Composite colloid action in Sr sorption by granite fracture filling materials

During geological disposal of radioactive waste, sorption of nuclide at solid-liquid interface is important for the safe disposal of nuclear waste. Granite fracture filling materials at high-level waste disposal site were examined for Sr sorption in batch experiments and by microscopic characterization. The way by which humic acid colloid and goethite colloid combine to form organic-inorganic composite colloid was found to mainly depend on ligand exchange reaction between hydroxyl group in goethite colloid and carboxyl group in humic acid colloid. The composite colloid was found to be dominated by goethite colloid, with humic acid attached to its surface. Effect of pH and solid-liquid ratio on Sr sorption from composite colloid was examined. Fitting isothermal sorption equation with initial Sr concentrations revealed that sorption was monolayer and reaction was fast. This work provides some understanding of Sr sorption in the treatment of radioactive wastes.