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Platinum group metals (PGMs) are strategic metals. Auto-exhaust catalysts are their main application fields. The recovery of PGMs from spent auto-exhaust catalysts has remarkable economic value and strategic significance. Aiming at the problems of ferrosilicon generation for Fe capturing and subsequent oxygen blowing to remove iron with high energy consumption and heat release, a technology of Fe–Sn synergistic capturing PGMs was proposed. Taking full the advantage of the lower melting point of Fe–Sn alloy (<1200 °C) and its unique affinity for PGMs, the PGMs were captured at approximate 1400 °C with Fe–Sn as the collector. In experiment, 500 g of spent auto-exhaust catalysts were employed to minimize error and approximate industrial production. The mechanism of Fe–Sn synergistic capturing PGMs was elucidated. The generation of Fe–Sn-PGMs alloy lowered the activity of [PGMs] in the system, accelerated the reduction of the PGMs oxides and promoted the alloying of [PGMs]. Therefore, Fe–Sn synergistic capturing PGMs was realized. The inability of Si to enter the alloy phase was confirmed by theoretical calculations, avoiding the generation of ferrosilicon. The effects of basicity, CaF 2 , m (Fe)/ m (Sn) and the amount of collector on capturing PGMs were optimized. Under the optimized conditions (basicity R = 1.1, spent auto-exhaust catalysts 70 wt%, CaO 30 wt%, B 2 O 3 10 wt%, CaF 2 7 wt%, m (Fe)/ m (Sn) = 1/1 and the collector 15 wt%), the content of PGMs in the slag phase was 2.46 g/t. It is feasible to remove Fe and Sn by oxidation to achieve the purpose of PGMs enrichment. This technology offers guidance on the safe, environmentally sound, and efficient disposal of spent auto-exhaust catalysts, promoting the sustainable development of PGMs. [Display omitted] [ABSTRACT FROM AUTHOR]

• Simple evaluation for platinum group metals (PGMs) recovery from primary and secondary sources was made. • Various separation technologies for PGMs recycling from secondary resources are reviewed. • Advantages, challenges and outlook of recycling technologies are discussed. • Considerations on further promotion have been proposed. In the past decades, the demand for platinum group metals (PGMs) has increased rapidly in various applications such as electronics, chemical engineering, biomedical devices, and automotive catalytic converters. Recovery of PGMs from secondary resources is necessary for addressing the supply issues. The migration of PGMs from solid to liquid streams is irreplaceable for achieving high-purity products. Hence, it is a meaningful issue to reduce resource depletion and avoid environmental pollution during separation processes. This paper systematically reviews various improvements and new technologies for the separation and purification of PGMs, including solvent extraction, membranes separation, supercritical fluids, solid-phase extraction, photoreduction, and electrochemical methods. The separation mechanism and optimized process parameters are summarized. Particularly, the advantages, challenges, and perspective are highlighted in terms of commercial applications. This study aims to present the current research for scholars, and to identify a promising PGMs separation method that is safe and effective. Finally, several recommendations have been proposed for the further promotion of separation technologies. [ABSTRACT FROM AUTHOR]

• Highly porous ceramics were fabricated by particle-stabilized foams method. • Slags from smelting of spent automotive catalysts have been utilized. • Sintering temperature and dosage of slag determined the properties of porous ceramics. • The obtained porous ceramics show excellent physical properties. Spent automotive catalysts are the most crucial secondary resources of platinum group metals (PGMs). Currently, the iron-capturing method is one of the most promising technologies for PGMs recycling. The residual smelting slags contain large amounts of CaO, Al 2 O 3 , MgO, SiO 2 , Na 2 O, and the trace of heavy metals (e.g. Cr, Pb, Ni), which are classified as solid waste or even hazardous waste, which are typically treated by landfills, and poses severe threats to the environment. In this paper, based on the specific chemical composition of smelting slags, ceramic foams with high porosity, low density and good thermal insulation were fabricated by particle-stabilized foams method, where long-chain surfactant hexadecyltrimethylammonium chloride served as the hydrophobic modifier of slag particles and colloidal silica as binding agent. Herein, the influence of sintering temperature and the amount of smelting slag on the physical properties of obtained porous ceramics were systematically investigated. The results showed that porous ceramics with a bulk density of 0.40–0.64 g/cm3, open porosity of 74.7–83.4%, thermal conductivity of 0.10–0.21 W/(m∙K) and compressive strength of 1.04–4.01 MPa can be obtained with the mass ratio of slag: colloidal silica of 2:1, 3:1 and 4:1 sintered at 1000°C for 2 h. The porous ceramics with these unique properties are promising to be applied as thermal insulation materials. This convenient, facile and versatile approach is also expected to fabricate porous ceramics by using other solid waste as raw materials. [ABSTRACT FROM AUTHOR]

The secondary production of platinum group metals (PGMs) occupies a 30% proportion of the global supply. The iron-capturing recycling technology produces Fe-PGMs alloy, of which PGMs need further enrichment for purification. We applied electrolytic refining method on Fe-PGMs alloy for separating PGMs from iron. Fe-PGMs alloy and titanium plates are used as anode and cathode. The main electrolyte is ferrous sulfate. During electrolysis, iron is electrolytically migrated to the cathode and electrodeposited, while PGMs settle to form anode slime. An appropriate parameters range for electrolysis is potential (0.5–0.8 V), concentration of Fe2+ (1.0–1.5 mol/L), temperature (60–80 °C), pH (3.0–3.5). The impurities like carbon and phosphorous can promote the dissolution of iron in the early electrolysis by expanding the coverage of reaction intermediates adsorbed on the anode surface but will hinder the dissolution and enrichment if forming a film layer. After electrolysis at 0.7 V constant voltage, PGMs were separated from the iron matrix and enriched in the anode slime (85–90%) and residual anode (10–15%). The recovery efficiency reached nearly 100%. Pure iron was prepared on the cathode and the electrolytic liquid can be reused. This electrolytic enrichment process has lower energy consumption, less wastewater, and higher recovery efficiency. • Specific properties of Fe-PGMs alloys were detected. • Appropriate process parameters for electrolysis were determined. • The recovery efficiency of PGMs was nearly 100% by electrorefining. • Enrichment concentration of PGMs was increased by 10 times. • Electrolytic refining consumes lower energy with less wastewater. [ABSTRACT FROM AUTHOR]

• Iron was used as collector for PGMs recovery. • Recovery efficiency of PGMs was 99.25 % by iron melting collection. • The formation of ferrosilicon was avoided at 1300–1400 °C. • The effect of slag have been studied in detail. • The recovery efficiency was over 99 % at 50 kg scale experiments. Automobile catalysts sector is the largest consumption field of platinum group metals (PGMs) worldwide, and they are the most important secondary resources of Pt, Pd, and Rh once they reach the end of life. However, recycling PGMs from spent automotive catalysts is of great difficulty due to their complex physicochemical characteristics and low concentrations. A highly efficient technology for recovery of Pt, Pd, and Rh by iron melting collection was proposed. Owing to the same face-centred cubic structure and close atomic radius, iron powder is used as collector since Fe and PGMs can form continuous solid solution. PGMs are concentrated and formed Fe-PGMs alloy phase at a relatively low temperature of 1300–1400 °C through adjustment of slag compositions. The principles of slag design were put forward, and the effects of basicity, slag compositions and collector dosage on the recovery efficiency of PGMs were studied. Factsage 7.0 software (CRCT-Thermfact and GTT-Technologies) was used to calculate slag viscosity and simulate slag reaction equilibrium during the melting process. The recovery efficiency of PGMs was 99.25 % under the optimized conditions: mass ratio of CaO/Na 2 O=35:20, CaF 2 5 wt.%, Na 2 B 4 O 7 8.5 wt.%, collector Fe 15 wt.%, and 5 wt.% C, where the concentration of Pt, Pd and Rh in slag phase were 2.398, 3.879, and 0.976 g/t, respectively. Meanwhile, the formation of ferrosilicon (FeSi 2 , FeSi) was avoided. 50 kg pilot-scale experiments also achieved over 99 % recovery efficiency of PGMs. [ABSTRACT FROM AUTHOR]