Study On The Adsorption Effect Of Different Crystalline MnO₂ Adsorbents On Thallium And Antimony In Water

In recent years,heavy metals have been widely used in industrial production.When the heavy metal mineral mining,smelting,processing and application,a large number of heavy metals get into the environment,resulting in heavy metal pollution.Antimony and thallium pollution is particularly serious,and the pollution events are frequent,which seriously affect the health and safety of the ecosystem and the people,and have received extensive attention.Manganese oxide is an important component and an adsorption carrier in soil and water.Because of their highly defective structure and non ideal proportioning,they have strong adsorption and immobilization ability to metal ions and organic compounds.The common crystal forms of manganese oxide are?-MnO₂,?-MnO₂,?-MnO₂,?-MnO₂,amorphous-MnO₂ and so on.However,the relationship between manganese oxides and thallium and antimony has less been studied.This article investigate the Sb???and Tl???adsorption properties on five different crystalline manganese dioxide??-MnO₂,?-MnO₂,?-MnO₂,?-MnO₂,amorphous MnO₂?,the static adsorption experiments were carried out.Then the adsorption-desorption kinetics characteristics,Thermodynamic properties and the influence of acidity and other reaction conditions on Sb???adsorption by?-MnO₂ were studied.Through the above experimental research,the following experimental results are obtained:?1?Characterization of manganese dioxide.By scanning electron microscope,it is found that the?-MnO₂ is spheroidal,and its particle size is smaller and reunion with each other.The five kinds of MnO₂ crystal form were confirmed by XRD analysis.Compared with other MnO₂,the?-MnO₂ peak width of the two MnO₂ is larger,and the peak tip is more gentle,indicating that the crystallinity of these two MnO₂ crystals is poor.It is found that the surface of?-MnO₂ has a rich Mn-OH group by Infrared spectrum.The pzc of the?-MnO₂ is measured by the salt addition method,which is 3.03.When the pH below 3.03,the?-MnO₂ surface has positive charge,and when the pH above 3.03,the?-MnO₂ surface has a negative charge.?2?By comparing the adsorption properties of five different crystalline forms of MnO₂,such as?-MnO₂,?-MnO₂,?-MnO₂,?-MnO₂ and amorphous MnO₂ on Sb???and Tl???:The results showed that the adsorption capacity to Sb???'s order of five kinds of manganese dioxide is?-MnO₂>?-MnO₂>?-MnO₂>amorphous MnO₂>?-MnO₂.The adsorption capacity to Tl???'s order of five kinds of manganese dioxide is?-MnO₂>?-MnO₂>?-MnO₂>amorphous MnO₂>?-MnO₂.The adsorption performance of?-MnO₂on Sb???and Tl???is the best,and the maximum adsorption capacity is 120mg.g^-1 and498mg.g^-1,respectively.?3?pH has great influence on antimony and thallium adsorption.The Sb???adsorption capacity on?-MnO₂ decreased with the increase of solution pH.The Tl???adsorption capacity on?-MnO₂ increased with the increase of solution pH.?4?In the process of the adsorption of Sb???by?-MnO₂,the effects of Humic acid?HA?and coexisting anion Cl^-on the adsorption of manganese dioxide on Sb???are not significant,PO₄^3-,SO₄^2-,SiO₃^2-have certain inhibitory effects on the adsorption process,while the Fulvic acid?FA?and CO₃^2-slightly promote adsorption.During the adsorption of Tl???by?-MnO₂,Humic acid?HA?,Fulvic acid?FA?and coexisting cations Mg²⁺ and Cu²⁺have a certain inhibitory effect on the adsorption of Tl???by manganese dioxide,the coexistence of cations Ca²⁺and K⁺can promote the adsorption of Tl???by manganese dioxide.?5?The thermodynamic experiments show that the adsorption process of?-MnO₂ on Sb???and Tl???is spontaneous endothermic reaction.The increase of temperature is beneficial to the reaction.Through the kinetic experiment and the analysis of the infrared spectra before and after adsorption,it is concluded that the chemical adsorption and ion exchange between the surface of the?-MnO₂ and the heavy metal ions are dominated by the ion exchange.