Valorisation of marble waste

Marble waste will be functionalized with HA through an ion-exchange reaction using Na₂HPO₄. The surface-modified calcite will be used to capture As, Zn, Cd, Cr, and Ni from wastewater, verifying improved removal efficiency compared to pure CaCO₃. This enhancement is especially significant when multiple toxic elements are present simultaneously, as they can interfere with the removal performance of unmodified CaCO₃.

The core-shell particles will be synthesized via sol-gel method, following the functionalization of calcium carbonate with molecules such as 3-aminopropyltriethoxysilane (APTES), to promote chemical interaction between calcium carbonate and the titania hybrid. The bulk architecture, on the other hand, will be obtained via sol-gel by dispersing non-functionalized calcium carbonate particles into alcoholic solutions of titanium precursors (e.g., titanium(IV) butoxide or propoxide), to which organic molecules derived from biomass—such as abietic acid—are added to form the hybrid. This work will be carried out in collaboration with a research group from the University of Naples Federico II, with whom an ongoing scientific partnership on organic–inorganic hybrids based on titanium oxide is in place.

Initially, CaCO₃ will undergo mechanical treatment in ball mills using small amounts of non-toxic organic liquids (Liquid Assisted Grinding, LAG), such as mixtures of H₂O, EtOH, and 2-THF (tetrahydrofuran), with the aim of generating particles in the micrometer range or smaller to increase surface area. Grinding under these operating conditions is intended to modify, where possible, the crystalline structure of the material to make it more reactive. The powders thus prepared will then be reacted—again through mechanochemical activation—with various molecular targets.

In this phase of the process, linkers composed of carboxylic acids functionalized with azide groups at the terminal positions will be anchored to the surface of the carbonate. The carboxylic group enables the organic molecule to bind to the granule, while the azide group allows for subsequent functionalization. The carbon chain, whose length will be defined through appropriate studies (including in silico), will ensure better interaction of the molecular weight with the components to be sequestered and will allow modulation of the hydrophilic/hydrophobic properties of the substrate as needed.

In the second phase of the project, the azide group will be reacted with organic molecules containing a triple bond, which will serve to anchor the part of the particle that directly interacts with the pollutant. The new bond will be formed via a “click chemistry” reaction, which involves the formation of a 1,2,3-triazole ring. The catalytic action of the metal (Cu), necessary for this type of reaction, will be provided by copper spheres placed inside the jars where the actual reaction will occur.

Various organic pendants will be analyzed, with particular attention given to cyclodextrins. Cyclodextrins (CDs) are organic molecules composed of cyclic oligosaccharides formed by 6, 7, or 8 (+)-glucopyranose monomers linked together by α-1,4-glycosidic bonds in a ring structure. Cyclodextrins are excellent chelating agents with a “cage-like” structure that interacts with other chemical components through host–guest reactions.

The organic chemistry team will also use various natural molecules extracted from Ferula and/or derivatives of ferulic acid, which will be functionalized and finally anchored to the CaCO₃ particles. The physicochemical properties of these organic components will be exploited to help reduce inorganic pollutants in water, especially heavy metals when multiple toxic elements are present in competition. Without surface functionalization, the concentrations of certain metals would not be reduced below legal limits.

Laboratory-scale reactors will be developed to test the composite materials based on marble waste (MW) and titania synthesized in activity A.2. These reactors will be carefully designed to address the main challenges that traditionally limit the application of photocatalytic materials:

• The internal parts of the reactors must be sufficiently irradiated, minimizing the shielding effect caused by nanoparticles.
• The reactor design should help reduce mass transfer resistance, which arises from the mismatch between the timescales of light–catalyst interactions (~1 μs) and substrate diffusion within the photocatalyst (~1 μs).

With this in mind, two different reactor configurations will be tested:

• Packed-bed reactor: a reactor in which solid particles occupy fixed positions within a bed. This setup minimizes photocatalyst loss and deactivation, as well as energy costs.
• Suspension reactor: a reactor in which solid particles are suspended in the reaction medium. This configuration enhances mass transfer, specific surface area, and irradiation efficiency.

In both cases, critical parameters affecting pollutant removal—such as particle size distribution, porosity of the solid particles, liquid flow rate, and light intensity—will be optimized. The use of internal optical fibers or central lamps will also be tested to improve irradiation efficiency.

The prototype will need to meet the requirements of simplicity and cost-effectiveness. The concept involves a device designed to pack marble powder in a way that facilitates the interaction between the surface of the granules and contaminated water. Initial tests will be carried out using model solutions, followed by trials with polluted water sourced from small businesses that have established partnerships for this collaboration.

Throughout the project, regular meetings will be held among participants at least every two months to facilitate the exchange of results, discussion of progress, and resolution of any issues that may arise during the experimental development of the planned activities. The results obtained will be published in journals widely read by entrepreneurs as well as in high-impact international scientific journals, and presented at national and international conferences and workshops.

Participants will engage potential stakeholders to gain a deeper understanding of the community context and to ensure effective communication of the results. Target groups include regional institutional authorities, environmental associations, and activist movements. Press releases, magazines, and educational brochures will be made available to the general public and citizens.

Online resources such as a dedicated website, social media platforms, and webinars will be utilized. Communication efforts will also include the organization of a workshop, meetings, and open days.

The results achieved during the project will be exploited for the development of a device capable of removing both toxic elements and persistent organic pollutants (POPs). If feasible, a patent application will be filed. Practical and technological solutions will be proposed to positively impact quality of life and public health.