Interception of phosphorus release from sediment by magnetite/lanthanum carbonate co modified activated attapulgite composite: Performance and mechanism

The release of phosphorus from sediment and the high concentration of phosphorus in the water environment make the water body continuously eutrophic, so it is very important to develop new phosphorus removal materials to reverse the eutrophication of river and lake. In this study, the effect and mechanism of magnetic lanthanum carbonate modified attapulgite (MT-LCMT) prepared by co-precipitation in fixed water and prime phosphorus were studied. The results showed that MT-LCMT had excellent magnetic hysteresis performance and its maximum model adsorption of phosphate could reach 51.69 mg/g. The phosphate adsorption process mainly followed the co-kinetics of intraparticle diffusion and membrane diffusion and conformed to the Redlich-Peterson model and Sips model. After five adsorption-desorption cycle experiments, MT-LCMT exhibited stable adsorption and regeneration properties, which may also be used for the removal of phosphate from actual water bodies. The experiment of exploring the factors affecting the adsorption of phosphate by MT-LCMT shows that the adsorption capacity of phosphate is the highest when the pH is between 3 and 8, and the existence of HCO3-, CO32- and humic acid reduce the adsorption capacity of phosphate. The binding mechanism of MT-LCMT to orthophosphate involves coordination exchange, precipitation and electrostatic attraction. MT-LCMT capping can significantly reduce the risk of sediment releasing mobile phosphorus (Mobile-P), bioavailable phosphorus (BAP), overlying water dissolve reactive phosphorus (DRP) and available phosphorus with medium diffusion gradient in thin film (DGT-P) to the overlying water, and the unstable phosphorus (NH4Cl-P and BD-P) of surface sediment are converted into stable phosphorus (HCl-P and NaOH85-P). The above results indicated that MT-LCMT had a high potential to be used as an active capping material for managing phosphorus loads inside surface water bodies and substrates.