Study On The Removal Performance Of Modified Iron Sulfide On Elemental Mercury From Smelting Flue Gas

Mercury is extremely toxic,volatile,and long-distance migration,which can cause serious harm to the environment and human health,and has become an environmental issue of global concern.China is a major global mercury emission country,and the non-ferrous metal smelting industry is one of the main sources of atmospheric mercury emissions in our country,accounting for about 30%of the total emissions.Controlling mercury emissions from the non-ferrous smelting industry is important for reducing our country's atmospheric mercury emissions.Significance.Non-ferrous smelting smoke has the characteristics of high-sulfur and high mercury,and the mercury in the flue gas mainly occurs in the form of zero-valent mercury(Hg⁰).Converting Hg⁰in the flue gas into particulate mercury(Hg^p)has become a viable option for mercury removal technology.Therefore,the development of a cheap and effective adsorbent to achieve high-efficiency adsorption of Hg⁰in high-sulfur flue gas is of great importance for reducing mercury pollution in the smelting industry.Iron sulfide(FeS_x)has a strong affinity for Hg⁰and can capture Hg⁰in a high-sulfur atmosphere,but its shortcomings such as narrow operating temperature window,slow adsorption rate,and low adsorption capacity limit its use in mercury removal in the smelting industry.In order to solve these problems,this project proposes the use of anion and cation modification strategies to improve the adsorption performance of FeS_xand realize the recycling of adsorbents,providing a reference for the removal of Hg⁰in smelting flue gas.For anion modification,FeS_xwas modified by selecting element Se of the same main group as S,and FeS_xSe_yadsorbents of different proportions were prepared,in order to improve the mercury removal performance of traditional iron sulfide adsorbents.XRD,Raman,XPS,SEM and TEM were used to characterize the selenium-modified iron sulfide,which confirmed the successful preparation of spherical FeS_xSe_y.The experimental study of adsorption performance shows that FeS_1.32Se_0.11have a good adsorption performance for Hg⁰in a wide temperature range(80-200?).At the same time,FeS_1.32Se_0.11has a good adsorption performance for FeS_1.32Se_0.11in O₂,SO₂,H₂O and other atmospheres.There is almost no change in mercury removal performance.FeS_1.32Se_0.11has excellent SO₂and oxidation resistance.The cycle regeneration experiment on FeS_1.32Se_0.11has been carried out.After 6 tests,it still maintains a mercury removal rate of more than 88%,which is good Renewable performance.The adsorbent is subjected to long-term saturated adsorption,and its saturated adsorption capacity is measured to be 23.52 mg/g,which is higher than other adsorbents of the same type.The adsorption kinetics and adsorption mechanism are studied.The entire adsorption process conforms to the pseudo-first-order kinetic model.XPS is used to analyze the valence states of the elements on the sample surface before and after the reaction.It is concluded that Se doping can be formed on the surface of the selenium-sulfur-iron composite adsorbent at high temperature.Se-S_n^2-active site,which has higher high temperature stability than S₂^2-,so that it can be used as the adsorption site of Hg⁰at high temperature,and chemically react with physically adsorbed Hg⁰to form HgSe.The above results indicate that the anionic selenium modification can promote the formation of highly stable Se-S_n^2-adsorption sites,thereby improving the adsorption performance and working temperature window of the adsorbent.For cationic modification,Co-modified FeS_xis used to form Co-doped Fe_xCo_(1-x)S_yadsorbents with different proportions.XRD,XPS,SEM and TEM were used to characterize the prepared adsorbent,and the results confirmed the successful preparation of spherical Fe_xCo_(1-x)S_yparticles.The adsorption performance test of Fe_xCo_(1-x)S_yadsorbents with different ratios of Fe/Co shows that Fe_0.5Co_0.5S₂has the best adsorption rate,and the specific adsorption rate order is Fe_0.5Co_0.5S₂>Fe_0.8Co_0.2S₂>Fe_0.2Co_0.8S₂>CoS_y>FeS₂.The factor experiment study on Fe_0.5Co_0.5S₂shows that the best adsorption temperature is 50-100?.At this time,the adsorption rate of Hg⁰exceeds 99%,and the atmosphere of O₂,SO₂,H₂O in the flue gas affects the adsorption rate of Hg⁰.Under the extreme conditions of a SO₂concentration of1.5%and a gas hourly space velocity of 398000h^-1,the capture efficiency of Fe_0.5Co_0.5S₂reached over 97.8%in the 180 min experiment time,and the average capture rate of Fe_0.5Co_0.5S₂for Hg⁰,and the adsorption capacity reached 2.5?g/g/min and 28.66 mg/g,respectively,which were higher than previously reported metal sulfides and carbon materials.The cyclic regeneration experiment was carried out on the adsorbent.Under the optimal conditions,after 4 cycles,Fe_0.5Co_0.5S₂still maintained 99%adsorption efficiency for Hg⁰.The above results confirm that Fe_xCo_(1-x)S_yprepared by cationic Co modification has excellent mercury removal performance.The adsorption kinetics and adsorption mechanism of Co doping are studied,and it is found that the adsorption of Hg⁰conforms to the pseudo first-order kinetic model.Through XPS analysis of Fe_xCo_(1-x)S_ybefore and after the mercury removal reaction,it is found that Co doping is beneficial to the formation of surface active short-chain sulfur S₂^2-,and the S₂^2-formed on the surface can quickly react with Hg⁰.A stable HgS product is generated to achieve efficient capture of Hg⁰in the flue gas.The above results indicate that cationic cobalt modification can promote the formation of active S₂^2-adsorption sites,thereby improving the adsorption performance of iron sulfide.By preparing anion-cation-modified iron sulfide,high-efficiency removal of mercury in flue gas is realized,and a feasible idea is provided for the control of mercury pollution in flue gas.