The significant increase in the demand for efficient electric energy storage during the past decade has promoted an increase in the production and use of Cd-containing batteries. On the one hand, the amount of toxic Cd-containing used batteries is growing, while on the other hand, Cd is on a list of critical raw materials (for Europe). Both of these factors call for the development of effective technology for Cd recovery from spent batteries. The present paper is aimed at providing a short review of the recent progress in Cd recovery from spent batteries. Statistical data from the past decade on the source of Cd, its global production, and Ni-Cd battery recycling are given in the introduction. A short overview of the pyro-and hydro-metallurgical methods of metal production is provided. Recent progress in Cd recovery by commercial methods during the past decade is reviewed.

Various metals and semiconductors containing printed circuit boards (PCBs) are abundant in any electronic device equipped with controlling and computing features. These devices inevitably constitute e-waste after the end of service life. The typical construction of PCBs includes mechanically and chemically resistive materials, which significantly reduce the reaction rate or even avoid accessing chemical reagents (dissolvents) to target metals. Additionally, the presence of relatively reactive polymers and compounds from PCBs requires high energy consumption and reactive supply due to the formation of undesirable and sometimes environmentally hazardous reaction products. Preliminarily milling PCBs into powder is a promising method for increasing the reaction rate and avoiding liquid and gaseous emissions. Unfortunately, current state-of-the-art milling methods also lead to the presence of significantly more reactive polymers still adhered to milled target metal particles. This paper aims to find a novel and double-step disintegration–milling approach that can provide the formation of metal-rich particle size fractions. The morphology, particle fraction sizes, bulk density, and metal content in produced particles were measured and compared. Research results show the highest bulk density (up to 6.8 g·cm⁻³) and total metal content (up to 95.2 wt.%) in finest sieved fractions after the one-step milling of PCBs. Therefore, about half of the tested metallic element concentrations are higher in the one-step milled specimen and with lower adhered plastics concentrations than in double-step milled samples.

Alkaline nickel-cadmium batteries are among the most used industrial high-power sources. Despite stricter environmental requirements, nickel-cadmium batteries still remain as the main choice for highly reliable power sources for heavy-loaded equipment. Therefore, recovery of cadmium (Cd) from spent batteries is a challenge for the modern recycling industry, particularly as it displays high bio-toxicity. The present study describes a new green approach for Cd recovery from cadmium oxide (CdO). The paper discusses using a ternary chloride composition consisting of calcium, potassium and sodium chloride, thereby avoiding the release of Cd vapour from the reaction volume during the reduction reaction from CdO. For the protective slag layer during the reduction process (which occurs at 650 °C), a 0.515:0.0796:0.405 molar ratio of CaCl₂:KCl:NaCl was chosen, with the aim of achieving a melting point at 483 °C. To describe phase and elemental composition of obtained products X-ray diffraction analysis and energy dispersive X-ray spectroscopy, respectively, were applied. Electron and optical microscopy were used for morphological observations. The presence of the metallic Cd was noted. During the reduction reaction, it was noted that slag separated into two parts: a protective upper layer and bottom layer. It was also noted that metallic Cd accumulated with increasing reaction time in the bottom part of the slag.

The recycling of nickel–cadmium batteries poses a significant environmental challenge due to cadmium’s high biotoxicity. This study proposes a green method for recovering cadmium from cadmium oxide (CdO) using carbon (coal) in the presence of a molten binary flux (KCl:NaCl = 0.507:0.493, melting point 667 °C). The flux’s relatively low density and conductivity enable cadmium reduction beneath and through the flux layer. Brown coal (5–25 mm) served as the reductant. The reduction of cadmium from cadmium oxide with carbon (brown coal) took place in the temperature range from 667 °C to 700 °C. To enhance the process, electrovortex flows (EVF) were employed—generated by the interaction between non-uniform AC electric currents and their self-induced magnetic fields resembling conditions in a fluidised bed reactor. The graphite crucible acted as both one of the electrodes, with a graphite rod as the second electrode. As Cd and CdO are denser than both the flux and coal, the reduction proceeded below the flux layer. The flux facilitated CdO transport to the reductant, speeding up the reaction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the formation of metallic cadmium beneath and within the flux layer. This method demonstrates the feasibility of flux-assisted cadmium recovery without prior mixing and offers a foundation for further optimisation of sustainable battery recycling.

This study presents a carbon footprint assessment of a novel electroslag method for cadmium (Cd) recovery from spent nickel–cadmium (Ni-Cd) batteries in comparison with the carbon footprints of pyrometallurgical and hydrometallurgical cadmium recovery methods. A comparison of CO₂ emissions in three types of technological processes during the recovery of 1 kg of cadmium is carried out. Energy inputs and CO₂ emissions are calculated for the electroslag process and compared to conventional methods, such as pyrometallurgical and hydrometallurgical reduction methods. The electroslag process eliminates cadmium vaporization by using molten KCl–NaCl flux and carbon under electromagnetic stirring. Cadmium reduction occurs under a layer of flux, which prevents the contact of the reduced cadmium with the atmosphere. The electroslag process temperature is limited to 700 °C, which is lower than the boiling point of cadmium (767 °C). The electroslag remelting process uses molten KCl–NaCl flux and carbon as a reductant under electrovortex flow stirring. The pyrometallurgical method for extracting cadmium from nickel–cadmium batteries is based on the reduction of cadmium with carbon at high temperatures. In the pyrometallurgical process, coal (anthracite) is used as the carbonaceous material, which can extract 99.92% of cadmium at 900 °C. Cadmium is separated using a vacuum at temperatures ranging from 800 °C to 950 °C for several hours. Hydrometallurgy is a metal extraction process involving chemical reactions that occur in organic or aqueous solutions at low temperatures. The hydrometallurgical process involves a series of acid or alkaline leaches, followed by separation and purification methods such as absorption, cementation, ion exchange, and solvent extraction to separate and concentrate metals from leach solutions.

The recycling of nickel-cadmium batteries poses a significant environmental challenge due to cadmium’s high biotoxicity. This study proposes a green method for recovering cadmium from cadmium oxide (CdO) using carbon (coal) in the presence of a molten binary flux (KCl:NaCl = 0.507:0.493, melting point 667°C). The flux's relatively low density and conductivity enable cadmium reduction beneath and through the flux layer, resembling conditions in a fluidised bed reactor. Coarse coal (5–25 mm) served as the reductant. To enhance the process, electrovortex flows (EVF) were employed—generated by the interaction between non-uniform AC electric currents and their self-induced magnetic fields. The graphite crucible acted as both one of the electrodes, with a graphite rod as the second electrode. As Cd and CdO are denser than both the flux and coal, the reduction proceeded below the flux layer. The flux facilitated CdO transport to the reductant, speeding up the reaction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the formation of metallic cadmium beneath and within the flux layer. This method demonstrates the feasibility of flux-assisted cadmium recovery without prior mixing and offers a foundation for further optimisation of sustainable battery recycling.