Effects of Water Treatment Residuals on the Kinetics of Ni(II) Sorption and Desorption in Some Arid Soils

The mobility and bioavailability of nickel (Ni) is strongly dependent on the mechanisms associated with Ni sorption and desorption kinetics in soils. In this contribution, the effects of drinking water treatment residuals (DWTR) applications, as a low-cost adsorbent, on characteristics of Ni sorption /desorption kinetics in three arid soils having different properties were studied by batch experiments. Batch sorption kinetic experiments revealed that Ni sorption behavior involves fast and slow sorption reactions. The fast reaction accounted for 70% of the total sorption within15 min (the first sampling time). Desorption experiments revealed that Ni desorption was hysteretic in nature, which indicated a irreversible process. The time-sorption and desorption data generated for the DWTR treated and untreated soils fitted well to Elovich , power function and parabolic models as evidenced by high coefficient of determination (R^2) and low standard error(SE). The rates of adsorptiondesorption in the soils studied were greatly influenced by the rate of DWTR added. Specifically, the rate of Ni sorption increased and the rate of released Ni decreased as the amount of DWTR added to the soils increased. The overall findings suggest that Ni retention capacity of soils can be increased via DWTR amendments to provide additional Al- based sorbents. Such information is critical for protecting natural resources, developing improved remediation strategies, and making better risk assessments.