Ceramsite obtained from water and wastewater sludge and its characteristics affected by Fe2O3, CaO, and MgO

To solve the disposal problems of residual sludges, wastewater treatment sludge (WWTS) and drinking-water treatment sludge (DWTS) were tested as components for producing ceramsite. Fe2O3, CaO, and MgO were the major basic oxides in WWTS and DWTS, so their effect on characteristics of ceramsite was also investigated to optimize the process. Results show that WWTS and DWTS can be utilized for producing ceramsite with optimal contents of Fe2O3, CaO, and MgO ranging 5–8%, 2.75–7%, and 1.6–4%, respectively. Ceramsite within the optimal Fe2O3, CaO, and MgO contents ranges was characterized using thermal analysis, X-ray diffraction (XRD), morphological structures analyses, and compressive strength measurements. Higher strength ceramsite with more complex crystalline phases and fewer pores can be obtained at 6% ≤ Fe2O3 ≤ 8%. Lower strength ceramsite with more pores and amorphous phases can be obtained at 5% ≤ CaO ≤ 7%, which implies that excessive Ca2+ exceeds the needed ions for producing electrical neutrality of silicate networks. Ceramsite characteristics are not dramatically influenced by MgO because Mg2+ cannot destroy the unity of crystalline structures. This revolutionary technology of utilization of WWTS and DWTS can produce high performance ceramsite thus reducing costs of sludge disposal, in accordance with the concept of sustainable development.