Sorption of humic acid to soil: the role of soil mineral composition

In this study, the importance of individual soil mineral constituents on humic acid (HA) sorption is evaluated by employing a scanning electron microscope (SEM) equipped for energy-dispersive X-ray analysis (EDAX). The goal of the study is to observe the microchemical surface composition of model soil colloids and relate the surface microchemical composition to the sorption behavior of a peat soil derived HA on selected model soil colloids. This information is critical to understanding the fate and transport of subsurface contaminants. Results obtained from this study indicate the existence of a correlation between the atomic ratio of (Al+Fe) : Si of soil colloid surfaces and the HA sorption capacity, where those soil colloids with larger values of the (Al+Fe) : Si ratio are able to sorb HA more efficiently. This allows us to predict that the HA sorption capacity for soil colloids increases with progressively increasing states of soil maturity.