Heavy water production methods

Electrolysis continued to be used for primary enrichment in countries with abundant electric power, such as Iceland and Norway, where the H2 is used in ammonia manufacture [9]. Molecular deuterium, D2, is produced in Norway by the electrolysis of DzO. For heavy water production, the method has, for the most part, been replaced by steam-H2S exchange columns for heavy water enrichment ... 

Dissolved Minerals. The most significant source of minerals for sustainable recovery may be ocean waters which contain nearly all the known elements in some degree of solution. Production of dissolved minerals from seawater is limited to fresh water, magnesium, magnesium compounds (qv), salt, bromine, and heavy water, ie, deuterium oxide. Considerable development of techniques for recovery of copper, gold, and uranium by solution or bacterial methods has been carried out in several countries for appHcation onshore. These methods are expected to be fully transferable to the marine environment (5). The potential for extraction of dissolved materials from naturally enriched sources, such as hydrothermal vents, may be high. 

Electrolysis. For reasons not fiiUy understood (76), the isotope separation factor commonly observed in the electrolysis of water is between 7 and 8. Because of the high separation factor and the ease with which it can be operated on the small scale, electrolysis has been the method of choice for the further enrichment of moderately enriched H2O—D2O mixtures. Its usefiilness for the production of heavy water from natural water is limited by the large amounts of water that must be handled, the relatively high unit costs of electrolysis, and the low recovery. 

A process involving water electrolysis is the production of heavy water. During cathodic polarization the relative rates of deuterium discharge and evolution are lower than those of the normal hydrogen isotope. Hence, during electrolysis the solution is enriched in heavy water. When the process is performed repeatedly, water with a D2O content of up to 99.7% can be produced. Electrochemical methods are also used widely in the manufacture of a variety of other inorganic and organic substances. 

Deuterium, 8 456—485 13 759. See also Canadian Deuterium Uranium (CANDU) reactors analytical methods, 8 467-468 economic aspects, 8 467 health and safety factors, 8 461-462 physical properties, 8 457-462, 459t production of heavy water, 8 459t, 462-467... 

The most important applications of hydrogen sulfide involve the production of sodium sulfide and other inorganic sulfides. Hydrogen sulfide obtained as a by-product often is converted into sulfuric acid. It also is used in organic synthesis to make thiols or mercaptans. Other applications are in metallurgy for extracting nickel, copper, and cobalt as sulfides from their minerals and in classical qualitative analytical methods for precipitation of many metals (see Reactions). It also is used in producing heavy water for nuclear reactors. 

The establishment of a nuclear power industry based on fission reactors involves the production of a number of materials that have only recently acquired commercial importance, notably uranium, thorium, zirconium, and heavy water, and on the operation of a number of novel chemical engineering processes, inciuding isotope separation, separation of metals by solvent extraction, and the separation and purification of intensely radioactive materials on a large scale. This text is concerned primarily with methods for producing the special materials used in nuclear fission reactors and with processes for separating isotopes and reclaiming radioactive fuel discharged from nuclear reactors. 

A second method for the industrial production of heavy water, used by the Manhattan Project in the United States [M5], was the distillation of water. Three plants having a total capacity of 13 MT DjO/year were built at Army Ordinance plants. Because the relative volatility for separating Hj 0 from HDO is only 1D3 at atmospheric pressure, the size of equipment and the heat consumption of these plants per unit of D O produced was very high, and the cost of heavy water was greater than in other processes. Nevertheless, the distillation of water was attractive as a wartime production method because the process needed little development work and used standard equipment. These plants were shut down after the war. Mote recently, distillation of water has come to be one of the most satisfactory methods for ftnal concentration of heavy water. 

As part of the Manhattan District Project during World War II, a small plant to produce heavy water 6 Mg/a) was built by Standard Oil Development Co. at Trail, B.C. and was operated by Cominco from 1944 to 1956 (14). It was based on steam-hydrogen catalytic exchange plus steam-water equilibration coupled to water electrolysis. However, byproduct heavy water from this process is economic only if the electrolysis cost is borne by the hydrogen product, which at Trail was used for ammonia production. In any case, the small scale of operation imposed by electrolytic capacity and the large exchange tower volume have made this production method economically unattractive. 

This method allows rapid production of large amounts of Dg and utilizes the entire D content of the heavy water. 

Although the formidable difficulties associated with isotope separation schemes based on photochemical vibrational excitation plus chemical reaction continue to attract considerable attention, some earlier hopes appear to have been dashed. An experiment performed in 1970 by Mayer et al. has been much quoted. They reported irradiating mixtures of CHjOH and CD3OD in the presence of Bts with lines from an HF laser that are absorbed only by CH3OH. Product analysis indicated the selective depletion of the CH3OH. This observation was interpreted in terms of a selective reaction between vibrationally excited CH3OM and Bra, nnd it appeared to point the way to an economic method for the production of heavy water. However, the results of a careful re-examination of this system have just... 

Probably the most efficient way of eliminating the fission products is by the solvent extraction method. We are much indebted to Mr. Tepe for discussing this system with us. The solvent extraction method would permit a continuous operation and cause a holdup of only one hour in the column. As a result it would appear that such a purification increases the amount of 23 required by only 4%. However, it is likely that it will be impossible to use the solution of uranium in heavy water directly in the column because the deuterium will exchange with the hydrogen of the solvent. For this reason it will be necessary to separate first the uranium salt from the heavy water which may be a more time consuming operation than the operation of the colmnn itself and consequently increase the holdup more than the fission product separation itself does. 

The method of obtaining nuclear fission products which comprises assembling a sufficient volume of a slurry comprising a thermal neutron fissionable material in heavy water to Initiate a self-sustaining nuclear chain reaction, maintaining said reaction for a period of time... 

The phenomenon was first observed in the electrolysis of water when it was found that the decomposition rate of H2O maybe several times higher than that of D2O. This observation led to the preparation of the first pure heavy water sample electrolytically and forms the basis of one of the methods of industrial production of heavy water. The study of isotope effects on reaction rates provides one of the most powerful and subtle methods for elucidation of reaction mechanisms and plays an important role in investigations using isotope labeling. 

Monodeuterated water HDO has an abundance in natural water of approximately 600 ppm. One of the methods used in early attempts to separate the two isotopes was fractional distillation, for which the separation factor at 1 atm was found to be 1.026. Although this procedure was ultimately superseded by the more efficient chemical-exchange processes for larger-scale production of heavy water, distillation remains the separation method of choice for upgrading small amounts of heavy water that have been contaminated by atmospheric water vapor. Distillation is in this case carried out at reduced pressure to take advantage of the higher separation factor. Suppose we wish to carry out the distillation of H2O-HDO at ambient temperatures, i.e., at subatmospheric... 

Another method to study higher order protein structure is hydrogen-deuterium exchange [31]. When a protein molecule is dissolved in deuterium oxide, DjO ( heavy water ), deuterium atoms start to exchange their accessible hydrogens. The resulting mass difference in the mass spectrum of the protein and its digestion products can reveal which part of the folded protein is accessible for the DjO molecules. 

One of the principal objections to using heavy water as a moderator was its cost. There were various methods of production one involved the electrolysis of water requiring large amounts of electricity, and both Canada and Norway had extensive hydroelectric schemes which could be used to produce heavy water. On the other hand, the heavy water would not need to be renewed it would merely add to tbe capital cost of a reactor in the same way that obtaining pure graphite added to the cost of the gas-cooled reactors. 

Catalyst recovery is a major operational problem because rhodium is a cosdy noble metal and every trace must be recovered for an economic process. Several methods have been patented (44—46). The catalyst is often reactivated by heating in the presence of an alcohol. In another technique, water is added to the homogeneous catalyst solution so that the rhodium compounds precipitate. Another way to separate rhodium involves a two-phase Hquid such as the immiscible mixture of octane or cyclohexane and aliphatic alcohols having 4—8 carbon atoms. In a typical instance, the carbonylation reactor is operated so the desired products and other low boiling materials are flash-distilled. The reacting mixture itself may be boiled, or a sidestream can be distilled, returning the heavy ends to the reactor. In either case, the heavier materials tend to accumulate. A part of these materials is separated, then concentrated to leave only the heaviest residues, and treated with the immiscible Hquid pair. The rhodium precipitates and is taken up in anhydride for recycling. 

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