温度对污泥焚烧灰中重金属迁移行为与浸出特性的影响

The Effect of Temperature on the Migration and the Leaching Behaviors of Heavy Metals in Incineration Ash of Sewage Sludge

实验考察了温度分别为500、600、700和800℃时,污泥在焚烧炉中停留25min后的污泥灰中和原污泥中重金属(Mn、Co、Ni、Cu、Cr、Cd、Pb)的含量;采用改进的分步BCR提取法来研究7种重金属的酸溶态、可还原态、可氧化态和残渣态的分布特征,并利用地累积指数法(Igeo)对重金属潜在风险进行了评价,模仿酸雨条件探讨了污泥焚烧前后重金属的浸出特性.实验结果表明,污泥焚烧温度达到500℃以上,焚烧灰中上述7种金属元素可氧化态和残渣态基本呈增长趋势,生态风险等级均不同程度的降低,700℃时,各元素主要以残渣态形式存在,此时,Pb、Cr、Co三种元素的Igeo潜在生态风险等级由原来的1级降为0级,Cd元素的Igeo风险等级由原来的9级降为7级,在800℃时,Cu元素的风险级别由2级降为1级.浸出毒性实验表明,焚烧灰中重金属浸出毒性远远低于焚烧前,随着温度的升高,浸出毒性呈现下降趋势,且随着时间的增加,浸出毒性含量逐渐增大.原污泥Mn元素在4h浸出率100%,700℃焚烧后,20h浸出率下降到27.1%;Cu元素800℃焚烧后,20h浸出率由原来的20.6%降低到4.2%;Co、Ni、Cr、Cd、Pb元素,700℃焚烧后,20h浸出率分别由原来的18.3%、22.7%、14.3%、9.4%、18.2%降低到3.0%、3.5%、0.31%、0.28%、0.21%,其整体浸出能力与重金属形态分析结果基本一致.

In the present work,the contents of heavy metals including Mn,Co,Ni,Cu,Cr,Cd and Pb in raw sludge and incineration after being calcined for 25 min at 500,600,700 and 800℃,respectively.The modified BCR state extraction method was used to characterize the acid soluble state,reduced state,oxidation state and residual state of the heavy metals.The potential risks for such heavy metals were evaluated by using geo-accumulation index method（Igeo）.The leaching toxicity of heavy metals in raw sludge and incineration after being calcined were discussed with the simulative conditions of acid rain.The results indicated both the oxidation state and the residual state of all selected heavy metals exhibited the trend of increase,while the ecological risk levels were decreased to some extent.After being calcined at 700℃,the elements mainly existed in the form of residual state.At this point,the potential eco-risk level of Igeofor Pb,Cr and Co was reduced from 1 to 0,while that for Cd was reduced from 9 to 7,and that for Cu was reduced from 2 to 1 at 800℃.The leaching toxicity analysis showed that all heavy metals in ash had far less toxicity than that in raw sludge.In addition,the leaching toxicity decreased with the increase of calcination temperature.The leaching rate for Mn in raw sludge reached 100% in 4 h,while that for the sample calcined at 700 ℃ decreased to 27.1%in 20 h.The leaching rate for Cu in 20 hwas reduced from 20.6%to 4.2%before and after being calcined at 800 ℃.The leaching rates in 20 hfor other metals including Co,Ni,Cr,Cd andPb before and after being calcined at 700 ℃ decreased from 18.3%,22.7%,14.3%,9.4% and 18.2%to 3.0%,3.5%,0.31%,0.28% and 0.21%,respectively.The overall leaching ability was in good agreement with the analysis on the existing states of heavy metals.