Kanchan Mondal

A parametric evaluation of the removal of As(V) and As(III) by carbon-based adsorbents

Abstract The As(V) and As(III) removal efficiency of a char-carbon (CC), derived from fly ash in this laboratory, is compared with those of a commercially available Darco activated carbon (DC) and a carbon produced by arcing of graphite rods (AC). The results indicate that CC and AC adsorbents remove almost equal amounts of As(V) at optimum conditions; however, on a percent basis CC removes more As(III) than does AC. In comparison, sample DC was found ineffective for the removal of As(III) and As(V). The present investigation revealed that the adsorption of As(V) onto CC is influenced by pH, initial metal concentration and temperature. Zeta potential measurements were obtained to explain the metal removal behavior of the adsorbents used in this investigation. Since CC shows significant removal efficiency for both As(V) and As(III), there are good prospects for arsenic fixation on CC in practical applications.

Selenate removal from sulfate containing aqueous solutions.

The performance of selenium remediation agents, mainly γ alumina sorbents and zerovalent metals is greatly inhibited in the presence of large concentrations of sulfate found in selenium-rich agricultural drainage water. It is therefore imperative to remove sulfates from these contaminated waters, prior to their treatment for selenium removal. This paper presents data on enhanced selenium removal resulting from a two stage process involving the use of barium chloride in the first stage followed by a selenium remediation agent in the second. Barium chloride is known to stoichiometrically precipitate out sulfates. In addition to the sulfate removal from the contaminated solutions, a significant amount of selenate immobilization in the precipitated solids was achieved. When a loading of 15 g l−1 of BaCl2 was employed, 100 % selenate removal from an aqueous solution (containing 1 mg l−1 selenate, 4 g l−1 of sulfate and 2.5 g l−1 of chloride) was achieved by the use of BaCl2 alone. Bimetallic NiFe particles, γ alumina and activated carbon were employed to further remove selenium in the second stage. A solution containing 1 mg l−1 and 4 g l−1 of selenate and sulfate, respectively, when treated sequentially with 10 g l−1 of BaCl2 and NiFe powder showed 100 % selenium removal.

Mediator-assisted electrochemical hydrogenation of soybean oil

Abstract In this study, formate ion was used as a shuttle for transferring hydrogen to the surface of a hydrogenation catalyst (7% Ni/SiO 2 ), where the soybean oil was reduced in such a way that the production of deleterious trans fatty acid was greatly reduced. The formate ion was regenerated at the cathode and thus acted as a mediator for the hydrogenation process. The effect of temperature, pH, and applied potential (current) on the fatty acid profile of the hydrogenated soybean oil was determined. The effects of oil and catalyst loadings on the final product quality were also determined. The application of a current density of 10 mA / cm 2 resulted in hydrogenated product with desired fatty acid composition. Kinetic studies were also performed for experiments conducted at constant potential conditions. A model that assumes: (i) the rate of regeneration of formate from its oxidized form (bicarbonate ion) is limited by the mass transport effects, and (ii) second-order elementary reaction rate expression was developed to describe the hydrogenation reaction was developed and tested. A good correlation between the model predictions and experimental data was observed.

Comparative study of selenite adsorption on carbon based adsorbents and activated alumina

Abstract The Sorption characteristics of carbon‐based adsorbents such as activated carbon and chitin for the removal of selenite, Se (IV), an anionic, hazardous contaminant, are compared with those of a and y alumina. Batch experiments were conducted to determine the influence of pH, concentration of adsorbate, adsorbent loading and temperature on the sorption characteristics of the adsorbents. Generally, low pH of the solution resulted in favorable selenium removal. With the exception of activated carbon, uptakes decreased with increase in temperature. In comparison, chitin was found to be far less effective for the removal of Se (IV) from aqueous solutions. The data also showed that y alumina provided higher selenium removal percentages (99%) compared to α alumina (94%), activated carbon (87%) and chitin (49%). The selenite removal was found to decrease with increasing initial Se (IV) concentration in the solution. Adsorption capacities of the adsorbents are reported in terms of their Langmuir adsorption isotherms. The adsorption capacity (on unit mass basis) of the adsorbents for selenite is in the order: chitin (specific area (sa) =9.58 m2g‐1) < activated carbon (sa = 96.37 m2g1) < a alumina (sa = 6 m2g‐1) < y alumina (sa = 150m2g‐1).

Regeneration of hexavalent chromium using a Bi-doped PbO2 anode

The rate of hexavalent chromium regeneration from trivalent chromium, present as an impurity in a chromium plating solution at the Bi-doped PbO2 anode, is found to be approximately four times greater than the corresponding rate observed for a PbO2 coated lead (anodized lead) anode. A mathematical model that takes into account species electromigration and associated mass transfer effects was developed and tested. Dynamic concentration data for various chromium species were used along with the mathematical model to evaluate the various rate parameters.

Recovery of metallic impurities from chromium plating solutions by electromigration

Conclusion The porous pot method appears to be a viable and a most cost-effective technique for the simultaneous regeneration and purification of the spent chromium plating solutions. The purification of the solution is brought about by the process of electromigration of metallic impurities to the cathode compartment where they are either deposited or precipitated de pending on the pH of the catholyte. Oxidation of trivalent chromium at the lead cathode results in further regeneration of the solution. The experiments strongly suggest that the chromic-oxide-containing solution serves as a most effective catholyte, since it prevents sludge formation, allows for metal electrodeposition, serves as a source for the makeup of hexavalent chromium needed in a spent plating solutions, in addition to being inexpensive and readily available to electroplaters. Work is in progress to use mathematical modeling to investigate the kinetics of the removal of metallic impurities and the reoxidation rate.

Magnesian calcite sorbent for carbon dioxide capture

Magnesian calcite with controlled properties was synthesized for the removal of carbon dioxide. The results from characterization, reactivity and CO2 capture capacity for different synthesis conditions are reported. The magnesian calcite samples (CaCO3:MgCO3) were synthesized by the coprecipitation of specific amounts of commercially available CaO and MgO by carbon dioxide. Characterization was done with BET, SEM/EDS, particle size analysis and XRD. The capacity was measured using TGA cycles at 800 °C and compared for different preparation conditions. The effects of CaO, MgO and surfactant loading on the physical properties and carbonation activity were studied to determine the optimal synthesis condition. A long‐term carbonation–calcination cycling test was conducted on the optimal sample. It was observed that the sample maintained its capacity to 86% of its original uptake even after 50 cycles.

Aligned carbon nanotube/zinc oxide nanowire hybrids as high performance electrodes for supercapacitor applications

Carbon nanotube/metal oxide based hybrids are envisioned as high performance electrochemical energy storage electrodes since these systems can provide improved performances utilizing an electric double layer coupled with fast faradaic pseudocapacitive charge storage mechanisms. In this work, we show that high performance supercapacitor electrodes with a specific capacitance of ∼192 F/g along with a maximum energy density of ∼3.8 W h/kg and a power density of ∼28 kW/kg can be achieved by synthesizing zinc oxide nanowires (ZnO NWs) directly on top of aligned multi-walled carbon nanotubes (MWCNTs). In comparison to pristine MWCNTs, these constitute a 12-fold of increase in specific capacitance as well as corresponding power and energy density values. These electrodes also possess high cycling stability and were able to retain ∼99% of their specific capacitance value over 2000 charging discharging cycles. These findings indicate potential use of a MWCNT/ZnO NW hybrid material for future electrochemical energy...

Simultaneous influence of gas mixture composition and process temperature on Fe2O3->FeO reduction kinetics: neural network modeling

The kinetics of Fe2O3®FeO reaction was investigated. The thermogravimetric (TGA) data covered the reduction of hematite both by pure species (nitrogen diluted CO or H2) and by their mixture. The conventional analysis has indicated that initially the reduction of hematite is a complex, surface controlled process, however once a thin layer of lower oxidation state iron oxides (magnetite, wustite) is formed on the surface, it changes to diffusion control. Artificial Neural Network (ANN) has proved to be a convenient tool for modeling of this complex, heterogeneous reaction runs within the both (kinetic and diffusion) regions, correctly considering influence of temperature and gas composition effects and their complex interactions. ANNs model shows the capability to mimic some extreme (minimum) of the reaction rate within the determined temperature window, while the Arrhenius dependency is of limited use.

Removal of Iron and Nickel from Solutions by Application of Electrical Fields

Metallic impurities such as Ni Fe, Cu ions in chromium plating solutions can be removed by electromigration followed by electrodeposition or coagulatiion using a porous pot, suspended in the bath and containing a lead cathode. In the same process, Cr(III) is oxidized to Cr (VI) at the insoluble lead anode leading to regeneration of the plating solution. Previous research and data from industrial operations have indicated the “porous pot” method could be a cost-effective and environmentally friendly method to continuously separate impurities and recycle spent chromium solutions. However, no data are available that relate the various concentrations of impurities to the extent and the rate of their removal. This investigation focused on the use of five suitable catholytes for the removal of impurities. Up to 60% nickel and 52% iron removal were observed in orthophosphoric acid and sodium monophosphate catholytes respectively. In addition to these two electrolytes, chromic acid appears to be a most suitable c...