Sorption of humic acids on zeolitic tuffs

The sorption of humic acids (HA) by phillipsite- and chabazite-rich Neapolitan Yellow Tuff (NYT) and a clinoptilolite-rich tuff from Turkey (CLT), both in the native and in Ca-enriched forms, have been investigated. Experimental data showed that the sorption capacity of the Ca-enriched forms was higher than that of the native forms. NYT, in particular, was very effective in removing humic acids from water. Its sorption capacity was higher than that of CLT, although the latter material had a higher zeolite content (CLT: 79% clinoptilolite; NYT: 37% phillipsite + 17% chabazite). HA sorption by Ca-enriched NYT readily attained a pseudo steady-state, after which the tuff/HA-solution system evolved in a few months to a final equilibrium state characterized by a much higher sorption capability. Desorption experiments at high pH levels resulted in a HA recovery >80%. The UV–vis spectrum and the gel permeation chromatogram of the recovered HA solution were indistinguishable from those obtained for a freshly prepared HA solution.