Journal of Wuhan University of Technology-Mater. Sci. Ed. Feb.2012 149 Preparation and Microstructure of Green Ceramsite Made from Sewage Sludge LIU Junzhe 1 , LIU Rui 2 , HE Zhimin 1 , BA Mingfang 1 , LI Yushun 1* (1. School of Civil Engineering, Ningbo University, Ningbo 315211, China; 2. Department of Civil Engineering, University of Colorado Denver, USA) Abstract: A pilot study was conducted to produce high performance green ceramsite by using sewage sludge, fly ash and silt. According to the theory of Riley, the proportions of raw materials were chosen to perform the sintering experiments. Thereby, the optimum proportion of sludge, fly ash and silt and sintering parameters were determined. The microstructure of the optimized mixture and the leaching of heavy metal elements were also analyzed. The lab testing results show that sintering parameters have significant impact on the performance of ceramsite. For solid waste ceramsite with high loss of ignition, inadequate pre-burning process lowers the strength and increases the water absorption. Low water absorption can be achieved by the enameled surface and closed pore structure. The high performance green ceramsite has the density grade of 700, water absorption of 6% and compressive strength of 6.6 MPa. The ceramsite is mainly composed of cristobalite and mullite. The leaching of heavy metal elements from the solid waste ceramsite are lower than the limits required by the national standard. This study shows that the utilization of solid waste ceramsite as the light weight aggregate is feasible and safe. Key words: ceramsite; sewage sludge; sintering parameters; microstructure ©Wuhan University of Technology and SpringerVerlag Berlin Heidelberg 2012 (Received: May 27, 2010; Accepted: Sept. 17, 2011) LIU Junzhe( 柳俊哲): Prof.; Ph D; E-mail: junzheliu@163.com *Corresponding author: LI Yushun(李玉顺): Prof.; Ph D; E-mail: lys0451@163.com Funded by the National Natural Science Foundation of China (No.51078189), the K.C.Wong Magna Fund in Ningbo University and Zhejiang Province Energy Conservation Innovative Team Project in Building (No.2009R50022) DOI 10.1007/s11595-012-0426-2 1 Introduction Ningbo is located at eastern coast of China, and has a large number of rivers and lakes. The city produces more than 22 million metric tones of silt every year. Meanwhile, over 250 m 3 sewage sludge is produced in Ningbo every day from three main sewage treatment plants. The sewage sludge has rich organic and inorganic components [1,2] . But only the inorganic composition has been utilized. Actually, it is proper and feasible to produce ceramsite by taking advantage of both organic and inorganic components in the sewage sludge [3] . However, in Ningbo, sewage sludge is mainly disposed in the landfill. it is not a wise choice due to the large landfill volume, difficulty to transport and secondary pollution. Using sewage sludge to produce ceramsite is in the line with national industrial sustainability policy, and has great development potential and market prospect [4] . 2 Experimental 2.1 Materials The sewage sludge was supplied by three waste water treatment plants in Ningbo Zhenhai, Jiangdong South District and Jiangdong North district. The silt was taken from Yongjiang, and the fly ash was taken from Beilun Power Plant. The chemical analyses of raw materials are shown in Table 1. Thermal analysis of raw materials show that the temperatures indicating LOI of three kinds of sludge are all less than 600 ℃ (Fig.1). Testing indicate that the plasticity of sludge cannot meet the requirements to produce ceramsite, but the plasticity PI value of silt is 14 , so incorporation of silt is able to increase the plasticity of the mixture. The sludge and fly ash are taken as the basic raw materials to produce ceramsite. Fig.2 shows Yongjiang silt has a endothermic peak at 400 ℃ due to the evaporation of physical adsorbed water; DTA curve shows evaporation of adsorbed water and crystal water when the temperature falls in the range of 100 ℃- 680 ℃, and also because LOI is up to 12%; therefore, ceramsite should be preheated properly before sintering [5] . 2.2 Experiment methods Pulverize dried raw materials, and mix the