Characteristics of Removing Heavy Metal by Chlorination in Process of Sludge Ash Calcination

SONG Mengnyu; LI Yanlong; ZHANG Yuanyuan; LI Jingshu; LI Rundong

doi:10.19672/j.cnki.1003-6504.0758.23.338

Abstract：Municipal sludge,in general,contains abundant phosphorus resources and incinerating the sludge can enrich the phosphorus;however,the potential environmental risks of heavy metal contained in the ash generated by incineration greatly limit its practical application.In this paper,a laboratory experiment was conducted with CaCl2 as a kind of oxidant added to the phosphorus-enriched sludge ash sample which was then calcinated at various temperatures(800～1 000 ℃),thereby effects on the removal of the heavy metals(Zn and Cu)by CaCl2 was studied,as well as the effects of calcination on the fixation of phosphorus and the transformation of phosphorus form.Consequently,the experiment showed that CaCl2 could effectively facilitate the removal of Zn and Cu during calcination,and the higher the temperature,the more effective for the removal of Zn and Cu:when the addition of CaCl2 was increased from 0 to 50 g Cl/kg SSA,the removal rates of Zn and Cu increased to 97.8％and 83.4％,respectively(at 1 000 ℃).On the other hand,without the addition of CaCl2 the removal rates of both Zn and Cu decreased lower than 5％.In comparison with the raw sludge,after calcination the sludge-ash showed a notably reduction of heavy metal(Zn and Cu)concentration in the leachates,and the proportion of residual and oxidative states increased,which meant the sludge-ash had lower eco-environmental risk.When calcination temperature was set in the range of 800～1 000 ℃,the fixation rates of phosphorus in phosphorus-enriched sludge-ash were more than 90％,so the addition of CaCl2 not only facilitated the complete transformation of NAIP to AP but also raised the biological availability of phosphorus,which therefore could provide a theoretical basis for the recovery and utilization of phosphorus resources in phosphorus-enriched sludge-ash.