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Orlando A.,CNR Institute of Geosciences and Earth Resources | Lelli M.,CNR Institute of Geosciences and Earth Resources | Marini L.,Consultant in Applied Geochemistry | Marini L.,I-Systems
Applied Geochemistry | Year: 2012

The evaluation of the feasibility of ex situ carbonation in landfills utilizing raw natural substances (namely serpentinites as Mg-source and the CO 2-rich fraction of biogas as C-source) was tested through a laboratory procedure comprising three steps. The first step is the acid attack of a serpentinite at 70°C, by means of HCl 2M, to get MgCl 2-rich solutions. Attacks of different durations were performed to evaluate the time needed. The second step is the neutralization of the MgCl 2-rich solution by addition of concentrated ammonia. The third (carbonation) step is mixing of the neutralized MgCl 2-rich solution with a solution of ammonium carbonate. This was produced in a landfill by absorption of CO 2 contained in biogas in a solution of ammonia. The neutralization of acid MgCl 2-rich solutions caused the precipitation of ferrihydrite with secondary ammonium carnallite and salammoniac, whereas abundant precipitation of Amorphous Hydrated Impure Magnesium Carbonate (AHIMC), sometimes with minor nesquehonite, occurred in the third step. This solid carbonate acts as a stable CO 2 sink up to 380°C. The geochemical behavior of some minor elements was also investigated during the experimental processes revealing that Al, Cr and Ni were removed during neutralization (second step), in contrast to Ca which remained in the circumneutral MgCl 2-rich solution and entered into the structure of AHIMC. During the carbonation step, precipitation of artinite, hydromagnesite, lansfordite, magnesite and nesquehonite was thermodynamically impossible as the aqueous phase was undersaturated with respect to these solid phases upon separation of AHIMC.The CO 2 sequestered through this multi-step procedure is 0.34ton for 1ton of serpentinite utilized. However, despite that the use of Mg-rich silicates is a suitable approach to ex situ carbonation, due to their huge availability worldwide, the CO 2 produced in making the chemicals and the overall energy balance of the process must be evaluated to assess its sustainability. Furthermore, this procedure could be of great interest in asbestos inertization and the AHIMC products could possibly be useful in industry. © 2012 Elsevier Ltd.


Orlando A.,CNR Institute of Geosciences and Earth Resources | Borrini D.,University of Florence | Marini L.,Consultant in Applied Geochemistry
Applied Geochemistry | Year: 2011

Dissolution experiments on a serpentinite were performed at 70°C, 0.1MPa, in H2SO4 solution, in open and closed systems, in order to evaluate the overall dissolution rate of mineral components over different times (4, 9 and 24h). In addition, the serpentinite powder was reacted with a NaCl-bearing aqueous solution and supercritical CO2 for 24h at higher pressures (9-30MPa) and temperatures (250-300°C) either in a stirred reactor or in an externally-heated pressure vessel to assess both the dissolution rate of serpentinite minerals and the progress of the carbonation reaction. Results show that, at 0.1MPa, MgO extraction from serpentinite ranges from 82% to 98% and dissolution rate varies from 8.5×10-10molem-2s-1 to 4.2×10-9molem-2s-1. Attempts to obtain carbonates from the Mg-rich solutions by increasing their pH failed since Mg- and NH4- bearing sulfates promptly precipitated. On the other hand, at higher pressures, significant crystallization (5.0-10.4wt%) of Ca- and Fe-bearing magnesite was accomplished at 30MPa and 300°C using 100gL-1 NaCl aqueous solutions. The corresponding amount of CO2 sequestered by crystallization of carbonates is 9.4-15.9mole%. Dissolution rate (from 6.3×10-11molem-2s-1 to 1.3×10-10molem-2s-1) is lower than that obtained at 0.1MPa and 70°C but it is related to pH values much higher (3.3-4.4) than that (-0.65) calculated for the H2SO4 solution. Through a thorough review of previous experimental investigations on the dissolution kinetics of serpentine minerals the authors propose adopting: (i) the log rate [molem-2s-1] value of -12.08±0.16 (1σ), as representative of the neutral dissolution mechanism at 25°C and (ii) the following relationship for the acidic dissolution mechanism at 25°C:log rate=-0.45(±0.09)×pH-10.01(±0.30).The initial dissolution rate (for 25°C) by acid attack obtained in this work is consistent with this relationship. In contrast, the average dissolution rate (for 25°C) determined in this study through the pressure-vessel experiments is ∼4.5 orders of magnitude lower than that computed through this equation, suggesting that silica armoring of serpentinite grains played a significant role in these experiments. Overall, the obtained data may improve both the planning of ex-situ mineral carbonation using the CO2 separated from biogas and the modeling of in-situ mineral carbonation. © 2011 Elsevier Ltd.


Apollaro C.,University of Calabria | Marini L.,Consultant in Applied Geochemistry | Critelli T.,University of Calabria | Barca D.,University of Calabria | And 4 more authors.
Applied Geochemistry | Year: 2011

The progressive dissolution of metabasalts and serpentinites hosting the shallow aquifer of Mt. Reventino was simulated by means of the EQ3/6 software package, version 8.0, adopting both the Ideal Solid Solution Approach (ISSA) and the Double Solid Reactant Method (DSRM), which provided comparable results. A detailed field and laboratory study was performed on rock samples and local groundwaters to constrain and validate reaction path modelling. The prevalence of Ca-HCO3 over Mg-HCO3 compositions suggests that groundwaters interact chiefly with metabasalts and secondarily with the less abundant and less permeable serpentinites. The most important and active Cr source is a tremolite-rich amphibole, whose role as supplier of dissolved Cr has rarely been recognized in previous studies carried out in areas where ophiolitic rocks crop out. Speciation calculations indicate that hexavalent dissolved Cr is mainly present as chromate ion, followed by the neutral complexes CaCrO4o (14-32mol%) and MgCrO4o (2-12mol%), which are more mobile and more bio-available than charged solutes.All dissolved trace elements are supplied to shallow groundwaters by gradual dissolution of local rocks and, therefore, contributions linked to anthropogenic sources can be ruled out. In particular: (i) Ni is chiefly contributed to the aqueous phase by the tremolite-rich amphibole; (ii) different amounts of Sr, Ba, and Pb are provided by calcite dissolution (with Sr≫Ba>Pb), whereas the solid solution of orthorhombic carbonates acts as sink for these trace elements (with Xstrontianite≫Xwitherite>Xcerussite); (iii) the principal source of Cu and Zn is again calcite, whereas the solid solution of trigonal carbonates represents their major sink. © 2011 Elsevier Ltd.


Apollaro C.,University of Calabria | Dotsika E.,Greek National Center For Scientific Research | Dotsika E.,CNR Institute of Neuroscience | Marini L.,Consultant in Applied Geochemistry | And 6 more authors.
Geochemical Journal | Year: 2012

The Terme Sibarite and nearby thermomineral water discharges have Ca-SO4 to Ca-SO4-HCO3 composition, near neutral pH value of 6.9 to 7.6, outlet temperatures of 16° to 25.5°C, variable redox potentials (-0.23 to 0.2 V) and total dissolved solids from 20 to 35 meq L-1. The total flow rate of the Terme Sibarite springs is about 130 L s-1. Solubility of chalcedony and the K-Mg geothermometer show a full equilibrium reservoir temperature of 33°C. The δ34S values of dissolved sulfate are constrained by mixing of thermomineral waters with cold waters, both interacting with Upper Triassic carbonate-evaporite rocks, as well as occurrence of bacterial sulfate reduction. In the light of the geological and hydrogeological framework of the study area, this chemical and isotopic evidence suggests that the thermal circuit develops entirely into the Upper Triassic sedimentary sequence, without any interaction with the Messinian evaporites which are possibly present below the Upper Triassic sedimentary sequence. The thermomineral waters are meteoric precipitations infiltrating in the Pollino Massif, at average altitudes of 950-1090 m a.s.l, as indicated by the δ18O values of water. These waters descend to maximum depths of 600 m below the Sibari Plain, where the geothermal reservoir is situated. Circulating into it, waters extract heat from reservoir rocks, attaining thermo-chemical equilibrium at the temperature suggested by chemical geothermometers. Then, the thermomineral waters locally rise relatively quickly to the surface, along subvertical faults and fractures, preserving part of their physical and chemical characteristics. The methodological approach utilized in this research may be applied to other fault-controlled, low-temperature geothermal systems in other zones of Italy and other nations. Copyright © 2012 by The Geochemical Society of Japan.


Critelli T.,University of Calabria | Marini L.,Consultant in Applied Geochemistry | Schott J.,French National Center for Scientific Research | Mavromatis V.,French National Center for Scientific Research | And 5 more authors.
Chemical Geology | Year: 2014

The dissolution rates of the minerals actinolite and chlorite were determined from metabasalt element release rates measured at 25°C and 2

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