Patent Number: 047642815
Section: summary

FIELD OF THE INVENTION The present invention is directed to a method for removing radioactive nuclear wastes from wastewater, oil or other liquids. This invention is especially useful in removing low levels of radiation, such as less than 1.times.10.sup.10 Becquerels per liter, or disintegrations per second per liter. More particularly, the present invention is directed to a method for treating these radioactive heavy metal-containing liquids, such as liquids containing the radioactive nuclear isotopes of radium, uranium, cesium, strontium, ruthenium, neptunium, technetium, iodine and/or other elements, with a carboxymethylcellulose, particularly an insoluble metal carboxymethylcellulose, such as aluminum carboxymethylcellulose, to remove radioactive heavy metals therefrom as a part of and along with the solid carboxymethylcellulose. BACKGROUND OF THE INVENTION Federal, state and local governmental bodies reacting to constituent pressures have instituted a series of laws and regulations aimed at preventing the continued contamination of the environment. Heavy metals are generally defined as hazardous and, therefore, must be removed from industrial effluent streams. Once removed from these streams, the heavy metals-containing waste has been containerized and then disposed of in government-sanctioned landfills. These special landfills are now being more closely monitored thereby forcing alternative methods of disposal of these solid heavy metal wastes. It is toward both the clean-up of these effluent streams and discontinued pollution of soil and ground waters that the invention of this method is aimed. Progressively stricter regulatory criteria have forced industry to drastically reduce the residual metal content in wastewater discharges. Obviously, regulations pertaining to wastes containing radioactive isotopes are among the most severe, and among the costliest with which to comply. Increased cost for disposal of any solid metal wastes have also forced industries to examine present treatment techniques and to demand more efficient and cost effective alternatives to those currently available. The ability of conventional wastewater treatment methods to achieve the low levels of residual metals required by the higher standards for wastewater purity in many cases is marginal. Recent legislation has made the disposal of sludge material extremely difficult and expensive, with no near term solution to the sludge disposal problem being apparent. Because of these problems, industry in general, and the nuclear reaction segments in particular, have been forced to consider alternative methods for heavy metals removal from wastewater streams. The major characteristics required in heavy metals removal from wastewater streams are: ability to reduce residual metal contents to extremely low levels (ultimately to the parts-per-billion range); production of minimal amounts of sludge; economical operation; production of effluent suitable for recycle to process operations; and ability for maximum retrofit into existing installations. Some of these problems were addressed in an analysis of the processes used in treating drinking water for the removal of radioactive contaminants, and of the disposal of wastes generated by these processes in TREATMENT, WASTE MANAGEMENT AND COST FOR REMOVAL OF RADIOACTIVITY FROM DRINKING WATER, G. W. Reid and P. Lassovszky, Health Physics, 48 (1985) pp. 671-694. The alternative processes, including ion exchange, reverse osmosis or electrodialysis, lime and lime-soda softening, greensand, manganese fiber, coagulation techniques and activated alumina, were evaluated in terms of cost, efficiency, reliability, process control and feasibility for the removal of u, Ra, and Rn from water. Each of these processes has disadvantages requiring the continued search for a safe, effective method of radioactive metals removal with a minimum of waste product formation. One of the more promising new alternative approaches that possesses the potential of fulfilling to a significant degree these desirable requirements for treating meal-bearing wastewaters is xanthate technology. A patent to John Hanway Jr. et al, U.S. Pat. No. 4,166,032, discloses the use of cellulose xanthate for heavy metals removal from wastewater streams. While cellulose xanthate is very effective for the removal of heavy metals from wastewater, the cellulose xanthate adds an amount of sludge equal to the dry weight of the cellulose xanthate added to the wastewater stream further increasing both the weight and volume of the sludge generated. Also, cellulose xanthate cannot be used successfully in a column through which a solution containing heavy metal ions is poured. In accordance with the present invention, it has been found that one or more water-insoluble cation-exchange carboxylated cellulosics, such as an aluminum salt of carboxymethylcellulose, can remove radioactive heavy metal isotopes from liquids, such as nuclear fuel manufacturing wastewater streams, natural waters, and other wastewaters and nuclear-contaminated oils in new and unexpected proportions, leaving a substantially non-polluted solution or effluent capable of plant recycle or legal discharge. In addition, the resulting radioactive carboxymethylcellulose bed from the column can be easily treated using existing technology, producing a small volume, radioactive ceramic fiber. The overall radioactive waste is thus reduced in volume by several factors, allowing for easier and less expensive disposal. It is known that insoluble cation-exchange forms of cellulose, such as carboxymethylcellulose, are effective in removing certain heavy metals such as Al, Cr, Sn, Pb, Fe, Cu, Ni and Zn from a wastewater, as disclosed in A SYSTEM OF ION-EXCHANGE CELLULOSES FOR THE PRODUCTION OF HIGH PURITY WATER, Horwath Zs, Journal of Chromatography, 102 (1974) pp. 409-412. However, such insoluble celluloses have not been used for removal of the radioactive isotopes of elements such as U, Cs, Sr, Ra, Ru, Rh, Np, Tc or I from waste streams. As disclosed in the Horwath article, the insoluble carboxymethylcellulose is disposed in a column in a sandwich-type arrangement with other forms of ion-exchange celluloses and the wastewater passed through the column, with the ion exchange celluloses acting as a filtering media for absorption of the heavy metals therein. U.S. Pat. No. 4,260,740, assigned to Pfizer, Inc., also discloses that insoluble carboxylated cellulose is useful as an ion exchange material for removal of heavy metals from an industrial effluent and for precious metal recovery. The process disclosed in U.S. Pat. No. 4,260,740 teaches a reaction of cellulose with polycarboxylic acids followed by a hydrolysis step in dilute alkali at a pH of 8 to 11 to bind each polycarboxylic acid moiety to the cellulose and thereby increase the ion exchange capacity towards heavy metal ions. U.S. Pat. No. 4,537,818 teaches the manufacture of thin free-standing metal oxide films by absorbing cations such as U, Zn, Nd, Ce, Th, Pr, Cr onto carboxymethylcellulose. The heavy metal-impregnated film is first heated in an inert atmosphere and then oxidized to form a carbonized metal oxide membrane useful as a nuclear acceleration target material. SUMMARY OF THE INVENTION In brief, the present invention is directed to a method for treating a radioactive metal-containing natural water or liquid such as a radioactive metal-containing wastewater stream, an oil containing one or more radioactive metals or other nuclear metal-bearing liquid. The process of the present invention has been found to be unexpectedly effective on radioactive wastewaters or any other liquid containing one or more radioactive heavy metal ions such as U, Ce, Sr, Ru, Ra, Np, Tc, as well as radioactive ions such as I. In accordance with the principles of the present invention, the radioactive heavy metal-containing liquid is contacted with a water-insoluble carboxylated cellulose to separate the heavy metals from the liquid. Accordingly, an object of the present invention is to provide a method for treating a liquid containing one or more radioisotopes to cause removal in an unexpected large proportion of the radioisotopes therefrom. Another object of the present invention is to provide a method for treating nuclear waste bearing water or other liquids with a water-insoluble form of a carboxylated cellulose for removal of the nuclear wastes therefrom. Yet another object of the present invention is to provide a method for contacting a liquid containing one or more nuclear isotopes of a heavy metal, with an insoluble form of carboxymethylcellulose to remove a substantial portion of the nuclear isotopes for recycle of the treated liquid to an industrial process.