Eduardo H. Tanabe

Recovery of cobalt from spent lithium-ion batteries using supercritical carbon dioxide extraction.

Continuing technological development decreases the useful lifetime of electronic equipment, resulting in the generation of waste and the need for new and more efficient recycling processes. The objective of this work is to study the effectiveness of supercritical fluids for the leaching of cobalt contained in lithium-ion batteries (LIBs). For comparative purposes, leaching tests are performed with supercritical CO2 and co-solvents, as well as under conventional conditions. In both cases, sulfuric acid and H2O2 are used as reagents. The solution obtained from the supercritical leaching is processed using electrowinning in order to recover the cobalt. The results show that at atmospheric pressure, cobalt leaching is favored by increasing the amount of H2O2 (from 0 to 8% v/v). The use of supercritical conditions enable extraction of more than 95wt% of the cobalt, with reduction of the reaction time from 60min (the time employed in leaching at atmospheric pressure) to 5min, and a reduction in the concentration of H2O2 required from 8 to 4% (v/v). Electrowinning using a leach solution achieve a current efficiency of 96% and a deposit with cobalt concentration of 99.5wt%.

Recovery of indium from LCD screens of discarded cell phones.

Advances in technological development have resulted in high consumption of electrical and electronic equipment (EEE), amongst which are cell phones, which have LCD (liquid crystal display) screens as one of their main components. These multilayer screens are composed of different materials, some with high added value, as in the case of the indium present in the form of indium tin oxide (ITO, or tin-doped indium oxide). Indium is a precious metal with relatively limited natural reserves (Dodbida et al., 2012), so it can be profitable to recover it from discarded LCD screens. The objective of this study was to develop a complete process for recovering indium from LCD screens. Firstly, the screens were manually removed from cell phones. In the next step, a pretreatment was developed for removal of the polarizing film from the glass of the LCD panels, because the adherence of this film to the glass complicated the comminution process. The choice of mill was based on tests using different equipment (knife mill, hammer mill, and ball mill) to disintegrate the LCD screens, either before or after removal of the polarizing film. In the leaching process, it was possible to extract 96.4 wt.% of the indium under the following conditions: 1.0M H2SO4, 1:50 solid/liquid ratio, 90°C, 1h, and stirring at 500 rpm. The results showed that the best experimental conditions enabled extraction of 613 mg of indium/kg of LCD powder. Finally, precipitation of the indium with NH4OH was tested at different pH values, and 99.8 wt.% precipitation was achieved at pH 7.4.

Fast copper extraction from printed circuit boards using supercritical carbon dioxide

Technological development and intensive marketing support the growth in demand for electrical and electronic equipment (EEE), for which printed circuit boards (PCBs) are vital components. As these devices become obsolete after short periods, waste PCBs present a problem and require recycling. PCBs are composed of ceramics, polymers, and metals, particularly Cu, which is present in highest percentages. The aim of this study was to develop an innovative method to recover Cu from the PCBs of old mobile phones, obtaining faster reaction kinetics by means of leaching with supercritical CO2 and co-solvents. The PCBs from waste mobile phones were characterized, and evaluation was made of the reaction kinetics during leaching at atmospheric pressure and using supercritical CO2 with H2O2 and H2SO4 as co-solvents. The results showed that the PCBs contained 34.83 wt% of Cu. It was found that the supercritical extraction was 9 times faster, compared to atmospheric pressure extraction. After 20 min of supercritical leaching, approximately 90% of the Cu contained in the PCB was extracted using a 1:20 solid:liquid ratio and 20% of H2O2 and H2SO4 (2.5 M). These results demonstrate the efficiency of the process. Therefore the supercritical CO2 employment in the PCBs recycling is a promising alternative and the CO2 is environmentally acceptable and reusable.

Surface modification of chitin using ultrasound-assisted and supercritical CO2 technologies for cobalt adsorption.

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.

Biosorption of gold from computer microprocessor leachate solutions using chitin

The biosorption of gold from discarded computer microprocessor (DCM) leachate solutions was studied using chitin as a biosorbent. The DCM components were leached with thiourea solutions, and two procedures were tested for recovery of gold from the leachates: (1) biosorption and (2) precipitation followed by biosorption. For each procedure, the biosorption was evaluated considering kinetic, equilibrium, and thermodynamic aspects. The general order model was able to represent the kinetic behavior, and the equilibrium was well represented by the BET model. The maximum biosorption capacities were around 35 mg g(-1) for both procedures. The biosorption of gold on chitin was a spontaneous, favorable, and exothermic process. It was found that precipitation followed by biosorption resulted in the best gold recovery, because other species were removed from the leachate solution in the precipitation step. This method enabled about 80% of the gold to be recovered, using 20 g L(-1) of chitin at 298 K for 4 h.

Alternative treatments to improve the potential of rice husk as adsorbent for methylene blue

Alternative treatments, such as, NaOH, ultrasound assisted (UA) and supercritical CO2 (SCO2), were performed to improve the potential of rice husk as adsorbent to remove methylene blue (MB) from aqueous media. All the treatments improved the surface characteristics of rice husk, exposing its organic fraction and/or providing more adsorption sites. The Langmuir and Hill models were able to explain the MB adsorption for all adsorbents in all studied temperatures. The experimental and modeled parameters demonstrated that the MB adsorption was favored by the temperature increase and by the use of NaOH-rice husk. The maximum adsorption capacities for the MB solutions (ranging from 10 to 100 mg L-1), estimated from the Langmuir model at 328 K, were in the following order: NaOH rice-husk (65.0 mg g-1) > UA-rice husk (58.7 mg g-1) > SCO2-rice husk (56.4 mg g-1) > raw rice husk (52.2 mg g-1). The adsorption was a spontaneous, favorable and endothermic process. In general, this work demonstrated that NaOH, UA and SCO2 treatments are alternatives to improve the potential of rice husk as adsorbent.

Continuous Adsorption of a Cationic Dye on Surface Modified Rice Husk: Statistical Optimization and Dynamic Models

The continuous adsorption of a cationic dye (Methylene Blue, MB) on surface-modified rice husk was investigated. First, rice husk was submitted to ultrasound-assisted, supercritical CO2 and NaOH treatments. The adsorbents were characterized. Then, the continuous adsorption was optimized by response surface methodology (RSM), using raw rice husk as the adsorbent. Finally, under the optimal conditions, breakthrough curves were obtained using all adsorbents and the models were used to interpret these curves. The optimal bed performance was reached at a flow rate of 5 mL min−1 and an initial MB concentration of 10 mg L−1. Under these conditions, the breakthrough time was 109 min, the length of the mass transfer zone was 20.1 cm, and the maximum capacity of the column was 1.55 mg g−1. All surface modifications were able to improve the rice husk characteristics in relation to the MB adsorption. Consequently, the bed performance was significantly improved when the surface-modified adsorbents were used. The breakthrough times were 109, 240, 155, and 385 min, respectively, when raw rice husk, UA–rice husk, SCO2–rice husk, and NaOH–rice husk were used. The length of the mass transfer zone was 20.1, 7.9, 15.9, and 9.3 cm for raw rice husk, UA–rice husk, SCO2–rice husk, and NaOH–rice husk, respectively. The dynamic models were able to fit the adsorption data and provided physically consistent parameters.

Comparison between Brazilian agro-wastes and activated carbon as adsorbents to remove Ni(II) from aqueous solutions

This research was performed to find an alternative, low-cost, competitive, locally available and efficient adsorbent to treat nickel (Ni) containing effluents. For this purpose, several Brazilian agro-wastes like sugarcane bagasse (SCB), passion fruit wastes (PFW), orange peel (OP) and pineapple peel (PP) were compared with an activated carbon (AC). The adsorbents were characterized. Effects of fundamental factors affecting the adsorption were investigated using batch tests. Kinetic and equilibrium studies were performed using conventional models. It was verified that the adsorption was favored at pH of 6.0 for all agro-wastes, being dependent of the Ni speciation, point of zero charge and surface area of the adsorbents. The Ni removal percentage was in the following order: SCB > OP > AC > PFW > PP. From the kinetic viewpoint, the Elovich model was appropriate to fit the Ni adsorption onto SCB, while for the other adsorbents, the pseudo-first-order model was the most suitable. For all adsorbents, the Langmuir model was the more adequate to represent the equilibrium data, being the maximum adsorption capacities of 64.1 mg g(-1), 60.7 mg g(-1), 63.1 mg g(-1), 48.1 mg g(-1) and 64.3 mg g(-1) for SCB, PFW, OP, PP and AC, respectively. These results indicated that mainly SCB and OP can be used as alternative adsorbents to treat Ni containing effluents.

Recovery of valuable materials from spent NIMH batteries using spouted bed elutriation.

In recent years, a great increase in the generation of spent batteries occurred. Then, efficient recycling ways and correct disposal of hazardous wastes are necessary. An alternative to recover the valuable materials from spent NiMH batteries is the spouted bed elutriation. The aim of this study was to apply the mechanical processing (grinding and sieving) followed by spouted bed elutriation to separate the valuable materials present in spent NiMH batteries. The results of the manual characterization showed that about 62 wt.% of the batteries are composed by positive and negative electrodes. After the mechanical separation processes (grinding, sieving and spouted bed elutriation), three different fractions were obtained: 24.21 wt.% of metals, 28.20 wt.% of polymers and 42.00 wt.% of powder (the positive and negative electrodes). It was demonstrated that the different materials present in the spent NiMH batteries can be efficiently separated using a simple and inexpensive mechanical processing.

Mathematical Modeling of Thin Layer Drying of Papaya Seeds in a Tunnel Dryer Using Particle Swarm Optimization Method

The processing of papaya generates a significant amount of solid wastes. The seeds represent a significant amount and a source of untapped products. Papaya seeds have useful compounds, which can be obtained from its extracts or oils and can be a very effective biosorbent. For good results in the compounds achievement and the pretreatment, it is essential the appropriated choice of the drying conditions. This article proposes the study of the drying of papaya seeds in a tunnel dryer at three drying temperatures (40, 70, and 100°C) and three air drying velocities (1.0, 1.5, and 2.0 m · s−1). Empirical and semi-empirical models were proposed to adjust the kinetic parameter as a function of the drying conditions. The particle swarm optimization method was used, obtaining, as a result, an exponential model with good prediction quality and with few parameters to be adjusted.