Study On The Technologies Of Sulfide Removal And Its Stablization From Wastewater

With the rapid development of industrial economy,numerous industrial wastewater has been discharged directly or indirectly,which generates a variety of environmental problems.Among them,the wastewater discharges from petrochemical,tanning,pharmaceutical and other industries contain high concentration sulfide.If the sulfide in the wastewater can not be effectively removed,it will cause serious harm to the ecological environment and human health.For the removal of sulfide from wastewater,there are traditional technologies such as physical coagulation,chemical precipitation and biological absorption.However,many of these technologies have problems such as high investment and operating costs,difficult treatment of high concentration sulfide,low sulfide removal efficiency and secondary pollution associated with the treatment process.In view of the properties of sulfide and its potential hazards,as well as the drawbacks of the current wastewater sulfide removal technology,this thesis established a sulfide mineralization technology system through the design and preparation of specific and cheap adsorbents,which can not only adsorb and remove sulfide from wastewater,but also transform it into more stable substances such as elemental sulfur,oraganosulfur compounds and pyrite.The removal and stabilization of sulfide in wastewater are realized,which provides a new idea for efficient treatment of sulfide containing wastewater.The major work was presented as follows:（1）Study on synthesis of reduced graphene oxide/ferric oxide and its stabilization of sulfide removal:The adsorbent RGO/Fe₃O₄ was synthesized by an in-situ chemical method.The morphology,structure and chemical composition of the adsorbent before and after the reaction were analyzed by SEM,XRD,XPS and other characterization methods.The effects of pH,ionic strength and other environmental factors on the adsorption performance of RGO/Fe₃O₄were investigated.Finally,the possible adsorption and transformation mechanism were elaborated by adsorption model fitting and theoretical analysis.The results showed that the prepared RGO/Fe₃O₄has sheet mesoporous and contains many oxygen-containing functional groups,which can transform sulfide in wastewater into elemental sulfur（hydroxyl（-OH）and carboxyl（-COOH））and sulfone organics（epoxy group（C-O-C）and carbonyl group（C=O））,thus realizing sulfide removal.At the same time,the sulfide can be removed by van der Waals force adsorption on the internal pore diameter.The adsorption equilibrium time of 25 mg RGO/Fe₃O₄ was 180 min with sulfide concentration of 133.14 mg/L under 298 K.The adsorption performance of RGO/Fe₃O₄ on sulfide is little affected by pH.The presence of sodium salt and calcium salt can improve the adsorption capacity of sulfide by reducing the electrostatic repulsion between RGO/Fe₃O₄ and sulfide.In addition,the adsorption process is a spontaneous endothermic process,and the adsorption behavior can be better described by the pseudo-second-order kinetic model and Langmuir linear isothermal model,with a maximum adsorption of 173.01 mg/g.（2）Study on sulfide mineralization removal by iron-based materials under the promotion of Ni²⁺:Different iron-based materials:nano zero valent iron（nZVI）,iron oxyhydroxides（β-FeOOH）,Fe/MgO were used to investigate sulfide mineralization removal effect under the promotion of Ni²⁺.Then,the optimal material was selected based on its sulfide removal effect by mineralization,environmental harm and practical application,and the morphology and structural composition before and after the reaction were analyzed by SEM,XRD,XPS,etc.The effect of different experimental parameters on the sulfide removal effect of the system through mineralization were explored,and the species and contents of other sulfur compounds in the corresponding solution after the reaction were measured.Finally,the possible mineralization mechanism was proposed based on the experimental results.The results showed that they can all remove sulfide from aqueous solution by oxidation or formation of FeS,the removal rate of Fe/MgO was the highest（98.28%）,while that ofβ-FeOOH was the lowest（92.96%）.After the addition of Ni²⁺,the removal rate of the three systems were 99.01%,but only nZVI and Fe/MgO could react with sulfide and form FeS₂within 24 h.The sulfide removal mechanism of nZVI is that the outer layer FeOOH first reacts with sulfide to produce FeS,and then reacts with polysulfide to produce FeS₂ under the action of Ni²⁺to promote the nucleation of FeS_2.In addition,the addition of Ni²⁺will reduce the pH,and when the applied material is Fe/MgO,more Ni²⁺can be absorbed,making it less harmful to the environment.Fe/MgO reacted with sulfide to produce FeS₂ through Ni²⁺promotion at at different pH values.Under acidic conditions,FeS reacts with elements sulfur,and under neutral or alkaline conditions,FeS reacts with polysulfide H₂S_n.The promotion mechanism of Ni²⁺is mainly to accelerate the formation of FeS₂ by replacing Fein FeS to form Ni-doped FeS precursors and promote nucleation of FeS₂.Under basic conditions and with Ni²⁺concentration of 164.52 mg/L,the system can remove entire sulfide within 1 min and produce FeS₂ after 6 h.After 24 h,the Ni²⁺in the solution partially formed Ni（OH）₂ attached to the material,and partially formed Ni-rich（Fe,Ni）S₂ nuclei existing in Fe/MgO,the concentration of S₂O₃^2-/SO₃^2-in the solution increases with reaction（103.70 to 122.28 mg/L）,SO₄^2-content changed little（0.78to 3.75 mg/L）,sulfides content is zero.The process of mineralization releases H⁺,which makes pH decrease overall.The mineralization process is almost unaffected by sodium salt,the content of SO₄^2–presented downtrend（15.65 to 3.75 mg/L）,but calcium salt can significantly increase the concentration of S₂O₃^2-/SO₃^2-（113.52 to 158.97 mg/L）and SO₄^2-（19.36 to 33.49 mg/L）.Higher temperature will weaken the adsorption and transformation of Fe/MgO to sulfide,and promote the release of more H⁺in the mineralization reaction,resulting in a greater decrease in the pH of the reaction solution.