a cid
oxa lic a cid
a cetic a cid
citric a cid
ma lic a cid
20
6
oxa lic a cid
a cetic a cid
15
4
10
2
5
0
2
5
10
15
24
37
50
2
5
10
15
24
37
50
rea ction time (h)
rea ction time (h)
Figure 2. The amount of P extracted by different extraction time of four organic acids in the two soil
solution. Symbols represent mean ± SEM.
 
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