Birnessite(δ-Mn(Ⅳ)O2)is a great manganese(Mn)adsorbent for dissolved divalent metals.In this study,we investigated the coprecipitation mechanism of 8-MnO2 in the presence of Zn(Ⅱ)and an oxidizing agent(sodium hypochlorite)under two neutral pH values(6.0 and 7.5).The mineralogical characteristics and Zn-Mn mixed products were compared with simple surface complexation by adsorption modeling and structural analysis.Batch copre-cipitation experiments at different Zn/Mn molar ratios showed a Langmuir-type isotherm at pH 6.0,which was similar to the result of adsorption experiments at pH 6.0 and 7.5.X-ray diffraction and X-ray absorption fine structure analysis revealed triple-corner-sharing inner-sphere complexation on the vacant sites was the dominant Zn sorption mechanism onδ-MnO2 under these experimental conditions.A coprecipitation experiment at pH 6.0 pro-duced some hetaerolite(ZnMn(Ⅲ)2O4)and manganite(γ-Mn(Ⅲ)OOH),but only at low Zn/Mn molar ratios(＜1).These secondary precipitates disappeared because of crystal dissolution at higher Zn/Mn molar ratios because they were thermodynamically unstable.Woodruf-fite(ZnMn(Ⅳ)3O7·2H2O)was produced in the coprecipitation experiment at pH 7.5 with a high Zn/Mn molar ratio of 5.This resulted in a Brunauer-Emmett-Teller(BET)-type sorption isotherm,in which formation was explained by transformation of the crystalline structure of δ-MnO2 to a tunnel structure.Our experiments demonstrate that abiotic coprecipitation reactions can induce Zn-Mn compound formation on the δ-MnO2 surface,and that the pH is an important controlling factor for the crystalline structures and thermodynamic stabilities.

Shota Tajima;Shigeshi Fuchida;Chiharu Tokoro

Graduate School of Creative Science and Engineering,Waseda University,3-4-1 Okubo,Shinjuku-ku,Tokyo 169-8555,Japan;Faculty of Science and Engineering,Waseda University,3-4-1 Okubo,Shinjuku-ku,Tokyo 169-8555,Japan;Faculty of Engineering,The University of Tokyo,7-3-1 Hongo,Bunkyo-ku,Tokyo 113-8656,Japan

环境科学学报（英文版）

[1]Shota Tajima;Shigeshi Fuchida;Chiharu Tokoro-.Coprecipitation mechanisms of Zn by birnessite formation and its mineralogy under neutral pH conditions)[J].环境科学学报（英文版）,2022(11):136-147

Coprecipitation,birnessite,copre,hetaerolite,ZnMn,Woodruf,fite,3O7

mechanisms,by,its,mineralogy,under,neutral,conditions,Birnessite,great,manganese,adsorbent,dissolved,divalent,metals,In,this,study,investigated,coprecipitation,MnO2,presence,oxidizing,agent,sodium,hypochlorite,two,values,mineralogical,characteristics,mixed,products,were,compared,simple,surface,complexation,adsorption,modeling,structural,analysis,Batch,experiments,different,molar,ratios,showed,Langmuir,type,isotherm,which,was,similar,ray,diffraction,absorption,fine,revealed,triple,corner,sharing,inner,sphere,vacant,sites,dominant,these,experimental,some,2O4,manganite,OOH,but,only,low,These,secondary,precipitates,disappeared,because,dissolution,higher,they,thermodynamically,unstable,2H2O,produced,This,resulted,Brunauer,Emmett,Teller,BET,explained,transformation,crystalline,tunnel,Our,demonstrate,that,abiotic,reactions,induce,compound,important,controlling,structures,stabilities

0.499557