Separation and recovery of Pd and Fe as nanosized metal sulphides by combining solvent extraction with biological strategies based on the use of sulphate-reducing bacteria

Selective removal and recovery of gallium and germanium from synthetic zinc refinery residues using biosorption and bioprecipitation

The depletion of primary ores, the environmental concerns related to mining activities, and the need to promote circular economy has drawn attention to the recycling of metallic compounds. Bio-based technologies are suitable for metal recovery, as they operate under mild conditions (ambient temperature and pressure) and are ideal for treating low-concentration waters. This study compared the effectiveness of adsorption and precipitation for the removal and recovery of gallium, germanium and zinc. Adsorption of the metallic ions on elemental forms of sulfur (S⁰), selenium (Se⁰) and tellurium (Te⁰), both of chemical and biological sources, was tested. Biosorption onto elemental forms of S⁰_bio, Se⁰_bio and Te⁰_bio effectively removed Ga and Zn. The highest removal efficiency (ղ) was obtained for Ga onto the adsorbent Te⁰_bio (69 ± 0.4%), with an adsorption capacity (q) of 74 mg Ga (g Te⁰_bio)^-1, followed by Zn (ղ = 40 ± 0.7%) with 43 mg Zn (g Te⁰_bio)^-1. Precipitation with chemical and biogenic sulfide at different metal to sulfide (Me/S) ratios was also assessed. Biologically produced sulfide was more efficient for Ga and Zn compared to chemical sulfide. Precipitation with biogenic sulfide was efficient for the removal of Ga (ղ = 59.9 ± 2.6%) and Zn (ղ = 44.2 ± 3.0%). The lowest ratio between metal to sulfide (Me/S = 0.2) achieved higher zinc removal efficiencies, whereas gallium removal was more efficient at Me/S = 1.5. None of the tested methods allowed for recovery of Ge. Biosorption and bioprecipitation gave nevertheless high removal and recovery of Ga and Zn.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

A Review of Recovery of Palladium from the Spent Automobile Catalysts

The spent automobile catalysts (SAC) is the major secondary source of palladium and the production of SAC is increasing rapidly over years. The price of palladium keeps rising over the years, which demonstrates its preciousness and urgent industrial demand. Recovering palladium from the spent automobile catalysts benefits a lot from economic and environmental protection aspects. This review aims to provide some new considerations of recovering palladium from the spent automotive catalysts by summarizing and discussing both hydrometallurgical and pyrometallurgical methods. The processes of pretreatment, leaching/extraction, and separation/recovery of palladium from the spent catalysts are introduced, and related reaction mechanisms and process flows are given, especially detailed for hydrometallurgical methods. Hydrometallurgical methods such as chloride leaching with oxidants possess a high selectivity of palladium and low consumption of energy, and are cost-effective and flexible for different volume feeds compared with pyrometallurgical methods. The recovery ratios of palladium and other platinum-group metals should be the focus of competition since their prices have been rapidly increased over the years, and hence more efficient extractants with high selectivity of palladium even in the complexed leachate should be proposed in the future.

Metal Sulfide Precipitation: Recent Breakthroughs and Future Outlooks

The interest in metal sulfide precipitation has recently increased given its capacity to efficiently recover several metals and metalloids from different aqueous sources, including wastewaters and hydrometallurgical solutions. This article reviews recent studies about metal sulfide precipitation, considering that the most relevant review article on the topic was published in 2010. Thus, our review emphasizes and focuses on the overall process and its main unit operations. This study follows the flow diagram definition, discussing the recent progress in the application of this process on different aqueous matrices to recover/remove diverse metals/metalloids from them, in addition to kinetic reaction and reactor types, different sulfide sources, precipitate behavior, improvements in solid–liquid separation, and future perspectives. The features included in this review are: operational conditions in terms of pH and Eh to perform a selective recovery of different metals contained in an aqueous source, the aggregation/colloidal behavior of precipitates, new materials for controlling sulfide release, and novel solid–liquid separation processes based on membrane filtration. It is therefore relevant that the direct production of nanoparticles (Nps) from this method could potentially become a future research approach with important implications on unit operations, which could possibly expand to several applications.

Extraction and separation of Pd(ii)/Pt(iv) by neutral sulfur-containing extractant from hydrochloric acid medium

Highly efficient extraction and separation of Pd(ii)/Pt(iv) by 2-mercaptobenzimidazole from hydrochloric acid medium.

Biorecovery of cobalt and nickel using biomass-free culture supernatants from Aspergillus niger

In this research, the capabilities of culture supernatants generated by the oxalate-producing fungus Aspergillus niger for the bioprecipitation and biorecovery of cobalt and nickel were investigated, as was the influence of extracellular polymeric substances (EPS) on these processes. The removal of cobalt from solution was >90% for all tested Co concentrations: maximal nickel recovery was >80%. Energy-dispersive X-ray analysis (EDXA) and X-ray diffraction (XRD) confirmed the formation of cobalt and nickel oxalate. In a mixture of cobalt and nickel, cobalt oxalate appeared to predominate precipitation and was dependent on the mixture ratios of the two metals. The presence of EPS together with oxalate in solution decreased the recovery of nickel but did not influence the recovery of cobalt. Concentrations of extracellular protein showed a significant decrease after precipitation while no significant difference was found for extracellular polysaccharide concentrations before and after oxalate precipitation. These results showed that extracellular protein rather than extracellular polysaccharide played a more important role in influencing the biorecovery of metal oxalates from solution. Excitation–emission matrix (EEM) fluorescence spectroscopy showed that aromatic protein-like and hydrophobic acid-like substances from the EPS complexed with cobalt but did not for nickel. The humic acid-like substances from the EPS showed a higher affinity for cobalt than for nickel.