Few studies have sought to investigate the potential for dissolved organic matter (DOM) to bind (and thus potentially transport) radionuclides under the high pH regimes that are expected in cementitious disposal. We have used equilibrium dialysis to investigate uranyl binding to humic acid over a pH range of ∼10 to 13. The experimental results provide evidence that DOM can bind uranyl ions over this pH range, including in the presence of competing ions. There is a general decrease in binding with increasing pH, from ∼80% of total uranyl bound at pH 9.8 to ∼10% at pH 12.9. Modelling of the system with WHAM/Model VII can yield representative results up to pH ∼10.5.
