Deep A, Kumar K, Kumar P, Kumar P, Sharma AL, Gupta B, Bharadwaj LM.
Environ Sci Technol. 2011 Dec 15;45(24):10551-6.
Biomolecular Electronics and Nanotechnology Division, Central Scientific Instruments Organization (CSIR-CSIO), Sector 30C, Chandigarh 160030, India. firstname.lastname@example.org
The recovery of pure ZnO (zinc oxide) nanoparticles from spent Zn-Mn dry alkaline batteries is reported. Spent batteries were dismantled to separate the contained valuable metals of the cell electrodes in the form of black powder. Treatment of this black powder with 5 mol L(-1) HCl produced leach liquor, primarily containing 2.90 g L(-1) Zn and 2.02 g L(-1) Mn. Selective and quantitative liquid-liquid extraction of Zn(II) was then carried out in three counter current steps by using Cyanex 923 (0.10 mol L(-1) in n-hexane). Zn(II) distributed in the organic phase as complex ZnCl(2)·2R (R = Cyanex 923 molecule). The metal loaded organic phase was subjected to combust at 600 °C to yield pure ZnO nanoparticles (40-50 nm). Important characteristics of the synthesized nanoparticles were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction spectroscopy (XRD), and atomic force microscopy (AFM).
Zinc-manganese oxide dry alkaline batteries are frequently used to operate many electronic and electrical appliances. Recycling of spent Zn-MnO2 batteries is very important to minimize the risk of environmental pollution. However, recycling with an unadorned purpose of waste treatment is not an attractive business, particularly in developing countries where economic interests supersede environmental obligations. In this scenario, the idea of recovering a valuable product (e.g., pure ZnO nanoparticles) from spent batteries may be useful to promote their
recycling due to the projected economic benefits. The market potential of pure ZnO nanoparticles is already quite huge and the demand is ever-growing. These nanoparticles find varied applications in piezoelectric transducers, gas sensors, photonic crystals, light-emitting devices, photodetectors, photodiodes, optical waveguides, transparent conductive films, varistors, and solar cell. Apart from the above listed applications, the recycled ZnO nanoparticles may find interesting uses in environmental, agricultural and medical sciences. These are useful as deodorizing and antibacterial agents for use in cotton fabric, rubber, and food packaging. Other related uses may be in products such as baby powder, calamine cream, anti-dandruff shampoos, antiseptic ointments, zinc oxide tape, and sunscreen lotions. Recovered ZnO nanoparticles could also play their role in drug delivery, clinical and biomedical areas like photodynamic cancer therapy.
We have demonstrates the successful recovery of the pure ZnO nanoparticles from the waste black powder of exhausted Zn-MnO2 dry alkaline batteries. The waste black powder is manually separated, leached with hydrochloric acid, followed by solvent extraction with a commercially available phosphine oxide reagent ‘Cyanex 923’. After extraction and a subsequent washing step, the pure zinc loaded organic phase has been subjected to combust at 600 C for the synthesis of high purity ZnO nanoparticles. Some important structural characteristics of the synthesized nanoparticles have been ascertained by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, atomic force microscopy, and ultraviolet-visible spectrometry. It may be pertinent to mention here that the treatment of vapors evolved during the combustion process may be required for the safety of the environment. The boiling points of the involved chemicals, i.e., n-hexane (69 C) and Cyanex 923 (310 C), are fairly distinct from the final annealing temperature (600 C). During practical operations, the whole setup can easily be designed to recycle the used reagents by introducing two fractional distillation steps before the final annealing. We have estimated the described recovery of the ZnO nanoparticles to be economically beneficial. The use of recycled chemicals may further improve the process economics.
Our research team is also working on the development of green processes for the recovery of pure cadmium, titanium and other useful nanoparticles from environmental wastes. In future, we are expecting to turn the different environmental wastes, such as spent batteries, biomass, electronic parts, LCD and LED panels, or semiconductor waste into lucrative raw materials for the recovery of high cost nanoparticles, quantum dots, nanowires etc. We invite the nano-, bio-, and environmental researchers, technologists and industry to collaborate in our efforts to revolutionize the recycling of general discards with an aim to produce specialized and strategic novel materials and composites.