Environmental assessment of red mud by determining natural radionuclides using neutron activation analysis

Bauxite residues (red mud) produced by digestion of bauxite ore during the production of alumina contain naturally occurring radionuclides such as ²³⁸U, ²³²Th and ⁴⁰K and toxic elements such as Al, Cr, Co, Mn and Ni. In this research, red mud collected from Eti Seydisehir Aluminium Plant in Turkey was studied to determine the concentration of natural radionuclides for evaluating their radiological effects. Short-term leaching tests of radionuclides were performed by Toxicity Characteristic Leaching Procedure (TCLP)-1311 method to assess in terms of their environmental impact. Furthermore, self-attenuation factors were experimentally determined using radioactive point sources with two different amounts to ascertain how gamma rays are attenuated in the residue depending on the energy and the volume of residue. The activity concentrations of ^234,235,238U, ²³²Th and ⁴⁰K in red mud and leachate samples were determined by neuron activation analysis and Compton suppression methods. The method was tested using NIST (National Institute of Standards and Technology) 1632d and 2709a reference materials. It can be concluded from the results of leaching tests that natural radionuclides may not easily be mobile under environmental conditions and the mobility of the radionuclides depends on the pH value of water and contact time with the water. The activity concentration index which is the most commonly used calculation method was applied to the samples and the results showed that the reuse of red mud as a secondary raw material may not be hazardous depending on the percentage of utilization of it.