In studies on heterogeneous material, requiring long equilibration times, it is hard to perform reliable calorimetric measurements. Thus, only carrying out experiments at variable temperature can give information on how this parameter affects the sorption of metal ions. From the limited extent of studies at variable temperature, only controversial conclusions can be reached. Most studies have been carried out at a fixed room temperature (20 or 25 °C). Some studies point out a low temperature influence or, at least, in a limited temperature range, giving evidence that ion exchange is the mechanisms responsible for the sorption process. Nevertheless, Kapoor and Viraraghavan, 1997, remarked that biosorption reactions are normally exothermic, which indicates that sorbent capacity increases with decreasing temperature. Conversely, Romero-Gonzalez et al., 2005, found that the sorption capacity of Agave lechuguilla leaves for Cr(VI) sorption increased on increasing the temperature from 10 to 40 °C, justifying this endothermicity with Cr(VI) reduction to Cr(III). Malkoc and Nuhoglu, 2007, confirmed the endothermicity of Cr(VI) sorption on tea factory waste, metal uptake increasing as temperature increas from 25 °C to 60 °C. The favorable temperature effect was attributed to a swelling effect within the internal structure of the sorbent enabling the large metal ions Cr(VI) to penetrate further.