Study On Removal/Solidification Of Lead In Desulfurization Waste Of Coal-fired Power Plant

Although the proportion of green energy is increasing year by year with the optimization and adjustment of China’s power supply structure,the power supply structure is still dominated by thermal power generation for a long time.At present,more than 85%of coal-fired power plants in China use limestone-gypsum wet desulfurization technology.The wide application of this technology makes desulfurization wastewater and desulfurization sludge increase day by day,and heavy metal pollutants in it will cause serious pollution to the environment.Heavy metal lead is listed as one of the strongest pollutants by the World Health Organization because of its high bioaccumulation,non-degradability and high toxicity.It is of great practical significance to study the removal and solidification of heavy metal lead in desulfurization wastewater and sludge.In this dissertation,lime-aluminum precipitation method is proposed to remove lead from desulfurization wastewater,and the effects of temperature,feed ratio and other parameters on removal efficiency are explored,and the precipitation mechanism of heavy metal lead in desulfurization wastewater is analyzed.The results show that,for the solution containing a single heavy metal lead ion,when the pH is about 10,the reaction temperature is about 35℃,and the feed ratio of precipitant is about CaO:NaAlO2=2:1,the removal efficiency is the best,reaching 97.5%.For the solution containing a variety of mixed heavy metal ions(Pb,Cr,Cd,Cu,Zn,Ni,As,Se),under the same pH and reaction temperature,the best feeding ratio of precipitant is about CaO:NaAlO2=2:1,and the lead removal efficiency is 88.66%.Its main mechanism is the removal of lead ions from the solution by alkaline environment caused by the hydrolysis of CaO and NaAlO2(OH-reacts with heavy metal ions to form water-insoluble or slightly water-soluble flocculent precipitate)and calcium and aluminum compounds generated by its hydration reaction.In this dissertation,the idea of using coal-fired fly ash as curing agent to cure heavy metals in desulfurization sludge is put forward,and compared with common curing agents such as cement and chelating agent,so as to analyze the stable curing mechanism of heavy metal lead in desulfurization sludge.The results show that among cement,fly ash,chelating agent DTC(dithiocarbamate)and chelating agent TMT-15(trisodium thiocyanate),fly ash has the best solidification effect on lead in desulfurization sludge,and the solidification efficiency of different fly ash and desulfurization sludge is between 40%and 100%.The main solidification and stabilization mechanism of fly ash for heavy metal lead in desulfurization sludge lies in the ion exchange and adsorption of ettringite and hydration products.The above methods provide certain experimental basis for optimizing desulfurization wastewater treatment and solidification stability of desulfurization sludge in coal-fired power plants,and have certain reference for realizing zero emission of desulfurization waste in coal-fired power plants and its resource utilization.