Ind. Eng. Chern. Prod. Res. Dev. 1980, 19, 282-285
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Stability of Xon-Exchange Resins. 3. Stability of Resins under Field Conditions and Correlation with Laboratory Data William M. Alvino" Polymers & Plastics Department, Westinghouse RbD Center, Pittsburgh, Pennsylvania 15235
Michael C. Skrlba Nuclear Fuel Fabrication, Westinghouse R&D Center, Pittsburgh, Pennsylvania 75235
The stability under field conditions of a number of ionexchange resins that are potential candidates for use in uranium extraction from acid leach liquors has been determined. The resins were subjected to 50 load/wash/elution cycles in a resin test apparatus to simulate actual plant conditions at Wyoming Mineral Corporation's Salt Lake City, Utah site. Resin attrition has been severe for some of these materials and negligible for others. This attrition manifested itself in the form of bead fragmentation and ranged from 0 to 90%. Comparison of the field test data with laboratory osmotic shock test data indicates that resin deterioration takes place in the same order but differs in magnitude: Le., those resins that deteriorated first under laboratory test conditions also were the first to deteriorate under field conditions. Resin fragmentation appears to be the pathway for deterioration in the field test, whereas resin cracking with little fragmentation is observed in the laboratory tests.
Introduction We are presently involved in a program to evaluate the stability of ion-exchange resins to osmotic shock. This program is aimed at developing a laboratory test that would enable one to distinguish between physically strong and weak resins and yield information on the long-term stability of these resins. Such a test has been developed to give information on the above items. What was needed was to determine how these laboratory tests relate to resin stability under actual field conditions. This paper deals with the evaluation under field conditions of the stability of a number of ion-exchange resins that are potential candidates for use in uranium hydrometallurgy. It is hoped that these tests will yield information on the following: (1) Is there a correlation between laboratory and field tests? (2) What is the deterioration rate of strong and weak resins? (3) Is there a significant difference in the rate of deterioration of these resins? (4) How can we best develop laboratory tests that are meaningful in predicting resin stability in the field? Experimental Section Laboratory based experimentation in ion-exchange systems becomes very difficult from a logistics standpoint whenever feed solutions with very low concentrations of the ionic species of interest are to be treated. This is due to the fact that very large volumes of fluid must be processed to get usable loadings on reasonable quantities of resin. For example, if 1 L of resin is desired for testing, and has an expected capacity of 2 g/L of the product, and if the feed is only 10 mg/L in product, then a minimum of 200 L of feed is necessary, assuming the resin is 100% efficient in removal. For a relatively short 100 cycle test, 20000 L of feed is required, and if five resins are to be tested, a total of 100000 L is needed. For this reason, under low feed concentration conditions, it is almost mandatory to field test when a serious experimental program is started. There is then no question of solution composition changes and there is no problem of preparing large volumes of synthetic feed. Unless the system is automated, however, a large amount of man0196-4321/80/1219-0282$01 .OO/O
power is necessary to conduct field tests (especially if they run around the clock) and the expense of field testing can quickly become prohibitive. To conduct the field tests for this program, therefore, it was decided to build an automated test unit which would operate continuously in the field with minimum attention to provision of supplies on a 1-2 h/day basis. The following was used as a design basis: (a) all plastic or glass construction due to the handling of feed solution (pH -2) and strong acid (3 N sulfuric); (b) columns (5) to have 150 mL WSBV (wet settled bed volume) resin capacity to enable all resin tests to be done and be glass for easy visual check; also to be removable by valve isolation for easy change out; (c) cycle to consist of load, backwash, strip, load using field solution, tap water, and 3 N H2S04,respectively; (d) unit to be designed for outside operation and all electricals to be protected from corrosive atmospheres. Figure 1 shows the flow schematic for the resin test apparatus. Solution is supplied by a positive displacement, variable speed pump which feeds a common header to the five columns. Flow is balanced by rotameters. Backwash and elution flows are provided by peristaltic type pumps with five channel heads each to ensure positive, controlled flow to each column. Flow switching is provided by a combination of solenoid valves and check valves. Rotameters act as a check on backwash and eluant flows. Feed was set at 1gpm/column, feed pressure was 10 psig, feed solution temperature was nearly constant at 15 "C with a pH of 2 and the resins were cycled at six cycles per day for a total of 50 cycles. A final rinse of 30 min with tap water was done before tests were started. The stability of the resins was then determined by measuring sphericity and percent whole perfect beads, as described in part 1 of this series. Resin Identification. All materials are classified as strong base anion-exchange gel type styrene-divinylbenzene resins except where noted: resin A, 16-20 mesh, batch no. 1, 2, and 3; resin B, 16-30 mesh, batch no. 1 and 2; resin C, 16-20 mesh, batch no. 1; resin D, 20-50 mesh batch no. 1,pyridinium based resin; resin E 16-40 mesh
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0 1980 American Chemical Society
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 2: 1980 I
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ELUANT F€€ S 7 0 W G . F Tc*
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Figure 1. Resin test apparatus. Table I. 50 Cycle Field Test Data on Ion-Exchange Resins” resin A resin A resin A batch 2 batch 1 batch 3
resin B resin B batch 2 batch 1 resin C
resin G
resin E
resin F
resin D
sphericity
(91) 34, 3 1
(99) 17,14
(95) 58,43
(89) 12, 73
(99) 96, 96
(93) 14,11
(93) 92, 93
(82) 80, 77
(98) 94, 95
(99) 88, 83
% perfect beads
(94) 96, 90
(99) 99, 93
(99) 99, 95
(94) 96, 92
(100) 99, 99
(94) 87, 94
(99) 99, 99
(94) 99, 98
(99) 99,99
(99) 95, 90
(86) 33, 28
(98) 76,68
(95) 58,40
(84)
70,67
(99) 95, 96
(88) 12, 10
(92) 92, 92
(78) 78, 76
(97) 94, 95
(99) 84, 75
% sphericity retained
34
77
54
81
96
13
100
95
96
86
% whole perfect beads
35
73
52
81
96
12
100
98
91
80
% w h o l e p e r f e c t beads
retained a Note: Numbers in parentheses are the values o n t h e “as-received” resins before testing. All other numbers are the results of duplicate tests.
batch no. 2, macroporous resin; resin F, 16-50 mesh batch no. 3; resin G, 16-35 mesh, batch no. 1. Bead Attrition. Resin stability was measured by the procedures outlined in part 1 of this series. Measurement of Residual Bead Strength. After the resins were analyzed by the procedures described in the preceding section, the remaining spheres minus the fragments were subjected to an additional laboratory osmotic shock test to test the residual strength of the resin. This test consisted of rehydrating the spheres in deionized water and cycling the resin alternatively in hot H,S04 and cold deionized H 2 0 as described in part 1.
Discussion Field Test Apparatus. The resin test apparatus in the field ran smoothly. No pressure drop was noted in any of the columns. No differences were noted in any of the columns that could be attributable to the resins in affecting the load, wash, or elute cycles. No fines were found in the
filter, which indicated that all of the fragments remained in each of the columns. No plugging of the resin columns was observed. Resin E did float to the top of the column and a portion of it was lost on backwash. None of the other resins exhibited this behavior. Resin Analysis. When the resins were received from the field, they were converted to the chloride form by treatment with excess sodium chloride solution (10%) and then washed thoroughly with deionized water. After washing, the resins were allowed to settle in their respective beakers. Some of these resins packed more densely than others. All of the resins were much darker in appearance compared to the original color of the resins before the field test. Duplicate tests were performed on each resin. The results are shown in Table I and illustrated in the bar graph in Figure 2. In general, the deterioration of the ion-exchange bead proceeds by a fragmentation process. This is substantiated by the rather low values for sphericity
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 2, 1980
Table 11. Comparison of Accelerated Laboratory Osmotic Shock Test Data with Corresponding Field Test Data. Resin A % whole perfect
beads retained" batch no.
lab test
2 3 1 a After 50 cycles. and H20a t 1 0 "C.
field test
89 93 97
35 54 73
Cycled between H,SO, a t 85 "C
Figure 2. Ion-exchange resin stability under field conditions using copper leach solutions.
Table 111. Comparison of Accelerated Laboratory Osmotic Shock Test Data with Corresponding Field Test Data. Resin A % sphericity retained"
batch no.
lab test
3 2 1 a After 50 cycles. and II,O a t 1 0 "C.
fie1d test
96 97 99
34 54 77
Cycled between H,SO, a t 85 "C
compared to the values for percent perfect beads. This latter quantity gives one a measure of the cracked whole beads remaining after the fragments have been separated from the spheres. Not all of the resins fragment to the same degree. In terms of sphericity, the resins fragment in the following order: resin C > resin A batch 2 > resin A batch 3 > resin B batch 2 > resin A batch 1 > resin E > resin D > resin G > resin F > resin B batch 1. After separation of the fragments, essentially all of the resins have about the same number of cracked beads (percent perfect beads), although there are some differences. The overall deterioration of the resin is reflected in the value of the percent whole perfect beads. This value predicts the same order of deterioration as the sphericity values predicted; however, the magnitude of the percent whole perfect beads is slightly greater. In terms of the total amount of resin attrition, the percent property retained is a useful indicator. Severe attrition has occurred with some of the resins. The order of decreasing attrition is resin C > resin A batch 2 > resin A batch 3 > resin A batch 1 > resin B batch 2 and resin D > resin B batch 1 > resin F > resin E > resin G. Comparison of Laboratory Test with Field Test Data. It should be made clear that there are two laboratory tests. One of these tests alternately cycles the resin between hot 20% H2S04at 6G63 "C and deionized water at 1G12 " C . This test is run for only 10 cycles and is used to differentiate between strong and weak batches of resin by measuring the percent whole perfect bead content before and after test. A value of >go% defines a weak resin
and a value >go% a strong resin. The other test is designed to measure the long term stability of the ion-exchange beads under accelerated conditions of temperature. In this test the resin is cycled between hot acid and cold deionized water for hundreds of cycles at three acid temperatures (60-63,72-75,85-87 "C). The water temperature is 10-12 " C . The results of this latter test were compared to those of the field test. More specifically, the data obtained on resin deterioration at 85-87 " C in the laboratory will be compared to the field test data. Only three batches of resin were run under the accelerated laboratory test conditions because of the time involved and because these beads represent different batches of the same ionexchange resin and also represent different degrees of strong and weak resins. In Table 11, a comparison of the resin deterioration data between the laboratory cycling test at 85-87 " C and the field test is presented. It is evident that resin deterioration is more severe in the field test. Although the magnitude of deterioration is greater in the field test, the direction of resin degradation between the laboratory and field test is the same. It appears that our initial classification to define their resistance of osmotic shock is verified by this data. In terms of percent difference in whole perfect beads between the laboratory test and field test data for a given resin, we have the following: for resin A batch 2,6070, for resin A batch 3,4170, and for resin A batch 1, 24% (calculated from Table 11). In examining the remainder of the resins in Table I, we see that all of them except resin C have superior resistance to deterioration than the three just examined. In Table I11 is presented a comparison of resin deterioration in terms of sphericity for the laboratory test and the field test. Here again the field test is more severe and, under these conditions, the resin beads undergo considerably greater fragmentation compared to the laboratory test. Some of these resins have an initial whole perfect bead content of
