By fusion with sodium hydroxide followed by a hydrothermal reaction, a thermally treated sediment was successively converted into zeolites Na-P1, Na-X, hydroxysodalite, F Linde A, and faujasite, which exist either as a monophase or as a mixture depending on synthesis conditions. The formation of zeolite was confirmed by XRD, FT-IR, and SEM. A great increase in cation exchange capacity (CEC) and specific surface area following zeolite conversion was observed. Among the synthesis conditions, the Si/Al ratio of the starting material, the NaOH/sediment ratio, and the liquid/solid ratio were found to be the most important factors influencing the type, the crystallinity, and the CEC value of zeolite product. However, the fusion temperature (350-750 degrees C), the fusion time (15-240 min), and the crystallization time (2-24 h) had only very limited effects. It is concluded that thermally treated sediment, produced as a solid waste following decontamination of polluted sediment, could be recycled as a raw material for zeolite synthesis.