Net efflux of Cu from a treatment wetland has been observed following a storm event.  Following a storm, pH increased and total metal concentrations decreased dramatically.  The drop in total metal concentrations was primarily due to iron oxide precipitation and coprecipitation.  Asymmetric flow field flow fractionation coupled to inductively coupled plasma mass spectrometry was used to examine metal size distribution.  Prior to the storm, all dissolved Cu was in the 1 nm or smaller size range, but following the storm, up to 60% of the dissolved Cu was associated with 1-5 nm sized colloids of iron and organic matter (OM).  Laboratory experiments mimicking the precipitation events in wetlands were conducted to assess the size and Cu sorption in iron oxide � OM coprecipitates formed with or without humic acids present.  Coprecipitation products were prepared by varying the molar ratio of Fe:OM from 1:0 to 1:10 with a fixed Cu concentration and a pH range of 4 to 7.  Scanning electron microscopy images indicate hydrous ferrous oxides precipitated alone are approximately 5 nm in diameter, while those precipitated in the presence of humic acids are in aggregates with less than 1 nm particles of iron oxides.  As the ratio of Fe:OM decreased, less coprecipitation of Cu occurred per gram of material; while increasing pH showed an increase of coprecipitated Cu for all Fe:OM ratios.  Additional samples were prepared with Cu added after precipitation to compare the in-situ conditions to conditions typically studied in laboratories. Preliminary results have shown that iron oxide-OM coprecipitates exposed to Cu after precipitation produce an increase in coprecipitated material when compared to those formed in the presence of Cu. Future experiments will focus on distinguishing the form of Cu in the solid phase, i.e. within the oxide structure, sorbed to the surface, or chelated by OM.

Iron oxide � organic matter coprecipitates and controls on copper fate and transport in wetlands

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.