Use of lanthanum/aluminum co-modified granulated attapulgite clay as a novel phosphorus (P) sorbent to immobilize P and stabilize surface sediment in shallow eutrophic lakes

It is crucial to develop a phosphorus (P) sorbent to immobilize sediment mobile P from shallow eutrophic lakes with frequent sediment resuspension and high pH values. In this study, lanthanum (La) and aluminum (Al) were co-incorporated into granulated thermally treated calcium-rich attapulgite (TCAP) to prepare a novel P sorbent to overcome these problems in eutrophic lake management. The maximum P sorption capacity of the La/Al comodified TCAP (LA@TCAP) is 10.6 mg/g, and the granulated P sorbent performs well in a wide range of pH values during sorption from solution. A total of 124 days of sediment incubation study (34 days of aerobic incubation and 90 days of anaerobic incubation) indicated that more than 50% of the soluble reactive phosphorus (SRP) in overlying water can be reduced with the theoretical dosage in comparison with the control treatment. More than 40% of P flux across the sediment-water can be reduced with a theoretical dosage, and 60% of the mobile fraction of P in surface sediment can be reduced and transformed into stable inert P fractions such as NaOH-rP (Al-P) and HCl-P (Ca-P) during the whole period of incubation. Results also indicated that the granule LA@TCAP can stabilize surface sediment and thus reduce suspended solids, SRP, and TP in a water column in simulated frequent sediment resuspension when compared with traditional P sorbent (aluminium sulfate). Furthermore, the inactivated P forms in sediment remained relatively stable under elevated pH values. XPS analysis indicated that P sorbed by LA@TCAP mainly formed by inner-sphere complexation with Al and La. All results of this study indicate that LA@TCAP has the potential for sediment P remediation from shallow eutrophic lakes.