New insights into the interaction mechanism of humic acids with phillipsite

In the present work, the kinetics of humic acid sorption onto a phillipsite-rich tuff sample from a quarry near Marano (Napoli, Italy) was thoroughly investigated by a batch method. Humic acids were extracted from a vegetable compost and characterized by size exclusion chromatography, dialysis experiments and UV–Vis analysis. Kinetic experiments revealed that sorption occurs through a multistep pathway: the kinetic profile was characterized by an initial fast humic acid uptake, followed by three consecutive plateau levels. This distinctive sorption behavior was related to conformational changes of the sorbate and to cooperative sorption effects. On this basis, a kinetic model was derived which accurately described the sorption experimental data.