Papers by Author: Fernanda Margarido

Abstract: Spent 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.

Abstract: In the industrial production of rice, large quantities of rice husk are generated constituting a residue with costs for the companies, which must be appropriately managed. The high grade of silica in the rice husk opens a possibility for its valorisation, through the production of amorphous silica with high porosity and potential application as ligand in construction materials, as catalyst support, as metals adsorbent, among others. In this research work a process was developed for the production of silica with amorphous properties from rice husk waste, and the products formed were characterised. The process involved three main operations: water washing for removal of some impurities, acid leaching with HCl or H₂SO₄ solutions for dissolution of contaminating metals and incineration for organics decomposition. The washing operation let a partial purification of the husk, allowing removal of 46-60% of contaminating metals such as K, Fe Mn and Zn. The leaching with 0.4M HCl and 0.2M H₂SO₄ allowed obtaining high metals removal efficiency, namely >99% for potassium, 85-90% for iron, >96% for manganese and >80% for zinc. The final composition of the leached husk was 0.003-0.006% K, 0.016-0.025% Fe, <0.001% Mn and <0.0007% Zn. The incineration of the rice husk after previous purification was performed at 540°C, by using samples obtained in the several chemical treatment conditions, and using different heating and cooling rates. As a result, a white colored final husk ash was produced, rich in quasi-amorphous silica (confirmed by X-ray diffraction). The analysis by scanning electron microscopy revealed that the organics removal allowed the formation of voids in the rice husk material, which became very porous and presented an alveolar morphology.

Abstract: The aluminum anodising industry is an important industrial sector that produces great amounts of polluted effluents, which after treatment generate sludge. This fact brings environmental and economical concerns to the companies. Best way to deal with the problem, according to the “prevention strategy” set by the European Directive on Integrated Pollution Prevention and Control, is to implement preventive techniques and technologies to optimise the use of resources and minimise losses, and in turn waste. Among the operations of an anodising line, the etching/satinising stage is responsible for the production of a huge quantity of wastewater neutralisation sludge and for the wrong use of caustic soda. “Caustic etch recovery” technology is claimed to drastically reduce the generation of neutralisation sludge and the purchasing of fresh caustic soda by regenerating the exhausted etching/satinising solution, through an aqueous precipitation reaction. This paper presents the capability of the technology to effectively regenerate the exhausted caustic solution, and investigated the parameters with major effect on the process yield, in order to optimise it. It was demonstrated that the technology effectively recovers the solution, increases its soda content and diminishes the dissolved aluminum content by precipitation. Moreover the conditions that optimise the process are simple and inexpensive. After treatment the solution present the properties to be recycled in the etching/satinising operation.

Abstract: Zinc 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.

Abstract: Circuit boards present in most electric and electronic devices are very important components, which should be removed during sorting and dismantling operations in order to allow further adequate treatment for recovering valuable metals such as copper, nickel, zinc, lead, tin and rare elements. This recovery can be made by physical and chemical processes being size reduction by shredding the first step. In this paper, the effect of particle size in physical and chemical processing of printed circuit boards is presented and discussed. Shredding using cutting-based equipment allowed the comminution of boards and the liberation of particles composed by different materials (mainly metals and resin). Particle sizes less than 1 mm seems to be appropriate to attain high liberation of materials, which is crucial for the physical separation using gravity or electrostatic processes. Concerning chemical treatment, hydrometallurgical processing involves a leaching operation which can be also influenced by particle size of shredded boards. Samples with different granulometries were leached with 1 M HNO₃ solutions, being leaching yields evaluated. It was concluded that particle size can be an important factor for the solubilization of some metals, but the effect is not similar for all elements. When average diameters change from 2.0 to 0.20 mm, nickel, aluminium and tin reactivity were not significantly affected, being this effect important for copper. Zinc behavior was very dependent from extreme particle sizes but was less affected in intermediate granulometries. Lead leaching showed also a peculiar behavior, exhibiting high and almost constant yields (80-90%) for particle size of solids up to 1.2 mm, and decreasing suddenly for higher granulometries. The effect of time on chemical reactivity for samples with different granulometries demonstrated that particle size affects reaction rates but eventually similar efficiencies can be obtained for long time periods. Therefore the relationship between results from shredding operation and chemical leaching step needs to be optimized, considering the balance between factors like consumption of energy during grinding operation and residence time in leaching.

Abstract: In electronic appliances, printed circuit boards (PCB) represent an important component, containing high grade of valuable metals, besides organic resins and some ceramic materials. Copper is the major metal in PBC’s composition (normally higher than 20% w/w) but many other secondary and minor metal elements, including precious metals, are found in PCB’s. Recycling of PCB´s involves firstly the shredding operation, which is crucial in order to liberate particles from different materials, allowing its further processing by other mechanical, physical and chemical technologies. An efficient shredding operation is difficult to achieve due to the high heterogeneity of these wastes involving materials with different mechanical properties and complex assemblies. This paper presents results from laboratorial studies of shredding of PCB’s and the evaluation of size reduction efficiency as well as the chemical characterization of the obtained shredded fractions. Results showed that an efficient size reduction (characteristic average diameter d50=1.0mm) is obtained using two shredding stages of PCB’s, the first one with a grab shredder and the second one with a cutting mill. Chemical analysis of shredded PCB’s indicated that copper is the principal metal present (28%) followed by Sn, Zn, Pb and Al (3-5%) and many other minor elements. The fine fractions were rich in plastic materials while the metals were essentially present in the intermediate fractions (0.3-1.5 mm). These results can lead to guidelines regarding further design of the physical separation steps in the recycling processes.

Abstract: Laboratorial studies were carried out to characterise the influence of different cutting systems (grab shredder and cutting mill) on the physical processing efficiency of spent Zn-MnO2 batteries. The grab shredder operate based on an indented cutting rotor which applies shear and abrasion stresses with a moderate rotation speed, while the cutting mill operation is based on shear and impact stresses at higher rotation speed. After shredding with the grab shredder, two fractions of material were obtained (above and below the 6 mm discharge grid), which allows a previous separation of the scrap. With the cutting mill, all the grinded material passed the bottom grid (with the same 6mm opening). Results obtained showed that alkaline batteries were more efficiently shredded than saline batteries, mainly with the grab shredder. Average diameters (d50) for saline and alkaline batteries fragmented with the grab shredder were 2.29 and 1.47 mm respectively, while with the cutting mill were 3.09 and 1.54 mm respectively. Chemical analyses were carried out for different size fractions allowing identifying metals distribution through size categories. In general chemical composition was not substantially different using both shredding systems. Zinc distribution was almost constant with the grain size while manganese distribution decreased with particle size. More than 94% of the iron scrap from the battery cases presents a particle size higher than 1.4 mm using both cutting systems. Due to this result, it is possible to separate the scrap retained in the coarse fraction by sieving with the identified mesh. Maximum selectivity points, corresponding to the maximum separation of zinc plus manganese from iron, were also determined. Higher zinc and manganese recoveries were obtained with the grab shredder, despite iron contamination (20-25%) can be considered significant.

Abstract: The main purpose of the present study is to assess the usefulness of filter cartridges from end-of-life biological and chemical protection masks, for other applications (with increased added value) instead of landfill deposition. Filters with different ages up to fifty years, were dismantled and divided in their components. Physico-chemical characterisation of each filter cartridge component was performed using different techniques such as: optical microscopy, Fourier transform infrared spectroscopy, pyrolysis, particle size distribution by laser diffraction, surface area determination from the nitrogen adsorption isotherms at 77K, determination of open porosity by helium pycnometry, and dynamic mechanical thermal analysis in the temperature range from -100°C to 200°C. It is shown that the loss of resilience of the rubber sealant is the main factor that controls the shelf life of filter cartridges. On the other hand, most of the charcoal in the activated carbon cloth remains active and can be useful for other less severe applications such as the removal of dissolved components from freshwater and/or marine systems.

Abstract: The hydrometallurgical processing of metal bearing residues is one of the established routes envisaging metals recovery. In these processes, the leaching operation plays a central role as allows the solubilization of metals for further separation and recovery as pure products. This route can be applied to spent domestic batteries recycling, which studies on sulphuric acid leaching of spent alkaline batteries are reported in this paper. Material samples used in the trials were prepared concerning the real proportion of the most common sizes and shapes of batteries found in the usual stream of this type of wastes. The research involved the evaluation of some factors which affect leaching yields namely temperature, reaction time and stirring speed, through a two-level factorial design methodology and analysis of variance. In this study, other factors related with leachant concentration and stoichiometry were maintained constant. Zinc leaching yields were generally high and even near 100% when the high levels of the variables were used, meaning that zinc oxides present in the electrodes are very reactive to acid leachant. The variables had all positive effects being temperature the most significant factor (confidence level 99%) while the other factors were less significant (98.8% for time and 95% for stirring speed). Concerning manganese, leaching yields obtained were more dependent from the factors, being also positive and varying from 11% (for low levels of factors combination) to 89% (for high levels of factors combination). Temperature and time were highly significant (confidence levels above 99.9%) while stirring speed was less significant (97%). Contamination of leach liquors with iron was also evaluated since it is an impurity which requires special attention during the process development. For the higher levels of the factors (t = 1 h, T=80°C and ω=400 rpm) the final solution contained 10 g/L Zn, 15 g/L Mn and 3.2 g/L Fe. The removal of the iron from the solution is a necessary step prior to the separation and recovery of zinc and manganese.

Abstract: Domestic-type batteries sample was tested aiming at its characterization and the evaluation of the feasibility of physical separation of its main components. The sample was essentially constituted by saline and alkaline types (Zn-MnO2 based systems, >90% w/w) and cylindrical shape (> 90% w/w). The mass balance of alkaline battery samples indicated as main battery components the steel case materials (25 %), the electrodes (71%) and the connector and separator/insulating materials (4 %), while the corresponding values to the saline type are 16%, 72% and 12% respectively. Despite electrochemical principles are similar, internal constitution of saline and alkaline batteries is different. Differences in electrolytes are also relevant (KOH in alkaline type and chloride salts in saline type) affecting therefore the mass balances in the chemical treatment. Fragmentation of batteries was done aiming at to evaluate the efficiency of the liberation of different components, namely scrap and electrodes. Results obtained are very promising considering the good efficiency reached on the physical separation treatment and consequently the chemical step will be necessarily improved.