Search

The contamination by plastics and electronic waste (e-waste) is considered a serious problem worldwide. The e-waste deposited in municipal dumps contains tons of headphones, speakers, credit cards etc., which are a source of magnetic materials, and those ones can contaminate the soil during their degradation. To give a second use to wasted magnetic materials and to avoid the contamination of the environment, we propose here the fabrication of supercapacitors (SCs) by employing the wasted magnetic materials. Firstly, barium hexaferrite (BaFe12O19, RMSP powder) and magnetite (Fe3O4, RMS-CC powder) were recovered/recycled from wasted speakers and from expired credit cards, respectively. Also, flexible plastics were recycled from single use packets and those ones were employed for the fabrication of the SC electrodes. The wasted magnetic materials were characterized by microscopy, and they had an irregular morphology. The sizes of the recycled magnetic particles were in the range of 0.7–11 μm. The SCs made with RMSP and RMS-CC powders (deposited on the SC electrodes) were named as RMSP/SC and RMS-CC/SC, respectively. The acidic electrolyte used in those SCs was made of Polyvinyl-alcohol/H3PO4. A reference device was made without magnetic materials and was named as GR/SC. The devices made with wasted magnetic materials were characterized electrochemically and found that the values of capacitance/energy-density were 634.5 F g−1/88.1 Wh kg−1, 391 F g−1/54.3 Wh kg−1and 295.3 F g−1/34.8 Wh kg−1for the RMSP/SC, RMS-CC/SC and GR/SC devices, respectively. Thus, introducing the recycled BaFe12O19and Fe3O4into the SCs enhanced their capacitance by 32–114 % compared with the reference GR/SC device. Additionally, eco-friendly SCs were made using natural seawater electrolyte (instead of acidic electrolyte) and recycled barium ferrite. As a result, a maximum capacitance/energy-density of 436.6 F g−1/60.7 Wh kg−1were obtained in the devices made with seawater electrolyte. Interestingly, the devices made with seawater electrolyte had ≈11–48 % higher capacitance than the RMS-CC/SC and GR/SC devices (made with acidic electrolyte), suggesting that the seawater electrolyte could be a substitute of acidic/toxic electrolytes. In addition, the curves of charge-discharge showed that a steady output voltage of 0.37–0.60 V is produced by the devices made with acidic electrolyte, but it is reduced to 0.1–0.52 V when the seawater electrolyte is used. The SC electrodes were analyzed by the Raman/XPS techniques and found the presence of Fe3+/Fe2+species as well as oxygen vacancies defects, which were responsible for the charge storage by redox reactions. Also, we found that the devices with the highest content of Fe3+on their electrodes had the highest values of capacitance. Overall, this work demonstrated that efficient and eco-friendly supercapacitors can be fabricated utilizing magnetic components recovered from e-waste and recycled plastics, which contribute to the reduction of contamination in the environment.

Biological scorodite is produced at 80°C and 1g L-1 As5+, using iron oxidizing bacteria Acidianus Sulfidivorans, with a molar ratio Fe/As of 1 and without the use of seeds. We investigated the effect of high ferrous concentration, Fe/As higher than 1, and the use of foreign seeds (gypsum) on biological scorodite crystallization. The use of high ferrous concentrations resulted in a retardation of the time of crystallization due to the high concentration of ferric produced by a high biological oxidation. However, ferrous biological oxidation might be controlled to avoid this effect. The use of seeds did not improve the kinetics of crystallization. Nonetheless, a high arsenic removal rate was observed in the presence of seeds probably as a result of the formation of less stable scorodite.