Concentration Of Platinum Group Metals Research Articles

Comparative catalytic performance of PGM-nanoparticle-doped alumina Xerogels and aerogels for potential application in automotive pollution mitigation

The structural (low density, high porosity), thermal (low thermal conductivity, high temperature stability), and chemical (high degree of tailorability) properties of aerogels make them attractive in a range of applications, including catalysis. The automotive industry relies on three-way-catalysts (TWCs) for automotive pollution mitigation, and TWCs in turn depend heavily on the use of platinum group metals (PGMs). Reduction of the use of PGMs in TWCs would be advantageous. To investigate the effect of aerogel structure and processing on three-way catalytic performance we prepared alumina wet gels doped with ca. 15 nm rhodium and palladium nanoparticles and dried them (1) supercritically to form aerogels and (2) under ambient conditions to form xerogels. Nanoparticle concentration was adjusted to ensure that both forms of the catalyst (aerogel and xerogel) had the same volumetric concentration of PGM after calcination to 800°C. Powder x-ray diffraction and transmission electron microscopy (TEM) confirmed the presence of PGMs. TEM images showed PGM particle agglomeration on the order of 40 to 200 nm in both the aerogel and xerogel materials. Gas adsorption analysis indicated that the aerogels have a surface area of 460 m2/g with most pores in the 2- to 100-nm range, whereas the xerogel surface area was 170 m2/g with a narrow pore distribution around 10 nm. Catalytic performance tests under a range of simulated automotive operating conditions show that, in all cases, the aerogels outperformed the xerogels. The aerogel light-off temperatures (the temperature at which a 50 % conversion is achieved) were 45 to 120 °C lower for the conversion of HCs, 25 to 55 °C lower for the conversion of CO and 40 to 145 °C lower for the conversion of NO. This study provides direct evidence that aerogel processing of catalysts provides catalytic performance benefits separate from the underlying chemistry of the catalysts.

Electrochemical Valorization of Glycerol: Catalyst Development and Product Analysis

The growing interest in biofuels as a substitute for traditional fossil fuels has raised environmental concerns about the extensive production of their by-products. Among these by-product, Glycerol, which accounts for over 10% of the total by-products, resulted in the production of nearly 4 billion liters in 2020. (1) Glycerol is a polyol organic molecule, viscous, and water-soluble liquid that if not disposed of properly, it can have detrimental impacts on the environment, including soil and water pollution, ultimately contributing to an increase in the carbon footprint. Hence, addressing this growing concern has prompted a surge of interest in developing sustainable and economically viable techniques for converting glycerol into value-added products.The electrochemical glycerol oxidation reaction (GOR) is a cost-effective and reliable method to enable circular economy practices by selectively producing highly value-added products such as dihydroxyacetone, glyceric acid, and glycolic acid from glycerol. However, it requires the development of active, selective, and stable electrocatalysts to steer GOR at low overpotentials. To date, catalysts based on platinum group metals (PGMs) have outperformed other GOR catalysts in terms of activity. However, in addition to the high cost of fabrication, these catalysts are susceptible to surface poisoning by glycerol intermediates, thereby impeding their commercialization due to the absence of long-term stability. (2) As a result, developing electrocatalysts based on earth-abundant element has become the focal point in GOR catalyst research.Here in, we highlight the latest advancements in the development of low-PGM content GOR catalysts. Our discussion focuses on the strategies for understanding how the type and concentration of PGM can influence selectivity, with a particular emphasis on the significance of GOR overpotentials. We also aim to highlight the inconsistencies in GOR product analyses, specifically regarding the use of H-NMR analysis, with an ultimate goal of advancing accurate GOR product quantification. References Nomanbhay S, Hussein R, Ong MY. Sustainability of biodiesel production in Malaysia by production of bio-oil from crude glycerol using microwave pyrolysis: a review. Green Chemistry Letters and Reviews. 2018;11(2):135-57. Li T, Harrington DA. An Overview of Glycerol Electrooxidation Mechanisms on Pt, Pd and Au. ChemSusChem. 2021;14(6):1472-95.

Novel Concentration Process for Platinum Group Metals in Automotive Exhaust Catalyst Using Electroless Copper Plating, Sulfurization, and Flotation

Platinum group metals (PGMs) are primarily used in automotive exhaust catalysts (autocatalysits). Spent autocatalysts are the most important secondary resource for PGMs. However, transporting autocatalyst scraps and recovering PGMs from the scraps are costly and time-consuming, owing to the low PGM content in spent autocatalysts. Thus, an effective PGM-concentration technology for the pretreatment of scrap prior to transport is required. This study develops a new pretreatment technique that is applied prior to the flotation concentration of PGMs in autocatalysts. This method utilizes electroless Cu plating followed by sulfurization. In the electroless Cu-plating process, which uses glyoxylic acid as a reducing agent, Cu is deposited on the PGM particles in the washcoat of the autocatalyst. During the sulfurization process, S vapor sulfurizes the deposited Cu into copper sulfide, which is hydrophobic. Prior to the experiments, thermodynamic considerations were made to predict the reactivity of Cu and the representative elements constituting the autocatalyst with S vapor, and the sulfurization conditions were designed. Sulfurization experiments were performed at 850 K (577 °C) in the presence of carbon (C), and the results show the successful conversion of only Cu to copper sulfide without sulfurizing the representative oxides (MgO, Al2O3, SiO2, CeO2, and ZrO2) present in the autocatalyst. Finally, in the flotation process, the copper sulfide-coated PGMs are separated from the ceramic components of the autocatalyst, which is hydrophilic; thus, it is concentrated in the froth. Flotation experiments utilizing a microbubble flotation method were successfully performed to recover the PGM concentrates. This innovative pretreatment technique is expected to reduce the cost and time required for the entire PGM recycling process.

High-value utilisation of PGM-containing residual oil: Recovery of inorganic acids, potassium, and PGMs using a zero-waste approach

Residual oil containing platinum group metals (PGMs), which is under-researched, can easily pose resource waste and environmental risks. PGMs feature as scarce strategic metals, and inorganic acids and potassium salts are also considered valuable. An integrated process for the harmless treatment and recovery of useful resources from residual oil is proposed herein. This work developed a zero-waste process based on the study of the main components and characteristics of the PGM-containing residual oil. The process consists of three modules: pre-treatment for phase separation, liquid-phase resource utilisation, and solid-phase resource utilisation. Separating the residual oil into liquid and solid phases allows for the maximum recovery of valuable components. However, concerns about the accurate determination of valued components emerged. Findings revealed that Fe and Ni are highly susceptible to spectral interference in the PGMs test when using the inductively coupled plasma method. After studying 26 PGM emission lines, Ir 212.681 nm, Pd 342.124 nm, Pt 299.797 nm, and Rh 343.489 nm were reliably identified. Finally, formic acid (81.5 g/t), acetic acid (117.2 kg/t), propionic acid (291.9 kg/t), butyric acid (3.6 kg/t), potassium salt (553.3 kg/t), Ir (27.8 g/t), Pd (10960.0 g/t), Pt (193.1 g/t), and Rh (109.8 g/t) were successfully obtained from the PGM-containing residual oil. This study provides a helpful reference for the determination of PGM concentrations and high-value utilisation of PGM-containing residual oil.

Обзор: Извлечение металлов платиновой группы из каталитических конвертеров

Металлы платиновой группы (PGM) широко используются в каталитической промышленности благодаря своим выдающимся физико-химическим свойствам (высокотемпературная стабильность, высокая каталитическая активность). Они используются в медицине, электронике, нефтепереработке, производстве аммиака, топливных элементов, автомобилестроении и т.д. Каталитические отходы являются важным вторичным источником металлов, поскольку переработка отходов является более экономичным и экологичным способом получения металлов по сравнению с добычей из руд. Отработанный автомобильный катализатор является богатым источником металлов платиновой группы [PGM: платина (Pt), палладий (Pd) и родий (Rh)], которые содержат более высокие концентрации PGM, чем в природных рудах. В данной статье представлен критический обзор состояния методов извлечения металлов платиновой группы из утилизированных катализаторов, их преимуществ и недостатков. В результате были проанализированы все методы и выделены наиболее перспективные (наиболее экологичные и экономичные).

Review: Extraction of platinum group metals from catalytic converters

Platinum group metals (PGM) are widely used in catalytic industry due to their outstanding physical and chemical properties (high-temperature stability, high catalyst activity, high heat resistance, high corrosion resistances). They are used in medical fields, electronics, oil refining, production of ammonia, fuel cells, automotive industry. Catalytic wastes are an important secondary source of metals because recycling of wastes is more economical and ecological way of metals obtaining compared to mining from ores. Spent automotive catalyst is a rich source of platinum group metals [PGM: platinum (Pt), palladium (Pd), and rhodium (Rh)] which contains higher concentrations of PGM than found in natural ores. This review presents the analysis of the recovery methods of platinum group metals from spent catalysts and their advantages and disadvantages. As a result, all methods were analyzed and the most promising (most environmentally friendly and economical) was pointed out.

Recovery of Platinum Group Metals from Leach Solutions of Spent Catalytic Converters Using Custom-Made Resins

Platinum group metals (PGMs) play a key role in modern society as they find application in clean technologies and other high-tech equipment. Spent catalytic converters as a secondary resource contain higher PGM concentrations and the recovery of these metals via leaching is continuously being improved but efforts are also directed at the purification of individual metal ions. The study presents the recovery of PGMs, namely, rhodium (Rh), platinum (Pt) and palladium (Pd) as well as base metals, namely, zinc (Zn), nickel (Ni), iron (Fe), manganese (Mn) and chromium (Cr) using leachates from spent diesel and petrol catalytic converters. The largest amount of Pt was leached from the diesel catalytic converter while the petrol gave the highest amount of Pd when leached with aqua regia. Merrifield beads (M) were functionalized with triethylenetetramine (TETA), ethane-1,2-dithiol (SS) and bis((1H-benzimidazol-2-yl)methyl)sulfide (NSN) to form M-TETA, M-SS and M-NSN, respectively, for recovery of PGMs and base metals from the leach solutions. The adsorption and loading capacities of the PGMs and base metals were investigated using column studies at 1 M HCl concentration. The loading capacity was observed in the increasing order of Pd to be 64.93 mmol/g (M-SS), 177.07 mmol/g (M-NSN), and 192.0 mmol/g (M-TETA), respectively, from a petrol catalytic converter. The M-NSN beads also had a much higher loading capacity for Fe (489.55 mmol/g) compared to other base metals. The finding showed that functionalized Merrifield resins were effective for the simultaneous recovery of PGMs and base metals from spent catalytic converters.

Recovery of platinum group metals from spent automotive catalysts: A review

In the last decades, a worldwide investment in the recovery or substitution of platinum group metals (PGMs) has been financed. PGMs have been classified as critical raw materials (CRMs), thus a circular economy model should be implemented for their effective recovery. PGM recovery from primary ores is expensive, due to low concentrations of their ores (lower than 10 g/tn) and sophisticated processes implicated, while secondary resources have been proven technoeconomically feasible sources for PGM recycling. Secondary resources of PGMs, such as spent automotive catalytic converters, contain considerably higher PGM concentrations than their corresponding ores. It is estimated that spent automotive catalytic converters deliver more than 57% of PGMs’ European supply, being considered a crucial resource for PGM recovery. Novel recovery techniques focus not only on high recovery rates, but also on cost efficiency and environmental protection. From an industrial viewpoint, pyrometallurgy is the dominant recovery technique, hydrometallurgy is secondly chosen and biometallurgy (bioleaching, bioabsorption) is applied for lab-scale recovery -at this moment. In the present review, all major PGM recovery techniques are presented and discussed. Hydrometallurgical processes could gain a foothold in industrial scale recycling, by adopting a direct, sustainable leaching design. Milder leaching conditions, greener solvents and high solid mass leached, are the keys for the hydrometallurgical upscaling.

Extraction of trace elements from platinum group metal concentrates in hydrothermal conditions

Concentrates of platinum group metals, despite the high proportion of precious metals, contain significant amounts of impurity non-ferrous elements, the presence of which negatively affects the technology of refining and leads to an increase in the cost of marketable products. In this connection, it is promising to develop approaches for the most complete, deep removal of base elements from concentrates received for processing. In doing so, an extremely important requirement is the complete prevention of the noble metals passing into the solution, since otherwise they “get smeared”, and the process chain is complicated. In the present work, there are data on the features of the composition of concentrates of four platinum group metals, and the possibilities of removing nonprecious metals from them under autoclave conditions are studied. It was found that concentrates, in which platinum metals are represented mainly by platinum and palladium (K1-K3), slightly dissolve in water both at 25 оС in open systems and at elevated temperatures (180 оС). They are characterized by rather high silver contents, and their solubility is due to the presence of a water-soluble form of silver sulfate in them. The transition to the solution of other noble metals (NM) was not detected. In the case of a concentrate enriched with rhodium, iridium and ruthenium (K4), anomalous solubility in water was observed, which was 25.1 and 23.8% at 25 оС and 180 оС, respectively. As this takes place, noble metals at 25 оС significantly passed into solution (34.3%), and under autoclave conditions, the degree of dissolution decreased by 15 times. The use of formic acid was supposed, on the one hand, to ensure the dissolution of metals which are placed below hydrogen in the electrochemical series (iron, nickel and cobalt), and on the other hand, to prevent the dissolution of noble metals. The degree of extraction of noble and impurity non-ferrous metals into the solution from rich concentrates at 120 оС and 180 оС during their treatment with aqueous solutions of formic acid was established. The use of 10% formic acid provides a transition into the solution of iron (90%) and nickel (55%), and is accompanied by a decrease in the mass of the C1 concentrate by about 6%. NM do not pass into the solution in this case. For C2, the mass reduction is 10.1% due to the removal of 94% iron and 82% nickel at a temperature of 180 оС. The total concentration of platinum group metals in the solution does not exceed 2 mg/L. When processing C3, among all the noble metals iridium noticeably passes into the solution (3.5 mg/l), and out of impurity elements 45% nickel and 47.5% iron dissolve with a total weight loss of the concentrate of 8%. As for C4, selectivity of separation of NM and impurity base elements was not achieved; significant amounts of rhodium, ruthenium and iridium were found in the solution.This research was partially carried out under a state assignment of the Institute of Chemistry and Chemical Technology of the Siberian Branch of the RAS (Project: 0287-2021-0014) using the equipment of the Krasnoyarsk Regional Shared Knowledge Centre of the Federal Research Center “Krasnoyarsk Scientific Center of the Siberian Branch of the RAS”. The authors would like to thank Ms Zhizhaeva, a holder of PhD degree in Engineering, for conducting electron microscopy and X-ray studies.

Skin and respiratory exposure to platinum group metals at two South African precious metals refineries.

Platinum Group Metals (PGMs) are mined and refined together and have the potential to elicit adverse respiratory and skin health effects. The aim of this study was to investigate the simultaneous skin and respiratory exposure of precious metals refinery workers to all six soluble PGMs. The simultaneous skin and respiratory exposure to soluble PGMs of forty workers at two precious metals refineries were measured over two consecutive work shifts using Ghostwipes™ and Methods for the Determination of Hazardous Substances method 46/2. Skin exposure was measured on the palm, wrist, neck, and forehead of workers. The highest geometric mean (GM) skin exposure (average of palm, wrist, neck and forehead) was found for soluble Pt (0.008µg/cm2) [95% confidence interval (CI) 0.005-0.013], followed, in order, by Rh, Ir, Pd, Ru, and Os. Significantly higher concentrations of soluble PGMs were found on the palm and wrist compared to the neck and forehead (p < 0.0001). The highest GM respiratory exposure was found for soluble Pd (0.342µg/m3 [95% CI 0.163-0.718]) followed, in order, by Pt, Rh, Ru, Ir, and Os. Skin exposure to all soluble PGMs was positively correlated with respiratory exposure (r = 0.466-0.702). This is the first study to report skin exposure to all six soluble PGMs. Precious metals refinery workers were exposed to quantifiable concentrations of soluble PGMs via both the skin and inhalation. Exposure via both routes occurred together and control measures should be aimed at reducing both skin and respiratory exposure.

Application of SWOT analysis to select pyrometallurgical techniques for copper-nickel sulphide concentrates. Part 1. Selecting pyrometallurgical techniques for copper-nickel sulphide concentrates with the help of SWOT analysis

This paper looks at substantiating the choice of a pyrometallurgical technique for processing of copper-nickel sulphide concentrates with a high concentration of platinum group metals. For this, it is proposed to use a modified SWOT analysis, which was also tested. The paper considers a classical SWOT analysis and its stages and gives examples of its application in different industries. Constraints have been identified for the pyrometallurgical processes recommended for analysis. Internal and external factors have been defined for the recommended pyrometallurgical processes. Each of the factors has been assigned relevance and impact coefficients with regard to an appropriate process. The obtained results have been included in an integrated estimator matrix. The obtained results have been evaluated on the basis of such indicators as overall, internal and external SWOT coefficients expressed as figures. The resultant data served as the basis for recommending the relatively most effective processes that would enable to achieve the project goals. This study can be used to issue recommendations on choosing the most advanced pyrometallurgical techniques for copper-nickel sulphide concentrates that will help reduce the number of processes involved and conduct a further detailed feasibility study. The given indicators may change considerably depending on the factor linked to the production hazards. That’s why a stability calculation was performed additionally for the overall SWOT estimates in relation to this criterion. The change dynamics of the overall coefficients is reflected in the graphs. Depending on the selected level of production hazards some processes may swap on the efficiency scale. The authors offer their recommendations on optimum processes that will enable to achieve the project goals considering the above mentioned factor.

Technological Capabilities of Hydrocarbonyl Processes in the Concentration and Separation of Platinum Group Metals

The principal possibility of processing the industrial poor collective concentrates of platinum group metals (pgms) using a hydrocarbonyl technology with the selective concentration of pgms from poor multicomponent chloride and chloride-sulfate solutions with the subsequent production of pure pgms is shown.

Determination of platinum group metals in dust, water, soil and sediments in the vicinity of a cement manufacturing plant

Global economic growth has led to an increase in cement production to meet the demand of infrastructural development over the past decades. This has resulted in cement factories being the major sources of dust pollution. Dust emanating from the cements plants deposits on buildings, roadways, on road pavements and plants. The purpose of this study was to determine the concentration of platinum group metals (PGMs) emitted with cement dust on a dust suppressed roadway next to a cement factory in Waterberg, South Africa. The concentrations of PGMs were determined using inductively coupled optical emission spectrometry. This region is well known for large reserves and mining of PGMs such as Pt, Rh, Ru and Pd. The highest concentration in the dust samples collected along the roadway was that of Pt followed by Ru, Rh and Pd. The concentrations of Pt, Ru, Rh and Pd in soil samples decreased with the increase of depth. Water concentration of PGMs decreased at each sampling point in the following order; Pt > Ru > Rh > Pd. Sediments samples were also sampled along the Crocodile River for characterisation of physico-chemical parameters. It was of great importance to also analyse PGMs in soils, water and sediments since, dust settles on them. Elevated concentrations of Pt were observed in all samples and the highest concentrations were partitioned to the small particle size fraction of 32 µm. The pH and electric conductivity (EC) of the sediments were measured and the pH values increased while EC values decreased moving along the river. The most common minerals identified in the dust samples were quartz and calcites. Vehicular emissions were also found to be the major contributor to suspended particulate matter and atmospheric deposition of dust dominantly result from emission from the cement plant. The cement plant was the major polluter through atmospheric deposition of dust particles. The result also revealed that the pH of the Crocodile River was slightly alkaline which was influenced by the effluent from the cement plant.

Single-Step Hydrometallurgical Method for the Platinum Group Metals Leaching from Commercial Spent Automotive Catalysts

Platinum group metals (PGMs) are considered critical raw materials, thus their recycling and re-use is of outmost importance. Among the PGMs, platinum (Pt), palladium (Pd) and rhodium (Rh) are the basic metals used in catalytic converters. Concerning the stringent EU standards for emission control imposed to car manufacturers (Euro 6d nowadays), the worldwide demand for PGMs is being increased. As for PGM recovery methods, research is focusing on greener, plain recovery techniques, which utilize milder reagents and offer energy efficiency. In this work, a state-of-the-art hydrometallurgical process is proposed resulting in recovery rates for Pt, Pd and Rh, namely 100%, 92% and around 60%, respectively. A batch of more than 20 commercial spent catalyst samples has been mechanically pre-processed (i.e. sorted, decanned, milled, grinded, homogenized and characterized), in order for a 20 kg sample of homogenized fine pent catalytic powder to be derived. The proposed hydrometallurgical method does not involve any kind of thermal pre-treatment or chemical reduction, thus energy consumption is minimized, while the use of chemicals has been restricted to simple and cheap inorganic solvents (namely HCl, NaCl and H2O2). The aforementioned recovery rates have been validated through X-ray fluorescence spectroscopy analysis (XRF). The equipment used has been successfully calibrated to measure low PGM concentrations (less than 50 ppm for each metal). The kinetics of the hydrometallurgical process have also been studied, in short intervals, and spent catalyst material has been characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy analysis (EDS) and X-ray powder diffraction (XRD).

Real life experimental determination of platinum group metals content in automotive catalytic converters

The real life experimental protocol for the preparation of spent automobile catalyst samples for elemental analysis is thoroughly described in the following study. Collection, sorting and dismantling, homogenization and sample preparation for X-Ray fluorescence spectroscopy and Atomic Adsorption Spectroscopy combined with Inductive coupled plasma mass spectrometry are discussed in detail for both ceramic and metallic spent catalysts. The concentrations of Platinum Group Metals (PGMs) in spent catalytic converters are presented based on typical consignments of recycled converters (more than 45,000 pieces) from the Greek Market. The conclusions clearly denoted commercial metallic catalytic foil contains higher PGMs loading than ceramic honeycombs. On the other hand, the total PGMs loading in spent ceramic catalytic converters has been found higher than the corresponding value for the metallic ones.

Occupational Respiratory Exposure to Platinum Group Metals: A Review and Recommendations.

Platinum group metals (PGMs) is a group of metals that include platinum, palladium, rhodium, ruthenium, iridium, and osmium. Occupational respiratory exposure to platinum has been reported since 1945, but studies investigating occupational exposure to palladium, rhodium, ruthenium, iridium, and osmium are scarce. This review provides a summation of the information available on the respiratory exposure to PGMs in various industrial settings, methods used to assess exposure, and the possible adverse health effects resulting from occupational exposure to PGMs. Of these effects, respiratory sensitization caused by soluble PGMs is of most importance. Metallic PGMs have not been shown to cause allergic reactions. This review reiterates that occupational respiratory exposure to PGMs is dependent on the type of industry where exposure takes place, the chemical form (soluble or insoluble) of the PGMs present in the workplace air, and the tasks performed by workers in the specific work areas. Sensitization to soluble platinum is associated with the degree of exposure to soluble platinum compounds, and the highest concentrations of soluble PGMs in workplace air have been reported for precious metals refineries where personal exposures frequently exceed the occupational exposure limit for soluble platinum (2 μg/m3). Additionally, this review emphasizes that personal exposure monitoring is preferred over area monitoring when assessing workers' exposure to PGMs. The legislation applicable to occupational exposure to PGMs is also discussed, and it is highlighted that the occupational exposure limit for soluble platinum has remained unchanged, in most countries, since 1970 and that too few countries have classified PGM compounds as respiratory or skin sensitizers. Finally, recommendations are made to ensure that future investigations are comparable in terms of the type of exposure monitoring (personal or area) conducted, the type of tasks included in the exposure monitoring program, and the format in which results are reported.

Magnetic Concentration of Platinum Group Metals from Catalyst Scraps Using Iron Deposition Pretreatment

Spent automobile catalysts are the most important secondary source of platinum group metals (PGMs). However, effective recovery of PGMs from catalyst scraps is difficult because they are present in only small quantities as chemically stable substances. In this study, in order to improve the efficiency of the existing recycling processes, the authors experimentally investigated a novel physical concentration pretreatment process for PGMs using samples that simulate an automobile catalyst. In order to magnetically separate PGMs directly from the catalysts, ferromagnetic Fe was deposited on the PGM particles (or the porous catalyst layer) using an electroless plating technique. By using a plating bath containing sodium borohydride and potassium sodium tartrate as the reducing and complexing agents, respectively, Fe was successfully deposited on the sample without requiring complicated pretreatments such as sensitization and activation. After Fe deposition and subsequent pulverization, the PGMs could be extracted and concentrated in the form of magnetic powder using a magnet. The proposed magnetic concentration process was demonstrated to be feasible, and it has the potential to make the recycling of PGMs more efficient and environmentally friendly.

A selective dynamic sorption-filtration process for separation of Pd(II) ions using an aminophosphine oxide polymer

Abstract In order to develop an industrially applicable method for the use of phosphine oxide-based powder material for the capture and concentration of platinum group metals (PGM) from acidic effluents, a two stage process is proposed in this work. The process steps involve coupling the metal sorption on the powder in a continuous stirred tank reactor (CSTR) with a microfiltration PTFE membrane enabling a subsequent stripping of the metals concentrated on the powder material using an acidified solution of thiourea. Using a model solution with 0.6 mM Pd(II) in HCl and common metals as impurities (0.6 mM of Ni(II) and Cu(II) each), the process was conducted for several cycles leading to the final solution containing up to 9.8 mM of Pd(II) with a purity of around 90%. In addition, this process was successfully applied to a leachate of a car catalyst converter, that contained not only palladium, but also platinum, rhodium, as well as large excess of aluminum, cerium and iron. We have thus arrived at a robust process for concentrating effluents containing precious metals, achieving high concentration factors and purities of the final stream, while having low material loss and/or fouling of equipment.

A New Trend of Physical Concentration in Resources Recycling

Physical separation is one of the key technologies in the field of resources recycling for concentrating targeted component(s) and could create an environment friendly recycling process because of their relatively low energy consumption and low cost required. Physical separation process involves two kinds of stages, one is comminution for achieving the liberation of targeted component(s) and the other is real separation of target component(s) from the others. Recently a variety of smart comminution processes, involving mechanical and electrical disintegration as well as the pre-treatment, is developed for aiming selective breakage of phase boundaries of the solid materials to be recycled. The paper indicated several examples of such processes, (1) selective mechanical comminution for effective utilization of aluminum dross, (2) two-stage comminution for recovering minor rare metals from electronic appliances, and (3) concentration of platinum group metals from spent automobile catalyst. The paper also mentioned a sensor based sorting (SBS) process by combining several sensing systems, XRT and XRF, to achieve a horizontal recycling of scrap aluminum.

Surface-Grinding Kinetics for the Concentration of PGMs from Spent Automobile Catalysts by Attritor Surface Grinding

Spent automobile catalyst is an important secondary resource of PGMs (platinum group metals), and the recovery is fairly significant. Various recovery technologies have been reported and applied in practical production, including pyroand hydrometallurgical processes. Because the grade of PGMs in the catalysts is quite low, approximately 0.5mass%, present recycling technologies involve high energy consumption. Enriching PGMs with energy-saving physical separation methods as a pre-treatment is therefore of great significance. Automobile catalyst is usually composed of cordierite phase as a substrate and an alumina/ceria phase, with PGMs, which covers the cordierite phase. In this research, a combined flowsheet, jaw crusher, crushing rolls, and attritor, was used to perform selective grinding and concentrate the alumina/ceria phase into finer size ranges. High-grade alumina/ceria phase was recovered into a 10.3mm size fraction with 57% recovery by using the jaw crusher and crushing rolls for pre-crushing. The coarser size fractions, in which the alumina/ceria phase was still present, was fed to the following surface-grinding step with an attritor to concentrate alumina/ceria phase further. By combining pre-crushing and surface grinding as described above, an alumina/ceria concentrate was produced with a grade of 66%, recovery of 76%, and separation efficiency of 52%. This research used the Ouchiyama model, a well-known surface-grinding model, to evaluate attritor surface grinding for various feed size fractions. Results of kinetic analyses and experiments demonstrated that surface grinding became predominant for larger feed size fractions under the condition of low ball-media content because of collisions between sample particles, but for smaller feed size fractions, surface grinding occurred mainly by collisions of sample particles with the grinding media because of the small size of the sample particles. Surface grinding of the cordierite phase was also observed, especially for coarser feed size particles for which the exposure ratio of the alumina coat layer was lower compared with finer feed particles. [doi:10.2320/matertrans.M2014082]