title: Adsorption of anionic surfactants onto sepiolite.
abstract: Anionic surfactants constitute the main ingredients of detergents and a number of surfactant formulations used in a spectrum of diverse industries. The aim of this study is to examine the amenability of natural sepiolite to the adsorption of anionic surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS). Adsorption isotherms exhibit three regions with distinctly different slopes. The first region is characterized by the complexation of anionic surfactants with Mg2+ ions at the octahedral sheet or hydrogen bonding between the oxygen groups of anionic head groups of surfactant and H+ of the bound or zeolitic water. The Mg2+ ions released from sepiolite leads to the precipitation of magnesium salt of surfactant in the second region. The third region marks both the beginning of plateau region and micellar dissolution of the precipitate. The effect of temperature on surfactant adsorption for SDS/sepiolite system was utilized to calculate such thermodynamic parameters as the free energy of adsorption (DeltaG(ads)(degrees)) and the heat of adsorption (DeltaH(ads)(degrees)). The low value of DeltaH(ads)(degrees) (1.87 kJ/mol) is an evidence for the physical adsorption of anionic surfactants onto sepiolite. The relatively large value of entropic contribution (-TDeltaS(ads)(degrees)) indicates that the adsorption of anionic surfactants onto sepiolite is entropically governed.
authors.affiliation: Mineral & Coal Processing Section, Istanbul Technical University, Maslak 80626, Istanbul, Turkey.
authors.forename: Orhan
authors.initials: O
authors.lastname: Ozdemir
authors.forename: Mustafa
authors.initials: M
authors.lastname: Cinar
authors.forename: Eyüp
authors.initials: E
authors.lastname: Sabah
authors.forename: Fatma
authors.initials: F
authors.lastname: Arslan
authors.forename: Mehmet Sabri
authors.initials: MS
authors.lastname: Celik
mesh_terms: D000327:Adsorption; D000838:Anions; D011232:Chemical Precipitation; D008274:Magnesium; D017633:Magnesium Silicates / Q000737:chemistry*; D008823:Micelles; D009282:Naphthalenesulfonates / Q000302:isolation & purification; D044367:Phase Transition; D012967:Sodium Dodecyl Sulfate / Q000302:isolation & purification; D013501:Surface-Active Agents / Q000302:isolation & purification*; D013816:Thermodynamics; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: D000838:Anions; D017633:Magnesium Silicates; D008823:Micelles; D009282:Naphthalenesulfonates; D013501:Surface-Active Agents; D014874:Water Pollutants, Chemical; D012967:Sodium Dodecyl Sulfate; C001671:magnesium trisilicate; D008274:Magnesium