Some thermodynamic data about amino chrysotile derivatives with nickel and cobalt cation interactions in aqueous solution

Two silylating agents yielded aminopropyl and propylethylenediamine chrysotile derivative fibers named CRII and CRI2. The amount of organic groups of 1.20 and 2.87 mmol per gram of the fibers, were anchored on surface, respectively. The interactions between the amino groups attached to organic chains of these modified chrysotiles and divalent nickel or cobalt cations in aqueous solution were followed through calorimetric titrations. The thermal effect obtained from the interactive process was subtracted the respective thermal effect of dilution, which net value was adjusted to a modified Langmuir equation. The adsorption capacities were more pronounced for CRI1 and both processes were associated with complexes formation and the calorimetric data showed two defined steps for this fiber. The enthalpy of interaction was calculated to give the following values for CRI2: -78.61 +/- 0.36 and -179.18 +/- 6.44 kJ mol(-1) for nickel and cobalt. Exothermic data for CRII contrasted to the previous values, giving 35.53 +/- 0.50 kJ mol(-1) for nickel and 25.73 +/- 0.64 kT mol(-1) for cobalt, which value is related to two individual contributions of 13.94 +/- 0.42 and 11.79 +/- 0.22 kJ mol(-1). The negative Gibbs free energy values indicated a more favorable reaction for CRI2. A linear correlation was obtained between Gibbs free energy and Pearson's parameters related to hard-soft properties, suggesting that these processes can be adjusted to acidic-basic interactions. By including copper, the sequence of acidic hardness was Co2+ > Ni2+ > Cu2+. which is the same order of free energy values found for both investigated systems. (C) 2001 Elsevier Science B.V. All rights reserved.