Sediment phosphorus immobilization with the addition of calcium/aluminum and lanthanum/calcium/aluminum composite materials under wide ranges of pH and redox conditions

Aquatic environment factors often influence and regulate the direction of phosphorus (P) flow at the sediment-water interface (SWI). High pH and low DO, common in eutrophic lakes, would induce large releases of P from sediment, and thus cause the negative effect on the efficiency of some P-passivators. Hence, the development of P passivators that could function over a wide range of pH condition and redox state in the overlaying water with reduced undesirable side effects is critical for the eutrophic lake remediation. In the present study, a calcium (Ca)/aluminum (Al) composite (CA) and a lanthanum (La)/Ca/Al composite (LCA) were prepared for P immobilization in lake sediments, using calcium and lanthanum coprecipitated with aluminum. CA and LCA were shown to have good P sorption performance at pH 4-11, particularly at pH 8-11. Furthermore, CA and LCA have an ability to correct the pH of water that deviates from neutral. The maximum P adsorption (Qmax) of sediment amended by 4 % CA and 4 % LCA increased by 83 % and 103 %, and their equilibrium P concentration (EPC0) decreased by 76 % and 88 %, respectively. Under various pH and DO conditions, the P concentration in overlying water was significantly decreased by CA and LCA amendment, and their addition could effectively counteract the P release from sediments induced by high pH and low DO. The mechanisms of P immobilization in amended sediments under various pH and DO levels are primarily the conversion of reactive P to stable P. The P immobilization performance of CA and LCA could cope with a wide range of pH and redox conditions in eutrophic lakes, and they would help to correct extreme pH values, thus they are expected to be a new generation of commercial P-passivators.