Distilled Water Supply for Small Schools SHIRLEY GADDIS and CONRAD KUBINA Eureka College, Eureka, Illinois
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N SECONDARY schools and small colleges it is usually difficult to maintain a supply of distilled water. This paper describes an economical and simple method for making a deionized water which is pure enough for most needs. The method removes the anions and cations in tap water by using the new organic type of ion exchangers called the Arnberlites.' THEORY
Amberlite IR-100 has the ability to exchange H+ for any positive ion; thus, H.R
+ Naf
+Na,R
+ HC
The cation exchanger, IR-100, thus gives an effluent with a low pH. To regenerate this Amberlite it is necessary to reverse the above reaction by treating the resin with an acid solution. Amberlite IR-4 will exchange OH- for any negative ion; thus, R.OH C1- ---+ R . C l + OH-
+
The effluent from the 1R-4 will be basic, unless, as in the present procedure the feed water contains H+ from the preceding exchange in the IR-100. To regenerate the IR-4, it is necessary to treat the resin with a basic solution to reverse the exchange reaction.
water during the next cycle. For this purpose, distilled water is introduced into the IR-4 column at D, coming out at C. The IR-100 is washed separately by introducing distilled water at C, coming out at A . The IR-100 is washed until the effluent shows no opalescence with 0.5 N AgN03; the IR-4 is washed until the d u e n t is neutral to phenolphthalein. Exchange Cycle: The tap water is allowed to flow in at A and through the two Amberlites in series a t the rate of one gallon an hour. Until experience is gained on a particular tap water, frequent tests should be made on the effluents. Test portions are drawn from the IR-100 column at outlet B. Test portions from the IR-4 column are taken at outlet D. The IR-100 effluent must stay on the acid side of methyl orange. The IR-4 effluent must remain in the pH range 4.8 to 8.2 (using methyl orange and phenolphthalein to determine this range). When either column breaks through the specified range, both columns should be sent through the regeneration and backwash cycles. ANALYSIS OF THE DEIONIZED WATER
A 500-ml. sample of the water is evaporated to dryness in a platinum evaporation dish under infrared
The accompanying diagram shows the apparatus needed. The outer jackets for Liebig condensers (25 mm. by 75 em.) are used for the columns. The first column contains eight ounces of IR-100. The second contains eight ounces of IR-4. The glass beads should average about 2 mm. in diameter.
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INLETS FOR
INLET
I I
OPERATION
Regeneration of the Amberlites: The IR-100 is regenerated with five per cent HCl solution, the IR-4 with four per cent Na&Oa. One liter of the regenerating solution is allowed to drip over the Amberlite at the rate of two drops a second. The spent solution from the IR-100 comes out at C; the spent solution from the IR-4 at D. Allow the last of the solution to remain in contact with the resin for two hours. The regeneration is considered complete if the effluent from the IR-100 is acid to methyl violet and the IR-4 effluent is basic to phenolphthalein. Backwashing the Amberlites: This is done to free the bed from all traces of the regenerant and also to expand the bed to permit better contact between resin and 1 Memes, EASTES. AND MYERS, "Synthetic resins as exchange adsorbents." Ind. Eng. Chem., 33, 697-706 (1941).
381
IR-~OO-,
BEADS
II
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-
OUTLET
DISTILLED WATER SUPPLY FOR SMALL SCHOOLS lamps. Twelve different batches of the deionized water were analyzed. The total solids present in the 500-ml. samples varied from 3.4 to 3.9 mg. This is appreciably less than the 10 p.p.m. of total solids allowed by the U.S.P. specifications for distilled water. The residues from the above evaparation were put into solution by adding 20 ml. of the respective water. All qualitative tests for the usual ions present in water were negative. NOTES
1. Eureka water is from an artificial lake and contains around 140 p.p.m. of total solids. 2. There was evidence that at least part of the organic matter of the original water WJS taken up by the Amberlites during the exchange cycle. This might indicate that some of the orgalic matter was present in an ionic form.
(Conhued from page 381)
3. After 28 gallons of Eureka water have passed through the exchange cycle, the resins are regenerated. This is enough pure water to last us for three or four weeks. 4. The cost of the 28 gallons is less than four cents -just the cost of the regenerating solutions. By ordinary distillation 28 gallons would cost a great deal more for the gas alone. 5. The iirst two batches of distilled water will be high in total solids since the Amberlites tend t o throw color a t first. After the second batch the columns operate consistently. 6. The Amberlites can be obtained for the present from the manufacturer, The Resinous Products and Chemicals Company a t Philadelphia. The IR-100 sells for 50 cents a pound, while the IR-4 costs $1.75 a pound. It is hoped that eventually these reagents will be made available through the usual supply channels.
