Experimental study on adsorption of arsenic and selenium in coal fired flue gas by Mn-Fe binary oxide

A series of Mn-Fe binary oxides with different molar ratios were synthesized by coprecipitation method, and their adsorption behaviors of gaseous arsenic and selenium in flue gas at different temperature were investigated. The simultaneous adsorption characteristics of As₂O₃ and SeO₂ on Mn-Fe binary oxide were studied. To avoid secondary pollution for adsorbent utilization, As/Se leaching properties in Mn-Fe binary oxides were evaluated. Results show that the adsorption capacity of As₂O₃ and SeO₂ on the Mn-Fe binary oxides increases firstly and then decreases with the increasing Mn content. The adsorption capacity reaches the maximum when the molar ratio is 1∶1. The optimum adsorption temperatures of As₂O₃ and SeO₂ are 750 and 600 ℃, respectively. During the process for As₂O₃ and SeO₂ adsorption on Mn-Fe binary oxide simultaneously, Mn-Fe binary oxides preferentially adsorb As₂O₃, while SeO₂ is inhibited. In addition, the pre-adsorption SeO₂ can enhance the adsorption activities of adjacent atoms, which is beneficial for As₂O₃ adsorption. The concentration of arsenic and selenium in the leaching solution of spent Mn-Fe binary oxide is far lower than the control limit, which will be no secondary pollution in the process of utilization with fly ash.