Study On Solidification Characteristics Of Heavy Metals In Solid Waste Ceramics From Kiln Slag

With the rapid development of Chinese industry,the output of solid waste also increases sharply.Improper storage,disposal or utilization of solid waste will cause a certain degree of pollution to soil,water,air and so on.A large amount of kiln slag produced by steel dust extraction of Zn and a large amount of silt dredged from riverbed pose a threat to the environment and human health.The rationalization and resource utilization of kiln slag and dredged mud is very important.It is an important direction to use kiln slag and dredged mud to produce qualified building materials.Therefore,this study used kiln slag and dredged mud to produce ceramics,analyzed the product performance and environmental risks of ceramics,and explored the release and solidification mechanism of heavy metals in ceramic products.Ceramic samples with three formulations(kiln slag and dredged mud 6:4,7:3,8:2),six sintering temperatures(1 090℃,1 110℃,1 130℃,1 150℃,1 170℃,1190℃)and four preheating temperatures(400℃,500℃,600℃,700℃)were designed.By analyzing the product properties(water absorption and bending strength)of the ceramics,the optimum formula and firing conditions of the ceramics were determined as follows:kiln slag and dredging mud 7:3,sintering temperature 1190 ℃,preheating temperature 500 ℃.Under this condition,the water absorption rate of the ceramic was 0.08%and the bending strength was 88.62MPa,which was in line with the GB/T4100-2015 "Ceramic Tile" standard.Water tank leaching experiments and effective release leaching experiments were carried out for optimal formulation ceramics,and the release law of heavy metals in ceramics were analyzed to assess the environmental risks of ceramics.Based on the experimental data of water tank leaching,the application of ceramics in permeable sidewalk scene was analyzed.The cumulative releases of eight major heavy metals(Cr,Mn,Ni,Zn,As,Cd,Ba,Pb)were all very low,ranging from 0.12 mg/m2 to 10.99 mg/m2.The release characteristic of Cr,Mn,Zn,As,Ba and Pb was mainly surface scour,while the release characteristic of Ni and Cd was dissolution.MATLAB software was used to fit the heavy metal leaching data,and the secondorder kinetic equation was selected for Cr,Zn,As and Ba,Elovich equation was selected for Mn and Pb,and Freundlich equation was selected for Ni and Cd.Through the equation model,the cumulative release of 8 kinds of heavy metals(Cr,Mn,Ni,Zn,As,Cd,Ba,Pb)in the permeable sidewalk for 20 years was calculated.The results showed that the long-term cumulative release of heavy metals was very small.The results of leaching experiments showed that the potential release amount and release rate of 16 kinds of heavy metals were very low during the long-term use of ceramics.This indicated that most heavy metals were solidified,and the environmental risk of the full-solid waste ceramics studied in this paper was very low.The characteristic heavy metals Cr,Zn and Ni were selected,and the stability mechanism of heavy metals in ceramics was analyzed by using thermodynamic equilibrium calculation software FactSage and XRD pattern.Using Equilib module calculated Cr,zinc,Ni solid phase in the ceramics.The results showed that Cr was mainly solidified in the form of chromium spinel,and MgCr2O4 and FeCr2O4[1+]spinel accounted for nearly 80%.Zn mainly existed in the form of ZnFe2O4,ZnAl2O4,ZnMg2O42-spinels and ZnO solids,with spinel accounting for 74%.Ni in ceramics was composed of spinel such as AlNi2O4[1-],FeNi2O4[1-],MgNi2O4[2-]and a small amount of NiO solid,with spinel accounting for 94.7%.In XRD analysis,crystals containing Cr,Zn and Ni were CaNiSi2O6,(Ca,Na)(Fe,Mn,Zn)Si2O6,Cr0.5Fe0.5VO4,Fe2+Cr2O4 and Ni0.4Zn0.6Fe1.998Nd0.002O+x4.It can be seen that Cr,Zn and Ni were solidified in both spinel and pyroxene structures.Cr,Zn and Ni were solidified into spinel,pyroxene and other crystals through homogeneity,and some of them were also encapsulated in the glass phase,thus being solidified.To sum up,the full-solid waste ceramics of kiln slag and dredged mud studied in this paper meet the national standards,have low environmental risk and realize the solidification of heavy metals,which provides a reference for the resource utilization of solid waste.