Thermodynamic characteristics and mechanisms of heavy metals adsorbed onto urban soil

Abstract

The thermodynamic characteristics of heavy metals adsorbed onto urban soil and the relative adsorption mechanisms were studied by the batch experiment. The results show that there existed dynamic adsorption-desorption equilibrium processes of cationic and anionic ions of heavy metals onto urban soil, which may have an impact on the pH of the adsorption system. The amounts of heavy metals adsorbed onto urban soil increased with the increase of the equilibrium concentration, but their adsorption amounts were not the maximum adsorption amounts. The higher the pH was, the greater the adsorption capacity of the urban soil at the same equilibrium concentration was, and the adsorption amounts of heavy metals onto urban soil followed the order of Pb>Cu>Cd>Zn>Ni. There were coordination reaction, hydrolysis reaction, exchange reaction in the adsorption processes of heavy metals onto urban soil. With the increase of pH, the influencing degree of pH on the different reactions of heavy metals in the soil increased, meanwhile the effects of other physicochemical properties of soil on the adsorption of heavy metals were weakened.