Study On The Salts Removal From Municipal Solid Waste Incineration Fly Ash Via Concentrated Leachate Solution

With the popularization and application of waste incineration technology in China,a large amount of heavy metal and dioxin-rich fly ash is produced,which makes the treatment and disposal of fly ash become the key link of the popularization and application of waste incineration technology.More importantly,the existence of a large amount of salt in fly ash seriously restricts its recycling and harmless treatment.In view of this,this paper combines waste water treatment of waste incineration plant with fly ash disposal,and puts forward a technical idea of using leachate concentrate to elute fly ash for desalination.In order to obtain better elution and desalination effect of concentrated leachate of fly ash,the salt distribution characteristics of concentrated leachate and fly ash of waste incineration plant were studied in detail,and the influence laws of liquid-solid ratio,elution times,p H and other factors in the elution and desalination of fly ash of concentrated leachate of waste incineration plant were explained.In this paper,the characteristics of salt removal and enrichment in leachate fly ash from the circulating elution of leachate concentrate were explored,and the migration and distribution of heavy metals such As and Se that were easily leached during the elution process were also discussed.The main research conclusions are As follows:（1）The soluble salts in fly ash mainly include KCl,Na Cl and Ca Cl₂.The composition of concentrated leachate is complex and the chemical oxygen demand is high.When the liquid-solid ratio of leachate concentrate to fly ash is 3m L/g,the removal efficiency of soluble salt in the incineration fly ash is the highest（60%～70%）,and the enhancement effect of increasing the liquid-solid ratio is very limited.（2）when the leachate concentrate circulation elution incineration fly ash,soluble salt elution effect increased with the increase of leachate concentrate use frequency is reduced,but the trend of soluble salt concentration in the eluent,second elution eluent for K⁺concentration in the leachate concentrate concentrate 8～11 times,Na⁺concentration of leachate concentrate concentrate of 5～16 times,12～14 times of the original solution of the concentrated leachate of Cl^-concentration;In the third elution,the concentration of K⁺was 10～15 times that of the original leachate,Na⁺was 7～23times that of the original leachate and Cl^-was 15～18 times that of the original leachate.The higher the concentration of salt ions in elution,the lower the removal rate of salt in fly ash.（3）The content of heavy metal elements As and Se in the incineration fly ash is relatively small.The average content of As and Se in the sample is 20～60mg/kg and2～19mg/kg,respectively.They exist in the form of oxygen anion and have poor solubility in the alkaline environment.The change of elution ratio and elution times had little effect on the change of heavy metal element content in the samples.The heavy metal element content in the samples before and after elution all met the national discharge standard.