Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1995-11-28
2000-06-06
Lithgow, Thomas M.
Liquid purification or separation
Processes
Ion exchange or selective sorption
210683, 210753, 210754, 210764, 210259, 210266, 210501, C02F 900, C02F 150, C02F 158, B01D 2402
Patent
active
060714158
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
Methods for impregnating activated carbon with silver to yield silver loadings much higher than that available commercially are provided, which provide products useful for purifying water, especially from iodides and bromides which may be eluted from iodinated and halogenated disinfecting resins, lowering the concentrations of the contaminating halides to levels acceptable for continuous drinking applications and enabling regeneration of the silver and possibly also of iodine from the precipitated silver halides.
BACKGROUND OF THE INVENTION
Silver impregnated activated carbon, (Ag-GAC), is a well known product, used widely for purifying process-water and drinking-water. The function of the silver bound to the activated carbon is to avoid bacterial growth on the carbon bed and in the water in contact with it. Filter cartridges containing Ag-GAC do not kill bacteria during normal filtration rates. For this reason Ag-GAC is described as a Bacteriostatic medium and not a Bactericide.
The maximum admissible concentration of silver in drinking water is: 0.05 mg/L (50 ppb) in the USA and Canada and 0.01 mg/L (10 ppb) in the EEC. Therefore, in order to enable application of Ag-GAC for purifying drinking water, the loading of silver on the carbon is low, usually lower than one percent. The highest silver loading offered commercially is 1.05%.
Recently iodinated and halogenated resins have been introduced as water purifiers capable of "instantaneously" killing bacteria and viruses upon contact between the treated water and the disinfecting resin. The use of equipment containing such disinfecting resins for purifying drinking water has been approved by the US-EPA for emergency and intermittent applications, not for continuous consumption, because disinfecting resins elute minute amounts of iodine and iodides into the treated water, and excessive consumption of iodine/iodide may cause hyperthyroidism. The "adjusted acceptable daily intake" (AADI), of iodine/iodide has been determined to be 1.19 mg/L (Handbook of Water Quality, Standards and Controls by John De Zuane, P. E., Van Nostrand Reinhold, New York 1990). The concentrations of iodine/iodide eluted to the treated water by commercial disinfecting resins vary between 2 to 15 ppm (mg/L), depending on the type of the resin and on the salinity and temperature of the treated water. Therefore, application of equipment containing iodinated resins for purifying drinking water for continuous consumption can be possible only if the drinking water purifier contains means which reduce the concentration of iodine/iodide in the product water to 1.19 ppm and preferably considerably lower.
Iodides can be removed almost absolutely from aqueous solutions by precipitating them with silver ions. The solubility product of AgI at 25.degree. C. is 1.5.times.10.sup.-16, a million times lower than that of AgCl (1.56.times.10.sup.-10) at the same temperature. Therefore, iodides can effectively be eliminated from drinking water via precipitation as AgI, even in the presence of a large excess of chloride ions such as those existing in drinking water. Metallic silver or silver chloride can generate sufficient concentrations of silver ions for precipitating iodides. However, in order to be effective, the surface area of the silver-ion generating solid must be very large. Otherwise it will very quickly be coated with AgI precipitate and become "blind" to the aqueous solution. Granular Activated Carbon (GAC), has a large surface area and can be an efficient "carrier" for silver. Indeed, Ag-GAC has proven to be effective in removing iodide ions from drinking water.
Nevertheless, commercially available Ag-GACs are not practical for removing iodides from water disinfected by iodinated resins because their silver loading is very low. Thus, even if we take GAC impregnated with 1.05% silver (the highest silver loading available commercially), than 300 ml of such Ag-GAC (the amount which can be included in a 10" CounterTop Drinking Water Purifier) weigh .about.150 grams and
REFERENCES:
patent: 3294572 (1966-12-01), Piccione
patent: 4187183 (1980-02-01), Hatch
patent: 4298475 (1981-11-01), Gartner
patent: 4461711 (1984-07-01), Behrens
patent: 4769143 (1988-09-01), Deutsch
patent: 4995976 (1991-02-01), Vermes
patent: 5061367 (1991-10-01), Hatch
patent: 5126044 (1992-06-01), Magnusson
patent: 5366636 (1994-11-01), Marchin
Dalven Israel
Frommer Moshe A
Lithgow Thomas M.
Purotech International Inc.
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