A simple simulation of adsorption equilibrium of Pb(II) on Andosols in the presence of dissolved humic substances for monitoring soil contamination

The adsorption equilibrium of Pb(II) on Andosols was investigated and described quantitatively in order to develop a simple method for the rapid monitoring of heavy metals in soils. The effect of solution pH on adsorption isotherms was investigated experimentally and in simulations. At pH 7, the considerable desorption of Pb(II) due to the extensive dissolution of humic substances (HS) from soils into aqueous phases is known to be an obstacle to carrying out simulations. In batch experiments, the total organic carbon (TOC) of the aqueous phases was shown to be enhanced by the addition of pre-extracted HS to soil suspensions. By combining the ion-exchange and Freundlich models, the adsorption equilibriums of free Pb2+ ions and Pb2+-HS were simulated and were shown to be in good agreement with the experimental results. By estimating the concentrations and adsorption amounts of Pb2+ and Pb2+-HS from measured C-Pb and TOC, it is possible to accurately simulate the soil contamination status even in in the presence of dissolved HS in the water in the solid-liquid extraction samples.