Structural characterization of arsenic compounds in volcanic ashes and sediments using X-ray absorption spectroscopy

BORGNINO, L.; GARCÍA M.G; BIA, G.

Estocolmo

Congreso; 6th International Congress on Arsenic in the Environment; 2016

X-ray absorption fine structure spectroscopy (XAFS) was used to determine the oxidation state of arsenic (As) and its local chemical coordination in recent and ancient volcanic ashes and Chacopampean loess sediments. XANES analysis allowed to discriminate the oxidation states of arsenic in the studied samples: As5+ is dominant in loess sediments while in volcanic ashes As-1 and As3+ were identified. The proposed EXAFS models fit well with the experimental data, suggesting that in loess sediments, As5+ could be in the form of arsenate ions adsorbed onto ferric oxyhydroxides. In recent volcanic ashes, the identified As-1 species is likely associated with arsenopyrite or arsenical pyrite. Besides, As3+ is likely related to As atoms present as impurities within the glass structure, in the form of oxy-hydroxide complexes. In ancient volcanic ashes As3+ is the dominant oxidation state but As5+ was also identified.