Study Tour

In the radionuclide laboratory of Eurofins IAF-Radioökologie GmbH, another RENO-TITAN partner, NORM residues from Vietnamese titanium mining were incorporated into Portland cement and geopolymer mortar. Key questions included: Can both binders retain radionuclides from the uranium and thorium decay series against leaching? Which formulations offer reliable immobilization of the radionuclides? What advantages and disadvantages emerge?

Portland cement is available worldwide, inexpensive, and forms a dense, alkaline matrix. Geopolymers, on the other hand, offer high chemical resistance and temperature resistance, but require more expensive raw materials, stricter occupational safety measures, and more precise process control.

A heavy mineral sand concentrate from the Vietnamese coastal region, consisting predominantly of ilmenite and zircon, served as the demonstration material. Radiological characterization revealed an equilibrium within the decay series of uranium-238 and thorium-232, with the specific activity of the nuclides in both decay series being approximately 1,500 Bq/kg. Between 9 and 20 percent of this concentrate was added to the binder and formed into cubes to immobilize the residue in a stable matrix.

To test long-term stability, the samples were stored for twelve weeks under various conditions: in water at room temperature and at 60 °C, in a slightly acidic environment (pH 4), and in wet-dry and freeze-thaw cycles. Subsequent elution tests showed that both samples remained robust, exhibited no mass loss or damage, and that radionuclide release was below the WHO's recommended guideline values ​​and the parameter values ​​of the German Drinking Water Ordinance in all cases. In contrast, the unimmobilized concentrate released significantly more radionuclides—in some cases exceeding the aforementioned guideline and parameter values, particularly radium-228, polonium-210, and lead-210. Incorporation into a binder thus considerably reduced the release.

The formulations with up to 20% residue by mass functioned reliably. Portland cement achieves good retention at lower costs and with easier procurement. Geopolymers prove particularly effective when special requirements for chemical resistance or temperature resistance are required. Both methods are suitable as safe pretreatments before landfilling and, after further testing, could enable material recycling in construction products. This is doubly interesting for Vietnam: it offers controlled binding of NORM residues and the option of replacing scarce construction sand with alternative aggregates.