The influences of grain sizes and chemical weathering level on extractability of elements from sedimentary rock

The extractability of elements (Cu, Rb, Sr, La and Pb) from sedimentary rock (black slate) was investigated for establishing reliable extraction method. At first, the influence of the grain sizes on the extractability was examined by using non-weathered sample. Cu, Sr, La and Pb were abundantly extracted from roughly crushed black slate, whereas Rb extraction from powdered one was more effective. Especially, the dissolutions of heavy metals from well-ground slate were drastically lowered maybe due to re-adsorption artifacts. The extraction experiments using the black slate with different weathering levels were also performed for the purpose of investigations of chemical weathering on the dissolution behavior of above elements. The extracted solutions were successively filtered through 0.45 μm, 0.20 μm and 100 kDa. The almost of all elements were extracted from non-weathered as truly dissolved species. On the other hand, the elements extracted from weathered slates were almost completely removed by the ultrafiltration except some of alkali and alkali earth elements, indicating no existence of truly dissolved species. They were adsorbates on Al and Fe-bearing colloidal particles or their components.