Zeolite-Clinoptilolite conditioning for improved heavy metals ions removal: a preliminary assessment

The emerging problem of nickel allergy is increasingly widespread due to the increase in nickel content in everyday foods. The physicochemical structure of the zeolites makes it possible to adsorb nickel ions in solution. The properties of molecular sieves, together with those of a size and a chemical composition compatible with the human gastrointestinal tract, are present in a particular zeolite called clinoptilolite. In this work, a type of natural clinoptilolite was characterized before and after being subjected to two different conditioning processes with NaCl to increase its adsorption efficiency and specificity against nickel. The three forms of clinoptilolite, natural, conditioned, and biconditioned, were compared based on analysis of absolute density, X-ray diffraction pattern, granulometry, porosity, chemical composition, and grain morphology. Finally, nickel ion removal tests were performed in an aqueous solution that simulates the conditions of the gastrointestinal tract. The Ni2+ removal efficiency of natural clinoptilolite is 73.2%, while after conditioning it reaches 96.6%. Double conditioning with Na does not generate a considerable increase in removal efficiency which remains at 96.8

Mechanical and physical characteristics of alkali- activated mortars incorporated with recycled polyvinyl chloride and rubber aggregates

One of the ways to achieving net-zero concept in the construction industry is to use alternatives to Portland cement (OPC) and virgin aggregates for concrete manufacturing. Recycled rubber and polyvinyl chloride (PVC) aggregates in conjunction with low-carbon binders can be potentially utilised to substitute natural sand and reduce the negative environmental impacts of OPC. A replacement of natural sand (up to 70% by volume) in alkali-activated materials (AAMs) with recycled rubber and PVC particles derived from tyre waste and insulation coating of electric wires, respectively, was investigated in this study. The performance of developed AAMs was evaluated using a comprehensive testing program including mechanical, physical and microstructure assessments. AAM composites with PVC and rubber particles outperformed natural aggregate composites in terms of thermal resistivity, water absorption, volume permeability voids (VPV), and high-frequency sound insulation. Results showed that 70% PVC mixture achieved the lowest water absorption rate and thermal conductivity with a reduction of 73% and 20%, respectively, compared to the control mixture. A maximum reduction of 34% in VPV was observed in the 70% rubber mixture when compared to the control mixture. In terms of mechanical properties of waste stream aggregates, PVC outperformed rubber. The results showed that 30% replacement of PVC and rubber would produce composites with 7-day compressive strengths of 35 MPa and 25 MPa, respectively, which can be used to produce high-load bearing structures. The Energy-dispersive X-ray Spectroscopy (EDX) was performed to detect chloride leaching from PVC aggregates, where results indicated that no leaching had occurred after more than 90 days of casting. Regarding the carbon emission, the carbon footprint of AAM composites is decreased by using the polymeric fractions in place of sand. The developed composites of this study can be used safely in non-load bearing structural elements with promising physical and mechanical performance

Alkali activated materials with recycled unplasticised polyvinyl chloride aggregates for sand replacement

Incorporating recycled Unplasticised Polyvinyl Chloride (UPVC) aggregates into Alkali Activated Materials (AAMs) presents a promising approach to alleviate the environmental drawbacks associated with conventional recycling methods for UPVC. The distinctive characteristics of UPVC aggregates, as compared to natural sand, pose a challenge in the pursuit of enhancing the mechanical properties of composites. This research aims to achieve net-zero goals and promote circular economy principles by replacing traditional Portland cement (OPC) with low-carbon AAMs and natural aggregates with recycled unplasticised polyvinyl chloride (UPVC) which, accounts for 12% of global plastic production. Coarse and fine UPVC aggregates, measuring 4–6 mm and 0–2 mm, respectively, were incorporated into AAMs. An extensive array of tests was performed to assess their environmental benefits and overall performance enhancements. The results unveiled notable advantages in terms of thermal resistivity and resistance to chloride penetration in the UPVC-infused AAMs. Notably, mixtures containing 100% fine UPVC aggregates exhibited a remarkable 70% reduction in thermal conductivity (0.465 W/mk) when compared to the control. In mechanical assessments, composites containing fine UPVC aggregates surpassed those with coarse UPVC aggregates, showcasing promise for load-bearing applications. Substituting 30% of both fine and coarse UPVC aggregates with sand yielded impressive 7-day compressive strengths of 41 MPa and 35 MPa, respectively. Moreover, the utilisation of energy-dispersive X-ray spectroscopy confirmed the absence of chloride leaching after three months. The incorporation of UPVC waste aggregates led to a significant reduction in the carbon footprint of the tested AAMs. In conclusion, these composites offer an appealing and sustainable solution for both load-bearing and non-load-bearing structures

Life Cycle Assessment (LCA) of 3D Concrete Printing and Casting Processes for Cementitious Materials Incorporating Ground Waste Tire Rubber

Ordinary concrete is an indispensable construction material of modern society which is used for everything from mundane road pavements to building structures. However, it is often used for non-load-bearing applications (for instance, insulating lightweight building units) where mechanical strength is not a priority. This leads to an avoidable depletion of natural aggregates which could instead be replaced by alternative waste materials capable of conferring to the material the desired performance while ensuring a “green” route for their disposal. Furthermore, the automation of production processes via 3D printing can further assist in the achievement of a more advanced and sustainable scenario in the construction sector. In this work, performance and environmental analyses were conducted on a 3D-printable cementitious mix engineered with ground waste tire rubber aggregates. The research proposed a comparative study between rubberized concrete mixes obtained by 3D printing and traditional mold-casting methods to achieve a comprehensive analysis in terms of the mix design and manufacturing process. To evaluate the environmental performance (global warming potential and cumulative energy demand) of the investigated samples, Life Cycle Assessment models were built by using the SimaPro software and the Ecoinvent database. The Empathetic Added Sustainability Index, which includes mechanical strength, durability, thermo-acoustic insulation, and environmental indicators, was defined to quantify the overall performance of the samples in relation to their engineering properties and eco-footprint

Thermoplastic Composite Materials Approach for More Circular Components: From Monomer to In Situ Polymerization, a Review

To move toward eco-sustainable and circular composites, one of the most effective solutions is to create thermoplastic composites. The strong commitment of world organizations in the field of safeguarding the planet has directed the research of these materials toward production processes with a lower environmental impact and a strong propensity to recycle the polymeric part. Under its chemical properties, Nylon 6 is the polymer that best satisfies this specific trade-off. The most common production processes that use a thermosetting matrix are described. Subsequently, the work aimed at investigating the use of thermoplastics in the same processes to obtain comparable performances with the materials that are currently used. Particular attention was given to the in situ anionic polymerization process of Nylon 6, starting from the ε-caprolactam monomer. The dependencies of the process parameters, such as temperature, time, pressure, humidity, and concentration of initiators and activators, were therefore investigated with reference to the vacuum infusion technique, currently optimized only to produce thermosetting matrix composites, but promising for the realization of thermoplastic matrix composite; this is the reason why we chose to focus our attention on the vacuum infusion. Finally, three production processes of the polymeric matrix and glass fiber composites were compared in terms of carbon footprint and cumulative energy demand (CED) through life-cycle assessment (LCA)

Nickel intolerance disease: surface modification of a zeolite for direct human assumption and cultivation eco-sustainable strategy

The presence of nickel in environments dedicated to the cultivation of nickel-fixing fruit and vegetables determines non-negligible concentrations of this element in food. Furthermore, its widespread use in the metal and electronics industry makes human exposure to nickel practically inevitable. The toxicity of this metal is widely demonstrated, and in thousands of clinical cases and targeted tests, it has been possible to find a sensitivity to nickel by more than 5% of the population. This project proposes two solutions to the problem in which the use of zeolites is foreseen. The first consists of the intake of alimentary zeolite as a detoxifier from heavy metals, and the second is based on a nickel-free diet, possible thanks to the products of aeroponic agriculture. The properties of molecular sieve, together with those of a size and a chemical-physical composition compatible with the gastrointestinal tract, are present in a particular form of zeolite called clinoptilolite. The use of this substance, suitably modified to increase its ion-selectivity, as a food supplement prevents, through adsorption and ion exchange, the accumulation of toxins, free radicals, and heavy metals, including nickel. A definitive solution to the problem of nickel sensitivity lies in the upstream elimination of this metal from the fruit and vegetable production process thanks to the use of aeroponic cultivation systems. This system consists of the growth of plants in ideally isolated environments in which the water used can be treated with zeolite to remove nickel. These conditions allow for more controlled, efficient, and nutritionally safe growth of foods with a saving of water (90-95% less), nutrients and soil (80-90% less) compared to classic agriculture. In both cases, the adsorption efficiency of the zeolites strictly depends on the degree of crystallinity. According to the most recent studies, high purity clinoptilolite is synthesized through the sol-gel method, with structure directing agent (SDA), combined with the hydrothermal method where silica dioxide is the source of silicon and aluminium hydroxide is that of aluminium. The possibility of synthesizing clinoptilolite with a high degree of crystallinity and with specific adsorption functions within the gastrointestinal environment and in aeroponic cultivation plants would make an effective contribution to the goals of 2030 Agenda in terms of nutrition improvement, water saving, sustainable models of production and mitigation of climate change

Performing composite materials: thermoplastic matrix for more circular components, from monomer to in situ polimeryzation

To move towards eco-sustainable and circular materials, one of the most effective solutions is to create thermoplastic composites. The strong commitment of world organizations in the field of safeguarding the planet has directed the research of these materials towards production processes with a lower environmental impact and strong propensity to recycle the polymeric part. The will to produce a composite with a thermoplastic matrix lies in its intrinsic value nature, which is the òpposite of thermosetting one, that is the possibility of recycling the material: the thermosetting polymer, such as epoxy resin, certainly guarantees the best mechanical characteristics, but once that the material has finished its function, it cannot be reworked and reused for other pùrposes. Up to now, indeed, incineration and landfilling are the main approaches for disposing of composite wastes. These routes, however, are not viable tools in view of the strong expected growth in waste production because they completely discard the related environmental impact, the waste accumulation of composites and they especially imply the loss of all the high-added value. On the other hand, the thermoplastic polymer can undergo a softening process which allows to obtain again a melt capable of being subjected to a new type of processing with a new purpose. What is being studied in recent times is the search for the application and implementation of impregnation processes used for thermosetting matrix composites towards thermoplastic matrix ones. The attempted infusion methods involved the use of an already polymerized thermoplastic matrix which was brought back to the molten state by applying heat, subsequently proceeding with the impregnation of the fiber fabrics. The problem encountered, however, lies in the difficulty of the actual impregnation due to the high viscosities of the thermoplastic polymers in the molten state. Under its chemical properties, Nylon 6 is the polymer that best satisfies this specific trade-off above all thanks to its precursor, Ɛ-caprolactam, a molecule that melts at about 70 °C which allows to obtain a liquid phase characterized by similar water viscosity. With this low viscosity it is possible to obtain a potentially optimal impregnation of the fibers, with subsequent reaction activated by the increase in temperature. The solution, therefore, lies in in-situ polymerization precisely because it no longer allows starting from a polymer, in which macromolecules are already formed, which results in high viscosity and process temperatures from 170 °C up to 200 °C, but from monomers which therefore allow a process not too far from those already known for thermosetting. However, it will be necessary to move towards an optimization of the process parameters and, consequently, of the impregnation phase, guaranteeing a greater homogeneity of dispersion of the reactive mixture and a better adhesion between fiber and matrix, aiming at the study of sizing compatible with thermoplastics matrices. These resolutions will lead to the real goal, which is the production of performing composite materials with a thermoplastic matrix, with increasing volumetric quantities of reinforcement, up to values equal to 40%, allowing a true comparison, in terms of both the quantity of filling and mechanical properties, with composite materials with a thermosetting matrix. It is a fact that, when taking into account factors such as climate change, global warming, environmental sustainability and circular economy, the landfill or incineration of composites wastes must be avoided. The future research studies must be focused on the following points: the production process and the chemistry of the matrices to obtain a performing thermoplastic matrix composite, with mechanical–functional characteristics suitable for completely replacing thermosetting agents; the use, recovery, and disposal of thermosetting and thermoplastic composites which re-enter the circulation to obtain manufactured articles; evaluation of the potential to close the life cycle loop of composites and reducing energy consumption and recycling cost. Thanks to the intelligent reaction and research of different groups around the world, the future looks bright for new possibilities

Valorization of a secondary stream of recycled carbon fibres in concrete application: compatibility, performance, and compounding optimization

Downcycling synthetic fibre waste for reinforced concrete in the construction sector can provide mutual benefits for both industries due to not only alleviating the strain on the environment and socio-economic impact but also enhancing the properties of the cementitious material. Incorporating carbon fibres to develop fibre-reinforced concrete (FRC) is an attractive route in enhancing some engineering performance for better applicability of the material, including mechanical strength, post-cracking behaviour, shrinkage mitigation, and thermal resistance. In the framework of eco-sustainable design of construction materials, this work dealt with the viability of engineering cementitious mixtures with scrap carbon fibres (sCF) deriving from an industrial thermal recycling processing of waste carbon-fibre composites. Due to the agglomerate-like structure of the recycled fraction, the main criticality that emerged in the manufacturing stage was to ensure adequate dispersion of the reinforcement in the matrix. Therefore, in this work, a de-agglomeration treatment of the fibres by nanoclay slurry was developed. Nanoclay-based functionalization aimed to ensure a more homogeneous distribution of the reinforcement while providing pozzolanic activity for concrete improving its microstructural characteristics. In the present research, different contents of sCF were implemented (from 0.25 w/w% to 1 w/w%) with respect to the amount of cement binder, studying FRC mix designs with and without nanoceramic treatment. The influence of the reinforcing fibres as well as the compatibilizing effect of nanoclay were investigated by a multi-methodological experimental analysis including, rheological tests, mechanical characterization, and microstructural assessment. The graphical abstract in Figure 1 illustrates the main phases of the research activity proposed in this study