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
AbstrakPemprosesan 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...
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