Efficiency And Mechanism Of Manganese Oxide @ Potassium Riched Biochar In The Treatment Of Tl(Ⅰ) Containing Wastewater

With the rapid development of China’s economy and the continuous improvement of people’s living standards,heavy metal pollution incidents occur frequently,which has attracted more and more attention.Heavy metal pollution in key industries such as mining,beneficiation and metallurgy and non-ferrous metal processing is still one of the key issues that need long-term attention in the field of ecological and environmental protection in China.Thallium（Tl）is one of the most toxic heavy metals.In recently,there have been many drinking water pollution incidents in our province,resulting in great hidden dangers.Thallium has two common valence states:monovalent and trivalent.Among them,monovalent thallium（Tl（I））is the main occurrence form of Tl in wastewater.Compared with relevant mineral colloids such as iron and aluminum oxides,manganese oxides generally have a better removal effect on Tl（I）.However,due to the variability of manganese oxide morphology and the complexity of the influence of coexisting anions and anions,there is a lack of systematic and in-depth understanding of the adsorption characteristics,mechanism and influence degree of Tl（I）by manganese oxides with different structures under the synergistic action of p H and coexisting ions,which limits its application scope to a certain extent.Based on this,Hydrothermal synthesis was used in this study to prepareα-Mn O₂,β-Mn O₂,γ-Mn O₂ andδ-Mn O₂,using a variety of characterization methods combined with visual MINTEQ software to analyze effects and mechanisms of different coexisting ions and p H on Tl（I）removed byα-Mn O₂,γ-Mn O₂ andδ-Mn O₂.The results showed that:（1）The Tl（I）which was adsorbed onα-Mn O₂,γ-Mn O₂ andδ-Mn O₂is oxidized to Tl（III）,but Tl（I）adsorbed onβ-Mn O₂ is not oxidized.There are a large amount of K onδ-Mn O₂,which adsorb Tl（I）through isomorphic substitution.The（1 1 0）,（2 00）,（2 2 0）and（3 1 0）crystal planes onα-Mn O₂,the（101）and（220）crystal planes onγ-Mn O₂,the（0 0 2）,（2 0 0）,（1 1-1）and（0 2 0）crystal planes onδ-Mn O₂ are related to the adsorption and removal of Tl（I）.The oxidation of Mn（IV）and Mn（III）onα-Mn O₂,γ-Mn O₂ andδ-Mn O₂is an important mechanism for the removal of Tl（I）.Mn-OH onγ-Mn O₂ andδ-Mn O₂ plays an important role in the adsorption of Tl（I）.（2）The removal of Tl（I）in water byα-Mn O₂ is slightly affected by Ca²⁺,Mg²⁺,Mn²⁺,Cl^-,CO₃^2-,PO₄^3-and Si O₃^2-,but greatly inhibited by Cu²⁺which would generate Cu O（s）when the value of p H was 6.5.The Ca²⁺,Mg²⁺,Mn²⁺and the Cu²⁺can inhibit the removal of Tl（I）byγ-Mn O₂.Ca²⁺,Mn²⁺and Cu²⁺have a strong inhibitory effect on the removal of Tl（I）byδ-Mn O₂.HCO₃^-,H₃Si O₄^-,H₂PO₄^-and HPO₄^2-can capture the H⁺generated in the system,making the reaction proceed in the direction conducive to the adsorption of Tl（I）,and promoting the adsorption of Tl（I）onγ-Mn O₂ andδ-Mn O₂.Most manganese oxides have strong adsorption capacity for thallium,but they are easy to agglomeration.Based on this,in order to overcome the defect of manganese oxide agglomeration,manganese oxide was loaded on low-temperature pyrolytic potassium rich biochar by coprecipitation method and solid-phase surface deposition method,respectively,to obtain two kinds of manganese oxide@potassium rich biochar(H-Mn₃O₄@BC and S-Mn₂O_3.12@BC),and their adsorption performance and mechanism for Tl（I）in water were studied.The results showed that:（1）The adsorption of Tl（I）on BC,H-Mn₃O₄@BC and S-Mn₂O_3.12@BC in water is most consistent with the pseudo second-order kinetic model.The adsorption rate is mainly determined by the chemical force between Tl（I）and the adsorption material,which has a good kinetic effect.（2）The p H has a great influence on BC system but slightly affected H-Mn₃O₄@BC and S-Mn₂O_3.12@BC systems.The removal rate of Tl（I）increases with the increase of p H in the range of 3.5-10.5.The adsorption of Tl（I）on H-Mn₃O₄@BC and S-Mn₂O_3.12@BC in water is most consistent with the Freundlich adsorption isothermal model,which proved that heterogeneous multilayer adsorption occurs on the surface,and the adsorbed Tl（I）has interaction force.Theoretical maximum adsorption capacity of S-Mn₂O_3.12@BC,H-Mn₃O₄@BC and BC were 136.94,122.91 and 95.25 mg/g respectively.The slight inhibition of Ca²⁺and Mg²⁺on S-Mn₂O_3.12@BC system was slightly.Appropriate amount of DTPA or EDTA can promote S-Mn₂O_3.12@BC and H-Mn₃O₄@BC to remove Tl（I）from water,while inhibit Tl（I）removal when overdose.（3）The adsorption and removal of Tl（I）by S-Mn₂O_3.12@BC,H-Mn₃O₄@BC or BC are realized by cation exchange with Tl（I）in water.In addition,the functional group O-H and C=O on the material are the active sites for Tl（I）adsorption.S-Mn₂O_3.12@BC and H-Mn₃O₄@BC can release Mn（III）into water to realize the oxidative and removal of Tl（Ⅰ）.