Valentina Prigiobbe

Impact of alkalinity sources on the life-cycle energy efficiency of mineral carbonation technologies

This study builds a holistic, transparent life cycle assessment model of a variety of aqueous mineral carbonation processes using a hybrid process model and economic input–output life cycle assessment approach (hybrid EIO-LCA). The model allows for the evaluation of the tradeoffs between different reaction enhancement processes while considering the larger lifecycle impacts on energy use and material consumption. A preliminary systematic investigation of the tradeoffs inherent in mineral carbonation processes is conducted to provide guidance for the optimization of the life-cycle energy efficiency of various proposed mineral carbonation processes. The life-cycle assessment of aqueous mineral carbonation suggests that a variety of alkalinity sources and process configurations are capable of net CO2 reductions. The total CO2 storage potential for the alkalinity sources considered in the U.S. ranges from 1.8% to 23.7% of U.S. CO2 emissions, depending on the assumed availability of natural alkalinity sources and efficiency of the mineral carbonation processes.

Measuring and modeling the magnetic settling of superparamagnetic nanoparticle dispersions.

In this paper, we present settling experiments and mathematical modeling to study the magnetic separation of superparamagnetic iron-oxide nanoparticles (SPIONs) from a brine. The experiments were performed using SPIONs suspensions of concentration between 3 and 202g/L dispersed in water and separated from the liquid under the effect of a permanent magnet. A 1D model was developed in the framework of the sedimentation theory with a conservation law for SPIONs and a mass flux function based on the Newtons law for motion in a magnetic field. The model describes both the hindering effect of suspension concentration (n) during settling due to particle collisions and the increase in settling rate due to the attraction of the SPIONs towards the magnet. The flux function was derived from the settling experiments and the numerical model validated against the analytical solution and the experimental data. Suspensions of SPIONs were of 2.8cm initial height, placed on a magnet, and monitored continuously with a digital camera. Applying a magnetic field of 0.5T of polarization, the SPIONs velocity was of approximately 3·10(-5)m/s close to the magnet and decreases of two orders of magnitude across the domain. The process was characterized initially by a classical sedimentation behavior, i.e., an upper interface between the clear water and the suspension slowly moving towards the magnet and a lower interface between the sediment layer and the suspension moving away from the magnet. Subsequently, a rapid separation of nanoparticle occured suggesting a non-classical settling phenomenon induced by magnetic forces which favor particle aggregation and therefore faster settling. The rate of settling decreased with n and an optimal condition for fast separation was found for an initial n of 120g/L. The model agrees well with the measurements in the early stage of the settling, but it fails to describe the upper interface movement during the later stage, probably because of particle aggregation induced by magnetization which is not accounted for in the model.

pH-dependent transport of metal cations in porous media.

We study the effect of pH-dependent adsorption and hydrodynamic dispersion on cation transport through a reactive porous medium with a hydrophilic surface. We investigate how competitive adsorption between a proton and a metal (which in some situations of practical interest may also be a radionuclide) can facilitate the migration of a certain fraction of the latter. We performed laboratory experiments using a chromatographic column filled with silica beads coated with iron oxide and flooded initially with an acidic solution (pH ≈ 3) and then with an alkaline solution (pH > 7) containing either sodium, potassium, lithium, calcium, magnesium, or barium. The composition of each injected solution was chosen to represent one of two possible theoretical predictions, either a retarded shock and a fast pulse, that is, traveling at the interstitial fluid velocity, or only a retarded shock. Highly resolved breakthrough curves measured with inline ion chromatography allowed us to observe in all cases agreement with theoretical predictions, including numerous observations of a fast pulse. The fast pulse is the result of the interaction between pH-dependent adsorption and hydrodynamic dispersion and has previously been observed in systems with strontium. Here, we show the fast pulse arises also in the case of other cations allowing a generalization of the physical mechanism underlying this phenomenon and consideration of it as a new fast transport behavior. A one-dimensional reactive transport model for an incompressible fluid was developed combining surface complexation with mass conservation equations for a solute and the acidity (difference between the total proton and hydroxide concentration). In all cases, the model agrees with the measurements capturing the underlying physics of the overall transport behavior. Our results suggest that the interplay between pH-dependent adsorption and hydrodynamic dispersion can give rise to the rapid migration of metals through reactive porous media with potential effects on, for example, the performance of subsurface engineering infrastructures for pollutant containment, the mobilization of metal contaminants by brine acidified upon contact with CO2 during geologic carbon storage, and the chromatographic separation processes in industrial applications.

Hyperbolic Theory for Flow in Permeable Media with pH-Dependent Adsorption

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Numerical Simulations of the Migration of Fine Particles Through Porous Media

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Sewer-Groundwater Interaction in Urban Coastal Areas

2 system of conservation laws describing reactive transport in a permeable medium with pH-dependent adsorption is developed. The system is strictly hyperbolic and nongenuinely nonlinear because the adsorption isotherms are not convex functions. The solution comprises nine fundamental structures, which are a concatenation of elementary and composed waves. In the limit of low pH, the isotherms reduce to convex two-component Langmuir isotherms considered in chromatography, and the solution comprises only four fundamental structures, as in classical theory. Semianalytical solutions and highly resolved numerical simulations show good agreement in all cases.

Effect of ionic strength on barium transport in porous media

The migration of fine particles (or fines) in an oil formation may cause its damage and decrease the well production rate, as several experimental and modeling studies have shown. The major challenge in the description of fines transport is the prediction of the location where particles are blocked. Classical mathematical models consider the fines as a solute and neglect the mechanism that couples fines transport and the fluid flow, without capturing therefore the single particle motion and blockage. Recent observations carried out using microfluidic systems to observe fines migration have shown limitations on tracing particles and on the analysis of the forces acting, e.g., on a single particle. This could be overcome with simulations using a new numerical approach. In this paper, a numerical model comprising lattice Boltzmann method, immersed boundary method, and discrete element method is presented. The model was developed to study fines migration in porous media at the pore scale. By considering the two-way coupling between the liquid and the solid phase (i.e., the particle), the model is able to capture particle motion in the porous medium and the effect of the particle transport on the fluid flow. Simulation results show that the fines migration is determined by the size of the particles as well as by the structure of the porous medium. Particle blockage alters the preferential flow path and decreases the permeability of the porous medium while increasing the swept area and the oil recovery. Moreover, simulations show that the increase of the pressure drop can displace blocked particles in the porous medium throats and allow restoring the initial permeability.

Assessing Exfiltration from a Sewer by Slug Dosing of a Chemical Tracer (NaCl)

Fecal Indicator Bacteria (FIB) are the primary tools recommended by the U.S. EPA to monitor sewage contamination in waterways. Their concentration along one of the most populated area in the U.S. can exceed the EPA guidelines for water quality after a minor rain event or even in dry weather conditions. Here, we present a study to investigate the role of groundwater infiltration into damaged sewer pipes on combined sewer overflow (CSOs) after a minor rain event or even in dry weather. Groundwater and sewer modelling were combined with a statistical model accounting for weighted risk factors, such as, e.g., pipe material and size, and type of soil, for a coastal city (Hoboken, NJ) located in one of the most populated areas of the U.S. A risk map of groundwater infiltration was then determined. Preliminary simulations of the groundwater accounting for the tide show that the large parts of the sewer network of the city may be submerged always by groundwater. Parts of the network present also high risk of failure, suggesting that they may be affected significantly by infiltration and may require, therefore, renovation or upgrading.

Precipitation in the Mg-carbonate system—effects of temperature and CO2 pressure

Hydraulic fracturing (or fracking) is a well stimulation technique used to extract resources from a low permeability formation. Currently, the most common application of fracking is for the extraction of oil and gas from shale. During the operation, a large volume of brine, rich in hazardous chemicals, is produced. Spills of brine from wells or pits might negatively impact underground water resources and, in particular, one of the major concerns is the migration of radionuclides, such as radium (Ra2+), into the shallow subsurface. However, the transport behaviour of Ra2+ through a reactive porous medium under conditions typical of a brine, i.e., high salinity, is not well understood, yet. Here, a study on the transport behaviour of barium (Ba2+, congener of radium) through a porous medium containing a common mineral such as goethite (FeO(OH)) is presented. Batch and column flood tests were carried out at conditions resembling the produced brine, i.e., large values of ionic strength (I), namely, 1 to 3mol/kg. The measurements were described with the triple layer surface complexation model coupled with the Pitzer activity coefficient method and a reactive transport model, in the case of the transport tests. The experimental results show that the adsorption of Ba2+ onto FeO(OH) increases with pH but decreases with I and it becomes negligible at the brine conditions. Moreover, even if isotherms show adsorption at large I, at the same conditions during transport, Ba2+ travels without retardation through the FeO(OH) porous medium. The triple layer model agrees very well with all batch data but it does not describe well the transport tests in all cases. In particular, the model cannot match the pH measurements at large I values. This suggests that the chemical reactions at the solid-liquid interface do not capture the mechanism of Ba2+ adsorption onto FeO(OH) at large salinity. Finally, this study suggests that barium, and potentially its congeners, namely, radium, calcium, magnesium, and strontium, may travel at the average flow velocity through a soil where the dominant reactive mineral is goethite.

Dissolution kinetics of fosteritic olivine at 90–150 °C including effects of the presence of CO2

Preliminary results were presented for estimating exfiltration from an urban sewer system by a novel method QUEST, which was developed by EAWAG in the European APUSS project. The application of this method to a structurally sound sewer in Rome proved that the method allows the assessment of exfiltration in an expedient and economic way. These results have provided reliable exfiltration rates on the basis of a sewer structural state. However, the QUEST method can not replace the use of common conventional techniques (e.g., CCTV) for finding exact locations of pipe defects. The paper highlighted the importance of preliminary testing (peak shape study, conductivity and flow rate measurements) and sewer system characterisation, in order to reduce the uncertainty in the results obtained from the proposed models.