Calculated Reduction of the Residual Adsorbent Mass Requiring Long-Term Storage in Radioactive Waste Processing by Magnetic Separation

This paper describes the uptake of plutonium, ²³⁸Pu, by an adsorbent consisting of Brimac 216 natural carbon, a type of bone char. A strongly magnetic Brimac 216 fine powder produced by Lidzey has been shown to be an excellent adsorbent for many radionuclides. After the adsorption of the radionuclides has taken place, from solution onto the magnetic Brimac 216 powder, the powder, together with the adsorbed radionuclides, can be rapidly removed from suspension, as a concentrate, using high gradient magnetic separation (HGMS). A comparison is drawn between experimental results using the conventional column filter, with bone char as the adsorbent medium, and calculations for the HGMS process to treat 3.22 m³ of solution containing 8 mgl^-1 of ²³⁸Pu and to remove the ²³⁸Pu from the suspension to reduce the effluent to less than the maximum concentration limit (MCL) for ²³⁸Pu, which is 0.74 Bql^-1; however, the minimum concentration value used here is less than the MCL and is 0.0444 Bql^-1 (7.006 × 10^-14 gl^-1 of ²³⁸Pu) and is denoted as the lower concentration level. Calculations indicate that HGMS is considerably faster than the column filtration method. This leads to a significant reduction in the time required to process the solution, even though the HGMS process is repeated a number of times. Also, the mass of adsorbent requiring long-term storage is much smaller for HGMS than for the column filtration method.