Phenol Sorption on Ion Exchaige Resins R. E. ANDERSON AND R. D. HANSENI The Dow Chemical Co., Midland, Mich.
w a s t e waters containing phenols present a serious disposal problem, particularly in the case of chlorinated phenols or strongly acid wastes. Organic ion exchange resins have been shown to sorb certain organic solutes beyond their exchange capacities for such materials. The quaternary ammonium anion exchangers have a rather high nonexchange capacity for phenolic compounds. Sorption isotherms were determined for phenol and p-nitrophenol on an anion exchange resin and found to be similar in nature to those observed in the sorption of phenols on charcoal. A number of other nonionic phenolic compounds were found to sorb without any accompanying release of exchangeable ions from the resin. A much lower extent of sorption occurs in alcohol and allows stripping of the phenol from the resin by the use of a solvent such as methanol. This phenomenon presents a new possibility for the removal of gross amounts of phenol or phenolic compounds from waste streams and their concentration for disposal or re-use. ASTE waters containing phenols present a serious disposal problem. This is particularly true of chlorinated phenols or strongly acidic phenolic wastes t h a t are difficult to destroy by bacterial oxidation. A number of references have been made in the literature to the fact t h a t ion exchange resins tend to sorb certain organic solutes beyond their exchange capacities for such materials ( l a ) . However, to the best of our knowledge, only one publication has appeared which deals specifically with the sorption of phenols by a synthetic ion exchange resin. I n a specialized German publication in 1951, Anders (a) described t h e use of Wofatit M, a weakly basic anion exchange resin manufactured from m-phenylenediamine, polyethylenediamine, and formaldehyde by I. G. Wolfen Farben ( I d ) , for t h e removal of phenols and fatty acids from a carbonization water by a nonexchange sorption. Phenol sorption on ion exchange resins was observed in this laboratory in 1949 when a n attempt was made t o remove trichlorophenol from a plant waste by hydroxide exchange on a quaternary ammonium resin, Dowex 2. Although the waste solution contained about 15y0 sodium sulfate and only about 0.3% trichlorophenol, passage through the resin reduced the trichlorophenol to about 1/10 of its original concentration. Only about l / 5 of the trichlorophenol held by the resin was eluted when the resin was washed with an excess of a sulfuric acid-sodium sulfate solution. Additional runs substantiated the fact that the sorption was of a nonexchange type in that resin in the sulfate form removed trichlorophenol from solution; the trichlorophenol could not be eluted effectively with acid or salt solutions but could be eluted effectively with an alcohol. I n agreement with this, Davies and Thomas (6) found that in the sorption of organic acids on cation exchange resins it was the undissociated acid that was being sorbed. Attention was then transferred to the sorption of reagent grade phenol from water, since this represented a more convenient system. COLUMN STUDIES
A number of column runs were made using various resins, solutions, and flow schemes. 1
The general nature of the results
Presently on leave for military servioe.
January 1955
is shown in the first four figures. Figure 1 shows the sorption of phenol on a hydroxide form, quaternary ammonium resin and the regeneration of the resin with alcoholic caustic. A 100-in1. buret column containing 60 ml. of Dowex 2-X7.5,20- to 50-mesh, OH- form, was used. A 0.1N phenol solution was passed through the column a t 10 ml. per minute (approximately 2 gallons per minute per square foot). The effluent was collected in suitable fractions which were titrated for phenol using the bromate-bromide method ( I S ) . A gradual break-through occurred, and the run was stopped when the phenol concentration reached 0.07N. The resin was then rinsed downflow with methanol which was 0.88N in sodium hydroxide I n the loading portion of the run 11.9 grams of phenol were removed from solution by t h e column of resin with a total exchange capacity equivalent to only 6.2 grams of phenol. Elution with 750 ml. of alcoholic sodium hydroxide removed 11.4 grams of phenol from the column. While the first 200 or 300 ml. of this regenerant solution removed a considerable portion of the phenol from the resin, each succeeding portion was less effective, and the phenol tailed out badly. When the column of resin was re-exhausted with 0.1N phenol, (not shown in the figure) it sorbed 11.3 grams of phenol. This phenol-loaded column wa9 then rinsed with methanol as shown in the first half of Figure 2. The methanol elution removed 6 3 grams of phenol from the resin-an amount comparable with the amount of phenol t h a t was picked up by the resin beyond its exchange capacity. When the resin was again exhausted with O.1N phenol, 6.1 grams were removed from solution. Thus, the shaded portion in t h e second half of Figure 2 represents the amount of phenol sorbed by the phenate salt of the resin. Figure 3 shows the sorption of phenol by the chloride salt of another quaternary ammonium resin. The flow scheme used was an attempt to approximate a practical method of operation with methanol elution. A 1-inch diameter column containing 255 ml. of Dowex 1-X7.5, 20- to 50-mesh, C1-, was used; 2 liters of 0.1N phenol solution were pumped into the bottom of the column at a rate of 50 ml. per minute (approximately 2.5 gallons per minute per square foot). The effluent was collected
INDUSTRIAL A N D ENGINEERING CHEMISTRY
71
a t a point immediately above the resin and analyzed. TJlien the 2 liters of solution had been pumped in the column, the solution remaining in the column was drained and the excess liquid blown out with alr. This residua' liquid is shown as the last cut prior to the methanol rinse in Figure 3 Then, 1 Iiter of niethanol was introduced a t the top of the column and allowed to trickle through the resin over a period of an hour. This elution removed 19.4 grams of the 19.5 grams of phenol picked up by t h e bed. KO chloride wa;9 di3placed froin the re-.in during the cycle.
07
0
-4
03
-
REGENERAT
1
i
ON
NoCH IN METHANOL
1
L
101
0 0
2b0
400
6b0
800
I000 ,200 1400
b
200
460
6b0
8100
VOLUME O F E F F L U E N T ( m l )
Figure 1. Phenol Sorption o n Dowex 2, 011- and Elution with NaOH in JIethanol
The relative sorptive capacities for phenol of four different resins are shown in Figure 4. In each case 75 nil. of resin was placed in a 100-1n1. buret column and 500 ml. of 0.1N phenol was passed through it a t 20 ml. per minute (4 gallons per minute per square foot). The effluent was collected and analyzed for phenol. I n Figure 4, a and b show the results with chloride forms of Dowex 1 and 2 These are quaternary ammonium type resin$, Dowex 2 differing from Dowex 1 only in the substitution of an ethanol group for a methyl group in the nitrogen substituents. Figure 4c shows the result with the hydrochloride form of Dowex 3, a weak base polyamine resin. Figure 4d shows the result with the hydrogen form of Dowex 50, a nuclear sulfonic acid resin. All four of these resins are made from a styrenedivinylbenzene copolymer The behavior of the two quaternary resins is essentially identical, the polyamine resin is a somewhat poorer sorbent €or phenol, and the sulfonic acid resin shows only limited Eorption. These results indicate that the functional group plays an important part in the phenol sorption proccss. Phenolic compounds which have been observed t o be sorbed on quaternary ammonium resins include-in addition to phenol and trichlorophenol-p-nitrophenol, pentachlorophenol, p-hydroxybenxaldehyde, and o-hydroxyphenylpropionic acid. The sorption of highly ionized phenolic compounds is somewhat obscured by the ion exchange that takes place siniultaneously and can only be observed as a net difference between total equivalents in and out of the column. I n experiments of this type, sodium phenate showed only slight nonexchange sorption on Dowex 1, C1- and phenolsulfonic acid shoTved no nonexchange aorption. Therefore, it seems probable t h a t any watersoluble phenolic compound will be sorbed as long as it is no: ionic enough to be excluded from the highly ionized interior of the resin (15). EQUILIBRIUM STUDIES
I n their paper on nonionic separations with ion euchenge resins, Wheaton and Rauman (261 presented distribution constants for a number of ovganic solutes between water solution and the resin phase. This distribution constant, Kd, was defined as 12
the ratio of the concentration of the solute in the water in the resin t o the concentration of the solute in the water outside the resin phase a t equilibrium. I p d had a value between 0.5 and 1.5 for most simple organic solutes and showed only moderate variation with chan,g$ng solution concentrations. However, t h e Kd for the system phenol-Dowex 1, C1- mas given as 17 7 . This value is of a different order of magnitude from the others presented and ie very hard to explain on the basis of a solvent solvent distribution action. A series of experiments was run to determine the dependence of this P ( d valiie on the solution concentration at equilibrium. The K d ' s obtained varied from 80.6 to 14.6 as the equilibrium solution changed from approsimately 0.1 % phenol to 5.3% phenol. The dependence of the sorption on solution concentration was also observed in column runs. While Dowex I , C1picked up about 1meq. Qf phenol per milliliter of resin froin a 0.1N solution, the same resin picked up only about of that amount when the solution concentration was reduced to 0.01N, and only about 1/12 as much when the solution concentration was reduced to 0.001N. Since this dependence of sorption on cancentration suggested a Aolution-solid sorption process such as observed with phenol OIJ charcoal, a sorption isotherm way determined for the system phenol-water-Dowex 1, C1-. The resin, Dowex 1-X7.5, 20- to 50-mesh, C1- form, was thoroughly washed and vacuum-dried t o constant weight. A sample of the dried resin was weighed in a small weighing bottle, a measured volume of a standard phenol solution added, and t h e bottle stoppered and shaken. After
---
ELUTION OF RESIN WITH M E T H A N O L
11 0
2 0 0 ,400
. 600
, 800
VOLUME O F E F F L U E N T ( m l . )
Figure 2. Phenol Sorption o n Dowex 2, Phenate after Elution of Exhausted Resin with Methanol
being allowed to equiiibrate in a water bath a t 25' C. for at least 20 hours, the supernatant liquid was analyzed by refractive index measurement. The sorption vyns calculated as
AC vo m where VOis the number of milliliters of solution added to m grams of dry resin, and AC is the change in concentration of the solution expressed as moles of phenol per liter. The sorption is thus expressed as millimoles per gram. The sorption isotherm for phenol on Dowex 1, GI- is shown in Figure 5 . Thia mrve has the shape commonly associated with sorption on porous sorbents, the sorption increasing rapidly at lorn concentrations and approaching a limiting value as the concentration of solute approaches the mkcibility limit, the leveling off being associated with a filling of the pores with sorbate ( 4 ) . Nunicrous investigators ( I , 5,8, IO) have determined the sorption of phenol from water on various charcoal sorbents, obtaining the same type of isotherm as t h a t found here with
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
VOl. 47, No. I.
L Dowex 1. In most cases the amounts sorbed on these charcoals were less than the sorption on Dowex 1; however, Boutaric and Beithier (5) determined an isotherm which showed a sorption greater by about 15% than that found for Dowex 1. Although the sorption kotherms obtained with phenol-waterDowex 1 are of the same type as those obtained with phenolwater-charcoal, this does not necessarily indicate that t,he mechanism is the same. The fact that Dowex 1, Dowex 3, and Dowex 50 exhibit markedly different degrem of sorption although all three have the same copolymer base, indicates that the resin's functional groups play an important part in the sorptive mechanism. However, the polarity of the resin framework which rcsulk from the presence of the functional groups may be the important factor in causing thebe marked differences in sorptive capacity of the different resins instead of actual interaction of phenol and the functional groups (6). Determination of the amount of solution held by the resin (9) obtained by centrifuging the resin to remove solution adhering to the outside of the beads together with the sorption isotherm allows calculation of the concentration of the solution in the interior of the resin. Buch a calculation for the system phenolwater-Dowex 1, GI- a t a solution concentration of 7.35 weight % phenol gives an interior solution approximately equal in composition to phenol Aaturated with water (71.3% phcnol a t 25' C ).
.-,
0.8
n Exchange-
o
WEIGHT P E R C E N T P H E N O L
2 0
4 0 60 I
a Y
0
01
0 2
0 3
05
04
CONCENTRATION
MOLES
Figure 5.
06
OF E Q U I L I B R I U M
07
08
03
I O
SOLUTION
PER LITER
Phenol Sorption from Aqueous Solution on Dowex 1, C1- at 25OC.
Vo AC
_ .
I
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
C O N C E N T R A T I O N OF E Q U I L I B R I U M S O L U T I O N MOLES
PER L I T E R
Figure 6. p-Nitrophenol Sorption from Aqueous Solution on Dowex 1, C1- at 25" C. _I
p
0.1
I w
0
500
1000 1500
2000
1060
500
V O L U M E O F E F F L U E N T (ml.)
Figure 3. Sorption of 0.1N Phenol on 255 M1. of Dowex 1, C1- and Elution with Methanol
I
id1 O N D O W E X 50, H'
0
,00
.FLUENT
Figure 4. January 1955
200
300
400 500
Imll
Phenol Sorption on Dowex Resins
Figure 6 shows the sorption isotherm for the system p-nitrophenol-water-Dowex 1, C1- at 25' C. This curve has the same charactenstic shape although the solubility of pnitrophenol in water is much fower than that of phenol. If the sorption proceed8 by a pore-filling mechanism, the volume of sorbate held by the resin a t the miscibility limit might be expected to be nearly the same for both systems (phenol-water and pnitrophenolwater), Using extrapolated values of 10.5 and 9 5 millimoles per gram of dry resin for the maximum amount sorbed for these t v o systems, the voluine of sorbate can be calculated if the sorbate is assumed to be pure phenol OT p-nitrophenol, obtaining values of 0.92 and 0.90 cc. sorbate per gram of dry resin respectively for the systems phenol-water and p-nitrophenol-water. These volumes of sorbate are in agreement within 3%. Since the the soibates undoubtedly are not pure phenol or pnitrophenol, but these compounds saturated with water, the molar volumes of the pure components should not be used for such calculation. Instead the volumes of the water saturated solutions should be used. However, in view of the limited solubility of water in these components, the approximation used in these calculations have but a slight dffect on the results. Other instances of constant volume of sorbate have been noted with porous sorbents. Dzhigit ( 7 ) studied the sorption of partly miscible fatty acids and alcohols from water solution on charcoal. The acids from valeric to octanoic and the alcohols from butyl to heptyl gave nearly constant volumes of sorbate at maximum sorption. Using the same charcoal sorbent, branching and cyclization decreased the sorption of alcohols, apparently by reducing the ability of the molecules to fill the pores of the
INDUSTRIAL AND ENGINEERING CHEMISTRY
73
sorbent. The same conclusions were arrived a t by Kiselev ( I I ) , using a different charcoal. Thus, the difference in the shapes of phenol and p-nitrophenol would be expected t.o give small differences in the volumes of sorbates a t maximum sorption. The sorption isotherm for the system phenol-methanolDomex I, C1- is shown in Figure 7 . Phenol and methanol are miscible in all proportions. The sorption of phenol as expressed as LroAC/rnmust, by definition, approach zero as the equilibrium solution approaches 100yophenol, since AC then approaches zero. However, over the concentration range studied, the isotherm has the same characteristic shape seen in Figures 5 and 6. The difference in the extent of sorpt'iori in water and in methanol can be seen in Figure 8 in which the two isotherms are plotted on the same axe.'
will depend on the particular type of phenol being sorbed. For unsubstituted phenol the minimum is about 0.1M. This capacity is not greatly affected by the presence of salts or acids in solution as long as the solution is not alkaline enough €or the phenol to be present as phenate ions. This then allows tho removal, and subsequent recovery, of all but small concentrations of phenols from even very concentrated ftcids and salt solutions Such solutions are difficult to treat by bacterial oxidation.
APPLICATION
Quaternary ammonium resins offer two possibilities for the rcmoval of phenols from solution-exchange and eorption on the hydroxide form of the resin, or sorption on a salt form of the resin. Each method has its own advantages and limitations. For phenol solutions relatively free of electrolytes a hydroxide cycle could be used, The efnuent would be free of phenol regardless of the original phenol concent,ration for a major portion of the exhaustion cycle. Regeneration could be carried out with a solution of caustic in methanol and the methanol recovered by distillation for re-use. Hoxever, all anions in the original solution would be picked up by the resin and mould require an equivalent quantity of caustic for removal from the resin. Thus the chemical cost would become exorbitant for wastes containing other than trace quantities of electrolytes. Even for wast,es free of electrolytes such a process would have to be very carefully engineered to compete costwise with bacterial oxidation on a disposal basis. Such a hydroxide cycle could well be the best method of treating wast'e streams cont,aining low concentrations of chlorinated phenols and relatively free of electrolytes.
I
0 0
1.0
I
2.0
I 3.0
I 4.0
5.0
C O N C E N T R A T I O N OF E Q U I L I B R I U M S O L U T I O N M O L E S PER L I T E R
Figure 7 . Phenol Sorption from Methanol on Dowex 1, C1- at 25' C.
The nature of the sorption of phenols on the salt forms of the quaternary ammonium resins places serious limitations on its usefulness but also allows it to do certain jobs which would be difficult otherwise. Since the capacity of the resin salt to sorb phenols is dependent on the concentration of the phenol eolution (Figure 5), the capacities realized ahen working with the very dilute solutions often encountered in industrial phenolic wastes would be prohibitively low. This sorption method also tends to allow a small amount of phenol leakage early in the run. This is particularly true when working in solutions of low pH With solutions of moderate phenol concentrations the resin salts show a very useful capacity for phenol. The minimum concentration a t which the capacity of the resin salt becomes useful 74
:K 0
I 0.2 0.4
S O R p IN~ MET ~ HA ~ NO^ ~
l l 0.6 0.8
1 1.0
I 1.5
C O N C E N T R A T I O N OF E C U l L B R l U M MOLES P E R L I T E R
~
-
I 2.0 SOLUTION
Figure 8. Phenol Sorption o n Dowex 1, C1-at 25" C.
The difference in the two isotherms in Figure 8 allows the react,ivation of the bed by means of a methanol rinse. The product obtained will be a methanol solution of phenol which may be distilled with recovery of both the methanol and phenol. Anders ( d ) tried a number of aqueous arid nonaqueous solutions and combinations as st'ripping agents but found none that were better than an alcohol mixture. A mixture of methanol and butyl acetate was said to offer advantages froin the Btandpoint of solvent recovery. A s the methanol dissolves phenol and the reEin becomes depleted in phenol during the stripping process, the efficiency of t'he extraction falls off rapidly. Most efficient, methanol use could probably be obtained by a Soxhlet type of operation in which the methanol was distilled from the effiuent and alloved to condense a t the top of the resin column. Although there R-ould be no chemical cost in the usual sense for such a process, the unit would have to be carefully engineered to keep methanol losses a t a minimum. Since phenol and water are completely miscible above 60' C., an efficient stripping should be obtained with water a t elevated temperatures. However, all attempts to carry this out a t near 100" C. were only moderately successful. Methanol stripping is two or three times as efficient as hot aqueous stripping. This sorptive capacity of ion exchange resins in general for phenolic type compounds should be borne in mind in chromatographic work and ion eschange processes in vvhich such compounds may occur. In certain cases resins may become fouled with phenolic compounds with a resulting loss in exchange capacity or efficiency. While this process has not been fully evaluated, it appears to be a practical method of removing, recovering, or concentrating phenols from solution. It ehould find application in chemical processes involving phenols, such as the recovery of coke oven bv-product,s and the manufacture of phenolic resins, and aid in the treatment of phenol wastes. ACKNOWLEDGMENT
The authors wish to thank H. L. Aanioth and R. McKeller for portions of the data reported in this paper.
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
Vol. 47, No. 1
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.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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