Joseph F. Mucci, Charlotte Hollister and Louise R. Marshall
Ion Exchange on a Natural Clay Mineral
Vorsar College Poughkeepsie, New York
A demonstration experiment
This demonstration experiment illustrates the exchange properties of the natural clay mineral montmorillonite as well as vividly displaying the relative ease of replacing cesium by cobalt and cobalt by cesium while using this exchanger. The methods developed by Thomas, et al.1-4have been used and the quantitative aspects of the process have been followed by use of radioactive '"Cs and T o . We use Cs+ and Go+¶ when referring to radioactive cesium and cobalt respectively. A small column (approximately 5 in. long and 1.25in. id) containing 2 g of montmorillonitc clay (from Chambers, Arizona, American Petroleum Institute Reference Clay Mineral No. 23--a portion of that used by Gaines and ThomasJ) mixed with asbestos in the manner described by Thomas, et a1.l-4 was used. The influents were introduced into the column by siphon action and the ratc of flow is regulated with a Hoffman clamp (see footnote 5 for setup). The column is not allowed to go dry during the entire experiment. 'FnUCHER. JOSEPH A,, SOUTH WORT^^, RAYMOND W., AND TAOMAS, HENRY C., J . C h m . Phys., 20, 157 (1952). 'FaUoHER, JOSEPH A., AND THOMAS, HENRY C., J . C h m . Phys., 22, 258 (1954). 3 GAINES,GEORGE L., AND THOMAS, HENRY C.. J. C h m . Phys., 23, 2322 (1955). ' FRYSINGER, GALENR., AND THOMAS, HENRY C.. J . Phys. C h m . , 64, 224 (1960). %m1, J. F., SPIEGEL, DOROTHY E., AND STEARNS, ROBERT L., J. CAEM.E I ~ c .38, , 348 (1961).
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Journal of Chemical Education
A 0.020 N aqueous solution of CsCI, "spiked" with enough "'Cs (half life -30 years) to give approximately 100 counts/sec, is allowed to flow through the column at the ratc of 1 ml/3 min. Fractions of the effluent are collected in previously dried and weighed test tubes by use of a sample collector (Model 1205, Automatic Fraction Collector, Research Specialties Co., Richmond, California). The volume of each fraction is determined by weighing and assuming that the density of the effluentis 1.00 g/ml. A 6-ml aliquot of each sample is then pipettcd into the receiving cup of a dip counter (Radiation Counter Laboratories, Inc., Model 10301). The geometry of the counting system is kept constant by housing the receiving cup and counter in a machined metal holder. A Baird-Atomic Model 123 GM Scaler is used for the counting measurements, and a 2-in. thickness of lead is used to shield the counter. If A is the number of counts/sec from each sample of effluent and A. is the number of counts/scc from the influent, a plot of A/Ao versus the efflucnt volume (midpoint of each sample) can be made as shown in Figure 1. A and A. are, of course, directly proportional to the concentrations of the efflucntand influent respectively. The area above the curve in the A/Ao versus volume plot determines the total exchange capacity of the ion exchange column (number of meq per column). When the column was saturated with cesium, water was introduced into the column to wash the excess
.
Cs+CI- from the column. At this point a 0.020 N cobalt chloride (not radioactive) solution was allowed to run through the column. The cobalt is present as C O ( H ~ O ) ~ +we ~ ; will refer to it simply as C O + ~ . Samples of the effluent were collected and counted
effluent was checked for radioactive Co. The normality of Co (i.e., A/Ao X 0.020) being displaced by Cs+
Figure 3.
Graph for the reaction: Cot4
Figure 1. Adsorption of 0.020 N &I radioactive Cst.)
on natural montmorillonite.
(Cs
-
for radioactive cesium. Figure 2 is a plot of the normality of cesium (i.e., A/Ao X 0.020) coming off the column versus the effluent volume (midpoint of each sample). Note the "long tail" exhibited by the curve. The exchange reaction
+ Cor)-Monl. (to*
--t
Cot4-Mont.
= Radioactive Cot4.)
vcrsus the effluent volume is plotted in Figure 4. The number of meq of Co displaced was 2.01. Enough counts were taken t o give about 0.5% counting statistics; background and resolving time corrections were made throughout. I n summary, the use of a clay mineral rn an exchanger has been demonstrated and the reaction Co+a + C s ~ M o n t+ . Co-Mont.
does not, therefore, take place readily. The exchange capacity (from Fig. 1) of the column is 1.95 meq. The number of meq of Csf displaced by Co+= (aq shown in Fig. 2) is 1.90. This is well within the experimental error for this type of column work. Next, a 0.020 N CoClg solution (spiked with *Co, half life 5.3 yrs, to give about 100 counts/sec) was * allowed to flow through the column. A/Ao for Co+= was plotted against effluent volume (midpoint of each
Figwe 2.
Graph for the reaction: CO*
+ Co*
+ ZCs+
(Figure 2)
is seen to be much more dfficult to carry out than 2Cs+ + Co-Mont. + CspMont. + Co+= (Figure 4)
I n addition, some important quantitative aspects of the system have also been pointed out. Parallel studies could be carried out using other ions as well as employing ion exchange resins. Elaboration of this technique to other systems and various aspects of exchange processes involving clay minerals have been discussed in detail by Thomas,
-
+ & , + - ~ ~ ~ t . Cot4-Mont. + 2 i r i
sample) as shown in Figure 3. The "hold-up" volu ~ c ' -is~not shown in the figure but must be taken into account when rechecking the exchange capacity of the column a t this point in the process. This is not the case in Figure 1 since we started with a dry column. When the column was saturated with radioactive cobalt, the excess cobalt chloride was washed off with distilled water. At this point, 0.020 N CsCl solution (not radioactive) was introduced into the column and the
Figure 4.
Graph for the reaction:
The authors wish to express their appreciation for financial aid received through an Undergraduate Research Trainmg Program Grant awarded by the National Science Foundation. Volume 41, Number 1 1 , November 1964
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