Title

Copper behaviour in a podosol. I: pH-dependent sorption-desorption, sorption isotherm analysis and aqueous speciation modelling

Document Type

Article

Publication details

Burton, ED, Phillips, IR, Hawker, DW & Lamb, DT 2005, ‘Copper behaviour in a podosol. I: pH-dependent sorption-desorption, sorption isotherm analysis and aqueous speciation modelling’, Australian Journal of Soil Research, vol. 43, no. 4, pp. 491 – 501.


The original publication is available at www.publish.csiro.au at http://dx.doi.org/10.1071/SR04117

Abstract

The effects of pH and Cu loading on the solid/solution partitioning of Cu in a Podosol from south-east Queensland, Australia was examined. Sorption–desorption of Cu exhibited maximum linear distribution coefficients (KD) at approximately pH 5. Observed decrease in KD values at pH >5 was attributed to increased solubility of native dissolved organic carbon (DOC) at higher pH and subsequent formation of non-sorbing Cu–DOC complexes. Speciation modelling with the MINTEQA2 code indicated that >90% of aqueous Cu was present as Cu–DOC complexes at pH >5.5. The effect of Cu loading was examined with sorption isotherm analysis at pH 5 using solid : solution ratio approaches that were both constant (1?:?2 and 1?:?10) and variable. As the solid : solution ratio increased, the proportion of Cu sorbed decreased due to the formation of Cu-DOC complexes. However, this effect was negligible once these Cu–DOC complexes were accounted for via free Cu2+ sorption isotherms. This indicated that Cu2+ sorption at concentrations <0.08 mg/L was described by a KD value of approximately 3000 L/kg. Despite this relatively high KD value for Cu2+ sorption, the results indicate that Cu–DOC complexes significantly enhance Cu solubility in soils high in DOC