R. Vijayalakshmi

Studies on uranium extraction from phosphoric acid using di-nonyl phenyl phosphoric acid-based synergistic mixtures

Abstract During acidulation of phosphate rock with sulphuric acid to produce phosphoric acid for fertilizer application, the uranium values contained in the rock also become solubilised. The phosphoric acid produced by the ‘di-hydrate’ process, containing 26–30% P2O5, called the ‘weak phosphoric acid’ (WPA), is concentrated to >50% P2O5 grade, known as ‘merchant grade acid’ (MGA). The ‘hemi-hydrate’ process directly yields acid of high P2O5 content. The uranium concentration varies with acid concentration, provided oxidising conditions are maintained so that selective precipitation of uranium does not take place. Depending on the rock used, the acid produced can contain 0.0050–0.05 g U3O8/L. Separation of uranium by solvent extraction employing a novel synergistic combination of organo-phosphorus reagents is reported in this paper. In particular, the solvent mixture of di-nonyl phenyl phosphoric acid (DNPPA) with di-butyl butyl phosphonate (DBBP) in an aliphatic diluent has been found to be a stronger extractant than the commonly used combination of di-(2-ethyl hexyl) phosphoric acid (DEHPA) with tri-n-octyl phosphine oxide (TOPO). The DNPPA–TOPO mixture is an even stronger extractant. Results on extraction from both WPA and MGA are reported. Stripping of uranium from the organic phase was achieved with concentrated phosphoric acid in the presence of Fe+2 reducing agent at elevated temperature. Stripped uranium was subjected to a second cycle of extraction-stripping and recovered as a peroxide precipitate of high purity. Brief results on allied areas of acid pre-treatment and post-treatment are included.

Uranium extraction from partially neutralised and diluted phosphoric acid using a synergistic organophosphorous solvent mixture

A process is described for the separation of uranium from partially neutralised and diluted phosphoric acid (PNDA) which is generated in fertiliser plants when phosphoric acid is used to scrub ammoniacal vapours from the neutralisation reactors. The separation process is based on solvent extraction using a synergistic mixture of di-2-ethyl hexyl phosphoric acid (DEHPA) with tri-n-alkyl phosphine oxide (TAPO). The effects of process parameters including concentration of DEHPA and TAPO, temperature and degree of neutralisation of acid have been investigated. Laboratory scale and pilot plant scale tests have been carried out. The extraction reaction is found to be exothermic with enthalpy effect of 30 kJ/mol. Tests on stripping of extracted uranium and recovery of uranium have been carried out and results are reported. Analysis of data indicates significant differences in the mechanism of uranium extraction from PNDA and the mechanism reported in literature for extraction of uranium from weak phosphoric acid using a similar solvent mixture.

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...

Separation of uranium from weak phosphoric acid using di-nonyl phenyl phosphoric acid in combination with tri-n-butyl phosphoric acid

A process has been described for the extraction of uranium from weak phosphoric acid using di-nonyl phenyl phosphoric acid in combination with synergistic reagent tri-n-butyl phosphate. The effect of process parameters including concentrations of extractant and phosphoric acid has been studied. A plausible extraction mechanism has been established using slope analysis technique. The enthalpy change for extraction process, ΔH, was determined for the solvent with and without synergistic reagent. Based on the optimised parameters batch counter current extraction and stripping have been studied and the uranium recovery was found to be ∼80%.

Studies on di-nonyl phenyl phosphoric acid (DNPPA): a potential extractant for uranium recovery from merchant grade phosphoric acid (MGA)

ABSTRACT Methods of purification of di-nonyl phenyl phosphoric acid (DNPPA), its solubility in different aqueous solutions and its recovery from acidic as well as alkaline solutions employing various diluents have been described. Liquid-solid separation method based on Nd-DNPPA salt precipitation route as well as by liquid-liquid separation based on mono ethylene glycol treatment has been studied for the purification of DNPPA. While the purity obtained in the two methods was >94%, the recovery in Nd-DNPPA salt method was only 50% as compared to 90% in mono ethylene glycol method. The solubility of DNPPA in aqueous streams like WPA (5.6 M), MGA (12 M), sulphuric acid (5.4 M), phosphoric acid (5.5 M), oxalic acid (0.95 M), sodium carbonate (1.13 M), water etc. has been determined. Recovery of DNPPA from aqueous phase was investigated employing various diluents such as petrofin, benzene, toluene, MIBK, iso-decanol, 1-octanol, etc. The effects of process variables such as phase ratio (O/A), pH, DNPPA concentr...

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.