New methods for extraction and separation of lanthanides with 2-octylaminopyridine

Transcription

1 A SYNOPSIS OF THE THESIS New methods for extraction and separation of lanthanides with 2-octylaminopyridine A great deal of attention has been devoted to study of extraction behaviour of rare earth metals for the last some decades, mainly due to emerging importance of these elements in various technologies related to metallurgy, nuclear energy, optical, magnetism, luminescence, laser materials, high temperature superconductors, secondary batteries, catalysis, red phosphors, among others. For a variety of uses in these specialized areas a high purity of the metals are often required. Being intricately similar in their chemical properties, lanthanides pose an exigent problem in their separations. The group separation methods for the lanthanides may be effected by one or other or some combination of the general procedures involving fractional crystallization of isomorphous salts, separations due to basicity differences, selective oxidation or reduction, physical differences in the respective elements. Basicity differences category of separation techniques involves fractional precipitation from solution, fractional thermal decomposition of salts, ion exchange and solvent extraction methods. It has been shown that ion exchange membranes could be used for separation of lanthanide elements. Although the method is of interest, since it offers the promise of a continuous process, more experimental work will be required to take assessment possible. Since the separations for a single cell are limited to a difference in the complexing constants with individual rare earths elements, a very large number of stages would be required to isolate pure material. Solvent extraction enjoys a favoured position among the separation techniques because of its ease, simplicity and wide scope. Its importance stems back to the rapid growth of science and technology. This is because an analytical i

2 scientist is always confronted with the problem of isolation of traces of metals from complex matrices. Solvent extraction is most rapid, selective and sensitive method of separation. The operation of equilibrium is possible in minimum time even by hand shaking. It is useful for isolation and purification of compounds, either inorganic materials or organic substances at macro and microgram concentration. That is the extraction efficiency or separation is independent of metal ion concentration. The technique has not only fascinated chemists, no matter whether they are analytical, inorganic, physical but also chemical engineers and technologists. Recent advances in analytical chemistry are characterized by great progress toward more powerful methods of separation, equalling in significance that great forward strides made in instrumental methods of determination. The application of zirconium as the cladding material in nuclear reactors, and demand for thorium in breeder reactors from thorium reach monazite sand of southern India is growing. Many of such separations have been carried out in process industries for pilot plant operations by solvent extraction technique. In the solvent extraction with high molecular weight amines all difficulties associated with the use of ion exchange are mitigated, the solvent extraction with HMWA facilitates selective transfer of solute between the organic and aqueous phase. The organic phase containing the high molecular weight amine is completely anhydrous in contrast to the usual ion exchange resin. This provoked our interest in extraction systems containing HMWA that are effective extractants. In the proposed work the studies has been undertaken on the development of new analytical methods for the extraction and separation of lanthanides like La(III), Ce(IV), Sm(III), Eu(III) and Dy(III) from weak organic acid media like sodium salicyalte and sodium succinate using 2-octylaminopyridine (2-OAP) in xylene. The work consist of the investigation of new liquid-liquid extractive separation procedures with the help of experimentation involving control of ph, salt concentration, concentration of extractant, equilibration period, effect of ii

3 diluents, aqueous to organic volume ratio, metal loading capacity of 2-OAP, effect of diverse ions and also effect of temperature on the extraction mechanism of respective metal ion. The developed method has been applied for the analysis of binary mixtures, ternary mixtures and for some real samples like monazite ore, composite material containing lanthanides. The present thesis is compiled with seven chapters. Chapter 1 describes the introductory part regarding the solvent exaction technique while chapter 2 deals with synthesis of 2-OAP and its characterization techniques. The actual experimental results obtained during different phases of investigation included in chapter 2 to 7. Upto date literature survey of extractive methods for respective metals is given in the beginning of each chapter. The details about these are given below. Chapter - 1 Introduction At the beginning a brief introduction of liquid-liquid extraction covering the theoretical aspects with special reference to principle, classification of extraction systems, factors affecting the extraction, criteria for selection of extractant and various techniques of solvent extraction has been described in chapter 1. Chapter - 2 Synthesis and characterization of 2-octylaminopyridine It includes a concise account of basic extractants and extraction mechanism related to respective systems. In this chapter synthesis of 2-OAP was carried out by using Borshch et. al. method. Synthesized 2-OAP was characterized by using UV, IR, and NMR spectroscopic techniques. iii

4 Chapter - 3 Analytical separation of lanthanum(iii) with 2-octylaminopyridine Systematic investigation of solvent extraction behaviour of lanthanum(iii) from salicylate medium in a xylene solution of 2-octylaminopyridine (2-OAP) is discussed. The effect of important variables like equilibrium time, nature of diluents, concentration of salicylic acid, extractant and metal ion on the extraction is discussed. Based on slope analysis method the stoichiometry of the extracting species is formulated as [2-OAPH +. La(Sal) - 2 ]. The reagents like sulphuric acid, acetic acid, hydrochloric acid, perchloric acid, water and buffer solutions are used for the stripping of the metal ions and the results are reported. The robustness of the recommended extraction procedure was demonstrated in the presence of several cations and anions which are commonly associated with it. The proposed method was satisfactorily applied to the separation of lanthanum(iii) from binary and ternary mixtures and also from real samples. Chapter - 4 Solvent extraction of quadrivalent cerium by using 2-octylaminopyridine from salicylate media. A new method for liquid-liquid extraction, separation and preconcentration of cerium(iv) with 2-OAP in salicylate solutions was investigated. The systematic experimental study has been done to find out hydrodynamic conditions so that we able to extract total cerium(iv) content present in the aqueous phase. Different physicochemical variables influencing the extraction of cerium(iv) such as ph, shaking time, nature of diluent, concentration of acids, extractant and metal ion has been studied. Also loading capacity of the extractant was assessed. The stoichiometric formula of ion-pair complex of cerium(iv) was proposed on the basis of slope analysis method which showed extraction proceeds via anion exchange mechanism from salicylate medium. Based on the partition data some important binary and ternary separations involving intra and inter group iv

5 elements have been achieved. The practical utility of the proposed procedure has been demonstrated by separating cerium(iv) from the solution of monazite sand and synthetic sample. The various thermodynamic functions like free energy( G), enthalpy( H) and entropy ( S) of extraction mechanism were explained by studying temperature effect experiment in the range of 308K to 315K. Chapter - 5 Liquid - liquid extraction of samarium(iii) from salicylate media using liquid anion exchanger Liquid - liquid extraction and separation of samarium(iii) was carried out by using M 2-octylaminopyridine in xylene at 298 K. The extraction behavior of samarium was studied as a function of equilibration time, diluent, ph, acid concentration, and extractant concentration. Samarium was quantitatively extracted at ph 7.5 to 10.0 from 0.01 M sodium salicylate with M 2-octylaminopyridine. The possible composition of the extracted species in organic phase have been determined by using model of slope analysis method and extraction mechanism was found to proceed via an anion exchange mechanism. The stripping efficiency was found to be quantitative in case of HNO 3, HCl and CH 3 COOH. The proposed method was satisfactorily applied to the separation of samarium(iii) from binary, ternary mixtures. The various thermodynamic functions like free energy( G), enthalpy( H) and entropy ( S) of extraction system were calculated. Chapter 6 Liquid anion-exchange extraction and separation of europium(iii) with 2-octylaminopyridine. Detailed account of liquid-liquid extractive separation studies of europium(iii) by using 2-octylaminopyridine in concentration range of 0.01 to v

6 0.5 M from xylene as a solvent. The extraction of europium(iii) was found to be quantitative in the 0.01 to 0.1 M sodium succinate. The effect of various physico chemical parameters were also investigated. The effect of various foreign ions on the proposed extraction extraction was discussed. Europium(III) was successfully separated and determined from binary and synthetic mixtures. Chapter 7 Solvent extraction studies of dysprosium(iii) using high molecular weight amine. A procedure is described for the liquid-liquid extraction and recovery of dysprosium(iii) from salicylate solution using 2-OAP as a extractant which is a high molecular weight amine. The quantitative extraction of dysprosium(iii) occurs from ph in between 8.0 to 10.5 using M 2-OAP in xylene. The extracted metal ion has been recovered by using (3 10 ml) 1.5 M acetic acid. The log-log plot of distribution ratio verses salicylate concentration and distribution ratio verses 2-OAP concentration indicates 1:2 and 1:1 stoichiometries respectively. The effect of various cations and anions on recovery of dysprosium(iii) was investigated. The tolerance limit was set as the amount of foreign ion causing a change ± 2 % error in the recovery of dysprosium(iii). The separation of dysprosium(iii) from binary and ternary mixtures containing commonly associated metal ions like U(VI), Th(IV), Nb(V), Zr(IV), La(III), and Ce(IV) using 2-octylaminopyridine has been achieved. (Dr. S. S. Kolekar) Research Guide (Mr. A. M. Mandhare) Research Student vi