Research Of Stabilization Effect Of Stabilizers On Heavy Metals In Municipal Solid Waste Incineration Fly Ash

With the rapid development of China's urbanization,the scale of cities has gradually increased,which has brought a series of disposal problems of domestic municipal solid waste?MSW?.but the fly ash in domestic MSW incineration contains heavy metals with high leaching toxicity,which causes great harm to the environment.Heavy metals are not easily decomposed.Over time,they will be continuously lost,migrated,transformed,and accumulated in the soil,water,and gas environment,and will be enriched through the biological chainIn view of the above problems,the leaching behavior of inorganic and organic stabilizers to heavy metals in MSW incineration fly ash by buffer solution method is studied in this paper,and the optimal inorganic and organic stabilizers based on the experimental results are selected.The investigation of inorganic stabilizers on Pb and Cd and impact of leaching behavior in MSW incineration fly ash are focused on.According to relative literature review of organic stabilizers,the modified lignin-based triaminotriethylamine salt?TATEL?stabilizers will be developed The main conclusions are as follows1)According to the two main incineration technologies in China,five kinds of bag filter fly ash in the circulating fluidized bed and mechanical grate furnace incinerators are selected as typical waste incineration fly ash,and the characteristics of the selected fly ash are analyzed.The results show that the content of Cd,Cu,Pb and Zn is higher than that of As,Ba,Cr,Hg,Ni and Se.For fluidized bed fly ash the average content of Pb is 1022.28 mg/kg,and the average content of Cd is 68.08 mg/kg.For the fly ash from grate furnace,the average value of Pb content i is 2548.48mg/kg,and the average value of Cd content is 180.84mg/kg.The content of heavy metals Pb and Cd in fly ash from grate furnace is 2-3 times higher than that in fly ash from circulating fluidized bed.The leaching toxicity of Pb and Cd in the original fly ash used in the experiment did not meet the“standard for pollution control on the landfill site of municipal solid waste”.Among them,The leaching toxicity of Cd and Pb in the fly ash of the circulating fluidized bed is respectively 9.4 times and 6.12 times of the standard value The leaching toxicity of Cd and Pb in the fly ash of the grate furnace is respectively 14.87 times and 13.04 times of the standard value The grate furnace burns heavy metals Pb and Cd in the fly ash.The overall leaching toxicity of Cd and Pb in the fly ash of the grate furnace is about 2 times higher than that of the fly ash of circulating fluidized bed2)Study on the stabilization of heavy metals by using inorganic agents was carried out for two furnace-type fly ash samples.The results show:Between the addition ratio of Na₂HPO₄,NaH₂PO₄,Na₃PO₄ stabilizer is 1 to 3%,the leaching concentration of Pb and Cd shows a downward trend when the addition amount increase.t,,which suggests that increasing the addition amount can improve the stabilization effect on Pb and Cd,but With the continuous increase of the addition amount,after the addition ratio is higher than 5%,the change weakens and tends to be flat,and there is basically no change when the addition amount reaches 10%.This shows that although the addition amount of Na₂HPO₄,NaH₂PO₄,Na₃PO₄ increases,it has a certain effect on the stability of heavy metals Pb and Cd.However,its stabilization effect cannot increase linearly with the increase in the amount of addition;On the whole,under the same inorganic stabilizer addition ratio,the order of stabilization treatment effect for most fly ash is as follows:Na₂HPO₄>NaH₂PO₄>Na₃PO₄>Na2S3)Study on the stabilization of heavy metals by organic agents was carried out for two furnace-type fly ash samples.The results show that the treatment effects of Pb and Cd for the fly ash of grate furnace have obvious consistency.When the addition ratio is 1.5?3%,the change of the leaching concentration of Pb and Cd shows a downward trend while the addition ratio increases.Diethyldithiocarbamate?DTC?and trisodium ethylenediaminetetraacetic acid?EDTA?in treating heavy metal Cd in fly ash are better than Pb,All of Cd of fly ash in grate furnace meet the“standard for pollution control on the landfill site of municipal solid waste" when the addition amount is 1.5%.and more than half of the fly ash species with a stabilization rate of 95%.On the whole,under the same stabilizer addition ratio,the order of stabilization treatment effect for most fly ash is as follows:DTC>EDTA.When the addition ratio is from 1.5%to 3%,The difference between the treatment effects of the two stabilizers gradually increases4)The average stabilization rate of heavy metals Pb and Cd in the fly ash treated by the agents shows that the organic stabilizer has a better stabilizing effect than the inorganic stabilizer.The overall order of the treatment effect is as follows:DTC>EDTA>Na₂HPO₄>NaH₂PO₄>Na₃PO₄>Na2S.5)The research results of the composite agent stabilizing fly ash heavy metals show that the composite agent exhibits very good stability.Under the same organic?inorganic?agent addition ratio,the leaching concentration of heavy metal Pb in fly ash of grate furnace and fluidized bed gradually decreases when the inorganic?organic?agent increases;the leaching concentration of heavy metal Cd of fly ash in fluidized bed is gradually decreasing.For the fly ash in fluidized bed,the efficiency of composite stabilizers C3,C6,and C9 to stabilize fly ash heavy metal Pb are 88.2%,90.3%,92.5%for each,and the efficiency of C7,C8,C9 to stabilize fly ash heavy metal Cd is 55.1%,70.3%,41.6%.For fly ash in grate furnace,the efficiency of composite stabilizers C3,C6,C9 to stabilize fly ash heavy metal Pb is 82.2%,86.9%,87.4%,the efficiency of composite stabilizers C4,C5,C6,C7,C8,C9 to stabilize fly ash heavy metal Cd is 90.2%,89.6%,96.6%,95.5%,97.7%,98.1%.It can be seen that the composite stabilizer designed in this paper has a better effect on the treatment of fly ash from grate furnace.With the same addition ratio,the treatment stabilization rate of the heavy metal Cd in the fly ash of the grate furnace is higher than that in the fly ash of the fluidized bed.The treatment stabilization rate of the heavy metal Pb of the fluidized bed fly ash is higher than that of the fly ash of the grate furnace.For most fly ash,the stabilization rate can reach more than 90%by adjusting different addition ratios.6)It is shown that there are no existing stabilizers which are good stabilization effects for all type of heavy metal in fly ash in our study.In order to overcome the disadvantages of existing stabilizerswhich preparation cost is relatively high,a new type heavy metal stabilizerfor fly ash of waste incineration of lignin-based triaminotriethylamine salt?TATEL?has been carried out.It is shown that the curing rates of Cd and Pb can reach 95.9%and 90%,respectively by the stabilization application of lignin-based triaminotriethy-lamine salt for heavy metals in fly ash.TATEL contains electron donating groups???,in which the coordinated S atom can chelate with heavy metals,free S2-and Pb2+ and Cd2+with electron donating can also form PbS and CdS precipitates,The resulting product of chelating for fly ash is a six-membered chelate complex containing double bonds,which has good stability.