Critelli T.,University of Calabria |
Marini L.,Geochemistry |
Schott J.,French National Center for Scientific Research |
Mavromatis V.,French National Center for Scientific Research |
And 6 more authors.
Applied Geochemistry | Year: 2015
Serpentinite rock dissolution experiments at 25. °C and 2 < pH < 9 were used to retrieve antigorite dissolution rates, as its high abundance and comparatively fast dissolution dominate element release from the rock. Retrieved antigorite dissolution rates at pH 2.02 and 3.06 are similar to previous literature data for serpentine minerals at corresponding pH. In contrast, retrieved rates at higher pH are considerably lower than corresponding literature data. Nonetheless, the retrieved rates at pH 5.76 and 7.28 are consistent with the linear log rate - pH relationship of Orlando et al. (2011), suggesting that rates follow a single 'acidic' mechanism to a pH of at least 7.3. The relatively low dissolution rates of serpentine minerals found in this study suggests that significantly more time is required for serpentine weathering than that estimated using the dissolution rates of these solids reported by Marini (2006) based on a review of literature data. As such, using enhanced serpentine weathering as a carbon capture/storage strategy may be less efficient than previously assumed. © 2015 Elsevier Ltd.
Lima A.T.,Geochemistry |
Rodrigues P.C.,New University of Lisbon |
Mexia J.T.,New University of Lisbon
Journal of Hazardous Materials | Year: 2010
Fly ash is an airborne material which is considered hazardous waste due to its enrichment on heavy metals. Depending on the waste from which they are originated, fly ash may be further valorised, e.g. as soil amendment or concrete and ceramics adjuvant, or landfilled, when defined as hazardous material. In any case, heavy metal content has to be decreased either for fly ash valorisation or for complying with landfill criteria. The electrodialytic (EDR) process is a remediation technique based on the principle of electrokinetics and dialysis, having the aim to remove heavy metals from contaminated solid media. EDR was here applied to fly ashes from the combustion of straw (ST), from the incineration of municipal solid waste (DK and PT) and from the co-combustion of wood (CW). A statistical study, using F tests, Bonferroni multiple comparison method and a categorical regression, was carried out to determine which variables ("Ash type", "Duration", "Initial pH", "Final pH", "Acidification" and "Dissolution") were the most significant for EDR efficiency. After establishing these, the selected variables were then used to characterize some kinetic parameters, from metals migration during EDR, using a biregressional design. Cd, Cr, Cu, Ca and Zn migration velocity and acceleration to the electrodes (anode and cathode) were then considered. Cd and Cu migration to the cathode were found to be significantly influenced by "Ash type", "Duration", "Final pH" and "Dissolution". © 2009 Elsevier B.V. All rights reserved.
Agency: Narcis | Branch: Project | Program: Completed | Phase: Physics, Chemistry and Medicine | Award Amount: | Year: 2007
Fluids are of crucial importance in the functioning of our planet. Without fluids, most pro-cesses in the earth including plate tectonics would not operate, halting, amongst others, the nutrient cycles critical to life. Fluids are also the main agents of element transport and redistribution, capable of highly selective leaching and enrichment. Fluids carry a distinct chemical signature, the combined result of interaction with different rocks at diverse pressure and temperature conditions, and variables including pH and WO2. Fluid chemistry and its evolution thus provide an unique window into the processes operating in the earth. Unfortunately, these deep fluids cannot be sampled directly. In this study we explore an alternative approach to quantify fluid chemistry and its evolution, using information stored in minerals. By determining the equilibrium element partitioning between minerals and fluids at relevant conditions, we will be able to reconstruct fluid chemistry from mineral composition. Element partitioning values will be derived from mineral synthesis experiments in fluids doped with elements of interest. To allow these values to be extrapolated beyond experimental conditions we will set up a mineral-fluid partitioning model following techniques developed for mineral-melt partitioning. Data will be derived for the common minerals tourmaline and fluorite, ensuring wide applicability of our results.
Agency: Narcis | Branch: Project | Program: Completed | Phase: Physics, Chemistry and Medicine | Award Amount: | Year: 2006
Kraal P.,Geochemistry |
Slomp C.P.,Geochemistry |
Forster A.,Netherlands Institute for Sea Research |
Kuypers M.M.M.,Max Planck Institute for Marine Microbiology
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2010
Phosphorus (P) burial during the Cenomanian/Turonian oceanic anoxic event (OAE 2, ~93.55Ma) was studied using sediment records from four sites in the proto-Atlantic Ocean. The sites represent a variety of depositional settings, from the continental margin and slope to the abyssal plain. Strong links between changing marine conditions during OAE 2 and P cycling were observed in black shale sections on the continental margin and slope. Sedimentary P contents and P MARs increased around the onset of OAE 2, which may reflect enhanced productivity and P burial, partly in the form of biogenic apatite (fish debris). During the main stage of OAE 2, phosphorus was efficiently regenerated from the sediment, resulting in P-depleted sediments and high organic C (Corg)/total P ratios. The increased availability of dissolved P may have helped to sustain high productivity during OAE 2. The termination of OAE 2 was associated with a strong recovery of P burial efficiency in the sediment. Sedimentary records from the two deep sites do not reveal such close links between different stages of OAE 2 and the characteristics of P cycling. Here, OAE 2 was a period with maximum deposition of relatively thin black shale intervals that alternate with more oxic deep sea sediments. The black shale layers record enhanced P regeneration from organic matter and, in some cases, P enrichment relative to the oxic sediments. Detailed chemical P fractionation was performed on sediment from all sites, but the results were found to mostly reflect diagenesis and sample handling artifacts. In these ancient sediments, total P concentrations and the Corg/total P ratio appear to be the most robust indicators of P cycling and regeneration. © 2010 Elsevier B.V.