The　DeterMination　of　Uranium　in　SeaWater　by　X−ray　FluorescenceSpectrometry　after　Coprecipitation　with

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The DeterMination of Uranium in Sea Water by X−ray Fluorescence

Spectrometry after Coprecipitation with

、4−Caprinoy1−3−Methy1−1−Pheny1−5−Pyrazolone

by Tos｝｝io NAKAI s＊＆Yoshi∫imm

i AKAMAき＊

Summary

A method is described for the determination of uranium dissolved三n sea water atμgl i level． The uranium is coprecipitated with 4−caprinoy！−3−methyl−1−phenyl−5−pyrazolone as precipitant． The precipitate is collected on a membrane創ter for x．ra｝・fluorescence spectro．

metry． The optimum pH range is 2．5−7．5for the maximum recovery of uranium． The llm輌t of detection of uranium is about 5μgZ 1． The procedure has been applied successfully to the determination Of uranium present in sea water at pPb Ie、・cls

I皿troduction

Recently， a growing demand for uranium as nuclear fuel and a increasing fear for the exhaustion of its resouces in the earth crust has stimulated the research on the

recovery of uranium from sea xvater． The uranium content of sea water is usually

at the ppb level， so that its determination requires a preliminary concentration step．

In this paper， a method was examined for the coprecipitation of uranium dissolved

in sea water using 4−caprinoyl−3−methyl−1−phenyl−5−pyrazolone as carrier compound．

The precipitate is collected on a membrane filter and is analyzed by x−ray fluores・

cence（x． r． f．）spectrometry． The x． r． f． spectrometry has been successfully employed

for the direct determination of metals without preliminary digestion of sample．

Luke（1）was the丘rst to report the application of coprecipitation in the analysis by

x．r． f． spectrometry． The coprecipitation method has been reported（2 6）on the collection of uranium using titanium hydroxide， iron−dibenzyldithiocarbamate and

etc． as carrier． In the coprecipitation， however， the solubility and the particle size of the precipitate are very important factors contributing to the quantitative recovery of the uranium． The purpose of this work is to establish rapid， simple and precise

techniques for the determination of uranium in sea water．

4−Caprinoyl−3−methyl−1−phenyl−5−pyrazolone （CMPP）was synthesized accord輌ng

＊理工学部化学科教授分析化学

＊＊理工学部化学科助教授分析化学

（本研究は，理工学研究科博士課程学生，佐藤健二との共同研究である．）

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to the standard method（7）． CMPP is easily prepared by caprinoylation of 3−methyl−

1−phenyl−5−pyrazolone， and is characterized by good chemical stability andエeasollable solubility in organic solvents． It is also known（s 10）that CMPP is very effective

extracting reagent and a number of metals are extracted with high distribution

ratio at relatively low pH．

Experimental

Apparatus and reagents：The x・−ray fluorescence measurements were carried out with a Rigaku−Denki KG−4 type spectrometer． Instrumental conditions are shown in Table 1． The precipitate was collected on a membrane filter（47−mm diameter，

Table l Instrumental conditions

Tube

Analyzing Crystal

・・llim・・er

｛1：：灘，y

Voltage（KV）

Current（rnA）

Path of x−ray

Peak angle （° 2θ）

Background angles（°2θ）

Counting method

w

LiF （200）

0．45mm×10 cm O．15mm×10 cm

42． 5

34

air

26．ユ8 25．5， 27．O

F三xed time method（40 s）

1．0一μmpore size， TM−100 type；Toyo・Roshi Co．）． A Toa electronics HM−5 BS type

pH Ineter was used for pH measurement． A stok standard solution（1000 mgZ−1）of uranium was prepared by dissolving O．3529 g of uranium sulfate（UO2SO4・3H20：

Mitsuwa s pure chemical）in 200 ml of distilled water． All other reagents used in

the work were of analytica1−reagent grade．

Procedure：The uranium standard solution was diluted to 50μgmZ−1 with distilled

water before use． The water sample solution was adlusted to pH 3． O with a small

amount of hydrochloric acid（1十1）and ammollium hydroxide（1十10）solution， to which l ml of 0．5％（W／V）CMPP−acetone solution was added and then the mixture was permitted to stand for 2 hours at ordinary temperature l〕efore collecting the precipitate oll a membrane丘lter． The precipitate on the五lter was air・dried before x−ray measurelnents． The angle for x−ray measurement was made of ULα（26．18°

2θ）and background were measured at the angles of 25．5°and 27．0°， respectively．

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0 tフ O LA

り乙ユー

（ o s

v／o︐o﹇× ︶﹀ J．IsZI．LNI

J n

n

ユ 2 3 4 5 6 7 8 9 pH

F輌g．1 Effect of pH on the coprecipitation of uranlum with CMPP：amount of uranium：50μg；added volume of O．5％（W／V）CMPP・acetone solution：1mZ；final volume of solution ：200 ml

Results and Discussion

Ef［ect of pH：The effect of pH on the coprecipitation of uranium with CMPP was studied． The results obtained are shown in Fig．1． The optimum pHエange for constant and maximum intensity of the ULαline was found to be 2．5−7．5． Hence，

in this experiment， pH 3． O was chosen for the coprecipitation of uranium．

Effect of concentration of CMPP：The effect of the concentratioll of CMPP in the acetone solution on the precipitation of the uranium was examined（Fig．2）．

It was found that l ml of 0．2％（W／V）CMPP・acetone solution is su｛五cient for the

quantitative coprecipitation of 50μg of uranium． Alarge excess had no adverse effect， and l ml of O．5％（W／V）reagent solution is recommended．

（

_の

o

v

！

Oc01X︶﹀．LtSNULNl Pln

20

ユ5

ユ0

5

0．1

0，2 0．3

^0．4 ^0．5 ^0，6 CONCEN丁RATION ／％（W／V）

Fig．2 Effect of varing the concentration of CMPP in acetone on the coprecipitation of uranium：

amo皿t of uranium：50μg；added volume of

each CMPP・acetone solution：1mZ；final

volume of solution：200 mZ， where pH was

3．0．

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Calibration curve， precision and detection limit：The x−ray intensities（x 103 counts ULα／40 s）of the ULα1ine were linearly related to the amo皿t of uranium over the range O−250μgZ エ． The coef五cients of variation were 15％and 1．6％for the 10μg and 50μg of uranium， respectively． The detection limit was ca．5μgZ−1

for a counting time of 40 seconds．

Determination of uranium in sea water samples：The applicability of the copre−

cipitation x． r． f． method to the determination of uranium in sea water was examined

by analyzing 31iters sea water samples． However， in the present method some

prol〕lems still remain． One is the influence of sample volume for determination of

uranium． Another problem is the influence of various ions（e． g． Na÷， Mg2＋and

Ca2＋）in sea water． Therefore， artifical sea water standard11）， was used to eliminate

there effects． Aliquots（3のof the sample and arti丘cal sea water were placed in beaker and 50μg of uranium was added to each beaker． The separation of uranium一

Table 2 Analvtical results

り

No． Ufound（μgl≡i） Average（μgl−！）

123

^3．3

4．3 2．6

3．4

CMpP complex was carried out as l〕efore． The sea water sample was taken at Ito in

Izu peninsula， Shizuoka Prefecture． From the comparison of the x−Fay intensity of ULαline for uranium in sea water sample with artifical sea water， it was found

that 3．4μgZ一工of uranium is present in sea water． The analytical results obtained by the method using x． r． f． spetrometry are given in Table 2．

These results indicate that the proposed method is satisfactory． The use of CMPP

as a coprecipitant for the uranium in sea water appears to be quite promising and

could be applied to other elements．

References

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The DeterMination of Uranium in SeaWater by X−ray FluorescenceSpectrometry after Coprecipitation with