Caterina De Vito

The thermal behaviour and structural stability of nesquehonite, MgCO3.3H2O, evaluated by in situ laboratory parallel-beam X-ray powder diffraction: new constraints on CO2 sequestration within minerals.

In order to gauge the appropriateness of CO(2) reaction with Mg chloride solutions as a process for storing carbon dioxide, the thermal behaviour and structural stability of its solid product, nesquehonite (MgCO(3).3H(2)O), were investigated in situ using real-time laboratory parallel-beam X-ray powder diffraction. The results suggest that the nesquehonite structure remains substantially unaffected up to 373 K, with the exception of a markedly anisotropic thermal expansion acting mainly along the c axis. In the 371-390 K range, the loss of one water molecule results in the nucleation of a phase of probable composition MgCO(3).2H(2)O, which is characterized by significant structural disorder. At higher temperatures (423-483 K), both magnesite and MgO.2MgCO(3) coexist. Finally, at 603 K, periclase nucleation starts and the disappearance of carbonate phases is completed at 683 K. Consequently, the structural stability of nesquehonite at high temperatures suggests that it will remain stable under the temperature conditions that prevail at the Earths surface. These results will help (a) to set constraints on the temperature conditions under which nesquehonite may be safely stored and (b) to develop CO(2) sequestration via the synthesis of nesquehonite for industrial application.

The key role of micro-Raman spectroscopy in the study of ancient pottery: the case of pre-classical Jordanian ceramics from the archaeological site of Khirbet al-Batrawy

Micro-Raman (μ-Raman) spectroscopy has been used, as a preliminary and non-destructive technique, in order to investigate the mineralogical composition and to define the maximum firing temperature and redox state of the firing atmosphere of ancient ceramic materials. The studied ceramics come from the archaeological site of Khirbet al-Batrawy (north-central Jordan), dating back to the Early Bronze Age (3000–2000 B.C.). The results show that the ceramic body is composed mainly by quartz and calcite, and minor amount of feldspars and hematite. In addition, apatite and zircon, important markers to identify the provenance of raw materials, have been detected. Furthermore, the occurrence of gypsum has been related to both rehydration of anhydrite and burial alteration processes. Micro-Raman spectroscopy was helpful to investigate the nature of the pigments of these ceramics: the red colour was obtained by hematite, the dark pigment by amorphous carbon. Mineral assemblage allowed estimating the maximum firing temperature of these pottery vessels between 850 and 950 °C. The comparison of the results of μ-Raman spectroscopy and of X-ray diffraction analysis suggests that μ-Raman spectroscopy could have a key role in the study of ceramic materials, especially the characterization of archaeological ceramic samples for which manipulation and/or consumption are not allowed.

Extreme sulphur isotope fractionation in the deep Cretaceous biosphere

Abstract: Isotopically light sulphur in sedimentary pyrite was generally predominant during the Cretaceous as a consequence of volcanic and hydrothermal activity and bacterial sulphate reduction (BSR). However, we report super-high sulphur isotopic compositions of sedimentary pyrite (δ34S +89.3‰) from late mid-Cretaceous sediments from the Central Apennines, Italy. These exceptionally high δ34S values are not consistent with current models for interpreting the geological record for sulphur isotopes because these cannot explain the extreme isotopic fractionation observed in our study. Precise details of the mechanism for producing pyrite so highly enriched in 34S remain elusive, but the large variation in δ34S values (>70‰) within the analysed samples and the considerable micro-scale variations in δ34S (up to 50‰ even within a single nodule) indicate a complex mechanism of sulphate reduction and pyrite precipitation. This includes early removal of isotopically light H2S by pyrite precipitation in the water column, diffusion and advection of H2S and SO42−, and finally BSR. Similar but less severe conditions occur in the Black Sea and in deep ocean sediments. These new findings provide new insights for the interpretation of the palaeoceanographic conditions that prevailed during the Mesozoic.

Progress in carbon dioxide sequestration via carbonation of aqueous saline wastes

In this article we report the progress made in CO 2 sequestration research via formation of synthetic carbonates and explore the engineering aspects of the proposed methodology. The approach to synthesize the carbonates involves the reaction of a flux of CO 2 with Mg chloride solution at room temperature. The kinetics of the carbonation reactions demonstrate that: a) in the experiments performed in solutions having both 7 and 16 g L −1 of Mg the rapid formation of nesquehonite occurred; b) in experiments with 32 g L −1 of Mg an initial precipitation of chlorartinite was followed by nesquehonite with a minor amount of lansfordite. Carbonation via magnesium chloride aqueous solutions at standard conditions, here reported, represents a simple and permanent method of trapping CO 2 in solid form. It could be applied at point-sources of CO 2 emission and could involve rejected brines from desalination plants and other saline aqueous wastes. Other various aspects such as the influence of the salinity of the solution on the efficiency of carbonation and the kinetics of the reaction are also discussed.

Why is amazonitic K-feldspar an earmark of NYF-type granitic pegmatites? Clues from hybrid pegmatites in Madagascar

Abstract The presence of amazonitic K-rich feldspar is considered an earmark of evolved granitic pegmatites of NYF type. Elements of an explanation of the “NYF pegmatite-amazonite” connection emerged in a study of the classic Anjanabonoina “hybrid” granitic pegmatite in Madagascar. The NYF assemblages there and at the Sakavalana and Anjahamiary pegmatites contain magmatic U- and Th-rich accessory phases and an amazonitic microcline perthite in miarolitic cavities. The early miarolitic minerals are overgrown by a Li- and Cs-enriched assemblage, depleted in HFSE, containing pale-gray microcline perthite. The amazonitic microcline perthite at Anjanabonoina has a δ18O value above 15‰, and that at Sakavalana, close to 13‰, indicative of formation of the NYF-pegmatite-forming magma by the melting of crustal rocks. Locally, the source rocks had become slightly alkaline and enriched in HFSE during periods of metasomatism of the hot granulitic crust accompanying episodes of distension over the course of the protracted Pan-African orogeny. The fertilized crust underwent local anatexis after the culmination of Gondwana re-assembly. The proximity of pyrochlore and other U- and Th-bearing accessory phases in the NYF assemblage provided the ionizing radiation required to interact with H2O trapped in the vacancy next to the Pb ions in the structure. The presence of an amazonitic K-feldspar ultimately signals net additions of Pb, U, Th, and the alkalis to the source prior to anatexis during a period of distension after a major orogenic disturbance. Plumbian K-feldspar also occurs in granitic pegmatite bodies formed by anatexis in the vicinity of a galena-bearing orebody (e.g., at Broken Hill, Australia); in this case, the resulting granitic pegmatite is neither of NYF type nor enriched in rare elements, however.

Is Khirbet Kerak Ware from Khirbet al-Batrawy (Jordan) local or imported pottery?

A multi-analytical approach has been applied to characterize Khirbet Kerak Ware from the archaeological site of Khirbet al-Batrawy (Jordan), a highly distinctive pottery production of Early Bronze III Levant. Sherds of Khirbet Kerak Ware vessels, dating back to 2750–2500 B.C., show peculiar shapes and a highly polished red/black coating, alien to other Levantine ceramic traditions. Micro-Raman, infrared spectroscopic and petrographic data have been obtained with the aim of defining the fabric, tracing the origin of the raw material used in the manufacturing process and exploring the technological aspects. The results on Khirbet Kerak Ware are then compared with those of ceramics of the same period found at that site in order to highlight possible differences or similarities in the manufacturing process. All these pottery productions reveal similar mineralogical composition, compatible with a local sourcing of the raw materials; moreover, the identification of a specific mineral assemblage allows to estimate a firing temperature ranging from 850 °C to 900 °C. In spite of the marked differences observed between macroscopic appearances of Khirbet Kerak Ware and those of other coeval and local pottery productions, the results are indicative of overall local manufacturing.

Reject Brines from Desalination as Possible Sources for Environmental Technologies

Desalination of seawater represents the way to increase the supply of water for domestic, agricultural and industrial purposes. The potential environmental impact of desalination needs to be thoroughly evaluated, and any environmentally adverse consequences must be promptly addressed in order to assure a sustainable development of this technology. The main concern in desalination is the management of the brines whose uncontrolled discharge has significant negative impacts on the environment. Indeed, even if the production costs have decreased in the last decade, those related to the disposal of the brine have shown only limited reduction of the relative costs. New production strategies benefit from modern and efficient freshwater-generation plants, but the management strategies are based only on the few traditional options for the disposal of wastes. Sustainability is currently a main focus of high-level political discussions in the world, as it directly involves environmental pollution and global warming. Economic geologists are very well placed to understand and contribute to issues of sustainability, and to evaluate alternative resources for the future development of humanity. We, as economic geologists, are trained to unravel the complex series of events that led to the formation of natural resources. Consequently, we can use this expertise to help develop manmade processes to convert waste into resources. Today, the challenge is to consider the brine, instead of a harmful by-product, as a valuable source for several compounds to be involved in diverse industrial processes. For example, the brines could provide significant amounts of magnesium, resulting in a very promising source of this element as an alternative to traditional mining. Indeed, today there are stringent regulations concerning mining in all most all countries to prevent or at least minimize damage to exploited properties. As traditional approaches in mining are costly in time or inapplicable in abandoned and remote regions, research needs to be focused on nontraditional sources such as brines coming from desalination plants. These brines certainly have several advantages, and in time can replace, at least in part, the conventional sources with an alternative, economically attractive process. Dual benefits can be achieved in recovering and recycling Mg from reject brines: reduction of large volumes of brines to be

Ex situ CO 2 mineralization via nesquehonite: A first attempt for an industrial application

A novel method to synthesize nesquehonite, MgCO3 · 3H2O, via reaction of a flux of gaseous CO2 with Mg chloride solution at ambient conditions, performed using a reactor, is here described. The reaction rate of the process is rapid, with deposition of abundant carbonate in few minutes. The results of a multi-disciplinary methodology, including SEM-EDAX, XRD, ICP-AES and thermal analysis, suggest that the application of our method at industrial scale can be considered. Moreover, the possibility to involve in the process saline wastewater as source of Mg makes the method a promising complementary solution in the sequestration of anthropogenic CO2 at the expense of saline wastewater.