利用高低频土壤介电常数预测土壤Cd质量比研究

Prediction of cadmium mass ratio in soil using relative permittivity in high and low frequency

通过研究Cd质量比对土壤相对介电常数影响的变化规律,为地质雷达快速无损地探测重金属污染程度提供理论依据。首先在100 MHz和15 MHz频率下,使用高频Q表对已知含水率(0.05 cm^(3)/cm^(3)、0.13 cm^(3)/cm^(3)、0.16 cm^(3)/cm^(3)、0.20 cm^(3)/cm^(3)、0.25 cm^(3)/cm^(3)和0.28 cm^(3)/cm^(3))和Cd质量比(0、15.2 mg/kg、68.4 mg/kg、83.6 mg/kg、100 mg/kg、152 mg/kg、190 mg/kg和250 mg/kg)的土壤样品进行相对介电常数的测量。在剔除异常值后,使用最小二乘法对所获得的数据进行拟合得到在100 MHz下的相对介电常数与含水率之间的关系,并在15 MHz的相对介电常数条件下得到2个经验公式,即不同含水率下的Cd质量比与相对介电常数的关系式。最后在100 MHz和15 MHz 2个频率下测试了验证组土壤样品的相对介电常数,并使用经验公式对验证组样品的含水率和Cd质量比进行预测计算。结果表明:1)测量频率为100 MHz时,土壤介电常数与水分含量的拟合系数高达0.9984;2)测量频率为15 MHz时,各含水率下的土壤介电常数与Cd质量比的拟合系数在0.85以上;3)使用验证组数据对前述两组定量公式的校验结果表明,含水率的预测值和实测值差异在0.01 cm^(3)/cm^(3),Cd质量比的预测值和实测值差异约为6 mg/kg。因此,使用多个频率测定土壤的相对介电常数,并根据得出的经验公式可以定量分析相对介电常数与含水率和Cd质量比的数量关系,这为定量估算土壤中重金属质量比提供了新途径。

The study aims to study the quantitative relationship between cadmium mass ratio and soil relative permittivity,to provide theoretical guidance for ground-penetrating radar(GPR)to detect the mass ratio of heavy metals in soil.First,we measured the relative permittivity at 100 MHz and 15 MHz for the soil samples with known moisture content(0.05 cm^(3)/cm^(3),0.13 cm^(3)/cm^(3),0.16 cm^(3)/cm^(3),0.20 cm^(3)/cm^(3),0.25 cm^(3)/cm^(3)and 0.28 cm^(3)/cm^(3))and cadmium mass ratio(0,15.2 mg/kg,68.4 mg/kg,83.6 mg/kg,100 mg/kg,152 mg/kg,190 mg/kg and 250 mg/kg)by using the high Frequency Q meter.After removing the abnormal values,we used the least-squares method to fit the data and obtained two empirical formulas.One was the relationship between the relative permittivity and moisture content at 100 MHz;the other one was the relationship between cadmium mass ratio and relative permittivity under different moisture content by using the relative permittivity at 15 MHz.Finally,we measured the relative permittivity of the soil samples in the verification groups at 100 MHz and 15 MHz,and predicted the moisture content and cadmium mass ratio(30.4 mg/kg and 76 mg/kg)using the aforementioned empirical formulas.The results showed that:(1)When the measurement frequency was 100 MHz,the fitting coefficient of relative permittivity and moisture content was up to 0.9984;(2)When the measurement frequency was 15 MHz,the fitting coefficients of relative permittivity and cadmium mass ratio under different moisture content were all above 0.85;(3)The verification results of the aforementioned quantitative formulas using verification groups showed that the difference between the predicted value and the measured value of moisture content was 0.01 cm^(3)/cm^(3),and the difference between them of cadmium mass ratio was about 6 mg/kg.We used multiple frequencies to determine the relative permittivity of the soil samples and get two empirical formulas that can explain the relationship among the relative permittivity,moisture content,and cadmium mass ratio.It provides a new way to quantitatively estimate the mass ratio of heavy metals in the soil.