Freeze dried and thermally dried anion exchanger doped with iron(III) (hydr)oxide - Thermogravimetric studies

This study focused on the thermal analysis of a hybrid ion exchanger (HIX) containing 23.0 wt% hydrated ferric oxides (HFO), in which a commercially available strongly basic macroreticular anion exchanger (An) was used as the supporting material. The freeze dried An/HFO and thermally dried An/HFO were analysed (under air and under nitrogen) using TG/DTG techniques to clarify the role of HFO in the decomposition processes. The TG/DTG curves for the differently dried An/HFO differed in their shape. Freeze drying was found to be a useful method of preparing HIX for thermal analysis, considering that it prevents anion exchanger shrinkage and pore blocking. When the thermal decomposition of the host material (An) was conducted more conversions, under both air (four steps) and nitrogen (three steps), were registered than in the previous studies by other authors. The decomposition of the anion exchanger in air was found to end at the temperature of 625 degrees C, while in nitrogen it ended at 450 degrees C. The presence of HFO in the anion exchanger was found to clearly affect its decomposition in air the decomposition ended at a temperature about 75 degrees C lower, while in nitrogen it ended at a temperature about 50 degrees C higher than in the case of the anion exchanger without the deposit under the above atmospheres. The results presented in this paper shed new light on the course of the thermal analysis of anion exchangers, indicate the possibility of an unconventional way of drying HIXs to be analysed by thermogravimetry, and show that thermal processes can be used to transform spent HIXs into new alternative sorption materials containing a considerable amount of iron oxides.