Pretreatment Stabilization Technology Research Of Incineration Fly Ash And Fluorine-containing Sludge

For hazardous materials, secure landfill disposal is one of the most important final disposal methods, but its processing capacity and pretreatment techniques are in short supply in all districts. The objective of this research project that cooperated with Nanjing only security landfill (Nanjing Green Central Waste Disposal Centre) was to investigate the stabilization pretreatment technology of two typical hazardous waste generated by industrial enterprises in Nanjing.The concentration of zinc in fly ash from an industrial waste incineration plant in Nanjing contained can reach up to 2000 mg/L in leaching toxicity test. Due to the fact that zinc is an amphoteric metal, and large majorities of zinc salt have high solubility, the stabilization efficiency is poor of common heavy metal stabilizing agent. Inorganic agents sodium sulfide (Na2S), organic reagents, including dimethyl dithiocarbamate resin (DTCR) and trisodium salt of trimercapto-s-triazine (TMT-15), and organic sulfur agents (trade name:DY-608 and ZB-HM) were chosen to pretreat this kind of hazardous waste. For the problems in engineering applications, for instance, non-uniform stirring, dust nuisance, etc, we explore a chemical agent stabilization technology by using low water-cement ratio and fluidized fogging agent, and comparing with the traditional mixing way in treating results.The results showed that the zincic stabilization efficiency of all chemical agents were between 70% and 85%, and its concentration in leaching toxicity test could not meet the standard limit of safety landfill for heavy metal waste, while the performances of these chemical agents to other heavy metals were much better. When the dosage of ZB-HM was over 1% and DY-608 over 5%, the leaching concentration of cadmium was close to zero, and the stabilization efficiency could reach up to 99%. When the dosage of ZB-HM and DY-608 was 3%, the stabilization efficiency of lead could reach up to 92%. All in all, the stabilization efficiency of organic reagents was better than inorganic agents, and organic sulfur agents (DY-608 and ZB-HM) better than DTCR and TMT-15. In order to ensure the stabilization effect of zinc, it is suggested that the combination process of joint chemical stabilization and cement solidification need to be utilized. Fluidized mixing model has a better stabilizing effect. The next research may focused on this technology on the chemical stabilization of fly ash, which need more further development.The fluorine-containing sludge was achieved from a liquid crystal display enterprises in Nanjing, the leaching concentration of fluoride ions is 308 mg/L, which was over the standard for pollution control on the security landfill site for hazardous waste with the value of 100 mg/L. The results of the presence state analysis of fluorine that containing in sludge shown that the fluorine element mainly existed in dissociative state. Though the fluorine-containing sludge occupied small proportion of the total hazardous waste, it was a kind of hazardous waste with high toxicity. Therefore, it’s necessary to investigate the effect of binder-waste ratio, water-cement ratio and curing time on fluorine-containing sludge with cement as the binder. Meanwhile, we also compared the results of calcium hydroxide pretreatment technology with the results of cement stabilization.The results shown that the binder-waste ratio was the main factor that affected the fluorine leaching concentration, but the water-waste ratio and curing time have little affect on the results. But when the binder-waste ratio under the condition of 45%, the leaching of fluorine concentrations of all cement blocks can reach the standard of hazardous waste landfill control, the stabilization efficiency can reach to 71.63%. The stabilization by using calcium hydroxide has better stabilization efficiency than using cement. When the dosage of calcium hydroxide was 30%, the leaching concentration of fluorine was lower than the standard for hazardous waste landfill, and the stabilization efficiency in different conditions of curing time were varied from 67.92% to 77.70%. Taking into account of the results of stabilization and the needs of actual engineering operation, we final chosen the stabilization pretreatment of fluorine-containing sludge by using calcium hydroxide, the appropriate parameters for the dosage of calcium hydroxide was 30%, water-cement ratio was 30%, and the curing time can be nature curing in hazardous waste landfill.