Study on the integrated distribution coefficient of ammonium N migration in layered soil

Adsorption is an important mechanism for contaminant transport in groundwater, which results in retardation of contaminant migration. Different types of soils have different amounts of ammonium N adsorption, and ammonium N will experience different types of soil as it migrates through the actual soil environment. To better explore the integrated adsorption effect of ammonium N as it moves through the soil, layered soil was considered as a whole in this study. Under the condition that ammonium N is not transformed, the relationship between the distribution coefficient of ammonium N in layered soil and that in a single soil layer was explored through batch and column experiments. The results showed that the integrated distribution coefficient of ammonium N in mixed soil was in good agreement with the linear superposition relationship between the distribution coefficient and mass of each single soil layer. In the one-dimensional column simulation experiment, a mathematical model of pollutant migration in soil was used to simulate the migration of ammonium N in the soil and verify parameters of the model. The model-fitted ammonium N concentration values were in good agreement with the measured values. The overall retardation factor of layered soil was linearly sum up of the retardation factor of a single soil layer by the thickness of each layer. The distribution coefficient of ammonium N in layered soil was integrated to the cumulative value of the product of the distribution coefficient and the thickness ratio of each single soil layer. When the difference in the density of the soil layers was small, the relationship between the integrated distribution coefficient of the layered soil and the distribution coefficient of a single layer could be adequately described by using the linear superposition relationship of the layered distribution coefficient and thickness.