Magnesium Recycling Research Articles

Grain refinement of magnesium castings using recycled machining chips

A simple and effective recycling approach of magnesium alloys can offer economic and environmental benefits. This study demonstrates that by simply remelting AZ91/AZ80 machining chips and shape casting, the tensile properties of the castings can be preserved and substantial grain refinement can be achieved, compared to casting from ingots using the same alloy. Cooling curves for the samples, obtained through the immersion thermocouple method, showed that nucleation event density in chip melts consistently exceeds that in ingot melts, particularly at low undercoolings. Tensile tests showed that chip castings exhibit a slightly higher 0.2% proof stress than castings from ingots, with increases of 5% and 1% for as-cast and solution-treated conditions, respectively, due to the Hall-Petch effect. Elongation to fracture was similar for both chip and ingot samples, with fractography indicating entrainment defects, rather than grain size, predominantly determined this outcome. These combined results indicate that the shape casting of AZ91/AZ80 machining chips could be used as part of the closed-loop recycling of magnesium.

Solid-state recycling of magnesium and its alloys via plastic deformation: An overview of processing and properties

The increasing demand for primary magnesium production poses significant environmental challenges, aggravated by the limited availability of raw materials, which can hinder supply. Consequently, the recycling of magnesium chips and waste is gaining importance. While conventional remelting techniques are prevalent as they suffer from drawbacks including high energy consumption, material loss, low purity, and inferior mechanical properties. Solid-state recycling (SSR) via plastic deformation processes has been introduced as a promising alternative for producing ultrafine-grained (UFG) magnesium materials with outstanding properties. Despite the absence of any reviews on SSR using plastic deformation methods for magnesium, this paper offers a detailed examination of SSR techniques. The mechanisms of bonding and grain refinement, crucial for determining the final properties of recycled magnesium, are explored. Furthermore, the discussion delves into corrosion, an essential aspect concerning magnesium and its alloys. Ultimately, the impact of various parameters such as process temperature, level of shear strain, chips size, and hydrostatic pressure on the quality of the final sample, to be used as guidance for the production of better-qualified specimens was examined.

Membrane pre-concentration as an efficient strategy to enhance the enrichment of rare earth by MgO precipitation

Taking advantage of the environmentally-friendly properties of a magnesium salt leaching agent, magnesium oxide (MgO) was used as a precipitant to enrich rare earth (RE) from leaching liquor in the magnesium salt system. This approach not only tackles the issue of ammonia–nitrogen pollution but also enables efficient magnesium recycling. However, due to the high concentration of magnesium ions and the low concentration of RE ions in the leaching solution, the precipitation kinetics of RE concentrates are sluggish, leading to low RE purity in the resulting precipitated product. In this work, we proposed a novel strategy that combines complexation-ultrafiltration (UF) pre-concentration with subsequent MgO precipitation to enhance the hydrolysis of MgO, promoting the precipitation of RE. We further improved the RE enrichment efficiency by optimizing membrane type, complexing agent selection, concentration levels, precipitation temperature, and MgO dosage. Under the conditions of concentrating the leaching solution using optimal UF membrane and employing glyphosate as the complexing agent, the RE ions concentration increased from 101 to 3940 mg/L, and we successfully separated magnesium ions with a separation factor of 36.4. A comparison between direct MgO precipitation and the pre-concentration approach revealed an 80 % reduction in precipitation time and an 80 % decrease in MgO usage with pre-concentration. Furthermore, this combined process led to an 8 % increase in RE recovery and a 2.8-fold enhancement in RE purity, and similar results were obtained when using actual mine leaching solutions. Additionally, the glyphosate present in the UF permeate and the precipitated mother liquor can be efficiently reclaimed through resin adsorption. This proposed process holds significant potential for engineering applications aimed at enriching RE.

Harvest Residue Decomposition from Eucalyptus sp. Plantations in Temperate Climate: Indicators and Contribution to Nutrient Cycling

The sustainable management of forest plantations by keeping the harvest residues on site improves the soil’s chemical, physical and biological properties while constituting an important nutrient reserve. Our objectives were: (a) to identify and quantify the characteristics of Eucalyptus dunnii, Eucalyptus grandis and Eucalyptus globulus that affect the decomposition rates of harvest residues, as well as indicators that can explain the process and (b) to quantify the potential recycling of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) to the soil from residue decomposition and the quantitative and qualitative differences between the species. We analyzed the information of five commercial plantations of Uruguay. At the harvest, the biomass of leaves, thin and thick branches, bark and their respective N, P, K, Ca and Mg contents were quantified. At each site, bags with samples of the different residues were left to decompose and were periodically collected throughout 24 months. Eucalyptus dunnii presented the largest amounts of residues of all parts. The decomposition rates of the different residues depended on their chemical constitution, part size and the species. Eucalyptus dunnii leaves showed the shortest half-life (0.94 years), while the bark of the same species presented the longest (5.62 years). Total nitrogen and carbon (total and soluble) contents, which can be easily determined, emerged as good predictors for half-life estimation. The release patterns of nutrients depended more on their dynamics in the plant and their parts than on the species itself. The results highlight the importance of nutrient recycling to ensure the sustainability of the productive system in the medium and long term.

Environmental Assessment of Global Magnesium Production

ABSTRACT Concerns about climate change call for a careful assessment of the environmental impact of the supply chain of critical materials such as magnesium (Mg) which has a broad range of applications. Enhancing the circularity of this material is vital for ensuring its sustainable use. However, systematic analysis of the sustainability of the global production of magnesium and its circularity is still missing. We propose a novel dynamic model based on geology and processing routes to quantify the key environmental concerns across the life cycle of primary and secondary magnesium. Energy consumption, water use and related emissions are assessed for recycling including functional (recovered Mg reused in the closed-loop supply chain) and nonfunctional (recovered Mg as an element used in aluminum alloys as open-loop supply chain), as well as casting and molding. Results show a significant potential contribution of circularity of magnesium to energy (up to 31 billion GJ) and water (up to 2.7 Km3) savings, as well as the mitigation of greenhouse gas (GHG) emissions (up to 3 billion tonnes CO2 eq), globally. However, the analysis indicates that 87% of secondary magnesium comes from nonfunctional recycling. The result shows the possible increase of nonfunctional recycling of magnesium from 612 kt in 2020 to 1 mt in 2050, and the growth of functional recycling of magnesium from 96 kt in 2020 to 161 kt in 2050. The finding highlights the necessity for improving supply chain policies of Mg through technological developments and operational changes to ensure its sustainable circular economy.

Understanding Combustion Mechanism of Magnesium for Better Safety Measures: An Experimental Study

With the growth of the magnesium recycling market, the risk of fire and explosion has been raised over time. In particular, dross generated in the process of magnesium recycling is not considered as a hazardous material even though it contains a lot of pure magnesium and/or magnesium compounds. There are few safety measures to prevent and respond to potential fires and explosions in the magnesium recycling process and to protect employees. Therefore, this study aims to identify appropriate safety measures to reduce the risk of fire and explosion in the magnesium recycling process by looking at two actual magnesium fire cases and relevant criteria in South Korea, the US, and Japan. Also, a combustion experiment using magnesium powder was conducted to identify the significant combustion phenomena of magnesium. Lastly, we developed a fire safety mechanism of magnesium, including chemical reaction, smoldering, and ignition. Each phase presents five contents for different safety measures in the visibility of combustion reaction, the velocity of the combustion reaction, identification methods, response measure, and possible responders. Although this study focused on dross from the magnesium recycling process, it is expected to be useful to develop a better risk management strategy to reduce the risks in the recycling process of metals.

Formation, stability, and presence of magnesium nitride in magnesium recycling processes

Abstract In this study an attempt has been made to identify analytical methods for detecting magnesium nitride, and document in which part of the magnesium recycling process this phase is concentrated. The samples were taken from a continuous fluxfree recycling session, where an AZ91D magnesium alloy was remelted and purified by blowing nitrogen through the melt. Exothermic reactions took place when magnesium nitride reacted to ammonia and Brucite and also when aluminium nitride reacted to ammonia and Gibbsite in a moisture-bearing environment. Because of this, it was essential to avoid any contact with moisture during the whole sampling and preparation process. The samples were exclusively handled in an argon atmosphere. Due to their crystallinity and Raman activity the nitrides were detected with X-ray diffraction and Raman spectroscopy, respectively. With the scanning electron microscope it was difficult to analyze small concentrations of nitrides since large, stable crystals were absent and the carbon coating absorbs the nitrogen Kα line. The Mg-alloy was found to be free of impurities. Although nitrides were expected to be concentrated in the slag because of their greater density, they were found adhering at the nitrogen bubbles and accumulating in the dross. Large amounts of oxides were concentrated in the slag.

Magnesium Life Cycle in Automotive Industry

The transportation sector is responsible for the largest share (29% in 2019) of greenhouse gas emissions (GHG). One of the ways to reduce this share consists in introducing lightweight vehicles in order to diminish fuel consumption, and, in consequence, GHG emissions. Magnesium (Mg) carries considerable potential as a lightweight material to be used in automotive industry, e.g., in gearboxes, front end and IP beams, steering column and driver’s airbag housings, steering wheels, seat frames and fuel tank covers. Weight savings resulting from the use of Mg could reach up to 70% of the conventional parts. However, energy consumption and emissions from magnesium primary production are higher than for steel and aluminum. Therefore, enhancing magnesium recycling would be vital for ensuring its sustainable use. This study assesses the life cycle of magnesium extracted from end-of-life products. Using system dynamics modelling, we quantify the potential environmental benefits and examine aspects related to circularity of magnesium to be used in the automotive industry. Energy consumption, water use and related emissions are assessed in processes of functional (recovered Mg reused in the vehicle manufacturing processes) and non-functional (recovered Mg as an element used in aluminum alloys) recycling as well as casting and molding. Obtained results show that the implementation of circular economy strategies may help in increasing the supply of magnesium from the automotive industry up to 0.70 million tonnes (mt) in 2050. As shown by the analysis, 43% of total energy consumption and water use at the global Mg recycling stage in 2050 corresponds to non-functional casting and molding in automotive industry, followed by non-functional recycling (11%), functional casting and molding (7%) and functional recycling (2%). Also, it is estimated that the existing technologies in functional and non-functional Mg recycling in automotive industry contribute to the global warming with an emission of 5.62 and 29.66 mt of CO2 eq. in 2050, respectively.

Room temperature magnesium electrorefining by using non-aqueous electrolyte

The increasing usage of magnesium inevitably leads to a fast increase in magnesium scrap, and magnesium recycling appears extremely beneficial for cost reduction, preservation of natural resources and protection of the environment. Magnesium refining for the recovery of high purity magnesium from metal scrap alloy (AZ31B composed of magnesium, aluminum, zinc, manganese and copper) at room temperature is investigated with a non-aqueous electrolyte (tetrahydrofuran with ethyl magnesium bromide). A high purity (99.999%) of electrorefined magneisum with a smooth and dense surface is obtained after potentiostatic electrolysis with an applied voltage of 2 V. The selective dissolution of magnesium from magnesium alloy is possible by applying an adequate potential considering the tolerable impurity level in electrorefined magnesium and processing time. The purity estimation method suggested in this study can be useful in evaluating the maximum content of impurity elements.

Pyrometallurgical Magnesium Recycling by Precipitation of Intermetallic Phases

AbstractDue to its high affinity to noble metals the recycling of magnesium is not trivial and the removal of corrosion promoting elements a challenge. Especially for the separation of nickel no industrially efficient method exists. In this work a reduction of the nickel content in contaminated magnesium‐aluminum alloys down to 100 ppmw could be achieved by the combined use of aluminum and zirconium. Although this residual content does not satisfy the highest purity grade of standard magnesium‐aluminum alloys (10 – 50 ppm) this still remains a great step towards an efficient magnesium recycling process.

Magnesium Recycling: To the Grave and Beyond

Demands for the reduction of carbon emissions imposed by the legislative bodies mean that magnesium and its alloys receive continued interest from the manufacturing industries. The use of alternative energy sources such as hybrid-, battery-, or fuel-cell-powered cars alleviates some of the environmental impact of using fossil fuels, but these technologies continue to require lighter materials to maintain fuel efficiency. Many of the lightweight materials such as fiber-reinforced polymers cannot be reused or recycled in the conventional ways. High-grade magnesium and magnesium alloy scrap can be easily recycled where the alloy composition can be controlled, such as defected parts in a die casting operation. However, where the alloys are mixed or the alloys contain impurity elements or oxide particles, the alloys cannot be easily recycled. As the use of the magnesium alloys increases the recycling of magnesium alloys becomes both environmentally and economically important. Moreover, various countries in the world regulate the end of life of the vehicles and the recycling of the parts. The European Union regulates the minimum amount for reuse and the recycling rates for automotive components. Canada, Japan, China, and some states in the United States also regulate the end of life of motor vehicles in order to recover, reuse, and recycle some of the materials. The production of primary magnesium is an energy-intensive process with a large carbon footprint. This is especially the case with the conventional pigeon process or the electrolytic reduction of magnesium chloride. However, the use of secondary magnesium is much less energy intensive compared with the primary production. At present, the aluminum and magnesium components are separated from heavy metals such as steel. The recovered magnesium is used in secondary aluminum processing to regulate the concentration of magnesium. However, with the increased use of magnesium, a commercially viable method to separate magnesium and aluminum is essential. A new system to separate magnesium has been developed in Germany that distinguishes between magnesium and aluminum through their coefficients of friction. Thus, a commercially viable and environmentally sound recycling process can lead to increased use of magnesium alloys. Recently, many different methods of recycling have been investigated to determine their viability. Several different technologies can be used to refine magnesium scrap, which can be broadly categorized as flux based and fluxless technologies. Flux refining technologies use a flux to protect the magnesium and another flux to clean the magnesium. An example of a refining process that uses fluxes to refine magnesium is described in the article titled ‘‘An Environmentally Friendly Process Involving Refining and Membrane Based Electrolysis for Magnesium Recovery from Partially Oxidized Scrap Alloy’’ by Xiaofei Guan, Uday B. Pal, and Adam C. Powell. They describe refinement of partially oxidized Mg-Al alloy to recover magnesium using a flux containing MgF2 and CaF2. The second mode for refining magnesium, the fluxless process, includes salt furnace technologies, gas filtering vacuum distillation, and hydrometallurgy. The methodology described by Fabrizio D’Errico, Gerardo Garces Plaza, Markus Hofer, and Shae K. Kim would be an example of a flux-free method. In their article titled ‘‘Final Assessment of Pre-industrial Solid-state Route for High Performance Mg-System Alloys Production: Toward Conclusion of the Green Metallurgy EU Project,’’ use of magnesium chips in the production of new alloys containing CaO has been discussed alongside commercialization of such a process. The third contribution is entitled ‘‘Life Cycle Assessment of Recycling of Magnesium Vehicle Components’’ by Simone Ehrenberger and Horst E. Friedrich. It looks at the life-cycle assessment of using magnesium alloys in automotive components. Chamini L. Mendis and Alok Singh are the guest editors for the Magnesium Committee of the TMS Light Metals Division and coordinators of the topic ‘‘Magnesium Recycling: To the Grave and Beyond’’ in this issue. JOM

Magnesium Recycling of Partially Oxidized, Mixed Magnesium-Aluminum Scrap through Combined Refining and Solid Oxide Membrane Electrolysis Processes

Pure magnesium (Mg) is recycled from 19g of partially oxidized 50.5wt.% Mg-Aluminum (Al) alloy. During the refining process, potentiodynamic scans (PDS) were performed to determine the electrorefining potential for magnesium. The PDS show that the electrorefining potential increases over time as the magnesium content inside the Mg-Al scrap decreases. Up to 100% percent of magnesium is refined from the Mg-Al scrap by a novel refining process of dissolving magnesium and its oxide into a flux followed by vapor phase removal of dissolved magnesium and subsequently condensing the magnesium vapor. The solid oxide membrane (SOM) electrolysis process is employed in the refining system to enable additional recycling of magnesium from magnesium oxide (MgO) in the partially oxidized Mg-Al scrap. The combination of the refining and SOM processes yields 7.4g of pure magnesium.

국내(國內) 마그네슘 리싸이클링 현황(現況)

마그네슘은 최근 자동차 부품, 전자기기 케이스 등으로 사용량이 증가하고 있는데, 아직까지는 마그네슘 부품소재의 사용 수명이 다 되어 발생된 폐기물은 많지 않고, 다이캐스팅 공정 중에서 발생되는 스크랩이 대부분 재활용되며 용해과정에서 드로스(dross)와 슬러지(sludge) 및 기계 가공에서 발생하는 절삭칩 등도 일부 재활용되고 있다. 본 고에서는 최근 몇 년간의 국내 마그네슘의 수요, 생산현황 등 일반 현황을 먼저 살펴보고, 스크랩 발생량과 리싸이클링 현황 및 국내업체의 처리기술들을 조사하였다. 2010년에 국내에서 8,840톤의 마그네슘스크랩을 처리하였으며, 마그네슘 금속 재활용률은 32.5%로 추산되고, 재생마그네슘은 대부분 마그네슘 부품 다이캐스팅용으로 사용되었다. Magnesium has been used as parts of vehicles, case materials of notebook PC and mobile phone, and its demand has been increasing recently. So until now, there has little magnesium scraps from the end of life vehicles or electronic parts, and most scraps has been generated from magnesium processing lines such as melting, die casting and machining. It is to review the present status of magnesium recycling. Here, domestic demand of magnesium, recycling amount and technologies used in domestic recycling companies were surveyed in recent years. In 2010, 8,840 tons of magnesium scraps were processed and used as raw materials for die casting products. The recycling ratio was estimated as 32.5%.

Practical Synthesis of Chiral 2-Morpholine: (4-Benzylmorpholin-2-(S)-yl)-(tetrahydropyran-4-yl)methanone Mesylate, a Useful Pharmaceutical Intermediate

A commercial synthesis was developed for the production of (4-benzylmorpholin-2-(S)-yl)-(tetrahydropyran-4-yl)methanone mesylate, 1a, a key starting material for a phase 2, new investigational drug candidate at Eli Lilly and Company. The target compound was produced in the clinical pilot plant by the combination of two key steps: resolution of a morpholine amide intermediate to install the S-morpholino stereocenter in 35% yield and a high-yielding (89%) Grignard reaction to generate the title compound 1a, isolated as a mesylate salt. The Grignard reaction was found to proceed optimally when using a combination of I2 and DIBAL-H for the initiation. In addition, the Grignard reagent formation was monitored by ReactMax calorimetry, and proof-of-concept studies were completed, demonstrating that the Grignard step could potentially be run as a continuous process with magnesium recycling.

Recycling of magnesium drive train components

With the development of new heat resistant magnesium alloys, the automotive industry has introduced several parts to the drive train. The rising number of large magnesium components will result in a higher quantity of automotive post consumer scrap. It was the aim of this work to find a reasonable alloy system for the recycling of these magnesium drive train components. A matrix of potential recycling alloys based on the magnesium alloy AM50 was prepared via permanent mould casting. The materials were investigated via tensile testing, creep tests and salt spray tests. Three alloys were selected for processing via high pressure die casting and the tests were repeated on the new materials. A promising system for recycling has been isolated and will be investigated more deeply for the influence of impurities.

State of the Art in the Refining and Recycling of Magnesium

In order for magnesium to continue to grow, all forms of magnesium scrap need to be recycled – for both economic and environmental reasons. This paper extensively reviews the techniques for the refining and recycling of magnesium. Removal of inter-metallic elements and inclusions through gas fluxing, filtration and other methods are summarized. Flux refining technology is the old but most common method to purify magnesium metal. Fluxless refining technologies are under development, such as salt furnace technology, inert gas and filter refining, vacuum distillation refining, and hydrometallurgical methods. Magnesium scraps recycling is discussed, techniques to protecting Mg (or Mg alloy) melt with protective atmosphere and salt flux are briefly introduced.

Development of a Magnesium Recycling Alloy Based on AM50

Magnesium applications for structural components in the automotive industry are constantly rising. This is based on the recent development of new alloys, new fabrication processes, and the ambition of car manufacturers to reduce the vehicles weight and CO2 emissions according to the EU and US policy [1, 2]. A rising quantity of magnesium per vehicle leads to a rising quantity of scrap which needs to be recycled according to the European Directive on end-of life vehicles [3]. So far post consumer scrap has not been used for structural parts. But since the metal is still expensive compared to aluminium or steel, and remelting saves more than 90 % of the energy for primary production, magnesium recycling will significantly contribute to cost savings. In comparison to steel or aluminium a recycling cycle for magnesium has not yet been established. Concerning post consumer scrap it is likely that many vehicles will end up in the shredder fraction or at least will be mixed up instead of being dismantled and separated according to their alloy. Thus it is reasonable to define secondary alloys which allow the use of post consumer scrap for structural applications. Creep resistant alloys have the potential of a broad application concerning the weight of the components and therefore a secondary alloy would be reasonable. The aim of this work is to examine a row of AM50-based alloys, modified with additions of Sr, Ca, and Si due to the importance of these elements to increase creep resistance and their usage in modern magnesium alloys. The corrosion properties as well as the mechanical properties and microstructures are investigated in the as-cast and annealed condition. Salt spray tests (using 5 % NaCl) and electrochemical corrosion methods are applied to investigate the corrosion properties which are then compared to the unmodified AM50. Tensile and compression tests at temperatures ranging from 20 °C to 200 °C are applied to investigate the mechanical properties.

A physical approach to the direct recycling of Mg-alloy scrap by the rheo-diecasting process

Due to the rapidly growing market for magnesium diecastings in the automotive industry in the past decade, there is a steady increase in magnesium scrap sourced from both end-of-life vehicles (old scrap) and the manufacturing processes (new scrap). In addition, the energy required to recycle magnesium is only 5% of that for extraction of primary magnesium from Mg-containing minerals. This makes magnesium recycling extremely beneficial for cost reduction, preservation of natural resources and protection of the environment. In this paper, a physical approach is presented to magnesium recycling using the rheo-diecasting (RDC) process. The RDC process was applied to process AZ91D alloy sourced from both primary alloy ingots and diecast scrap. The experimental results showed that the RDC process could be used to produce recycled AZ91D alloy with fine and uniform microstructure and very low level of porosity. The intermetallic compounds containing the impurity elements were fine and spherical particles distributed uniformly in the alloy matrix. No oxide particle clusters and oxide films were found in the RDC microstructure. The tensile properties of the recycled AZ91D alloy were comparable to those produced from the primary alloy ingots.

Removal of ammonia as struvite from anaerobic digester effluents and recycling of magnesium and phosphate

A second order kinetic model was developed to predict the rate and extent of NH 4 + removal as struvite from anaerobic digester effluents. Alternative to this, NH 4 + can be recovered from struvite and the remaining Mg 2+ and PO 4 3 - can be recycled back to the wastewater to fix more NH 4 + . The NH 4 + solution was retained and the remaining Mg 2+ and PO 4 3 - were returned back to be mixed with wastewater. In a five-step process, NH 4 + recovery was initially 92% and progressively decreased to 77% in the fifth stage, due to loss of Mg 2+ and PO 4 3 - at each step in the supernatant. Finally, economic analysis of recycling nutrients was performed and compared to the one step process. The cost of NH 4 + recovery was calculated as $0.36/kg NH 4-N which is lower than $7.7/kg NH 4-N the cost of one step process without considering the market value of struvite obtained in one step process.

Formation, stability, and presence of magnesium nitride in magnesium recycling processes

Abstract In this study an attempt has been made to identify analytical methods for detecting magnesium nitride, and document in which part of the magnesium recycling process this phase is concentrated. The samples were taken from a continuous fluxfree recycling session, where an AZ91D magnesium alloy was remelted and purified by blowing nitrogen through the melt. Exothermic reactions took place when magnesium nitride reacted to ammonia and Brucite and also when aluminium nitride reacted to ammonia and Gibbsite in a moisture-bearing environment. Because of this, it was essential to avoid any contact with moisture during the whole sampling and preparation process. The samples were exclusively handled in an argon atmosphere. Due to their crystallinity and Raman activity the nitrides were detected with X-ray diffraction and Raman spectroscopy, respectively. With the scanning electron microscope it was difficult to analyze small concentrations of nitrides since large, stable crystals were absent and the carbon coating absorbs the nitrogen Kα line. The Mg-alloy was found to be free of impurities. Although nitrides were expected to be concentrated in the slag because of their greater density, they were found adhering at the nitrogen bubbles and accumulating in the dross. Large amounts of oxides were concentrated in the slag.