Sulfation roasting followed by water leaching has been proposed as an alternative route for recycling valuable metals from spent lithium-ion batteries (LIBs). In the present work, the reaction mechanism of the sulfation roasting of synthetic LiCoO₂ was investigated by both thermodynamic calculations and roasting experiments under flowing 10% SO₂-1% O₂-89% Ar gas atmosphere at 700°C. The products and microstructural evolution processes were characterized by x-ray diffraction, scanning electron microscope and energy dispersive x-ray spectrometer, and atomic absorption spectroscopy. It was confirmed that Co₃O₄ was formed as an intermedia product, and the final roasted products were composed by Li₂SO₄, Li₂Co(SO₄)₂, and CoO. The leaching results indicated that 99.5% Li and 17.4% Co could be recovered into water after 120 min of roasting. The present results will provide the basis and solid guidelines for recycling of Li and Co from spent LIBs.

The aim of this study was to investigate the oxidation kinetics of copper at low temperatures (60 °C to 100 °C) in air by isothermal thermogravimetric analysis (TGA) and quartz crystal microbalance (QCM). The weight change in thermogravimetric tests showed periodic weight increase and decrease. In thermogravimetric tests the mass of the copper sample increased until the oxidation gradually slowed down and finally started to decrease due to cracking and spalling of the oxide formed on the surface. In QCM tests using electrodeposited copper film, the weight change was rapid at the beginning but slowed to a linear relationship after few minutes. Temperature and exposure time appeared to have a large effect on oxide film thickness and composition. With QCM, oxidation at 60–80 °C produced less than 40 nm films in 10 days. Oxidation at 90–100 °C produced 40 nm thick films in a day and over 100 nm films in a week. Although SEM-EDS analyses in TGA tests indicated that oxygen was adsorbed on the copper surface, neither XRD patterns nor Raman spectroscopy measurements showed any trace of Cu₂O or CuO formation on the copper surface. Electrochemical reduction analysis of oxidized massive copper samples indicated that the oxide film is mostly Cu₂O, and CuO develops only after several days at 90–100 °C.

Since the current volumes of collected end-of-life lithium ion batteries (LIBs) are low, one option to increase the feasibility of their recycling is to feed them to existing metals production processes. This work presents a novel approach to integrate froth flotation as a mechanical treatment to optimize the recovery of valuable metals from LIB scrap and minimize their loss in the nickel slag cleaning process. Additionally, the conventional reducing agent in slag cleaning, namely coke, is replaced with graphite contained in the LIB waste flotation products. Using proper conditioning procedures, froth flotation was able to recover up to 81.3% Co in active materials from a Cu-Al rich feed stream. A selected froth product was used as feed for nickel slag cleaning process, and the recovery of metals from a slag (80%)–froth fraction (20%) mixture was investigated in an inert atmosphere at 1350 °C and 1400 °C at varying reduction times. The experimental conditions in combination with the graphite allowed for a very rapid reduction. After 5 min reduction time, the valuable metals Co, Ni, and Cu were found to be distributed to the iron rich metal alloy, while the remaining fraction of Mn and Al present in the froth fraction was deported in the slag.

The world of stainless steel production was 52 Mt in 2019, and the annual amount of slags including electric furnace, AOD converter, ladle, and casting tundish, was estimated at 15–17 Mt. Nowadays, only a minor fraction of slags from stainless steel production is utilized and a major part goes to landfilling. These slags contain high-value elements (Cr, Ni, Mo, Ti, V…) as oxides or in metallic form, some of them being environmentally problematic if dumped. Thus, any approach toward circular economy solutions for stainless steel slags would have great economic and environmental impacts. This contribution examines the slags from different process stages, and the available and new potential means to increase internal recycling and to modify slags composition and structure by optimizing their properties for reclaiming in high-value applications. Eventual methods are, e.g., fast controlled cooling and modifying additives. Means to recover valuable metals are discussed as well as potential product applications to utilize various slags with different chemical, physical, and mechanical properties. By integrating the treatments and steering of slags′ properties to the total process optimization system, the principles of circular economy could be achieved. Graphical