Effect of pH, flow rate and concentration on the sorption of Pb and Cd on montmorillonite: II. Modelling

A mathematical model is proposed and compared with experimental data for th e migration of heavy metal ions (Pb and Cd) during the flow of aqueous solu tions through calcium-saturated montmorillonite packing. The main system pa rameters are pH, flow rate and concentration. It is assumed that the Liquid phase in the porous montmorillonite can be divided into two regions, mobil e and immobile; that adsorption and ion exchange on the clay surface are in stantaneous, and that adsorption isotherms are Linear throughout the modell ing considered. The Ranges of experimental parameters are: pH 2.5-7.3, solu tion flow rate of 0.1-1 cm(3) min(-1) and heavy metal concentrations of 5-1 0 ppm. Breakthrough curves (BTCs) obtained experimentally are affected by c hanges in pH and flow rates. Between pH 2.5 and 4, the model equations desc ribe the process quite well but from 4 to 7 a large deviation between the m odel and experimental data is observed due to precipitation of metals. (C) 1999 Society of Chemical Industry.