Water-soluble fluorine detoxification mechanisms of spent potlining incineration in response to calcium compounds

Abstract

In this study, the detoxification mechanisms of water-soluble fluorine in the bottom ash and the distribution of fluorine during the spent potlining (SPL) incineration were characterized in response to four calcium compounds using an experimental tube furnace. CaSiO3, CaO, Ca(OH)2, and CaCO3-assisted SPL incineration converted NaF to low toxicity compounds in the bottom ash yielding a conversion range of 54.24–99.45% relative to the individual SPL incineration. The two main mechanisms of the fluorine transformation were the formations of CaF2 and Ca4Si2O7F2. The fluorine transformation efficiency was greater with CaSiO3 than CaO, Ca(OH)2, and CaCO3. Our simulations demonstrated that SiO2 enhanced the conversion of NaF. The fluorine leaching content of the bottom ash was estimated at 13.71 mg⋅L−1 after the SPL co-incineration with CaSiO3 (Ca:F = 1.2:1). The acid-alkali solutions had no significant effect on the fluorine leaching content of the bottom ash when 3 ≤ pH ≤ 12. Fluorine during the SPL co-incineration with CaSiO3 (Ca:F = 1.2:1) at 850 °C for 60 min was partitioned into 83.37, 13.90, and 2.72% in the bottom ash, fly ash, and flue gas, respectively. The transformation and detoxification mechanisms of water-soluble fluorine provide new insights into controls on fluorine emission from the SPL incineration.