Multi-elemental analysis in size fractions of fine-grained solid residue of ore grinding

Suspensions of fine-grained material originated from a former uranium mine in Central Germany and deposited in a settling plant were investigated. Tot al 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) (Z n). In order to find a correlation between particle size and the concentrat ion of selected elements (As, U, Cu, Zn, Ni, Mn, Fe and Pb) the material wa s separated into different particle size fractions by independent procedure s: (I) subsequent step-by-step fractionation (standard cascade) and (II) on -line multistage membrane filtration (OMFD). Using ICP-AES and ICP-MS the c oncentration of these elements in the particles, in solution and in the mat erial deposited on filter (after dissolution with aqua regia) were determin ed. The main advantage of OMFD over cascade filtration exists therein, that the clogging of the membranes by particles is diminished indicated by a si gnificant increase of the yield of particles in the individual fractions. I t was shown that the sample preparation is very important for size fraction ation of fine-grained materials. Surfactants, like sodium metaphosphate, le d 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 fract ions 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 mu m. High amounts of U are sorbed on the particle surface.