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.

 




Previous                    Content                    Next