Process and apparatus for decontamination of milk products by electrodialysis

摘要

Radioactive ionized contaminants are removed from milk by D.C. electrodialysis in a cell having between end electrodes two or more repeating units each comprising three compartments, the centre compartment being bounded on both sides by ion-exchange diaphragms of the same selectivity and the compartments adjacent thereto being defined on their outer sides by an ion exchange diaphragm of opposite selectivity to those bounding the centre compartment, the contaminated milk being passed through the centre compartment while electrolyte solutions are passed through the adjacent compartments whereby the milk leaving the centre compartment is of reduced radioactive content due to the radioactive ions having migrated into one adjacent compartment while ions from the other adjacent compartment migrate into the centre compartment to replenish the normal non-radioactive mineral salt content depleted by migration of ions from the centre compartment simultaneously with the radioactive ions. As shown, for removing strontium 90 from milk, the milk which is brought to pH 4.8-6 with citric acid, is fed into the centre compartment 2 of a 5-unit cell, compartment 2 being bounded by cation exchange diaphragms K1 K2, and a solution of pH 6 containing Ca, Mg, Na, K and Cl ions is fed through compartment 3, while waste compartment 1 which initially contains an electrolyte is thereafter fed with water. The effluent decontaminated milk is brought to pH 6.6 with aqueous potassium hydroxide. If milk deficient in sodium is required this is omitted from the feed to the reconstituting compartment 3, while in place of adding citric acid to the contaminated milk this may be made acid by suitably acidifying with hydrochloric acid the reconstituting compartment 3. In a modification, Fig. 2 (not shown), the centre compartment is divided by a microporous diaphragm as of rubber, asbestos, ceramic, polyvinyl chloride, polythene, the milk entering on the cathode side of the diaphragm and flowing under hydrostatic pressure through the diaphragm against the movement of the cations but at a slower rate and being removed from the compartment on the anode side of the porous diaphragm. Iodine 137 may be removed by defining centre compartment by anion exchange membranes and supplying the reconstituting compartment with a solution containing phosphate, citrate, sulphate and chloride anions with sodium cations. Common inlet and outlet manifolds for all the conduits handling the same liquid may be provided connecting a series of cell units such as above described, the liquid being fed to the different units in series or parallel and different liquids passing through the cell units in the same or opposite directions. Milk to be treated may be fed batchwise through the same decontaminating compartment several times to reduce its level of contamination to the desired value. Specifications 720,002, 772,861, 772,862, 792,623 and 821,229 are referred to.