The interactions of transition metals with natural systems play an important role in the mobility and the bioavailability of these metals in soils.In this study,the adsorption of copper-Ill)onto natural soil particles was studied as a function of pH and metal concentration.The retention capacity of soil particles was determined at pH 6.2 to be equal to 6.7 mg of copper/g of solid.The Langmuir and Freundlich isotherm equations were then used to describe the partitioning behavior of the system at different pH values.A combination of EPR,extended X-ray absorption fine structure(EXAFS),and X-ray absorption near-edge structure(XANES)spectroscopies was used to probe the Cu atomic environment at the soil particles/aqueous interface.The spectroscopic study revealed that copper(ll)ions are held in inner-sphere surface complexes.It also revealed that Cu was in an octahedral coordination with first-shell oxygen atoms.A weak tetragonal distortion was pointed out due to the Jahn-Teller effect,with a mean Cu-O_equatorial bond distance of 1.96 A and a Cu-0_axial bond distance of 2.06 A.A detailed analysis of the spectroscopic data suggested that Cu(ll)was bonded to organic matter coated onto the mineral fraction of soil particles.
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