Kartikey K. Yadav

Spectroscopic investigation on europium complexation with humic acid and its model compounds.

Time resolved fluorescence spectroscopy (TRFS) of Eu(III) (an analogue of trivalent actinides) complexation with humic acid (HA) and its model compounds, namely phthalic acid (PA), mandelic acid (MA) and succinic acid (SA) has been carried out at varying concentration ratios of ligand to metal ion. The emission spectra were recorded in the range of 550-650nm by exciting at an appropriate wavelength. The intensity of the 616nm peak of Eu(III) was found to be sensitive to complexation. The ratio of the intensities of 616 and 592nm peaks was used to determine the stability constants of Eu-phthalate, Eu-mandelate and Eu-succinate complexes. In the case of model compounds, the life-time was found to increase with increasing ligand to metal ratio (L/M) indicating the decrease in quenching of the fluorescence by coordinated water molecules with increasing complexation. On the other hand in the case of HA, the life-time was found to be constant at least up to L/M of 5, indicating the formation of outer sphere complex. Beyond L/M=5 the life-time value was found to increase which can be attributed to the binding of the metal ion to the higher affinity sites in the HA macromolecule.

Extraction and Stripping Behavior of Iron (III) from Phosphoric Acid Medium by D2EHPA Alone and Its Mixtures with TBP/TOPO

In the present study an attempt has been made to understand the extraction and stripping behavior of iron (III) with D2EHPA alone and its mixture with TBP or TOPO in phosphoric acid medium. Effect of variables such as concentrations of iron (III), phosphoric acid, and phosphate in the aqueous phase, D2EHPA, TBP, and TOPO concentrations in the organic phase and temperature on the extraction process has been studied. The extraction of iron (III) decreased with increase in phosphoric acid concentration. The increase in D2EHPA concentration increased the extraction of iron (III). The presence of TOPO or TBP with D2EHPA showed antagonism. The increase in temperature decreased the extraction of iron (III) with D2EHPA alone and its mixture with either TOPO or TBP showing the exothermic nature of the extraction reaction. The stripping of iron (III) by various reagents followed the order: oxalic acid > phosphoric acid > hydrochloric acid > sulphuric acid > mixture of sulphuric and hydrofluoric acids > ascorbic acid > citric acid irrespective of extraction systems. Higher temperature favors the stripping. The effect of diluents on iron (III) extraction has also been studied. The mechanism of extraction has been explained in the light of the results obtained.

Simultaneous recovery of yttrium and uranium using D2EHPA–TBP and DNPPA–TOPO from phosphoric acid

ABSTRACT A method to simultaneously recover yttrium and uranium from phosphoric acid using DNPPA + TOPO and D2EHPA + TBP solvent systems has been developed. The solvent mixture DNPPA + TOPO is employed for merchant grade phosphoric acid, while the D2EHPA + TBP solvent system is employed for wet process phosphoric acid to recover uranium and yttrium. In the method, four steps are involved for the yttrium recovery: (1) yttrium is co-extracted with uranium using the two organic systems; (2) yttrium is selectively stripped from the loaded organic solutions; (3) yttrium is recovered from the strip liquor by double sulphate salt precipitation; (4) yttrium double sulphate salt is dissolved and precipitated with oxalic acid to generate pure yttrium product. Selective stripping of yttrium from the loaded organic solutions with various strip solutions was tested. It was found that 10% (w/v) Na2SO4 + 30% H2SO4 and H2SO4 (30 to 40%) are the most preferable conditions with more than 95% of yttrium recovered and less t...

Sorption Behavior of Y(III) from Chloride Medium with Polymer Composites Containing Di-2-ethyl Hexyl Phosphoric Acid and Multiwall Carbon Nanotube

Extractant impregnated polyethersulfone beads have been prepared by phase inversion method and investigated for yttrium recovery from aqueous medium. The effect of experimental parameters on yttrium sorption has been studied. Quantitative sorption of yttrium (> 90%) was attained after 8 hours of equilibration time in the case of D2EHPA impregnated composite beads. Analysis of sorption data by different kinetic and diffusion models suggested that the sorption of Y(III) followed the pseudo-second order model. Stability tests with polymeric composite beads by multiple cycles of sorption and desorption of Y(III) have established the feasibility of reusing the beads for sorption of metal ions.

Dysprosium sorption by polymeric composite bead: Robust parametric optimization using Taguchi method

Polyethersulfone-based beads encapsulating di-2-ethylhexyl phosphoric acid have been synthesized and evaluated for the recovery of rare earth values from the aqueous media. Percentage recovery and the sorption behavior of Dy(III) have been investigated under wide range of experimental parameters using these beads. Taguchi method utilizing L-18 orthogonal array has been adopted to identify the most influential process parameters responsible for higher degree of recovery with enhanced sorption of Dy(III) from chloride medium. Analysis of variance indicated that the feed concentration of Dy(III) is the most influential factor for equilibrium sorption capacity, whereas aqueous phase acidity influences the percentage recovery most. The presence of polyvinyl alcohol and multiwalled carbon nanotube modified the internal structure of the composite beads and resulted in uniform distribution of organic extractant inside polymeric matrix. The experiment performed under optimum process conditions as predicted by Taguchi method resulted in enhanced Dy(III) recovery and sorption capacity by polymeric beads with minimum standard deviation.

Adsorptive Separation of Entrained Di-Nonyl Phenyl Phosphoric Acid from Merchant Grade Phosphoric Acid by Activated Charcoal: Kinetic and Equilibrium Studies

The separation of entrained di-nonyl phenyl phosphoric acid (DNPPA) from merchant grade phosphoric acid (MGA) by adsorption on the coconut shell based activated charcoal has been carried out. The effect of various process parameters, such as DNPPA concentration in aqueous phase of MGA, equilibrium time, amount of activated charcoal and temperature upon adsorption capacity of activated charcoal has been studied. The results showed that the adsorption equilibrium was reached after 240 minutes. The adsorption phenomenon followed pseudo-second order kinetics. Adsorption of DNPPA increased with initial concentration of DNPPA in the range of 50 to 200 mg/L. The experimental data fitted well with the Freundlich isotherm model. Decrease in adsorption with increase in temperature suggests that the adsorption process is exothermic in nature. The value of enthalpy change (ΔH = −35.52 kJ/mol) indicated that DNPPA adsorption on activated charcoal is a physisorption phenomenon. Column operation was carried out to obtain a breakthrough curve. Desorption of DNPPA with 10% NaOH yielded near quantitative regeneration of activated charcoal in three contacts.

Statistical study of factors affecting the phase separation kinetics in solvent extraction for uranium recovery from phosphoric acid

ABSTRACT The phase separation kinetics for the process of recovering uranium from phosphoric acid medium (WPA) with 1.5 M D2EHPA + 0.2 M TBP is influenced by process variables such as D2EHPA/TBP concentration in the organic phase, acid concentration of the aqueous phase, temperature, phase ratio (A/O). To correlate the effect of these variables on phase separation kinetics (phase separation time, specific settling rate (SSR) for aqueous and organic), a statistical approach of data generation and analysis using factorial design of experimentation (DOE) has been adopted. The significance of individual variables and their mutual interactions on phase separation behaviour in WPA-D2EHPA + TBP process was statistically derived using the DOE data. Mathematical models representing a relation between the responses (phase separation time, SSR organic or SSR aqueous) and variables were established. The percentage effects of each variable on response were calculated from these models. Further a real variable mathemat...

Role of additives in the matrix of solvent encapsulated beads on its yttrium sorption from aqueous streams

ABSTRACT Polyethersulfone (PES)-based beads encapsulating organic extractant PC88A and additives have been prepared, characterized and evaluated for yttrium sorption from aqueous chloride medium. The role of additives on modifying the morphological structure of the beads resulting in varying degrees of sorption has been examined. Amongst the various additives investigated, polyvinyl alcohol (PVA) led to significantly enhanced sorption of yttrium. The sorption data were analyzed by different isotherms. The mechanism of sorption was found to proceed via intraparticle diffusion as well as film diffusion following pseudo-second-order kinetics and chemisorption. The polymeric beads were found to be highly stable toward repeated numbers of sorption and desorption of yttrium.

Studies on Phase Separation Kinetics in Solvent Extraction for Uranium Recovery in DNPPA + TOPO/MGA System

The present paper deals with the study on phase separation kinetics of di nonyl phenyl phosphoric acid (DNPPA)–tri octyl phosphine oxide (TOPO)–petrofin–phosphoric acid system. Factorial design of experiment (DOE) has been utilized to illustrate the effect of different process variables such as extractant concentration in the organic phase, phosphoric acid concentration in the aqueous phase, temperature, phase ratio, and stirring speed on phase separation time (tp) and specific settling rates (SSR of organic and aqueous phase). The dependence of individual variables and their mutual interactions on phase separation kinetics was also deduced. A mathematical correlation relating process variables and response (tp and SSR) was developed which allows defining the percent effect of each of the variables on response. The influence of variables on response was found to be significant at 99% confidence level, while the interaction effect among variables aqueous acid concentration, organic concentration, and temperature on tp was significant at 95% confidence level. Dimensionless mathematical correlations were transferred to real variables empirical model to predict the phase separation behavior of DNNPA-TOPO-petrofin-phosphoric acid system and found to be in good agreement with the experimental data.