Ion Exchange IJTERATURE CITED (1) Amiot, R., Compt. rend., 197, 325 (1933). (2) Anders, H., Gas-u.-Wasserjueh, 92, No. 17, (Gas) 238 (1951). (3) Boutaric, A., and Berthier, P., BulE. SOC. chim., 1 ( 5 ) , 1549 (1934). (4) Cassidy, H. G., “Adsorption and Chromatography,” p. 71, Interscience Pub., New York, 1951. (5) Ibid., p. 104. (6) Davies, C. W., and Thomas, G. G., J. Chem. Soc., 1951,2624. (7) Dzhigit, D. M., Kiseler, A. V., Terekhova, M. G., and Shcherbakova, K. D., J . Phys. Chem. (U.S.S.R.), 22, 107 (1948). (8) Fu, Y., Hansen, R. S.,and Bartell, F. E., J . Phys. Chem., 53, 1141 (1949). (9) Gregor, H. P., Held, K. M., and Bellin, J., Anal. Chem., 23, 620 (1961).
(10) Heyne, W., and Polany, M., 2. physik. Chem., 132, 384 (1928). (11) Kiselev, A. V., and Shcherbakova, K. D., Acta Physicochim. U.S.S.R., 21, 539 (1946). (12) Samuelson, O., “Ion Exchangers in Analytical Chemistry,” p. 121, John Wiley & Sons, New York, 1953. (13) Scott, W. W., “Standard Methods of Chemical Analysis,” 5th ed., p. 2253, D. Van Nostrand & Co., New York, 1939. (14) Topp, N. E., ”The Manufacture of Wofatit Base-Exchange
Resins,” British Intelligence Objectives Sub-committee. Final Report No. 621, Item No. 22. (15) Wheaton, R. M., and Bauman, W. C., IND.ENG.CHEY.,45, 228 (1953). (16) Wheaton, R. M., and Bauman, (Art. 3), 159 (1953). RECEIVED for review March 29, 1954
W.C., A n n . N . Y . Aeud. Sci., 57 ACCEPTED October 12, 1954.
Anion Exchange Removal of Iron from Chloride-Solutions A. C. REENTS AND F. H. KAHLER,
Zllinois Water Treatment Co., Rockford, I l l .
T h e industrial utility of an ion exchange process for removal of iron from 18” to 22’ BQ hydrochloric acid was investigated. Passage of hydrochloric acid contaminated with ferric iron through a column of quaternary type anion exchanger produced an effluent acid, free from iron. Regeneration of the resin is performed with water. Laboratory studies were made on this process for the removal of iron from hydrochloric acid pickling solutions. Data are included on exchange capacity, resin stability, and process economics. removal of dissolved iron from solutions of hydrochloric Later work by Kraus and his coworkers (6-6)was devoted primarily to the separation of various cations by means of a difference in their tendency t o form complex anions in relatively concentrated hydrochloric acid. Kraus and Moore also suggested the possibility of applying this process not t o effect a separation of metallic ions but purely for the removal of iron from hydrochloric acid. The Kraus reports indicated a possibility of this but did not indicate practical methods. This paper cover8 the work done to determine the industrial utility of the process. The initial work in the laboratory was carried out in 25-mm. diameter columns with resin bed depths of 3 to 4 feet. The hydrochloric acid used ranged in concentration from 18” to 22” B6 with ferric iron contents of 10 to 600 p.p.m. This hydrochloric acid was manufactured by the saltacid process, Later experiments used by-product acid, as well a s hydrochloric acid manufactured from chlorine and hydrogen. Removal of iron from hydrochloric acid is a problem common t o all these methods of manufacture.
T acid V was first reported by Kraus and Moore ( I ).
METHOD FOR REMOVING IRON FROM HYDROCHLORIC ACID
The sequence of operation is indicated in the flow sheet (Figure 1). The Contaminated acid passes downflow through the resin and directly to storage or to be used. At the end of a n operating cycle, the influent flow of acid is stopped, and water is fed t o the top of the column. As the hydrochloric acid concentration decreases, the FeCI.4- complex ion dissociates, and the iron is eluted as FeC13. +4fter the passage of water in the amount of 3 t o 4 resin volumes, the iron is completely eluted. After a backwash operation with water, contaminated acid is again fed t o the top of the column and the cycle repeated. Such experimental cycles were carried out with a number of commercially available anion exchange resins of the quaternary January 1955
type, as earlier checks had shown that the weak base or tertiarv type were not suitable. Both Type I and Type I1 quaternary resins were effective in the process. Type I exchanger contains the active grouping RN(CH&+. I n Type I1 quaternary eschanger, the active exchange group is RN(CHp)z CZHdOH T. “R” represents the resin matrix. Both types are based on styrene, divinylbenzene copolymers. However, leas iron leakage was noted for the Type I anion exchanger. Type I resins, cross-linked with 4 and 8% divinylbenzene, were used. There was little difference in the total iron removal capacity. The highly cross-linked resins showed less swelling when the influent changed from acid to water. As less swelling is advantageous in industrial equipment, the work was confined to Type I highly cross-linked anion exchangers. Figure 2 shows data for the beginning of a typical column cycle. The column was 1.25 inches in diameter with a resin bed depth of 48 inches. The influent material was a technical grade hydrochloric acid (28y0 HC1) containing 125 p.p.m. iron, all as ferric iron. The flow was maintained at 1.5 gallons per minute per cubic foot of resin. Effluent samples were collected and analyzed for iron and hydrochloric acid. The hydrochloric acid concentration of the samples was checked by titration with standard sodium hydroxide. The total iron concentration was determined spectrophotometrically, using the thioglycolic acid method. Figure 2 indicates that the residual iron decreases very rapidly at first and then more slowly. The curve shows conditions with the column flooded with water when the acid feed is started. After the passage of a volume of hydrochloric acid equal to the void volume of the resin, the presence of hydrochloric acid is noted in the effluent, and this concentration rises until it equals the influent concentration a t approximately 18 gallons per cubic foot. The iron concentration then approaches zero asymptotically, and for all practical purposes reaches 0.0 after 27 gallons per cubic foot of effluent have been collected.
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Operation was continued until iron began to leak. This part of the cycle is not shown, but in this case it occurred after the passage of 2460 gallons of hydrochloiic acid per cubic foot. When iron appeared in the effluent, the flow of acid was stopped and the column regenerated. same rate as the acid.
Water is passed downflow a t the
TABLE 11. CYCLES VERSUS EXCHANGE CAPACITY Capacity, Meq / D r y Gram Total Quaternary 3 28 3.07 3.20 3.01 3.16 2.95
Cyole NO.
Kew resin 105 203
Loss,
% 2:i 3 7
Wet Screen an alp^ Retained, Screen Size 16
20 30 40 50 Thiough 50
J&?UCE
R&fiV'2,97/ON
B?7Ce..PS,Y
Figure 1. Iron Removal from Hydrochloric Acid
Figure 3 ahoms the regeneration cycle. The acid concentration fa119 quite uniformly from that of the influent to 0.0, and no hydrochloric acid is detected after 18 gallons per cubic foot. The iron concentration rises rapidly and a t the maximum reaches a concentration of 0.85%. Regeneration was complete after the passage of 27 gallons per cubic foot.
New resin 0 a0 44 70 43 90 IO 80 0 30
Anion exchanger after 203 cycles 0 06 33 60 50 05 13 50 2 07
0.10 100.00
100 00
0 72
To accelerate the work, and to shorten the cycle, an influent acid of 28.7% containing 4350 p.p.m. of iron was used. I n the cycling work, water was passed through the column in a volume corrcsponding to the elution curve shown in Figure 3. This was followed by contaminated acid in a volume calculated to exhaust the resin, and then repeated continuously. A total of 203 cycles was run on Type 18% cross-linked resm. Table 11 shoas capacity at intervals and the screen analyses of new resin and of the resin after 203 cycles. The capacity loss is only 3.7%. There is a slight shift in the particle distribution curve, but this shift is no greater than normally expected after thia number of cycles. From a practical standpoint, the cost of any process is always of interest. I n ion exchange, there are several factors which contribute to total cost. Primary among these are product loss, regenerant costs, resin amortization, and labor. The cost of these factors for an influent hydrochloric acid a t a concentration of 30y0,containing 10 p.p.m. iron, is shown in Table 111. These costs are based on a reactor vessel containing 20 cubic feet of resin designed to operate a t approximately 6 tons per hour. REMOVAL OF IRON FROM ALUMIhUE-P CHLORIDE
EFFl UFWT GZ?L!DNS HO CFP fU /7 A V K l J LXCHAANGE4
Figure 2* Iron from Exydroch'oric Acid Beginning of Typical Column Cycle
In the cycle shown in Figures 2 and 3, the capacity of the resin was 2.97 pounds of iron per cubic foot. ilnalyses of sample increments showed iron contents of 0 0 to 0.05 p p.m. Determinations made on the total iron recovered during regeneration account for 99.2% of the iron as calculated in the influent. Table I is a comparison of the analyses of Contaminated and treated acid. To determine the stability of the resins in repeated cycling operation, a column mas set up on an automatic cycling basis.
TABLE
I.
ANALYSES O F
Specific gravity, 15' C HC1 normality Free chloiine Iron, p TI m a s F e h-onvolatile material, p p In
76
Hydrochloric acid plants frequently produce aluminum chloride. This material is usually sold as a 32' BB solution, containing 35% aluminum chloride, and is almost always contaminated u i t h ferric iron. As an iron-free product is desirable, the feasibility of iron removal from this solution was investigated. The sample, as received, was lorn, in iron content (93 p.p.m.), and ferric chloride was added to shorten the operating cycle. As finally treated, the material contained 1395 p.p.m. ferric iron, as Fe, and the concentration of the aluminum chloride was 33.2" BB. This S O ~ U tion was passed through the same column used for the hydrochloric acid study.
HYDROCHLORIC ACID Anion Exchange Before Aftei 1 176 1 170 11 5 2 11 52 None None 125 310
0 01 235
EFFLUE4T GflllOAJ t/CI Pf# CU f T flhL?/V tXkANG€/
Figure 3.
Iron Removal from Hydrochloric Acid in Regeneration Cycle
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 1
-Ion REiMOVAL OF IRON
Exchange
FROM PICKLING BATHS
TABLE 111. COSTOF IRON REMOVAL FROM 30% HYDROCHLORIC Many plants use hydrochloric acid for pickling steel. I n ACID this process, the acid concentration of the pickling bath steadily Cost/Ton, Cents
Product loss, 0.05% Regenerant (water only), 1150 gal./oycle Resin amortization (amume 3-:vr.life), $71.5O/cu. ft. Labor, $2,OO/hr. Total cost
0.800 0.008
12.000
0.150 13.056
Kraus and Moore (1)reported that aluminum is not adsorbed by strong base anion exchangers in the presence of hydrochloric acid. The iron chloride complex anion is removed by anion exchange in the same manner as in the removal of iron from hydrochloric acid. However, iron is completely removed from the solution even a t the high iron concentration used. At the start-up of a cycle, the iron concentration dropped to an undetectable quantity after the passage of approximately 6 gallons per cubic foot. At the end of the cycle, when water was added for regeneration, the iron concentration rose very rapidly, reaching 11.82 grams per liter after 6 gallons per cubic foot of water were added (Figure 4). Figure 4 gives elution data for the regeneration of the anion exchange column used to remove iron from the aluminum chloride solution. These curves indicate a loss of aluminum chloride due to contamination with eluted iron. The early appearance of iron in the effluent means that if water is added t o a column filled with aluminum chloride solution, the effluent must be discarded a t appreciable aluminum chloride concentration. Much of this aluminum chloride loss can be eliminated by anticipating the break-through point and by draining the aluminum chloride solution from the bed before water is introduced.
Figure 4.
Elution Data for Tron Removal from Aluminum Chloride Solution
As shown in Figure 4, the loss of aluminum chloride would correspond to approximately 3%. This, however, is much higher than vould be found in a plant operation, because the iron content of the aluminum chloride solution was increased for this work. I n this case, the iron was 1395 p.p.m. compared to a probable maximum of 100 p.p.m. in plant production. The total number of gallons that would be treated in plant operation would consequently be 14 times as great as the minimum. This would decrease the percentage loss by approximately the same factor. Because OP frequent requests concerning the removal of iron from chloride salts, investigative work was carried out to learn if the process might be applied to the relatively neutral salts. When using the system described, iron removal was not complete when treating 25% salt solutions of sodium, magnesium, and calcium chlorides. January 1955
falls, and the iron concentration increases. When the rate of pickling is too slow, the entire solution is discarded. Under these conditions, there is always present the problem of disposal of the acidic solutions. In addition, there is a tendency for the rate of pickling to vary, falling off as the iron concentration increases. This is most noticeable in continuous pickling operations where the work automatically moves through the acid a t a fixed rate. The method of iron removal from hydrochloric acid discussed offers a possible solution to both these problems.
I
I Figure 5.
Flow Sheet for Iron Removal from Hydrochloric Acid Pickling Solutions
I n a typical exhausted pickling bath, the iron is present primarily in the ferrous state. As iron does not form the chloride complex in this state, i t must be oxidized first. This can be done conveniently by aeration. Passage of a stream of air through a typical solution gave complete conversion of the iron t o the ferric state in about 1 hour. The solution then contained approximately 25,000 p.p.m. ferric iron, as Fe, and about 10% hydrochloric acid. P.assage of this material through a n anion exchange material does not give iron-free acid, but it does remove a large percentage of the iron. I n plant operation, the recommended procedure would be to continuously or intermittently, a t short intervals, draw off a portion of the pickling solution. This would be aerated to oxidize the iron t o the ferric state, passed through an anion exchange unit, and returned t o the pickling bank simultaneously with the removal of the next batch. Under such a n arrangement, relatively little excess acid would be required above the normal operating amount. If the solution were treated with the iron content in the range of 1000 to 1500 p.p.m., the loss of acid due to start-up and regeneration would be in the range of 1%. There would also be lost that acid which reacted with the iron to form ferric chloride. Figure 5 shows a flow sheet for such equipment. In production of hydrochloric acid, iron contamination can be removed by anion exchange resins in conventional ion exchange equipment a t very low operating costs. The application of this process for treatment of hydrochloric acid pickling wastes presents very interesting possibilities, but as get it has not been applied commercially. LITERATURE CITED
K. A., and Moore, G. E., J . Am. Chem. SOC.,72, 5792 (1950). Zbid., 73, 9 (1951). Zbid., 74, 843 (1952). Zbid., 75, 1460 (1953). Kraus, K. A., Nelson, F., and Smith, G. W., J . Phus. Chem., 58, 11 (1954).
(1) Kraua,
(2) (3) (4)
(5)
RECEIVED for review March 29, 1954.
ACCEPTED September 20, 1954.
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