Anthropogenic CO2 emissions can be mitigated through the implementation of Carbon Capture Utilization and Storage (CCUS) technologies where CO2 is either
injected underground, e.g., in saline aquifers or is reacted above ground with oxide-bearing minerals to form stable and environmental benign minerals.
The latter occurs through the mineral carbonation reaction, which resembles the weathering of natural materials such as silicates, basalts, and other
ultramafic rocks as well as industrial alkaline waste such as
fly-ash, brines, and mine tailings. Mineral carbonation guaranties the definite sequestration of CO2 from the atmosphere, however many aspects
of the reaction are still unknown.
In my research, I study the fundamental mechanism and the kinetics of mineral carbonation reactions and, in particular, I study the dissolution of silicates,
the precipitation of carbonates, and the carbonation of fly-ash.
I have investigated the dissolution of olivine and the precipitation of Mg-carbonates through high-pressure and high temperature experiments and described
these processes with population balance equation (PBE) coupled with geochemistry. I have studied the effect of thermodynamic parameters such as temperature, pressure and solution
composition on the mechanism and kinetics of the dissolution of olivine and the precipitation of Mg-carbonate with the final aim to select the optimal operating conditions and
the chemical components for a fast mineral carbonation process where dissolution and precipitation can be combined in a single step.
I showed that the addition of organic acids such as oxalic and citric acids increases the dissolution rates at high pH where precipitation is favorable.
This allows a single step mineral carbonation process that avoids costly pH swings.
The derivation of analytical solutions to reactive transport models is important to understand the mathematical structure of the solutions, to develop an intuition for the solutions,
and to benchmark numerical solutions of complex reactive transport problems. I am working on the development of mathematical and numerical models based on the theory of hyperbolic conservation laws coupled with surface complexation
and I am performing experiments in the laboratory to verify the hypothesis. Currently, I am focused on the analysis of the non-classical reactive transport of solutes through a porous media, a newly discovered phenomenon arising
conditionswhen a dispersion induced pH change dramatically increases the solute mobility. This leads to the formation of a strongly retarded solute front predicted by the theory and the formation of a fast pulse without retardation.
This pulse is a notable exception to the classical theory, which neglects dispersion. I have derived the analytical and numerical solutions for the case of strontium
travelling through an iron-oxide porous media and I have experimentally verified the conditions leading to the non-classical transport behaviour. This newly recognized phenomenon complements other
well-known fast transport pathways such as colloid-facilitated transport and flow in fractures, and raises important questions regarding the prediction of the migration of solutes in the
subsurface and in chromatographic separation processes. It also presents a theortically interesting example of a model where the vanishing diffusion solution does not approach the diffusion free (hyperbolic) limit uniformly in all cases.
Density functional theory
The understanding of chemical reactions at the solid-liquid interface at the atomistic level is fundamental for the description of processes such as adsorption,
dissolution, and precipitation. In my work, I use density functional theory (DFT)-based calculations to study the mechanism of the reaction of forsterite (Mg2SiO4) with H2O
and CO2 under the conditions suitable for CO2 storage underground and above ground.
The kinetics of the reaction, which resembles natural weathering, is controlled by the hydration and the dissolution of Mg2SiO4 and may be catalyzed by organic and inorganic molecules.
The interaction of these molecules with the Mg2SiO4 surface depends on the atomic and electronic structure of the interface, the bulk structure and
composition, and the impact of thermodynamic conditions such as temperature and pressure.
Therefore, the selection or the design of the best catalyzing compound requires a deep understanding of this interaction.
Ab initio methods using electronic structure calculations based on DFT are powerful computational tools to investigate chemical reaction mechanisms at the interface, i.e.,
to identify the type of adsorption mechanism at the reactive site and the subsequent change of its electronic structure.
Moreover, the effect of temperature, pressure, and entropic effects can be taken into account through ab initio thermodynamics calculations
verified with experimentation.
Sewer systems may experience major deterioration of infrastructure due to inadequate and insufficient maintenance and rehabilitation. Structural defects
such as cracks, fractures, joint displacements, deformations, and collapses as well as operational damages such as roots, siltation, and blockage, may allow sewage to exit (exfiltration)
or groundwater to enter (infiltration). Exfiltration can contaminate the adjacent groundwater while infiltration can increase the frequencies of overflows contaminating the surface water as well
as wastewater dilution, which causes management problems at wastewater treatment plants. My research on urban hydrology is focused on the quantification of the interaction between urban water
systems and sewer networks and the location of the most deteriorated reaches which need rehabilitation or even substitution. I have carried out field experiments to quantify exfiltration and
infiltration using both artificial and natural tracers. Each campaign was designed to minimize the uncertainty of the measured exfiltrated and infiltrated flow. Experimental design was performed
coupling uncertainty analysis, error propagation, and Monte Carlo simulation with numerical model of sewer networks. The best combination of experimental variables was derived and used
to define an experimental protocol to apply in the field, e.g., the location of sensors throught the sewer network, the period of the day/week when to perform the measurements, and the duration of each experiment.
Exfiltration were measuered using artificial tracers (NaCl, LiCl, and NaBr) injected into the wastewater flow and measured through online conductivity measurements or offline ion chromatography
(IC). Infiltration were determined using natural tracers such as total suspended solids (TSS) and chemical oxygen demand (COD) measured at the network scale with online monitoring UV-VIS probe;
and 18O and 3H at the catchment scale using offline mass spectrometer. I calculated about 20% of exfiltration and 45% of infiltration of the dry weather flow (DWF) in two urban sewer in Rome (Italy).