Competitive sorption of lead and cadmium onto sediments

Single- and bi-solute competitive sorptions of Pb and Cd onto sediments were investigated. In single-solute sorption, Khan model was fitting better than the other models such as Freundlich, Langmuir, Dubinin–Radushkevich, Sips, Redlich–Peterson and Kargi–Ozmıhcı models. In bi-solute sorption, competition between the solutes reduced the sorbed amount of each solute compared with that in the single-solute system. Langmuir model parameters for single-solute (qmL and bL) and bi-solute (qmL* and bL*) competitive sorptions were compared. Sediment with higher pH, CEC and BET surface area had higher maximum sorption capacity (qmL).(qmL). In all sediments, maximum sorption capacity (qmL)(qmL) of Pb was higher than that of Cd, and the presence of both metals reduced the tendency to be sorbed although Cd sorption was more affected than Pb. The bL* values of Pb decreased while those of Cd increased indicating that competition for sorption sites promotes the retention of Cd on more specific sorption sites. The competitive Langmuir model (CLM) and ideal adsorbed solution theory (IAST) coupled to the single-solute sorption models predicted Pb sorption in bi-solute competitive sorption favorably but not Cd sorption.