The Research Of Removal Of Heavy Metals In Calcination Of The High Phosphorus Incinarated Sludge Bottom Ash

Sludge is now considered the maximum secondary resources of phosphate, and therecovery of phosphate resources can be achieved by heating sludge. The quality ofphosphorus can be improved by the incineration of sludge, but there are still pollutionproblems of heavy metals. The further processing of heavy metals is necessary. In this paper,ceramic fiber muffle furnace is used. Dry sewage sludge with CaO together are incinerated,then collecting the bottom ash. The bottom ash with the additives fo Cl together are calcined.After tow-step heat treatment, the analysis of the total amount and chemical speciationobtained by the BCR of heavy metals (Pb, Zn, Cu) could be achieved. Meanwhile thepollution control evaluation of heavy metals in the treated bottom ash could be carried out.After all, we can study the features of the migration and pollution control of heavy metals.Experimental results of the incineration of sewage sludge show that: the rising ofincineration temperature is not conducive to the residues of heavy metals in incinerationbottom ash; the residual rate of Zn increases after adding CaO; after incineration the amountof the oxidation states of all studied heavy metals are lower than those without, and theresidual form of heavy metals increase a lot. With the rising of incineration temperature, theacid-soluble content of the three heavy metals decresse; after the addition of CaO three typicalpatterns of heavy metals are converted to stabilized forms, and reduce the migration.The calcination experiments of sludge incineration bottom ash show that: when theCaCl22H2O is the additive, the evaporation rate of Pb will increase with the rising ofemperature, time and Cl content, and the maximum value is82.4%at1200℃and5.0%of Clcontent; In the bottom ash Pb all exists in residual fraction. The evaporation rate of Zn isobviously affected by the temperature, and the maximum value is83.9%at1100℃and5.0%of Cl content; Zn mainly exists in residual fraction in the bottom ash. The evaporation rate ofCu changes larger, arranging3.2%to68.2%, the acid-soluble fraction of Cu also contains acertain proportion in bottom ash. MgCl6H2O is unsuitable for the additive of Cl to calcinesludge ash in muffle furnace. The results of whole process of treatment show that: Pb largely exists in the calcined fluegas(purer Pb can be recoverd in calcinations flue gas); Zn mainly exists in incineration fluegas; there is certain proportion (850℃incineration,1100℃+5%Cl calcination,34.5%)ofCu in the final bottom ash,which are used to recover P. individual heavy metal’s (except Cu)the potential ecological risk index decreased and Igeolevels also decreased; the change of Znis the most obvious. The comprehensive potential ecological risk index and Igeoof three kindsof heavy metals reduce. The combined toxicity index of heavy metals forms BCR-based showthat the toxicity of heavy metals from one metal to all of three metals reduce1orders ofmagnitude to1.5.