Copper sorption in clay fractions of alluvial soils

The influence of copper sorption by iron hydroxides with different degrees of crystallization in clay fractions of several alluvial cultivated soils of the fertile lowlands of the Manzanares river (Madrid) has been studied. Mineralogical study of the < 2-μm clay fraction allows us to differentiate two major zones, which are also different as far as their contents of copper and iron oxide and their degree of crystallization is concerned. There is a generalized tendency of Cu association towards the amorphous and microcrystalline iron oxides. This fact is confirmed through the copper sorption studies on the untreated clay fraction and on those treated with oxalate and citrate-bicarbonate-dithionite. Sorption studies also highlight the influence of the different phyllosilicates on the sorption process of this metal.