Humic acids are complex organic molecules ubiquitous in both terrestrial and aqueous environments. In addition, several studies have shown a large fraction of humic acid-like substances on tropospheric aerosol particles. Humic acids are well-known chelating agents, a property that makes them a fundamental part of metal transport mechanisms in the environment. In particular, the chelating properties of humic acids may increase the mobility of iron, an element that can be toxic to plants at high levels and can stimulate plant growth at lower levels. Additionally, the humic acid-iron complex can be impacted by other environmentally abundant cations. In this work, we use colorimetric methods to examine the cation exchange of aluminum(III) with both iron oxidation states in humic acids. The colorimetric methods employed are selective for iron speciation with no significant interferences observed by aluminum and humic acids.  An effective complex formation of aqueous phase iron with humic acids was observed during suspension experiments. In addition, the redox properties of humic acids show no oxidation of iron (II) after chelation by humic acid. Cation exchange with aluminum suggests that iron chelates with humic acids in a combination of exchangeable and inexchangable iron, with a higher proportion of exchangeable iron incidence.<br/>

Colorimetric evaluation of the cation exchange of aluminum with iron in humic acids

249th National Meeting (2015)

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