Fabrication Of Magnetic La-Based Nanocomposites For Phosphate Removal:Adsorption Behavior And Mechanism

Phosphorus（P）pollution in water and P resource shortage have become the urgent problems in recent years.Hence,controlling P discharge is essential.Adsorption is an efficient and easy method to remove and recover P from wastewater.The principle objective is to develop adsorbents with the advantages of cost-effectiveness,greater selectivity and faster regeneration.Iron oxide（Fe₃O₄）nanoparticle has been identified as a P adsorbent with high adsorption capacity in our previous researches.Fe₃O₄is not very stable under ambient conditions and its adsorption capacity and selectivity still need improving.In this dissertation,three types of La species based adsorbents were prepared and applied in P removal in water.The main study focused as follows:1.The polyethyleneimine（PEI）was used to modify Fe₃O₄and La（OH）₃by co-precipitation.The results indicated that PEI not only improved the dispersity of Fe₃O₄/La（OH）₃,but also increased its positive charge.The adsorbent exhibited a fast adsorption kinetics and a high Langmuir maximum adsorption capacity of 87.52 mg·g^-1.Remarkably,this adsorbent demonstrated high adsorption selectivity to P in the presence of competing anions(SO₄^2-,Cl^-and NO₃^-).The five adsorption–desorption cycling experiments suggested that PEI-Fe₃O₄/La（OH）₃could be regenerated by 1 M Na OH solution and maintained 90%phosphate adsorption capacity.2.Hydrochar was chosen as support material for loading Fe₃O₄and La（OH）₃nanoparticles.The obtained adsorbent La-MHTC showed porous structure,relatively high specific surface area and enhancement of the La and Fe dispersion.The batch adsorption experiment showed that the optimal sample 2-La-MHTC had a preferable adsorption of P and relative high efficiencies.Its Langmuir maximum adsorption capacity was 100.25 mg·g^-1.This sample demonstrated high stability within the p H range 3.0-9.0 and high adsorption selectivity in the presence of competing anions(SO₄^2-,Cl^-and NO₃^-).Moreover,real wastewater adsorption experiment also indicated the efficient performance on removal of P.The 2-La-MHTC could also be regenerated after five adsorption–desorption cycling experiments.3.Zeolite was also used as support material due to its porous structure and high adsorption ability.Meanwhile,magnesium（Mg）element is used to enhance P removal due quite high p H_pzc.A noval Mg-La-Fe/zeolite（MLFZ）composite was fabricated by a facile coprecipitation method.The MLFZ showed increased surface charge and enhanced nanoparticles dispersion.The adsorption law of MLFZ matched well with the Langmuir model and the pseudo-second-order model.The maximum adsorption capacity of MLFZ was determined at 13.46 mg·g^-1at p H 7 in the equilibrium adsorption isotherm study.The coexisting anions(SO₄^2-,Cl^-and NO₃^-)had insignificant effects on P adsorption.MLFZ exhibited ultrahigh stability within the p H range 3.0-11.0 with negligible La leakage.MLFZ could be regenerated by 1 M Na OH solution and maintained 90%P adsorption capacity at the fifth adsorption–desorption cycle.Thereby,in this study,the noval La-based adsorbents（PEI-Fe₃O₄/La（OH）₃,La-MHTC and MLFZ）were prepared and employed for enhancing phosphate removal.La played a key role in the complexation of phosphate,in which the electrostatic attraction and complexation mechanisms contributed to phosphate adsorption.We believe this study could promote the develpoment of La-based adsorbents in real wastewater treatment.