Patent Number: 
Section: description

An embodiment of a process in accordance with the present invention will now be described with reference to the accompanying drawing which is a flow chart showing processes for the treatment of a solvent comprising tributyl phosphate and adourless kerosene in which the amount of tributyl phosphate is about 30% by volume. The first stage in the process is the distillation, under reduced pressure, of solvent which has become too degraded for further use. The distillation is carried out to remove substantially al the diluent and a major proportion of the phosphate ester, for example, 90% of the total volume of organic material. This distillate is returned to the reprocessing or ore purification process. The residual volume consists essentially of organophosphate plus some phosphatic and diluent degradation products. This material is treated to convert the organophosphate to inorganic phosphate salts, such as a calcium salt. Preferred processes are high temperature processes or chemical oxidation processes. A high temperature process may be carried out by mixing the residue solvent with a metal salt hydroxide in aqueous solution or suspension for instance, calcium hydroxide, and then feeding the mixture to a stirred pebble ball reactor at about 550xc2x0 C., thereby producing a metal phosphate ash. This ash may be fed to a vitrification plant and the organics volatilised from the reactor and combusted. An alternative process is chemical oxidation, typically using a metallic catalyst such as sodium dichromate and hydrogen peroxide at a temperature of between ambient and boiling point (around 100xc2x0 C.) in an aqueous medium. This reaction produces an aqueous phosphoric acid, which is then reacted with an aqueous solution or suspension of a metal hydroxide such as calcium hydroxide. A metal phosphate salt solution is produced which is fed to vitrification or an alternative encapsulation method, such as encapsulation in cement. Prior to encapsulation, the material may be mixed with other radioactive waste. A process in accordance with the present invention is applicable to the treatment of a variety of solvents comprising an organophosphate ester and a hydrocarbon diluent. Mention has been made above to a number of hydrocarbon diluents. Two further examples of such diluents are Exxsol D80 and Isopar L. Exxsol D80 is a kerosene type material which can be used as a direct replacement for OK in reprocessing plants and has a narrower boiling point (202xc2x0-240xc2x0 C.) than OK (180xc2x0-280xc2x0 C.). Isopar L is a highly branched chain material with a very narrow boiling point range (190xc2x0-210xc2x0 C.).