Environmental Engineering Reference
In-Depth Information
aluminum. For citric acid, the soil phosphorus began to be leached out when the volume of
the leaching solution reached 310ml (Table 2). With the continuous leaching by citric acid,
the amount of phosphorus leached rapidly increased to its maximum level (8.4mg kg
-1
) and a
relatively high release amount could be maintained at this point. The amount of phosphorus
leached began to decline when it reached 2,710ml, and the concentration of phosphorus
became 0 at the point of 3,550ml. For malic acid, the amount of phosphorus leached began to
gradually increase when the leaching volume reached 430ml and then decrease after the
leaching volume was above 4150ml. A stable release amount (4.5mg kg
-1
) was maintained
when the leaching volume was between 760 and 4,150ml. For oxalic acid, the soil phosphorus
began to be leached out when the leaching volume reached 1,030ml. When the leaching
volume was between 1,030 and 3,100ml, the amount of phosphorus leached was maintained
at a relatively low level, which might be explained by the fact that the oxalic acid is more
easily adsorbed by the soil. When the leaching volume reached 3,100ml, the amount of
phosphorus leached began to gradually increase to its peak (4.5mg kg
-1
) and then rapidly
decreased to 0 after the point of 3,550ml. Affected by acetic acid, the release amount of
phosphorus also showed a trend of increasing first and decreasing then; however, its
maximum release amount of phosphorus (2.7mg kg
-1
) was lower than that of citric acid, malic
acid and oxalic acid. In addition, the activation of soil phosphorus by acetic acid is a stable
and slow process. After the leaching volume reached 12,000ml, there was still phosphorus
being leached out, but the concentration was already very low. The following order could be
observed in terms of the maximum release amount of phosphorus: citric acid>malic
acid>oxalic acid>acetic acid. For the accumulated release amount of phosphorus, the order
was malic acid>citric acid>acetic acid>oxalic acid.
Table 2. The effects of four organic acids on the soil P release with soft leaching
P/T(cumulative)
(%)
Citric acid 310 8.4 1.1 469.1 62.7
Malic acid 430 5.4 0.7 507.8 67.9
Oxalic acid 1030 4.5 0.6 267.5 35.8
Acetic acid 970 2.7 0.36 445.2 60.0
(V(min): least organic acid for P release; P(maxi) and P/T(maxi): maximum phosphorus and rate of
total phosphorus released at leaching experiment; P(total) P/T(total): cumulative phosphorus and
cumulative rate of total phosphorus released at leaching experiment).
V(min)
(ml)
P(maxi)
(mg/kg)
P/T(maxi)
(%)
P(cumulative)
(mg/kg)
acid
9
a
6
3
0
0
1000
2000
3000
4000
Leching volume(mL)
