Removal from nuclear waste streams

The crown ethers were investigated mainly for the removal of Sr or Cs from nuclear-waste streams (246-250), and some studies reported their interest as selective extractants of plutonium (251). Different crown ether derivatives with the addition of alkyl chains have been examined, in order to increase the lipophilicity of the molecule and prevent major extractant losses due to high solubility in aqueous phases. These extractants were described as radiolytically resistant, and their stability increased in the order benzocrown > dicyclohexanocrown > crown (44). 

Published experimental smdies of the FM21 cell are fewer in number but include comparisons of mass transport in the FMO1 and FM21 cells [48,49]. In addition to operation in the chlor-alkali industry [50], the electrolyzer has been used for diverse applications including the removal of nitrate from nuclear waste streams [51], the destruction of contaminated solids via silver(ll) [52,53], and the electrosynthesis of a pharmaceutical intermediate [54]. 

Potential Applications. Potential applications for ELMs include 1) wastewater treatment 2) biochemical processing 3) extraction of rare earth metals from dilute solutions 4) removal of radioactive materials from nuclear waste streams and 5) recovery of nickel from electroplating solutions. 

Removal of Radioactive Materials from Nuclear Waste Streams. ELMs have potential for the removal of radioactive materials such as strontium, plutonium, cesium, uranium, and americium from nuclear waste streams. Eroglu et al. (57) reported an ELM system for the extraction of strontium, which is shown in Table XHI. They extract about 92% of Sr " " from a feed containing 100 mg/L Sr " by the use of D2EHPA as the extractant. 

For the removal of americium from nuclear waste streams, Muscatello and Navratil (61) employed dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP) as the extractant without a diluent in a supported liquid membrane. They removed more than 95% of americium from the waste streams. The DHDECMP extractant and a surfactant, e.g., SPAN 80 or LMS-2, with 0.25M oxalic acid as the internal phase could constitute an effective ELM system for americium removal. 

The relatively high Si/Al content of mordenite confers on it a certain acid stabihty that enables it to be used to remove water from acid gas streams such as reformer recycle hydrogen, reformer catalyst regeneration gas, HCl, CI2, and chlorinated hydrocarbons. It can also be used to treat off-gas for removal of oxides of sulfur and nitrogen (SO and NO ). Mordenite s ion-exchange selectivity for Cs has been used to remove Cs radioisotopes from nuclear waste (Zeolon 900) and it is used in Japan on a plant scale to separate gases from the air. 

Other gas-treating processes involving sulfolane are (/) hydrogen selenide removal from gasification of coal, shale, or tar sands (qv) (108) (2) olefin removal from alkanes (109) (J) nitrogen, helium, and argon removal from natural gas (110) (4) atmospheric CO2 removal in nuclear submarines (5) ammonia and H2S removal from waste streams (6) H2S, HCl, N2O, and CO2 removal from various streams (111—120) and (7) H2S and SO2 removal from... 

D. W. Holladay, A Eiterature Survey Methodsfor the Removal of Iodine Speciesfrom Off-Gases and Uquid Waste Streams ofNuclear Power and Nuclear Fuel Reprocessing Plants, with Emphasis on Solid Sorbents, Report ORNL/TM-6350 (January, 1979), p. 46, available from National Technical Information Service, Springfield, Va. 

Several plate and frame MF units have been installed in Japanese nuclear power plants. The units operate with automatic periodic backwash using accumulated filtrate. Typically, the units backwash every 3 hours at a back pressure twice that of the final forward pressure. The backwashed crud is removed from the system as concentrated RAD wastes. In this sense, these back-wash systems are not dissimilar to cross-flow units using MF or UF-membranes. In either case, a reject stream containing concentrated crud must be disposed of. 

Holladay, D.W. 1979. A literature survey Methods for the removal of iodine species from off-gases and liquid waste streams of nuclear power and nuclear fuel reprocessing plants, with emphasis on solid sorbents. ORNL/TM-6350. Oak Ridge, TN Oak Ridge National Laboratory. 

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