A critical updated review of the hydrometallurgical routes for recycling zinc and manganese from spent zinc-based batteries

Preparation of Mn/TiO2 catalysts using recovered manganese from spent alkaline batteries for low-temperature NH3-SCR

Black mass (BM) from spent alkaline Zn-MnO2 batteries was used for the first time as a Mn source in the preparation of Mn/TiO2 catalysts for low-temperature NH3-selective catalytic reduction (SCR) of NOx. To recover Mn species and eliminate alkali and Zn species, BM powder underwent DI-water washing, followed by carbothermal reduction. The resulting slags were further dissolved in HNO3, loaded onto TiO2 particles with ball milling, and then subjected to calcination. Nearly 100% of Zn species were removed from the BM via carbothermal reduction at 950 °C for 4 h with 5.0 wt% activated carbon. The resulting catalyst, derived from the treated BM, achieved similar NOx conversion (97%) as the catalyst prepared using a reagent-grade Mn chemical at 160 °C but a higher NOx-to-N2 conversion rate at 78%. The promoted N2 selectivity was attributed to a high Mn4+/Ti ratio and the presence of impurities from BM, such as Fe3+ ions, which enhanced oxidation ability of the catalyst. Conversely, insufficient removal of Zn or carbon additives in the slags led to a decreased Mn concentration, an increased proportion of Mn2+/Mn3+ species, increased surface OH groups, and reduced oxidation ability on the surface, thus reducing NOx conversion and N2 selectivity.

Towards More Sustainable Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are considered as the promising candidates for large-scale energy storage because of their high safety, low cost and environmental benignity. The large-scale applications of AZIBs will inevitably result in a large amount of spent AZIBs, which not only induce the waste of resources, but also pose environmental risks. Therefore, sustainable AZIBs have to be considered to minimize the risk of environmental pollution and maximize the utilization of spent compounds. Herein, this minireview focuses on the sustainability of AZIBs from material design and recycling techniques. The structure and degradation mechanism of AZIBs are discussed to guide the recycling design of the materials. Subsequently, the sustainability of component materials in AZIBs is further analysed to pre-evaluate their recycling behaviors and mentor the selection of more sustainable component materials, including active materials in cathodes, Zn anodes, and aqueous electrolytes, respectively. According to the features of component materials, corresponding green and economic approaches are further proposed to realize the recycling of active materials in cathodes, Zn anodes and electrolytes, respectively. These advanced technologies endow the recycling of component materials with high efficiency and a closed-loop control, ensuring that AZIBs will be the promising candidates of sustainable energy storage devices. This review will offer insight into potential future directions in the design of sustainable AZIBs.

Functionalized graphene/polystyrene composite, green synthesis and characterization

A composite of sulfonated waste polystyrene (SWPS) and graphene oxide was synthetized by an inverse coprecipitation in-situ compound technology. Polystyrene (PS) has a wide range of applications due to its high mechanical property. the graphene were incorporated into sulfonated polystyrene (SPS) to improve the thermal stability and mechanical performance of the composites. Functionalized graphene were synthesized with tour method by using recovered anode (graphite) of dry batteries while sulfonated waste expanded polystyrene was obtained through sulfonation of the polymer. The SPS and GO + SPS composite were characterized using by Fourier Transform Infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). While the degree of sulfonation (DS) was determined through elemental analysis. The results show the degree of sulfonation of the composite is 23.5% and its ion exchange capacity is 1.2 meq g^-1. TEM analysis revealed that the GO particles were loaded on the surface of sulphonated polystyrene and that the SWPS was intercalated into the sub-layers of nanoG homogeneously, which result in an increase in electrical conduction.

Direct recovery of Zn from wasted alkaline batteries through selective anode's separation

In the present study, a leaner process for recovering zinc from spent alkaline batteries is studied at a laboratory scale. Such process is part of a diagram, under development, that aims at maximizing the value of all the battery components while reducing the costs of treatment and the environmental footprint involved in recycling this waste. It starts by a physical and selective pre-treatment stage that separates the anode from the remaining components followed by neutral leaching (three washing cycles at room temperature, S/L ratio of 1/5 (w/v), magnetic stirring for 15 min and settling during 45 min), acid leaching of the washed solid (4 mol/L of sulphuric acid, S/L ratio of 1/3 (w/v), 120 min at room temperature under magnetic stirring) and, finally, electrowinning of zinc from the pregnant leach solution (100 mA/cm², 120 min under slow magnetic stirring). By leaching the anode alone, it is possible to obtain a solution rich in zinc (86 g/L), with very low concentration of other metals (<0.08 g/L). Such solution was adequate for zinc electrowinning, allowing an average recovery rate of 58%, without applying any purification stages, at the same time regenerating sulphuric acid for its recirculation. In conclusion, the results demonstrate that a more specific physical pre-treatment stage is highly desirable to recycle spent alkaline batteries in order to reduce the number of stages involved and the overall complexity, thus, reducing the costs involved and the potential environmental impacts, while maintaining high recovery rates of zinc.

Synthesis of nZnO from waste batteries by hydrometallurgical method for photocatalytic degradation of organic pollutants under visible light irradiation

Waste zinc carbon (Zn-C) batteries are generated worldwide in a large amount. They are non-rechargeable and costly to recycle. Therefore, they end up in the landfills where they create hazards for humans and for environment as well. Zn-C batteries are rich in concentration of different heavy metals so they can be subjected for the recovery of metals for the development of valuable new materials. In this study authors have proposed an easy hydrometallurgical method for the recovery of zinc from waste Zn-C batteries to synthesize nano zinc oxide (nZnO) photocatalyst. The prepared nZnO particles were irregular in shape, highly crystalline in nature with crystallite size 23.94 nm. The band gap of the photocatalyst was 3.1 eV. The photocatalytic activity of the synthesised nZnO was tested for the degradation of three organic pollutants namely; phenol, p-nitrophenol (PNP) and crystal violet dye (CV) in an aqueous solution under visible light irradiation. nZnO showed a good catalytic efficiency for the degradation of all the three pollutants, however, the crystal violet (CV) removal was best in comparison with the other pollutants, it was minimally effected by the increase in CV concentration. The maximum degradation of phenol, PNP and CV was found to be 95.03 ± 0.2%, 88.63 ± 0.1% and 97.87 ± 0.4%, respectively. The degradation data was fitted best with pseudo-first-order kinetic model. The photocatalyst was recyclable and its regeneration ability was higher for initial three cycles. The intermediate compounds formed in the process of degradation were determined by liquid chromatography and mass spectroscopy (LC-MS) analysis.

Studies of Selective Recovery of Zinc and Manganese from Alkaline Batteries Scrap by Leaching and Precipitation

Recovery of zinc and manganese from scrapped alkaline batteries were carried out in the following way: leaching in H₂SO₄ and selective precipitation of zinc and manganese by alkalization/neutralization. As a result of non-selective leaching, 95.6-99.7% Zn was leached and 83.7-99.3% Mn was leached. A critical technological parameter is the liquid/solid treatment (l/s) ratio, which should be at least 20 mL∙g^-1. Selective leaching, which allows the leaching of zinc only, takes place with a leaching yield of 84.8-98.5% Zn, with minimal manganese co-leaching, 0.7-12.3%. The optimal H₂SO₄ concentration is 0.25 mol∙L^-1. Precipitation of zinc and manganese from the solution after non-selective leaching, with the use of NaOH at pH = 13, and then with H₂SO₄ to pH = 9, turned out to be ineffective: the manganese concentrate contained 19.9 wt.% Zn and zinc concentrate, and 21.46 wt.% Mn. Better selectivity results were obtained if zinc was precipitated from the solution after selective leaching: at pH = 6.5, 90% of Zn precipitated, and only 2% manganese. Moreover, the obtained concentrate contained over 90% of ZnO. The precipitation of zinc with sodium phosphate and sodium carbonate is non-selective, despite its relatively high efficiency: up to 93.70% of Zn and 4.48-93.18% of Mn and up to 95.22% of Zn and 19.55-99.71% Mn, respectively for Na₃PO₄ and Na₂CO₃. Recovered zinc and manganese compounds could have commercial values with suitable refining processes.