Browsing by Author "Cabral, Marta"
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- Characterization of spent Ni-MH batteriesPublication . Cabral, Marta; Nogueira, Carlos; Margarido, F.
- Characterization of Spent Ni-MH BatteriesPublication . Cabral, Marta; Margarido, F.; Nogueira, CarlosSpent Ni-MH batteries are not considered too dangerous for the environment, but they have a considerable economical value due to the chemical composition of electrodes which are highly concentrated in metals. The present work aimed at the physical and chemical characterisation of spent cylindrical and thin prismatic Ni-MH batteries, contributing for a better definition of the recycling process of these spent products. The electrode materials correspond to more than 50% of the batteries weight and contain essentially nickel and rare earths (RE), and other secondary elements (Co, Mn, Al). The remaining components are the steel parts from the external case and supporting grids (near 30%) containing Fe and Ni, and the plastic components (<10%). Elemental quantitative analysis showed that the electrodes are highly concentrated in metals. Phase identification by X-ray powder diffraction combined with chemical analysis and leaching experiments allowed advancing the electrode materials composition. The cathode is essentially constituted by 6% metallic Ni, 66% Ni(OH)2, 4.3% Co(OH)2 and the anode consists mainly in 62% RENi5 and 17% of substitutes and/or additives such as Co, Mn and Al.
- End-of-life Zn–MnO2 batteries: electrode materials characterizationPublication . Cabral, Marta; Pedrosa, Fátima; Margarido, F.; Nogueira, CarlosPhysical and chemical characterization of several sizes and shapes of alkaline and saline spent Zn–MnO2 batteries was carried out, aiming at contributing for a better definition of the applicable recycling processes. The characterization essays included the mass balance of the components, cathode and anode elemental analysis, the identification of zinc and manganese bearing phases and the morphology analysis of the electrode particles. The electrode materials correspond to 64–79% of the total weigh of the batteries, with the cathodes having clearly the highest contribution (usually more than 50%). The steel components, mainly from the cases, are also important (17–30%). Elemental analysis showed that the electrodes are highly concentrated in zinc (from 48–87% in anodes) and manganese (from 35–50% in cathodes). X-Ray powder diffraction allowed for identifying several phases in the electrodes, namely zinc oxide, in the anodes of all the types of saline and alkaline batteries tested, while zinc hydroxide chloride and ammine zinc chloride only appear in some types of saline batteries. The manganese found in the cathode materials is present as two main phases, MnO·Mn2O3 and ZnO·Mn2O3, the latter corroborating that zinc migration from anode to cathode occurs during the batteries lifespan. A unreacted MnO2 phase was also found presenting a low crystalline level. Leaching trials with diluted HCl solutions of alkaline and saline battery samples showed that all zinc species are reactive attaining easily over than 90% leaching yields, and about 30% of manganese, present as Mn(ii/iii) forms. The MnO2 phase is less reactive and requires higher temperatures to achieve a more efficient solubilization.
- Integration of physical operations in the hydrometallurgical processing of spent Zn-MnO2 batteriesPublication . Pedrosa, Fátima; Feu, J. P.; Cabral, Marta; Nogueira, Carlos; Margarido, F.The recycling of spent Zn-MnO2 batteries by hydrometallurgy involves the leaching of material previously treated by physical processing to allow the liberation of electrode particles and the separation of unwanted scrap. The integration of these physical operations with leaching is therefore crucial for the optimization of the process, allowing achieving high recovery yields of zinc and manganese and minimizing reactants consumption and iron contamination. In this paper, several options involving physical processing and leaching with sulphuric acid are presented and discussed. After batteries shredding and disaggregation, the separation of steel scrap was performed by sieving or magnetic separation, and the remaining solids were treated by leaching. These options were compared, in terms of metals recovery and contamination, with the alternative of direct leaching of all the shredded fractions without physical treatment. The separation of the steel scrap by sieving or magnetic separation allowed the removal from the circuit of 37 or 49% of iron, respectively, with losses of 15 or 6% of zinc and 2 or 4% of manganese. Therefore more than 50% of iron remained in the process, which was attributed to the presence of iron oxides formed by the corrosion of the battery cases. In the leaching operation, zinc dissolution was very effective (yields above 97%) while manganese is strongly depended from the process option, being its leaching proportional to the presence of scrap (yields of 80%, 56% and 43%, respectively in direct leaching, sieving / leaching and magnetic separation / leaching). These results showed that iron plays an important role in the reductive leaching of manganese species (III or IV), and so the presence of steel scrap in leaching, besides disadvantages concerning solutions contamination, contributes positively for the leaching efficiency
- Leaching behavior of several zinc rich residues in a hydrometallurgical recycling processPublication . Pedrosa, Fátima; Cabral, Marta; Nogueira, Carlos; Margarido, F.The leaching of metals contained in spent Zn-MnO2 batteries and electric arc furnace (EAF) dusts using sulfuric acid solutions was studied, in order to evaluate the feasibility of simultaneous treatment of both wastes by a hydrometallurgical process. In both residues, a substantial quantity of zinc was solubilized (about 100% in batteries and 70-80% in EAF dusts) in diluted acid solutions and room temperature, corresponding to the reaction of zinc oxide species. Other species were more refractory to the chemical attack, namely the manganese (III or IV) oxides in batteries and the zinc ferrite in dusts, requiring higher temperatures (e.g. 90ºC) and higher leachant concentrations. Lead present in EAF dusts was not solubilized in sulfate media, thus remaining in the leach residue. Results seem to confirm the possibility of treatment of both zinc-containing residues by the same hydrometallurgical process, eventually involving two leaching stages – diluted acid leaching and hot acid leaching – followed by solution purification through iron precipitation and Zn/Mn separation and recovery. Concerning lead, a second leaching circuit in chloride media could be developed for its potential recovery.
- Leaching studies for metals recovery from printed circuit boards scrapPublication . Oliveira, Paula; Cabral, Marta; Taborda, F. Charters; Margarido, F.; Nogueira, CarlosIn this paper, the leaching behavior of the major metals present in printed circuit boards waste is evaluated, aiming at its recycling by hydrometallurgy. Several leachants were compared (sulfuric, hydrochloric and nitric acids, at 2 M H+ concentration), at temperatures of 25ºC and 90ºC and 4 hours of reaction time. Sulfuric acid leaching was not very promising concerning metals dissolution being only effective for iron. Hydrochloric acid allowed the leaching up to 60% of tin and about 50% of lead, as well as the iron. Nitric acid was the most efficient leachant due to its oxidizing properties. Recoveries of 90% or more for copper, iron, nickel and zinc were achieved at the higher temperature. Lead was also dissolved (up to 80%), as well as silver (more than 70%). These results show that the hydrometallurgical recovery of most of the metals present in PCB’s scrap is a technically feasible alternative that shall be considered and evaluated.
- Physical processing efficiency of saline vs. alkaline spent batteriesPublication . Cabral, Marta; Nogueira, Carlos; Margarido, F.Physical processing of spent batteries which includes shredding and sieving operation is the first step for chemical treatment by hydrometallurgy. A laboratory study was carried out to evaluate physical processing efficiency, by analysing the resulting particle size, of alkaline and saline mignon-type Zn-MnO2 batteries. After shredding with a tip shredder, results obtained showed that alkaline batteries were more efficiently size reduced than saline batteries. Difference in particle size distribution was larger for granulometric fraction -20+11.2 mm and also higher for saline batteries. Average diameters (d50) for saline and alkaline batteries were respectively 9.1 and 6.2 mm. Chemical composition carried out on several granulometric fractions allowed to identify metals distribution through size categories. This analysis showed that zinc concentration with the grain size was almost constant, while manganese decreased when particle size increased. More than 95% of iron scarp from the battery cases had a particle size higher than 5.6 mm.
- Recycling of exhausted batteries and EAF dusts by leaching with several aqueous mediaPublication . Pedrosa, Fátima; Cabral, Marta; Margarido, F.; Nogueira, CarlosZinc is a base metal present in several products of general use, and therefore found in numerous residues and end-of-life products. The two main sources of zinc containing wastes are spent Zn-MnO2 portable batteries and electric arc furnace (EAF) dusts from steelmaking plants. The recovery of metals from these residues by appropriate recycling processes is mandatory due to environmental, economic and resource conservation issues. Concerning the similar composition of both residues, their simultaneous processing can be envisaged. The research herein described consists on the hydrometallurgical treatment of zinc bearing waste, where several leaching routes for solubilising metals, mainly zinc, are studied. The leaching of shredded batteries and EAF dusts was carried out using three different leaching solutions containing sulfuric acid, hydrochloric acid or ammonium chloride. The acid leaching of zinc in the oxide form (zincite) using both acids, was very efficient and quick, allowing the recovery of practically all Zn contained in batteries and about of 80% of Zn in dusts. Regarding to the leaching media the behaviour of lead oxides present in dusts was different, being insoluble with H2SO4 and partially soluble with HCl (40-90% yield, depending on conditions). For battery waste stream, manganese is also other important metal, which oxides were only partially soluble in acid media, attaining a maximum leaching yield of 90% Mn. Iron, considered a contaminant in both residues, was partially leached and required further purification steps. The use of an ammoniacal medium (NH4Cl) was very selective for zinc, being iron practically insoluble. However, the maximum zinc leaching yield attained for both residues was only near 60%. Under these conditions, manganese contained in batteries was very insoluble while lead from dusts was leached up to 70% due to the relative solubility of lead chloride. This research showed that hydrometallurgical treatment can provide versatile solutions for recycling metals from Zn waste. Ammoniacal leaching allows high selectivity for zinc but less recovery efficiency is attained, while acid leaching allows higher metal recovery yields but unwanted elements like iron are co-dissolved.
- Recycling of zinc bearing residues: leaching behavior of spent batteries and eaf dusts in several aqueous mediaPublication . Pedrosa, Fátima; Cabral, Marta; Nogueira, Carlos