Adsorption Isotherms and Breakthrough Curves to Study How Humic Acids Influence Heavy Metal–Soil Interactions

Abstract

In the present work we studied the role of humic acids in the heavy metal–soil interaction after the addition of different amounts of humic acids to a soil poor in organic matter. Both adsorption isotherms and breakthrough curves of cadmium(II) and nickel(II) were examined. Using the multi-method approach it is possible to obtain a greater amount of information than that obtained by employing only adsorption isotherms or breakthrough curves. Both methods show that the amount of cadmium retained by the soil is greater than that of nickel and that the two metals are characterised by different sorption mechanisms. Moreover, adsorption isotherms evidence the humic acids–soil interaction whereas breakthrough curves indicate that two different types of sites or two different mechanisms are involved in the sorption process. For nickel humic acid addition increases only the metal fraction strongly bound to the soil, whereas for cadmium both fractions (strongly bound and weakly bound) increase.