Fluoride Action Network

Thermal behaviors of fluoride during (co-)incinerations of spent potlining and red mud: Transformation, retention, leaching and thermodynamic modeling analyses

Source: Chemosphere [Epub ahead of print] | February 14th, 2020 | Authors: Zhang G, Sun G, Liu J, Evrendilek F, Buyukada M, Xie W.
Location: International
Industry type: Aluminum Industry


  • Inorganic fluoride behaviors of spent potlining co-incineration were quantified.
  • Addition of red mud positively affected fluoride transformations. .
  • 30% red mud reduced fluoride leaching rate and enhanced retention rate of bottom ash.
  • 66.01% of the total fluoride of the bottom ash was found to be insoluble fluorine.
  • SiO2 and Al2O3 positively affected NaF conversion into CaF2.


Spent potlining (SPL) as a hazardous solid waste has a high content of inorganic fluoride. This study aimed at characterizing its transformation, retention and leaching behaviors with(out) the addition of red mud (RM) during the SPL incineration. The RM addition positively affected its retention and leaching rates. Its Ca-containing compounds caused Na3AlF6 and NaF to turn into more CaF2. 30% RM converted water-soluble NaF into more stable CaF2 than did SPL at 850?°C, thus reducing the leaching rate by 45.15%. 30% RM captured HF through its Ca content and enhanced its retention rate by 66.96%. 66.01% of the total fluoride as fluorine was stably retained in the bottom ash, and thus, significantly reduced the toxicity of the SPL incineration products. SiO2 and Al2O3 exerted a thermally positive effect on NaF turning into CaF2. The fluoride retention of the bottom ash was mainly dominated by CaF2 and NaF with(out) RM. Smaller, coarser and more loose structures of the co-incinerated solid particles pointed to a synergistic interaction between SPL and RM.