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Experimental simulation and dynamic model analysis of Cadmium (Cd) release in soil affected by rainfall leaching in a coal-mining area
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Abstract: In order to explore the influence of rainfall on the release of heavy metal Cadmium (Cd) in soil in a coal-mining area,soil column leaching experiments were carried out by simulating 3 types of rainfall (acid rain,normal rainfall,and actual rainfall) with 5 different pH values (4,5,6,6.7,7),and 65 groups of data about leachate pH value and Cd concentration were obtained respectively. The results indicate the general change rule of Cd concentration in leachate: (1) the easiness of Cd release is negatively correlated to the pH value of leaching solution and positively correlated the leaching amount; (2) leaching solution with lower pH values shows more obvious release stages. Leached by solution with different pH values,the release of Cd in soil ranks as follows: Acid rain group > normal rainfall group > actual rainfall group. In the first stage,the acidity of rainfall has a significant impact on the release of Cd in soil,but in the second stage,the release of Cd is alleviated due to the soil buffering. Among the four dynamic equations to simulate the release of Cd in soil,the modified Elovich equation can describe the process most accurately,with the highest coefficient of determination R2 of 0.997 5. These results can serve as a reference for further study on the migration,transformation and enrichment of Cd in soil.
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Key words:
- Rainfall /
- pH value /
- Soil /
- Cd /
- Dynamic equation
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Table 1. Kinetic fitted results of Cd release in soil under simulated rainfall conditions
Subject First-order kinetics equation y=ax+b Parabolic equation y=a+bx+cx2 Double constant rate equation y=axb Modified Elovich equation y=a-b*ln(x+c) pH a b R2 a b c R2 a b R2 a b c R2 4 0.062 9 0.099 5 0.925 1 0.061 4 0.118 6 -0.012 5 0.970 5 0.174 5 0.480 5 0.983 7 0.160 7 -0.118 4 0.210 2 0.992 0 5 0.050 2 0.069 7 0.974 8 0.052 0 0.076 0 -0.005 8 0.990 9 0.127 9 0.517 3 0.997 3 -0.040 1 -0.175 6 1.572 0 0.994 6 6 0.048 1 0.049 8 0.956 8 0.025 5 0.083 6 -0.008 0 0.989 5 0.105 2 0.579 0 0.993 6 0.042 1 -0.121 5 0.713 1 0.997 4 6.7 0.037 1 0.054 7 0.943 4 0.032 8 0.069 1 -0.007 2 0.987 4 0.098 5 0.498 4 0.993 4 0.070 1 -0.082 2 0.457 0 0.997 5 7 0.036 2 0.056 4 0.936 8 0.034 8 0.067 6 -0.007 1 0.981 1 0.099 4 0.485 1 0.990 9 0.081 2 -0.074 5 0.338 0 0.996 0 Note: X is the leaching amount, L; Y is the cumulative leaching loss of Cd, μg. 
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Table 2. Mathematical statistics of pH value of leachate
Soil column Number Maximum pH Minimum pH Average pH Standard deviation Mean square deviation Coefficient of variation (%) pH=4 13 7.46 7.02 7.18 0.128 0.133 1.78 pH=5 13 7.39 7.06 7.22 0.105 0.109 1.45 pH=6 13 7.63 7.18 7.33 0.135 0.140 1.84 pH=6.7 13 7.66 7.23 7.38 0.119 0.124 1.61 pH=7 13 7.61 7.29 7.45 0.087 0.090 1.17 Results 65 7.66 7.02 7.31 0.154 0.155 2.11
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