Stabilization of heavy metals in wastewater treatment sludge from power plants air heater washing.

In the present investigation, for the first time in Iran, dewatered sludge waste from the air heater washing wastewater treatment of a thermal power plant was subject to investigation with regard to cement-based stabilization in order to reduce the mobility of heavy metals. Studies of the chemical composition, mineralogy, morphology and leaching characteristics of the untreated and treated waste were conducted. The stabilization was done with two cement-based mix designs with different waste/cement ratios in different samples. In the cement stabilization process the leaching of V, Ni, Zn and Cr could be decreased from 314.1, 209.1, 24.8 and 5.5 mg L(-1), respectively, in the untreated waste to 6.02, 32.11, 3.57 and 3.68 mg L(-1) in a mixture with 20% waste/cement ratio, while during stabilization with cement + sand, the toxicity characteristic leaching procedure (TCLP) leachate contents of the mentioned metals were decreased to 4.24, 16.2, 2.51 and 2.2 mg L(-1) for the same waste/cement ratio. Stabilization with sand/cement seemed to be more efficient in reducing metal leaching from the waste. X-ray diffraction studies showed that portlandite, calcite, lime, larnite and quartz were produced during the stabilization process.