Effects of clay minerals on the transport of perfluorooctanoic acid in saturated porous media

Abstract

We examined the effects of representative clay minerals, montmorillonite (M) and kaolin (K), on perfluorooctanoic acid (PFOA) transport under saturated conditions. Results showed that low amounts of M or K addition increased and high addition amounts reduced PFOA retardation in quartz sand during the transport. With increasing addition of clay minerals (0-50%, weight ratio), the retardation factor of the M-added system increased from 1.03±0.00 to 1.31±0.03 and then decreased to 0.72±0.06, while that of the K-added system increased to 1.30±0.02 and then decreased to 0.49±0.11. Results of the tracer experiment showed that low amount of M or K addition did not produce preferential flow, while high amount addition induced obvious preferential flow, which resulted in the decrease in PFOA retardation. In addition, due to limitations of the highly negative-charged surface of the M or K modified sand and the solid-liquid ratio of column experiment, the modified M or K sand had low adsorption capacity of PFOA and thus almost did not affect PFOA retention. However, the adsorption and desorption of PFOA by clay minerals might still be responsible for the increases in PFOA retardation with low amount of M or K addition. The results are of great significance for accurately assessing the transport process and eco-environmental risks of PFOA in soil-groundwater systems.