Performance and microscopic characteristics of industrial waste residues and bentonite-solidified sludge
To explore the synergistic treatment effect of municipal sludge using industrial waste residues and bentonite,a low-cement-content composite solidification agent(referred to as the composite solidification agent)was designed and prepared by substituting an equivalent amount of industrial waste residues(blast furnace slag and desulfurization gypsum)for a portion of the cement.Tests for unconfined compressive strength,leaching of heavy metals,and COD were conducted to assess both the mechanical properties and environmental safety performance of the composite curing agent and bentonite-solidified sludge.Additionally,the microscopic characteristics of the composite curing agent and bentonite-solidified sludge were illustrated through micro-testing approaches including XRD,TG/DTG,BET,and SEM.The results demonstrated that replacing a portion of cement with blast furnace slag and desulfurization gypsum could substantially enhance the strength of solidified sludge.Furthermore,the optimal mass ratio for the composite curing agent was constituted by blast furnace slag:desulfurization gypsum∶cement=6∶1∶3.On the basis of the composite curing agent-solidified sludge,adding bentonite could remarkably enhance the strength and environmental safety performance of solidified sludge,as well as the optimal content of bentonite was 10％.Substituting a portion of the composite curing agent with an equivalent quantity of 10％bentonite resulted in a 17％to 23％increase in the strength of the solidified sludge.Concurrently,the leaching concentration of heavy metals and COD values decreased by 40％to 60％.Compared with the cement-solidified sludge system,more hydration products,namely,C-S-H gel,and ettringite crystal,were generated in the system of the composite curing agent and bentonite-solidified sludge.Moreover,bentonite exhibited a favorable effect in refining pores.Consequently,the combined effect of the hydration products and bentonite substantially increased the compactness and strength of the solidified sludge.Meanwhile,the stability of heavy metal and organic matter in the solidified sludge was effectively enhanced by the physical wrapping of cementitious substances as well as the physical adsorption and ion exchange effect of bentonite.The findings of this study provide a reference for the low-carbon solidification and resource utilization of municipal sludge.
sludgeindustrial waste residuebentonitestrengthheavy metal leachingmicroscopic characteristics
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