MnO2 Resin is one of the new products we launched in 2005. It’s first application, the separation of Ra in water samples, was developed and published by Moon, et al.1 The next few paragraphs highlight their work.
Different parameters such as pH, reaction time, resin quantity, salt effect and flow rate have been evaluated when separating Ra from water using MnO2. For most of the experiments, Ba-133 was used as tracer for Ra.
According to Figure 1, MnO2 Resin shows the greatest affinity for Ba-133 when the pH of the solution is between 4 and 8.
The higher the salt content of the water, the slower the kinetics of Ba (or Ra) uptake. (figure 2). The equilibrium is reached after 15 minutes of contact for samples with a salt content between 0 and 0.02%, whereas 25 minutes are required when the water contains 0.35% salt. For waters which composition is similar to seawater (3.5% salts), the equilibrium is reached in 90 minutes.
The batch uptake of radium and barium by the MnO2 Resin from deionised water and seawater have been studied and found comparable. The data in Figure 3 indicates equivalent uptake by the resin under the two conditions of deionized water and seawater at 1 gram resin per liter of water.
The recovery of Ba-133 and Ra-228 with respect to flow rate has been studied for 2 types of waters : deionised and artificial seawater. For salt water, the flow rate must not exceed 20mL/min, otherwise a loss in recovery of 30% may be observed. Additionally the chemical recoveries of Ba and Ra start to differ from each other, Ba-133 can thus no longer be considered as a chemical homologue, making it’s use as an internal standard undesirable.
The MnO2 resin is currently used with Ln Resin and DGA, Normal Resin in a method developed by Sherrod Maxwell2 of Westinghouse Savannah River.. It is used to pre-concentrate Ra from 1 to 1.5L water samples. 1.25 g/L of MnO2 resin is used per sample. The sample is initially stabilized at pH 6-7 and 25 mg Ca are added per liter. The sample is then loaded onto MnO2 Resin with a flow rate of about 15 mL/min. Ra is eluted with 15mL 4M HCl/1.5% H2O2. The 15 mL solution are, left a minimum of 36 hours for Ac-228 ingrowth before being loaded onto 2 cartridges stacked on top of each other : LN Resin (retention of U and Th) and DGA, Normal Resin (retention of Ac-228). Ac-228 is eluted from DGA resin with 10 mL 0.5M HCl, then micro-precipitated with CeF3 on Resolve™ Filter. This method is currently under validation in our laboratory.
(1) Moon D.S., Burnett W.C., Nour S., Horwitz P., Bond A., Applied Rad. Isot.., 59, 255 (2003).
(2) Maxwell, S.L., presented at Eichrom’s North American Users’ Meeting, Oak Ridge, TN, May 3, 2005