A stability study of a strongly basic anion exchanger modified with Cr3+-containing compounds was conducted. The AV-17(Cr) sorbent described in this paper was prepared by reacting commercial gel-type AV-17 resin bearing -N(CH3)(3)Cl groups with Cr-2(SO4)(3) solution. The results show that the material is unstable in HNO3 and H2SO4 solutions with a concentration of 1-5 N, while in HCl solutions with a concentration higher than 2 N, the sorbent becomes more stable due to the transformation of jarosite type compounds into R4N[Cr-3(OH)(6)Cl-6] and R4N[Cr3(Cl)(6)Cl-6](2-). Sorbent samples were investigated using FT-IR, SEM spectroscopy, TG-DTG and TG-MS-FTIR. The obtained results reveal a complex degradation mechanism, depending on the chemical structure of the compounds, and on the atmosphere in which the degradation process was conducted. The first degradation stages consist in water removal, followed by trimethylamine (N(CH3)(3)), ethane (C2H6), sulphur dioxide (SO2), and oxygen (O-2) release at temperatures higher than 300 degrees C and by release of an additional amount of water (H2O) resulted from the dehydoxylation process. (C) 2013 Elsevier B.V. All rights reserved.