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Wax obtained from the pyrolysis of polyethylene waste can contain inorganic contaminants and must be purified before application. We evaluated different filter aids (perlite, sand, and rice husk ash) for the filtration of a crude wax and a pyrolysis wax through a filter medium that was coated with nylon 6 nanofibers to improve filtration efficiency. We first examined the performance of the filter aids in improving crude wax filtration, with the filtration time, temperature, and pressure held constant at 1 h, 170 °C, and 2.5 bar, respectively. Oily wax was then produced by pyrolysis of high-density polyethylene (HDPE) waste in the temperature range 425⿿475 °C. The best filter aid was perlite, which had a filtrate production rate of 5.47 y 10⿿5 m3/h. The highest oily wax yield (87.8%) was achieved at a pyrolysis temperature of 425 °C. The assembly comprising the filter medium coated with nylon 6 nanofibers plus perlite as a filter aid was most suitable for removing impurities from the oily wax generated by the HDPE pyrolysis as it achieved a purification efficiency of 99.9%.

This work investigates the use of supercritical CO2, with organic acid solutions as cosolvents, for the recovery of neodymium (Nd) from the NdFeB permanent magnets of hard disk drives (HDDs). Atmospheric leaching experiments were performed at 90 °C, solid:liquid ratio of 1:20, and acid concentration of 1.0 M, using malic and citric acids. Extraction using supercritical CO2 was performed using different pressures, temperatures and extraction times. Leaching of the unroasted NdFeB powder at 90 °C resulted in Nd recoveries of 99.9% after 360 min using malic acid. With roasted NdFeB powder, low Nd recovery efficiencies of 21% and 32.1% after 900 min were obtained using malic and citric acid, respectively, at pressure of 1.01 bar and temperature of 90 °C. Extraction of the unroasted powder with supercritical CO2, at 90 °C and 120 bar, resulted in Nd recovery efficiencies of 99.4% and 50.5% after 30 min, using malic acid and citric acid, respectively. In the case of the roasted NdFeB powder, the efficiencies were 99.5% and 30.6% after 120 min using malic acid and citric acid, respectively, at 90 °C and 100 bar. The use of supercritical CO2 was highly effective for the recovery of Nd from the unroasted powder using malic acid, enabling a significant reduction of the extraction time from 360 min to 30 min. For the roasted NdFeB powder, it was possible to extract 99.5% of the Nd after 120 min using supercritical CO2 and malic acid, whereas the maximum recovery obtained with atmospheric leaching was 21.0% after 360 min.

A falling film molecular distillation (FFMD) process was used in a pilot plant to fractionate a polyethylene wax (PE-Wax) into light paraffin wax (LP-Wax) and super-microcrystalline wax (SM-Wax). The pseudoization technique was applied to represent the molecular distribution of the PE-Wax by pseudo-components (PS1 and PS2). Investigation was made of the influences of the evaporator temperature (EVT), feed flow rate (FF), and condenser temperature (CT) on the percent recovery of distillate (DP), the yield of PS1 in the distillate ( Y D _ P S 1 ), and the distillate flow rate/feed flow rate ratio (DF). The predictive models and the multi-response optimization provided decision criteria about the most suitable operating conditions for fractionating PE-Wax. The best experimental data for DP, Y D _ P S 1 , and DF (63.4%, 81.5%, and 0.60, respectively) were obtained with EVT of 184 °C, FF of 1.81 kg/h, and CT of 28 °C, at 0.1 Pa. The LP-Wax, recovered mainly in the distillate, exhibited a normal distribution throughout the carbon number range from n-C13 to n-C30. The SM-Wax, recovered in the residue, showed a higher latent heat of storage (>169 kJ/kg), according to the phase-change performance of the material. These results offer new insights into processing PE-Wax to obtain value-added products with narrower carbon number distributions.

Cables and wires, which are essential parts of equipment for the transmission of both information and electricity, contain valuable materials including copper (Cu) and aluminum (Al). This experimental work evaluates the use of mechanical processing (grinding and sieving), followed by spouted bed elutriation, for separation of the valuable materials (steel-coated copper, copper, and aluminum) present in waste coaxial and internet cables. A recovery efficiency of approximately 90% was achieved for the steel-coated copper in coaxial cables. For internet cables, the copper recovery efficiency was approximately 87%. These findings demonstrate that it is possible to separate, recover, and recycle the valuable materials (metals) present in waste cables using simple, low-cost, and efficient mechanical processing followed by spouted bed elutriation.

The main objective of this work was to develop a nanomaterial able to selectively extract and recover indium (In) from obsolete cell phone LCD screens. For this, Nylon 6 nanofibers were produced and modified with di-(2-ethylhexyl)phosphoric acid (DEHPA) for application in the solid-phase extraction of In. The best extraction conditions for concentration of In were 30% DEHPA, pH 0.5, 7.5 min contact time, and S:L ratio of 1:300. In this step, an In extraction efficiency of around 74% was obtained. In stripping steps, an efficiency of 92% was achieved using 1.5 M HCl, S:L ratio of 1:20, and 5 min contact time. Under the best extraction and stripping conditions, it was possible to obtain up to 6-fold concentration of In, compared to the initial concentration. In addition, the nanofibers were evaluated in terms of their stability and capacity for reuse, which showed that there was no significant loss of DEHPA and that the extraction efficiency remained almost constant. The findings demonstrated the possibility of using the Nylon 6/DEHPA nanofibers in a highly efficient extraction/stripping procedure for the selective recovery of In and Sn, with reduced environmental impacts.

The aim of this work was to develop new materials employing polymeric nanofibers modified with an organic extractant for the extraction of metals. For this purpose, nylon-6 nanofibers were modified with di-(2-ethylhexyl) phosphoric acid (DEHPA) for use in the selective extraction of zinc and nickel. The best extraction efficiencies were 85.5% for Zn and 4.6% for Ni, achieved under the following conditions: pH 2, solid:liquid (S:L) ratio of 1:40, and contact time of 7.5 min. In the stripping, the best efficiencies were 85.9% for Zn and 90.1% for Ni, using a concentration of HCl of 0.5 M, S:L ratio of 1:10, and contact time of 5 min. The nanofibers were evaluated in terms of their stability and capacity for reuse, and it was found that there was no loss of the DEHPA extractant from the nanofibers, while the extraction efficiency remained almost constant. Regarding to environmental aspects of the new technology, the results confirm that nanofibers exhibit the same efficiency of conventional liquid-liquid extraction, without the disadvantage of the use of organic solvents. In this way, this new technology brings an enormous gain in environmental terms, since it drastically reduces the use of hazardous substances.

The presence of inorganic substances in the composition of crude wax decreases its commercial value, necessitating purification of the product. A new physical surface treatment for filter media involving the application of nanofibers of Nylon-6 polymer was developed using the Forcespinning® equipment. The performance of the nanofiber-coated filter was compared with the results obtained for other filter media of the same composition (nonwoven aramid fiber fabric), one without physical treatment, and another treated using singeing. An experimental design was carried out to find the optimum operating temperature and pressure (170 °C and 2.5 bar, respectively). The filtrate volume, specific resistance of the filter cake, and filter medium resistance were determined, keeping the filtration time, temperature, and pressure constant at 1 h, 170 °C, and 2.5 bar, respectively. The nanofiber-coated filter showed the best performance, providing a higher wax filtrate volume and greater retention of inorganics, with values of 5.39 × 10−5 m3 and 99.6%, respectively.

One of the greatest challenges in the development of hydrometallurgical processes for the recovery of indium from secondary sources is the fact that the leaching step generally results in very dilute solutions. Therefore, this diluted indium solution must be concentrated before being sent to a subsequent step such as recovery of the metal by electrowinning. The aim of the present work was to apply solvent extraction using bis(2-ethylhexyl) phosphate (D2EHPA) in order to maximize the indium concentration in the solution. Firstly, the extraction and stripping steps were investigated using a synthetic solution. After definition of the best conditions using a synthetic solution, a real solution obtained from the leaching of discarded LCDs was employed.

In the last decades, increasing industrial development has led to huge consumption of plastic materials, due to their versatility and low cost. Therefore, the implementation of efficient and environmentally friendly recycling technologies is of great importance. This study proposes an alternative separation process for recycling mixtures of plastic wastes, using a tribo-electrostatic separation process. The methodology adopted in this work was firstly characterization of the polymeric wastes, followed by preparation of the wastes using different unit operation processes (washing, drying, and comminution), tribo-charging, and electrostatic separation of different combinations of plastics (HDPE/PP, LDPE/PP, and PET/PVC). Various parameters were evaluated in the tribo-charging process and the electrostatic deflection. Separation of a mixture of HDPE and PP achieved PP recovery of 92.8% (purity of 95.7%) and HDPE recovery of 95.9% (purity of 93.1%). Recovery and purity values higher than 90.2% and 95.9% were obtained for PP/LDPE and PET/PVC mixtures, respectively. These results demonstrated that tribo-electrostatic separation is a promising and efficient method for use in the recycling of plastic wastes. The process studied enabled significant recoveries of the components at high levels of purity.

This work presents the development of a novel highly efficient adsorbent produced from CaAl/LDH supported on biochar chemically activated with phosphoric acid [CaAl/Biochar(H3PO4)] in order to maintain a great adsorbent capacity and prevent LDH disintegration. Its adsorptive efficiency was compared to an adsorbent formed from CaAl/LDH supported on untreated biochar (CaAl/Biochar). Biochar was produced from the pyrolysis of Eucalyptus saligna sawdust. The adsorbents were applied to remove crystal violet (CV) dye from aqueous solutions in a batch adsorption process. The adsorbents were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and scanning electron microscopy (SEM). Adsorption kinetics, isotherms and thermodynamics were evaluated. The characterization results suggested that the CaAl/LDH was successfully synthesized and supported on biochar. The results indicate that pH 8 was more suitable for CV dye adsorption, with an adsorptive capacity over 101 mg g−1 for CaAl/Biochar(H3PO4). Furthermore, adsorption experimental data fitted well with the pseudo-second order kinetics model and the Freundlich isotherm model. It was obtained a maximum adsorption capacity of 496.55 mg·g−1 at 50 °C. For CaAl/Biochar(H3PO4), the thermodynamic results revealed a favorable, spontaneous and endothermic process. In addition, the results showed that the pre-treatment of the biochar with phosphoric acid maintained 71% of the initial adsorptive capacity even after four cycles of reuse. Therefore, CaAl/Biochar(H3PO4) is a sustainable adsorbent with high performance for CV contaminated wastewater treatment and groundwater remediation.

Continuing industrial development results in ever greater consumption of products and materials. These include electrical and electronic equipment (EEE) such as mobile phones and, consequently, lithium ion batteries (LIBs). Therefore, an efficient and environmentally friendly recycling technology is vital for the recovery of valuable materials from spent LIBs. This work describes an alternative process for the recovery of these materials, using mechanical processing and electrostatic separation. Firstly, the batteries are dismantled and their components are characterized. This is followed by comminution, drying (to remove the organic electrolyte), separation according to particle size, and electrostatic separation of the conductive and nonconductive parts of the LIBs. Parameters evaluated in the electrostatic separation were the electrode voltage, roll rotation speed, distance of the electrostatic electrode, and the inclination angle of the deflector. The results showed recovery of a conductive fraction containing 98.98% of metals and a nonconductive fraction containing 99.6% of polymers, demonstrating that electrostatic separation is a promising and efficient method for the recovery of high purity materials from spent LIBs.

The printed circuit boards are the fundamental components of waste electrical and electronic equipment (WEEE). The PCBs stand out due to the amount of metals in their composition as well for their complex and heterogeneous constitution that make their recycling difficult. In this context, the aims of the study was to evaluate the application of supercritical CO2 modified with ethanol in order to remove the polymers contained in PCBs from discarded mobile phones. The PCBs were characterized and an evaluation of the supercritical extraction was performed through experimental design. The characterization showed that PCBs contained 64.02 wt% of metals, 20.51 wt% of ceramics and 15.47 wt% of polymers. The fractional factorial experimental design showed that 69.53 wt% of the polymers present in the PCBs were extracted, at 170 °C and 7.5 MPa. As the remaining polymers are no longer covering the metals, they could be more easily leached and therefore more effectively recovered.

The growth in the generation of the waste of electrical and electronic equipment (WEEE) has won global importance. Cell phones are highlighted between these wastes because of its short life cycle and its great amount of hazardous materials. Thus, this work aims to obtain an effective method for indium extraction from liquid crystal displays (LCD) screens of cell phones using alternative organic acids. For comparative purposes, leaching tests are performed with supercritical CO2 and co-solvents, as well as under conventional conditions using citric and malic acids. The results showed that at atmospheric pressure, 76.5% of indium was extracted after 180 min. The use of supercritical CO2 besides providing a reduction in extraction time also provides a higher extraction, reaching 94.6% in just 30 min. In summary, a novel method for indium recovery was developed. Furthermore, the process was more efficient using supercritical CO2, increasing the extraction and turning the process 6 times faster than conventional extraction.

Chitosan/polyamide nanofibers (CP nanofibers) were prepared by a new Forcespinning® technology, and used as alternative adsorbent to remove Reactive Black 5 (RB5) and Ponceau 4R (P4R) dyes from aqueous solutions. The results demonstrated that under the best operational conditions (30 G½” needles, spinneret rotation of 12000 rpm for 10 min and chitosan polyamide ratio of 1.00/1.50), chitosan/polyamide nanofibers were produced at a rate of 3 g h−1. CP nanofibers presented a semi–crystalline structure, with several functional groups and diameter from 100 to 500 nm. The adsorption of RB5 and P4R on the CP nanofibers was favored at pH of 1.0. Pseudo–second order (RB5) and Elovich (P4R) models were the more adequate to represent the kinetic data. The equilibrium data followed the Langmuir model, being the maximum adsorption capacities of 456.9 mg g−1 for RB5 and 502.4 mg g−1 for P4R. The adsorption was spontaneous, favorable and endothermic. Desorption and reuse was possible for four times, maintaining the same adsorption capacity. In brief, it can be concluded that the Forcespinning® technology is an alternative to obtain chitosan/polyamide nanofibers with suitable characteristics. These nanofibers in turn, can be successfully applied to remove dyes from aqueous media.

The demand for photovoltaic panels has increased in recent years and the resources used in its production such as silicon, with high production costs and silver that is becoming scarce, in addition to the presence of toxic metals such as lead, highlight the importance of recycling of these materials. One of the main challenges for recycling is the delamination of the panels, for which supercritical fluids can be an effective option. Constituents of a photovoltaic module were analyzed using SEM/EDS, XRD, XRF, TGA, DSC, and FTIR techniques. The efficiency of the delamination process was evaluated using tests carried out at atmospheric pressure, in the presence of different cosolvents. Comparative tests were performed using supercritical CO2 (ScCO2). For both processes, after delamination, the components that still showed low release of adhered materials were processed in a planetary ball mill. Determinations were then made of the recovery and purity of the delaminated fractions, as well as the separation of the adhered materials. The best results for recovery and purity of the glass, metallic filaments, and backsheet were obtained using ScCO2 with toluene, together with planetary ball milling, achieving values over 96 %. For the solar cell and EVA (cell + EVA), the recovery was greater than 85 %, including high value materials such as Si and Ag. In addition to recovering high value metals and reducing the volume of solvent, the use of ScCO2 enabled delamination of the photovoltaic panel with a time around 3.5 times shorter than at atmospheric pressure.

Chitosan/bentonite hybrid composite (CBC) was developed and successfully applied to remove anionic (Amaranth Red (AR)) and cationic (Methylene Blue (MB)) dyes from colored effluents. The influence of several factors on the dyes adsorption capacity was investigated. Kinetic, equilibrium and thermodynamic viewpoints were elucidated. Desorption and reuse studies were performed. It was found that CBC presented a heterogeneous structure with good mechanical and swelling properties, which facilitates the phase separation after adsorption. The adsorption was favored at pH 2 for AR and 10 for MB. Elovich model was the more adequate to represent the kinetic data. The equilibrium data followed the Langmuir model, being the maximum adsorption capacities of 362.1 mg g−1 for AR and 496.5 mg g−1 for MB. The adsorption process was spontaneous, favorable and exothermic. Desorption and reuse was possible three times for AR and two times for MB, maintaining the same adsorption capacity. These results demonstrated that chitosan/bentonite hybrid composite is an advanced adsorbent with advantages, such as, easy phase separation, capability to remove anionic and cationic dyes and potential for reuse.

The convective air drying of papaya seeds was studied in order to optimize the seed oil yield. Papaya seeds were dried under different conditions of air temperature and air velocity. The operation was characterized by drying rate and drying kinetic curves. Oil was extracted from the seeds, obtained in all drying conditions and, the yield was optimized. The results revealed that the constant rate and falling rate periods occurred during the convective air drying of papaya seeds. The Overhults kinetic model was suitable to represent the experimental drying curves. The optimal drying conditions, which provided the maximum seed oil yield, were: air temperature of 70 °C and air velocity of 2.0 m s−1. In these conditions, the seed oil yield was 19.23% and the final moisture content was 7.40% (w.b.). High quality oil, with about 90% of oleic acid, was obtained from papaya seeds.

An efficient and environmentally friendly new process is described for the recovery of platinum group metals from spent automotive catalysts. The process consists of the application of mechanical processing followed by heat treatment and leaching, with the aim of reducing the use of acids that can have adverse effects in the environment. The extraction of PGMs was carried out using HCl associated with malic, formic, and citric acids. Evaluation was made of the effects of parameters including acid concentration, volumes of inorganic and organic acids, solid to liquid (S/L) ratio, and extraction time. The automotive catalyst powders were characterized using XRD, SEM/EDS, particle size distribution, and EDXRF techniques. The spent automotive catalysts contained reasonable concentrations of Pt and Pd. Over 90% of the Pt and Pd could be recovered in a leaching process using 6 M HCl, S/L ratio of 1:30, and 20% (v/v) citric acid. The findings showed that citric acid can be used in the recovery of PGMs from spent automotive catalysts, decreasing the use of aggressive and corrosive acids often employed in the recovery of these metals. Hence, the addition of organic acids can contribute to efficient and environmentally friendly processes for the recovery of Pt and Pd.

Technological development has led to increasing quantities of waste electrical and electronic equipment. At the same time, the search for more efficient uses of energy is an urgent current issue. Both problems have relations to LED bulbs. The presence of hazardous and valuable materials in these bulbs makes their recycling essential. However, due to the many different parts that compose an LED bulb, the separation of LEDs from the bulbs is difficult, but is crucial for proper recycling. This work describes a recycling process for LED bulbs solely using mechanical processing. Firstly, the LED bulbs were dismantled and their components were characterized in terms of their weight and by DSC and SEM/EDS analyses. Then, operations including comminution, sieving, electrostatic separation, magnetic separation, and gravity separation were applied to separate the LED bulb components, according to their characteristics. The operations were adapted in order to achieve the maximum possible separation of the components. A mechanical processing flowchart was proposed for LED bulb recycling. Characterization of LED bulbs revealed the presence of polymers and valuable and/or hazardous materials including copper, silver, and lead. The results showed separation efficiencies in the range 98-100% for many components (polymeric cover, metallic housing, Edison screw, PCB, and heat sink with LEDs). A simplified economic analysis of the recycling process showed it to be feasible, with estimated profit of US$ 639.82/ton of processed LED bulbs. The results indicated that the proposed mechanical processing was highly effective for the recovery of materials at high purity from LED bulbs.

Aromatization of extra-virgin olive oil (EVOO) with aromatic plants is commonly used to enrich the oil with aromatic and antioxidant compounds. Ultrasound can be an alternative to accelerate this process. The objective of this work was to determine if ultrasound is able to accelerate EVOO aromatization with rosemary and basil and how it affects the migration of volatile and other compounds, the oxidative stability and the antioxidant capacity of the aromatized products. Ultrasound parameters (amplitude, time, and temperature of extraction) were optimized for each herb with central composite designs. Free fatty acid, peroxide value, K232, K270, ΔK, fatty acid profile, total phenolics, antioxidant capacity, polar compounds, oxidative stability and volatile compounds profile were evaluated in all samples. Physical effects of ultrasound on the herbs were observed by scanning electron microscopy. In the optimization, variables related to the oxidative processes were minimized and compounds migration and oxidative stability were maximized. Results were 70.09% amplitude, 36.6 min and 35 °C for rosemary and 95.98% amplitude, 9.9 min and 30 °C for basil. These conditions were compared to 7 and 15 days of conventional maceration (CM). Aromatization of EVOO with rosemary, both by ultrasound assisted maceration (UAM) or CM, improved total phenolics, terpenes, esters, ketones, stability and induction times, as well as decreased the values for the quality parameters. The use of UAM accelerated the process to 37 min. However, aromatization with basil by CM increased the values for the quality parameters and reduced the total phenolics, the antioxidant capacity and the induction and stability times. UAM with basil reached better results than those observed for CM, in only 10 min. In conclusion, rosemary is more appropriate than basil for EVOO aromatization, and UAM was the best choice to accelerate the processes when compared to CM.

Ultrasound-assisted (UA) and supercritical CO2 technologies (SCO2) were used to modify the chitin surface and, improve its adsorption characteristics regarding to cobalt. Chitin, before and after the treatments, was characterized by N2 adsorption isotherms (BET), infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Unmodified and surface modified chitins were used as adsorbents to remove cobalt from aqueous solutions. The adsorption study was performed by equilibrium isotherms and kinetic curves. The chitin particle characteristics, such as, surface area, pore volume and porosity were improved by the UA and SCO2 treatments. The crystallinity index decreased after the UA and SCO2 treatments, and also, intense surface modifications were observed. Langmuir and Freundlich models were adequate to represent the adsorption equilibrium. The maximum adsorption capacities were 50.03, 83.94 and 63.08 mg g(-1) for unmodified chitin, UA surface modified chitin and SCO2 surface modified chitin. The adsorption kinetic curves were well represented by the pseudo-second order model. UA and SCO2 technologies are alternatives to modify the chitin surface and improve its adsorption characteristics.

Zinc aluminate (ZnAl2O4) particles with a spinel structure were prepared by metal-chitosan complexation method. The solids were obtained by the thermal decomposition of precursor compound of metallic hydroxides mixture and the biopolymer chitosan. X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and N2-adsorption–desorption isotherms were used for the characterization of the products. The results showed that the ZnAl2O4 spinel can be obtained by heating the precursor at temperatures above of 500 °C, resulting in a material with porous structure and large surface area and high purity.

An effective and environmentally friendly process was developed for recovering metals present in lithium-ion batteries (LIBs), using a mechanical process followed by heat treatment and leaching using malic, citric, and formic acids at concentrations of 2 M. The techniques employed to characterize the process were TGA, DSC, XRD, SEM, FT-IR, and EDXRF. The leaching was carried out using different experimental conditions of temperature, volume of hydrogen peroxide (H2O2), S/L ratio, and extraction time. The leachate solutions were analyzed by FAAS. The characterization results showed that heat treatment at 700 °C for 2 h was effective for degradation of the graphite and PVDF present in the LIBs. Over 90% of the Co, Li, and Mn present could be extracted using the following conditions: 2 M DL-malic acid, 6% (v/v) H2O2, S/L of 1:20 (m/v), 95 °C, and extraction time of 60 min. The process for recovering metals from spent LIBs using DL-malic acid could be considered economically and environmentally correct, avoiding negative impacts in the environment and recovering metals with high added value that could be used in the manufacturing of new products.

This work investigates the use of leaching with malic and citric acids for the recovery of neodymium (Nd) from the NdFeB permanent magnets of discarded hard disk drives (HDDs). Evaluation was made of the effect of previous roasting of NdFeB powder on the recovery of Nd. The HDDs were manually disassembled and the magnets were removed, demagnetized, and comminuted. The roasted NdFeB powder was produced by heating in a muffle furnace at 900 °C for 480 min, resulting in complete transformation of the metals into their oxides. Evaluation was made of the effects of the following leaching parameters: temperature (30–90 °C), acid concentration (0.2–1.2 M), solid:liquid ratio (1:10–1:50), and leaching time (10–900 min). For both organic acids, the best values for the first three parameters were 90 °C, 1.0 M, and 1:20. Using malic acid, the best leaching time for the unroasted NdFeB powder was 360 min, which resulted in 99% recovery of Nd. Leaching with citric acid showed good efficiency up to 60 min, with 72.8% recovery of Nd. However, for longer times, complexation between Fe and citrate led to the formation of a thick sludge, which prevented continuation of the leach. Leaching of the unroasted NdFeB powder resulted in low selectivity between Nd and Fe. In the case of the roasted NdFeB powder, the Nd recovery efficiencies achieved using malic acid and citric acid were 22% and 32.1%, respectively. However, high selectivity was obtained, with 86.0% and 98.0% Nd, relative to Fe, using malic acid and citric acid, respectively.

The production of electronic equipment, such as computers and cell phones, and, consequently, batteries, has increased dramatically. One of the types of batteries whose production and consumption has increased in recent times is the nickel metal hydride (NiMH) battery. This study evaluated a hydrometallurgical method of recovery of rare earths and a simple method to obtain a solution rich in Ni–Co from spent NiMH batteries. The active materials from both electrodes were manually removed from the accumulators and leached. Several acid and basic solutions for the recovery of rare earths were evaluated. Results showed that more than 98 wt.% of the rare earths were recovered as sulfate salts by dissolution with sulfuric acid, followed by selective precipitation at pH 1.2 using sodium hydroxide. The complete process, precipitation at pH 1.2 followed by precipitation at pH 7, removed about 100 wt.% of iron and 70 wt.% of zinc from the leaching solution. Results were similar to those found in studies that used solvent extraction. This method is easy, economic, and does not pose environmental threats of solvent extraction.

In this study, different membranes were prepared using conventional polymer (high impact polystyrene) and polyaniline to evaluate their use in electrodialysis. Two different preparation modes were tested: chemical mixture with subsequent solvent evaporation; and mechanical mixture with subsequent pressing under heating. The purpose was to understand the effect of production methods on membrane microstructure and ionic transport. Membranes were characterized by swelling study, Fourier transformed infrared spectroscopic, scanning electron microscopy, thermogravimetric analysis and dynamic mechanical analysis. Ionic transport through the membranes was evaluated using a three-compartment cell. The results of the produced membranes were compared with those of the commercial Nafion 450 membrane.

The growing concern about the environment, associated with the continuous increase in the production of electronic equipment, such as computers, cell phones, mobile devices and consequently batteries, has induced research to develop new technologies to recycle the huge numbers of spent batteries generated in the last few years. The amount of spent NiMH batteries will tend to grow continually over the next few years. These batteries have in their chemical composition, valuable metals such as Ni, Co and rare earths. In the first stage of this work a characterization of NiMH batteries was done. Batteries from different brands and models were disembled and their components were characterized in relation to their chemical composition and main phases. In a second stage of this work, a sample of spent NiMH batteries was milled and the polymeric and metallic fractions were magnetically separated. The results obtained demonstrate that the recycling study, aimed at the recovery of Ni, Co and rare earths, is viable due to the great amount of these metals that are present batteries. It also demonstrates that magnetic separation is a very efficient process to recovery nickel alloys. However the effects of cadmium contamination (originating from fake batteries) will cause the recycling processes to be re-evaluated.