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The Separation of Rhodium from Other Platinum-Group

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The Separation of Rhodium from Other Platinum-Group THE SEPARATION OF RHODIUM FROM OTHER PLATINUM-GROUP METALS BY ION EXGHANGE DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By EDWARD STEPHEN MCKAY, B. S., M. S. ****** The Ohio State University 1956 Approved by: I_ Aclvi sers Department of Chemi stry DEDICATION In memory of my sister, Jean ii AC KNOWLEDGMENT The author wishes to express his deep appreciation and gratitude to Professor William M. MacNevin for his guidance* encouragement, friendship, and wise counsel during the course of this study. Also, acknowledgment is made of the financial assistance pro­ vided by the Graduate School in the form of the various teaching and assisting positions that it has been my privilege to hold during my stay at The Ohio State University. Finally, the author expresses his thanks to Mr. Harold D. McBride for his assistance with the spectrographic analysis of the platinum m e t a l s . TABLE OF CONTENTS I Page INTRODUCTION............................................................... 1 The Platinum-Group Metalsi Their History and Occurrence. 1 Economic Importance of the Platinum Metals .......... 2 Relationship of the Platinum Metals to Other Metals in the Periodic Table. ............................................. 4 Separation of the Platinum Metals by Gravimetric Methods . 6 Separation of the Platinum Metals by Ion Exchange................. 8 Objectives and Approach to the Problem .............. 1 0 The Ion Exchange Process ......................................... 1 1 EXPERIMENTAL . 15 Preparation of Standard Solutions of the Platinum Metals . 15 Qualitative and Quantitative Methods for the Platinum Metals . 16 Properties of the Ion Exchange Resins Used in This Work. 17 Preparation of Ion Exchange Columns................. ......18 The Behavior of Platinum and Palladium Chlorides on Ion Exchange Resins .......................... 21 Conclusions .................................................... 2 8 The Behavior of Iridium Chloride on Ion Exchange Resins. 28 Conclusions ..... .................................... ..31 Some Properties of Rhodium Chloride and its Behavior on Ion Exchange Resins ........ ................ ......32 Conclusions ............. 36 The Elution of Rhodium Chloride from Cation Exchange Resin3 . 37 The Separation of Rhodium Chloride from Platinum Chloride. 38 iv The Separation of Rhodium Chloride from Palladium Chloride • 41 The Separation of Rhodium Chloride from Iridium Chloride • • 45 The Separation of Rhodium Chloride from Platinum and Palladium Chlorides ......................................... 47 The Separation of Rhodium Chloride from Palladium and Iridium Chlorides ............................. 48 The Separation of Rhodium Chloride from Platinum and Iridium Chlorides ..... ............................. .51 The Separation of Rhodium Chloride from Platinum, Palladium, and Iridium Chlorides......................... 52 DISCUSSION........................................................... 54 SUMMARY ..................................................... 55 BIBLIOGRAPHY......................................................... 57 AUTOBIOGRAPHY .......................................................61 ► INTRODUCTION j The Platinum-Group Metals: Their History and Occurrence The metals of the platinum-group consist of the siac transitional elements: ruthenium, osmium, platinum, palladium, rhodium, and iridium. — 5 Of these, platinum is the most abundant and makes up 2 x 10 per cent of the earth's crust. It was known to pre-Columbian Indians of Ecuador (26,36,44) and first recognized as a metal by Scalinger of Italy in 1557. Early discoveries of platinum were made in South America where it was alloyed with gold. Because of the alloy's resistance to melting by fire, it was often separated and thrown back into streams as waste. Platinum occurs chiefly in the metallic state in granular alloys con­ taining the other platinum metals and gold, copper, nickel, iron, and cobalt. Numerous deposits of platinum occur in the Ural Mountains of Russia; Columbia, South America; Abyssinia; and in the Sudbury district of Ontario, Canada. Palladium, the second most widely used metal of the group, was known as a metal to Brazilian miners in 1700, (21), but it was not until 1803 that Wollaston, (48), contemporary of Berzelius, separated it from platinum and identified it as a new element. Rhodium, another metal discovered by Wollaston in 1804 (47), repre­ sents about 1 x 10“ 6 per cent of the earth's crust. It ocours chiefly in a gold-rhodium ore known as rhodite and is found alloyed with plati­ num and osmiridium. 1 Iridium, present in the same abundance as rhodium, was discovered in 1803 by Tennant (40,41), an English contemporary of Wollaston* It is most often found alloyed with osmium in iridosmine and siserskite. Iridium is also alloyed with platinum and gold in platiniridium and aurosmiridium, respectively. Osann, a professor at Dorpat, Russia, is credited with the discovery of ruthenium in 1828, but it was not until 1845 that Claus prepared the pure metal* Osmium was discovered simultaneously with iridium by Tennant in 1804 (40,41). It represents 5 x 10" 6 per cent of the earth's crust. It oocurs alloyed with iridium as osmiridium in platinum sands of North and South America and in the Ural Mountains of Russia. Economic Importance of the Platinum Metals The platinum-group metals are of interest because of their unique physical and chemical properties. Table 1 illustrates the more common properties of these elements. Because of their great stability and low reactivity, they are termed "noble” metals. The platinum-group metals are utilized.as pure metals, combined, or alloyed with other metals or as coatings in the chemical and electrical industries, in dentistry and jewelry, and for numerous miscellaneous purposes. Their chemical applications arise from their catalytic activity and resistance to corrosive chemical action, even at high temperatures. Platinum oatalysts are used mainly for hydrogenation and dehydrogenation reactions; in oxidations and reductions; as reforming catalysts, and in many types of syntheses (17). Pure platinum and iridium-platinum alloys are used as insoluble anodes in various elec- Table 1. Physical Properties of the Platinum Metals (20) Property Ruthenium Rhodium Palladium Osmium Iridium Platinum Atomic Number 44 45 46 76 77 78 Atomic Wei ght 101.7 102.91 106.7 190.2 193.1 195.23 Color G-Wf GWf S-WS B-G6 G-Wf B-W6 Density 20°C 12.2 12.44 12.02 22.48a 22.5 21.45 Melting Point °C 2400 1966 1554 2700 2454 1774 Boiling Point °C 4900 4500 3980 5500 5300 4530 Crystal Lattice HCPd FCCb FCCb HCPd FCCb FCCb Common Oxidation 2,3,4 2,3,4 2,4 2,3,4,8 2,3,4 2,4 States a At 18°C b Face-centered cubic c Silvery-white d Hexagonal close-packed e Blue-white f Grey-white g Blue-grey 4 troplating prooesses. Platinum-gold and platinum-rhodium alloys have been used many years for preparation of spinnerets for making rayon fiber from viscose. Fiber glass in rapidly increasing quantities is produced in a somewhat similar manner by forcing molten glass through banks of platinum nozzles, whence it emerges in fine streams that are blown into fine diameter filaments. New combinations of the platinum- group metals are constantly being sought in the glass fiber industry in order to reduce contamination of the spinnerets with base metals. Relationship of the Platinum Metals to Other Metals in the Periodic Table The platinum-group elements, as members of the transition series, have many properties in common with the other members of this group. Table 2 indicates the electronic configurations of several of the transi­ tion elements as recorded by Pauling (55). Ordinarily the orbitals in each shell of an element are filled before those of the succeeding shell begin to fill. In such cases, of which the alkali metals and halides are examples, the combining properties of the atoms are largely controlled by the electrons in the outer shell. However, in the case of the transition metals, the outermost shell has acquired some electrons before the d orbital of the preceding shell has been filled. The change in the electron configuration in an inner shell has less effect upon the properties of an element than a similar change in the outermost shell. This accounts for the horizontal similarities in properties of the transition elements. Because of such electronic configurations and a combination of such favorable factors as small cation size, comparatively large nuclear or ionic charges, and multiple oxidation states, the ability to form complexes is at a maximum. 5 Table 2. The Electronio Con.figuratione of the Group VIII Elements SHELL K L M N 0 P Atom ORBITAL Is 2s,2p 3s,Sp,3d 4s,4p,4d,4f 5s,5p,5d 6 s Fe 22626626 Co 2262672 Hi 2262682 Ru 2 2 6 2 6 10 268 1 Rh 22626 10 268 1 Pd 2 2 6 2 6 10 2 6 10 Os 2 26 26 10 26 10 14 2 6 6 2 Ir 2 2 6 2 6 10 2 6 10 14 2 6 9 Pt 2 26 26 10 26 10 14 269 1 The platinum-group metals are characterized by a multiplicity of oxidation states which are difficult to systematize. Few compounds containing uncomplexed species are known, the only real exceptions being oxides, sulfides, and a few halides and sulfates. Parallels may be found among the complexes of iron, ruthenium, and osmium, of cobalt, rhodium, and iridium, and of nickel, palladium, and platinums, but complications are introduced by the great number of oxidation states among the platinum metal derivatives. In general, reduction of any oxidation 3tate to the free metal is rather readily effected. Separation of the Platinum Metals by Gravimetric Methods Berzelius (7,9) published a method of separation of the platinum metals in 1828 which was based on the action of aqua regia on the metals and the precipitation of platinum and iridium with potassium chloride. In 1854, Claus (9) published a method which depended on the insolubility of the chloroplatinate, chlororuthenate, and the chloroiridate in a saturated solution of ammonium chloride, and the reducibility of the ammonium chloroiridate to ammonium chloroiridite through the use of hydrogen sulfide gas.
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