Influence of calcium hydroxide on the fate of perfluorooctanesulfonate under thermal conditions

Abstract

To explore the potential fate and transport of perfluorochemicals in the thermal treatment of sludge, perfluorooctanesulfonate (PFOS), a perfluorochemical species commonly dominant in wastewater sludge, was mixed with hydrated lime (Ca(OH)(2)) to quantitatively observe their interaction under different temperatures. The phase compositions of the mixtures after the reactions were qualitatively identified and quantitatively determined using X-ray diffraction technique. The results of the thermogravimetry and differential scanning calorimetry analyses indicate that PFOS gasified directly during the thermal treatment process when the temperature was increased to around 425 degrees C. However, the formation of CaF(2) at 350 degrees C suggests that the presence of Ca(OH)(2) in the mixture can lead to the decomposition of PFOS at 350 degrees C, which is lower than the decomposition temperature of PFOS alone (425 degrees C). The increase of temperature promoted a solid state reaction between PFOS and Ca(OH)(2), and also enhanced the interaction between the gaseous products of PFOS and CaO (or Ca(OH)(2)). The preferred Ca/F molar ratio to achieve fluorine stabilization by Ca(OH)(2) was above 1:1 in the experiment involving 400 degrees C and 600 degrees C treatment. It also showed that equilibrium efficiency is achieved within 5 min at 400 degrees C and within 1 min above 600 degrees C.