Stabilizing Effect Of FeS,Modified Steel Slag And Modified Fly Ash On Mercury-contaminated Soil

As a highly toxic and heavy metal,mercury can exist in the atmosphere,water,soil and living organisms,and will cause great harm to the environment and human beings.About one-third of the mercury is released in our country each year.The impact on the environment can not be ignored,especially the hazards posed by mercury in the soil.So remediation of mercury-contaminated soils has become an important task.In this experiment,mercury-contaminated soils were stabilized by using a wide range of sources,low-cost converter steel slag,thermal power plant fly ash,FeS and its compounding combination reagent.Conducting a safety analysis on steel slag and fly ash.In order to get high efficiency remediation of mercury contaminated soil,stabilization reagents and materials will be modified.According to the stabilization efficiency and its late toxicity leaching effect of screening out the highest stabilization of single reagent and compound reagent.To explore the changes of mercury content in soil before and after stabilization and its mechanism of stabilization and restoration.Experiment explored the effect of stabilization time,stabilization temperature and soil organic matter content on the recovery of mercury-containing soil by steel slag and fly ash.The main conclusions of this thesis are as follows:(1)The leaching toxicity of steel slag and fly ash shows that these two minerals are non-toxic,friendly to the environment and more stable in physical and chemical properties,and are suitable for the remediation of mercury-contaminated soil;(2)After the mineral steel slag and the fly ash were modified by acid and nano,the structure,specific surface area,activity index and so on were tested and characterized by SEM and BET.The results showed that the spacing of the two mineral layers changed,the activity index and the specific surface area increased significantly,the number of pores increased and the pores became larger,and there were more active adsorption sites on the mineral surface,which could adsorb heavy metal mercury in the soil with high efficiency;(3)The treatment of mercury-contaminated soils with FeS,steel slag,fly ash and self-made modified materials,the stabilization effect is:acid nano modified steel slag/acid nano modified fly ash>acid nano modified steel slag/FeS>acid nano modified fly ash/FeS>acid nano modified steel slag>FeS>acid nano modified fly ash>nano modified steel slag>nano modified fly ash>acid modified steel slag>acid modified fly ash>steel slag>fly ash.The stability of 5%acid nano-modified steel slag is the best in a single reagent experiment.In the compound reagent experiment,2.5%acid nano steel slag+2.5%acid nano modified fly ash has the best stability,which can reach 99.89%and 99.94%.The mercury content of soil leachate in the whole molar ratio is lower than 0.10 mg/L(the toxic leaching value of soil mercury is 28.163 mg/L)as stipulated in GB 5085.3-2007.FeS reagent over-investment will lead to increased exchangeable mercury content,so need to pay attention to the amount of stabilizer input;(4)In the process of stabilization,the various forms of mercury in the soil greatly changed,the content of exchangeable mercury and reducible mercury decreased significantly,the content of oxidizable mercury changed little,the content of residual mercury increased significantly,of the soil,the bio-mobility of Hg significantly decreased and the potential harm to the environment was greatly reduced.Most of the Hg forms in the soil were changed from exchangeable state,reducible state and oxidizable state to residual state,as high as 75%or more,the bioavailability of mercury is significantly reduced;(5)The results of scanning electron microscope showed that HgS,Hg(OH)2 and Hg2(OH)2 were formed in the restored soil,which indicated that the experimental stabilization of mercury-contaminated soil was achieved through chemical reaction,physical adsorption,adsorption,ion exchange adsorption and so on;(6)The concentration of mercury in soil leachate gradually decreased with the increase of restoration time and stabilized after 10 days of stabilization.According to the actual application,the optimal stabilization of mercury-containing soil with modified steel slag and modified fly ash was considered the time is 10 days.In the range of 5?35?,the mercury concentration in soil leachate gradually decreases with the increase of temperature,and the optimal stabilization temperature is 35?.According to the actual application of restoration environment,organic matter(corn stover)can inhibit the stabilization of acid nano-modified steel slag,but it can promote the stabilization of acid nano-modified fly ash.It is suggested that a certain amount of soil organic matter may be added within the appropriate range(more than 4%of soil mass fraction).