Identification of the As-bearing phases in fresh volcanic Andean ashes

BIA, G; BORGNINO L; GARCIA M.G.; GAIERO, D.

Congreso; 5th International Congress on Arsenic in the Environment; 2014; 2014

The sources and dynamics of arsenic in fresh volcanic ashes collected during the eruptions of Hudson (1991) and Puyehue (2011) volcanos, have been studied. The chemical and mineralogical compositions of both volcanic ashes were analyzed by ICP/OES, DRX, and SEM-EDS. Batch experiments were conducted to evaluate the kinetics of the arsenic release under variable pH. Results indicate that the release is enhanced under both, acidic and alkaline conditions. Besides, the positive linear trends found between Fe and As concentrations in the leachates (p= 0.0107 miliQ water; p=0.0022 pH 3; and p=0.0081 pH 10)  suggest that arsenopyrite or/and its alteration product scorodite is one important As-bearing phase present in the ash samples. This phase would be the main responsible of the As release under acidic conditions. At higher pH, other mechanisms are involved: desorption from Fe (hydr)oxide coatings (at neutral to slightly alkaline conditions) and dissolution of both arsenopyrite and volcanic glass at pH higher than 9