Studies On Oxidant-Fe₂O₃ Composite Adsorbent And Its Catalytic Oxidation Of Gas-phase Arsenic

The discharge of heavy metal pollutants during the coal burning process has caused serious damage to the ecological environment and human health.Arsenic is highly volatile,highly toxic,and highly carcinogenic,and has attracted worldwide attention.The high-valence state As2O5(g)is easily removed by the wet desulfurization device because of its good water solubility.The low-cost As2O3(g)and the simple substance As(g)are hardly soluble in water and volatile,so it is difficult to be effectively removed by the desulfurization device and the precipitator.As2O3 is more toxic and less soluble in water,so it is easier to accumulate in the body.Therefore,the key to arsenic pollution control is the removal of As2O3.How to promote the catalytic oxidation of low-cost As2O3 to improve the efficiency of total arsenic removal is of great significance for further exploration of reasonable arsenic pollution control methods.Iron-based adsorbent materials have attracted extensive attention due to their strong adsorption activity,low cost and easy to manufacture,good resistance to water and sulfur,and no toxicity to the environment.They are ideal catalytic adsorbent.Therefore,based on the green oxidation ability of H2O2,NaCIO and NaBr and the high adsorption characteristics of Fe2O3,an oxidant-modified Fe2O3 composite adsorbent is proposed to study the catalytic oxidation and enhanced adsorption of gas-phase arsenic.The oxidant-Fe2O3 composite adsorbents including H2O2-Fe2O3,NaClO-Fe2O3 and NaBr-Fe2O3 were prepared by chemical impregnation method.The oxidative adsorption of gas-phase As2O3 by Fe2O3 and the above three composite adsorbents was investigated through using the self-made arsenic generation and fixed bed adsorption reaction device.The total amount and valence of arsenic in the adsorbed products were detected nondestructively by high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry.The mechanism of catalytic oxidation of As(?)/As(V)by Fe2O3 and NaBr-Fe2O3 adsorbents was deeply investigated.The results showed that the adsorption capacity of NaBr-Fe2O3 was significantly enhanced,and it was about 2.3 times of that of Fe2O3.However,the adsorption properties of H2O2-Fe2O3 and NaClO-Fe2O3 were not improved.Both Fe2O3 and NaBr-Fe2O3 could oxidize As(?)to As(V),and the higher the Br-loading,the stronger the catalytic oxidation ability,and the stronger the adsorption capacity.The oxidative adsorption of gas-phase arsenic by Fe2O3 original sample followed the Mars-Maessen lattice oxygen oxidation mechanism.As(?)oxidation could only be carried out in flue gas with the presence of oxygen.However,NaBr-Fe2O3 adsorbent could still oxidize As(?)in the absence of O2,the reason was that the strong electronegativity of Br?excited the activity of Fe-O bond of Fe2O3,and furthermore,Fe(?)in the bulk phase acted as the electron acceptor for oxygen-return reaction instead of O2 in flue gas.