Solidification/Stabilization of Heavy Metals from Air Heater Washing Wastewater Treatment in Thermal Power Plants

Abstract

In the present investigation, for the first time in Iran, dewatered sludge waste from air heater washing wastewater treatment of a thermal power plant was subjected to investigation of the cement base stabilization and solidification experiments in order to reduce the mobility of heavy and other hazardous metals as well as increasing the compressive strength of the solidified product for possible reuse of the waste. The solidification was done with two cement based mix designs with different waste/cement ratio is different samples. The results of leaching test on the solidified samples revealed that regarding the sand-cement mixture even with 25% waste/cement ratio, the leaching of heavy metals has completely been controlled up to 95%. In 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 respectively in the raw waste to 6, 32.1, 3.6 and 3.6 mg/L in a mixture with 20% waste/cement ratio. During stabilization with cement-sand, the TCLP leachate contents of mentioned metals have been decreased to 4.2, 16.2, 2.5 and 2.2 mg/L with waste/cement ratio of 20%. X-ray diffraction studies showed that portlandite, calcite, lime, larnite and quartz have been shaped during the stabilization process. The compressive strength test results revealed that in both mixture samples, decreasing the compressive strength with increasing the amount of waste content in the mixture occurs. In sand-cement solidified samples with waste/cement ratio 25% and in cement solidified samples with waste/cement ratio 20%, a 40% decrease occurs in the compressive strength in comparison with the waste free mixtures.