Research On The Adsorption Characteristics And Mechanism Of Gas-phase Arsenic In Iron-manganese Adsorbent

Arsenic released form coal combustion has been attracted increasing attention for its characteristics of high toxicity,carcinogenicity and bioaccumulation.The arsenic in the flue gas was mainly in the form of gaseous As₂O₃.Addition of solid adsorbent is a promising way to control the arsenic emission.In this study,the Fe-Mn-based adsorbent was adopted to explore the gaseous As₂O₃adsorption mechansim,the effect of the experimental conditions were also taken in consideration.Firstly,a method for extraction of arsenic valence state was established,and the content of arsenic in different valence states in the adsorption product was successfully quantitatively analyzed.The effect of different experimental conditions on the arsenic adsorption performance of the adsorbent was explored.The adsorption product was analyzed byXPS characterization technology,the reaction process and mechanism of gas-phase arsenic oxidation-adsorption on Fe-Mnadsorbent were studied.The main contents and results of this study are as follows:（1）A new method of arsenic valence extraction was established.The influence of phosphoric acid concentration,extraction time,hydrochloric acid concentration,and ascorbic acid concentration on the arsenic extraction were explored.Results showed that the arsenic extraction increased with the phosphoric acid concentration in the extraction solution,the arsenic extraction increased with the extraction time.Due to excessively high concentrations of phosphoric acid will affect the accuracy of As⁵⁺in the determination of arsenic valence,a certain concentration of hydrochloric acid were used.Ascorbic acid can inhibit the oxidation of As³⁺into As⁵⁺during the extraction process,the inhibitory effect increased with the ascorbic acid.The experiment determined that phosphoric acid-hydrochloric acid-ascorbic acid was used as the extraction solution,and the extraction experiment process and experimental parameters were optimized.（2）The study of the gas-arsenic adsorption performance on FeMnO_X/γ-Al₂O₃adsorbent.A series of FeMnO_X/γ-Al₂O₃adsorbents were prepared by the ultrasonic-assisted impregnation method.The effects of Mncontent,reaction temperature,O₂and SO₂on the arsenic adsorption performance over FeMnO_X/γ-Al₂O₃adsorbent were studied.Results showed that the Mncontent will change the specific surface area,pore size,and oxidation performance of the adsorbent,thereby affecting the adsorption performance of arsenic.Appropriate amount of Mnis conducive to the gas-phase arsenic adsorption.The adsorption performance is strongest when the Mn-Femolar ratio is 0.5.The gas-phase arsenic adsorption performance of FeMnO_X/γ-Al₂O₃in the temperature range of300℃～1050℃increases firstly and then decreases with the increase of temperature.The increasesing temperature promotes the diffusion of gas-phase arsenic,and enhances the adsorption of the chemisorption.However,when the temperature is too high,the surface structure of the adsorbent will deteriorate,resulting in a decrease in adsorption performance.SO₂and O₂can promote the adsorption of arsenic,and SO₂will affect the surface properties of the adsorbent,O₂can supply the consumed lattice oxygen.The promotion trend to be flat as the concentration of O₂and SO₂increases.（3）Gas-phase arsenic adsorption mechanism on FeMnO_X/γ-Al₂O₃.The influence of different Mncontent and different O₂content in the adsorption atmosphere on the As³⁺and As⁵⁺in the adsorption product was analyzed.The XPS characterization method was used to analyze the valence state of iron and manganese..It is found that the adsorption mechanism of gas-phase arsenic by iron-manganese-based adsorbents mainly involves three steps:arsenic oxidation,arsenic adsorption,supplement of the lattice oxygen.