Potentially toxic elements distribution in the serpentinized and deformed ultramafic rocks from the Voltri Massif (NW, Italy)

The aim of the work is to assess the role of local-scale lithological, textural, and structural factors in the distribution of potentially toxic elements (PTEs) in different ultramafic rocks from the high-pressure ophiolitic Voltri Massif (Central Liguria, NW Italy). The results evidenced that Cr (up to 4183 ppm), Ni (up to 3900 ppm), and Co (up to 334 ppm) are invariably the PTEs with the highest concentrations; in addition, V, Cu, and Zn are systematically found in non-negligible amounts. Spinel-group minerals (chromium spinel, ferrian chromite, chromium magnetite, and magnetite) are by far the main potential source of the PTEs. Nevertheless, several PTEs are also present within serpentines, olivines, pyroxenes, chlorites, as well as within accessory phases (e.g., ilmenite and Ni-sulphides) and within authigenic minerals formed in the early stages of rock weathering (cryptocrystalline to amorphous Fe-oxides and -oxyhydroxides). The result obtained allowed to evidence that the main factors controlling the PTEs distribution within the rocks resulted to be the serpentinization degree and the deformation style and intensity which, in turn, strictly control the mineral assemblages and the mineral chemistry

Primary and authigenic minerals in serpentine soils under temperate climate conditions: source or trap for potentially toxic elements (PTEs)

In this study, we have analysed the mineralogy and the crystal chemistry of serpentine soils from ultramafic rocks of the metaophiolitic Voltri Massif (Liguria, Italy), in order to determine the primary and authigenic mineral species controlling the distribution and the mobility of PTEs during pedogenic processes. These serpentine soils were characterised by PTEs contents commonly exceeding the concentration limits laid down by environmental agencies, particularly for Cr (1200-2500 mg/kg) and Ni (1000-4200 mg/kg). With these hazardous PTEs concentrations, the knowledge of the distribution of PTEs-bearing minerals is of paramount importance for understanding their origin and their fate during the development of serpentine soil profiles and can allow to evaluate their effective bioavailability. All the studied soil profiles were restricted in depth (10-50 cm) and showed a low degree of maturity with weakly developed A-C horizons. Soil samples were subdivided into three aliquots in order to separate the soil skeleton (2 mm-63 \u3bc m) from the silt (63-2 \u3bc m) and clay fraction (<2 \u3bc m). Quantitative mineralogical analyses were performed in all aliquots by using XRPD data collected with synchrotron sources at the MCX beamline (ELETTRA - Synchrotron, Trieste, Italy) and refined with EXP-GUI GSAS software. Trace metals were determined with energy and wavelength electron microscopy. The mineralogy of the coarse and silty fractions was closely related to bedrock mineralogy. The following minerals were detected in decreasing order of abundance: antigorite, chlorite, tremolite, magnetite, Cr-rich spinel, chrysotile, ilmenite, clinopyroxenes, olivine. Allochthonous quartz and albite were always present as minor to trace constituents. The clay fraction was mainly composed by Fe-oxides and -oxyhydroxides (mainly hematite and goethite) with subordinate amounts of mixed-layer clay minerals (chlorite-smectite, chlorite-vermiculite). These authigenic secondary minerals were characterised by poor crystallinity, intimate intergrowths, and fine-scale heterogeneities. PTEs were hosted mainly in the residual primary minerals deriving from the underlying parent material and subordinately in secondary authigenic phases. Cr was mainly contained within spinels (magnetite, Cr-magnetite, ferrichromite, picotite, and hercynite), antigorite, diopside and augite. Nonnegligible amounts of Cr was also present in authigenic hematite (up to 0.1 wt%) and goethite (up to 0.15 wt%). The main Ni-bearing minerals were olivine and antigorite but significant Ni concentration was also detected in authigenic hematite (up to 2.8 wt%) and goethite (up to 4.2 wt%) which thus represented effective traps for Ni leached through mineral weathering to the soils solution. These results are the preliminary step for the evaluation of the role of mineral species in controlling the PTEs mobility during the evolution of serpentine soil profiles. Quantitative mineralogical data will be further used to perform mass balance calculations as well as to interpret and model the results of batch leaching experiments that will be conducted on the different soil fractions

Potentially Toxic Elements in Ultramafic Soils: A Study from Metamorphic Ophiolites of the Voltri Massif (Western Alps, Italy)

Ultramafic soils are characterized by severe edaphic conditions induced by a low content of essential nutrients, an adverse Ca/Mg ratio, a low water-holding capacity, and high contents of geogenic potentially toxic elements (PTEs), in particular Cr, Ni, and Co. These metals commonly exceed the content limits set by environmental agencies and governments, representing serious environmental risks for ecosystems and human health. In alpine environments, ultramafic soils are characterized by modest thickness and poor horizon differentiation. Several studies on ultramafic soils have shown that their properties may be directly related to the characteristics of the parent rocks, but most of these studies deal with soil chemistry, metal availability, isotopic composition, and pedological characterization. The aim of this research is to investigate how much the geotectonic characteristics of ultramafic bedrocks, such as the degree of serpentinization, metamorphic imprint, and deformation, may affect the mineralogical and chemical variations of ultramafic soils, including the occurrence and potential mobility of the PTEs. Using a multiscale and multi-analytical approach, we fully characterize the properties and mineralogical composition of soil profiles with different ultramafic parent rocks, i.e., partially serpentinized peridotite, massive serpentinites, and foliated serpentinites, sampled within the Voltri Massif High Pressure\u2013 Low Temperature (HP\u2013LT) metaophiolite (Western Alps, Italy). Our results, related to soils located at comparable latitude, altitude, landscape position, and pedological environment, outline that the degree of serpentinization, the metamorphic imprint, and the deformation history of the ultramafic parent rocks are key factors influencing soil evolution, mineralogy, and chemistry, as well as PTEs distribution and mobility. Moreover, this study shows that the high content of Cr, Ni, and Co in the studied ultramafic soils has to be considered of geogenic origin and highlights the need for new approaches and methods to obtain indications on the potential contamination of natural or anthropogenic soils

The Achievements of the RockStar Group (Perugia) on Astrophysical Modelling and Pallasite Geochemistry

In the present work we summarize the first achievements of the RockStar Group of the Department of Physics and Geology (at the University of Perugia, Italy), which is made of a strict collaboration between Physicists and Geologists on astrophysical and planetological studies. The RockStar Group acts on two research lines: (i) astrophysical modeling and (ii) mineralogical and geochemical studies of meteorites. In the first part of the article we review the recent results concerning the development of theoretical modeling of nucleosynthesis and mixing process in asymptotic giant branch. In the second part we report (1) the catalog of the Meteorite collection of University of Perugia and (2) major and trace elements mapping, performed through EPMA and LA-ICP-MS, of the Mineo pallasite, a unique sample hosted by the collection. The new data constrain the Mineo meteorite among the Main Group Pallasites and support the hypothesis of the "early giant impact" formation

Effect of the Nano-Ca(OH)2 addition on the Portland clinker cooking efficiency

A new technology was tested to improve the cooking efficiency of the raw mixture for Portland clinker production by the use of nano-Ca(OH)2. A decrease in the free lime concentration after the firing of approximately 35% and 55% in the nano-added clinkers burned at 1350 °C and 1450 °C, respectively, with respect to the standard Portland clinkers was observed. Moreover, in the nano-added clinkers, a slight decrease in alite (C3S), of approximately 2-4 wt%, and increase in belite (C2S), of approximately 5-6 wt%, were observed. Despite these variations, the C2S and C3S abundance lies within the ranges for standard Portland clinkers. The results showed that the nano-addition leads to an increase of the raw mixtures' cooking efficiency. The relatively low energy required for the clinker firing could be used to increase the plant productivity and decrease the CO2 emissions during clinker burning. The decrease of the work index of the clinkers produced by the use of the nano-Ca(OH)2 also contributes to the energy saving during clinker grinding. Differences were also found in the pore size distribution among nano-added clinkers and the standard Portland clinker. The smallest porosities with the modal volume lying in the class of 3 × 10-6 mm3 were found to increase by the use of nano-Ca(OH)2. However, the pore volumes higher than 2.0 × 10-5 mm3 decreased in the nano-added clinkers. © 2019 by the authors

High- Pressure single-crystal synchrotron X-ray diffraction of kainite (KMg(SO4) Cl 3H2O)

The paper reports the results of high pressure single-crystal X-ray diffraction experiments carried out at the European Synchrotron Radiation Facility (Grenoble, France) on the kainite phase a “mixed salt” sulphate (KMg(SO4) Cl 3H2O). The compressibility and structural modifications are reported up to 14 GPa. The complex structural configuration explains the axial compressibility (with c direction softer than a and b directions) that seems to contrast with the (100) cleavage. Following the structure modification increasing pressure a new sets of hydrogens bonds could form as oxygens and chlorine atoms get at less than 3Å distance from the Ow Kainite is an interesting sulphate mineral because it could be present together with other hydrous minerals in the extra-terrestrial planets (like Mars) and it is a relevant mineral in potash deposits, largely used in the extraction and production of fertilizers. Moreover the simultaneous presence of Cl and H2O makes this mineral interesting to study the behaviour of these two components at high pressure