Suspensions of fine-grained material originated from a former uranium mine in Central Germany and deposited in a settling plant were investigated. Total concentrations in the waste material ranged from 150 mg kg⁻¹ (Ni), 215 mg kg⁻¹ (As), 285 mg kg⁻¹ (U), 290 mg kg⁻¹ (Pb) to 1230 mg kg⁻¹ (Zn). In order to find a correlation between particle size and the concentration of selected elements (As, U, Cu, Zn, Ni, Mn, Fe and Pb) the material was separated into different particle size fractions by independent procedures: (I) subsequent step-by-step fractionation (standard cascade) and (II) on-line multistage membrane filtration (OMFD). Using ICP-AES and ICP-MS the concentration of these elements in the particles, in solution and in the material deposited on filter (after dissolution with aqua regia) were determined. The main advantage of OMFD over cascade filtration exists therein, that the clogging of the membranes by particles is diminished indicated by a significant increase of the yield of particles in the individual fractions. It was shown that the sample preparation is very important for size fractionation of fine-grained materials. Surfactants, like sodium metaphosphate, led to an increase of the concentration of several elements in the dissolved form. This could be mainly attributed to the dissolution of analytes which were bounded on the particle surfaces as shown for uranium.

It was found that As and Pb are homogeneously distributed in all size fractions of the uranium processing waste. The concentration of the elements Fe, Zn, Cu and Mn varied with particle size. They showed a similar pattern in size distribution. The highest amounts of these elements were found in the particular fraction > 8 μm. High amounts of U are sorbed on the particle surface.