Sorption of trace metals by humic materials in soils and natural waters

Trace metal sorption by coagulated humic acid and peat materials can be described macroscopically either as a complexation or a cation exchange phenomenon. Model equilibrium constants or selectivity coefficients for trace metal sorption by H‐form humic materials are special cases of two general models which do not depend on the sorption mechanism. Sorption mechanisms can be elucidated by spectroscopic techniques, both optical and magnetic resonance, but no information about mechanisms can be inferred from equilbrium constants.