Experimental Study On Phosphorus Adsorption And Phosphorus Control Of Lanthanide LDHs Modified Bentonite

The eutrophication degree of most freshwater lakes in China is increasing year by year.Phosphorus is the key factor of lake eutrophication.In order to control the release of phosphorus from sediment,it is necessary to develop new phosphorus locking agents.In this paper,LDH containing lanthanum was developed and coated on the surface of bentonite for phosphorus locking.Zn-Al-La-LDHs modified bentonite was characterized.A series of tests and analyses were carried out on the preparation conditions,adsorption properties,influencing factors of phosphorus removal and the dosage of phosphorus locking agent.The research conclusions were summarized as follows:（1）The optimum preparation conditions of Zn-Al-La-LDHs were as follows:the time of water bath with stirring was 2h,aging time was 18h,Al-La molar concentration ratio was 10,p H=9,c(Zn²⁺)∶(c(Al³⁺)+c(La³⁺))=3 water bath temperature was40℃,and aging temperature was 100℃.（2）In the process of bentonite modification,the mass ratio of bentonite to Zn Cl₂,Al Cl₃·6H₂O and La Cl₃·x H₂O was:m _Be∶m _Zn∶m _Al∶m _La=17.85∶18.25∶9.8∶1.The prepared Zn-Al-La-LDHs modified bentonite had the higher ratio of performance to price.（3）The characterization results of modified bentonite by X-ray diffraction and so on showed that it was technically feasible to load Zn-Al-La-LDHs on the surface of bentonite.（4）The adsorption capacity of Zn-Al-La-LDHs modified bentonite was nearly 6times higher than that of original bentonite,and the adsorption capacity of Zn-Al-La-LDHs modified bentonite was 65.5%higher than that of Zn-Al-LDHs modified bentonite.The adsorption process of modified bentonite to phosphate was mainly monolayer adsorption,which belonged to chemical adsorption.Compared with original bentonite and Zn-Al-LDHs modified bentonite,Zn-Al-La-LDHs modified bentonite was more suitable for phosphorus locking as it was less prone to desorption.（5）Zn-Al-La-LDHs modified bentonite had good phosphorus removal effect in the range of p H=3～9;Cl^-and SO₄^2-in water had little effect on the adsorption of phosphate by Zn-Al-La-LDHs modified bentonite;CO₃^2-had a great influence on its adsorption of phosphate.（6）The adsorption rate and capacity of Zn-Al-La-LDHs modified bentonite were better than those of Lock P1,Lock P2,Lock P3 and other common phosphorus locking agents in the market.（7）The Zn-Al-La-LDHs modified bentonite locking phosphorus in sediment was mainly used to remove soluble phosphate（SRP）in overlying water and active phosphorus（Na OH-P）within 8cm effective phosphorus release depth in the surface of sediment,according to which the dosage of phosphorus locking agent could be calculated.