Implementing a sustainable process for the recovery of palladium from spent catalysts at industrial scale: A LCA approach.

Due to its unique physicochemical properties, palladium is widely used in several industry applications (e.g., vehicle emission control). In view of the circular economy, it is essential to explore secondary sources of palladium, such as urban mines. Current technologies for effective palladium recovery involve high energy consumption and severe environmental impact. More recently, a novel green method for recovering palladium from spent catalysts through a combination of mild acidic leaching and photodeposition on ZnO nanoparticles was proposed on a laboratory scale. In the present study, the environmental impacts of this recovery method, properly upscaled and modelled, was assessed by employing the LCA approach. Specifically, a comparative LCA was carried out for the process with as well as without recycling key components, such as Cu (II) and NaCl for the leaching solution and ZnO. The outcomes identified critical areas and drove the investigation of alternative process configurations to reduce its environmental footprint, such as the use of carbon dioxide in the photodeposition process with the aim of decreasing the resulting terrestrial ecotoxicity. This study marks a significant step forward in advancing research toward industrial-scale implementation of palladium recovery. It provides valuable insights for researchers in the field of green physicochemical processes for metal recovery, thus offering guidance for future decision-making towards more sustainable practices.

Reuse of polymeric waste for the treatment of marine water polluted by diesel.

Accidental diesel spills can occur in marine environments such as harbors, leading to adverse effects on the environmental compartment and humans. This study proposes the surgical mask as an affordable and sustainable adsorbent for the remediation of diesel-contaminated seawater to cope with the polymeric waste generated monthly in hospital facilities. This approach can also be helpful considering a possible future pandemic, alleviating the pressure on the waste management system by avoiding improper mask incineration and landfilling, as instead occurred during the previous COVID-19. Batch adsorption-desorption experiments revealed a complete diesel removal from seawater after 120 min with the intact laceless mask, which showed an adsorption capacity of up to 3.43 g/g. The adsorption curve was better predicted via Weber and Morris's kinetic (R2 = 0.876) and, in general, with Temkin isotherm (R2 = 0.965-0.996) probably due to the occurrence of chemisorption with intraparticle diffusion as one of the rates-determining steps. A hysteresis index of 0.23-0.36 was obtained from the desorption isotherms, suggesting that diesel adsorption onto surgical masks was faster than the desorption mechanism. Also, the effect of pH, ionic strength and temperature on diesel adsorption was examined. The results from the reusability tests indicated that the surgical mask can be regenerated for 5 consecutive cycles while decreasing the adsorption capacity by only approximately 11%.

A novel green approach for silver recovery from chloride leaching solutions through photodeposition on zinc oxide.

Silver is extensively used in electronics, industrial catalysis, and biomedical sector owing to its enhanced physicochemical properties. E-waste recycling may contribute significantly to enhance silver recovery in the view of a circular economy and limit the depletion of mineral sources. In this scenario, hydrometallurgical routes represent the most widely used techniques for silver extraction/recovery and require strong acidic solutions, high temperatures, and multiple operating units. An alternative sustainable route for silver recovery from leaching solutions used for silver extraction in industrial applications is herein proposed for the first time. The novel green process of silver recovery is based on the UV/vis light-driven photocatalytic deposition of pure metallic silver over low-cost and non-toxic ZnO photocatalyst. In the second step, ZnO is dissolved by slight acidification and pure metallic silver is easily recovered. Low environmental impact, mild operating conditions, and economic viability are among the major perks of the new silver recovery process developed. In the view of a full-scale implementation, several operating conditions of the recovery process (i.e., photocatalyst load, starting silver concentration, type of hole scavenger and irradiation) were thoroughly investigated. A mathematical model capable of describing the system behaviour under different operating conditions was also developed and allowed to estimate unknown kinetic parameters for the Ag-photodeposition process.

Humic substance/metal-oxide multifunctional nanoparticles as advanced antibacterial-antimycotic agents and photocatalysts for the degradation of PLA microplastics under UVA/solar radiation.

As a result of the accumulation of plastic in the environment, microplastics have become part of the food chain, boosting the resistance of fungi and bacteria which can frequently encounter human beings. Employing photocatalytic degradation is a possible route towards the removal of chemical and biological pollutants, such as plastics and microplastic wastes as well as microorganisms. Using biowaste materials to design hybrid nanoparticles with enhanced photocatalytic and antimicrobial features would uphold the principles of the circular bioeconomy. Here, two unexpensive semiconductors-namely titanium dioxide (TiO2) and zinc oxide (ZnO) - were synthetized through solvothermal synthesis and combined with humic substances deriving from agrifood biomass. The preparation led to hybrid nanoparticles exhibiting enhanced ROS-generating properties for simultaneous applications as antimicrobial agents against different bacterial and fungal strains and as photoactive catalysts to degrade polylactic acid (PLA) microplastics under UVA and solar irradiation. In comparison to bare nanoparticles, hybrid nanoparticles demonstrated higher antibacterial and antimycotic capabilities toward various pathogenic microorganisms as well as advanced photocatalytic activity in the degradation of PLA with a carbonyl index reduction in the range of 15-23%, thus confirming a noteworthy ability in microplastics photodegradation under UVA and solar irradiation.

Zero-valent palladium dissolution using NaCl/CuCl2 solutions.

Pd, Rh, Pt are employed in a wide range of applications, such as catalytic converters, fuel cells and electronic devices. In the last years, an increasing pressure on their market was recorded due to a growing demand and limited resources. Therefore, the recovery of these materials from wastes represents an interesting goal to be achieved. The most widely proposed techniques for recovering the palladium from wastes are leaching and ion exchange. Strong oxidizers, acids and high temperature (343-363 K) are used for leaching, leading problems for the environment and the safety. In this work the attention was focused on a system containing zero-valent palladium nanoparticles in which the leaching is performed in mild acidic conditions, by using chloride solutions containing cupric ions (NaCl/CuCl2). The process was studied at varying temperature, pH, chloride and cupric ion concentrations. Good results were obtained at pH 5.0 and temperatures between 288 K and 333 K. The process is more acceptable than the traditional ones from a safety point of view being characterized by less severe conditions (pH and temperatures). A shrinking spherical particles model was adopted to analyse the experimental data from which a development under a kinetic control was demonstrated.