Adsorption of ions onto high silica volcanic glass

Chemical fingerprint techniques are frequently applied to airborne volcanic eruption products, so-called tephra, such as ash and pumice for archeological and geoscientific purposes. However, in some cases, a meaningful interpretation of the results is complicated by superficial contaminations. Therefore, this situation was simulated by the use of powdered rhyolitic pumice to investigate its capability to adsorb several ions from aqueous solutions. Using neutron activation analysis, adsorption could be proven for Cr3+, Cr2O72− (dichromate), Fe3+, Co2+, HAsO42− (hydrogen arsenate), Rb+, Sr2+, Cs+, Ba2+, La3+, Ce3+, Ce4+, Sm3+, Th4+ and UO22+, which is a clear evidence for the interaction of those ions with the volcanic glass. In our experiments, pumice powder showed the ability to adsorb ions in the range from 1.8 mg kg−1 (in case of HAsO42−) to 5.8 wt% (in case of Fe3+). Adsorption is probably due to ion-exchange reactions. It could also be shown that a few ions are not adsorbed in detectable quantities: Na+, K+, Fe2+, Zn2+ and Nd3+. The knowledge about adsorption of ions enables us not only to examine the possible influence of contaminations where chemical fingerprinting methods are applied to volcanic material for archaeometry, but it also suggests the technical application of pumiceous materials for technical purposes, like water purification or as an adsorbent in the final storage of nuclear waste. In another series of INAA supported experiments, the influence of chemicals like ascorbic acid, acetic acid, HCl, HF, HNO3, H2O, H2O2, H3PO4, H2SO4, NaOH and NH3 on the bulk composition of pumice powder was investigated—resulting in no detectable change. We conclude that superficially contaminated tephra can be washed in diluted HF to remove contaminations without influencing the chemical fingerprint.