title: Cr(VI) sorption behavior from aqueous solutions onto polymeric microcapsules containing a long-chain quaternary ammonium salt: kinetics and thermodynamics analysis.
abstract: This work studies the adsorption of Cr(VI) ions from an aqueous acid solution on hydrophobic polymeric microcapsules containing a long-chain quaternary ammonium salt-type extractant immobilized in their pore structure. The microcapsules were synthesized by adding the extractant Aliquat 336 during the in situ radical copolymerization of the monomers styrene (ST) and ethylene glycol dimethacrylate (EGDMA). The microcapsules, which had a spherical shape with a rough surface, behaved as efficient adsorbents for Cr(VI) at the tested temperatures. The results of kinetics experiments carried out at different temperatures showed that the adsorption process fits well to a pseudo-second-order with an activation energy of 82.7 kJ mol(-1), confirming that the sorption process is controlled by a chemisorption mechanism. Langmuir's isotherms were found to represent well the experimentally observed sorption data. Thermodynamics parameters, namely, changes in standard free energy (DeltaG(0)), enthalpy (DeltaH(0)), and entropy (DeltaS(0)), are also calculated. The results indicate that the chemisorption process is spontaneous and exothermic. The entropy change value measured in this study shows that metal adsorbed on microcapsules leads to a less chaotic system than a liquid-liquid extraction system.
authors.affiliation: Laboratorio de Operaciones Unitarias, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Av. Vicuña Mackenna 20, Santiago, Chile.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Barassi
authors.forename: Andrea
authors.initials: A
authors.lastname: Valdés
authors.forename: Claudio
authors.initials: C
authors.lastname: Araneda
authors.forename: Carlos
authors.initials: C
authors.lastname: Basualto
authors.forename: Jaime
authors.initials: J
authors.lastname: Sapag
authors.forename: Cristián
authors.initials: C
authors.lastname: Tapia
authors.forename: Fernando
authors.initials: F
authors.lastname: Valenzuela
mesh_terms: D000327:Adsorption; D002214:Capsules; D002857:Chromium / Q000737:chemistry / Q000302:isolation & purification*; D007477:Ions; D007700:Kinetics; D008689:Methacrylates / Q000737:chemistry; D008956:Models, Chemical; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012996:Solutions; D020058:Styrene / Q000737:chemistry; D013816:Thermodynamics; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D002214:Capsules; D007477:Ions; D008689:Methacrylates; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D014874:Water Pollutants, Chemical; D002857:Chromium; D020058:Styrene; C004919:ethylene dimethacrylate