Method for the decontamination of radioactively contaminated liquids
BACKGROUND OF THE INVENTION 
     The invention relates to a method for the decontamination of radioactively contaminated liquids. 
     A method for the decontamination of radioactive liquids is known from the DE-AS 12 18 964. In this method the liquid to be decontaminated is mechanically filtered, an acid solution of the elements whose radionuclids are to be removed is added, and the products of precipitation are separated from the liquid. 
     Furthermore methods both for separating radioactive isotopes from liquids and gases (see De-OS 35 13 943), and for the decontamination of radioactively contaminated scrap-iron and/or-steel (see DE-OS 33 18 377) are known. 
     The aim of the invention is the further development of the above mentioned method for the decontamination of lubricating oil. 
     SUMMARY OF THE INVENTION 
     According to the invention this aim is achieved by the features of the characterizing part of claim 1. The sub claims give details of advantageous forms of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the invention, the addition of an acid solution, preferably in a aqueous sulfuric acid, of a salt of the element or elements respectively, whose radionuclids are to be removed, to the lubricating oil which is regularly first to be mechanically filtered, is suggested. For example, for the removal of radionuclids of cobalt a 2% sulfuric acid in which the cobalt chloride is dissolved can be added. This acid solution of the salt is to be thoroughly mixed with the lubricating oil, preferably being heated at the same time, over a lengthy period, forming an emulsion. The sulfuric acid thus causes a disassociation of the metal oxides and other metal salts in the aqueous sulfuric acid phase of the lubricating oil emulsion. The now freely mobile active cobalt ions including any respective radionuclids exchange with the inactive cobalt ions of the added cobalt salt. If this constant substitution process is maintained over a sufficiently long period the thorough mixing will not continue further. The aqueous sulfuric acid is deposited with the cobalt salt dissolved in it and the cobalt ions in the depositing phase consists of active and inactive ions. Already in this first step a considerable decontamination effect is achieved. 
     In a next step an aqueous solution of the salt of a precipitation partner of the element whose radionuclids are to removed (in this example cobalt) is added in doses, whereby this partner may be sodium sulphide. Now too a thorough mixing of the salt, preferably under simultaneous eating, takes place. The increase in the number of cobalt ions in the lubricating oil via the addition of cobalt salt in the first step causes a definite exceeding of the solution threshold and allows suitable precipitation. In a further step the precipitation products are separated from the lubricating oil, preferably with the use of a centrifuge. 
     Experiments have shown that in the suggested method the level of radionuclids remaining in the lubricating oil lies, already after one run-through, in the vicinity of the usual measureable proof level. When after one run-through a given limit is not reached, then some or all of the steps of the suggested method may be repeated until the active elements remaining in the lubricating oil lie below the limit. 
     The parameters of the process have to be chosen according to the given conditions, especially according to the composition of the lubricating oil to be decontaminated and the type and intensity of radioactive pollution. 
     When removing radionuclids of different elements various specific salt solution can be added simultaneously.