EXTRACTION AND ESTIMATION OF THORIUM (IV) IN THE ENVIRONMENTAL SAMPLES

A dissertation submitted as a partial fulfillment of the requirements for the Degree

of Master of Science in Chemistry Tribhuvan University, Kirtipur, Kathmandu, NEPAL

By RAMJEE KANDEL

Central Department of Chemistry Institute of Science and Technology

Tribhuvan University Kirtipur, Kathmandu, NEPAL.

2006

ACKNOWLEDGEMENT

I would like to proffer my esteem gratitude to my research supervisor, Dr. kamal K. Shrestha, Assoc. Professor and co-supervisor Dr. Sabita Shrestha, Lecturer, Central Department of Chemistry for their painstaking effort and encouragement to bring this research work to a successful conclusion. My sincere thank goes to Prof. Dr Raja Ram Pradhananga, Head, Central Department of Chemistry and Research committee of this Department for necessary guidelines and facilities during my research work. I am equally dept to Mr. Krishna Mani Bhandary, Chief, Central Library, Tribhuvan University, to Superintendent Geologist Krishna Kafle, The Department of Mines and Geology, Lainchaur and to Mr. Buddha Ram Shah, NAST for their co-operation and advice. Lastly, I would like to express heartfelt thanks to my beloved colleagues Mr. Bishnu Bastakoti, Binaya, Daya Nidhi, Homnath and Tara for their help during this research work.

Ramjee Kandel

ABSTRACT Spectrophotometric method for the determination of thorium (IV) in the environmental samples are investigated. This method, based on arsenazo III as the complexing agent in acidic medium is found to be sensitive in the range of 0.02- 0.8 μg Th/ml at λmax 660nm. The molar absorptivity is 11.59×104 Lmole-1 cm-1. The convenient process for the extraction of thorium is the liquid – liquid extraction. Thorium is extracted into Isobutyl Methyl Ketone (IBMK) from aluminium nitrate at the pH 0.8-0.9, in the presence of hexadecayltrimethylammonium bromide (CTAB). Benzene is used to bring the thorium in the aqueous phase as a result of which the extraction percentage is increased. This method is used to determine the amount of water soluble thorium ions in the water, sand and soil.

1

1.0 INTRODUCTION

1.1 General Introduction

Human beings have direct and inevitable relation with water. We depend

on different sources of water such as underground water, surface water as

well as rain water. The presence of dissolved radioactive substances like

thorium in drinking water prevails in minute quantities from continuous

weathering of such minerals which is present naturally in the

environment. Thorium was discovered in 1829 by Berzelius in a mineral,

now known as thorite. Natural thorium consists of two long lived

radioactive isotopes namely, 232Th (~100%) t1/2 = 1.405×1010y and trace

amounts of its descendant 228Th with t1/2 = 1.913y of atomic weight

232.08 (Haissinsky and Adloff, 1965).The decay of 232Th leads to 238Th

as follows –

With the discovery of U233 and its slow-neutron fission properties, a new

stimulus has been given to the detailed study of the thorium chemistry

(Katzin, 1955). It is used in atomic energy program. Because of its low

work function and high emissivity for electrons, thorium is used in a

number of gaseous discharge lamps. This metal has been continuously

used to generate strong monochromatic X-ray (Hampel, 1968)

1.2 Natural Occurance

Thorium makes up to about 0.0015 percentage of the earths’ crust. A

large number of minerals in association with the rare earths and uranium

(Hampel, 1968) makes this in outer crust contain about 12 grams per ton.

232Th 228Ra 228Ac 228Th α β- β-

2

Thorium is less abundant than lead but about three times as abundant as

uranium (Frondel, 1956) in contrast, the concentration of thorium in seas

and oceans are nearly a thousand times smaller than that of uranium

(Haissinsky and Adloff, 1965). Deposits of monazite containing sands

occur mainly in countries like India, Brazil, Australia, Malagasy, Ceylon,

South-Africa, the U.S. and Canada. Although the sands that extend along

the seacoast of Travoncore in India contain less than one percentage

monazite, this is considered as the worlds’ most important source of

thorium (Hampel, 1968). The concentration of thorium is 2×10-8g/l in

rivers and 4×10-5 percentage in stony meteorites and its cosmic

abundance is 0.02 atoms per 106 atoms of Si (Haissinsky and Adloff,

1965)

1.3 Mineralogy of thorium

Currently about 100 mineral species that contain various amount of

thorium are reported. The most important minerals are monazite,

thorianite, thorite and thorogummite. Other minerals that contain

significant amount of thorium are allanite, bastnaesite, xenotime,

fluorapatite and zircon. The uranium content in thorianite and

bastnaesite is less while thorite contains up to 10.1% and in

thorogummite up to 31.4% of uranium (Twenhofel and Buck, 1956).

Monazite is the principal ore of thorium (Twenhofel and Buck,

1956) with commercial concentration. The thorium content of this

mineral is about in 8-10 percentage. In some of the rare earth with

silicates, such as, orthite and gadolinite, the thorium concentration is

of the order of 1 percent. On the other hand, in the ninobates and

titanoniobates of rare earths in which thorium is concentrated up to 25

3

percent. Some of the important ores of thorium is given in Table 1.1

below:

Table 1.1. : Thorium Content in Different Ores -

Ores Composition Th content (%)

Monazite (Ce, Y, La, Th) (PO4) ~ 10

Cheralite (Th, Ca, Ce) (PO4, SiO2) ~ 30

Thorite ThSiO4 ~ 80

Thorianite ThO2 ~ 90

Pilbarite ThO2.UO3.PbO.2SiO2.4H2O ~ 30

Source: Encyclopedia of Geochemistry and Environmental Science

(Fairbridge, 1972).

1.4 Thorium Deposits

No known thorium deposits comparable in grade and size of the uranium

deposits are known. Thorium is relatively insoluble and it occurs with

highly refractory minerals. No deposits of supergene origin are reported

(Twenhofel and Buck, 1956). The main types of deposits that carry

concentrations of thorium minerals are pegmatites, hydrothermal veins

and detrital deposits. Pegmatites associated with alkali igneous rocks are

rich in thorium with minor concentrations of Zr, Nb, Ca, P, Ta and U.

Apatite is a characteristic accessory minerals in pegmatites. Pegmatites

derived from granitic rocks differ from alkali rocks in containing small

amount of thorium but enriched in uranium. Thorium occurs as a very

minor constituent in deposits other than veins and pegmatites, such as

with Nb in carbonates (Frondel, 1956). Thorium is concentrated in felsic

igneous rocks during magmatic differentiation. The granitic rocks contain

three to six times as much thorium as do basaltic rocks. Thorium content

4

in most igneous rocks is within 0-25 ppm; up to several 100 ppm has also

been reported. Thorium and uranium seem to be closely associated in

igneous rocks. The thorium-uranium ratio of various rocks throughout the

world is approximately uniform; the ratio ranging from 3-1 up to 0-20

(Twenhofel and Buck, 1956). The concentration of thorium in different

types of rock varies widely as shown in Table 1.2 below:

Table 1.2 : Thorium Deposits

Rocks Concentration (ppm) References

Granite 18.5 Heier et al. (1963)

Basalt 2.7 Heier et al. (1963)

Eclogite 0.18-0.45 Tilton and Reed (1963); Heier (1963)

Shales 12 Adams (1959)

Source: Encyclopedia of Geochemistry and Environmental Science

(Fairbridge, 1972).

In Nepal, exploration of thorium has not been done. However thorium in

basic rocks (Basalt) contain less amount than the acidic rocks (Granite)

are reported. Gneiss rocks from Shivapuri is expected to contain

appreciable amount of thorium. The Siwalik range hills in Kathmandu

Valley in Southern Nepal contains large amount of sand derived from

granite and metamorphic rocks (Aryal, 1994).

Studies in the Southern lap of Shivapuri hills shows high grade

metamorphic rocks like garnet mica schist, kyanite schist, gneiss, granite

gneiss in the north and some quartzite, dolomite, limestone and phyllite in

the South. Some of the pegmatite bodies of Jagate area in the Northern

Kathmandu Valley consists of autunite (uranium oxide) and uranite. High

radioactive Intensity (RI) values up to 9015 cps total count were reported

5

in which 11 cps was for thorium against background value 200 cps as

total count and 1 cps thorium was recorded (Shrestha, 2004)

1.5 Geochemistry of Thorium

Thorium is not known to occur in elemental form in nature. It occurs

chiefly in combined forms with oxygen and other elements to form

oxides, silicates, phosphates, carbonates and fluorides (Twenhofel and

Buck, 1956); the oxidation states of thorium in these are four. Thorium is

conspicuously concentrated in the lithosphere, particularly in the upper

parts of this geosphere (Rankama and Sharma, 1950). Salts of thorium in

solution or in solid state, thorium dioxide and volatile compounds such

as, thorium acetylacetone all contain thorium in the oxidation state of 4+

(Katzin, 1955). The geochemistry is governed largely by the low

concentration and high valence of the ions mainly four. The activation

energy of migration of ions [E-value] (Wickman, 1943) is relatively high,

which would tend to freeze the ions in the main stage of crystallization of

the magma. The high charge and large size of quadrivalent ions do not

permit entrance of thorium into the normal rock (Frondel, 1956). Thorium

is not rendered more soluble by the change to oxidizing condition.

Because of the change in solubility of uranium and lack of change in

solubility of thorium, the two elements naturally become separated under

hydrothermal and later magmatic conditions (Twenhofel and Buck,

1956).

1.6 Chemistry of Thorium

Even though, thorium exists in solution in small and highly charged

cation, it undergoes extensive interaction with water and many anions.

Thus the solution chemistry of thorium is primarily a study of its complex

6

ions. The complexing agents with thorium are Cl-, NO3-, ClO3

-, BrO3-,

IO3-, HSO4

-, PO43- and F-. Some ions of many organic acids that form

varities of complexes are oxalates, citrates, pthalates, maleates and even

EDTA. All of these are positively charged or cation complexes. In nitric

acid solution of >3M, however, thorium forms an anionic complex. At pH

values greater than three, thorium undergoes hydrolysis in aqueous

solution. The common insoluble compounds used in thorium separation

are the hydroxides, fluorides, chromates, phosphates and oxalates while

the soluble compounds include the chloride, nitrate and sulfate

(Fairbridge, 1972). Thorium forms numerous chelated compounds,

insoluble in water but soluble in organic solvents (Haissinsky and Adloff,

1965).

1.7 Thorium in Weathering Cycle

The original sources of radioactive elements that include thorium in the

terrestrial environment are the earth’s crust and the mantle formed by the

magmatic differentation. As the cooling and differentation progress,

different rocks are formed. Igneous rocks break down into soil by both

physical and chemical processes. Weathering plays a key role in these

processes. In physical process, separation of minor minerals like zircon

and monazite are formed which are stable and resistant to chemical decay

and often found as small individual grains. Sedimentation processes

naturally sort the products of weathering and develop several major

sedimentary rocks types of significantly differing radionuclide

concentrations (www.whoi.edu/education/gsp/MCG/BPE, 2005).

Radioactivity in soil results from the weathering of radioactive rocks

from which it is derived. It is diminished by leaching of water, diluted by

increased porosity and by added water and organic matter, and

7

augmented by sorption and precipitation of radionuclides of incoming

water. The top level of about 0.25 m of soil contributes significantly to

background radiation dose. Background concentrations of radionuclides

in soil varies because of many factors. Soil may have been produced from

the weathered top layer of still-intact bedrock below or transported

laterally from the same rock unit. Some methods of transport are natural

phenomena such as- earthquakes, volcanoes, glaciers and changes in soil

composition from flooding. Water is the dominant transporting medium

in the environment. Outwash erosion products from mountain produces a

soil surface that is more radioactive than the underlying bedrocks. Wind

also play a significant role in the transportation of weathered radioactive

rocks from one location to another (www.whori.edu/education/gsp/

Mcg/BPE, 2005).

Because of high ionic potential of Th+4, the thorium brought in solution is

quickly adsorbed or precipitated as hydrolysates or oxides (Fairbridge,

1972). The solubility product of Th(OH)4 is approximately 10-42

(Wedepohl, 1969).

1.8 Health Hazards

Breathing of air containing the thorium dust may increase the chance of

developing lung disease. On many years of exposure and in extreme

cases, cancer of the lung or pancreas can result. Even changes in the

genetic material of body cells have also been reported. If it is

accumulated in bones for a long period, bone cancer can result which is a

potential hazard. These factors, however include on the dose, the

duration, the pathway exposed of thorium inhalation and the food intake

etc. (www.abuse.com/environment/EPA-Home/Radition/ Information/

Radionuclides, 2005).

8

The Environment Protection Agency, USA, has set a drinking limit of 15

pCi/L for water with gross alpha particles and 4 millirems per year for

beta particles and photon activity. The tolerance value for natural thorium

are 10-5µC/mL of water, 2×10-13µC/cm3 in air, and 0.02 µC for the whole

body before developing radiotoxicity (Haissinsky and Adloff, 1965). The

Maximum Allowable Concentration (MAC) of 21 µg Th/gm of tissue is

calculated to give approximately the tolerance dose. However, if the

thorium is in partial equilibrium with its daughters, the tolerance dose rise

up to 25 µg per gram of tissue, a value numerically identical with that for

uranium (Hodge and Thomas, 1958).

2.0 Methods for determination of Thorium

There are many methods for determination of thorium such as

(a) Spectrophotometric method (b) X-ray fluorescence (c) Radiochemical

(d) Emission-Spectrometric (e) Mass-Spectrometric and (f) Titration

process based on Oxidimetric-Reductrometric, Potentiometric or

Amperometric. Apart from chemical methods, others include, the use of

Scintillation Counter with integral/differential single gamma-ray

spectrophotometer (GAD-1) and Multichannel Analyser (MCA) are two

physical methods applied for the estimation of thorium in the given

environmental samples by the direct measurement of radioactivity of this

element.

2.1 Spectrophotometric Method

Spectrophotometric method has been chosen for this work to determine

the low concentration of thorium. Complex formation with thorium either

by use of indicators or without use of such indicators are the effective

ways of determining thorium. A suitable calibration curve can be drawn

9

by the help of known concentration of thorium following the Lambert-

Beer’s law and unknown concentration can be found by reading the

absorbance and using the calibration curve. In this method, thorium

present in the sample was extracted from acid-deficient aluminium nitrate

medium into isobutyl methyl ketone (IBMK). Further addition of

hexadecyltrimethyl ammonium bromide (CTAB) solution enabled the

quantitative extraction of thorium into isobutyl methyl ketone.

Sequentially extracted thorium from uranium was complexed with

arsenazo (III) and the concentration calculated from the measured

absorbance or optical density(Ramakrishna and Murthy, 1980).

2.2 MCA Method

Analysis of radioactive substance by spectral means is very simple and

fast and leads to qualitative determination of thorium. However, it gives

barely semi-quantitative indications of the contents of elements. For

gamma determination, Multichannel pulse amplitude analysis is in use.

The gamma rays are emitted when there is a return of a nucleus from an

excited condition to its ground state. Between the excited and the ground

state, several transitions (therefore gamma emissions) of various energy

are possible (Collee, 1958). In radioactivity measurement technology, the

output electric pulse amplitudes proportional to the radiation energy is

utilized by NaI crystal scintillators; a complete gamma energy analysis is

made.

Selection of Gamma-Ray Peak

The MCA (529 780-E) having MCA-CASSY converts the pulse

amplitude to a number between 0 to 1023 (at a user-definable resolution

of 10 bits). In MCA, energy is first calibrated with Cesium-137 standard

source with a prominent gamma ray peak at 662 KeV. In thorium

10

spectrum the prominent gamma peaks are at 0.024, 0.94 and 2.62 meV

(Aryal, 1994). Only gamma-ray peak of 2.62 meV for thorium is used for

the analysis because, this high energy combination is found to be most

suitable due to-

(a) High ratio of total count to the background count(T/B) under

gamma peak,

(b) Low relative error and,

(c) The ease in computation work.

2.3 Theoretical Basis of Analytical Technique

The working instrument is based on some theoretical basis on which the

experimental determination is dependent in the spectrophotometric

method.

Spectrophotometric Method:

The theoretical basis of spectrophotometric and colorimetric analysis is

provided by Lambert and Beer in the form of laws, known as Lambert’s

and Beer’s law respectively. In a mathematical form, Beer-Lambert law

(Lohman, 1955) is expressed as:

A = abc -------------------------------------- (1)

Where,

A = Absorbance or optical density (O.D.)

a = Absorbtivity when c is expressed in gram per liter.

b = Length of the absorbing homogeneous medium.

c = Concentration of the absorbing species in gram per liter or

moles per liter.

On the other hand, absorbance is also given by :

11

A = log IiIt

-------------------------------------- (2)

Where,

Ii = Intensity of the incident radiation.

It = Intensity of the transmitted radiation.

When the concentration of absorbing species 'c' is measured in moles per

liter, the Lambert-Beer's law is expressed as:

A = εbc -------------------------------------- (3)

Where,

ε = Molar extinction coefficient

The sensitivity of a spectrophotometeric method depends upon the value

of ε; the higher is its value, the more sensitive is the method.

The absorbance 'A' also depends upon the wavelength, λ, of the incident

light and there is particular wavelength for which the absorbance is

maximum called λmax which is characteristic of the colored absorbing

species.

The applicability of the Lambert-Beer's law may be tested for any

particular system by measuring the absorbance for each of a series of

solutions of known concentration of the absorbing species. A plot of the

experimental data in terms of absorbance against concentration will yield

a straight line passing through the origin if the Lambert-Beer's law is

obeyed. A suitable calibration plot is first prepared from a series of

solutions containing known concentration of the absorbing species. It is

possible to determine the concentration of the absorbing substance of an

unknown sample from this calibration curve. Usually the Lambert-Beer's

12

plot gives a straight line at low concentration range and the deviation

from the linearity occurs as the concentration increases. Higher

concentrations of some other colourless salts even adversely affect

absorption of light (Khopkar, 1998). At high concentration, deviation

from Lambert Beer's law occurs which are due to the intermolecular

interactions and concentration dependent dissociations or associations.

The reaction with solvent or with hydrogen ions or formation of complex

ions with varying number of ligands also influence these results.

3.0 Literature Survey

Before 1939, very little was known about the analytical chemistry of

thorium. During and since the World War II, however, the literature on

the analytical chemistry of thorium has grown tremendously. The first

comprehensive survey appeared in 1948 (Moeller et al., 1948). The

precipitation method by the use of sodium oxalate followed by digestion

with permanganate, the excess of which is measured colorimetrically had

the drawback as the solubility of thorium oxalate was approximately 0.1

mg/lit (Kall and Gordon, 1953). Colorimetry of the iodine released by

thorium iodate was not sufficiently sensitive for the analysis of low grade

ores (Rodden, 1950). Para-arsonic acid was excellent (Grimaldi and

Fairchild, 1945) but this reagent was not commonly found. In addition, it

was difficult to wash and filter the complex formed by the reagent with

the thorium. Determination of the color developed by the derivatives of

benzoic acid and particularly m-dinitrobenzoic acid (Rodden, 1950)

cannot be adopted owing to the lack of accuracy. Alizarine is easy to

obtain and highly sensitive and thorium-alizarin complex has high rate of

extinction to allow the determination of tens of micrograms of thorium in

common colorimetric devices. However, in order to reach this limit, it

13

was necessary to eliminate the interference factor. The resulted in

interference gives an error of about 10 percent (Suner, 1958).

The iodate method developed (Meyer and Speter, 1910) has been widely

used for separation and determination of thorium. Other metals that were

also precipitated as iodates under the same conditions were subsequently

removed by precipitating thorium as an oxalate (Rodden, 1950). When

oxalic acid was used as a precipitant, the losses of thorium were too high

(Clinch and Simpson, 1957). Photometric determination in weakly acidic

or neutral medium form with 1-(pyridyl-2'-azo)-resorcinol was found to

be suitable after separating the thorium in the form of the oxalate

(Alimarin et al., 1957). The use of aspartic acid as titrant and

bromophenol blue as indicator permited thorium to be determined in

presence of large amount based on spectrophotometric titration of their

anionic fluoride complexes in a 90 percent dimethylsulfoxide with

potassium salt solution in presence of nitchromazo as metalloindicator

(Sergeev and Korenman, 1978). Mesotartaric acid used as a masking

agent permited the determination of thorium with thorin in presence of

zirconium (Grimaldi and Fletcher, 1956). The colour reaction between

morin and thorium were also carefully studied during the determination

thorium (Fletcher and Milkey, 1956).

Photometric studies with arsenazo I (Nemodruk and Kochetkova, 1962)

and arsenazo II (Vladimirova et al., 1960) were equally studied. The

studies conducted with arsenazo III was found to be superior method due

to its stability (Leib, 1984), however, the solvent medium selected was

different. Differential spectrophotometric variation method of analysis

developed by use of arsenazo III has low sensitivity, which is associated

with low color intensity (Nikitina, 1978). Study of the color reaction of

14

Tc-arsenazo with thorium along its application used 7.2 mol/lit. of HCl

have been also studied (Chen, 2002).

On solvent extraction from HNO3 solution, the structural effect of N, N-

dialkylamide on thorium (IV) was studied (Cui et al., 2003) and also with

TOPO solution. Phosphoryl containing ligand i.e. TOPO in

dichloromethane has been used as an extracting agent for Th (IV) from

1 M sodium nitrates (Yaftian et al., 2003). Hydrolytic behaviour of Th

(IV) and dioxo – U (VI) in the absence and presence of fluoride ions and

thorium recovery from waste water by extraction was recently studied

(Kudryavskii et al., 2003).

Extraction methods have not been extensively explored for the sequential

separation of uranium and thorium probably because their extraction

takes place from medium of widely differing composition. Synergistic

extraction of Th (IV) and U (VI) from nitric acid by using HBMPPT and

TOPO was found to be successful as the extraction increased on addition

of TOPO in toluene (Yu et al., 2001). In extraction of U (VI) and Th (IV)

with N, N-dibutyl alkylamide, the change in length of carbonyl chain was

found not to affect the extraction of U (VI) but extraction of Th (IV)

falled with increase in length of carbonyl chain (Sun et al., 1999).

Simultaneous determination of uranium and thorium with standard dual

addition method showed that the recoveries of (96.8-102.3)% of thorium

by spectroscopic analysis (He et al., 1998). Since, the extraction

behaviour of these metal ions is spectrophotometrically followed using

arsenazo III (Savvin, 1961) at present suitable conditions for the selective

and sequential extraction of thorium in the mixture of thorium and

uranium has been studied from acid deficient aluminium nitrate solution

into IBMK by the use of spectrophotometer.

15

4.0 Objectives of the Work

The specific objectives for the determination of thorium in water as

environmental samples are as follows :

a) To standardize a spectrophotometric method for the quantative

determination of thorium.

b) To estimate the water soluble thorium by the liquid-liquid

extraction process in the environmental samples.

5.0 Experimentation

The following instruments and the steps for the procedure of preparation

of reagents were undertaken. Collection of the samples and extraction

proceeded.

5.1 Instrumentation

The instruments used for the determination of thorium are :

a) Spectrophotometer of type S-104, WPA. Linton Cambridge with

10 mm cubate.

b) A pH meter 3010, JENWAY with glass electrode.

c) A protable scintillation counter (Scintrex Model DGS-1SL).

d) The MCA (529 780-E) having MCA-CASSY.

5.2 Preparation of Reagents

The details of the quality and manufacture of the respective chemicals are

given in Appendix I.

16

a) Stock Thorium Nitrate Solution (1000 µg Th/ml)

2.457 gm of Th(NO3)4.5H2O (G.R. grade, Loba-Chemie) was dried in a

desiccators and weighed out accurately. Then, this was dissolved in 10%

nitric acid which was prepared in double distilled water. The final volume

in 1000 ml volumetric flask was made up to the mark by adding 10

percent HNO3.

b) Working solution

Standard thorium solutions were prepared by appropriate dilution of stock

thorium nitrate solution in 25 ml volumetric flask.

c) Aluminium Nitrate

Saturated solution of Al(NO3)3.9H2O (G.R. grade, 98.5%) was prepared

in 100 ml beaker. Everyday, a fresh solution was prepared in distilled

water.

d) 0.1 M HCl Solution

2.2 ml of concentrated Hydrochloric acid was diluted in 250 ml.

volumetric flask with distilled water by constant chilling.

e) 1:1 HCl Solution

50 ml. of distilled water was taken in 100 ml. beaker and 50 ml of

concentrated HCl was added slowly with constant stirring.

f) 0.5 Percent CTAB Solution

0.125 gm of CTAB (G.R. grade, Loba-Chemie 99%) was dissolved in

distilled water in a 25 ml volumetric flask. The final volume was made up

to the mark by distilled water.

17

g) 0.02 Percent arsenazo III

0.02 gm of arsenazo III (G.R. grade), a coloring and complexing agent

was weighed out accurately and transferred to 100 ml volumetric flask.

The final volume was made up to the mark after it was dissolved.

5.3 Absorption Spectra of Thorium Complex

For absorption spectra, standard solution of 10 ppm was prepared by

dilution of required amount of stock solution in 100 ml volumetric flask.

1 ml of 10 ppm of thorium was pipetted into a 25 ml volumetric flask.

Firstly, about 10 ml of 1:1 HCl was poured in the same volumetric flask

followed by the 5 ml of the 0.02 percent of arsenazo III. To ensure

complete dissolution, it was shaken for about 2 minutes. The final volume

was made up to the mark and the concentration of thorium was 0.4 µg/ml

The absorbance from 630-700 nm was measured against reagent blank,

after about 33 to 40 minutes using WPA S-104 spectrophotometer. A plot

of absorbance against the wavelength is shown in Fig. 5.1 below.

Fig. 5.1 : Plot of absorbance against wavelength for determination of λmax.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

620 630 640 650 660 670 680 690 700 710

Wavelength in nm

Abs

orba

nce

18

5.4 Calibration Curve for Thorium Determination

In different 25 ml volumetric flasks, the required amount of working

solutions were poured. Then about 10 ml of 1:1 HCl were added on each

followed by 5 ml of arsenazo III as described in step 5.3. Final volume

was made up to the mark. The prepared concentrations of thorium were

from 0.01 to 0.8 µg/ml. At λmax = 660 nm, the absorbance of standard

solutions were measured with respect to reagent blank using WPA S-104

spectrophotometer. A plot of absorbance against the concentration of

thorium is shown in Fig. 5.2 below.

Fig. 5.2 : Calibration curve of absorbance against concentration for

thorium determination

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 0.2 0.4 0.6 0.8 1 1.2

Concentraction (ppm)

Abs

orba

nce

19

5.5 Collection of Samples

Brief description of the site and method of collection of samples are as

follows:

a. Description of the Site

The samples were collected from the northern part of the Kathmandu

valley at the Shivapuri hillside of Bramakhel and Chudikhel areas.

Samples of water, sand and some soils were taken for this study. There

were more than 1200 people in this village who are directly dependent on

the source of these samples. The villagers used water for drinking,

washing, bathing and irrigation. Domestic cattle were also found to be

consuming water of those sites. These source of water supplied the

nearby pond. The sand extracted from those sites were used for

construction work in Kathmandu city too. The grass grown on these study

sites were used for grazing of cattle. Vegetables and other food grown

here were sold in the capital city.

b. Method of Collection

Water sample were collected from the river where the bed of the running

water had stones and gravels of different formation. Collected water

samples were stored in 1 liter and 5 liter plastic jars in which about 1 ml

of concentrated HNO3 was added per liter as a preservative. Collection of

the sand and soil samples were determined at these locations with the

ground radiometric survey portable Scintillation Counter. At the field

with higher cps first 10 cm depth of the sample was discarded. Samples

of 1 kg from the banks of riversides were weighed in a spring balance and

kept in a plastic bag. The samples were immediately labelled as – w, st

and s for water, sand and soil respectively as shown in Table 6.5 and 6.6.

20

5.6 Extraction of Thorium

Different procedures were adopted for extraction of thorium from water,

sand and soil samples as follows:

a) From Water

At first 25 ml of the sample solution was taken in a 50 ml beaker and

heated on a hot plate till the volume was reduced to nearly 5 ml. Then

10 grams of aluminium nitrate was added and stirred to dissolve. The

pH of the solution was adjusted to 0.8-0.9 using ammonium carbonate

using a pH meter. The solution was transferred to a 100 cc separating

funnel. For each sample, 1 ml of saturated aluminium nitrate solution

was used for rinsing and 5 ml of isobutyl methylketone was added and

shaked for 3 to 5 minutes. The undisturbed solution, resulted after a

while was separated as the organic and the aqueous phase (I). In the

organic phase, 5 ml of saturated aluminium nitrate was added followed

by 5 ml of benzene. After shaking for about two to three minutes, the

aqueous phase (II) was separated from the organic phase (Ramakrishna

and Murthy, 1980).

Two aqueous phases (I and II) obtained were taken in a 100 cc separating

funnel. Then 1 ml of CTAB solution and 10 ml of IBMK were added

into it and shaken for about 5 minutes. The aqueous phase was discarded

while the organic phase was retained for the recovery of thorium.

To the organic phase (5 ml), 0.1 M HCl each was added twice to strip the

thorium content. Few drops of concentrated H2SO4 was added to the

resulting aqueous phase collected in 25 ml of beaker. It was evaporated

till all fumes of sulfur trioxide ceased to evolve. The residue obtained was

dissolved in 5 ml of water, then this was transferred to the 25 cc

21

volumetric flask where 1:1 HCl was used for rinsing. 5 ml of 0.02 percent

of arsenazo III was added and to the rest, 1:1 HCl was used up to the

mark. After 35-40 minutes, the absorbance or optical density was read at

the λmax value of 660 nm. The concentration of thorium was calculated

directly from the calibration curve (Fig. 5.2).

b. From Sand and Soil

The sand and soil samples collected from different places, were taken for

analysis. Firstly, homogeneous distribution of sand was made by

shoveling. Out of four fractions of sand, opposite side samples were

mixed and again homogeneously distributed. 100 ml of water was poured

in 200 gms of sand where, (2-3) drops of concentrated nitric acid was

added and stirred well. After sedimentation, it was filtered. The resulting

filtrate was evaporated, in such a way that only about 5 ml of liquid was

left over. Further work was performed as shown in the Flow Diagram Fig.

5.3 below:

22

Fig. 5.3 : Extraction of thorium

5 ml of sample solution in 25

ml beaker

Sample solution at pH meter

Sample in 100 cc separating funnel

Organic phase

Organic phase

Aqueous phase (II)

Aqueous phase (I)

Aqueous phases (I) & (II) in separating

funnel

Aqueous phase

Organic phase

Residue

Thorium ready for determination in 25 cc. volumentric flask

Concentration calculated

(NH4)2CO3 1 ml Al (NO3)3

.9H2O

Shaken (3-5) minutes

Shaken (2-3) minutes

5 ml of Al (NO3)3 . 9H2O 5 ml of benzene solution

Added

(discarded)

1 cc of CTAB and 10 ml of IBMK solution

Added

Mixed

(discarded) Evaporated

5 ml of arsenazo III + 1:1 HCl up to mark

Spectro- photometer

~10 gm of

aluminium nitrate

Added

pH (0.8-0.9) 5 ml. of IBMK

few drops of Conc. H2SO4

Added

5 ml of H2O Added

Solution

Shaken 5 minutes

Organic phase

Aqueous phase

0.1 M HCL Strip twice

(discarded)

23

6.0 Results and Discussion

The absorption spectra and calibration is first discussed followed by the

extraction of known quantities of thorium and the standardization of the

method.

6.1 Absorption Spectra and Calibration Curve

The absorption spectra of the thorium formed by the complexation of

arsenazo III is shown in Fig. 5.1. This spectra was symmetrical with

absorption maxima centered at 660 nm. This wavelength has been used

for the quantitative determination of thorium in water sample. The λmax

centered at 660 nm was comparable in the determination of thorium by

same arsenazo III (Ramakrishna and Murthy, 1980).

To determine thorium in water sample, a calibration curve was prepared

as shown in Fig. 5.2. The plot of absorbance of thorium-arsenazo at λmax

660 nm against concentration of thorium in µg/ml was made. The plot

was linear up to 0.8 µg Th/ml. The apparent molar absorptivity in region

of least photometric error was 11.59 × 104 L mole-1 cm-1 and applicable

range was 0.02-0.8 µg Th/ml. This molar absorptivity was comparable

with (5.8 - 5.9) × 104 L mole-1cm-1 obtained at the λmax = 665 using the

arsenazo III (Akimov et al., 1977) having the applicable range of

0.2-0.8 µg Th/ml. The amount of thorium within this range was

determined directly. Above this range, sample was diluted with water and

below this range, it was concentrated so as to bring the concentration of

thorium to measurable range.

This process of determination was time dependent. Absorbance was read

after 35-40 minutes (Akimov et al., 1977) and absorbance after an hour or

24

latter did not give effective result. Among other reagents, an organic

reagent arsenazo III (Fig. 6.1 below), used in this method was more easily

available and cheaper than the reagent used in other method of extraction.

Interestingly, arsenazo III suppress the reverse reaction, increases the

sensitivity forming very stable and highly colored complexes with the

dissociation products of complexonates (free cations) as well

characteristics of forming complex with the indicated elements within a

broad range of hydrogen ion concentrations (Savvin, 1971) and

intracomplex with thorium (IV) (Leib, 1984). Measurements were carried

out against the reagent blank for the determination of thorium.

6.2 Extraction of Known Quantities and Study of Different

Effects

The study of thorium by liquid-liquid extraction was particularly

convenient for the separation of small quantities of thorium (Andjelkovic

and Rajkovic, 1958). During the process of extraction effect of pH, effect

of concentration of aluminium nitrate, the separation of uranium from

thorium samples and behaviors of some anions were studied as described

below:

HO As OH

N=N

O

SO3H

N=N

HO As OH

O

OH OH

SO3H

(SO3H2)C10H2 (OH) [N-NC6H4 AsO (OH)2]2

Fig. 6.1 : Arsenazo III

25

(i) Effect of the pH

Effect of pH on thorium have been continuously studied for the last few

decades. In complexometric titration of thorium in presence of

1-(Pyridyl-2'-azo)-2-naphthol (Meyer and Speter, 1960), pH was

monitered at 1.8 and other values. The amount of aluminimum nitrate at

different pH was studied with and without addition of CTAB. When 10

grams of aluminum nitrate was added to 5 ml. of known sample, the raise

in volume was by ~10 cc and molarity of aluminium nitrate was 2.6 mol

per liter. The variation in pH were made by the help of ammonium

carbonate (Ramakrishna and Murthy, 1979). Table 6.1 below showed the

extraction percentage of thorium, when (NH4)2CO3 was not added only

64 percentage of thorium was extracted. The extraction percentage was

decreased with increase in pH of the solution. With addition of CTAB

there was remarkable difference in extraction behaviour. Although

addition of 1 ml of 0.5 percentage of CTAB at lower pH did not have

much effect, however, with increasing pH its extraction percentage

increased slowly and even up to 100 percentage at pH of 0.9. Thereafter,

again it decreased with further increase in pH. The addition of 2 m, 3 ml

etc. of 0.5 percent of CTAB resulted in the values same as those of 1 ml

of 0.5 percent of CTAB in the percentage of extraction. This confirmed

that addition of more CTAB has no further significance and pH value of

0.9 was found effective condition for cent percent extraction.

26

Table 6.1 : Effect of pH in Thorium Extraction with and without CTAB

Without the use of CTAB With the use of

CTAB

S.N.

pH of

the

solution

Th

taken

(µg/ml)

Absorbance

Th

extraction

(µg/ml)

%

extraction

Th

extraction

(µg/ml)

%

extraction

1 0.5 0.5 0.14 0.29 58 0.41 82

2 0.8 0.5 0.13 0.26 52 0.49 98

3 0.9 0.5 0.12 0.25 50 0.50 100

4 1.5 0.5 0.07 0.15 30 0.43 86

5 2.0 0.5 0.01 0.02 4 0.36 72

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5

pH of Al (NO3)3. 9H2O at 2.62 mol dm-3

% E

xtr

acti

on

Without CTAB in aluminium nitrate at different % extraction of the thorium With addition of CTAB in aluminium nitrate

Fig. 6.2 : Effect on Thorium Extraction at different pH of aluminium

nitrate

27

(ii) Effect of Aluminium Nitrate Concentration

Table 6.2, showed the effect of aluminium nitrate concentration with pH

range from 0.8 to 0.9 with addition and without addition of CTAB. The

experiment was performed by taking 0.8 µg Th/ml. At ~3.15 and 2.62

mole per dm3 of aluminium nitrate only 50 percentage of extraction were

possible while decrease in concentration (molarity) of aluminium nitrate

hindered the extraction. Addition of 1 ml of CTAB at different

concentration of Al(NO3)3.9H2O foster in the extraction. At 3.15, 2.62

and 2.36 mole per dm3 of aluminium nitrate up to ~99 percentage of

thorium were extracted. However, at lower concentration of aluminium

nitrate, the percentage of extraction decreased even with the addition of

CTAB. Hence, the extraction process was found to be soley dependent on

the concentration of aluminium nitrate and CTAB at fixed pH

(Ramakrishna and Murthy, 1980). The result of Fig. 6.3 explained how

the percentage of extraction increased or decreased with and without

using CTAB.

Table 6.2 : Effect of Aluminium nitrate Concentration with and without

CTAB for Thorium Extraction .

Without the use of CTAB With the use of

CTAB

S.N.

Aluminium nitrate

Th taken

(µg/ml) Absorbance

Th extraction

(µg/ml)

% extraction

Th extraction

(µg/ml)

% extraction

Grams Molarity

1 12 3.15 0.8 0.21 0.4 50 0.78 97.5 2 10 2.62 0.8 0.20 0.4 50 0.79 98.5

3 9 2.36 0.8 0.11 0.24 30 0.78 97.5

4 8 2.06 0.8 0.02 0.04 5 0.64 80.0

5 6 1.57 0.8 - - - 0.4 50.0 6 5 1.31 0.8 - - - 0.16 20.0

28

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5

Molarity of aluminium nitrate

% E

xtra

ctio

n

% Thorium in IBMK at pH of 0.8-0.9 without CTAB % Thorium in IBMK at pH of 0.8-0.9 with CTAB

Fig. 6.3 : Effect of aluminium nitrate concentration on thorium extraction

at pH 0.8-0.9 with and without CTAB

(iii) Effect of Uranium in Thorium Extraction

Uranium and thorium were together extracted for the colorimetric

determination, with thorin to produce positive error but up to the point

where the U/Th ratio does not exceed 25; these error remain below 5%

(Andjelković and Rajković, 1958). Similarly, there was maximum chance

for uranium and thorium to be in aqueous phase of thorium if present

during extraction IBMK: benzene: saturated aluminium nitrate were at

once mixed. So the addition of IBMK and aluminium nitrate and benzene

were done one after another (Ramakrishna and Murthy, 1980). When

extraction proceeded with only adding 0.5 µg/ml of uranium and no

thorium the absorbance was zero and with addition of certain amount of

uranium and thorium, then extraction resembled that of taken amount of

thorium as shown in Table 6.3 given below. Hence the extracted metal

29

ion was no more than thorium, and uranium had no effect in the whole

process.

Table 6.3 : Effect of Uranium in Thorium Extraction

S.N. U taken

(µg/ml)

Th taken

(µg/ml)

Absorbance Concentration

recovered (µg/ml)

% Recovery

of thorium

1 0.5 0.0 - - -

2 0.2 0.2 0.1 0.2 100

3 0.1 0.2 0.09 0.19 95

(iv) Behaviour of Some Anions in the Extraction

Since the water and sand samples were collected from rivers and its bed, it

could have various anions present which as such might affect the

extraction. Qualitative tests of some anions like PO43-, SO4

2- and F- were

done. Test of PO43- was performed by adding 3 drops of HNO3 in a nitric

acid acidified sample, slightly warmed where slight excess of ammonium

molybdate was added. The sulfate test was performed by the use of lead

acetate and barium chloride solution. Similarly F- test was done by

acidifying test solution with CH3COOH and again CH3COOH in excess

then CaCl2 solution and warmed. No ppt in any sample solution was

observed; however, quantitative test of PO43- showed that up to 0.3 ppm of

phosphate was present. Spectrophotometric determination of phosphate

was performed by using stannous chloride (2.5 g SnCl2.2H2O in 100 ml

glycerol and ammonium molybdate (NH4)6 Mo7O24.4H2O in acidified

H2SO4) reagents. In 25 ml of sample solution, 1 ml ammonium molybdate

and 2 drops of SnCl2 reagent were added. It was shaken and left for color

development. Then spectrophotometric analysis of blue coloured sample

was performed between 10 minutes and 12 minutes at λmax of 690 nm

(Clesceri, 1998). This experiment showed presence of 0-0.3 ppm of

30

phosphate in water sample. Anions like chlorides and nitrates were not

studied as they do not interfere in thorium determination while PO43-, SO4

2-,

F- and also organic acid anions may form stable complex (Sergeev and

Korenman, 1978) but the organic reagent arsenazo III made it possible to

determine thorium in strongly acidic medium without the preliminary

separation of those ions (Leib, 1984).

6.3 Standardization of the Method and Reagent Selection

In this method, applied for the liquid-liquid extraction of thorium, to see

the effect of the pH and effect of concentration on the aluminium nitrate.

The addition of CTAB on aluminium nitrate at fixed pH showed up to

100 percentage extraction of the thorium. Table 6.4 showed the extraction

of thorium at different concentration. The accuracy and precision of this

method were checked by performing three replicate determinations,

taking 0.02, 0.06, 0.1, 0.4 and 0.8 µg thorium in final volume of 25 ml.

Those indicated that results were reproducible and the method was

reliable for the low concentration of thorium at our laboratory at the room

temperature.

31

Table 6.4 : Standardization of Method with known Quantities of Thorium

(Accuracy and Precision)

S.N. Th

taken

(µg/ml)

Absorbance Th

found

(µg/ml)

Mean Standard

deviation

(S.D.)

Relative

S.D.

95%

confidence

interval

1 0.02

0.02

0.02

0.01

0.01

0.01

0.02

0.02

0.02

0.02 - - 0.02 ± 0

2 0.06

0.06

0.06

0.02

0.03

0.03

0.05

0.06

0.06

0.056 0.0047 7.14 0.056 ±

0.011

3 0.1

0.1

0.1

0.05

0.06

0.05

0.09

0.1

0.09

0.093 0.004 4.30 0.093 ±

0.009

4 0.4

0.4

0.4

0.19

0.20

0.21

0.35

0.40

0.45

0.40 0.04 10 0.4 ±

0.099

5 0.8

0.8

0.8

0.40

0.40

0.39

0.80

0.80

0.75

0.783 0.023 2.9 0.783 ±

0.057

Although the solution or sample extraction could be best carried by HNO3

solution (Katzin, 1955), the extraction by salting agent Al(NO3)3. 9H2O was

also equally suitable as it resisted hydrolysis at low pH. The thorium

present in the sample in the nitrate medium would be present as the

species [Th(NO3)6]2- (Carswell and Lawrence, 1959), nevertheless, the

effective extraction was only favoured, when 2.6 mole per dm3 of

aluminium nitrate was used and pH maintained at the range of 0.8 – 0.9

by the help of ammonium carbonate. Organic solvent used for the

extraction like ketone proved that out of various class of organic

32

compounds, best results were obtained with ketone (Katzin, 1955).

Among so many ketones, IBMK was selected because of its lower

solubility in the aqueous phase and rapid separation of both phases

(Ramakrishna and Murthy, 1979). To the organic phase 5 ml of saturated

aluminum nitrate and 5 ml of benzene were added as the remainder of

thorium in organic phase would again get attached as the species

[Th(NO3)6]2- and the benzene as organic solvent was used because it

neither extract thorium nor uranium but had the property of bringing

down thorium in aqueous phase completely. The second aqueous phase

was separated and mixed with first aqueous phase, then 1 ml of 0.5

percentage of CTAB and 10 ml of IBMK were added. CTAB was

selected because it is an excellent cationic surfactant that has the property

of lowering surface tension and lower solubility when added in aqueous

phase in small quantity. It had the behaviour like that of TOPO used in

toluene, where extraction ability was increased in appreciable quantity

(Yu et al., 2001). The structure of CTAB(C19H42BrN) is as shown in Fig.

6.4 below.

Fig. 6.4 : Structure of CTAB

Organic phase was only taken after discarding aqueous phase for the

recovery of thorium. Thorium present was striped twice by the help of

0.1 M HCl. After addition of 2-3 drops of concentrated H2SO4, the solution

was evapourated till the fuming of sulfur trioxide ceased and the residue

was obtained to eliminated most of the acid (Suner, 1958) and oxidised any

organic matter (Andjelković and Rajković, 1958). The residue thus

CH3

N

CH3

CH3 Br(-)

33

obtained was dissolved in nearly 5 ml. of water then transferred to 25 cc

volumetric flask using 1:1 HCl for rinsing. 5 ml of arsenazo III was added

and the volume diluted up to the mark with 1:1 HCl. Eventually, the

concentration of thorium was determined by extraction process after the

lapse of 35-40 minutes of reagent added.

6.4 Analysis of Test Samples

In Central Siwalik Region, thorium present was low to the value of ratio

Th/U = 0.0686, where total count rate was up to 27,437 cps in variable

weight (less than a kg), (Aryal, 1994). Ground radiometric survey in

Tinbhangale area (Makwanpur), the radioactive intensity (RI) by the use

of four channel Gamma-ray Spectrometer, the total count was up to

27,405 cps where thorium alone counts up to 30 cps (Kaphle and Khan,

2003). Similarly, by the use of this instrument up to 2,839 cps total count

out of which thorium present was 27 cps alone in (Mahadev Khola) of the

Brahmakhel area was reported (Shrestha, 2004).

Chemical test analysis of both water and sand were shown in Table 6.5

and 6.6 respectively collected from different sites of Bramakhel and

Chudikhel area. Out of fifteen water samples, six samples showed certain

quantities of thorium ranging from 20 ppb to 100 ppb where the gross

radioactive was from (100.8-163.7) Bq/lit (Shrestha, 2004).

The extraction of thorium from 200 mg of sand from the same site

depicits that 12 samples contained the thorium ranging from 20 ppb to 80

ppb out of 18 sand samples taken into analysis. The extraction of thorium

from second washed sand did not show the presence of thorium. That is

so because, either all the soluble thorium in sand were washed at first part

of the experiment or the thorium remained in the second wash were

below the detection limit of the experiment. The gross radioactive were in

34

range from (30.4 – 21655.7) Bq/kg (Shrestha, 2004). The results showed

that the homogenous content of thorium was more in sand in comparison

to water.

Table 6.5 : Chemical Analysis of Water

S.N. Sample No. *Gross radioactive Bq/lit Absorbance Concentration (PPb)

1 RH/W – 1 - - -

2 RH/W – 2 - - -

3 RH/W – 3 - - -

4 RH/W – 4 - - -

5 RH/W – 5 - 0.02 40

6 RH/W – 6 122.3 - -

7 RH/W – 7 112.5 0.01 20

8 RH/W – 8 118.7 - -

9 RH/W – 9 163.7 - -

10 RH/W – 10 - 0.01 20

11 RH/W – 11 100.8 0.02 40

12 RH/W – 12 114.5 - -

13 RH/W – 13 130.5 - -

14 RH/W – 14 - 0.05 100

15 RH/W –15 - 0.03 60

* Source: Report on Radiometric Survey/Mapping and Appraisal of BCR

Threats in Kathmandu Valley (Shrestha, 2004).

35

Table 6.6 : Chemical Analysis of Sand

S.N. Sample No. *Gross radioactive Bq/kg Absorbance Concentration (PPb)

1 RH/st 1 2643.1 0.02 40

2 RH/st 2 412.7 - -

3 RH/st 3 1740.2 0.01 20

4 RH/st 4 869.7 - -

5 RH/st 5 9230.7 - -

6 RH/s 6 - 0.01 20

7 RH/st 7 30.4 0.01 20

8 RH/st 8 21655.7 0.02 40

9 RH/st 9 346.0 0.02 40

10 RH/st 10 - - -

11 RH/st 11 - 0.01 20

12 RH/st 12 1570.4 - -

13 RH/st 13 17449.5 0.02 40

14 RH/st 14 14043.2 0.01 20

15 RH/st 15 7804.2 0.02 40

16 RH/st 16 1358.8 0.04 80

17 RH/st 17 11457.7 - -

18 RH/st 18 - 0.03 60

* Source: Report on Radiometric Survey/Mapping and Appraisal of BCR

Threats in Kathmandu Valley (Shrestha, 2004).

36

7.0 Conclusion

A method for the extraction and determination of thorium from different

environmental samples were investigated. Thorium can be determined by

forming intracomplex compound with arsenazo III in acidic medium.

Liquid-liquid extraction methodology was simple and precise method in

relation to other separation method. For the extraction of thorium,

aluminium nitrate with organic solvent IBMK and CTAB as a surfactant

was found to be useful.

The determination of thorium by organic reagent arsenazo III was

reliable, and the results obtained were reproducible. The soluble thorium

present in microgram level could be determined in environmental

samples like water, sand and soil by this method. This extraction method

was found to be simple but required strict control of pH and concentration

of aluminium nitrate. For the determination of lower concentration of

thorium, the method of sample concentration and time lapse of 35-40

minutes after addition of arsenazo III to form stable complex was tedious

and time consuming. This method was suitable to determine 0.02 to 0.8

µg Th/ml. Field survey and the report showed the presence of RI up to

2839 total cps which included 27 cps for thorium that justified the

decision to obtain environmental samples at these areas. Long term and

continuous exposure of radiation could be harmful for population of those

areas like Bramahakhel and Chudikhel located inside Kathmandu valley.

Chemical analysis investigated the presence of up to 100 ppb of thorium

in water sample. Hence, the present method could be used in routine

analysis of thorium in various water, sand and soil samples containing

micro quantities of thorium with fair accuracy.

37

8.0 Suggestions for Further Work

1. Exploration of the thorium minerals need to be done throughout the

country.

2. Laboratory techniques to determine the insoluble thorium ions

need to be maintain at the national level.

3. The effect of radioactivity on the health of people living at

localities like Bramakhel and Chudikhel have to be checked.

4. Effective method to determine the thorium from the rock sample

need to be undertaken.

5. Radiochemical analysis of plants and/or crop products grown and

produced respectively at areas with high environmental

radioactivity need to be carried out.

6. WHO guideline for thorium in food and water consumed at highly

radioactive areas need to be made at the national level.

38

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Geneva, 7, 407, U.N., New York (1956).

Khopkar, S.M., Basic Concepts of Analytical Chemistry, 2nd Edition, New

Age International (P) Limited Pub., p. 210 (1998).

Kudryavskii, Y.; Strelkov, V.V.; Trapeznikov, Yu. F. and Kazantsev, V.P.,

Thorium Recovery and Concentration from Process Solutions or Waste

Water by Extraction, Russ Ru 2, 207, 393 (2003).

Lambert, J.H., Photometria de Mensura et Gradibus Luminus, Colorum et

Umbrae, Augsberg. Reprinted in W Ostwald 1892 Klassiker der

Exakten Wissenschaften, 64 (32), (1970).

Leib, G.; A Guide to Practical Radiochemistry, Mir Publishers, Moscow, 2,

104 (1984).

Lohman, F.H., J. Chem. Edu., 32, 155 (1955).

41

Meyer, R.J. and Speter, M., Chem. Ztg., 34, 606 (1910).

Moeller, T.; Schweitzer, G.K. and Star, D.D., Analytical Aspects of Thorium

Chemistry, Chem. Revs, 42, 63 (1948).

Nemodruk, A.A. and Kochetkova, N.E., Zh. Anal. Khim, 17, 330 (1962).

Nikitina, S.A.; Lipovskii, A.A.; Dem'Yanova, T.A.; Nemtsova, M.A. and

Mavvicheva, A.M., Differential Spectrophotometric Method of

Determination of Uranium, Thorium and Plutonium using Arsenazo III,

Soviet Radiochemistry, 20 (6), 769 (1978).

Ramakrishna, T.V. and Murthy, R.S.S., Determination of Uranium and

Thorium with Arsenazo III after Sequential Extraction from Acid-

deficient Aluminium Nitrate Medium, Bull. Chem. Soc., Japan, 53 (8),

2376-2379 (1980).

Rankama, K. and Sahama, Th. G., Geochemistry, University of Chicago Press,

Chicago (1950).

Rodden, C.J., Analytical Chemistry of the Manhattan Project, p. 178, McGraw-

Hill Book Co. (1950).

Savvin, S.B., Organic Reagents of the Arsenazo III group [in Russian],

Atomizdat, Moscow (1971).

Savvin, S.B., Talanta, 11, 673 (1961)

Sergeev, G.M. and Korenman, I.M., Selective Determination of Thorium by

Titration with Aspartic Acid, J. Anal. Chem., 33 (7) Part 2, 1120 (1978).

Shrestha, K.K., Report on Radiometric Survey/Mapping and Appraisal of

Biological, Chemical and Radiological (BCR) Threats in Kathmandu

Valley, MOEST, Kathmandu, p. 9 (2004).

42

Sun, G.; Bao, B. and Cui, Y., Extraction of U (VI) and Th (IV) with N, N-

dibutyl-alkylamides, He HuaxueYu Fangshe Huaxue 21 (2), 119-123

(ch) (1999)

Suner, A.A., Determination of Thorium in Low-Grade Ores, International

Conference on the Peaceful uses of Atomic Energy, Geneva, 3, 580,

U.N., New York (1958).

Thomas, R.G., The Metabolism of 230Th (Ionium) Administered by

Intratracheal Injection to the Rat, University of Rochester Atomic Energy

Project Report, UR-980 (1956).

Twenhofel, W.S. and Buck, K.L, The Geology of Thorium Deposits in the

United States, International Conference on the Peaceful uses of Atomic

Energy, Geneva, 6, 586, U.N., New York (1956).

Vladimirova, V.M. and Davidovich, N.K., Zavodskaya laboratoriya, 26, 1210

(1960).

Wedepohl, K.H., Handbook of Geochemistry, Springer-Verlag Berlin.

Heidelberg. New York, 11 (1), 90-H-1, (1969).

Wickman, F.E., Some Aspects of the Geochemistry of Igneous Rocks and of

Differentiation by Crystallization, Geologiska Foreningens i Stockholm

Forhandlingar, 65, 37 (1943).

Yaftin, M.R.; Eshraghi, M.E. and Hassanzadeh, L., Extraction Properties of

Tri-n-octylphosphine Oxide towards Th (IV) and Eu (III) ion in an

Aqueous Media, Iranian Journal Chemistry and Chemical Engineering,

Jahad Daneshgahi, 21 (1), 71-76 (Eng.) (2003).

Yu, S.; Ma, L. and Bao, B., Synergistic Extraction of U (VI) and Th (IV) rom

nitric acid with HBMPPT and TOPO in Toluene, Solvent extraction for

the 21st century, proceeding of ISEC '99 Barcelona, Spain, 2, 1357-1359

(Eng.) (2001).

38

Appendix I Chemical Assay Values

Thorium nitrate Loba Chemie Minimum assay (gravimetric)- 99% Maximum Limits of Impurities : Chloride (Cl) - 0.002% Sulphate (SO4) - 0.01% Heavy metals (as Pb) - 0.002% Iron (Fe) - 0.001% Titanium (Ti) - 0.005% Rare ground (as La) - 0.2% by NH3 (as sulphate) - 0.2% Aluminium nitrate Al (NO3)3.9H2O – Merck Minimum assay - 98.5% Chlorine (Cl) - max. 0.001% Sulfate (SO4) - max. 0.005% Lead (Pb) - max. 0.01% Iron (Fe) - max. 0.002% Calcium (Ca) - max. 0.005% Sodium (Na) - max. 0.005% Potassium (K) - max. 0.002% Ammonium carbonate (NH4)2CO3 – Merck Assay (NH3) - 30% Chloride - 0.002% Sulphate - 0.005% Heavy metals (as Pb) - 0.002% Iron (Fe) - 0.001% Calcium (Ca) - 0.02% IBMK (CH3)2 CHCH2COCH3 - Qualigens Minimum assay - 98% Refractive index - 1.3965 Free acid - 1% Water - 0.5% Wt. per ml at 20°C - 0.79-0.802 g Arsenazo III - Loba chemie

39

Benzene Extra Pure 78.11 S.d. fine chem.. Ltd. Minimum Assay (GLC) - 99.0% Boiling Range (79-81°C) - Min 95% Freezing point - not below 5.2°C Wt per ml at 20°C - 0.875-0.879g Maximum limits of impurities Non volatile matter - 0.002 Water - 0.1% Hydrochloric acid - 36.46 (Qualigens) Assay (acidimetric) - 35.37% wt. per ml at 20°C - 1.18 g Maximum limits of impurities Non-volatile matter - 0.01% Sulphuric acid (H2SO4) - 0.02% Arsenic (As) - 0.0001% Iron (Fe) - 0.0005% Lead (Pb) - 0.0005% Free chlorine - 0.0005% Sulphuric Acid - 98.08 (Qualigens) Assay (acidimetric) - 97.99% Wt. per ml. at 20°C - about 1.835 g Maximum limits of impurities Non-volatile matter - 0.01% Hydrochloric acid - 0.0005% Nitric acid - 0.001% Arsenic - 0.0002% Iron - 0.002% Lead - 0.002% Reducing substances - 0.02 ml. N/1% HNO3 - 63.01 Assay (HNO3) - 66-75% Chloride (Cl) - < 0.005% Sulfate - < 0.001% Heavy metals (Pb) - 0.001%

40

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104 (1984).

Lohman, F.H., J. Chem. Edu., 32, 155 (1955).

43

Meyer, R.J. and Speter, M., Chem. Ztg., 34, 606 (1910).

Moeller, T.; Schweitzer, G.K. and Star, D.D., Analytical Aspects of Thorium

Chemistry, Chem. Revs, 42, 63 (1948).

Nemodruk, A.A. and Kochetkova, N.E., Zh. Anal. Khim, 17, 330 (1962).

Nikitina, S.A.; Lipovskii, A.A.; Dem'Yanova, T.A.; Nemtsova, M.A. and

Mavvicheva, A.M., Differential Spectrophotometric Method of

Determination of Uranium, Thorium and Plutonium using Arsenazo III,

Soviet Radiochemistry, 20 (6), 769 (1978).

Ramakrishna, T.V. and Murthy, R.S.S., Determination of Uranium and

Thorium with Arsenazo III after Sequential Extraction from Acid-

deficient Aluminium Nitrate Medium, Bull. Chem. Soc., Japan, 53 (8),

2376-2379 (1980).

Rankama, K. and Sahama, Th. G., Geochemistry, University of Chicago Press,

Chicago (1950).

Rodden, C.J., Analytical Chemistry of the Manhattan Project, p. 178, McGraw-

Hill Book Co. (1950).

Savvin, S.B., Organic Reagents of the Arsenazo III group [in Russian],

Atomizdat, Moscow (1971).

Savvin, S.B., Talanta, 11, 673 (1961)

Sergeev, G.M. and Korenman, I.M., Selective Determination of Thorium by

Titration with Aspartic Acid, J. Anal. Chem., 33 (7) Part 2, 1120 (1978).

Shrestha, K.K., Report on Radiometric Survey/Mapping and Appraisal of

Biological, Chemical and Radiological (BCR) Threats in Kathmandu

Valley, MOEST, Kathmandu, p. 9 (2004).

44

Sun, G.; Bao, B. and Cui, Y., Extraction of U (VI) and Th (IV) with N, N-

dibutyl-alkylamides, He HuaxueYu Fangshe Huaxue 21 (2), 119-123

(ch) (1999)

Suner, A.A., Determination of Thorium in Low-Grade Ores, International

Conference on the Peaceful uses of Atomic Energy, Geneva, 3, 580,

U.N., New York (1958).

Thomas, R.G., The Metabolism of 230Th (Ionium) Administered by

Intratracheal Injection to the Rat, University of Rochester Atomic Energy

Project Report, UR-980 (1956).

Twenhofel, W.S. and Buck, K.L, The Geology of Thorium Deposits in the

United States, International Conference on the Peaceful uses of Atomic

Energy, Geneva, 6, 586, U.N., New York (1956).

Vladimirova, V.M. and Davidovich, N.K., Zavodskaya laboratoriya, 26, 1210

(1960).

Wedepohl, K.H., Handbook of Geochemistry, Springer-Verlag Berlin.

Heidelberg. New York, 11 (1), 90-H-1, (1969).

Wickman, F.E., Some Aspects of the Geochemistry of Igneous Rocks and of

Differentiation by Crystallization, Geologiska Foreningens i Stockholm

Forhandlingar, 65, 37 (1943).

Yaftin, M.R.; Eshraghi, M.E. and Hassanzadeh, L., Extraction Properties of

Tri-n-octylphosphine Oxide towards Th (IV) and Eu (III) ion in an

Aqueous Media, Iranian Journal Chemistry and Chemical Engineering,

Jahad Daneshgahi, 21 (1), 71-76 (Eng.) (2003).

Yu, S.; Ma, L. and Bao, B., Synergistic Extraction of U (VI) and Th (IV) rom

nitric acid with HBMPPT and TOPO in Toluene, Solvent extraction for

the 21st century, proceeding of ISEC '99 Barcelona, Spain, 2, 1357-1359

(Eng.) (2001).