Effect of Leonardite on the desorption kinetics of heavy metals in in contaminated soils with different maternal materials

Leonardite is containing humic and fulvic acids, and possesses number of functional groups that play an important role on forming complex with heavy. In order to investigate the effect of Leonardite on the desorption kinetics of Cd, Zn and Pb in soils with different maternal sources, an experiment was conducted as a factorial based on a completely randomized design with two factors: 1. soil type (Syenite, Schist and Gabbro) and 2. Leonardite levels (0, 2 and 5%) in three replications. To carry out the experiment, soils were spiked with studied heavy metals and after adding Leonardite, samples were taken at 2, 24, 48, 7, 15, 30, 45, 60 and 90 days. Some physical and chemical properties, mineralogy (XRD) and desorption kinetics of heavy metals were performed at different levels of Leonardite. The amount of metals desorption in the sample treated with Leonardite decreased with time. Kinetics equations of exponential function, exponential function and parabolic diffusion were selected with a high coefficient of explanation (R2) and the lowest standard error (SE). The results showed that the composition and type of clay minerals were different. According to kinetics studies, the amount of metal desorption was significant between the different levels of Leonardite as well as the soils studied and the highest amount of desorption (a and b) of the heavy metals was observed in the Syenite soil.So, due to lower pH and CEC of Syenite soil, diffusion coefficient (Kd) showed a significant increase for the heavy metals (Cd,Pb and Zn) in comparison with other soils. Thus, Leonardite application must on the basis economic and physical and chemical properties of soil will be done.