Adsorption Characteristics Of Modified Phosphate Flotation Tailing For Heavy Metals And Its Remediation Effect On Contaminated Soils

Heavy metal pollution of soils has become a serious problem of China,the development of effective soil remediation technologies has become one of the current urgent tasks.Due to the advantages of simple operation,quick results,and wide application range,the chemical immobilization technology has widely used in the remediation of heavy metal contaminated soils.The core of chemical immobilization technology is immobilization materials.Because of their excellent properties,phosphorus-containing mineral materials have been widely used as heavy metals immobilization materials.Phosphate flotation tailing was an important phosphorus-containing mineral material,but there're few reports on ues this material as immobilization material for heavy metals contaminated soils.In this study,a new type of immobilization material has been developed,using ammonium oxalate to modify the phosphate flotation tailing.A series of modern analysis methods were used to characterize the physicochemical properties of modified material,batch adsorption experiments were used to explore adsorption characteristics and mechanism of modified material on typical heavy metals?Cd,Pb and Cu?,and laboratory culture experiments were used to study the immobilization effect of modified material on typical heavy metals in different soils.The main results are as follows:?1?The content of heavy metals in the modified material were lower than the limits of relevant national environmental protection standards,indicated that thts material has the potential to be a soil remediation material.The modified material has a slightly alkaline pH value?7.65?,the contents of cation exchange capacity and available phosphorus increased significantly,especially the content of available phosphorus has increased about 10 times.The main components of the modified material were calcium oxalate and magnesium oxalate,and its surface has loaded with oxygen-containing functional groups such as oxalate,carboxyl,and hydroxyl groups,and the phosphorus-containing functional groups become the form which can easily bind with heavy metals.The specific surface area of the modified material was significantly reduced,the main pore distribution become micropores,and its surface morphology was an amorphous structure,which is smoother.?2?The dosage and pH significantly affected the adsorption of typical heavy metals by the modified phosphate flotation tailing.When the amount of modified material was 1 g·L^-1,the adsorption amount of Cd²⁺,Pb²⁺and Cu²⁺was the largest.The adsorption of modified material on Cd²⁺,Pb²⁺and Cu²⁺is better at pH 3-5.The experimental results of the adsorption kinetics of modified material on Cd²⁺,Pb²⁺and Cu²⁺were in line with 2^nd kinetic equation,which means the adsorption was chemisorption.Isothermal adsorption analysis showed that the adsorption of Cd²⁺,Pb²⁺and Cu²⁺by modified material were all conformed to the Langmuir isothermal adsorption model,indicate that the adsorption type is single-layer homogeneous adsorption.The modified material significantly increased the adsorption rate of Pb²⁺and slightly reduced the adsorption rates of Cd²⁺and Cu²⁺;the max adsorption amounts of Cd²⁺,Pb²⁺and Cu²⁺increased by 11 to 50 times,respectively,which reaching 279.88 mg·g^-1,764.34 mg·g^-1 and 245.53 mg·g^-1,respectively.The stability of adsorption increased,which has low desorption rate of less than 15%.In binary system the modified material has a strong affinity for Pb²⁺.SEM/EDS,XRD,FITR,and XPS analysis revealed that modified material adsorb and hold Cd²⁺,Pb²⁺and Cu²⁺through precipitation of phosphate,ion-exchange and co-precipitation of active calcium-magnesium,and complex precipitation of oxalate,hydroxyl,and carboxyl groups,and the contribution of precipitation of oxalate was greater.?3?The application of the two materials?modified or not?increased the pH of neural and acid soils used in this study,decreased the pH of alkaline soil,and the content of available phosphorus in all soils increased significantly,while the increase in the treatment of modified materials was more significant.The ammonium oxalate modified material significantly reduced the content of available Cd and Pb in acid soil in this study under the dosage of 5%by 44.56%and 62.75%respectively,but the content of available Cu increased significantly.The occurrence forms of heavy metals in the soils changed significantly after the application of the modified material,the proportions of weak acid extraction states of Cd and Pb in neutral and acidic soils reduced significantly.In general,modified material is suitable for the remediation of Cd and Pb contaminated neutral or acidic soils.However,the more exact application conditions and popular pattern need further study in the future.