Surface interaction of humic acids with natural and synthetic phillipsite

Starting from previous encouraging results, pointing out the ability of natural zeolites to remove large, hydrophilic, organic molecules from water, this paper deals with the surface interactions between humic acids, a frequent contaminant of natural waters, and the zeolite phillipsite, with the aim to obtain valuable insights on the possible use of low-cost, natural phillipsite-rich materials in decontamination technology. Accordingly, an enriched sample of Neapolitan yellow tuff, containing ca. 70 % phillipsite, was compared with a synthetic phillipsite in both kinetic and equilibrium sorption experiments of humic acids from model waters. Tests, carried out at 25 °C, were performed on Ca2+-pre-exchanged samples, which proved to be more effective in the sorption process. The results highlighted the marked affinity of phillipsite for the humic acids, better than any other zeolite tested previously, pointing out, moreover, that natural phillipsite behaves as a slightly diluted phillipsite, with no adverse effects from the mineral impurities present in the sample. Moreover, natural phillipsite performance, in both kinetic tests and in sorption capacity, was comparatively better than the synthetic counterpart, which was attributed to the presence of structural defects in the latter, due to the stressing conditions under which it had been obtained.