GB790474A - Improvements in or relating to means and methods of treating water - Google Patents

Abstract

790,474. Purifying water and trade effluents. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. April 18, 1952 [March 2, 1951], No. 5065/61. Classes 46 and 111. A method of removing radioactivity from water contaminated therewith comprises forming a precipitate from tannic acid and a soluble calcium compound, maintaining the precipitate in suspension in the water under alkaline conditions for from 3 to 20 hours and then separating the precipitate with its content of radioactivity from the water. Aqueous radioactive effluent to be decontaminated prior to disposal or re-use flows through a valve 2 into an open vessel 3 and thence by a conduit 5 to a mixing flume 6 where tannic acid and a soluble calcium compound (e.g. the hydroxide) are introduced at 7 and 8 respectively. The valve 2 is adjusted to maintain a slight overflow of liquid back to the supply by means of device 4, so that the vessel 3 maintains a constant head of liquid for treatment. A precipitate of calcium tannate is formed by the reaction, and is maintained in suspension in the liquid by stirrers 14 in a holding tank 13, to which the mixture passes via a #H cell 10. The rate of flow of incoming liquid is so adjusted in relation to the volume of the vessel 13 that the liquid takes from 3 to 20 hours (preferably from 3 to 5 hours) to traverse the vessel. The mixture in tank 13 must be alkaline and for this purpose ammonia or further calcium hydroxide may be added, e.g., in the flume 6, preferably in amount to maintain the pH at from 8À5 to 9. From tank 13 the mixture passes to a continuous settling vessel 16 where suspended matter, bearing nearly all the radioactive matter originally present, settles and is withdrawn at 19. Clear effluent is withdrawn via a filter 21 by a pump 23 and discharged at 24. Salts, e.g., ferric chloride or other iron salts, and sodium phosphate, may be added with the reactants, and the liquid being treated may be acidified to a #H of approximately 4 prior to the vessel 3. The ratio of tannic acid to liquid treated may be as high as 100 parts per million but 50 parts per million is preferred.