Layerer Double Hydroxides Supported Chalcogenides For Elemental Mercury Removal

Mercury is a highly toxic substance,which brings great troubles to human production and life.Mercury always exists in lithosphere as the state of HgS.Nature movements such as volcanic eruption and geothermal movement,can make mercury emit to the atmosphere and then transferred to water-system or soil by dry or wet settlement process,which would cause mercury global transmission.Human industrial production can also make mercury release from fuel,forming S-Hg composite flue gas.Traditional gaseous mercury adsorbents often suffer from SO₂ poison and low mercury capacity.In this paper,chalcogenides and LDHs materials,as active site and substrate respectively,were combined together to solve those defects and realized efficient Hg⁰uptake under S-Hg mixed gas.Results show that a novel[MoS₄]^2-/CoFe-LDH was synthesized using ion-exchange method.The material showed excellent Hg⁰ removal performance at 75 ^oC in the simulated gas of 350?g/m³ Hg⁰.Meanwhile,it can be used in low and high SO₂ concentration.The theoretical maximum mercury capacity more than16.39 mg/g.[MoS₄]^2-clusters exchanged the NO₃^-and intercalated into the CoFe-LDH layered sheets,enlarged the inter-lamellar spacing?from 0.622 nm to 0.880 nm?and enhanced to BET surface area of the material.During the adsorption process,Porous structures are beneficial for gaseous transformation and elemental mercury?Hg⁰?capture.Gaseous mercury was adsorbed on the materials surface,the interlayer[MoS₄]^2-cluster was the primary active and contained a lot of Mo-S network for mercury capture;the adsorbed mercury was bonded with S and formed HgS.In order to explore the effect of mercury removal in high mercury concentration and the effect of different combinations of active components and carriers on mercury removal,different ratio of CuS/CoFe-LDH materials were successfully synthesized in a facile method.The material showed excellent Hg⁰ removal performance at 75^oC in the simulated gas of 1.2 mg/m³ Hg⁰ and different concentrations of SO₂.On one hand,the content of CuS was the most important part as it reacted as the main active component.On the other hand,the reasonable dispersion of CuS on CoFe-LDH can enhance its activity.The results showed that the CuS/CoFe-LDH composite with ratio of 1:1 of CuS to CoFe-LDH has the best performance.In order to widen the temperature window of material application and explore the influence of material morphology on mercury removal,two kinds of hierarchical porous layered double hydroxides?LDHs?were synthesized through an in-situ growth method.Two as-prepared NiAl-S₄@SiO₂ microspheres displayed three-dimensional morphologies,accordingly exhibited as core-shell and urchin-like morphologies.The SiO₂ and LDHs host layer provide a stable environmental space for the interlayer polysulfide guests.Generally,the polysulfide of[S₄]^2-contains S^2-and S⁰.The S⁰ plays a main ingredient in the process of removal mercury.However,the remnant S^2-has nearly no affinity to mercury,and it is easily oxidized to form SO₄^2-in the basic LDHs environment.At the same time,the addition of SiO₂,which makes the temperature of the material window has a certain improvement,within 150 ^oC can keep a good performance of mercury removal.In this study,[MoS₄]^2-/CoFe-LDH,CuS/CoFe-LDH with different proportions and NiAl-S₄@SiO₂ with special morphologies were prepared for mercury removal.These materials have good anti-sulfur and mercury removal properties respectively under the condition of S-Hg composite flue gas,and they can be used in different flue gas conditions,which improve new ideas for future material design.