Selective Removal Of Divalent Mercury From Waste Acid By Regenerable Magnetic Sulfureted Fe₂TiO₅

China,with the largest emission of mercury in the world,is facing enormous pressure for mercury abatement as a party to the Minamata Convention.The non-ferrous metal smelting industry is one of the main sources of anthropogenic mercury emissions in China,and the generated waste acid contains high concentrations of divalent mercury(Hg²⁺).Therefore,controlling the emission of Hg²⁺in waste acids is of great significance for solving the problem of mercury emissions in China.Adsorption method is a technology with practical application prospects for controlling the emission of Hg²⁺in waste acid,with the core of developing efficient adsorbents suitable for waste acid systems.Therefore,this study developed a sulfureted Fe₂TiO₅ with excellent Hg²⁺removal performance by modifying a layer of Fe S_x on the surface of magnetic iron titanium spinel（Fe₂TiO₅）through sulfurization（H₂S pretreatment）.On this basis,the sulfurization of Fe₂TiO₅ was optimized by increasing the sulfurization temperature and time.On the one hand,the content of surface Fe S_x was increased,and on the other hand,the morphology of surface Fe S_x was changed.A sulfureted Fe₂TiO₅-400 with better Hg²⁺removal performance was developed.The main research results are as follows:（1）When Fe₂TiO₅ was vulcanized at 300℃ for 1 hour,a layer of Fe S₂ was formed on its surface,significantly improving its Hg²⁺removal performance.The adsorption capacity of sulfureted Fe₂TiO₅ reached 292-317 mg g^-1,and the adsorption rate reached 49.5-57.6 mg g^-1h^-1.At the same time,sulfureted Fe₂TiO₅ exhibits excellent selectivity for the removal of Hg²⁺,and its performance in removing Hg²⁺is basically unaffected by coexisting metal ions such as Zn²⁺,Cu²⁺,and Cd²⁺.In addition,the mechanism and kinetic studies show that Fe²⁺in Fe S₂ can be adsorbed to Hg²⁺on the ratio of 1:2 molar ratio for isomorphic substitution to compounds of Hg and S.The used sulfureted Fe₂TiO₅ can be magnetically separated from the waste acid.After heat treatment,the adsorbed mercury can be desorbed in the form of high concentration gaseous elemental mercury.At the same time,the recovery device for elemental mercury in smelting flue gas is used to condense it into liquid elemental mercury for centralized control.In addition,the adsorbent after thermal desorption can be regenerated and used through re vulcanization cycle.（2）When Fe₂TiO₅ was vulcanized at 400℃ for 2 hours,multiple layers of Fe S were formed on its surface,further improving its Hg²⁺removal performance.The adsorption capacity of sulfureted Fe₂TiO₅-400 reaches 1285-1304 mg g^-1,and the adsorption rate reaches 120-123mg g^-1 h^-1.Compared to sulfureted Fe₂TiO₅,the increase exceeds 300%and 100%,respectively.At the same time,sulfureted Fe₂TiO₅-400 also exhibits excellent selectivity for the removal of Hg²⁺.Mechanism and kinetic studies indicate that Fe S reacts with Hg Cl₂ in a stoichiometric ratio of 2:3 to generate Hg₃S₂Cl₂.Sulfureted Fe₂TiO₅-400 can also be magnetically separated and recovered from waste acids,which can achieve centralized control of mercury on the one hand and continuous recycling and regeneration on the other hand.