Research On Efficient Removal Of Mercuryand Arsenic From Acid Mine Drainage By Alzn Alloy In Suit LDH

The high concentration of heavy metals in acid mine drainage（AMD）has caused serious harm to the surrounding ecological environment,among which Hg（Ⅱ）and As（Ⅲ）are highly toxic and harmful to human health when they enter the environment.Due to the strong acidity（p H 2-3）of AMD and the problems of inactivation and secondary pollution of current remediation materials,a new method of in-situ hydrotalcite remediation of AMD with Al Zn alloy is proposed in this paper.The removal effect of Hg（Ⅱ）and As（Ⅲ）can be improved by using in-situ layered double hydroxide（i LDH）to form Al Zn@i LDH composite material in the reaction process.The effects of Zn content,pollutant concentration,i LDH on the removal rate of Hg（Ⅱ）and As（Ⅲ）,and the effects of Fe（III）concentration in solution and Fe content on the surface of composite materials on the removal of As（Ⅲ）were studied.The removal mechanism of Hg（Ⅱ）and As（Ⅲ）by in-situ hydrotalcite of Al Zn alloy and its application in AMD repair were preliminarily discussed.The main results are as follows:（1）Al Zn50 alloy treatment p H 2.02,containing 10 mg/L Hg（Ⅱ）wastewater,30 min removal rate of 99.8%,p H increased to 6.28,pseudo-second-order kinetics and Freundlich adsorption,the rate constant is 0.0554g/（mg·min）.The adsorption capacity of Hg（Ⅱ）was 4929 mg/g.In the treatment of AMD containing 10 mg/L Hg（Ⅱ）and other heavy metals 0.0758-3303 mg/L,the removal rate of Hg（II）was 99.3%,and the removal rate of other heavy metals was more than 50%.（2）The removal rate of 10 mg/L As（Ⅲ）and Al Zn20 alloy reached 99.9%in 30 min,and the solution p H increased from 2.01 to 4.73,which belonged to pseudo-second-order kinetics and Freundlich adsorption.The rate constant was 0.373 g/（mg·min）.Fe（III）in solution and Fe（III）on alloy surface promoted the adsorption of As（Ⅲ）.The adsorption capacity increased from19.8 mg/g to 54.1 mg/g.（3）The removal mechanism of Hg（Ⅱ）is physical adsorption-chemical reduction amalgamation-i LDH chemisorption:Hg（Ⅱ）adsorbed on the surface of Al Zn50 alloy is first reduced to Hg（0）by Zn and Al,and amalgamated.The dissolved Zn²⁺and Al³⁺form in situ Zn Al-LDH,and Hg（Ⅱ）is further adsorbed by surface hydroxyl complexation.（4）In the presence of Fe（III）,the removal mechanism of As（Ⅲ）is physical adsorption-redox-chemisorption:In the solution,part of As（Ⅲ）was adsorbed on the surface of the alloy,and part was oxidized to As（Ⅴ）by active oxygen and Fe（III）.As（Ⅴ）was removed by hydroxyl complexation on the surface of i LDH,interlayer anion intercalation and Fe-O-As coordination bond.Al³⁺dissolution concentration and p H are the key factors for in situ self-assembly of Zn Al-LDH on alloy surface,while i LDH is the main mechanism for synchronous removal of other heavy metal ions and Al³⁺secondary pollution.This study provides a new method and a new idea for AMD treatment which is simple and efficient and atomic economy.