Site-energy distribution analysis of humic acids adsorption by zeolitic tuff

Within a research program aimed to utilize natural zeolites for pedotechnical purposes, such as to rebuild degraded soils, to improve soil fertility and to remove soil pollutants, the adsorption process of humic acids (HAs) on untreated Neapolitan Yellow Tuff and on Ca2+-enriched samples was investigated in the temperature range 1-45°C. Experimental data showed a negligible temperature effect indicating that ΔH ≈ 0. Moreover, Scatchard-like plots suggested the occurrence of more than one adsorption sites for both samples. A good fit of the adsorption isotherms was obtained by two-site Langmuir equation. For both sites the HAs affinity was not modified by Ca2+-enrichment and ΔS° was >0. The adsorption of HAs on tuff is an entropy-driven process. © 2007 Springer Science+Business Media, LLC