Novel, recyclable active capping systems using fabric-wrapped zirconium-modified magnetite/bentonite composite for sedimentary phosphorus release control

August 10, 2020

Shanghai Ocean University use EasySensor DGT devices and HR-Peeper publish the article as below:


A zirconium-modified magnetite/bentonite composite (M-ZrFeBT) was synthesized, characterized and combined with water-permeable fabric to construct novel, recyclable active capping systems for sedimentary phosphorus (P) release control. Three fabric-wrapped M-ZrFeBT capping devices with different shapes were designed,
i.e., CAP-1, CAP-2 and CAP-3, and they are disc-shaped, cuboid-shaped and spindle-shaped capping devices, respectively. The behavior and mechanism for phosphate adsorption onto M-ZrFeBT was studied. The impact of
CAP-1, CAP-2 and CAP-3 capping on the mobilization of P in sediments was investigated. The results showed
that M-ZrFeBT possessed good phosphate adsorption ability, with a largest monolayer adsorption capacity of
8.02 mg P/g. The replacement of Fe/Zr bound hydroxyl groups with phosphate through ligand-exchange reactions to generate the inner-sphere Fe-O-P and Zr-O-P bonding played a key part in the uptake of phosphate
from water by M-ZrFeBT. Sediment capping with fabric-wrapped M-ZrFeBT not only brought about a significant
decline in the concentrations of soluble reactive P (SRP) and DGT (diffusive gradient in thin films)-labile P (LPDGT)
in the overlying water, but also gave rise to the diminished SRP and LPDGT concentrations in the upper sediment.
Most (96.5%-98.2%) of P bound by the M-ZrFeBT in the capping layers was in the form of NaOH extractable inorganic P, HCl-extractable P and residual P, which were considered to be hard to be released back into the water
column under common pH and oxygen-deficient conditions. The reduction of pore water SRP and LPDGT in the
upper sediment layer induced by the adsorption of SRP on the M-ZrFeBT-based capping layer played a key part in the interception of SRP liberation from the sediment solid into the overlying water. Results indicate that
fabric-wrapped M-ZrFeBT capping is promising for controlling the internal P loading from sediments in shallow
freshwater bodies.

Writers: Jianwei Lin⁎, Yan Wang, Yanhui Zhan