Analysis Of Characteristics Of Fly Ash From Typical Municipal Solid Waste Incineration And Study On Stabilization Effect Of Heavy Metals

With the increase in the proportion of municipal solid waste（MSW）treatment in my country,the amount of incineration fly ash has increased significantly.Due to the accumulation of heavy metals in fly ash,unreasonable disposal will cause relatively high environmental risks.Based on the current research status at home and abroad,this article selected conventional stabilizing agents（chelators and phosphates）and new adsorbent materials（aluminum mud,Al-WTR;biological hydroxyphosphorus,Bio-HAP）by obtaining municipal solid waste incineration（MSWI）fly ash from multiple cities in China.Studyed on the occurrence status,dissolution behavior and environmental risks of heavy metals（Pb,Zn,Cd,Cr,As,Sb）before and after stabilization,and provided a basis and theoretical reference for standardizing the management of coal ash from the incineration of domestic waste.The main conclusions were as follows:（1）Collected in fly ash samples from Zhejiang,Shanghai,Chengdu,Qingdao,Weihai and other provinces/cities to explore the pollution characteristics of heavy metals in fly ash.The results of the study showed that the fly ash sample has a spherical surface microstructure on the whole,and some of it has a needle-shaped structure;the main chemical components in the fly ash are Ca O,SO₃,Cl,etc.,and the main minerals contained in the fly ash are Na Cl,KCl,Ca Cl OH,Ca SO₄,Ca Cl₂,etc.;the p H of fly ash was generally higher than 12,the conductivity was higher than 9 m S/cm,the redox potential was negative,and it contained a lot of alkaline substances and soluble salt substances,with strong acid neutralization ability and extremely strong reducibility;overall,heavy metals showed a trend of Zn>Pb>Ba>Cu>Sb>Cd>Cr>As>Ni>Se;continuous extraction experiments showed that Zn,Cu,Cd,Ni,Ba mainly existed in acid extraction state and residue state,Cr,Sb and As mainly existed in surface adsorption state,acid extraction state and residue state,Pb mainly existed in water-soluble state and acid extraction state,Se mainly existed in water-soluble state,surface adsorption state,and acid-extracted state;the leaching results showed that the leaching concentration of Zn,Cr,As,Ni,Ba and Se in the fly ash did not exceed the standard,and the leaching concentration of Pb,Cd,Sb was relatively high,and there was a high environmental risk.（2）Selected conventional stabilizing agents,chelating agents and phosphates,and explored the effects of compounding ratio and stabilization time on the stabilization effect of heavy metals.The research results showed that:different stabilization time had no obvious influence on the stabilization effect of heavy metals.After stabilization,the main minerals in the fly ash did not change significantly,and the p H and EC of the extract were significantly reduced.After the stabilization treatment,Pb in fly ash changed from water-soluble state and acid-extracted state to iron-aluminum oxide combined state and residue state,Zn,Cd,Cr,Cu,Ba and Ni were mainly acid-extracted state and residue state,the binding form of As changed from the surface adsorption state and acid extraction state to the residue state,while Sb changed to the water-soluble state,the surface adsorption state and the iron-aluminum oxide binding state,and the Se was still in the surface adsorption state,acid extraction state and residue state.After stabilization,the leaching concentration of Pb and Cd in the fly ash was reduced,and the environmental risk was reduced.The chelating agent had the best stabilization effect,and the removal rate is up to 95%or more,the effect of the complex ratio of chelating agent and phosphate was better than that of phosphate stabilization.The leaching concentration of heavy metals Cr,Cu,Ba and Ni had not exceeded the standard,and the environmental risk was low,the effect of the compound ratio treatment was better than the stabilization of the chelating agent or the stabilization of the phosphate;while there were still exceeding the standard in the Zn,As and Sb phenomenon,the environmental risk of Zn ws reduced,but As and Sb still had higher environmental risks.（3）Selected Al-WTR and Bio-HAP as adsorption materials to explore the stabilization effect of fly ash heavy metals under the composite ratio of Al-WTR and Bio-HAP.The research results showed that Pb,Zn,Cd,Cu and Cr in fly ash after stabilization still mainly existed in acid-extracted state and residue state,and the surface adsorption state content of As was significantly reduced,which was converted to iron-aluminum oxide combined state and acid-extracted,while the content of Sb in the acid-extracted state and residue state was reduced,and it was transformed into water-soluble state,surface adsorption state and iron-aluminum oxide combined state.Al-WTR alone had the best stabilizing effect on Pb and Cd,the concentration was lower and the environmental risk was reduced after stabilization;the leaching concentration of Zn,Cu,Cr,As and Sb was significantly reduced,and the environmental risk was reduced,the composite ratio of Al-WTR and Bio-HAP had the best stabilization effect.In summary,conventional stabilizing agents（chelators and phosphates）and adsorption materials（Al-WTR and Bio-HAP）can effectively fix heavy metals in fly ash,and the chemical form of heavy metals changed significantly during the stabilization process,the leaching concentration was reduced,and the stabilization effect in the compound ratio was better than that of a single agent.