Particle size distributions of clay-rich sediments and pure clay minerals:A comparison of grain size analysis with sedimentation field-flow fractionation

Two clay-rich coastal sediment samples have been characterised together wit h three pure clays identified as major components of the sediment samples. The mineralogy of the sediments was determined by X-ray diffraction, and th eir bulk properties measured (organic carbon content, leachable iron and ma nganese, surface area and cation exchange capacity). A simple approach is u sed to model the properties of the sediments from those of their pure clay components. Good agreement is found for cation exchange capacity and specif ic surface area indicating that the clay minerals are the most important co nstituents influencing the sediments' surface properties. Particle size dis tributions were assessed by conventional grain size analysis, and also by S edimentation Field-Flow Fractionation (SedFFF). These two approaches yield sharply differing size distributions; in particular, conventional grain siz e analysis indicates a much greater proportion of submicron particles. Simi lar results are obtained from analysis of pure clays. The most likely reaso n for this is artifacts introduced in the unavoidable 1 mum prefractionatio n used for SedFFF.