Comparison of the Control of Sedimentary Phosphorus Release Using Zirconium-, Lanthanum-, and Lanthanum/Zirconium-Modified Zeolites as Sediment Amendments

Abstract

In this study, the adsorption characteristics of phosphate on zirconium-modified zeolite (ZrMZ), lanthanum-modified zeolite (LaMZ) and lanthanum/zirconium-modified zeolite (LaZrMZ) were comparatively investigated, and the effect of ZrMZ, LaMZ, and LaZrMZ addition on the mobilization of phosphorus (P) in sediments was comparatively studied. Results showed that the phosphate adsorption capacity decreased in the order of LaZrMZ > LaMZ > ZrMZ. The addition of LaZrMZ, LaMZ, and ZrMZ in sediments all could effectively reduce the concentrations of soluble reactive P (SRP) in the overlying and pore waters. Furthermore, the addition of LaZrMZ, LaMZ and ZrMZ all could decrease the amount of mobile P in sediments, and the reduction rate decreased in the order of LaMZ > LaZrMZ > ZrMZ. The amendment of sediments with LaZrMZ, LaMZ, and ZrMZ all could lead to a decrease in the amount of water-soluble P (WSP), algal available P (AA-P) and iron oxide-filter paper extractable P (FeO-P) in the sediments. The reduction rate of WSP and AA-P decreased in the order of LaMZ > LaZrMZ > ZrMZ, and the reduction rate of FeO-P decreased in the order of LaZrMZ > ZrMZ > LaMZ. The addition of LaZrMZ and LaMZ both could reduce the content of readily desorbed P (RDP), and the reduction rate decreased in the order of LaMZ>LaZrMZ. The LaZrMZ and ZrMZ amendments both could decrease the concentration of NaHCO3 extractable P (Olsen-P) in sediments, and the reduction rate decreased in the order of LaZrMZ>ZrMZ. The results of this study demonstrate that the addition of ZrMZ, LaMZ, and LaZrMZ in sediments all could effectively intercept the upward mobilization of sedimentary P to the overlying water, and LaZrMZ is a very promising amendment for the control of the internal P loading from the point of view of both phosphate adsorption ability and bioavailable P immobilization efficiency.