Study on Sorption and Desorption of Nickel in Soil Samples Collected from Oases

The mobility and bioavailability of heavy metals depend on the sorption,desorption and chemical forms. Laboratory experiments,single extraction procedure,sequential extraction and simple correlation analysis were carried out to study the sorption and desorption of nickel ( Ni) in soil samples collected from oases and the speciation of sorbbed Ni. Soil samples were characterized by the low organic matter content and high CaCO3 and could be considered uncontaminated. Sorption of Ni in soils was well described by the Freundlich equation. The correlation results reveal that the soils with higher silt,clay,total P and organic matter contents and CEC will retain Ni in greater amount than the sandy soils with lower total P and organic matter content and CEC. Soil pH value is not an important factor affecting Ni sorption. Sorption of Ni in oasis soils is likely to be affected by a combination of soil properties,such as pH value,CaCO3 and CEC. Sorption capacity of Ni is in an order of marshland soil ag-ricultural soil desert soil and shrub soil. Land use affects the sorption of Ni in oasis soils. Desorption of Ni in soil samples collected from oases varied in a range from 26. 79% to 99. 09% ,and bioavailability of Ni in oasis soils was high. Ni desorption was increased with the increase of Ni sorption in oasis soils. Power function can be used to simulate the relationship between desorption and sorption of Ni before desorption. Exchangeable Ni concentration in oasis soils was significantly decreased with the increase of soil pH value. There was a significant positive correlation between soil CEC and carbonate,Fe-Mn bound and residual nickel concentration,and also between total soil N content and Fe-Mn bound,organic bound and residual nickel concentration.