Sorption-desorption column tests to evaluate the attenuation layer using soil amended with a stabilising agent

Sorption-desorption column tests using acrylic columns (ϕ 5 cm × h10 cm) were employed to evaluate the sorption performance of an attenuation layer against geogenic contamination. The attenuation layer material was silica sand amended with 1, 5, or 10% of a stabilising agent. The main component of the agent was magnesium oxide. The sorption behaviour of the materials was determined by a fluoride solution (C0 = 80 mg/L F-), while the desorption behaviour was determined by distilled water. Breakthroughs (C/C0 > 0.05) occurred after approximately 1, 20, and 50 PVF for stabilising agent contents of 1, 5, and 10%, respectively. The one-dimensional advection-dispersion equation modelled the breakthrough curves obtained from the tests. The predictions gave unrealistic estimates, especially for the breakthrough point where C/C0 = 0.05. For the 1% agent content, approximately 20% of the sorbed mass, Ss, was desorbed, but the percentage of desorbed mass, Sd, was much smaller for the higher agent contents. The difference between the sorbed and desorbed masses was defined as the immobilised fraction, Ss- Sd. For the 5% agent content, Ss − Sd = 4.0 mg/g. The results suggest that when silica sand is amended with magnesium oxide as an agent, the mixture can immobilise the fluoride in the attenuation layer.