The main objective described in this paper is the optimization of technological parameters in the production of varistors based on recycled zinc oxide (ZnO). The content of this paper builds on our previous research aimed at proving that hydrometallurgically recovered ZnO material, from electric arc furnace dust, is suitable for applications in these semiconductors, an issue which has received very little attention at present. The focus of this research also corresponds to and supports the visions and strategies of environmental sustainability and the circular economy. Samples of ZnO varistors manufactured for this purpose were analyzed by scanning electron microscopy and then the electrical parameters were measured and calculated. Based on the results of the microstructural analysis and electrical properties, prerequisites for the optimal adjustment of technological parameters such as sintering temperature and sintering time were derived, which will be the starting point for further research.

In this work, a method for leaching black mass from spent Li batteries using oxalic acid was developed and experimentally verified with the objective of selectively separating lithium and cobalt. Oxalic acid proved to be an efficient and selective leaching agent. Under 1 M C₂H₂O₄, 120 min, L:S = 20, 80 °C and 300 rpm, a lithium yield of 90% was achieved, while cobalt dissolution remained low at 1.57%. Subsequently, cobalt spontaneously precipitated from the leachate within several hours, and the solid phase was fully separated after 24 h. The leachate contained minor amounts of accompanying metals, with dissolution yields of 0.5% Mn, 8% Fe and 1.4% Cu. These impurities were removed from the leachate by controlled pH adjustment using NaOH at ambient temperature and 450 rpm, with complete precipitation at pH 12. This procedure generated a purified lithium-rich leachate, which was converted into lithium oxalate by crystallisation at 105 °C. Subsequent calcination of the resulting solid at 450 °C for 30 min produced Li₂CO₃ with a purity of 91%. Based on the experimental findings, a conceptual technological process for selective lithium leaching using oxalic acid was proposed, demonstrating the potential of this method for sustainable lithium recovery.

This paper presents a literature review on the processing of used lithium-ion batteries in both industry and research. On an industrial scale, lithium-ion batteries are primarily processed through pyrometallurgical methods, leading to incomplete utilisation of lithium cells. On the other hand, the hydrometallurgical route of recycling lithium-ion batteries poses challenges, such as large-scale discharging or inert gas pretreatment, largely due to explosion hazards. Modern methods of lithium-ion battery recycling are oriented toward refining the leach liquor through solvent extraction methods using D2EHPA and Cyanex 272, to recover Co, Mn, and Ni. The final Li product is obtained through Na2CO3 precipitation.