Environmental Engineering Reference
In-Depth Information
column was required be coarse, so as to prevent the preferential flow of the water along the
inner wall of the tube.
Citric acid, malic acid, oxalic acid and acetic acid were prepared in a concentration of 10,
1 and 0.1mmol L -1 , respectively. The organic acids were provided by supply bottles and
entered the bottom of the soil column through the peristaltic pump at a flow rate of
0.4ml min -1 . The leaching solution was then flowed out from the top and collected by an
automatic collector. The concentration of phosphorus in the leaching solution was determined
by molybdenum blue method (Murphy et al., 1962).
1.3. Data Processing
1.3.1. Kinetic Fitting of Phosphorus Release
In order to accurately and quantitatively describe the dynamic release process of soil
phosphorus under the condition of continuous leaching by low molecular weight organic
acids, the parabolic diffusion equation was employed for the fitting of the experimental
results.
1/ 2
Q

Q
Rt
(9)
Q
Q
R
- Release amount of phosphorus within time t;
- Release amount of phosphorus when reaching balance;
- Diffusion rate constant of phosphorus.
1.3.2. Statistical Analysis
The data obtained were processed by Microsoft Excel 2007 and SPSS 17.0 software
packages. The mapping was conducted by Microsoft Excel 2007 and Matlab software
packages. The significance test of processing differences was conducted with the One-Way
ANOVA method of SPSS 17.0, showing a significance level of P <0.05.
2. R ESULTS AND A NALYSIS
2.1. Curves of Soil Phosphorus Leaching by Different Types
of Low Molecular Weight Organic Acids
As shown in Figure 1, the curves of soil phosphorus leaching by the four types of low
molecular weight organic acids present different characteristics. At the beginning of leaching,
none of them could leach out the soil phosphorus, which might be explained by the
adsorption of these four organic acids (citric acid, malic acid, oxalic acid and acetic acid) by
the soil. In the study conducted by Xu Renkou et al., (2007) on the dynamic leaching of
aluminum by organic acids, due to the adsorption of salicylic acid by the soil, no aluminum
was leached out at the beginning of leaching; when the adsorption of organic acids by the soil
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