The geochemical cycle of Tellurium in volcanic environments

This research is focused on the geochemistry of Tellurium (Te) in active volcanic environments. To this end concentrations of Te have been measured on different matrices (plume, ashes, soils, atmospheric depositions and plants). Samples were collected from different volcanoes around the world: volcanic aerosols from Etna and Vulcano (Italy), Turrialba (Costa Rica), Myakejima, Asama and Aso (Japan), Mutnovsky and Gorely (Kamchatka, Russia), Copahue (Argentina), Nyamuragira and Nyiragongo (D.R. Congo); atmospheric depositions from Etna and Vulcano (Italy), Nyiragongo (D.R. Congo); ash from Etna (Italy), Copahue (Argentina), San Miguel (El Salvador). Among with plume and rain samples, several leaves of plants from volcanic areas were collected for biomonitoring investigations: Etna, Vulcano and Stromboli (Italy), Nyiragongo (D.R. Congo), Nisyros (Greece), Gorely (Kamchatka), Turrialba (Costarica), Masaya (Nicaragua), Soufriere (Guadalupe); for comparison plant samples were collected also from an industrial area (Augusta, Italy) and a rural forest (Ficuzza, Italy). Samples of soils were also collected from Nisyros (Greece) to better understand the soil-plant distribution. From a literature review, there is a scarcity of data available about Tellurium abundances in the environment, expecialy for volcanic areas. This fact can be ascribed to the scarce use of this element in the past. During the last decades, the use of Te increased considerably due to its importance for electronics and solar photovoltaic manufacturing. Moreover, the recent natural disaster of Fukushima in March 2011 drew attention to the environmental impact of isotope Tellurium-132, produced after the nuclear power plant failure. As consequence, a lot of new studies are focused on Te behaviour in the environment. Regarding Te plume concentrations and fluxes from active volcanoes, only few estimations were reported in previous studies. Sixty-five plume samples were collected and analysed thus significantly increasing the existing worldwide dataset. The concentrations of Te detected range from <0.003 to 0.15 µg/m3, significantly higher than the background level. The atmospheric depositions are the most important way to transfer the elements from the atmosphere to the ground and consequently to all the terrestrial environments (soils, groundwater, plants, animals and humans). Nowadays very few data are available about Te abundances in atmospheric deposition and no data in volcanic environments. The data here reported are the first results of the concentrations of Te in rainwater collected close to active volcanoes. The samples of rainwater samples (bulk deposition) representative of the bulk deposition, were collected from three different volcanoes (Etna, Vulcano and Nyiragongo). A total of 98 rainwater samples were analysed for the major and minor constituents including Te, so creating a complete and unique dataset. The results show clearly higher Te contents close to the crater with values up to 3.20 µg/l with respect to far away background values below 0.04 µg/l, suggesting a volcanogenic origin. In particular, the concentrations of Te, among with other volatile metals e.g. As, Bi, Cs, Cu, Cd, Tl, Pb, are inversely correlated with pH values. This trend confirms that the volcanic emissions can significantly impact the chemical composition of atmospheric deposition. In the same way it influences the geochemical cycle of Te, causing a major accumulation into the soil-plants system. Interesting results were obtained by chemical analysis of Te contents in ash leachates. As well as for rainwaters, no data of volcanic ashes leachates are reported in the literature. For this study we analysed the fresh ashes ejected from: Copahue (Argentina) emitted in December 2012, after 12 years of inactivity; Etna (Italy), collected during 20 paroxysmal events occurred in 2011 and 2012; San Miguel (El Salvador) erupted in December 2013. The samples, when possible, were divided in the different grain size, otherwise the bulk grain size was studied. The results highlight the rapid dissolution of Te from the ash surface indicating high mobility of this element among with other known mobile metals. Te is probably carried out during the volcanic explosion forming hydro-soluble salts with the main acid volatile species (SO2, HCl, HF), Te(SO4)2, TeCl4 and TeF4 but also in elemental form. As expected, the experiments showed that the Te concentrations increase with decreasing grain size, due to the increase of specific surface of the ash. This process, including Te dissolution, have important implications on atmospheric deposition chemistry: when the smaller particles are injected into the atmosphere they can be transported for long distance from the source-point, participating in the cloud processing and affecting sequentially the chemistry of the rain, plants and soils in the surrounding of active volcanoes. The plants commonly contain low contents of Te with variable range. The highest concentration of Te is reported in onion and garlic (up to 300 µg/g) and the characteristic garlic odour is caused by vapours of dimethyl telluride. In the last frame of this study, leaves of 11 species were collected and analysed from 9 different volcanic areas; for comparison samples from an industrial area (Augusta) and a rural area (Ficuzza) were also investigated. The same species but in different volcanoes are featuring the same range, while plants that bioaccumulate more Te are Senecio sp., mosses and lichens with values up to 0.575 µg/g. At Nisyros island (Greece), concentrations of Te in two indigenous plants (Cistus sp. and Erica sp.) were compared with those in the soils. For this study, the soil samples were taken in the Lakki Plain caldera inside and outside the main fumarolic areas. Also in this case, the data show the influence of volcanic emissions on Te concentrations, recording the highest values within the active fumarolic areas. Anyway, in general the concentrations inside the caldera (0.056 – 0.746 µg/g) are higher than the local background (0.004 µg/g). Comparing the soil with the plants, the values of Te in plants tend to grow with the increase of this element in soils. The plants, particularly Cistus, tend to take up more Te near the active fumarolic areas. The results showed very high enrichments of Te in volcanic emissions comparable with other volatile elements like selenium, arsenic, thallium and bismuth. Concluding, the results of this study increase our knowledge about abundances and distribution of Te in volcanic areas, providing a great amount of unpublished data regarding Te, among with many others major and trace elements, in different matrices. We highlighted the prevailing volcanogenic origin of Te and the potential impact of this toxic metalloid on the environment. The results also suggest a primary transport of Te in the volatile phase, probably in gaseous form (as also suggested by recent studies) and/or as soluble salts (halides and/or sulfates) adsorbed on the surface of volcanic particles and ashes. Comparison between different volcanic systems, Etna and Nyiragongo with persistent passive degassing from one side and Nisyros without a volcanic plume, suggest a bioaccumulation of Te in vegetation both from soils and directly from the atmosphere, confirming the high geochemical mobility of this element in volcanic emissions. New flux estimations confirm the relevance of this element in the total volatile output from active volcanoes. The first estimates of volcanic flux of tellurium from Etna range from 0.26 to 12.3 tons per year, confirming that this volcano is one of the biggest point sources to the atmosphere also for this element. The new dataset, among with previous data, allowed to extrapolate a Global Volcanogenic Flux of Te (GVF-Te) through the Te/SO2 ratios and the global budget of SO2 from active volcanoes taken from literature. The total output estimated range from 15.3 to 316 ton/a with a median value of 98, coherently with the estimation obtained from previous authors. Moreover, this value is significantly high if compared with the global production of Te (about 500 ton/a in 2010) by human industrial activities

Volcanogenic particulates and gases from Etna volcano (Italy)

Volcanic emissions represent one of the most relevant natural sources of trace elements to the troposphere. Due to their potential toxicity they may have important environmental impacts from the local to the global scale and they can severely affect the atmospheric and terrestrial environment also at timescales ranging from a few to million years. Etna volcano is known as one of the largest global contributors of magmatic gases (CO2, SO2, and halogens) and particulate matter, including some toxic trace elements. The aim of this study was to characterize the chemical composition and the mineralogical features of the volcanogenic aerosol passively emitted from Mt. Etna. Nine samples were collected by using the filtration technique at different sites on summer 2010 and 2011. Chemical and mineralogical analyses allowed to discriminate two main constituents: the first is mainly referable to the silicate component in the volcanic plume, like lithic and juvenile fragments, crystals (e.g., plagioclases, pyroxenes, oxides) and shards of volcanic glass; the second one is linked to the soluble components like sulfosalts or halide minerals (sulfates, chlorides and fluorides). These investigations are especially important in the study area because the summit of Mt. Etna is yearly visited by nearly one hundred thousand tourists that are exposed to potentially harmful compounds

Spontaneous galvanic displacement of Pt nanostructures on nickel foam: Synthesis, characterization and use for hydrogen evolution reaction

Abstract In this paper we propose the use of spontaneous galvanic displacement as a promising solution to produce nickel foam electrodes functionalized with interconnected platinum nanoparticles. Scanning Electron Microscopy analyses, coupled with X-ray Energy Dispersive Spectroscopy show that, under proper conditions, we can overcome the limits of other deposition techniques, achieving a uniform Pt coverage throughout the 3D structure of the Ni foam. We show that such a condition, not deeply investigated in previous literature, turns out to be crucial for the long term stability of the electrodes under constant current stress. The amount of Pt on the Ni foam has been experimentally evaluated, obtaining optimal results with 0.015 mg cm−2 of noble metal in a 0.16 cm thick electrode. Such a low amount corresponds to a Ni foam cost increase of less than 0.1%

Ultralow loading electroless deposition of IrOx on nickel foam for efficient and stable water oxidation catalysis

Abstract Photocatalysis and electrolysis are crucial processes for the development of a sustainable, clean energy system, since they enable solar fuel production, such as hydrogen by water splitting, as well as CO2 reduction. In these processes efficient and robust catalysts for water oxidation are required and the reduction of employed amount of noble metals is crucial to reduce costs and increase the sustainability of the technology. To obtain extremely low iridium loading on nickel foam electrodes we have employed electroless deposition by spontaneous galvanic displacement as a simple, low cost, highly scalable technique. After deposition the Ir oxidation has been achieved by annealing in air at 250 °C. By varying the deposition parameters, an optimal condition has been achieved, with an overpotential for water oxidation of 360 mV at 10 mA cm−2 in 1.0 M KOH solution. The Ni foam coverage with Ir oxide has also a positive impact on the electrode stability, strongly decreasing the degradation rate, compared to the case of bare Ni foam. The average amount of noble metal in the best performing electrode is only 35 μg cm−2 for a 1.6 mm thick Ni foam electrode. The proposed approach is highly promising for gas diffusion electrodes, and can be implemented in electrolytic cells, as well as in fuel cells

Plants as biomonitors for volcanic emissions

Biomonitoring techniques have been widely used in environmental studies to monitor anthropogenic pollutant. Recently such techniques have been applied also to ascertain the impact of contaminants naturally released by volcanic activity. In the present study a biomonitoring surveys has been performed in many different active volcanic systems: Mt. Etna and Vulcano (Italy), Nisyros (Greece), Nyiragongo (DRC), Masaya (Nicaragua), Gorely (Kamchatka, Russia). We sampled leaves of different species Betulla aethnensis, Pinus nigra, Populus tremula, Senecio aethnensis and Rumex aethnensis on Etna, Cistus creticus and salvifolius on Vulcano and Nisyros, Senecio ssp. on Nyiragongo, a Fern on Masaya and Salix arctica at Gorely. All samples were analyzed by ICP-MS and ICP-OES for 49 elements after acid digestion with a microwave oven (HNO3 + H2O2). Major constituents in leaves are K, Ca, Mg, Na, Si, Al and Fe ranging from about 10 3 to 105 ppm. Manganesium, Sr, Rb, Ba, Zn, B, Cu show also relatively high concentrations (100-103 ppm) while the remaining elements (As, Bi, Cd, Ce, Co, Cr, Cs, Ga, Li, Mo, Ni, Pb, Sb, Sc, Se, Th, Tl, U, V, Y and lanthanide series) display much lower values (10-4-101 ppm). Nearly all investigated elements show their highest concentrations in the samples collected closest to the main degassing vents (open craters, fumarolic fields). Increased concentrations are also found in the samples collected in the downwind direction where volcanic emissions are prevailingly dispersed. Leaves collected along radial transects from the active vents, highlight that the levels of metals decrease from one to two orders of magnitude with increasing distance from the source. The decrease is stronger for volatile elements, which are highly enriched in volcanic emissions, (As, Bi, Cd, Cs, Pb, Sb, Tl) than for more refractory elements (Al, Ba, Sc, Si, Sr, Th, U). The different species of plants show significant differences in the bioaccumulation processes for most of the analyzed elements, in particular lanthanides, which are systematically enriched in Rumex leaves. Needles of pine (non-deciduous tree) represent a good tool for biomonitoring investigation because they are important tracers of accumulation with time. The high concentrations of many toxic elements in the leaves allow us to consider some of these plants as highly tolerant species to the volcanic emissions, and suitable for biomonitoring researches further confirming their strong potential in tracing the impact and geographic distribution of these natural contaminants

Passive degassing at Nyiragongo (D.R. Congo) and Etna (Italy) volcanoes

Volcanoes are well known as an impressive large natural source of trace elements into the troposphere. Etna (Italy) and Nyiragongo (D.R. Congo) are two stratovolcanoes located in different geological settings, both characterized by persistent passive degassing from their summit craters. Here, we present some re-sults on trace element composition in volcanic plume emissions, atmospheric bulk deposition (rainwater) and their uptake by the surrounding vegetation, with the aim to compare and identify differences and sim-ilarities between these two volcanoes. Volcanic emissions were sampled by using active filter-pack for acid gases (sulfur and halogens) and specific teflon filters for particulates (major and trace elements). The im-pact of the volcanogenic deposition in the surrounding of the crater rims was investigated by using differ-ent sampling techniques: bulk rain collectors gauges were used to collect atmospheric bulk deposition, and biomonitoring technique was carried out to collect gases and particulates by using endemic plant species. The estimates of the trace element fluxes confirm that Etna and Nyiragongo are large sources of metals in-to the atmosphere, especially considering their persistent state of passive degassing. The large amount of emitted trace elements has a strong impact on the close surrounding of both volcanoes. This is clearly re-flected by in the chemical composition of rainwater collected at the summit areas both for Etna and Nyira-gongo. Moreover, the biomonitoring results highlight that bioaccumulation of trace elements is extremely high in the proximity of the crater rim and decreases with the distance from the active craters