Introducing hydrate aluminum into porous thermally-treated calcium-rich attapulgite to enhance its phosphorus sorption capacity for sediment internal loading management

Solid-phase P sorbents are increasingly used in shallow eutrophic lakes for sediment internal loading management due to their strong ability to resist frequent resuspension. In this study, hydrate aluminum was incorporated into porous thermally-treated calcium-rich attapulgite (TCAP) to enhance its P sorption capacity for sediment internal P loading management. Batch studies indicated that 2 mol/L of aluminum modified TCAP (Al@TCAP) has the optimal P sorption performance and was well characterized. The maximum P sorption capacity of Al@TCAP with particle sizes 1-2 mm increased to 8.79 mg P/g at a pH of 7, which was nearly 2 times that of TCAP. P sorption on Al@TCAP performs well when the solution pH is in the range of 4-10, but efficiency decreases sharply when the solution pH exceeds 11. The co-existing ions including SO42−, Cl−, NO3−, and HCO3− that are frequently found in eutrophic lake waters have little effect on P sorption of Al@TCAP. Laboratory experiments showed that adding Al@TCAP does not cause pH changes in overlying water. An average P reduction of 59.7 to 72.5% in overlying water was recorded during the experiment's 63 days of aerobic and anaerobic incubation. Mobile P in surface sediment (0-2 cm) was significantly reduced and was accompanied by an evident Al-P increase and a moderate Ca-P increase in sediment when compared to the control treatment. This was further confirmed by 31P solid-state NMR and XPS spectroscopy analysis, which indicated that P bound by Al@TCAP was mainly through formation of the Al-P complex. All results indicate that Al@TCAP can be used in eutrophic lake for sediment internal P loading management.