Mechanism Of Slag-fly Ash-desulphurization Gypsum Modified Solidified Sludge

Using slag,desulfurized gypsum and fly ash as curing agents to solidify municipal sludge into a landfill construction material is a means of sustainable disposal of solid waste.In this paper,based on the solidification mechanism of sludge,the macroscopic mechanical strength,the evolution of mineral composition,the change of molecular groups,the phase transition of crystal decomposition and other processes of sludge,fly ash and slag modified sludge were studied by laboratory test and theoretical analysis.The unconfined compressive strength,direct shear strength and permeability of the solidified block were tested in macroscopic mechanics.In terms of the microscopic mechanism,X-ray diffraction,Fourier infrared spectroscopy,thermogravimetric differential thermal analysis,nitrogen adsorption and desorption experiments,and sem+eds were used to study the microscopic mechanism of the pore structure of the test block.The modification mechanism of municipal sludge modified by industrial solid waste was explained from macroscopic and microscopic aspects,and the correlation between macroscopic mechanical parameters and microstructure parameters was established.Based on the above experiments,the following research results were obtained:(1)moisture content plays a key role in the early stage of sludge curing,and the compressive strength increases to different degrees with the decrease of sludge content.Alkalinity can obviously enhance the compressive strength,but the strength decreases when it exceeds a certain amount.After curing,the strength and permeability characteristics can meet the requirements of landfill covering materials.(2)from the perspective of mineral composition analysis,XRD analysis of solidified sludge revealed a large number of hydrated silicoaluminate,zeolite and feldspar crystals,among which the cementing substances mainly existed in the form of calcium silicoaluminate hydrate.With the increase of alkalinity,the cementing substances gradually changed into the form of sodium silicoaluminate hydrate.(3)According to the detection and analysis of the microstructure parameters,the specific surface area of the solidified sludge test block was distributed in the range of112.288～198.415m~2/g,the total pore volume was in the range of 0.1522～0.4838cm~3/g,the average pore diameter was concentrated in the range of 5.194～14.635nm,and the pores were mainly mesoporous.(4)Scanning electron microscopy(sem)can see that with the prolonging of curing time,a large number of granular substances gradually become disorderly and disorderly,and fly ash globular particles gradually reduce.In the later stage of the reaction,they are gradually tightly connected together,forming a gel network with higher interconnection.The particle size of ettringite increased obviously,and the rod-shaped ettringite distributed in clusters.According to the elemental analysis results of energy spectrum(EDS)points,the gel products can be analyzed as calcium silicate chlorate oxide and sodium silicate chlorate oxide.(5)the use of SPSS statistical software to draw the two can express the sludge solidification body comprehensive index is deduced expression characteristic parameters of microstructure.Furthermore,the relationship between the macroscopic mechanical index and the microscopic structural parameters was analyzed,and the correlation between the structural comprehensive parameters and the macroscopic mechanical strength parameters was established.