F. Margarido

Leaching behaviour of electrode materials of spent nickel–cadmium batteries in sulphuric acid media

Abstract The improving awareness of environmental problems associated with the toxicity of heavy metals keeps the recycling of spent nickel–cadmium batteries an important assignment due to the presence of cadmium, nickel and cobalt on the electrode material. While cadmium from batteries is one of the major sources of cadmium contamination of the environment, the other heavy metals contained on the electrode material have a considerable economic value. Therefore a complete and valorising solution to the management of this type of residues is not possible through the existing pyrometallurgical processes because the treatment of complex materials in order to recycle all materials is difficult. An integrated process based on physical and hydroelectrometallurgical operations seems to be more efficient because it is possible to recover the three metals, Cd, Ni and Co, present on the electrode material. The study here presented deals with the first chemical stage of an integrated process, the leaching of spent nickel–cadmium electrodes with sulphuric acid. The electrode materials essentially composed of Ni, Cd and Co hydroxides were readily solubilised in 0.5 h with low acid concentrations (pH∼1) at ambient temperature. At higher pH values the solubilisation of metal hydroxides was inefficient, except when using long residence times. The leaching of nickel present in the metallic form, in the electrodes, was more difficult due to kinetic constraints, applying high temperature (e.g. 95 °C) and acid concentration (e.g. 2.5 M H 2 SO 4 ) in order to obtain complete conversions in acceptable time (∼4 h).

Kinetics of acid leaching refining of an industrial Fe-Si alloy

Abstract The effects of the three leaching parameters (concentration of HCl and FeCl 3 and stirring) on the purification of an industrial Fe-Si alloy, containing phases such as Fe-Al-Si-Ca (caalsifer) and FeSi 2 , with a high Ca/Al ratio, were studied. The leaching residues, after analysis for particle size distribution, were characterized chemically, morphologically by scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and structurally by X-ray diffraction. The experimental results conform with the cracking shrinking model, according to which a mechanism is proposed for the dissolution of the main impurities (Ca, Al and Fe). The leaching of these impurities was found to depend on the composition of the phases and nature of their distribution. For the proposed model, the leaching of the impurities are under chemical reaction control, which is in agreement with the microstructure observed by SEM/EDS.

The structural effect on the kinetics of acid leaching refining of Fe-Si alloys

Abstract The kinetics of refinement of Fe-Si alloys by acid leaching is affected by their structural state. Two different phase constitutions were studied to access this effect: an industrial alloy with a low Al Ca ratio and a laboratory-prepared alloy with a high Al content. The first contains silicon, FeSi 2 (tet.), FeSi 2 (orth.), beyond a quaternary phase Fe-Al-Si-Ca (Caalsifer), CaAi 2 Si 1.5 , CaSi 2 , Al-Fe-Si as minor phases. The precipitation of Al-Fe-Si phases is induced in the second by the high Al Ca ratio. In a previous study, leaching experiments by a two-step procedure have shown that Ca-Al-Si, Caalsifer and Al-Fe-Si phases are more soluble. The Cracking Shrinking Model (CSM) was applied to explain the behaviour of the industrial alloy. In the present study, it is shown that the same model applies to the kinetics of dissolution of the laboratory-prepared alloy and also, that an adequate control of Fe Al vs. Si Ca ratios may improve the attainable refining yield.

The cracking shrinking model for solid-fluid reactions

A model based on the shrinking principle is developed to describe the non-catalytic solid-fluid reactions when particles crack during the process. Analytical and numerical solutions of the governing equations under isothermal conditions are presented for some reaction orders, valid for all geometries considered. Experimental results of refining of Fe-Si alloys by acid leaching are suggested as an example of data-fitting.

End-of-life Zn–MnO2 batteries: electrode materials characterization

Physical 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.

CAALSIFER: A quaternary FeAlSiCa phase isotypic with α-leboite (Fe1−xSi2)

Abstract The results of a structural and chemical study of a quaternary Feue5f8Alue5f8Siue5f8Ca phase detected by scanning electron microscopy in ferrosilicon industrial alloys are reported. Experimental and calculated X-ray diffraction intensities are compared for α-Fe1−xSi2 (leboite) and the new phase assuming four models with respect to the nature and distribution of substitutional impurities (aluminium and calcium) and other structural defects (vacancies): FeSi2, Fe0.8Si2, Fe(Si0.8Ca0.2)2 and Fe0.8Al0.1)(Si0.8Ca0.2)2. The best fit is attained for the last crystal chemical model. The presence of the new phase (which we designate CAALSIFER)is discussed in connection with the possible hindering of α-to-β transformation in industrial leboite, which is a main component in 75 wt.% Si alloys. Implications for the hydrometallurgical process of Feue5f8Si refining are briefly considered.

Refining of FeSi alloys by acid leaching

Abstract The effect of structural composition on the purification of Feue5f8Si alloys by acid leaching is analyzed. Two alloys with different phase constitution were studied: industrial ferro-silicon, with a high Ca Al ratio containing a quaternary phase Feue5f8Alue5f8Siue5f8Ca (Caalsifer) together with FeSi2 phases; and a laboratory prepared alloy in which the high Al content induces the precipitation of Alue5f8Feue5f8Si phases preferably to Caalsifer, and hinders the formation of tetragonal and orthorhombic FeSi2. The leaching behaviour of the various phases, which incorporate the major impurities (Alue5f8Feue5f8Si, FeSi2, Caalsifer, Caue5f8Si and CaAl2Si1.5) was studied using a two-step procedure: the first stage with HCl (22%, 6 h, 102°C) and the second with HCl+FeCl3·6H2O (22%+40%, 12 h, 102°C). The results show that both Caalsifer and Alue5f8Feue5f8Si phases are susceptible to leaching, while tetragonal and orthorhombic FeSi2 remain as solid residues.

Hydrometallurgical recycling of lithium-ion batteries by reductive leaching with sodium metabisulphite

The hydrometallurgical extraction of metals from spent lithium-ion batteries (LIBs) was investigated. LIBs were first dismantled and a fraction rich in the active material was obtained by physical separation, containing 95% of the initial electrode, 2% of the initial steel and 22% of plastic materials. Several reducers were tested to improve metals dissolution in the leaching step using sulphuric acid. Sodium metabisulphite led to the best results and was studied in more detail. The best concentration of Na2S2O5 was 0.1u202fM. The metals dissolution increased with acid concentration, however, concentrations higher than 1.25u202fM are unnecessary. Best results were reached using a stirring speed of 400u202fmin-1. The metals leaching efficiency from the active material (Li, Mn, Ni, Co) increased with the temperature and was above 80% for temperatures higher than 60u202f°C. The dissolution of metals also rose with the increase in the liquid/solid ratio (L/S), however, extractions above 85% can be reached at L/S as lower as 4.5u202fL/kg, which is favourable for further purification and recovery operations. About 90% of metals extraction can be achieved after only 0.5u202fh of leaching. Sodium metabisulphite can be an alternative reducer to increase the leaching of Li, Mn, Co, and Ni from spent LIBs.

Economics of End-of-Life Materials Recovery: A Study of Small Appliances and Computer Devices in Portugal

The challenges brought on by the increasing complexity of electronic products, and the criticality of the materials these devices contain, present an opportunity for maximizing the economic and societal benefits derived from recovery and recycling. Small appliances and computer devices (SACD), including mobile phones, contain significant amounts of precious metals including gold and platinum, the present value of which should serve as a key economic driver for many recycling decisions. However, a detailed analysis is required to estimate the economic value that is unrealized by incomplete recovery of these and other materials, and to ascertain how such value could be reinvested to improve recovery processes. We present a dynamic product flow analysis for SACD throughout Portugal, a European Union member, including annual data detailing product sales and industrial-scale preprocessing data for recovery of specific materials from devices. We employ preprocessing facility and metals pricing data to identify losses, and develop an economic framework around the value of recycling including uncertainty. We show that significant economic losses occur during preprocessing (over

Kinetic approach to the study of froth flotation applied to a lepidolite ore

70 M USD unrecovered in computers and mobile phones, 2006-2014) due to operations that fail to target high value materials, and characterize preprocessing operations according to material recovery and total costs.