SEPARATION AND RADIOLOGICAL IMPACT ASSESSMENT OF THORIUM IN MALAYSIAN MONAZITE PROCESSING

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.