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Copper(II) Activity in Aged Suspensions of Goethite and Organic Matter
Author(s) -
McBride M.,
Martínez C. E.,
Sauvé S.
Publication year - 1998
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1998.03615995006200060010x
Subject(s) - chemistry , goethite , organic matter , adsorption , phosphate , copper , inorganic chemistry , oxide , solubility , chelation , iron oxide , organic chemistry
Suspensions of natural organic matter and iron oxide (FeOOH) were equilibrated with a wide range of concentrations of added Cu 2+ (50–5000 mg kg ‐1 ) for as long as 400 d, in order to observe the time‐dependent solubility of the free Cu 2+ ion. Adsorption was conducted at two pH ranges (5.0–5.5 and 6.5–7.0) and in the presence and absence of phosphate. The Cu 2+ activity, measured by ion‐selective electrode, was one to two orders of magnitude lower for the organic systems at all Cu loadings investigated when the pH was near 5.5, indicating that the organic matter was a more effective adsorbent for Cu 2+ than goethite. Longer reaction times generally caused the Cu 2+ activities to decrease due to drifting pH and slow reactions. At higher pH, organic matter again resulted in lower Cu 2+ activity than the oxide at all Cu loading levels, but the difference was generally less than at low pH. A downward pH trend in the organic system initially at pH 6.5 caused the Cu 2+ activity to increase with longer reaction times. Most of the long‐term changes in Cu 2+ activity could be attributed to shifting pH, although an aging effect on activity could be discerned. Phosphate added to the oxide or organic matter had little effect on the activity of Cu 2+ . The EDTA extracted a larger fraction of Cu 2+ adsorbed on organic matter than on the oxide, suggesting that strong chelating agents selectively extract metals in quantities not directly related to activity or potential toxicity.