Anchored fibrous chrysotile silica and its ability in using nitrogen basic centers on cation complexing from aqueous solution

Amorphous silica gel obtained through natural chrysotile was lixiviated with hydrochloric acid, which was chemically modified with organosilanes (H3CO)(3)SiR, where R corresponds to the organic moieties -CH2CH2CH2NH2 and -CH2CH2CH2NHCH2CH2NH2, yielding solids named SIL1 and SIL2. These anchored silicas showed 2.14 +/- 0.05 and 1.90 +/- 0.04 mmol g(-1) of attached amino groups on surfaces SIL1 and SIL2, respectively. The isotherms of adsorption data were obtained by batchwise process, whose values were adjusted to a modified Langmuir equation. The maximum adsorption capacity showed the sequence for copper and cobalt as 1.02, 0.35 mmol g(-1) on SIL2 and 0.71, 0.26 mmol g(-1) on SIL1, respectively. By using calorimetric titration, the enthalpy change of the adsorption process was 18.77 +/- 0.75 and -43.29 +/- 1.08 kJ mol(-1) for copper, 12.70 +/- 0.57 and -169.3 +/- 1.23 kJ mol(-1) for cobalt on SIL1 and SIL2, respectively. Negative Gibbs free energy values are in agreement with the spontaneity of the proposed reactions involving both divalent cations, when complexed by basic amino groups attached to pendant chain covalently bonded to the inorganic surface. (C) 2003 Elsevier B.V. All rights reserved.