Effect Of Chelating Agents Stabilization Conditions On Leaching Behavior Of Pb And Cd In Municipal Solid Waste Incineration Fly Ash

With the increase in the amount of waste incineration,the secondary pollutants produced by incineration also increased year by year.Fly ash contains a large amount of leachable toxic and harmful heavy metals so that it must undergo a certain stabilization before landfill landfill disposal.At present,it can be seen that the stabilization of macromolecule chelating agent for waste incineration fly ash is an effective solution for heavy metal stabilization.However,there are more easily leached Pb and Cd in fly ash,And in the process of stabilization is susceptible to stabilization conditions,after stabilization still exists the phenomenon of excessive leaching.Based on this,in this paper,the physical and chemical properties of different incineration fly ash and the Morphological distribution of heavy metals Pb and Cd were analyzed;The leaching behavior of Pb and Cd after stabilization of fly ash with cement-chelating agent was studied;The effects of different inorganic agents-chelating agent combination on the leaching behavior of Pb and Cd were investigated.To explore the stability of the best compatibility of Pb and Cd ratio and conditions to further enhance the stability of the effect,and to support the improvement of application technology for stabilization of fly ash.The main contents and conclusions are as follows:1.Morphological Distribution of Heavy Metals in Fly Ash from Different Years:the presence of heavy metals Pb and Cd in different years fly ash is mainly iron-manganese oxide-bound state,and there is a certain amount of exchangeable and carbonate-bound state.The Pb and Cd in these forms are extremely unstable in the complex physical and chemical environment of landfill,which is the main reason for the excessive leaching of Pb and Cd in fly ash.2.Leaching behavior and regularity of Pb and Cd under the compatibility of cement-chelating agents:the stabilization system of cement and chelating agent has certain effect on the stabilization of Pb and Cd in fly ash.The stability of Pb and Cd in fly ash can be achieved by adding 4%of chelating agent.The effect of cement in the system is limited,the increase of cement amount under the same chelating agent has less effect on the stabilization,and the main stabilizing ability is from the chelating agent.The effect of cement on the chelating stability of Pb is synergistic and antagonistic.In the 2015 cement-chelator fly ash experimental group with 2%addition of chelating agent,the leaching concentration of Pb and Cd was higher than that of less cement when the cement was added at 5%,7%and 10%.For the 2017 ash experimental in the chelating agent dosage of 1.5%,with the addition of cement,Pb leaching showed the increase at first and then slow decline in the change.The main reason for this change is the competition between cement hydration and chelating stabilization.The addition of cement to the chelating stability of Cd is mainly synergistic effect,the addition of cement can promote the reduction of Cd concentration.3.Leaching Behavior and Regularity of Pb and Cd in the Interaction of Inorganic Pharmacy Phosphoric Acid?H₃PO₄?and Disodium Phosphate?Na₂HPO₄?with Chelating Agents:the addition of phosphate ions during the stabilization of chelating agents is beneficial to the further stabilization of Pb and Cd in fly ash.However,different inorganic phosphate in the provision of phosphate at the same time will stabilize the chelating agent and fly ash in the Pb,Cd leaching have different effects.The addition of phosphoric acid can lead to the increase of Pb and Cd leaching in fly ash,This is mainly due to the fact that H⁺from H₃PO₄ will destroy the stability of Pb and Cd that exists in the presence of iron and manganese oxide in fly ash,resulting in an increase in the amount of leachable Pb and Cd in fly ash,exceeding the stabilized capacity provided by the added PO₄^3-and chelating agent.And the effect of the addition of phosphoric acid on Cd leaching is greater than that of Pb.In contrast,disodium hydrogen phosphate showed a synergistic effect on the chelator stabilization system.When the addition ratio of chelating agent to disodium hydrogen phosphate is 3:2,4:1.5,4:2,the leaching of Pb can meet the standard limit requirement.When the addition ratio of chelating agent to phosphoric acid is 4:2,the leaching concentration of Pb is 0.28mg/L,which is close to the standard requirement.The leaching concentration of Cd can meet the requirements only when the addition ratio of chelating agent and disodium hydrogen phosphate is 4:2.4.Effect of Water Content on Stabilization of Pb and Cd during the Stabilization of Chelating Agents:The addition of deionized water during the stabilization process not only facilitates the rapid binding of chelating agents to Pb and Cd in fly ash.Due to the overbased nature of fly ash,the addition of water has a negative effect on the stabilizing effect when the chelating dose is low.And the effect of stabilization on Pb is greater than that of Cd.