Research On Solidified/Stabilized Of Cement-based Materials And Mechanism Of Heavy Metals In Municipal Solid Waste Incineration Fly Ash

Waste incineration for power generation technology is a commonly used method of garbage disposal at present,but the fly ash produced during the incineration process.The fly ash contains a large amount of harmful substances such as heavy metals and belongs to hazardous waste.Cement Solidified treatment is the most commonly used fly ash treatment method,but the treatment effect of fly ash with high concentration of heavy metals is poor.Therefore,this topic is based on cement-solidified fly ash,and explores the effect of calcium oxide and the aluminum-silicon ratio of the external substrate on the Solidified of fly ash.Several main hydration products of cement were synthesized,and the mechanism of their Solidified of heavy metals was discussed.Studies have found that calcium oxide has an effect on the leaching toxicity and compressive strength of cement solidified fly ash samples.The cement solidified sample with 8%calcium oxide has the best treatment effect on Cd.The solidification rate of the sample after Solidified for 7 days is increased from 63.5%to 99.4%,and the Cd leaching concentration is 0.089 mg/L.The compressive strength of the solidified sample increases first and then decreases with the increase of calcium oxide dosage,and reaches the maximum value of 2.77 MPa at 1%dosage,which is higher than the standard requirement of 1 MPa.The exchangeable state of Pb in the solidified sample treated by calcium oxide and cement was reduced from 21.6%to 6.2%,the carbonate state of Cd was reduced from 34.4%to 4.1%,and the content of iron and manganese oxidation state of Pb and Cd was reduced from 32.1%,respectively.And 13.2%increased to 49.2%and 50.2%.In addition,the acid neutralization ability test results show that after calcium oxide is added,the solidified sample is more stable in a multi-pH environment.Studies have shown that the aluminum-silicon ratio of the external substrate has an effect on the leaching toxicity and compressive strength of the solidified sample.When the ratio of aluminum to silicon(molar ratio)is 3.5,the Solidified effect is the best.The solidification rate for Cd is 42.3%,the leaching concentration is 8.19 mg/L,the solidification rate for Pb is 77.9%,and the leaching concentration is 2.47 mg./L.When 8%calcium oxide is added to the aluminum-silicon ratio,the fixed rate distribution of Cd and Pb increases to 94.4%and 95.6%.The compressive strength of the solidified sample with sodium silicate and sodium metaaluminate was significantly lower than that of the cement solidified sample.The compressive strength first increased and then decreased with the decrease of the aluminum-silicon ratio,reaching the maximum value of 0.74 MPa when the aluminum-silicon ratio was 1.75.The type and content of hydration products in the solidified sample are related to the added aluminum to silicon ratio.When the aluminum to silicon ratio is 17.the XRD of the solidified sample finds the presence of calcium chloroaluminate.and as the aluminum to silicon ratio decreases,the calcium chloroaluminate disappear.The types of hydration products in the solidified samples treated with calcium oxide and aluminum silicon plus substrates were increased,and ettringite and calcium chloroaluminate appeared.Experiments confirmed that hydrated calcium silicate,ettringite,and calcium chloroaluminate can fix Cd.Comparison of Cd solidification ability of three hydration products:calcium chloroaluminate>calcium silicate hydrate>calcium chloroaluminate.The solidification rate of calcium chloroaluminate is greater than 99%at the dosage of Cd 0.3%and 5%.Under the dosage of 0.3%Cd,the solidification rate of hydrated calcium silicate is close to that of calcium chloroaluminate,but as the dosage increases,the solidification rate decreases but is still greater than 90%.The Solidified ability of ettringite is the worst,and the solidification rate under the two dosages is the highest and it does not exceed 80%.The dosing time and the type of Cd dosing also have an impact on the hydration products.The fixing mechanism of Cd in different hydration products is different.In calcium silicate hydrate and ettringite,the mechanism of Solidified of Cd is mainly isostructural substitution and adsorption.The main mechanism of calcium chloroaluminate Solidified of Cd is co-precipitation and isostructural substitution.