Migration And Distribution Of Volatile Metals In Sintering Ceramsite From Electroplating Sludge

Electroplating sludge usually contains a lot of harmful components such as copper,zinc,chromium and nickel,which has been listed as hazardous waste in China.In recent years,the output of electroplating sludge has increased rapidly.The safe and economical disposal way has become a realistic demand.Traditional landfill disposal method has some problems,such as potential environmental pollution risk and large area occupied,so the reasonable and effective utilization of resources has become a new development direction.Preparation of ceramsite from electroplating sludge was a potential way to realize the recycling and harmless disposal of waste.However,the release of heavy metal in the sintering process is still unclear,which restricts the control of heavy metal pollution.Therefore,this study carried out the simulation experiment of firing ceramsite,that is,by setting different firing temperatures,the effects of raw material ratios and additives on the migration and distribution of heavy metals and the changes of mineral phase composition were studied.It is expected to provide a theoretical basis for pollution control and environmental safety assessment in the process of electroplating sludge resource utilization.The migration and distribution characteristics of Zn,Pb,As and Sb were studied based on different raw material ratios.The results showed that when the ratios of electroplating sludge:municipal sludge:shale were 3:2:5 and 3.5:1.5:5,the contents of Zn and Pb increased with the increase of temperature,while the contents of As and Sb increased first and then decreased,and the content reached the highest at 700℃.When the ratio of electroplating sludge:municipal sludge:shale was 4:1:5,the contents of four heavy metals reached the highest at 700℃.Among the three raw material ratios,the highest proportions of Zn,Pb,As and Sb in the volatile phase were 44.3%,98.0%,99.0%and 96.6%,respectively.The proportion of Zn in solid phase of ceramsite was higher than that of other three metals.With the increase of temperature,XRD analysis of ceramsite showed that calcite decomposition,hematite,feldspar and other components increase.The SEM analysis results showed that pores and micropores gradually appeared inside the ceramsite.The effects of additives on gaseous heavy metal content,gas-solid phase distribution and mineral composition were studied.The results showed that chloride can promote the release of heavy metals.The higher gaseous contents of heavy metals were occurred in higher temperatures.The promotion effect of PVC on metal release was greater than that of CaCl2.At 1140℃,with the addition of CaCl2,the proportions of Zn,Pb,As and Sb in volatile phases increased by 50.8%,3.21%,1.71%and 2.99%,respectively.And with the addition of PVC,the proportions of the four metals in the volatile phases increased by 54.3%,2.87%,0.93%and 4.12%,respectively.On the whole,the addition of chloride reduced the proportion of heavy metals in the solid phase of ceramsite.Sulfide can inhibit the releases of metals.The inhibition effect of Na2S on Zn and Sb was stronger than that of Na2SO4,but the inhibition effect of Na2S on Pb and As was weaker than that of Na2SO4.However,at the highest sintering temperature,the addition of Na2S and Na2SO4 decreased the proportions of Zn,Pb and As in the solid phase of the ceramsite by 1.45～56.7%and 1.93～55.7%,respectively,which may be due to the effect of sodium sulfate.The addition of oxides also inhibited the releases of metals,and the inhibition effect on metals was CaO>Al2O3.And the proportion of heavy metals in ceramsite solid phase increased with the addition of oxides.The addition of CaO and Al2O3 at high temperature decreased the proportion of ceramsite solid phase of Zn,Pb and As by 1.73～51.1%and 1.62～51.9%,respectively,which may be due to the decomposition of metal complexes.XRD analysis of the ceramsite with additives showed that the calcite decomposed completely at 700℃ with the addition of chloride,while the calcite disappeared at 1140℃ with the addition of sulfide and oxides.The other components were mainly in the form of quartz,feldspar and magnetite.