Co-Presence Effects of Anionic and Cationic Metallic Compounds on the Attenuation Behavior in a Mine Site.

The mobility of metals can be attenuated through soil sorption processes during the down-gradient transport with mine leachate. In mine leachate, metals concurrently co-exist and affect each other’s sorption behavior. Therefore, it is necessary to exactly evaluate the sorption behavior of co-present metals and their effects on binding strength between soil components and metals. The objectives of this study were to examine the sorption behavior of metals in the multi-metal systems and to evaluate the impact of co-presence on sorption and transport through down-gradient soil in a mine site.

Down-gradient soils were collected from the abandoned mine site in Korea. A series of sorption batch experiments were conducted using single-, binary-, ternary-metal solutions (As, Zn and Cd). 1-D transport experiments were carried out and interpreted using HYDRUS 1-D program. Upon completing column experiments, soil samples were extruded and three-sectioned for sequential extraction; (i) F1: nonspecifically sorbed (As), extractable (Zn, Cd) , (ii) F2: specifically sorbed (As), bound to carbonates (Zn, Cd), (iii) F3: bound to amorphous Fe-Al hydrous oxides (As), Fe-Mn oxides (Zn, Cd), (iv) F4: bound to crystallized Fe-Al hydrous oxides (As), OM (Zn, Cd), (v) F5: residual

Zn was strongly attenuated more than As and Cd in single metal system. However, in multi metal systems, sorption of metals was affected by the presence of other metals (i.e., sorption of cationic metal was suppressed by another cationic metal, and the co-presence of anionic As and cationic Cd and Zn leaded to enhanced sorption.). From the sequential extraction results, distribution of metals in soil in multi-metal system changed compared to single system. For As, proportion of F1, F4 and F5 increased but F2 and F3 decreased compared to the single solution.

Knowledge of attenuation behavior of metals from single metal system fails to appropriately describe the fate and transport in mine soils, which is largely due to misunderstanding of chemistry of multi-metal systems and possibility for underestimating sorption capacity. Competition for sorption sites and formation of ternary complexes have to be considered to evaluate the fate and transport of metals in heterogeneous solution.