Vanadium is a valuable and rare resource widely used in chemical manufacturing, military affairs, aerospace, metallurgical industry and other fields [1], and China is rich in vanadium resources, accounting for 34% of the world's total, ranking first in the world. Vanadium mainly in the form of vanadium-titanium magnetite and vanadium-bearing coal [2]. As a new type of energy storage technology, vanadium redox flow battery has been widely studied due to its advantages of environmental protection, long-life, safety and flexible power design [3]. Vanadium electrolyte is an important component of vanadium batteries, and it is directly related to the performance and cycle life of vanadium batteries [4]. Solvent extraction is widely used for the extraction of vanadium. It can prepare electrolyte from vanadium-containing solution, eliminating the steps of vanadium precipitation, impurity removal and dissolution, which meets the requirements of energy saving and environmental protection. Based on the above, we propose a clean and short process for the preparation of vanadium electrolyte from vanadium shale leaching solution by solvent extraction.

An oxidative stripping system, with the low concentrations of hydrogen peroxide and sodium hypochlorite was introduced to facilitate vanadium recovery and further separation of impurities from the leach solution. In order to investigate the mechanism, FTIR and Raman spectroscopy were used to investigate the changes in valence bonding before and after extraction and stripping. The concentration of vanadium and other impurities in the vanadium-rich liquid was investigated by ICP to determine whether it complied with national standards（GB/T 37204-2018）.

After reduction and enrichment, a high purity vanadium electrolyte with low concentration of impurities was prepared. The prepared electrolyte exhibits acceptable electrochemical and charge/discharge properties. The method saves a large amount of preparation cost than the traditional method and does not produce ammonia, nitrogen or harmful gases. The technology is economically reasonable and eco-friendly, and is expected to be applied to large-scale production and promote the development of vanadium redox flow battery and new energy.

 

What kind of motoring is both sustainable and resilient? And what specific societal shift will allow us to move into it? Until now, motoring has not been fully considered as a means of environmental resiliency in production. Too often it is seen as a problem rather than the means toward shifting sectors into a more sustainable future. This is a blind spot because motoring is at the heart of production, manufacturing, and economics, and a foundational aspect of our systems of resiliency in wider society. Those systems dependent on motoring are matters of urban planning, infrastructure, policy, food and disaster systems, social and community disaster relief, etc., and yet many advocates of sustainability and resiliency within those sectors assume motoring is an obstacle rather than a portal into the change they desire. This paper examines that assumption and offers a model whereby we can turn this dissonance into collaboration, ultimately arguing that a cognitive shift about what motoring is and can do is necessary across sections if we wish to develop a sustainable future.

Motoring, which is any form of movement powered by energy that is not one’s own, includes internal combustion, diesel, electric, hydrogen, gas, steam, and solar sources, and is a necessary part of our systems of communication, nourishment, and disaster services. It could also become a tool towards resilience rather than its obstacle, though the necessary shift, as this paper argues, will be a cognitive one. For motoring to promote resiliency, we must have a clear understanding of what it means for motoring to be ecological, which means getting beyond the current either/or debate about fuel sources and focusing on use patterns and planetary motoring needs. In that respect, this paper establishes ecological motoring as that which “meets the motoring needs of all within the means of the living planet,” a definition inspired by and modelled upon the Doughnut model of economics by Kate Raworth. To move towards ecological motoring—motoring that is sustainable and resilient—we need to understand these motoring needs from a different cognitive perspective, which means releasing old judgements and debates, and reconfiguring our understanding of the needs and uses of motoring for the planet. Using the opensource tools and workbooks of the Doughnut Economics Action Lab (DEAL) as its methodology, this paper proposes four main quadrants of ecological motoring—system, materials, energy exchange, and scope—which can be understood as motoring’s core components of resiliency at various nested scales among sectors of society. Towards demonstrating these findings, it looks at the case study of Riversimple and shows how we might be able to shift (regardless what the fuel source of our company is) towards a more sustainable and lucrative reality by using these four quadrants.

Black shale is a unique vanadium-bearing resource in China. Therefore, extraction of vanadium from black shale for high value applications becomes important [1]. Biological vanadium extraction from black shale is an emerging alternative to conventional metal extraction. During bioleaching, rare metals in minerals are converted to a soluble or extractable state by the action of bacteria [2,3,4]. Compared with traditional recycling process, the bioleaching is greener, more efficient and requires lower cost as well as energy [5]. Acidithiobacillus ferrooxidans (A. ferrooxidans) is one of the most important autotrophic bacterium involved in bioleaching. It is also a bioleaching microorganism that was well studied and was of most economic benefits in biological metallurgy.

However, the biotechnology of vanadium extraction still faces problems such as irrational regulation of influencing factors, low leaching rate, and poor fluorine tolerance of bacterial strains. To address the above problems, this paper domesticates a fluoride-tolerant bacterium, utilizes the role of fluoride in chemical leaching that can destroy the mica crystal lattice, and uses fluoride as a leaching aid to improve vanadium bioleaching in a new process.

In this paper, the fluoride tolerance domestication of the leaching strain Acidithiobacillus ferrooxidans and its mechanism and the parameters of the factors affecting the bioleaching process of vanadium-bearing shale was investigated. On the one hand, fluoride-tolerant strains were obtained by successive transient domestication, and the mechanism of fluoride tolerance in mineral-leaching strains was investigated from the genomic point of view; On the other hand, the influence of various factors on the bioleaching efficiency of vanadium-bearing shale was investigated, and the optimal process parameters for vanadium bioleaching were determined.

A strain tolerant to 0.05 mol/L F^- was obtained by eight consecutive transplants, and the enriched culture was used for vanadium biorefining, which showed good leaching performance on vanadium shale, with an increase of about 15% in leaching rate compared with chemical leaching.

Zinc (Zn) is utilized in many industrial applications, such as batteries, cosmetics, pharmaceuticals, and metal production. Due to urbanization and the depletion of high-grade ore deposits, efficient resource management is required from both primary and secondary resources. In terms of the latter, the most widely used recycling method of Zn-containing scrap is the Waelz process, particularly for electric arc furnace dust (EAFD). The Waelz process is a pyrometallurgical technique where the Zn scrap is loaded into a rotary kiln with a carbon-containing reducing agent at 1200-1300 ^oC to extract Zn [1]. Zn subsequently vaporizes and oxidizes in the gas stream to form particulate ZnO, which is then collected on bag filters.

In Europe, approximately 250,000 tons/year of Zn is recovered via the Waelz process. However, the process also generates nearly 800,000 tons/year of slag. Utilization of the “Waelz Slag” is hindered due to the lack of environmental compatibility [2], mainly because of the complex chemical and mineralogical composition. As a result, Waelz slag is largely landfilled, even though the iron content exceeds that of high-grade iron ores (~25% iron). 

Numerous studies have investigated the recycling potential of Waelz slag by different methods, such as in a vertical retort [1], in a top-blown rotary converter, and as a charge to an electric arc steelmaking furnace. However, these studies were either theoretical, or in the early stages of development. Nevertheless, the main component of Waelz slag is iron (Fe), followed by Zn, manganese (Mn), and lead (Pb). Of these, Fe and Zn represent the target elements for downstream utilization. 

The project’s primary goals are to generate pig iron, slag (ideal for the building materials sector), and Zn-rich fly ash (for Zn recovery). Information from a number of analytical techniques, including X-ray fluorescence (XRF), X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), and mineral liberation analysis (MLA), were employed to augment parameters for simulation of one-kilogram experiments conducted in an induction furnace using FactSage 8.2.

The study employs an iterative approach where the result of each experiment serves as a guide for the subsequent experiments. The highest total iron recovery is 83.18%. A combination of the FactSage and Einstein-Roscoe viscosity models was used to determine slag viscosity, implying that viscosity depends more on composition than temperature. Addition of 16% SiO₂ and 3% Al₂O₃ shows a high slag viscosity and delayed Mn reduction, possibly due to insufficient Si dissolved in the metal phase and the system being furnace cooled, giving time for nucleation of Mn-containing phases. The calculated actual oxygen partial pressure on all experiments ranges from 10^-8 to 10^-21. XRD analysis of dust recovery filter paper confirmed the presence of Zn. The slag produced in this study has similar compositions to those studied by Grudinsky et al. that can be used as concrete material to enhance its properties [3]. Overall, the study opens the way for holistic valorization of Waelz slag, resulting in more sustainable Zn resource management.

During secondary copper production both internal slags and a final copper slag is produced. In contrast to the final copper slag, which is a process by-product, internal slags are typically recycled to the preceding aggregate. Therefore also the part of copper and other valuable elements like nickel, tin, lead and zinc reporting to the final slag is kept low. On the other hand, other elements which influence the process negatively like aluminium and chromium are also recirculated and lead to an increase of density, melting temperature and therefore also viscosity of the resulting slags. This results in a more complicated slag treatment and influences aggregate capacity, i.e. (black copper smelter and the converter) and copper loss to slag, negatively.

This study is investigating a slag treatment (slag reduction) of high-copper bearing slags from secondary copper production to meet the described challenges by avoiding internal slag recirculation. But besides that, the process results to additional value in that the secondary slag produced through appropriate fluxing (i.e., through slag design) can be easily used for construction purposes. For this investigation an in-depth knowledge about not only the thermodynamics but also kinetics of this process is required.

This study is built on three pillars: Thermodynamical modelling, kinetic investigations and experimental tests in a medium scale. The thermodynamical modelling is conducted using FactSage™ with inclusion of the copper database. An open-system approach is used to model the reduction process by hydrogen. Through that several simulation steps are taken into account, where the hydrogen is added in fractions which are forming a thermochemical equilibrium with the slag and the resulting metal phase. After reaching equilibrium (during each step) the gas phase is removed and a new gas phase is formed by a new addition of hydrogen and the creation of a new thermodynamical equilibrium.

Kinetics investigations were performed by using thermogravimetric methods with the combined analysis of the off-gas stream using mass spectrometry for the achieved ratio of hydrogen to steam. This ratio can be used as a measure for the reduction progress. Firstly, the slag under investigation is mixed with hematite (Fe₂O₃) and silica (SiO₂) to achieve a secondary slag near fayalitic composition (45-50 wt.-% FeO and 35 wt.-% SiO₂). The non-fluxed slag would for be rich in alumina but contains also a non-negligible proportion of chromium(III)-oxide. Both compounds are known for increasing slag viscosity. The chemical composition of the resulting metal phase and the secondary slag is analysed using SEM-EDX.

The experimental trials in medium scale are performed with around 0.5-0.75 kg slag material, depending on the mass of needed fluxes. Here the gas is injected via a lance in the molten slag system at given temperature. Via weighing before and after the experiment the mass loss during reduction, i.e., due to zinc and lead fuming can be estimated. By means of chemical analysis of the achieved metal phase as well as of the resulting secondary slag the reduction degree in this scale can be evaluated. The main goal is to achieve a secondary slag which contains less than 1 wt.-% of copper and other valuable elements and a secondary slag with an iron oxide content and silica content of 45-50 wt.-% and 35 wt.-%, respectively.

It can be seen that the majority of slag reduction is completed within a few minutes and is therefore faster than when using carbon monoxide as a typical reducing agent, as long as diffusion can be neglected. In reality, this is not the case: due to the distance e.g., between the lance tip and the outer diameter of the reaction vessel, the necessary reduction time is extended, as the process is increasingly diffusion-controlled.

With increasing temperature, an accelerated reduction can be observed due to a reduced viscosity of the slag and an improved mobility of the hydrogen, whereby the reduction of the hematite added as an additive can be considered complete even before the reduction of the slag.

Roasting processes in the pyrometallurgical production of non-ferrous metals are very complex, taking into account the chemical and mineralogical composition of the raw materials, as well as the complexity of the chemical reactions which take place in the roasting aggregate. Laboratory-scale characterization of the initial materials, intermediates, and final products gives researchers the possibility to propose the most likely possible reaction mechanism in order to guide the roasting process towards the desired products. On the other hand, studying the microstructure of materials helps to understand the reasons for the lack of the roasting process efficiency for a certain application case. More recently, the development and application of advanced thermodynamic software additionally helps to predict more accurately the phase distribution and overall dynamics of the roasting process, prior to experimental laboratory tests, thus increasing the probability of successful replication on a larger scale.

This paper presents the results of microstructural investigation of three different materials which are used in non-ferrous metallurgy as primary or secondary raw materials: 1) copper-iron sulphide flotation concentrate (Republic of Serbia), 2) lead and arsenic containing dust from copper smelter (Republic of Kazakhstan), and 3) gold containing residues from gold winning plant (Republic of Uzbekistan).

Samples of sulphide copper concentrate were roasted at 425°C, 675°C and 950°C in an air atmosphere for 1 hour. The experimental characterization included chemical and quantitative microstructural analysis of the initial sample, XRD and SEM/EDS analyses of the initial sample and roasted products. Thermodynamic prediction of the equilibrium compositions and phase distribution at elevated temperatures was done using HSC Chemistry software (ver. 6.1) under the incomplete and complete roasting conditions.

Samples of lead- and arsenic-containing dust from copper smelter were subjected to sulphatising roasting in a pilot-scale fluidised bed furnace at temperatures of 400-550°C for 1 hour.  The data of the initial dust and calcine samples investigation by scanning electron microscopy and X-ray spectral microanalysis (SEM and XRMS) allowed to detect and eliminate the cause of insufficient efficiency of impurity removal into the gas phase. The samples were also studied by chemical analysis and X-Ray diffraction analysis.

In the next example under consideration, the starting material and products of oxidative roasting of sulphide- and carbonaceous-bearing gold plant residues at 500-700°C were investigated. In addition to the methods of chemical analysis, optical studies, X-ray phase analysis and diagnostic leach, the use of the scanning electron microscope study equipped with a dual-detector X-ray microanalysis system provided the most complete information explaining the cause of incomplete gold recovery at the downstream roasting stage of cyanidation.

Application of the scanning electron microscopy method with local X-ray spectral analysis allows not only to establish the percentual content of minerals in the investigated sample, but also to determine the elemental distribution within the mineral, the degree of mineral liberation in individual particles of the sample, as well as to determine the association of the mineral/component of interest with other minerals, the quality of its surface, size and shape. This information helps the scientists and experts to optimise metallurgical processes, particularly, as the results have shown, the roasting process.

A wide variety of metals of considerable relevance to the European high-tech industry, and therefore also for our society, are supplied by the nonferrous metal industry. As the technologies became rapidly more complex in the last decades, the number and kind of metals and alloys utilized were getting more specialized and unique. With this technological innovation, the demand for minor elements increases steadily. Since their primary production, in most cases, can only be achieved economically as a by-product, it is difficult to respond to peaks in demand for minor elements. This, in turn, underlines the great need for recycling to compensate for these gaps. 
In this context, together with the industry partners of the Christian Doppler Laboratory, methods for determining the distribution of metals in the phases and compounds that occur in industrial intermediates, by-products, and residues are developed and applied, and the possibilities of influencing the behavior in hydro- and pyrometallurgical processes are investigated. This subsequently enables the development of extraction methods for selected elements.
Since residual industrial materials can differ significantly in their behaviour, various innovative processes using chemical and physical properties for separation are used. These include, for example, chlorination of valuables or artificial mineral production by targeted crystallization during the cooling of slags. The paper gives an overview of the activities of the Christian Doppler Laboratory and will then focus on the area of artificial mineral growth to enrich chromium in special spinel phases. 

In this present work, a computational fluid dynamics (CFD) model is devised to study and understand the flow hydrodynamics and chemical reactions occurring between the liquid molten concentrate containing cassiterite and gas phase containing hydrogen. 

This study is motivated by the goal for CO2-neutral production and recovery of valuable non-ferrous metals, e.g. copper, tin and zinc. The metallurgical industry is facing major challenges in transforming existing processes in terms of substitution of fossil fuels, considering costs and safety of plant operation and maintaining product quality. [1] Hydrogen is considered as a promising substituent to fossil fuels as reducing agent in high-temperature metallurgical applications, like smelting in top-submerged-lance (TSL) processes. [2] However, replacing traditional systems with hydrogen has a major influence on the process itself. Hence, numerical models enable a more detailed understanding of hydrodynamics between gas and slag phase as well as thermochemical interactions at the reactive interphase.  

In order to study the effect of hydrogen, a CFD model has been developed according to an experimental setup. [3] In the experiment a lance was introduced into the molten cassiterite though which a mixture of hydrogen and argon is injected into the molten concentrate. A one-fluid approach has been used to understand the interactions and track the interface between the gas and slag phase. Simulations have been carried out to investigate the influence of varying interphase reaction rates and gas flow rates on the flow hydrodynamics and the reduction performance.  

In consideration of the growing production of stainless steel, which averaged at about 6 %/year between 2012 and 2021 and reached 58.3 Mio t/year in 2021, the accumulation of the corresponding residues such as dust increases as well [1]. During the production of stainless steel via electrical arc furnace (EAF), which is the most commonly applied production route, approximately between 10-20 kg of dust accrue per ton of steel [2]. This dust contains a quite significant amount of Cr and Ni. If no recycling of those dusts is carried out, these metals are lost for further operations and potentially interact in a harmful way with the environment in case of present leachable components, such as Cr^VI+. This would lead to economic loss as well as ecological harm. All of todays in industry applied processes to recover valuable metals from such dusts are of pyrometallurgical nature, which are carbon based and quite energy intensive. 

Hydrometallurgical operations for the recovery of metals from Cr-Ni-rich AOD and EAFD have been examined by Aromaa et all. and Stefanova et all. but with the goal to selectively extract Zn [3, 4]. Therefore, after thoroughly charactering the dust including X‑Ray diffraction (XRD), scanning electron microscope-energy dispersive X‑ray (SEM‑EDX), Elemental analysis with inductively coupled plasma‑optical emission spectroscopy (ICP‑OES) and thermogravimetric analysis (TGA), five different acids (hydrochloric, sulphuric, nitric, vinegar and citric acid) were investigated in their potential to leach Cr and Ni. Out of the five acids used, hydrochloric acid was the most promising candidate to conduct a parameter variation with. In the conducted follow-up experiments, a clear trend of increased extraction rates can be observed for higher temperatures and longer leaching times. To counter specific problems observed in previous experiments, a double walled reaction vessel including a lid with four openings for stirrer, reflux condenser, acid addition and pH‑electrode was used. Through applying these methods, the FeCr₂O₄ and NiFe₂O₄ spinel phases, which contain the metals of interest, were able to be leached in a satisfactory amount. The paper summarizes the results of the characterization in conjunction with the obtained extraction rates and conclusions on the mineralogical phases and their leachabilities under different conditions.

Tin is one of the earliest metals used in human history. The amount of tin produced and consumed worldwide in the last ten years has been estimated to be between 300,000 - 400,000 tons annually [1]. Not only is tin an essential constituent of tin bronze, it is also a critical component of alloys for making solders, which are essential for the major drivers of green energy transition; electric and autonomous vehicles, solar PV, semiconductors, etc. [2]. Tin from cassiterite, SnO₂ (main source of tin), has over the years been processed via the pyrometallurgical route. Sulfurization and roasting are primary steps in the process, which are carried out to thermally enrich SnO₂ content in case of low-grade concentrates. Afterwards SnO₂ is treated in reactors, where carbon-based reducing agents are used to reduce tin to the metallic form at high temperatures [3], after which the resulting tin produced is further refined to obtain a marketable grade [4]. The carbothermic reduction of cassiterite, has however, seen several drawbacks such as the generation of environmentally harmful waste gases (e.g., CO₂), high energy and equipment costs, as well as low selectivity with regard to impurities contained in the ore which are difficult to be separated at elevated temperatures [5]. 

A hydrometallurgical extraction route is proposed as a potential alternative processing method for tin extraction from cassiterite to achieve a higher degree of sustainability. This is because it ensures the reuse of chemicals in the process loop and allows for a higher metal recovery at a significantly lower energy consumption and greenhouse emissions [6]. Three different acids, (methanesulfonic acid, sulfuric acid, and oxalic acid) were investigated for their potential to leach tin from cassiterite, and they all proved futile, which supports already existing literature regarding the high chemical stability of cassiterite. A pre-treatment step was deemed necessary to render tin water soluble for subsequent hydrometallurgical processes. 

A reduction of cassiterite in a hydrogen-controlled environment to produce SnO slag, from which tin can easily be leached in acid or alkaline media was investigated.  The formation of SnO slag can be accompanied with the production of a tin metal phase depending on the H₂/concentrate ratio used. During experimentation, a high purity tin nugget (99.5 wt.%) was produced at a reduction temperature of 1300 ⁰C at 30 g H₂/ kg concentrate. The slag formed was soluble in sulfuric acid solution, from which tin extraction is being examined. Other pre-treatment options such as soda roasting and alkaline fusion are being investigated with regard to technological, economic and environmental feasibility.

Increasingly, scientific and technological developments are moving to a more environmentally friendly direction [1]. Therefore, the necessary adaptation of state-of-the-art processes with modified systems to an overall cleaner and more energy efficient state is imminent and requires a lot of research work, a more detailed look at processes and new test equipment. This is particularly true for the metallurgical industry, where carbon is needed not only as an energy source but also for reduction, and where the transition to greener processes has to work in tandem with the difficulties of recycling new complex multi-metal wastes such as magnets, batteries, e-waste and complex slag systems.

The Institute of Nonferrous Metallurgy and Purest Materials (INEMET) aims to look more closely at utilizing hydrogen as a key challenge for the near future with regard to metallurgical process decarbonization [2]. This is planned as a substitute for fossil fuels, e.g., natural gas for smelting copper cathodes prior to casting; nonetheless the influence of hydrogen on the copper melt, furnace refractory, fluid-dynamics, heat transfer and process control have to be assessed. In addition, the utilization of hydrogen for the molten phase reduction, e.g., in the reduction metal oxides, e,g. SnO2 in the context of a smelting process or of iron ore in the context of fluidized bed gas-solid processes is planned. [3].

The use of atmospheric thermal plasma jets as an alternative to conventional gas burners is also being investigated. The ability to use different gas compositions enables new ways of heating and treating slags, scrap and ores and is identified as a key technology in modern metallurgy [4]. Thermal plasma can be used to form species such as atomic hydrogen or even H⁺, which can reduce any metal oxide, allowing processes that cannot be decarbonized with molecular H₂ to be carried out completely without CO₂ emissions [5]. The fuming behavior of melt components can differ in these systems hence opening further pathways for metal refining.

Various new sensors are being installed and used to improve the measurement capabilities and to combine all the sensor data to gain better process knowledge. For example, new phase-differentiating melt height measurements are being tested with radar sensors. The aim is to identify the height of the slag and metal phases in a smelting unit operation. In addition, acoustic measurements may aid to analyze process fluid-dynamics. To link the different parameters of the experiments, a digital twin (on-line process model receiving experimental data) of the Institute's TSL is being built. Developments realized within the EU-HORIZON Mine.io project will be analyzed in detail.

In order to enable new process designs for industrial use, the key expertise lies in scaling up from laboratory scale to pilot scale experimental campaigns. To this end, new experimental fields are being designed within a newly planned furnace hall.

All in all, the directions for future-oriented pyrometallurgical research have been set and will be realized and carried out hand in hand throughout the university, by undergraduate/ graduate students, technical/ academic staff and industry alike.

Recyco, part of the Aperam group, built its pyrometallurgical recycling expertise by recovering valuable elements from stainless steel meltshop dusts. Since 2019, a real evolution of the site started, following the receival of an extended environmental permit allowing the treatment of a broader range of wastes, including hazardous ones. This capability expansion goes along with the development of new processes and products, and is now a real asset for the ongoing transformation of Aperam into a climate-neutral stainless steel producer.

The production of high Ni containing alloys from a multitude of different wastes is described in this paper. This case study is an excellent example of cooperation between R&D and operations, supported by internal customers and aided by sourcing, legal and environmental teams. The development started with preliminary design and simulation of the process using thermodynamic simulations [1, 2]. Slag design and reduction equilibria studies were an important part of the fundamental investigation. Lab-scale experiments supported this development, before a step-by-step transfer to operations, following learning cycles and inspired by the minimalist approach [1], was performed. These cycles are closed by the comparison of the experimental and industrial results to the thermodynamic simulations, and the generated knowledge has been used as the basis for an in-house developed process model of our operation. This model now allows us to simulate the behavior of new wastes in our process, reducing the risk of downtime and production being out of speciation. 

The produced alloys are in line with our meltshop specifications replacing primary nickel. As these alloys have a significantly lower CO₂ footprint than primary Ni units normally used, Recyco is transforming into an important player in reducing Aperam’s scope 3 emissions.

The rare earth elements (REE) play an important role in modern technology due to its wide applicability in various sectors of the world economy. The REE configures a select group of elements with exceptional properties physicochemical, catalytic, electrical, magnetic, and optical attributes [1]. Usually, the REEs are obtained from ore concentrates. However, secondary sources, such as effluents resulting from acid mining drainage (AMD) [2], could be an alternative to the conventional mining and represent an important source of these elements [3]. 

The current work addresses the study of the recovery of rare earth elements (REE) from acid mine drainage (AMD) by using cationic exchange resin. The acid water was obtained from one closed uranium mine at Caldas Municipality (Brazil). The total REE concentration was approx. 0,90 mmol/L, i.e, the sum of the concentrations of lights REE (LREE) and heavies REE (HREE), total impurities 12,9 mmol/L (Al; Ca; Mg; Mn and Zn), sulfate 10 mmol/L, fluoride 5,26 mmol/L, iron <0.09 mmol /L, and the pH around 3.4. 

The loading experiments were carried out in columns at a temperature of 25±1⁰C and the cation exchange resins used were Dowex 50WX8, Lewatit MDS 200H, and Purolite C160. The best results for loading capacity and percentages of efficient removal (%) for total REE and impurities were obtained for the resin Lewatit MDS 200H with 0,566 mmol/g (92%) (LREE = 0,501 + HREE = 0,065) and 1,64 mmol/g (60%), respectively. The selectivity of the resins for the REE can be described as LREE > HREE. Regarding the impurities (Ca, Mn, Mg, Zn, and Al), the resin presents greater loading for calcium and aluminum. The elution experiments with inorganic and organic acids showed that hydrochloric acid and EDTA were more appropriate for the desorption and/or separation of the REE. 

Developing sustainable processes to minimize greenhouse gases is an ongoing effort in various industries around the world. Wind energy or electrical vehicles are two prominent technologies driving the green transition. Neodymium-iron-boron (NdFeB) permanent magnets with a rare earth element (REE) content of around 30 wt.% are typically used within electric motors. Large wind turbines can contain more than a ton of rare earths. The above mentioned factors are causing an increasing demand for these metals whilst industrial nations being heavily dependent on producing countries in Asia. Developing new recycling methods to recover REE from scrap materials (termed as long-loop recycling processes) is an internationally growing topic.

A pyrometallurgical recycling process for waste NdFeB permanent magnets named as slag extraction method is discussed in detail here. Recently, it was found that selective oxidation of REE by metal oxides is promising to recover REE in a slag phase while iron, boron, alloying elements (e.g., cobalt) or coating elements (e.g., nickel) are efficiently collected in an iron phase. This efficient separation of impurities leads to a concentration of REE in a single-stage process providing a significant advantage over direct chemical leaching of permanent magnets. Moreover, the remaining iron phase contains >3 wt.% cobalt and can be utilized to further extract other valuable metals.

In this approach boron oxide was added as flux and ferric oxide as oxidant to produce a slag with concentrations >85 wt.% RE₂O₃. Beside sintered also polymer-bonded NdFeB magnets were investigated in this study which are typically not treatable by direct leaching due to high organic content. Different crucible materials such as graphite, clay-graphite or alumina were tested. Experiments were performed at temperatures between 1300 °C and 1500 °C under inert argon atmosphere. High REE extraction rates of >99 % could be achieved at 1400 °C and 2 h dwell time. In the slag phase, the concentration of impurities such as iron, nickel or cobalt were <1 wt.% detected by ICP-OES and SEM-EDX. The use of clay-graphite crucibles leads to Al and Si contaminations in the slag phase which were avoided in pure graphite crucibles. The developed process can be used as pre-concentration step prior to hydrometallurgical refining of REE. To further optimize the process parameters and provide a scalable technology, kinetic studies are currently conducted. 

The composition of the metal melt plays an important role in the production of high-quality aluminum castings. A melt with high hydrogen content often leads to defects and macro porosity [1]. Gas purging treatment and the use of melting salts for degassing are commonly used to reduce the hydrogen content. However, a consistent solidification of the entire cast part cannot always be realized. In these cases, undesired macro porosity may occur due to hydrogen excess in comparison to the amount of porous seeds in the melt. 

In recent years, the Institute of Nonferrous Metallurgy and Purest Materials has identified two ways of positively influencing this hydrogen porosity. On the one hand, it was found out that it is possible to use a special melt additive to adjust the ratio between the hydrogen dissolved in the melt and the existing pore nuclei so that the hydrogen released during solidification is finely distributed in the casting [2]. On the other hand, it was shown that the use of reactive filter materials can positively influence the precipitation of the atomically dissolved hydrogen and thus generate denser castings [3,4]. Both processes are presented and the efficiency and influence of the respective filter materials and additives is explained. 

This study explores a sustainable approach to pyro-metallurgical recovery of metallic raw materials from mixed sulfidic fine-grained waste streams, named as Theisenschlamm [1, 2]. As part of the FINEST project (https://finest-project.de/), Subproject 3 "FINEST Disperse Metals," our focus is on optimizing the secure blending of fine and ultra-fine-grained material flows to recover valuable metals through a multi-stage pyro-metallurgical recycling process. Specifically, we investigate the utilization of calcium- and zinc-rich industrial residues as alternative feeds for pyro metallurgical metal recovery process.
Using FactSage™ 8.2 software, we simulate and evaluate the behavior of the slag systems throughout both oxidation and reduction stages of the process. Ternary phase diagrams are constructed for the key components of the slag systems, providing insights into phase equilibria, solidification behavior, and the stability of various phases under different thermal conditions [3].
A significant aspect of this work involves calculating the viscosity of the slag during the high-temperature processing stages, as this property is critical for ensuring efficient metal separation and refining [4]. Viscosity calculations are performed using the Einstein-Roscoe model, integrated within the FactSage™ platform, to predict the flow behavior of the slag in relation to its composition and temperature. These findings offer a deeper understanding of the impact of alternative flux materials on slag characteristics, contributing to process optimization.
This detailed modeling-driven approach not only facilitates the refinement of metal recovery processes from complex waste streams but also promotes sustainable circular economy practices
by reducing dependence on traditional flux materials and enhancing resource efficiency in pyro-metallurgical recycling [5].

The metallurgical industry is continuously seeking sustainable methods for the valorization of materials, such as tin residues, which arise as a byproduct during production processes for example in soldering printed circuit boards. This study focuses on the utilization of green, non-fossil reducing agents, specifically biomasses, for the recovery of tin from industrial residues. These can contain valuable amounts of tin and other valuable metals (e.g. Ag and Cu) that can be recovered and reused, essentially making its valorization not only environmentally imperative, but also economically beneficial. When treated correctly the produced secondary slag can become a valuable base product for cement production. This study aims to prove exemplary pathways for holistic valorization of two distinct tin residues.

Biomasses, abundant and renewable, from agricultural, forestry and other organic sources, are considered carbon-neutral due to the fact that they absorb as much carbon during their “life”, as they release when utilized. This more climate friendly status holds especially true for low-grade byproducts. In pyrometallurgy, the use of biomasses as reducing agents is a rapidly growing field of research, providing greener alternatives to the traditional reducing agents such as coke [1][2][3]. This work, is also aimed to explore the effectiveness of different biomasses in the reduction of tin oxides from the residues to their metallic form [4]. 

With regard to the experimental procedure, various biomass types such as straw, wood, coconut shells etc. were used [5] and compared against traditional coke. The reduction process was carried out in crucible experiments under inert gas in completely molten systems, while optimizing the parameters of temperature, reaction time and tin residue / biomass ratio as well as fluxing, in order to minimize the concentration of impurities in the metallic phases. 

For some residues a prior leaching step is explored and compared against direct pyrometallurgical treatment. Neutral and acidic leaching was investigated with the purpose of decreasing Cl and S amounts which are potentially undesired in the following pyrometallurgical step.

In conclusion, the study demonstrates the feasibility of using biomass reducing agents as greener reducing agents for the valorization of tin residues. The approach aligns with the principles of circular economy and offers a pathway towards more sustainable metallurgical processes. The successful recovery of tin using biomasses could lead to a reduction in the industry’s carbon footprint and contribute to the conservation of natural resources.