Vincenzo Ferrini

Evaluation of the effectiveness of phosphate treatment for the remediation of mine waste soils contaminated with Cd, Cu, Pb, and Zn

The effectiveness of phosphate treatment for Cd, Cu, Pb, and Zn immobilization in mine waste soils was examined using batch conditions. Application of synthetic hydroxyapatite (HA) and natural phosphate rock (FAP) effectively reduced the heavy metal water solubility generally by about 84-99%. The results showed that HA was slightly superior to FAP for immobilizing heavy metals. The possible mechanisms for heavy metal immobilization in the soil involve both surface complexation of the metal ions on the phosphate grains and partial dissolution of the phosphate amendments and precipitation of heavy metal-containing phosphates. HA and FAP could significantly reduce Cd, Cu, Pb, and Zn availability in terms of water solubility in contaminated soils while minimizing soil acidification and potential risk of eutrophication associated with the application of highly soluble phosphate sources.

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.

Behavior of cation vacancy in kenotetrahedral Cr-spinels from Albanian eastern belt ophiolites

Abstract The crystal chemistry of 17 Cr-spinels from the Albanian eastern belt ophiolites was studied by a multi-analytical approach (EMPA, MS, SREF), processing the data with a tested optimization model to obtain site populations. The samples come from the three most important ultramafic massifs of Albania (Tropoja, Bulqiza, and Shebenik), and occur in ultramafic cumulates as well as in ultramafic mantle tectonites, associated with serpentinized olivine. All samples are characterized by Cr ↔ Al and minor Mg ↔ Fe2+ substitutions, and may be classified as magnesiochromite, except one, which is spinel s.s. Cation distributions showed that Cr and Al are ordered in M, and Fe2+ and Mg in the T site. Contents of Fe3+ measured by MS were always higher than those calculated from EMPA, and this non-stoichiometry reveals that the Albanian crystals underwent an increase in fO₂ conditions after mineral formation. Cation vacancies produced by Fe2+ oxidation occur in the T site, and the oxidation mechanism, is described by: 2 TFe2+ + ½ O2 → 2 TFe3+ + O2- + T⃞. T-O variations show a non-linear regression with TFe2+, and this trend is due to both the cooperative effects of TMg ↔ TFe2+ substitution and TFe2+ oxidation. Cation vacancy in the T site does not impart rigidity to the polyhedron, because it cannot have chemical bonds with ligands: this feature, together with the spinel topology, makes the tetrahedron adopt .soft. behavior. In effect, the T⃞-O distance does not have a single value, but changes according to the population of the M site, as confirmed by comparison with literature data and also by application of the Bond Valence Model.

The efficiency of CO2 sequestration via carbonate mineralization with simulated wastewaters of high salinity

Salinity generally strongly affects the solubility of carbon dioxide in aqueous solution. This would seem to involve a reduction of the efficiency of the carbonate mineralization process with the objective to sequester this greenhouse gas. On the contrary, we demonstrate here that with a more concentrated solution of magnesium chloride, the residence time of CO(2) is enhanced in the aqueous medium because of a reduced tendency to produce CO(2(g)). Experiments intended to simulate more closely the Mg-rich wastewaters that are industrially available have been carried out using solutions differing in Mg concentration (7, 16, 32 g L(-1) Mg). A comparison of the efficiency of the CO(2) mineralization process among sets of experiments shows that the reduction of the efficiency, to about 65%, was lower than that expected, as the low degree of CO(2) degassing results in the enhanced availability of carbonic ions to react with Mg ions to form stable carbonate minerals over a longer time.

Nb-Ta oxide minerals from miarolitic pegmatites of the Baveno pink granite, NW Italy

Abstract Chemical composition and cell parameters were ascertained on new data from Ti-Nb-Ta complex oxides from the miarolitic pegmatites of the Baveno pink granite (Southern Alps, NW Italy). The crystals are tiny, single or aggregated in small sprays, prismatic or tabular, from yellow-orange to brownish in colour. Typical associated minerals include fluorite, zinnwaldite, gadolinite-groupminerals and Sc-minerals. Cavity paragenesis is typical of NYF pegmatites, and shows two stages of crystallization developing in magmatic-pneumatolitic and hydrothermal conditions. X-ray data show that some oxides belong to the aeschynite mineral group; others are polycrase and fersmite. Aeschynite and polycrase are chemically heterogeneous and structurally disordered because of their metamict state. This disorder does not always seem to be related to radionuclide contents. Two main trends are indicated, considering the behaviour of Y. The high Y contents fit with very low Ca and LREE contents in the A site; the HREE contents follow the Y trend. In the B site, Ti is the dominant cation, followed by some Nb and very little Ta. Small quantities of Y fit with increasing Ca, U, Th and REE contents. In the B site, Nb cations often exceed those of Ti. The Th contents are often greater than those of U. Besides the already known aeschynite-(Y) and vigezzite, new varieties, ‘titano-vigezzite’ and ‘niobo-aeschynite-(Y)’, are identified here in the Baveno miarolitic cavities. Samples 14 (analysis a) and 2502 (analysis b) have Ca as the main occupant of the A site, followed by Y, Th and REE; in the B site, Ti prevails over Nb. These compositions cannot be considered as pure vigezzite, but as a new variety called ‘titano-vigezzite’. In the same way, analysis a of sample 3 may be considered a new variety of aeschynite-(Y), with Nb prevailing over Ti in the B site, and here called ‘niobo-aeschynite- (Y)’. Neither variety has ever been mentioned in the literature. Epitaxial growth of aeschynite on polycrase (sample 3194) allows some inferences on the crystallization sequence.

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.

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.

Distribution and significance of Pb and Tl in the sulfides and host rocks from the hydrothermal mineralization of the Tolfa Mountains (Latium, Central Italy)

Abstract Tl and Pb contents of 29 samples of sulfide minerals (mainly pyrite) from the hydrothermal Pliocene vein mineralization of the Tolfa Mountains volcanic district have been measured by a polarographic technique. Abundances of Tl and Pb have also been measured in selected host rocks and travertines to establish the relationship between ores and possible source rocks. Hydrothermal pyrites of the various stages of the mineralization show similar ranges of Tl contents (220–7320 ppb, X = 2101 ppb ), while the Pb content is higher in late-stage pyrites (23–3650 ppm, X = 1791 ppm ) relative to early ones (8–246 ppm, X = 95 ppm ). This latter feature suggests a different Pb content of the ore-bearing solutions of the two stages of mineralization. The Pb/Tl ratio distinguishes the pyrites of the main stage of mineralization from the different mines and is roughly constant in most pyrites from the same locality. It is suggested that Pb and Tl contents in pyrites merease with evolution of the mineralizing process. Volcanic pyrites are enriched in Tl (9000–28000 ppb, X = 16,666 ppb ) relative to hydrothermal pyrites due to the greater availability of Tl in magmatic processes. The Pb content of volcanic pyrites is as low as that of early hydrothermal pyrites. Disseminated pyrites in the unaltered flysch rocks show higher Pb and Tl levels than those expected in sedimentary pyrites and are comparable with those of hydrothermal pyrites, thus suggesting an origin or interaction with hydrothermal solutions. Tl and Pb contents in the hydrothermally-altered flysch ( X = 962 ppb and 16 ppm, respectively) are much higher than in the unaltered flysch ( X = 5 ppb and 4 ppm, respectively), indicating that Pb and Tl were carried by the hydrothermal fluids. Thus the origin of mineralization appears to be strictly related to the hydrothermal process, the ore potential being limited to the alteration zone. The source of Pb and Tl was represented by sedimentary rocks and magmatic fluids involved in the formation of the buried skarns. Tl is retained in the gossans formed on the mineralized zones, whereas the element is absent in ironstones not related to ores. This suggests its potential use as a pathfinder during prospecting for sulfide ores. On the contrary, Pb is retained in both gossans and ironstones at roughly comparable levels, and is, therefore, of limited use for geochemical prospecting. Finally, Pb and Tl are detectable in the travertines from the eastern and southern parts of the Tolfa Mountains area, where the thermal waters leached Pb and Tl, circulating deeply through volcanic rocks and/or sulfide ores. Thus, both the Pb and Tl contents in travertines may be used in prospecting.