Thermodynamics data of interaction of copper nitrate with native and modified chrysotile fibers in aqueous solution

The interactions involving chrysotile (CRIO) and propylamine (CRI1), and propyethylenediamine (CRI2) chrysotiles with copper nitrate in aqueous solution were followed through a calorimetric titration technique. The net thermal effects were calculated after subtracting the respective thermal effect of dilution for all systems. The degree of adsorption gave the order CRI0 < CRI1 < CRI2. The mechanism of reaction for copper/chrysotile interaction is due to the ion exchange between the H+ of the external hydroxyl groups of the inorganic matrix, which is covered by the presence of 0.26 mmol g(-1) of basic sites on fibers. On the other hand, the interactions on modified chrysotile can be associated to complex formation with the free pendant amine groups. The enthalpy of these processes gave the following values: -4.25 +/- 0.27, 19.47 +/- 0.60, and -26.55 +/- 0.16 kJ mol(-1) for CRI0, CRI1, and CR12 systems, respectively. The different behavior of propylamine chrysotile indicated that the hydration effect is more pronounced than complex formation. The free Gibbs energy values are in agreement with favorable processes. The high entropic values for CRI1 and CRI0 indicated that the adsorption occurs by entropic reasons, while on CR12 the enthalpic contribution is more pronounced. (C) 2001 Academic Press.