Enrichment of heavy metal elements and their adsorption on iron oxides during carbonate rock weathering process

Analysis of trace elements in the Lower Palaeozoic carbonate rock strata of the Beijing area shows that the Cr, Zn, Cd and Pb contents increase from primary carbonate rocks to weathered carbonate rocks and from primary carbonate rocks to the soil coexisting with carbonate rock. Distributions of Cr, Zn, Cd and Pb have the same trends as that of Fe2O3. Iron oxides play different roles at different stages of weathering of carbonate rock. The adsorption of Cr, Zn, Cd and Pb on Fe2O3 is greater than on FeO in soil. However, FeO, as a main component of clay mineral, is a better adsorbent of Cr, Zn, Cd and Pb than Fe2O3 in weathered and primary carbonate rocks. According to R-type clustering analysis, the main components of carbonate rock are divided into marine and continental sediments. Correlation analysis shows that heavy metal elements mainly exist in continental substances.