Redistribution index and relative binding intensity of heavy metals in salt-amended soils

Redistribution processes of heavy metals and their binding intensity in salt-amended arid-zone soils were analyzed under saturated, field capacity and wetting-drying cycle moisture regimes. Two newly developed parameters, redistribution index and reduced partitioning parameter, were used to depict the removal/attainment of metal-amended soils from/to the fractional distribution pattern in the native soils and the relative binding intensity of metals in the amended soils, respectively. Metal-amended soils, in forms of salts approached the fractional distribution pattern in the non-amended soils with time. The rates at which the metal-amended arid-zone soils approached the fractional distribution pattern characteristic of the native soil were affected by the nature and loading levels of the metals, soil properties and time. Metals in amended soils at low loading levels approach the fractional distribution pattern characteristic of non-amended soil more rapidly than at high loading levels. The sequences of approach by various metals to the fractional distribution pattern in the native soil are as follows: Cd > Cu > Ni, Zn > Cr. Moisture regime, however, did not considerably affect the metal-amended soils' overall rates of approach to the fractional distribution pattern prevailing in the non-amended soils. The binding intensity of metals in soils was affected by the nature of metal, loading level, soil properties and time. In both non-amended and amended soils, Cr had highest binding intensity, Cd lowest and Cu, Ni and Zn intermediate. The binding intensity decreased with the loading level of the metals and increased with time. The redistribution index and reduced partitioning index can quantitatively and effectively depict the kinetics of redistribution processes of metals and their relatively binding intensity in waste-amended soils.