STUDIES ON SYNERGISM IN THE EXTRACTION OF SOME METAL CARBOXYLATES AND THE EXTRACTION OF METAL CITRATE COMPLEXES BY HIGH MOLECULAR WEIGHT AMINES

Abstract

Among the various separation techniques solvent extraction is rated as one of the most useful techniques, mainly, because of its versatility, speed and ease of operation. This can be safely extended from microlevels to macroconcentrations. The technique is used for the purposes of purification, enrichment and analysis. Besides having an extremely wide range of applications, it involves the study of some of the fundamental principles of chemistry. Scientists working in a wide variety of professions are interested in the technique and the research publications appear in journals of diverse fields. A variety of extraction systems with high capacity and good recycling properties are being investigated and put to various analytical and industrial applications. In the last two decades carboxylic acids and high molecular weight amines have gained enough popularity as extractants because of certain inherent advantages. The extraction behaviour of metal ions in solutions of carboxylic acids in non-polar solvents is more or less similar to their uptake on resinous cation exchangers and sometimes they are referred as liquid cation exchangers. A variety of carboxylic acids, singly or in conjunction with some other compounds, have been explored for the extraction of different metal ions. The various extraction systems can be broadly classified under the following heads s ~ii~ (i) Extraction of metal ions with carboxylic acids by simple compound formation. ( ii) Synergistic extraction of metal carboxylates in the presence of neutral organophosphorus compounds and nitrogen containing organic bases. (iii) Extraction of anionic metal carboxylates with high molecular weight amines (HMWA) by ion pair formation. A survey of literature reveals that a major portion of the work on the extraction of metal carboxylates deals with the systems belonging to category (i). However, there Is a sufficient scope of work on the systems under (ii) and (iii). High molecular weight amines, sometimes referred as liquid anion exchangers, uniquely combine some of the advantages of liquid-liquid extraction and icn-exchange. They have been extensively used for the extraction of various anionic metal complexes and find a variety of applications. Most of the work on these extractants involves the extraction of metal ions from inorganic acid media. It is only in the last decade that some interest has been shown towards the extraction of metal ions in these extractants from organic acid media. Relatively little information is available on the extraction of anionic metal citrate complexes in HMWA. The present thesis embodies work on the synergistic extraction of some metal ions with, lower fatty acids (C^ - CL) -111- in the presence of nitrogen containing organic bases and the extraction of a few anionic metal citrate complexes in long chain alkylamines. For the convenience of presentation the thesis has been divided into the following five chapters. Chapter I gives a brief introduction to the carboxylic acids and high molecular weight amines as extractants for metal ions. A detailed report of the status of research on these extraction systems is also presented. Chapter II includes details about the various materials and the equipment used for the present investigations. Chapter III deals with the extraction of Zn(II), Cd(Il) and Co(H) with chloroform solution of lower fatty acids namely; propionic, butyric and valeric acids in the presence of some aliphatic and heterocyclic amines. The effect of such variables as the pH of the aqueous phase, concentrations of metal ion, acid and amine and the nature of organic diluent on extraction has been investigated. The relevant equilibrium treatment for the system considering the dimerization of the acids and the formation of amine salt in the organic phase has been discussed. The extraction efficiency of different acids follows an order; Propionic < Butyric < Valeric The most probable composition of the synergistic adduct has been proposed on the basis of slope analysis. In the cases of -iv- Zn(II) and Cd(II) the extracted species are MA2.3HA.B and MAp.2HA.2B (M2+ • metal ion, HA =acid and B• amine) in the presence of aliphatic and heterocyclic amines, respectively. For Co(Il) the extracted species is found to be MA2.2HA,2B except in the butyric acid - quinoline system where it is MAp.HiU2B,H20. From the partition data the values of extraction constants (K) have been calculated and the relative effectiveness of different amines as synergists is compared. The heterocyclic amines are found to be better synergists than the aliphatic counterparts. Chapter IV reports the extraction of anionic citrate complexes of Mn(II), Co(ll), Zn(II), Cd(II), Cr(lII) and Fe(III) by chloroform solution of some of the high molecular weight amines. Prim^ne JM-T, Amberlite LA-2, Alamine 336 and Aliquat 336 have been used as the representatives of primary, secondary and tertiary amines and quaternary ammonium salt, respectively. The effect of various parameters such as, pH of the aqueous phase, pre treating acid, cation of the citrate, type of amine and concentrations of metal ion, ligand and amine on extraction has been investigated. Besides chloroform some other solvents have also been used to study the effect of the nature of organic diluent on extraction. It was observed that sulphuric acid pretreated Primene JM-T and Aliquat 336 arc the best extractants for these anionic metal citrate complexes. On the basis of the results of log-log plots of amine concentration versus distribution ratio the compositions of the species -Vextracted into the organic phase have been proposed as given below, Primene JM-T — *" / OMU*\ "Hi «*-,,} [*Ml/n44-^" " / CM^ 2— S( Cit) 3"[, (RNH+) :j and [M•(Cit) 'J ~£(RNH+) ] Aliquat 336 CM(Cit)l""L(R3R,N'"):i and [M'(Cit)2- E(R3R'N+)2^ (M =Mn(II), Co(II) andM' = Zn(Il), Cd(II), Cr(IIl)f Fe(lII)). An anion-exchange mechanism is supposed to be responsible for extraction. The results of ir spectra of organic extracts indicated the existence of metal citrate complex in the organic phase. Chapter V has been subdivided into two sections. Section A deals with the separations based on extraction data in carboxylic acid-amine extraction system and Section B includes the separations achieved from the HMWA-citrate extraction system, Variation in some of the organic and aqueous phase parameters has been utilized to find out the optimum conditions for achieving some topical separations. The proposed separations seem to be useful for the analysis of alloys, minerals and ores. A few of these are also important from the radiochemical point of view. Some of the separations reported herein involve cadmium and mercury which are of particular interest to environmentalists.