The transport of humic acid in soils

The transport of humic acid in different soils at various conditions was studied. The transport of humic acid varied markedly with experimental conditions. Under the conditions of high solution pH values, high humic acid concentrations and fluid velocities, the retardation and humic acid adsorption on soil particles were less than that at the condition of low solution pH values, low humic acid concentrations and fluid velocities, indicating that the transport of humic acid was favored with the increase of solution pH values, humic acid concentrations and fluid velocities. The transport of humic acid was also related with soil properties. The high clay content and cation exchange capacity enhanced the adsorption of humic acid in soils, thus retarded the transport in soils. Humic acid adsorption was the major process controlling the transport of humic acid in soils. The adsorption of humic acid varied with solution chemical properties and soil properties and should be considered in predicting humic acid behaviors in soil and water environment.