Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/514
AuthorsAiuppa, A.* 
D'Alessandro, W.* 
Federico, C.* 
Palumbo, B.* 
Valenza, M.* 
TitleThe aquatic geochemistry of arsenic in volcanic groundwaters from southern Italy
Issue Date2003
Series/Report no.18(2003)
DOI10.1016/S0883-2927(03)00051-9
URIhttp://hdl.handle.net/2122/514
KeywordsHydrogeochemistry
Arsenic
volcanic groundwaters
speciation
Subject Classification03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling 
03. Hydrosphere::03.02. Hydrology::03.02.02. Hydrological processes: interaction, transport, dynamics 
03. Hydrosphere::03.02. Hydrology::03.02.03. Groundwater processes 
03. Hydrosphere::03.04. Chemical and biological::03.04.03. Chemistry of waters 
03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems 
AbstractThis paper discusses the abundance, speciation and mobility of As in groundwater systems from active volcanic areas in Italy. Using literature data and new additional determinations, the main geochemical processes controlling the fate of As during gas–water–rock interaction in these systems are examined. Arsenic concentrations in the fluids range from 0.1 to 6940 mg/l, with wide differences observed among the different volcanoes and within each area. The dependence of As content on water temperature, pH, redox potential and major ions is investigated. Results demonstrate that As concentrations are highest where active hydrothermal circulation takes place at shallow levels, i.e. at Vulcano Island and the Phlegrean Fields. In both areas the dissolution of As-bearing sulphides is likely to be the main source of As. Mature Cl-rich groundwaters, representative of the discharge from the deep thermal reservoirs, are typically enriched in As with respect to SO4-rich ‘‘steam heated groundwaters’’. In the HCO3 groundwaters recovered at Vesuvius and Etna, aqueous As cycling is limited by the absence of high-temperature interactions and by high-Fe content of the host rocks, resulting in oxidative As adsorption. Thermodynamic modelling suggests that reducing H2S-rich groundwaters are in equilibrium with realgar, whereas in oxidising environments over-saturation with respect to Fe oxyhydroxides is indicated. Under these oxidising conditions, As solubility decreases controlled by As co-precipitation with, or adsorption on, Fe oxy-hydroxides. Consistent with thermodynamic considerations, As mobility in the studied areas is enhanced in intermediate redox environments, where both sulphides and Fe hydroxides are unstable.
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