Decontamination of radioactive waste water by ferric hydroxide flocculation

Recently flocculators of slurry circulation type have been adopted at various institutes in Japan for the treatment of weakly contaminated radioactive waste water. The mechanism of decontamination in the flocculator is, however, still not enough realized. There are some problems which should be solved in order to make best use of the flocculator. For this purpose, the experiments involving the test flocculations in beakers and in a small flocculator have been carried out in the case of ferric hydroxide flocculation. Among the results obtained, the following facts were considered to be noticeable. (1) The pH value of the reacting medium has a serious effect on the removal. (2) As for radioactive ions, the main decontamination process is completed in the stage that the ferric hydroxide particles are formed in the reacting medium. The continuation of stirring after this stage gives rise to no further improvement in the removal. (3) The removal of Sr is effectively raised by the addition of equivalent or more amount of carbonate ion when the waste water to be decontaminated contains alkali earth metal ions. (4) Noticeable difference in the removal is not found between the flocculations in a beaker and in a flocculator under the same flocculation conditions. (5) The main role of slurry circulation type flocculator in the decontamination of radioactive waste water is to clarify the effluent by dynamical separation of solid from liquid. (author)