Modeling pedogenization of zeolitized tuffs. II: Medium-term weathering of Neapolitan Yellow Tuff and Red Tuff with Black Scoriae by water and humic acids

An experimental pedology research program was started aiming at modeling the potential pedogenization of zeolitized tuffs. The present study deals with a medium-term weathering of Phlegraean Yellow Tuff (PYT, with phillipsite=chabazite) and Red Tuff with Black Scoriae (RTBS, with chabazite=phillipsite) under discontinuous treatment by water (W) and by humic acids (HA). Significant amounts of cations, increasing in the sequence Al<Fe<Mg<Ca, were extracted by both water and humic acids. The humic acids showed in all cases the highest extracting efficiency. All cations, especially calcium, were more easily removed from PYT than from RTBS. The only exception was iron which was preferentially removed from RTBS by HA. At the end of the experiment, smectite was not any more detected in the PYT residues. On the whole, the results indicate that PYT is more prone than RTBS to both humic acid and water weathering due to its different mineralogy.