SUMMARY
Pyrometallurgy is a family of processes that converts metal-containing ores, scrap and wastes into metal-rich phases through operations such as melting, reduction, oxidation, roasting or thermal separation at high temperatures. Particularly for multi-component feeds such as electronic waste and spent lithium-ion batteries, process temperature, atmosphere, slag chemistry and metal-slag separation are key parameters determining recovery performance.
1. Introduction: Waste or Secondary Raw Material?
As the strategic importance of metal resources increases, end-of-life products are increasingly being evaluated as “secondary raw materials.” One of the most prominent examples is electronic waste. According to the Global E-waste Monitor 2024 published by ITU and UNITAR, 62 million tonnes of electronic waste were generated worldwide in 2022, while only 22.3% was formally collected and recycled in an environmentally sound manner. The same report projects that, if current trends continue, global e-waste generation will reach 82 million tonnes by 2030.
This growth makes it necessary to improve not only waste management but also the capacity and efficiency of metal recovery technologies. E-waste can contain base metals such as copper, iron, aluminum, tin, nickel and zinc, as well as valuable metals such as gold, silver and palladium. However, because these metals are present together with plastics, ceramics, glass fibers and different metal alloys, direct single-stage separation is often not feasible.
2. What Is Pyrometallurgy?
Pyrometallurgy can broadly be defined as the conversion of metal-containing materials into metal-rich products through physical and chemical transformations at high temperatures. The objective is not simply to melt the material. Melting, reduction, oxidation, roasting, pyrolysis, slag formation and control of phase distribution can all form part of the same process chain.
A pyrometallurgical system can be simplified as follows:
Feed → Pre-treatment → Thermal Treatment → Melting/Reduction → Metal + Slag + Gas → Refining
The key is to use the thermodynamic and physical properties of the elements in the feed to concentrate the target elements in the appropriate phase. For example, elements with a high affinity for oxygen can be oxidized and directed into the slag under suitable conditions, while elements that form a metallic phase, such as copper, can accumulate in the liquid metal phase. Valuable metals are often concentrated in the main metal phase and transferred to the subsequent refining stage.
3. Critical Parameters in Process Design
3.1 Temperature
Temperature is one of the most critical variables in a pyrometallurgical process. Sufficient temperature enables feed melting, reaction progression and metal-slag separation. However, the assumption that “higher temperature = better process” is not correct. Unnecessarily high temperatures can increase energy consumption, increase the load on refractories and promote the transfer of some volatile components into the gas phase. Therefore, the design objective is to determine the optimum temperature window that enables the required metallurgical reactions.
For spent lithium-ion batteries, industrial pyrometallurgical operating temperatures above 1,000 °C are widely reported in the literature; some melting studies use temperatures in the range of 1,450–1,550 °C. The actual range varies depending on battery chemistry and process route.
PROSES MAKİNA APPLICATION NOTE
At Proses Makina, we use a horizontally rotating reaction vessel in our rotary furnace systems and design solutions capable of reaching temperatures above 1,500 °C. The rotary motion enables us to achieve more controlled heat distribution and material contact within the process. Therefore, in furnace selection, we evaluate not only maximum temperature but also homogeneous material heating, atmosphere control, capacity and casting/discharge scenarios.
3.2 Atmosphere and Oxygen Control
Even at the same temperature, changing the process atmosphere can alter metal behavior. In an oxidizing environment, some elements are oxidized and transferred to the slag, while reducing conditions can promote the conversion of metal oxides into the metallic phase. Therefore, oxygen flow rate, fuel-air ratio and, where required, controlled gas atmospheres are important parts of the process recipe.
In electronic waste processing, atmosphere control is critical not only for metallurgical efficiency but also for emissions control. Because PCBs contain polymers and brominated flame retardants, gases that may form during thermal treatment must be captured and treated in a controlled manner.
PROSES MAKİNA APPLICATION NOTE
At Proses Makina, we design our e-waste recycling solutions with the rotary furnace together with downstream processes such as mechanical preparation, anode casting and copper electrolysis. For e-waste plants, we provide turnkey solutions covering engineering, machine manufacturing, installation, process consulting and operator training.
3.3 Slag Chemistry and Metal-Slag Separation
Slag chemistry is one of the most important factors determining metal recovery in pyrometallurgical processes. Slag is the liquid phase in which metal oxides, gangue minerals and other oxide components formed during processing are collected. Slag viscosity, basicity and oxide composition can affect the separation rate of metal droplets and therefore metal losses.
Recent reviews on PCB recycling particularly emphasize that slag formation is one of the fundamental steps in the process and that improving slag chemistry can increase metal recovery efficiency.
4. Pyrometallurgy in E-Waste and PCB Recycling
Waste printed circuit boards (WPCBs) are complex feeds containing numerous metals together with polymeric and ceramic components. The literature identifies pyrometallurgy as an important industrial route for large-scale WPCB processing, particularly through melting-refining approaches.
A typical process flow can be designed as follows:
- Crushing and size reduction
- Physical preparation of the metal-rich fraction
- Drying or thermal pre-treatment
- Pyrolysis/roasting or direct melting
- Separation of the metal phase from the slag phase
- Casting of the metal phase
- Electrolytic or chemical refining
The 2022 review by Faraji et al. highlights the suitability of pyrometallurgical WPCB processes for large-scale processing, while identifying energy demand, slag management and emissions control as key areas for further development.
5. Industrial Furnace Technologies
In pyrometallurgical applications, furnace selection should not be based solely on temperature requirements. Feed form, batch size, target metal, slag quantity, atmosphere requirements, discharge method and subsequent casting/refining steps should all be evaluated together.
At Proses Makina, we use a horizontally rotating reaction vessel and hydraulic tilting mechanism in our rotary furnace systems. This enables us to discharge molten metal from the furnace door in a controlled manner. We also provide solutions that transfer the material from the furnace to a fully automatic casting unit.
6. Induction Melting: When Should It Be Preferred?
In induction melting, electric current is passed through a coil to generate a magnetic field, which produces heat within the conductive metal. This approach offers advantages for the fast, controlled and repeatable melting of precious and non-ferrous metals.
At Proses Makina, we develop induction systems for melting metals such as copper, gold, silver, platinum and palladium. We take advantage of the rapid and precise temperature control offered by induction heating and design systems capable of melting within 15–60 minutes depending on capacity.
7. Pyrometallurgy for Lithium-Ion Batteries
The main objective of pyrometallurgical recycling of lithium-ion batteries is to concentrate economically valuable metals such as nickel, cobalt and copper in the metallic alloy phase. The literature shows that industrial processes use different temperature and pre-treatment stages.
For example, one study reported recovery rates of 98.67% for Cu, 99.84% for Co and 99.77% for Ni by pre-roasting spent lithium-ion batteries at 800 °C followed by melting at 1,550 °C for 15 minutes. This result belongs to a single process study; results can vary significantly with different battery chemistries and process recipes.
| Furnace / Technology | Main Application | Process Advantage | Proses Makina Solution |
|---|---|---|---|
| Rotary Furnace | Metal recovery, melting and thermal treatment | Rotating reaction vessel promotes material movement and more homogeneous heat distribution | Systems capable of reaching temperatures above 1,500 °C; gas- or electrically heated rotary furnace solutions |
| Induction Furnace | Gold, silver, copper, platinum, palladium and other non-ferrous metals | Rapid heating and precise temperature control | Induction melting systems in different power and volume configurations according to capacity and material characteristics |
| Casting Systems | Transfer of molten metal into molds | Controlled and repeatable metal casting | Automatic or semi-automatic casting solutions designed according to melting-system capacity and product form |
However, the tendency of lithium to enter the slag at high temperatures is one of the important limitations of pyrometallurgy. Recent reviews show that, while pyrometallurgy can process different electrode chemistries, operating temperatures above 1,000 °C can result in high energy consumption; hydrometallurgical methods can provide high selectivity at lower temperatures.
8. Pyrometallurgy + Hydrometallurgy: A Hybrid Process Approach
A single process cannot always recover all metals at the same efficiency. For this reason, hybrid routes in which pyrometallurgy and hydrometallurgy are used sequentially are gaining importance in industrial recycling.
Waste → Mechanical Pre-treatment → Pyrometallurgy → Metal Alloy → Hydrometallurgy → Pure Metal/Metal Salt
In this approach, pyrometallurgy handles high-capacity and complex feeds, while hydrometallurgy can selectively dissolve the resulting metal alloy and convert it into separate products. Such integrated routes are frequently investigated in PCB and battery recycling literature to achieve high recovery and product purity together.
PROSES MAKİNA’S INTEGRATED APPROACH
At Proses Makina, we bring different process steps such as crushing/separation, rotary furnace, anode casting, copper electrolysis and chemical refining together within the same plant approach. We design turnkey process solutions according to feed type and capacity targets. This approach is important because the pyrometallurgical furnace should be designed as part of the overall metal recovery chain rather than as a standalone unit.
9. Environmental Performance and Emissions Control
The high-temperature requirements of pyrometallurgy make control of gas emissions as critical as energy consumption. Especially when processing complex feeds such as e-waste and batteries, volatile metal compounds, halogenated compounds and organic decomposition products may be generated.
Therefore, a modern pyrometallurgical plant is not limited to furnace, burner and refractory design. Gas collection, secondary combustion/post-combustion, filtration, appropriate neutralization and monitoring systems are integral parts of the process. WPCB literature particularly emphasizes the need to control dioxins, brominated compounds and gases containing heavy metals.
At Proses Makina, we incorporate a closed-system approach, gas and dust management, subsequent metal refining and wastewater treatment units into our e-waste system designs together with the rotary furnace. This demonstrates why the environmental performance of a high-temperature process must be evaluated across the entire process chain, not only by furnace temperature.
10. Advantages and Limitations of Pyrometallurgy
| Advantages | Limitations |
|---|---|
| Complex and heterogeneous feeds can be processed | High energy consumption |
| Suitable for high-capacity operation | Need for flue-gas and emissions control |
| Fast reaction kinetics | Slag formation and metal losses in slag |
| Concentration of metals such as Cu, Co and Ni in the metallic phase | Selective recovery of some elements can be difficult |
| Mature technology at industrial scale | Metal phase often requires additional refining |
| Thermal removal of organic components | Increased equipment/refractory load due to high temperatures |
11. Key Considerations in Process Design at Proses Makina
In a pyrometallurgical recovery line, furnace selection should begin with chemical characterization of the feed. The target metal, feed quantity, moisture, organic content, ash/slag-forming components, desired product form and subsequent refining steps should all be evaluated together.
- Determination of feed characterization and capacity target
- Selection of the appropriate furnace type
- Development of the temperature and atmosphere control strategy
- Design of the metal-slag balance and slag chemistry
- Design of gas collection and emissions control
- Safe and repeatable discharge of molten metal
- Integration with casting and/or subsequent hydrometallurgical-electrometallurgical processes
- Implementation of PLC/automation and process monitoring infrastructure
At Proses Makina, we cover different points of this chain with our existing product and process portfolio. With our rotary furnace solutions, we can perform thermal treatment and melting at temperatures above 1,500 °C, while our induction systems provide more controlled heating, particularly for precious metal melting applications. On the e-waste side, we can integrate mechanical preparation, pyrometallurgical processing, casting and electrolytic/chemical refining within the same project.
12. Conclusion
Pyrometallurgy uses high temperature in metal recovery not merely as a heating tool, but also as a process tool that controls chemical reactions and phase separation. It is particularly important for forming metal-rich phases from complex feeds such as electronic waste and spent lithium-ion batteries.
However, successful pyrometallurgical plant design requires more than focusing on the furnace’s maximum temperature. Temperature profile, atmosphere, slag chemistry, metal-slag separation, gas treatment, energy efficiency and subsequent refining stages must all be evaluated together.
At Proses Makina, we combine our 15 years of know-how in pyrometallurgical and chemical refining with our rotary furnace, induction melting, e-waste recycling and refining solutions. We approach pyrometallurgy not merely as “a single furnace,” but as an end-to-end metal recovery system.
In future metal recovery plants, the strongest approach is expected to be the integration of mechanical separation, pyrometallurgy, hydrometallurgy and electrometallurgy according to the characteristics of the feed, rather than relying on a single technology. The goal is not only to recover more metal, but to do so with lower energy consumption, controlled emissions, higher product purity and an economically sustainable process.