Study On Removal Of Thallium From Wastewater Using Zero-valent Manganese Nanomaterials

Thallium?Tl?is a highly toxic rare heavy metal.Recently,due to frequent occurrence of thallium pollution and the toxicity of thallium in recent years,thallium gradually attractsthe public attention and also gains focus from scientific researchers.With the continuous occurrenceof thallium pollution to the environment,it is urgent to seek efficient and economical methods to control the Tl-related water pollution.Compared with other wastewater treatment technology regarding heavy metal,adsorption has become one of the most effective methods because of its low operating cost,simple operation,easy reuse,and no secondary pollution.Recently,the search for adsorbents with good adsorbent properties has become the research hotspot.Biochar has become a hot research topic in the field of environment due to its excellent pollutant removal performance and ecological effects.In particular,the novel adsorption material with better adsorption performance via composite or surface modification method has gained momentum.Nano-zero-valent manganese?Mn⁰?particles are small in size,have high adsorption ability and strong reduction ability,may have high petential to the removal of Tl from wastewater.Therefore,this study explores the preparation of nanoMn⁰and nano-zero-valent-manganese-biocharcomposite?Mn@BC?,and investigates the related factors,efficacy and mechanism of Tl removal by Mn⁰-oxidants and by Mn@BC from wastewater.First of all,solution reduction method was used to prepare Mn⁰ as an adsorbent and catalyst,to combine with oxidants?sulphates,hypochlorite or hydrogen peroxide?for Tlremoval,and thenthe effects ofsolution pH,ionic strength,oxidant dosageand co-existence of organic matter on the removal of Tl were examined.The results show that the surface of Mn⁰ was readily oxidized to form a core-shell composite?MnO_x@Mn⁰?,which consists of Mn⁰ as the inner core and MnO_x?MnO,Mn₂O₃,and Mn₃O₄?as the outer shell.When Mn⁰was added alone,effective Tl?I?removal was only achieved at high pH levels?>12?.The Mn⁰-H₂O₂ system was also only effective in Tl?I?removal at high pH?>12?,while the Mn⁰-S₂O₈^2-or Mn⁰-ClO^-system had excellent Tl?I?removal?>95%?over a broad pH range?4–12?.The Mn⁰-S₂O₈^2-oxidation system provided the best resistance to interference from an external organic matrix.The isotherm of Tl?I?removal through the Mn⁰-S₂O₈^2-system followed the Freundlich model.The Mn⁰ nanomaterials can activate persulfate to produce sulfate radicals and hydroxyl radicals.The FT-IR and XRD characterizations suggested that oxidation-induced precipitation,surface adsorption,and electrostatic attraction are the main mechanisms for Tl?I?removal resulting from the combination of Mn⁰ and oxidants.Nano-zero-valent-manganese adsorbent exposured in the air is easy to be oxidized to form a metal oxide layer,which can be dissolved in acidic wastewater.Therefore,the follow-up study was to harness the high adsorptive ability of biochr to synthesize Mn@BCwith waste banana peel for Tl removal from acidic wastewater.The results show that under acidic conditions?pH=1.5?,the removal efficiency of Tl using Mn@BC for Tl?I?and Tl?III?was 97%and 94%,respectively,which is much higher than that when using the rawbiochar orthe individual Mn⁰.Co-existing cations including Na⁺and Mg²⁺had little effect on the removal of Tl.The isothermal adsorption show that the Tl removal conformedto the Freundlich model.The results of XPS,FT-IR and TEM characterization indicate that the removal of Tl by Mn@BC included reduction of Tl?I?/Tl?III?ions to elemental Tl and subsequent immobilization on the surface and pores of Mn@BC.Therefore,the Mn@BC is a simple and effective adsorbent,which can effectively remove Tl from acidic Tl-containing wastewater.