Study On The Effect Of Layered Double Hydroxide(LDH) On Soil Phosphorus Migration

Phosphorus pollution poses an increasingly serious threat to the natural environment and human health.The problems of eutrophication and non-point source pollution caused by the accumulation of high concentrations of phosphorus in the environment have aroused great concern.Therefore,studying the absorption,desorption,migration and transformation of phosphorus in soil and its mechanism of action have a profound impact on the protection of environmental issues such as soil phosphorus loss.Layered double hydroxide?LDH?has been widely used in water body phosphorus removal technology system due to its excellent adsorption performance.This paper takes LDH and phosphorus as research objects and soil as research medium,and evaluates the effects of LDH on phosphorus adsorption and migration mechanism in soil.Provide scientific basis and theoretical support for soil phosphorus loss control and slow-release potential.In this paper,Muyang sand soil is selected as the soil medium.Use indoor soil column leaching experiments to conduct research on the migration and interaction of LDH and phosphorus in soil media,and to clarify different rainfall conditions?such as intermittent rainfall,changes in ionic strength and ionic types,etc.?and different background systems?leaching velocity,soil physicochemical Changes in properties,carbonate exchange,etc.?The mechanism of phosphorus adsorption,desorption,migration,and remigration in LDH-added soil.The main findings are as follows:?1?With the addition of LDH to soil?1%,2%;With the increase of mass fraction?,the penetration curve of phosphorus in the soil shows obvious hysteresis,and the retention of phosphorus in the closure curve increases correspondingly.Due to the particularity of LDH structure,more adsorption sites are provided for the migration of phosphorus in the soil.Through electrostatic attraction,ion exchange,surface complexation and other forces,the migration ability of phosphorus in the soil is reduced,and the migration and solidification of phosphorus is realized.?2?Compared with the Ca²⁺in the background solution,the adsorption amount of phosphorus in the soil was 3.9-12.2%higher with or without the addition of LDH.At the same time,in the process of increasing K⁺intensity from 1 mol/L to 100 mol/L,the penetration curve showed a tendency of first lagging and then returning.The level and strength of ions affect the migration of phosphorus.Ca²⁺can react with phosphate to form metastable minerals and reduce the outflow rate of phosphorus in soil.At the same time,Ca²⁺enhanced the adsorption capacity of soil and LDH through local cation bridging,thus increasing the adsorption capacity of phosphorus.K⁺strength is within a certain range,and the adsorption of phosphorus is a promoting effect.Later,electrostatic repulsion reduces the adsorption effect of phosphorus,and the above changes occur in the penetration curve.?3?At different leaching flow rates?5,9 rpm?,0.5%LDH of mass fraction was added to the soil.It was found that the lower the flow rate,the slower the penetration curve,and the higher the phosphorus content in the interception curve.Under the condition of the same total phosphorus,the shorter the time,the less the penetration time of phosphorus in the soil column,and the lower the adsorption efficiency of phosphorus on the soil and LDH.Therefore,the higher the flow rate,the less the retention.?4?LDH with a mass fraction of 0.5%was added to the soil,and the pH value of the background solution was adjusted to 5,7 and 8,respectively.The lower the pH value,the more positive charges in the medium,promoting the protonation reaction of phosphate anion,reducing the attraction between the surface of LDH and phosphate,thus reducing the retention rate of phosphorus.Correspondingly,the pH value is enhanced,and there are more negative charges,which promote the electric neutralization reaction of phosphate ions,and enhance the attraction between them and LDH,thus increasing the retention rate of phosphorus.?5?Through the above leaching experiment,LDH fixed the phosphorus in the soil,and then carbonate and bicarbonate with the same ionic strength were introduced to release the phosphorus fixed in LDH again,and the sustained release status of phosphorus was clarified.In addition,under the simulated real soil environment,the re-release of phosphorus after full contact with carbonate was studied at an interval of 3 days,and a good release status was found.It was confirmed that carbonate and bicarbonate achieved a sustained release of phosphorus by means of ion exchange,and the sustained release effect of carbonate was better than that of bicarbonate.