elemental analysis of selected indian monazite ores by energy dispersive x-ray fluorescence /edxrf/...
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J.RADIOANAL.NUCL.CHEM.,LETTERS 137 /2/ 127-133 /1989/
ELEMENTAL ANALYSIS OF SELECTED INDIAN MONAZITE ORES By ENERGY DISPERSIVE X-RAY FLUORESCENCE [EDXRF]
SPECTROSCOPY
.x Madan Lal, R.K. Choudhury, D. Joseph, H.N. "Bajpal ,
C.S.P. Iyer x
Nuclear Physics Division /BARC/ Bombay - 400 085, India
XAnalytical Chemistry Division /BARC/ Bhabha Atomic Research Centre,
Bombay - 400 085, India
Received 8 May 1989 Accepted 14 June 1989
Analysis by Energy Dispersive X-ray Fluores- cence spectroscopy of monazite ores from Ke- rala /Chavara and Manavalakurichi/, Orissa /Chattrapur/ and Tamil Nadu [Tirunelveli/ has been carried out for the determination of their elemental composition using IO9cd /annular] and 2~iAm /disc/ radioisotope sources. The elements Y, Zr, Mo, Pb, Th and U were analyzed using a iO9Cd source, and the elements La, Ce, Pr, Nd, Sm, Gd and Dy were analyzed using the 241Am source in side source geometry. Quantitative results on these 13 elements present in these ores were obtained by the EDXRF technique. It was seen that despite the diverse geological settings, there is remarkable similarity in the ele- mental composition of these ores, although some trace elements do show certain variations from sample to sample. These results are pre- sented and discussed in this paper.
!27 Elsevier Sequoia $. A., Lausanne A k ad grniai K iad 6, Budapest
MADAN LAL et al.: ANALYSIS OF INDIAN MONAZITE ORES BY EDXRF
INTRODUCTION
Analysis of rare earth elements /57 _<~ Z _< 69/ has been 1-6
carried out using EDXRF spectroscopy and other tech-
niques 7-12 Earlier we have reported 5'6 that better sen-
sitivity and accuracy of analysis in this region can be
achieved by employing K X-rays of these elements excited
by a disc source of 241Am in the side source geometry.
Since the analysis of monazite ores has many useful
applications in mineral and geological sciences, we have
carried out the analysis of the elements present in these
ores by EDXRF technique. Rare earth elements /La, Ce, Pg,
Nd, Sm, Gd, Dy/ were analyzed using their K X-rays ex-
cited with a disc source of 241Am in side source geo-
metry. Other elements such as Y, Zr, Mo, Pb, Th and U
present in the ores were analyzed with a 109Cd source
using both K- and L X-ray excitationS. The monazite ore
samples were collected from different regions of India,
namely Chavara and Manavalakurichi of Kerala, Chhatrapur
of Orissa and Tirunelveli of Tamil Nadu. The experimental
method and data analysis are given below, followed by the
results and discussion of the present work.
EXPERIMENTAL METHOD AND DATA ANALYSIS
The experimental set-up consists of a Si/Li/ detector
coupled to radioisotope sources to excite the character-
istic X-rays /K and L/ of the elements present in the
samples. The energy resolution of the Si/Li/ detector is
170 eV for 5.9 keV Mn K X-rays. The samples were first
ground and sieved to a mesh size of 350 and then mixed
and homogenized with cellulose which acts as a binder
material and provides a low Z matrix of the samples. The
amount of cellulose in the mixture is kept to the level
128
MADAN LAL et al.: ANALYSIS OF INDIAN MONAZITE ORES BY EDXRF
of 75 to 85% by weight. This is done to obtain a thin
sample by making a pellet of uniform thikness under 15.0
t/sq. inch pressure. The advantage of making these pel-
lets is that the inter-element enhancement effects in
the sample are minimized 13 and one can also determine
the mass-absorption coefficient by transmission method.
These pellets of 3.0 cm in diameter weigh about 500 mg
each. For calculation of geometrical factor for quanti-
tative analysis, one standard for each excitation source
was employed, the first containing Pr /2187 ppm/ and Sm
/3675 ppm/ and the second containing Y /302 ppm/ in cel-
lulose matrix of the same diameter /3 cm/ and weighing
aboug 500 mg.
The samples and standards were mounted in optimum add
identical geometry fo9 excitation of the characteristic
X-rays. The spectrum was stored in a multichannel analy-
zer for a counting time of 2000 sec for each sample. In
a separate experiment, the mass-absorption coefficients
for each sample were determined by measuring the trans-
mission of X-rays of a number of source energies simul-
taneously. The intensity of X-rays with and without the
sample are measured tO obtain the absorption factors for
each sample at these energies. The absorption correction
for X-ray line of each element present in the sample is
obtained by interpolation of the measured mass-absorption
coefficients as obtained by theabove method. The method
of interpolation is justified 13 since the matrix is di-
luted with the cellulose material and the sample thick-
ness fs kept small.
Figures 1 and 2 show the typical X2ray spectra of
Chavara monazite excited with 109Cd and 241Am sources,
respectively. The X-ray lines corresponding to each p~ak
is indicated in the figures since there are a large num-
129
MADAN LAL et al.: ANALYSIS OF INDIAN MONAZiTE ORES BY EDXRF
u
Z0
15
c
P ,
I0 �9 _j
10.2 12.1 14.0 15.9 17.8 19.7 Energy, keV
Fig. i. X-ray spectrum of Chavara monazite /Kerala/. Exciting source: 109Cd /annular/
~4f~g3c" -.~'~ "
~.. 2 o �9 �9 , . ~ = ~ '~'~
* j
�9 . _ ~o ~
~ ~ ~. �9 II - ~ X ~ �9 ~ "v % O ; " en ~" = Z Z I~ I=
" :" ~: i . 7 / : : ~ ~ , ' : ^ ~. % . - , - , ~
31.( 33.5 35.4 37.3 39.2 41.1 43.0 44.9 46. Energy, keY
Fig. 2. X-ray spectrum of Chavara monazite ore. Ex- citing source /side source geometry/: 241Am
her of elements present in the sample, the X-ray lines
of different elements overlap very strongly in the
spectra�9 In order to obtain the intensities of each X-
130
MADAN LAL et at.: ANALYSIS OF INDIAN MONAZITE ORES BY EDXRF
ray line, the observed spectra were unfolded by using
the intensity ratios of the X-ray lines corresponding to
pure elements excited in the same geometry. These pure
element Samples were prepared in a similar way as the mo-
nazite ore samples. As an example, Zr K line overlaps
strongly with ~he L~ llne. In this case, the Zr K in-
tensity was determined by subtracting the Th L8 inten-
sity as measured with a pure elemental sample ~f Th.
This procedure was adopted for the Other elements also
in the rare earth region. The observed X-ray line inten-
sities after correction for self'absorption in the sample
were converted into the elemental concentrations by em-
ploying the computedexcitation-cum-detection factors.
Table 1 shows the results of the present analysis for
different monazite ores.
RESULTS AND DISCUSSION
It is s~en from Tabie I, that the elemental concentra-
tions in the monazite Ores obtained from different regions
of India show remarkable similarity in case of all the
major constituents. Variation of concentration from the
mean values for the elements La, Ca, Pr, Nd and Sm is
less than i0%~ ~sults of analysis of rare earth elements
for some of these 0res were reported earlier using the
neutron acti~as 7 and these results agree well with the ~e~uits Obtained in the present work. Using EDXRF
techniqUe we have also analyzed the other elements Y, Zr,
Mo, Pb, Th and ~ in addition to rare-earth elements
analyzed7 eariier. Concentration of Pb is also consistent
for all the four Ores analyzed. Thes~ results provide use-
ful data for geochemical studies.
131
M A D A N L A L a t ~1.: A N A L Y S I S O F I N D I A N M O N A Z I T E O R E S B Y E I 3 X R F
O0
0 -,-I
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q.4 q-.i ,r"l ' 0
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I..I -,..t
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+1 +1 +1 +1 +1- +1 +1 +1 +1 +1 +1 + i +1 O~
0 0 ' ~ ,.n e-~ ~ c~ 0 0 0 ~ 0
0 m 0 ~ ~ ,~ o~ ~ ~ 0 0 r~ 0 0 0 0 0 0 0 0 0 0 0 0 0 0
+1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1
o~ ,-I ~ 0 0 co ~D co e-i ,~ ,-~ ,-~
0 0 0 ~ ~ ~ o~ c~ 0 0 0 u~ 0
0 ~ 0 ~ ~ ~ ~ ~ ~ 0 ~ ~ 0 0 0 0 0 0 0 0 0 0 0 0 0 0
+1 + 1 + 1 + i + 1 +1 + 1 +1 + 1 + 1 + 1 + 1 + i
0 ~ 0 ~ M m 0 ~ H 0 0 ~ 0
r,") o4 ~ co ~ L~ 0 "~ 0 ~ ~ ~ ~ .~ ~ 0 0 ~ 0 0 0 0 0 0 0 0 0 0 0 0 0 0
+1 +1 +1 +1 4-I +1 +1 +1 +1 +1 -'l'-I + l + i
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MADAN LAL et al.: ANALYSIS OF INDIAN MONAZITE ORES BY EDXRF
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