Ceramsite obtained from water and wastewater sludge and its characteristics affected by (Fe2O3 + CaO + Mgo)/(SiO2 + Al2O3)

To control and optimize the process for making ceramsite from wastewater treatment sludge (WWTS) and drinking-water treatment one (DWTS), the effect of mass ratios of (Fe2O3 + CaO + MgO)/(SiO2 + Al2O3) (defined as F/SA ratios); SiO2:Al2O3 and Fe2O3:CaO:MgO (under the condition of fixed F/SA ratio) on the characteristics of ceramsite were investigated. it was found that the optimal F/SA ratios for making ceramsite range 0.175-0.45. Na-Ca feldspars and amorphous phases increase in ceramsite as F/SA ratios increase. Ceramsite with porous surfaces, expanded structures, and complex crystalline phases can be obtained at 0.275 <= F/SA <= 0.45, which accordingly cause the decrease in compressive strength. Higher strength of ceramsite with lower porosity can be obtained at 0.175 <= F/SA < 0.275, and under the condition of F/SA ratio = 0.275, the raw materials can produce ceramsite with desired physical properties at 18.2:35 <= SiO2:Al2O3 < 45:10.2 and 10:2.7:1.4 <= Fe2O3:CaO:MgO <= 5.3:6:1.6. Ceramsite with higher compressive strength and lower porosity can be obtained at SiO2:Al2O3 > 27.2:15.8 and Fe2O3:CaO:MgO > 6:3.5:1.8. Results indicate that F/SA ratios could be used as an important parameter to control the production process of ceramsite with desired physicochemical properties and resolve the disposal problems of residual sludges. (C) 2009 Elsevier Ltd. All rights reserved.