Adsorption of chlorinated hydrocarbons by different kinds of soils: Kinetics, influencing factors, mechanism

• Characterization of adsorption of three CHCs by three soil types was explored. • Effect of pH change on adsorption capacity. • Factor importance in adsorption process ranked using Gray Correlation Analysis. • The mechanism of influencing factors on adsorption is explored. Chlorinated hydrocarbons (CHCs), toxic and persistent pollutants from pesticides/solvents, threaten groundwater and human health. At this stage, research on soil adsorption of CHCs has many limitations in terms of soil media, pollutant types and the influence of soil properties, which restricts the in-depth development of pollution prevention and control and risk assessment. This study investigated the adsorption behavior of three CHCs in different soil types through batch static adsorption experiments, combined with adsorption kinetics and isotherm models. Grey correlation analysis was used to determine the relative importance of various influencing factors. Results indicated that clay soil exhibited the highest adsorption capacity for CHCs, with the highest adsorption level of 1,2,4-trichlorobenzen. The results of the study showed that clay soil showed the highest adsorption of 58.86 μg/g of the three CHCs, which was greater than loam soil (52.4 μg/g) and sand soil (46.5 μg/g). The maximum adsorbing capacity of 1,2,4-Trichlorobenzene was reaching 58.86 μg/g, which was greater than that of p-chlorobenzene (50.1 μg/g) and carbon tetrachloride (40.5 μg/g) in the same soil medium. Furthermore, the study revealed that soil pH influenced the adsorption capacity of CHCs, with neutral pH resulting in the weakest adsorption. The analysis also identified the order of importance of influencing factors for different CHCs. For 1,2,4-trichlorobenzene and chlorobenzene, pollutant concentration was the most influential factor, followed by particle size, zeta potential, pH, and organic matter content. On the other hand, for carbon tetrachloride, pollutant concentration was the most significant factor, followed by particle size, organic matter content, zeta potential, and pH. This study effectively remedied the limitations of the research on soil adsorption of CHCs at the present stage, and provided an important scientific basis for environmental risk assessment and soil pollution prevention and control.