Application of zeolite/hydrous zirconia composite as a novel sediment capping material to immobilize phosphorus

A unique sediment-capping agent consisting of a zeolite/hydrous zirconia composite (ZHZ) was developed and tested for P-immobilization in the overlying water and sediment cores from a freshwater pond. In the ZHZ, NaP1 zeolite was covered with hydrous zirconia, which existed as an amorphous phase. Experimental results in pond water indicated that ZHZ could efficiently remove soluble reactive phosphorus. The 28-day sediment incubation experiments showed that capping sediment with ZHZ resulted in a more efficient, rapid and sustained decrease in P concentration when compared with the traditional alum treatment method. Furthermore, ZHZ increased the sediment stability, resulting in the lowest turbidity, total phosphorus and soluble reactive phosphorus concentrations in overlying water following artificially induced resuspension of sediment. Phosphorus fractionation of sediment showed that the dominant P form transferred from HCl-extractable P to residual P, and the most release-sensitive P (labile P and reductant reactive P) was decreased after ZHZ application. Overall, ZHZ is a highly effective P-immobilization material. ZHZ has high potential as a sediment capping material to control internal P loading in eutrophic water bodies.