Please use this identifier to cite or link to this item: http://localhost:8081/xmlui/handle/123456789/1247
Authors: Nath, K. V. Surendra
Issue Date: 1990
Abstract: Ion exchange chromatography is one of the most widely used separation techniques in many industrial processes and chemical laboratories. Besides its well known application in water purification, it finds use in analytical chemistry, separation and isolation of new elements, hydrometallurgy and in many specialized fields related to the utilization of atomic energy. The scene of ion exchange chromatography has been mainly dominated by the synthetic organic resins because of the ease with which they can be synthesized with reproducible properties and their excellent mechanical and chemical stability. In the late fifties with the developments in the nuclear fuel technology the interest in synthetic inorganic ion exchangers revived because the need for ion exchangers which can withstand higher temperatures and radiation doses was felt. These materials are also known to be more stable in highly acidic and oxidizing media than their organic counterparts. A number of these inorganic ion exchangers possess unusual selectivities towards certain metal ions. Over a period of three decades a large variety of inorganic ion exchangers, both amorphous and crystalline, have been synthesized and studied for their ion exchange characteristics. Besides their use in ion exchange chromatography the studies on inorganic ion exchange materials are able to throw sufficient light on problems such as the sorption of ions by precipitates, the electrophoretic behaviour of suspensions, the diffusion Ill of ions in crystals, and isotopic exchange in heterogeneous systems. They have also started finding use as catalysts. Out of the different categories of inorganic ion exchangers hydrous oxides and polybasic acidic salts of polyvalent metals have received the maximum attention. Hydrous oxides of quadrivalent metals exhibit amphoteric behaviour, exchanging anions in acidic and cations in basic solutions. They are reported to be fairly stable in acidic medium which makes them to be useful as anion exchangers. However, they have not been thoroughly explored as anion exchangers. Scanty information exists on the anion exchange behaviour of hydrous titanium oxide. Amongst the insoluble polybasic acidic salts the phosphates and arsenates of quadrivalent metals form the two most extensively studied group of compounds. Some of them have been synthesized with different degree of crystallinity and in different crystalline forms. The crystalline materials possess higher exchange capacity, chemical and thermal stability than the amorphous varieties. Moreover, a well defined crystalline structure of fixed composition facilitates a better understanding of the exchange process. However, these crystalline materials are hydrolyzed in basic medium and pose difficulty in exchanging metal ions of bigger size. Recently mixed crystalline compounds containing two different tetravalent metals or two different anions have been synthesized mainly to stabilize the structure towards hydrolysis and to control IV their ion sieving properties. The two noteworthy compounds synthesized in this class are crystalline titanium - zirconium phosphate and zirconium arsenophosphate ion exhangers. In the light of above discussion it was planned to systematically study the anion exchange behaviour of hydrous titanium oxide and ion exchange properties of a new mixed crystalline tin(IV) arsenophosphate exchanger. For the convenience of presentation the work embodied in the thesis is divided into following seven chapters: Chapter I Chapter II Chapter III Chapter IV Chapter V Chapter VI Chapter VII : General Introduction♦ : Materials and Equipment. : Anion Exchange Properties of Hydrous Titanium Oxide and Chromatographic Separations of Some Anions. : Kinetics and Thermodynamics of Ion Exchange of CI - N0~ and CrO ~ - N0~ Systems on Hydrous Titanium Oxide. : Synthesis and Characterization of Crystalline Tin(IV) Arsenophosphate Ion Exchanger. : Ion Exchange Behaviour of Crystalline Tin(IV) Arsenophosphate Towards Alkali and Some First Row Transition Metal Ions. : Surface Area, Acidity and Catalytic Activity of Crystalline Tin(IV) Arsenophosphate. Chapter I contains a brief introduction about ion exchange phenomenon and synthetic inorganic ion exchangers. An up-to-date literature survey report on hydrous oxides and crystalline acidic salts of quadrivalent metals with special referrence to their analytical applications has also been presented. Chapter II deals with the materials and equipment used for various studies. X-ray Powder Diffractometer, Simultaneous DTG-DTA-TG Thermal Analyzer, IR Spectrophotometer were used for characterization of the ion exchangers. Inductively Coupled Plasma - Atomic Emission Spectrophotometer (ICPAES) was employed for the determination of various metal ions. Studies on ion exchange equilibria have been carried out using radiotracers. Chapter III comprises of the report on synthesis and characterization of hydrous titanium oxide ion exchanger. Hydrous titanium oxide acts both as cation and an anion exchanger above and below pH 4.5. Effect of particle size, pH and concentration of electrolyte on exchange capacity has been examined. The data on the distribution coefficients of various anions reveal that the polyvalent anions such as Cr04", SO^", AsO^", W0^~, PO^" and VO^" are selectively adsorbed on hydrous titanium oxide. The trends in Rf values of various anions on hydrous titanium oxide impregnated papers are similar to those observed in the sorption studies. Based on these preliminary investigations several VI binary and ternary separations of anions have been achieved using hydrous titanium oxide papers and columns. Chapter iv includes the studies on the kinetics and thermodynamics of ion exchange of Cl~ - N0~ and CrO^~ - N03 systems on hydrous titanium oxide. The studies on uptake show reversible nature of Cl~-N0~ system indicating the predominance of ion exchange phenomenon while adsorption 2 — or complexation of Cr04 ions leads to a degree of irreversibility. Exchange isotherms also reveal that there is a greater selectivity for Cr04~ ions. Effective diffusion coefficients, energy of activation and entropy of activation have been calculated. Selectivity coefficients and thermodynamic equilibrium constants have also been evaluated. Chapter V deals with the synthesis and characterization of a new mixed tin(IV) arsenophosphate ion exchanger. Its ion exchange behaviour has been compared with the parent single salts i.e. tin(IV) phosphate and tin(IV) arsenate. It shows X-ray diffraction patterns similar to crystalline a-layered structure compounds and has an ion exchange capacity of 5.36 meg/g for Na ions. Based on the chemical analysis and thermal behaviour the exchanger has been assigned the formula Sn(HAsO.)(HPO.).H?0. The detailed investigations on the ion exchange properties of crystalline tin(IV) arsenophosphate towards alkali and some first row transition metal ions constitute the Chapter VI. The uptake curves and the ion exchange Vll capacities show the preference of alkali metal ions in the . + + + + order Li > Na > K . K ion is exchanged partially on the H form of the exchanger. However, the exchange to full capacity takes place when the exchanger is taken in the sodium form. Severe hydrolysis of the exchanger takes place in basic medium* The transition metal ions were exchanged as their acetate salts so as to avoid degradation in the crystallinity vis-a-vis thermal stability of the exchanger. Normally at room temperature transition metal ions are exchanged to about 30% of the exchange capacity and near quantitative uptake is possible at 100°C. The affinity series for transition metal ions is Cu2+> Zn2+> Co2+> Ni2+ Chapter VII deals with the surface area and acidity measurements of the crystalline tin(IV) arsenophosphate. Preliminar investigations on the dehydration of cyclohexanol have been carried out to explore the possibility of this materials as a catalyst. The dehydration reaction of cyclohexanol has been found to follow the first order kinetics. The catalytic activity of the SnAsP for the dehydration reaction is 1.81 min at 300°C.
Other Identifiers: Ph.D
Research Supervisor/ Guide: Tandon, S. N.
metadata.dc.type: Doctoral Thesis
Appears in Collections:DOCTORAL THESES (chemistry)

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