Efficiency of Gypsum as a Capping Material for the Capturing of Phosphorus Release from Contaminated Lake Sediments
Lab-scale batch experiments using several 150-L transparent acrylic reactors were conducted to develop optimum capping materials that can capture phosphorous released from polluted lake sediments. The sediment used in the experiment was very fine clay (7.7 Φ in mean grain size), and organic carbon (Corg) content was as high as 2%. Four kinds of batches with different capping materials; powdered-gypsum (CaSO4·2H2O), granular-gypsum, sand, composite material (gypsum+sand), and one control batch were operated for 45 days. Phosphorous fluxes released from bottom sediments in the control batch were estimated to be 4.3 mg·m-2·d-1, while 0.9 mg·m-2·d-1, 1.0 mg·m-2·d-1, 2.2 mg·m-2·d-1, and 0.5 mg·m-2·d-1 in the batch capped with powdered-gypsum, granular-gypsum, sand, and composite material, respectively. The results obtained from lab-scale batch experiments show that there were 80% reduction of phosphorous for some materials such as powdered-gypsum, granular-gypsum, and composite material, whereas sand only about 50%. Increase in apatite-P fraction (48% → 80%) in the gypsum batches, compared to the control batch, indicates that abundant Ca2+ and SO4 2- ions from the gypsum added into oxygen-depleted sediment surface might have supplied abundant oxygen by reducing the sulfate ions very actively, resulting in Ca-P precipitates.
Hyungsun Kim, Junichi Hojo and Soo Wohn Lee
S. K. Kim et al., "Efficiency of Gypsum as a Capping Material for the Capturing of Phosphorus Release from Contaminated Lake Sediments", Materials Science Forum, Vols. 544-545, pp. 561-564, 2007