This study investigated the efficacy of using phosphate-modified zeolite (PZ) as an adsorbent for removing thorium from aqueous solutions. The effects of various factors such as contact time, adsorbent mass, initial thorium concentration, and pH value of the solution on the removal efficiency were analyzed using the batch technique to obtain optimum adsorption condition. The results revealed that the optimal conditions for thorium adsorption were a contact time of 24 h, 0.03 g of PZ adsorbent, pH 3, and a temperature of 25 °C. Isotherm and kinetics parameters of the thorium adsorption on PZ were also determined, with equilibrium studies showing that the experimental data followed the Langmuir isotherm model. The maximum adsorption capacity (Qo) for thorium was found to be 17.3 mg/g with the Langmuir isotherm coefficient of 0.09 L/mg. Using phosphate anions to modify natural zeolite increased its adsorption capacity. Furthermore, adsorption kinetics studies demonstrated that the adsorption of thorium onto PZ adsorbent fitted well with the pseudo-second-order model. The applicability of the PZ adsorbent in removing thorium from real radioactive waste was also investigated, and nearly complete thorium removal was achieved (> 99%) from the leached solution obtained from cracking and leaching processes of rare earth industrial residue under optimized conditions. This study elucidates the potential of PZ adsorbent for efficient removal of thorium from rare earth residue via adsorption, leading to a reduction in waste volume for ultimate disposition.
The study aims to assess long-term radiological exposure risks and effects to both industrial workers and occupants living in the near vicinity of local tailing processing plants. The detrimental effects of licensing exemption were studied by comparing contaminated soil collected from 7 unlicensed-by the Atomic Energy Licensing Board-tailing processing plants with soil from control location. It was found that the average concentration of 226Ra, 232Th, and 40 K for all seven processing plants fell between the range of 0.1 ± 0.0-7.21 ± 0.1 Bqg-1, 0.1 ± 0.0-16.34 ± 0.27 Bqg-1, and 0.18 ± 0.01-1.74 ± 0.01 Bqg-1, respectively, showing observable indication of soil contamination with Technologically Enhanced Naturally Occurring Radioactive (TENORM) material. The annual effective dose was calculated which showed that most samples exceeded the recommended value of the ICRP of 1 mSvy-1 for non-radiation workers. Assessment of radiological hazards in the environment was done by calculating the radium equivalent value; revealing the exposure risk posed by the contaminated soil is substantial. Using the relatable inputs, the RESRAD-ONSITE computed code revealed that the dose due to internal exposure via inhalation of radon gas contributes the most to the overall exposure. The covering of the contaminated soil with a clean layer is effective in reducing external dose but ineffective for radon inhalation. RESRAD-OFFSITE computer code also revealed that the contribution of exposure via contaminated soil in the neighbouring vicinity is below the recommended 1 mSvy-1 threshold but still contributes to a significant amount cumulatively when considering other exposure pathways as well. The study proposes the introduction of clean cover soil as a viable option in reducing external dose from contaminated soil as 1 m of clean cover soil is able to reduce dose exposure by 23.8-30.5%.