Journal of Radioanalytical Chemistry, Vol. 58 (1980) 215-220

P R E P A R A T I O N O F Z I R C O N I U M P H O S P H A T E ON S U P P O R T M A T E R I A L A N D ITS A P P L I C A T I O N F O R T H E S O R P T I O N O F SOME R A D I O I O N S L. G. NAGY, G. TOROK, N. VAJDA, I.'GERLEI

Technical University of Budapest, Department of Applied Chemistry, Budapest (Hungary) (Received March 15, 1980) Several sorbents were prepared by precipitating zirconium phosphate on activated carbon support material. The main parameters of the chemical procedure were optimized in order to obtain the highest decontamination factors which can be achieved in the case of Cs§ St 2" and F ions. For the characterization of the sorbents, sorption isotherms and capacity data were determined. The reproducibility of the preparation is about 10%.

Introduction The application of inorganic sorbents has become a standard technique in radiochemical and radioanalytical procedures because of their high resistance to radiation and the extremely high decontamination factors which can be achieved, Zirconium phosphate is one of the most carefully studied sorbents. Several samples of this material with amorphous structure were prepared in our laboratory. These products were used for the retention of Cs+, Sr 2+ and I- ions in aqueous media. ~ To avoid the main drawback of these materials - the high flow resistance owing to the poor mechanical properties - and to make advantage of the fact that sorption is a surface reaction, investigations were carried out to prepare a sorbent on an appropriate support. Design of experiments Various types of activated carbon were selected as support materials, and the sorbents were synthesized by the "standard" procedure, the basic steps of which are given as follows. Activated carbon was treated with phosphoric acid, zirconyl chloride was added; zirconium phosphate precipitate formed on the surface of the support material; it was washed, centrifuged and dried. J. Radioanal. Chem. 58 (1980)

215

L. G. NAGY et al.: PREPARATION OF ZIRCONIUM PHOSPHATE Contrary to the self-consisting (support-free) material, the sorption properties of the products thus obtained varied within several orders of magnitude. Because of this reason, we had to determine which parameters of the chemical preparation influence the sorption properties and following this they were to be optimized. The effect of the following parameters was investigated: - type of support material, - quantity ratio, - rate of precipitation; - washing conditions of the raw product, - drying temperature and time. Because of the li~nited time and space, only some of the optimization steps will be discussed here in more detail, in order to illustrate the way which led to an appropriate sorption material.

Experiments

The sorption propeties were determined by means of elution and frontal chromatography using a tracer technique. The gamma-radiation of S SSr, 137Cs and 1311 was measured by a two-channel analyzer equipped with a scintillation detector. In elution chromatography, the column loading was in the range of 25-100/zg ion/g sorbent, distilled water was used as eluent. In the case of frontal chromatography the concentration of the inactive carrier was about 50-300/~g ion/cm 3 solution. The weight of the sorbent was always 2.00 g. The flow rate was 1.0-1.5 cm3/min. The differential and the integral elution curves as well as the break-through curves were calculated. Plotting the numerical values of the asymptotes of the integral elution curves against the column loading, sorption isotherms were obtained.

Results

and

discussion

For the preparation of an effective sorbent on a support, two requirements should be fulfiUed: stable chemical or/and physical bonds should be formed between the support and zirconium phosphate, and more or less stable chemical bonds should be formed between the sorbing ions and the sorbent. According to these principles, the addition of phosphoric acid in excess was assumed to favour ,the sorption of cations by the formation of chemisorptive bonds. Fixing the amount of activated carbon and zirconyl chloride, the amount o f phos216

d. Radioanal. Chem. 58 (19801

L. G. NAGY et aL: PREPARATION OF ZIRCONIUM PHOSPHATE

o

2

0.4--

Phosphorus to Zirconium rolio x 25.5 t~ 12.7 6.3 v 2.5 9 1.7 o 0.6

0.2!~.~~x 0 20 "40

I I ~,1. I I ; ' ~ 60 80 100 120 140 160 180 Column Looding ~Pg Sr2"/g sorbent

Fig. 1. Effect of the ratio of the reagents on the sorption properties

phoric acid was varied in a wide range, lne results are demonstrated in Fig. 1. The optimum of the phosphorous to zirconium ratio was at about 6. Numerous data have been reported 2'3 about the relationship between the sorption properties and the structure of zirconium phosphates; all of them agree in the fact that the more amorphous the sorbent is, the higher sorption capacities it has. Naturally this is not true for reversible ion exchange processes. To prepare samples of amorphous structure, the rate of precipitation should be increased, and concentrated reagents should be used. As the precipitate thus obtained is rather thick, it is impossible to mix it in standard equipment. Even shakers are inadequate to some extent. To solve this problem, a simple process was elabotared by drying phosphoric acid on activated carbon prior to the precipitation reaction. Drying can be accomplished below the sublimation temperature of P2Os, i.e. 300 ~ The effect of the reaction rate on the sorption properties of the product can be seen in Fig. 2. In the case of drying phosphoric acid on carbon even the reproducibility was improved. Washing conditions influence the sorption properties significantly. Insufficiently washed products contain colloidal fractions disturbing the sorption processes. By the analysis of the washing fractions, it can be established that about five times more phosphoric acid is removed by the first two fractions than by the third one. On the contrary, the third washing liquor contains about fifteen times more zirconium than the first two fractions. (The amount of distilled water used -

-

J. Radioanal. Chem. 58 (1980)

217

L. G. NAGY et al.: PREPARATION OF ZIRCONIUM PHOSPHATE

l

.~coo.,;~ -5"~k~ 0,2

0 20

40

60 80 1 0 0 I Z O t 4 0 160 180 Column Ioocling 1 pcJ Sr2"lg sorbent

Fig. 2. Effect of the rate of precipitation on the sorptton properties. Way of reagent addition: o - slow (over 1 hour), D - rapid (intensive mixing in a mixe~), • - rapid (intensive mixing in a shaker), 9 - rapid (after drying phosphoric acid on carbon), 9 - rapid (after drying phosphoric acid on carbon)

co O,E

0z

~. 0.2

i

20

40

60

, -T,

,

,

,

,

,

9

,

.

80 100 120 140 160 IBO 200 Column looding ~ ,ug Sr2"1g sorbenl

Fig. 3. Effect of washing on the sorption properties: 9 - twice, o - three times

tbr each wastUng was three times more than the amount of the sorbent.) According to elution chromatographic measurements, the raw products must be washed three times. The results are demonstrated in Fig. 3. It is well k n o w n from the literature that the properties of inorganic sorbents are very sensitive to heat treatment. By elution chromatographic and thermogravimetric measurements, the drying temperature could be optimized at a fairly high level, at 180 ~ The results are shown in Fig. 4. It is worth noting that the sorption properties are improved by increasing the temperature. 218

Z Radioanal. Chem. 58 {1980)

L. G. N A G Y e t al.: P R E P A R A T I O N

OF ZIRCONIUM

PHOSPHATE

t o

22 lo8 ~ eJ

0.6

0.2

Or-, t--, i , [ L:I , I , I , I . I , I ~

20 40 60 80 100 120140160 180 Column Io(3dincj 1 p g Sr2"/cj sorbent

Fig. 4. Effect of heat treatment in the sorption properties. Drying temperature and time: X 90 ~

5 h r s , [] -

90 ~

9 hrs, o -

1 5 0 ~C, 4 h r s , 9 -

180 ~

4 hrs

Table 1 Retention capacity data o f zirconium phosphate on activated carbon and of activated c a r b o n

Element

Zirconium phosphate on activated carbon

Activated carbon

Capacity, mg ion/g

Capacity. mg ion/g

At 95%

At 99%

At 95%

At 99%

retention

retention

retention

retention

14.4

9.6

1.5

1.0

S [ 2+

2.9

2.1

0.1

0.1

I-

4.t

t.3

3.0

1.4

Cs +

Summing up the optimizing steps, the following procedure can be suggested for the preparation of zirconium phosphate on activated carbon. The suitably chosen activated carbon is treated with phosphoric acid and is dried below 300 ~ A fast precipitation is carried out by adding zirconyl chloride previously dissolved in dilute hydrochloric acid. The product is washed three times, centrifuged and dried at 108 ~ until constant weight. The sorption capacities of zirconium phosphate on activated carbon compared with the values of untreated activated carbon were determined by the frontal chromatographic method. The results are summarized in Table I. Beside the relaJ. Radioanal. Chem. 58 (1980)

219

L. G. NAGY et al.: PREPARATION OF ZIRCONIUMPHOSPHATE

tively high value

of Cs* retention on the sorbent, the significant I- retention of the activated carbon can be emphasized. The reproducibility of the formation of zirconium phosphate on activated carbon was determined by measuring the Cs§ retention capacities of five parallel sorbents. A reproducibility of about 10% was achieved.

References 1. Hungarianpatent No: 11878/77. 2. C. B. AMPHLET!r, InorganicIon-Exchangers,Elsevier, London, 1964. 3. V. VESELY,V. PEKAREK,Talanta, 19 (1972) 219.

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