Migration And Transformation Of Polycyclic Aromatic Hydrocarbons In Sintering Ceramsite From Electroplating Sludge

The amount of electroplating sludge increased in recent years.Electroplating sludge,containing high concentrations of heavy metals,is a typical hazardous waste.Improper disposal of electroplating sludge can harm the environment and human health.At present,preparing ceramsite from electroplating sludge is a potential resource utilization method.However,most previous studies focused on the optimization of process and the curing effect of heavy metals,few studies focused on the generation and release of polycyclic aromatic hydrocarbons(PAHs)in the process.Therefore,this study simulated the sintering process of preparing ceramsite by electroplating sludge under laboratory conditions,and researched the formation,phase distribution and release of PAHs.The results are as follows:In gas phase,the total concentrations of 16 PAHs ranged in 161-5,903 ng·g-1,the toxicity equivalent ranged from 0.16 to 358 ng,and their values reached highest under 800℃.In the sintering process,2-3 ring PAHs dominated.In the drying stage(100-200℃),the proportion of low molar weight PAHs reached 100%;In the calcinating stage(400-1100℃),the proportion of middle(2-3 ring)and high(4 ring)molar weight PAHs increased(31.4%-53.7%),indicating that high temperature environment can promote the formation of middle and high molar weight PAHs.In this study,PAHs were only observed in the solid phase at the drying stage(100 and 200℃),and the concentraions of PAHs were low(16.6-27.2 ng·g-1).This indicated that PAHs tend to distribute in the gas phase with the increase of sintering temperature.Low(2-3 ring)and middle(4 ring)molar weight PAHs dominated in the solid phases,which may be related to the dominance of 4-ring PAHs in ceramic materials.The gas-solid phase distribution of PAHs varied with temperature.In the drying stage,the total concentrations of PAHs in the solid phase dominated.In the calcination stage,the total concentraions of gaseous PAHs was much higher than that in the solid phase,suggesting that PAHs in the solid phase have been completely converted into gas phase.In addition to the influence of temperature,the distribution of PAHs was affected by the composition of raw materials,ventilation rate and sintering time.The results showed that the content of organic matter in raw materials were positively correlated with the amount and toxicity equivalent of PAHs in gaseous phase,and high organic matter content can promote the polymerization reaction of low molar weight PAHs to high molar weight ones.Increasing ventilation rate,the residence time of gas in the furnace was shortened,low-molecule-weight PAHs cannot be completely synthesized into high ones,the amount of gaseous PAHs decreased;However,the concentraions of PAHs in the solid phase increased likely due to more complete reaction between the organic matter in the raw ceramsite and oxygen.Prolonging the sintering time significantly increased the contents of PAHs in gas phase;but affected PAHs composition little,which was dominated by low-molecule-weight(2-3 ring)PAHs.