Kali Sanjay

Electrolytic manganese dioxide (EMD): a perspective on worldwide production, reserves and its role in electrochemistry

Electrolytic manganese dioxide (EMD) is the critical component of the cathode material in modern alkaline, lithium, and sodium batteries including electrochemical capacitors and hydrogen production. In terms of environmental and cost considerations, EMD is likely to remain the preferred energy material for the future generation, as it has been in recent decades. Diminishing fossil fuels and increasing oil prices have created the need to derive energy from sustainable sources. The energy storage device from alternative and inexpensive sources, such as low grade manganese ores, has a niche in the renewable energy and portable electronics market. Despite vast manganese sources along with the current activity in producing modified EMD materials from secondary sources, to a surprise, India mostly imports EMD to meet its demand. Keeping this in view, a comprehensive review has been prepared on the synthesis, physical and electrochemical characterization of EMD produced from synthetic solutions and secondary sources. This review summarizes the available EMD sources in the world including Indian deposits and the recent investigations of fundamental advances in understanding the electrochemical mechanism involved in aqueous rechargeable batteries and electrochemical capacitors, thus leading to an improved energy storage performance, which is essential for their long term use in storing renewable energy supply.

Influence of Synthesis Temperature on the Growth and Surface Morphology of Co3O4 Nanocubes for Supercapacitor Applications

A facile hydrothermal route to control the crystal growth on the synthesis of Co3O4 nanostructures with cube-like morphologies has been reported and tested its suitability for supercapacitor applications. The chemical composition and morphologies of the as-prepared Co3O4 nanoparticles were extensively characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Varying the temperature caused considerable changes in the morphology, the electrochemical performance increased with rising temperature, and the redox reactions become more reversible. The results showed that the Co3O4 synthesized at a higher temperature (180 °C) demonstrated a high specific capacitance of 833 F/g. This is attributed to the optimal temperature and the controlled growth of nanocubes.

Aqueous processing of nickel spent catalyst for a value added product

Nickel was recovered from a fertilizer industry spent catalyst by leaching with nitric acid followed by nickel hydroxide precipitation. The optimization of temperature, initial acid concentration and particle size for leaching of the spent catalyst was done through 23 factorial design. A maximum extraction of 91.9% was achieved at 90 °C, 1.5M HNO3 and 62.5 μm particle size. Temperature and acid concentration showed positive effect, while particle size showed no effect. A regression equation was developed and employed to predict conditions for 100% extraction which were experimentally tested. Nickel hydroxide was electrochemically precipitated from the leach liquor and its maximum discharge capacity was found to be 155 mAh/g. A 3-stage counter current leaching circuit was designed to obtain a leach liquor of suitable pH. XRD characterization of the precipitated Ni(OH)2 shows to consist of both α- and β-forms.

Factorial design for process optimization and generation of kinetic data for yttrium and europium leaching

Factorial design has been implemented to develop regression equations for leaching of Y and Eu from phosphor coating of spent fluorescent lamps (FLs). On the basis of leaching extent, H2SO4 was the...

Electrochemical Fencing of Cr(VI) from Industrial Wastes to Mitigate Ground Water Contamination

Indiscriminate dumping of solid industrial wastes and the consequent ground water contamination by heavy metals such as Cr(VI) is a major environmental concern. Electrochemical fencing, an extension of electroremediation, appears to be a viable technique for impeding the vertical transport of heavy metals, dissolved in rain water, through the soil to mitigate ground water contamination. Preliminary experiments showed that electrochemical fencing captured 50% of the Cr(VI) dissolved in rain water. However, this percentage can be increased by changing, for example, electrode configuration or electrolyte composition. A novel mathematical model, that calculates the trajectory of Cr(VI) ions, was developed to provide practicing engineers a simple methodology to design and implement real-life electrochemical fencing systems. Because of its versatility, electrochemical fencing can be used to capture a wide variety of carcinogenic heavy metals, or even water soluble organic molecules, and hence warrants further investigation.

Electro-Crystallization of Antimony from Acidic and Alkaline Baths in Diaphragm-Less Cell

Studies based on electrocrystallization of antimony were carried out to evaluate the effects of current density and antimony concentration in the electrolytic bath on cathodic current efficiency, energy consumption, and quality of the deposits during electrowinning of antimony from Sb2O3-HCl and Sb2S3-NaOH systems. In acidic bath, current efficiency for electrodeposition of antimony increases with the increase in current density till 150 A/m2, beyond which it follows a trend of gradual diminution. On varying antimony concentration in the bath, current efficiency was found to improve significantly and the optimum antimony concentration in Sb2O3-HCl system was evaluated to be about 60 g/L. In alkaline bath, current efficiency was observed to be maximum at 50 A/m2 and further, with the increase in current density it progressively decreases. However, energy consumption for electrowinning of antimony in both of the baths gradually increases with the increase in current density. At a current density less than 150 A/m2, alkaline bath was found to be more current efficient in comparison to the acidic bath. Crystallographic studies by XRD, imaging by optical microscopic technique and morphological studies by SEM were also carried out to differentiate antimony deposits obtained from acidic and alkaline baths.

Electrokinetic cleaning of industrial residues

Abstract Processing of low grade ores for metal extraction leaves behind a huge mass of residue, which may be disposed by land filling. However, prior removal of toxic heavy metals is imperative to prevent ground water pollution. Electrokinetic remediation used for treating contaminated soils could be adapted for the removal of heavy metals from industrial residues. Preliminary electrokinetic cleaning experiments on dichromate residue showed the feasibility of removal of Cr(VI) from residue along with pH modification. From an initial concentration of 1758 mg kg−1, the concentration of Cr(VI) could be brought down to 615 mg kg−1, besides the drop in pH from 10·9 to 6·8 in 72 h. The residue thus can be a start-up material for other remediation processes such as phytoremediation.