抄録
The extraction method from soils by water is authorized in the Soil Contamination Law in Japan for heavy metal dissolution risk assessment. However, the applications to rocks are not accepted, although there are several kinds of rocks from which toxic heavy metals are possibly eluted. For examinations, differently from soils, rocks need to be crushed to appropriate grain size or powdered. To establish the risk assessment for rocks, we prepared the powdered and crushed (grain size: 2-1mm, 1-0.5mm, 0.5-0.25mm, < 0.25mm) sedimentary rocks, and examined the effects of grain sizes against the extractability of heavy metals (Mn, Co, Ni, Cu, Zn, Cd, Pb and U) by water.
Each heavy metal concentration in extracts from the crushed rock samples having any grain sizes was almost similar, and this result indicates that over-dissolution, which may be caused by crushing rocks to extremely smaller grains, does not arise in the extractions from the crushed samples less than 2mm. The repeatability of the extraction test was good, meaning that the mineral compositions exposing on grain surfaces crushed to less than 2mm were relatively homogeneous.
Some heavy metal concentrations in extracts from powdered rock samples were decreased compared to those from the crushed samples, and the over-dissolution could not be observed. The heavy metals once eluted from powdered rocks were inferred to be re-sorbed.
