The central temperature of impurity ions in the TJ-I Tokamak has been found to behave anomalously as a function of plasma density in comparison with the central proton temperature. This effect is interpreted with a simple model as being due to a non-pure Coulombic ion heating, with an enhancement factor proportional to the ion mass and the electron drift velocity. The distinct influence of charge exchange losses on high Z ions and protons contributes partly to the thermal decoupling.