Preparation Of La-Mn Binary Oxide And The Adsorption Properties And Mechanisms Of As(Ⅲ) And As(Ⅴ) In Water

Excessive intake of arsenic poses a potential threat to human health and ecosystem security,leading to a series of carcinogenic and non-carcinogenic diseases.In natural water,inorganic As（Ⅲ）and As（V）are the main forms of arsenic,which has garnered increased attention for its pollution in water.Among the many arsenic removal technologies,adsorption stands out due to its advantages of low cost,strong pertinence,high removal rate,and low secondary pollution.Metal oxides have been widely studied as adsorption materials because of their high affinity for arsenic and good removal effect.However,single-component metal oxides often have the disadvantage of only acting on a certain valence state of arsenic.Lanthanum and its compounds can effectively adsorb As（V）in the form of anions,while Mn O₂can efficiently oxidize As（Ⅲ）to As（V）because of its excellent oxidation properties.Therefore,a powder-type LaMn binary oxide adsorption material was prepared by combining lanthanum compounds with Mn O₂.The composite material exhibited excellent removal efficiency for both As（Ⅲ）and As（V）.However,this powder material has the drawback of easy agglomeration and difficulty in separation from the aqueous solution.To address this issue,a granular resin-coated material（D401-LaMn）was prepared by loading the LaMn binary oxide onto D401 resin.The materials were systematically studied regarding their preparation conditions,characterization,arsenic removal performance,and mechanism.The following research results are obtained:（1）A batch of LaMn composite metal oxides with different molar ratios of lanthanum and manganese were prepared using the oxidation co-precipitation method,and the material with a La/Mn molar ratio of 2:1 was selected for further investigation.Through comprehensive analysis by SEM,TEM and other characterization methods,it is found that the La-Mn binary oxide is amorphous or weak mesoporous materials with a surface area of 108.85 m²/g and an average pore size of 9.10 nm,making it suitable for the adsorption of inorganic arsenic in water.The removal of inorganic arsenic by La-Mn binary oxide is rapid and efficient,and the adsorption capacity of As（Ⅲ）and As（V）can reach 79.75 mg/g and 205.80 mg/g,respectively.The lower the p H and stronger the acidity of the aqueous solution,the stronger the removal ability of the material for As（Ⅲ）and As（V）,and most of the coexistence of canions in water have no significant interference on the adsorption process.Additionally,the material demonstrated good regeneration capabilities.（2）The mechanism of adsorption and removal of As（Ⅲ）from water by LaMn binary oxide involves first oxidizing As（Ⅲ）to As（V）,followed by a ligand exchange reaction between As（V）and the abundant hydroxyl groups on the surface of the adsorbent.This generates an endo-ligand complex that remains on the surface of the adsorbent material.For As（V）adsorption and removal,As（V）undergoes a ligand exchange reaction with the hydroxyl groups on the surface of the adsorbent,forming an internal ligand complex that binds As（V）to the surface of the adsorbent.After a series of chemical reactions,both valence states of inorganic arsenic can be separated and removed from the aqueous solution.（3）The D401-LaMn adsorption material,composed of La-Mn binary oxide coated resin granules,is brown and has an average diameter of 0.5-0.65 nm.The surface is rough,and the material has a strong ability to remove both As（Ⅲ）and As（V）and is resistant to the coexisting ions in water.The material performs best under acidic conditions and has demonstrated excellent removal efficiency in both simulated and continuous arsenic removal experiments.D401-LaMn has significant potential for use in the arsenic removal field.