Research On Disposal Of Solid Waste Incineration Fly Ashes By Cement Rotary Kiln Co-processing

The solid waste incineration fly ashes are difficult to be treated in China because they are mostly in high concentration of many hazardous compounds, such as heavy metals, dioxins, chloride, sulphur and alkali. The present study shows the fly ashes have a silicate characteristic and the main components of fly ashes are very similar to that of the cement raw material. The technique of cement kiln may be suitable for the co-processing of solid waste incineration fly ashes.Heavy metals and PCDD/Fs were chemically analyzed in fly ashes from solid waste incinerators in six cities in Zhejiang province, where about 1/5 of solid waste incinerators in China are located. The results indicated that the main elements of fly ashes were Si, Ca, Al, Fe, K, Na, Cl. The contents of Cu, Zn, As, Cr, Hg, Ni, Cd and Pb are enriched in the fly ash samples. Therefore MSWI fly ashes must be controlled as hazardous materials because of its potential environmental risk. Moreover, the fly ash samples were extracted by HJ/T299-2007 and TCLP procedure. The heavy metal toxicity of the leachate was evaluated. The leaching ratios of heavy metals in fly ashes were low to some extent according to the results of batch tests such as Toxicity Characteristic Leaching Procedure (TCLP) of U.S. EPA and HJ/T299-2007. The notable difference of TCLP and HJ/T299-2007 when evaluating the same sample was due to the obvious difference of pH values in the leachate. The total content of 17 PCDD/Fs varied from 0.113 to 43.63 ng/g dw, and the TEQ of PCDD/Fs ranged from 0.009 to 5.679 ng/g dw. It is of significance to study the particular pollution characteristics of a certain fly ash before disposal or reuse for the purpose of adequate risk assessment and management.Solid waste incineration fly ashes are rich in heavy metals and salts. A three-step washing procedure was adopted to remove the chlorides, which could cause serious corrosion in the cement kiln. Various amount of pre-washed fly ashes were added to replace the clay components of the raw materials for cement production, aiming to assess the possibility of incineration ashes reused as raw materials for cement production. The results indicated that cement rotary kiln co-processing could be a feasible alternative for ash management. All parameters of fly ashes cement products conformed to the Chinese National Standard (CNS) of Common Portland Cement with no exception. It was also demonstrated that the addition of fly ashes had no negative effect on the compressive strength or any other cement quality parameters of the clinker.The toxicity of the original fly ashes, pre-washed fly ashes, cement samples and S/S samples to Chlorella pyrenoidosa were determined and compared in this study, based on two different test endpoints:the growth inhibition rate and the ultrastructural morphology of cells. In the comparison of the EC50 of fly ashes and the samples from different stages of treatments, the biotoxicity of the samples was reduced step by step. The ultrastructural morphologies of cells growing in the leachates of the samples of the four stages were observed by transmission electron microscopy. The cell wall separated from the cell membrane,and accumulated starch granules were observed in the chloroplast, suggesting that these samples had toxic effects to Chlorella pyrenoidosa. However, it showed no difference in both the cement samples and S/S samples, indicating that the biotoxicity levels of cements produced by fly ashes are the same as that of the ordinary cements, and these cements are safe for application.