Malaysian Journal of Analytical Sciences Vol 20 No 4 (2016): 770 -
776
DOI:
http://dx.doi.org/10.17576/mjas-2016-2004-09
SEPARATION AND RADIOLOGICAL IMPACT
ASSESSMENT OF THORIUM IN MALAYSIAN MONAZITE PROCESSING
(Pengasingan
dan Penilaian Impak Radiologi Torium dalam Pemprosesan
Monazit di
Malaysia)
Wadeeah M.
Al-Areqi*, Che Nor Aniza Che Zainul Bahri, Amran Ab. Majid, Sukiman Sarmani
Nuclear
Science Program, School of Applied Physics,
Faculty
of Science and Technology,
Universiti
Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia
*Corresponding author: walareqi@yahoo.com
Received: 2
November 2015; Accepted: 6 April 2016
Abstract
The processing of
mineral monazite to produce thorium (Th) and rare earth elements may create a radiological
impact if the processing and residue are not properly or safely managed.
Malaysian Atomic Energy Licensing Board (AELB) categorized monazite as a radioactive
material because the concentration of thorium in the mineral is higher than 1Bq/g.
Therefore, the current study aimed to determine the separation percentage of thorium
from Malaysian monazite and to assess the radiological impact of thorium during
various stages involved in the processing. In this study, monazite was digested
by hot sulphuric acid followed by selective precipitation of thorium using
ammonia. Neutron Activation
Analysis (NAA) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) techniques were used to determine thorium. The
result of the study showed that the average concentration of thorium in
Malaysian monazite ore was 17,990.5 ± 1,239.3 ppm. After digestion, 46.56 % of thorium was
recovered and about 97.68 % of thorium was separated as thorium hydroxide from
the obtained sulphate leach solution. The study also indicated that less than
3% of Thorium entered in the rich rare earth elements filtrate during the
separation. The calculated maximum dose that could be received by workers and
public from the monazite ore were 61.91 ± 4.27 mSv/y and 54.24 ± 3.73 mSv/y
respectively. However, during the processing of 25 g the monazite ore, the
worker and public will receive a lower dose in the range of 0.01 – 0.72 and 0.01 – 0.63mSv/y respectively. Based
on the results, useful suggestions on how to improve thorium recovery and how
to minimize the radiological impact as a whole are provided.
Keywords: thorium, monazite, radiological
impact, separation, dose
Abstrak
Pemprosesan
mineral monazit untuk menghasilkan torium (Th) dan unsur nadir bumi boleh menyebabkan
impak radiologi sekiranya pemprosesan dan residu tidak diuruskan dengan baik. Lembaga
Perlesenan Tenaga Atom Malaysia (AELB) telah mengkategorikan monazit sebagai bahan
beradioaktif kerana kepekatan torium dalam mineral adalah tinggi iaitu melebihi
1Bq/g. Oleh itu, tujuan utama kajian ini adalah untuk menentukan peratus pengasingan
torium daripada bijih monazit dan menilai impak radiologi torium dalam beberapa
peringkat yang terlibat dalam pemprosesan. Dalam kajian ini, asid sulfurik telah
digunakan untuk menghadam monazit dan diikuti dengan pemendakan terpilih torium
menggunakan ammonia. Teknik Analisis Pengaktifan Neutron (NAA) dan Induktif
Plasma Pendua – Spektrometri Jisim (ICP-MS) telah digunakan untuk menentukan kandungan
torium. Hasil kajian menunjukkan purata kepekatan torium dalam bijih monazit
Malaysia adalah 17,990.5 ± 1,239.3 ppm. Selepas penghadaman, peratus mendapatkan
torium adalah 46.56 % dan 97.68 % torium telah diasingkan sebagai torium hidroksida
daripada larutan larut lesap sulfat. Kajian juga menunjukkan kurang daripada 3 %
torium terdapat dalam turasan unsur nadir bumi semasa pengasingan. Dos maksimum
yang boleh diterima oleh pekerja dan orang awam daripada bijih monazit telah
dikira dan masing – masing adalah 61.91 ± 4.27 mSv/y dan 54.24 ± 3.73 mSv/y.
Walau bagaimanapun, semasa pemprosesan bijih monazit, pekerja dan orang awam akan
menerima dos yang rendah iaitu masing – masing dalam julat 0.01 – 0.72 dan 0.01
– 0.63mSv/y. Berdasarkan hasil kajian ini, cadangan penambah baikan dalam
mendapatkan torium dan bagaimana untuk meminimumkan impak radiologi secara
menyeluruh dapat disediakan.
Kata kunci:
torium, monazit, impak radiologi, pengasingan, dos
References
1.
Pontedeiro, E. M., Heilbron, P. F. L and Cotta, R. M. (2007).
Assessment of the mineral industry NORM/TENORM disposal in hazardous landfills.
Journal of Hazardous Materials, 139: 563 – 568.
2.
Omar, M. (2010). NORM processing in Malaysia: An
overview nuclear Malaysia/L/2010/11.1
3.
Al-Areqi, W. M, Ab. Majid, .A. and Sarmani, S. (2015). Thorium:
Issues and prospects in Malaysia. AIP conference proceedings 1659: 1 – 7.
4.
IAEA. (2011). Radiation protection and safety of
radiation sources: International basic safety standards, GSR Part 3.Access
online http://www-pub.iaea.org/MTCD/publications/PDF/Pub1578_web-57265295.pdf
5.
The Atomic Energy Licensing (Radioactive Waste
Management) Regulations (2011).
http://www.ecolex.org/details/legislation/atomic-energy-licensing-radioactive-waste-management-regulations-2011-lex-faoc107766/
6.
The Academy of Sciences Malaysia (2013). Revitalising
of rare earth mineral programme in Peninsula Malaysia as a strategic industry,
The Academy of Sciences Malaysia (ASM) study report 1/2013.
7.
Radiological impact assessment (2011). Radiological
impact assessment of Lynas Advanced Materials Plant 2011: Executive Summary.
Access online 4 November 2011.
8.
Al-Areqi, W. M, Ab. Majid, A. and Sarmani, S. (2014).
Digestion study of water leach purification (WLP) residue for possibility of
thorium extraction. Malaysian Journal of Analytical Sciences, 18(1): 221
– 225.
9.
Al-Areqi, W. M, Ab. Majid, A. and Sarmani, S. (2014).
Separation of thorium (IV) from lanthanide concentrate (LC) and water leach
purification (WLP) residue. AIP conference proceedings 1614: 482.
10.
Vijayalakshmi, R., Mishra, S. L., Singh, H. and Gupta,
C. K. (2001). Processing of xenotime concentrate by sulphuric acid digestion
and selective thorium precipitation for separation of rare earths. Hydrometallurgy,
61: 75 – 80.
11.
Crouse D. J. and Brown K. B. (1959). Recovery of
thorium, uranium, and rare earths from monazite sulfate liquors by amine
extraction (AMEX) process, USA: Oak Ridge National Laboratory, pp 5 – 66.
12.
Wang L., Y. Yu, X. Luang, Z. Long and D. Cui. (2013).
Toward greener comprehensive utilization of bastnaesite: Simultaneous recovery
of cerium, fluorine, and thorium from bastnaesite leach liquor using HEH(EHP) .
Chemical Engineering Journal, 215-216: 162 – 167.
13.
Amaral, J.C.B.S. and Morais, C. A. (2010).Thorium and
uranium extraction from rare earth elements in monazite sulphuric acid liquor
through solvent extraction. Minerals Engineering, 23:498 – 503.
14.
Wickleder, M. S. Fourest, B. and Dorhout, P. K. (2010).
The chemistry of the actinide and transactinide Elements, Chapter three:
Thorium pp 52.
15.
Ali, A. M. I, El-Nadi, Y. A, Daoud, J. A. and Aly, H. F.
(2007). Recovery of thorium (IV) from leached monazite solutionsusing
counter-current extraction. International Journal of Mineral Processing,
8: 217 – 223.
16.
Hughes, K. C. and Singh, R. (1980). The isolation of
thorium from monazite by solvent extraction. Hydrometallurgy, 6: 25 – 33.
17.
Balakrishna, P., Varma, B. P., Krishnan, T. S., Mohan,
T. R. R. and Ramakrishnan, P. (1988). Thorium oxide: calcination, compaction
and sintering. Journal of Nuclear Materials, 160: 88 – 94.
18.
Abrao, A., Alves de Freitas, A. and Sequeira de
Carvalho, F. M. (2001). Preparation of highly pure thorium nitrate via thorium
sulfate and thorium peroxide. Journal of Alloys and Compounds, 323–324:
53 – 56.
19.
UNSCEAR (2000). Sources and effects of ionizing
radiation. united nations scientific committee on the effects of atomic
radiation. Report to the general assembly with annexes. United Nations
Publication, New York.
20.
IAEA
(2011). Radiation protection and NORM residue management in the production of
rare earths from thorium containing minerals, Safety reports series No. 68.
21.
Cardarelli,
F. (2008). Materials Handbook: A Concise Desktop Reference, 2nd Edition.
22.
Zhu, Z.,
Pranolo, Y. and Cheng, C. Y. (2015). Separation of uranium and thorium from
rare earths for rare earth production – A review. Minerals Engineering, 77:
185 – 196.