Purification of Hg 0 from flue gas by wet oxidation method and its mechanism: a review

Abstract

The vast majority of Hg²⁺ can be removed while elemental mercury (Hg⁰) can hardly be removed due to its characteristic of high volatility and insolubility in water. Till now, how to oxidize Hg⁰ to Hg²⁺ is the key for the purification of Hg⁰, especially when there are others pollutants, such as HCl, SO₂, and NOx. In this review, the method and mechanism of Hg⁰ purification from flue gas by H₂O₂, KMnO₄, NaClO₂, and O₃ are reviewed comprehensively. It is concluded that the oxidation of Hg⁰ mainly depends on the electronic supply efficiency from the solution. The Fenton reagent, composed of H₂O₂ and metal cations, is superior to O₃ and the solution of KMnO₄ and NaClO₂. Moreover, HCl, SO₂, and NOx in the flue gas can influence the oxidation and purification mechanism of Hg⁰. It is found that HCl in flue gas had obvious auxo-action on the oxidation of mercury, and SO₂ and NOx have different effects on the oxidation of Hg⁰ with the change of compositions and concentration of pollutants in the flue gas. In general, SO₂ and NOx can slightly promote the oxidation of Hg⁰ due to the synergistic effect.