Study On The Transformation And Immobilization Of Arsenic And Antimony On Iron/Manganese Oxides

Arsenic（As）and antimony（Sb）are two metal（loid）s belong to Group VA with varied oxidation states of+3 and+5,which has been identified as priority-controlled pollutants.The dominant trivalent species of As and Sb usually exists as neutral form,exhibited not only higher toxicity but also more difficult to removal than that of pentavalent species.Furthermore,arsenic occurs together with Sb in mining areas of antimony mine,Au-mine and copper mine.So,more attention should be paid to the same and difference removal behaviors of As/Sb together its competitive properties under the situation of As/Sb co-contamination.Iron and manganese are the two of most abundant transition metal elements with varied oxidation states in the earth’s crust,their oxides play important role in the geochemical cycle of As and Sb.Investigating the difference redox conversion and the competitive behavior as well as its controlling mechanism of As and Sb on iron and manganese oxides,are beneficial for revealing the basic rules and the pathways of simultaneous removal of As and Sb,which is of guiding significance for practical control of As and Sb.（1）For the highly toxic Sb（III）and high valent Sb（V）in single system,the low cost and environmental friendly manganese oxide nanoparticles was grew on a three-dimensional（3D）carbon foam,to removal Sb through synergistic oxidation-adsorption by the fabricated Mn₃O₄NPs/CF composite.Study the comparative removal behavior of Sb（III）and Sb（V）for simultaneous removal of Sb（III）and Sb（V）.The study found that the Mn₃O₄ nanoparticle was successfully loaded on the carbon foam skeleton,with the size of 60-120 nm,which reduced the agglomeration of Mn₃O₄ particles.The maximum adsorption capacity of Sb（III）and Sb（V）on Mn₃O₄ NPs/CF were 67.6 and 57.8 mg/g,respectively.The adsorption and oxidation process involved in the removal of Sb（III）.The Mn₃O₄ nanoparticle is responsible for oxidizing Sb（III）to Sb（V）,through two-step pathway[reduction of Mn（IV）to Mn（III）and subsequent Mn（III）to Mn（II）].Explicitly demonstrated the oxidation-adsorption mechanism of Sb（III）on Mn₃O₄nanoparticle,achieved the transformation of highly toxic Sb（III）to less toxic Sb（V）,and the generated Sb（V）further sequestered by Mn₃O₄ nanoparticle.These results provided the guidance of valence adjustment,toxicity transformation and the removal behavior of varied oxidation states heavy metal（loids）.（2）For the high concentration As（V）and Sb（V）in single system,the low cost and environmental friendly iron oxide was selected,and its structural composition as well as the surface properties were adjusted by sulfide-modification,to effectively removal As（V）and Sb（V）through synergistic adsorption-reduction by the fabricated sulfide-modifiedα-Fe OOH.Comparatively study the same and difference adsorption behavior of As（V）and Sb（V）on sulfide-modifiedα-Fe OOH to achieve effectively removal of As（V）and Sb（V）.The similarity adsorption behaviors of As（V）and Sb（V）were:sulfide-modification could effectively improve the adsorption capacity and adsorption affinity ofα-Fe OOH to both As（V）and Sb（V）,adsorption process of As（V）and Sb（V）on sulfide-modifiedα-Fe OOH was controlled by a chemical reaction mechanism,the removal of As（V）and Sb（V）were significantly interfered by p H and co-existed PO₄^3-.While the differences are:The sulfide-modifiedα-Fe OOH increased the adsorption capacities of As（V）and Sb（V）,but it was more notable for Sb（V）,the adsorption capacity for Sb（V）is 3.5 times as As（V）.A conversion of As（V）to As（III）during the adsorption process was demonstrated,despite there was no obvious variation of Sb（V）speciation on the surface,the etched XPS demonstrated the conversion of Sb（V）to Sb（III）inside the material.These results demonstrated the mechanism of synergistic adsorption-reduction to enhance the removal of As（V）and Sb（V）.（3）For the As（V）,Sb（III）and Sb（V）in single system,the Fe-Mn binary oxide that combines the oxidation property of manganese oxide and the high adsorption features of iron oxide was fabricated,the Fe-Mn binary oxide-CMC（carboxymethyl cellulose）bead was fabricated through impregnating Fe-Mn binary oxide into CMC matrix to achieve effectively removal of As（V）,Sb（III）and Sb（V）.The study found that the particle size distribution of dry Fe-Mn binary oxide-CMC bead is between 1.50-2.40 mm,and the average particle size is 1.94mm.The bead could effectively removal As（V）,Sb（III）and Sb（V）from water,the maximum adsorption capacity of As（V）,Sb（III）and Sb（V）on Fe-Mn binary oxide-CMC bead were 48.3,51.5 and 81.9 mg/g,respectively.The adsorption of both As（V）,Sb（III）and Sb（V）was not interfered by various coexisting anions such as Cl^-、NO₃^-and SO₄^2-,while HCO₃^-、Si O₃^2-and H₂PO₄^-exhibited obvious inhibition on As（V）,Sb（III）and Sb（V）adsorption.The As（V）and Sb（V）were partially reduced to As（III）and Sb（III）in adsorption process,while the Sb（III）was oxidized to Sb（V）.（4）Based on the problem of As（V）and Sb（V）co-contamination in water,the competitive adsorption behavior and its controlling mechanism of As（V）and Sb（V）on Fe-Mn binary oxide were comprehensively investigated.The study found that the adsorption capacity of Sb（V）on Fe-Mn binary oxide in binary system was decreased from 147.1 mg/g in single system to 125.0mg/g,while the adsorption capacity of As（V）in single and binary system were 95.24 and 100.0mg/g,respectively.As（V）exhibits a significant inhibitory effect on the adsorption of Sb（V）on Fe-Mn binary oxides,while the adsorption of As（V）on the Fe-Mn binary oxides is almost not affected by Sb（V）.The sequence of introduction of As（V）or Sb（V）has an marginal influence on the adsorption behavior of firstly adsorbed Sb（V）or As（V）in the coexistence system.The firstly adsorbed As（V）or Sb（V）could form stable inner layer complex on Fe-Mn binary oxides,and the later introduced Sb（V）or As（V）is difficult to replace the first adsorbed As（V）or Sb（V）.（5）For the problem of As and Sb co-contaminated soil,the Fe-Mn binary oxide was adopted to explored the immobilization behavior of As and Sb by Fe-Mn binary oxide.Comparatively investigated the same and difference immobilization behavior of As and Sb on sulfide-modifiedα-Fe OOH to achieve effectively removal of As and Sb.The addition of Fe-Mn binary oxide exhibited marginal effect on soil p H,electrical conductivity,cation exchange capacity and organic matter,and it could effectively increase soil enzyme activity and improve the living environment of soil microorganisms.The similarity immobilization behavior of As and Sb were:the Fe-Mn binary oxide could effectively reduce TCLP extractable concentration,available content and bioavailability of As and Sb,promote the conversion of unstable forms of As and Sb to more stable forms,and reduces the mobility of As and Sb in the soil.It could also increase the soil resistance to the external p H changes resulted in the leaching risk of As and Sb,and further reduce the bioaccumulation factor（BAF）of As and Sb in root and shoot of Setaria viridis.While the differences are:The Fe-Mn binary oxide exhibited superior remediation effect on As than Sb,the co-existed Si O₃^2-、HPO₄^2-and HCO₃^-exhibited significant effect on the immobilization of As,while there was marginal effect in the case of Sb.This result demonstrating that Fe-Mn binary oxide exhibited a great application prospect for in situ remediation of As and Sb co-contaminated soil.This study provides a theoretical basis for understanding redox conversion and the competitive behavior as well as its controlling mechanism of As and Sb on iron and manganese oxides,and provide useful reference and technical support for actual As and Sb remediation.