Preparation Of Nano Lanthanum Carbonate By High Gravity Technology And Study On Its Application Performance

In recent years,as a kind of efficient phosphate adhesive,lanthanum carbonate（LC）has attracted much attention,which was mainly used in biomedicine,sewage treatment and other fields.However,currently reported LC is mostly micron-sized with irregular morphology and wide particle size distribution,which greatly affects its application properties.Therefore,it is necessary to prepare nano LC with controllable morphology and uniform particle size.In this thesis,nano LC with polymorphs and various morphologies were prepared by precipitation method combined with high gravity technology.Its application performances of removing phosphate and tetracycline（TC）in water were further explored.The main research contents and results are as follows:（1）With La（NO₃）₃·6H₂O as the lanthanum precursor and Na HCO₃as the precipitator,nano LC with polymorphs and various morphologies was prepared by precipitation method combined with high gravity technology.Firstly,the effects of different reaction conditions on the product were investigated in a stirred tank reactor（STR）.When the solvent was deionized water,the product was hydrated LC,and the morphology of the product changed with the change of reaction temperature.The product of 298 K is flower-like LC formed by self-assembly of two-dimensional nano-sheets with a thickness of about100 nm.The product of 313 K is two-dimensional layer-like LC with a thickness of about 100 nm,and the product of 333 K is rod-like LC with a width of about 200 nm.When the solvent is a mixed solution of methanol and deionized water,the product is amorphous lanthanum carbonate（ALC）with uniform particle size of about 30 nm.Based on the better process conditions obtained by STR,LC was further prepared by rotating packed bed（RPB）.The optimum process conditions were determined:the rotating speed was 2000 rpm and the feed flow rate was 100 m L/min.Compared with STR,the LC synthesized by RPB has smaller size,more regular morphology,more uniform particle size distribution and shorter reaction time,realizing the preparation process from batch（30 min,STR）to continuous operation（1 s,RPB）.Among them,ALC has the best dissolution performance,which can reach more than 90%dissolution within 15 minutes.Additionally,the dissolution performance of all LC obtained by RPB is better than that obtained by STR and commercial LC.（2）The phosphate adsorption performances of four LCs with polymorphs and various morphologies prepared by RPB for phosphate radical were studied.The effects of different reaction conditions on the removal of phosphate were explored.The results showed that ALC had the highest equilibrium adsorption capacity and the fastest adsorption rate.Under the condition of 298 K and no p H control,ALC could reach the adsorption equilibrium in 1 h,and the maximum adsorption capacity was162 mg P/g.Especially,its adsorption capacity per unit time（162 mg P/（g h））is currently at the leading level reported in the literature.Temperature has little effect on adsorption performance.ALC can maintain high adsorption performance in a wide p H range（3-9）,and the removal rate of phosphate can also remain above 90%in the presence of coexisting ions.The study of adsorption mechanism reveals that a large number of La³⁺ions are released by LC dissolution and then bound with phosphate in solution to form La PO₄precipitate for phosphate removal.（3）The adsorption performance of four LCs with polymorphs and various morphologies prepared by RPB for tetracycline（TC）were studied.The effects of different reaction conditions on the removal of TC was mainly explored.The results showed that the adsorption of TC on nano LC conformed to the pseudo-second-order kinetic model and Freundlich model.The adsorption capacity of TC increased with the adsorption temperature,initial concentration of TC,and time rising.Under the condition of 298 K and no p H control,ALC can reach the adsorption equilibrium in 3 hours with the maximum adsorption capacity of 154.78 mg/g,which is higher than most carbon-containing materials reported in the current literature.Its maximum adsorption capacity can maintain stable in a wide p H range（3-8）.It can also maintain high selectivity for TC with the presence of coexisting ions.The study of adsorption mechanism indicates that the interaction between LC and TC is attributed to the electrostatic interaction,complexation and hydrogen bond.