P.K. Tewari

Polyhydroxamic Acid Sorbents for Uranium Recovery

Crosslinked polyacrylamides were synthesized by solution polymerization using benzoyl peroxide as the radical initiator. The water–insoluble polymer obtained was functionalized by reacting with hydroxylamine to convert the amide group into hydroxamic acid group. The resultant functionalized polymer was characterized in terms of moisture uptake, elemental composition, IR spectra, thermal stability, exchange capacity and heavy metal sorption. The sorbent, obtained in particulate form, was investigated for its sorption properties with respect to uranium from uranyl nitrate solutions under unstirred batch conditions. This paper will concentrate on preparation, characterization and performance evaluation with respect to uranium sorption as a function of concentration, time, solution pH and temperature. The potential of this sorbent for uranium and other heavy metal ion recovery from sea water is ascertained.

Potential of carbon nanotubes in water purification: an approach towards the development of an integrated membrane system

The problems of water shortages and lack of access to safe drinking water have been and will continue to grow as major global problems. To alleviate these problems, water purification technologies are being updated. Recent years have witnessed impressive breakthroughs towards practical application of nanostructured materials such as Carbon Nanotubes (CNTs) in the field of water purification owing to their unique thermal, electrical and mechanical properties. These nanoscale structures need to be arranged into well-defined configurations in order to build integrated systems with high efficiency (the nanotubes being reusable, whereas the traditional membranes foul easily and require frequent replacements), high flux (owing to the hydrophobic super smooth inner surface of nanotubes), and with improvements in chemical selectivity (through suitable chemical functionalisation of the CNTs), so that the idea of using CNTs in separation technology can be made realistic and the potential benefits of practical application of these unique materials can be exploited. This paper assesses the CNTs as an emerging technology in water purification system, particularly with respect to its potential for the removal of arsenic, fluoride, heavy metals and toxic organic components.

Development, Characterization and Performance Evaluation of Positively-Charged Thin Film-Composite Nanofiltration Membrane Containing Fixed Quaternary Ammonium Moieties

Thin film composite (TFC) type positively-charged nanofiltration membranes, bearing fixed quaternary ammonium moieties, have been developed and studied. Branched polyethyleneimine (PEI) was functionalized by reaction with glycidyl trimethyl ammonium chloride (GTACl) to introduce quaternary ammonium chloride. Positively-charged TFC membranes were prepared by in situ interfacial polymerization of functionalized PEI and terephthaloyl chloride. The effects of variation of chemical compositions and other experimental conditions such as curing temperature and duration of curing on the performances of the membrane were studied. ATR FT-IR spectroscopy was done to establish the presence of charge-bearing groups in the membrane. The membranes were tested using single solute feed solutions of NaCl, Na2SO4, CaCl2, and MgSO4. Positive charges on the membranes were estimated in terms of their ion-exchange capacities (IEC). The values were also correlated to the solute-rejection properties of the membranes.

Separation Behavior of Composite Polyamide Membranes from Mixed Amines: Effects of Interfacial Reaction Condition and Chemical Post-Treatment

Abstract Composite polyamide membranes are prepared using in-situ interfacial polymerization using mixed amine system comprising 1,4-phenylene diamine and pipperazine. Separation performance of the membranes are studied as a function of the concentration of amine and acid chloride, the concentration ratio of the amines, nature of the acid chloride, and the presence of surfactant and acid acceptor in the aqueous reagent. The effect of esterification and hydrazide reactions involving residual carboxylic acid groups in the polymeric membranes on the co-polymeric composite membrane performance is also studied. The membrane performance can be tailored easily by conversion of the residual reactive functional groups in post-treatment.

Relative technoeconomics of multistage flash distillation and reverse osmosis for seawater desalination - a case study

Abstract A case study has been carried out for putting up a 225,000 cubic meter/day desalination plant in the city of Madras on south east coast of India and relative techno-economics of single purpose and dual purpose Multistage Flash (MSF) and Reverse Osmosis (RO) has been presented.

Preparation, characterisation and performance evaluation of anti-biofouling property of carbon nanotube-polysulfone nanocomposite membranes

Membrane based process assumes a significant importance among all the separation practices being followed in the present time. Among the limitations faced by the membrane process, the most critical one is the bio-fouling, which results in lesser throughput as well as deterioration in membrane life. To enhance the anti-biofouling behaviour of the membrane surface, nanostructured materials offer a tremendous opportunity. One potential candidate among them is the carbon nanotubes (CNTs). With the objective of having improvement over the existing anti-biofouling tendency of polysulfone membranes, nanocomposites were developed with impregnation of both single walled as well as multi walled CNTs. The performance of the membranes was evaluated in terms of pure water permeability and solute rejection studies. The membranes were characterised using scanning electron microscopy, atomic force microscopy and contact angle studies. The anti-biofouling performance of the membrane surfaces was examined using E. Coli culture and a comparison of antibiofouling tendency obtained with the nanocomposites over the pure polysulfone membranes has been made. It was confirmed that membranes with impregnation of single walled CNTs possess better antibiofouling behaviour as compared to pure polysulfone as well as polysulfone membrane embedded with multi walled CNTs.

Strategy of deriving 'wealth from waste' from concentrated brine of desalination plant

Research and technological developments are being pursued vigorously all over the world to reduce the cost of desalinated water. Thermal and membrane-based desalination processes are very well known and plants are being operated to augment the demand of fresh water essential for drinking in water-scarce countries and to sustain the industrial processes. Any further improvement in energy reduction can only be marginal considering the complexity of the desalination system. The alternative approach is to add value by recovering edible salt, rare and valuable metals, such as caesium, titanium, uranium and vanadium, from the reject brine streams. In this regard, a novel polymeric chelating resin was designed and developed in Desalination Division, BARC laboratory with significant potential for this achievement. In this paper, the characteristics and potential of the resin have been described for the recovery of valuable elements based on experimental findings.

Effect of surface roughness & polymeric additive on nucleate pool boiling at subatmospheric pressures

Abstract This investigation pertains to boiling heat transfer from a submerged flat surface at subatmospheric and atmospheric pressures in the presence of hydroxy ethyl cellulose (HEC) as a polymeric additive in small doses. Boiling was carried out in presence of the additive on smooth and rough aluminium surfaces having effective cavity size within the range as predicted by Hsu model and the pressure was kept in the range of 8 – 100 KN/sq.m (abs). Effects of surface roughness, saturation pressure and polymer concentration on boiling heat transfer were studied and the results were compared with Rohsenows correlation.

Uranium Permeation from Nitrate Medium Across Supported Liquid Membrane Containing Acidic Organophosphorous Extractants and their Mixtures with Neutral Oxodonors

Permeation of U(VI) from nitric acid solution has been studied across supported liquid membrane (SLM) using bis[2,4,4 trimethyl pentyl] phosphinic acid (Cyanex 272) either alone or in combination with neutral donors like Cyanex 923 (a mixture of four trialkyl phosphine oxides viz. R3PO, R2R′PO, RR′2PO, and R′3PO where R: n-octyl and R′: n-hexyl chain), TBP (tri-n-butyl phosphate), and TEHP (tris-2-ethylhexyl phosphate) dissolved in n-paraffin as carriers. Effect of various other parameters such as nature and concentration of receiver phase, feed acidity, uranium concentration, pore size, and membrane thickness on U(VI) transport across SLM were investigated. Transport behavior of U(VI) was also compared with other derivatives of phosphoric acids like 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A), dinonyl phenyl phosphoric acid (DNPPA) under identical conditions and it followed the order: Cyanex 272 > PC88A > DNPPA. 2 M H2SO4 was suitable for effective U(VI) transport across SLM. Presence of neutral donors in carrier showed significant enhancement in U(VI) permeation in the order: Cyanex 923 > TBP > TEHP. U(VI) transport decreased with increased membrane thickness as well as decrease in pore size. The optimized conditions were tested for recovery of U(VI) from uranyl nitrate raffinate (UNR) waste generated during purification of uranium.

Membrane development for applications in hydrogen production using the sulphur-iodine thermochemical route

Careful optimisation of a safe and sustainable route for hydrogen production is a pressing need. Thermochemical processes employing water as raw material and nuclear/renewable energies as energy source are believed to be the best possible option in this direction, while alarming issues such as climate change and global warming are being taken into account. Amongst the well-identified cycles, the sulphur-iodine (S-I) thermochemical route assumes the highest thermal efficiency and the best one as regards its coupling to a high temperature nuclear reactor. Material development is the key issue to be addressed to realise successfully the potential of the S-I cycle. The most important area is development of gas-permeable membranes for enhancement of the equilibrium decomposition of HI, which is the most intricate step as far as the overall process efficiency is concerned. In order to overcome the low efficiency associated with the low equilibrium decomposition of HI, the authors intend to develop a hydrogen pe...