title: Adsorption of dyes on Sahara desert sand.
abstract: Sahara desert sand (SaDeS) was employed as a mineral sorbent for retaining organic dyes from aqueous solutions. Natural sand has demonstrated a strong affinity for organic dyes but significantly lost its adsorption capacity when it was washed with water. Therefore, characterization of both natural and water washed sand was performed by XRD, BET, SEM and FTIR techniques. It was found that water-soluble kyanite, which is detected in natural sand, is the dominant factor affecting adsorbance of cationic dyes. The sand adsorbs over 75% of cationic dyes but less than 21% for anionic ones. Among the dyes studied, Methylene Blue (MB) demonstrated the strongest affinity for Sahara desert sand (Q(e)=11.98 mg/g, for initial dye solution concentration 3.5 x 10(-5)mol/L). The effects of initial dye concentration, the amount of the adsorbent, the temperature and the pH of the solution on adsorption capacity were tested by using Methylene Blue as model dye. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were applied. It was concluded that adsorption of Methylene Blue on Sahara desert sand followed pseudo-second order kinetics. Gibbs free energy, enthalpy change and entropy change were calculated and found -6411 J/mol, -30360 J/mol and -76.58 J/mol K, respectively. These values indicate that the adsorption is an exothermic process and has a spontaneous nature at low temperatures.
authors.affiliation: Ege University, Solar Energy Institute, Izmir, Turkey. canan.varlikli@ege.edu.tr
authors.forename: Canan
authors.initials: C
authors.lastname: Varlikli
authors.forename: Vlasoula
authors.initials: V
authors.lastname: Bekiari
authors.forename: Mahmut
authors.initials: M
authors.lastname: Kus
authors.forename: Numan
authors.initials: N
authors.lastname: Boduroglu
authors.forename: Ilker
authors.initials: I
authors.lastname: Oner
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Lianos
authors.forename: Gerasimos
authors.initials: G
authors.lastname: Lyberatos
authors.forename: Siddik
authors.initials: S
authors.lastname: Icli
mesh_terms: D000327:Adsorption; D000352:Africa, Northern; D000538:Aluminum Silicates; D002412:Cations; D004396:Coloring Agents / Q000302:isolation & purification*; D004058:Diffusion; D007700:Kinetics; D008751:Methylene Blue / Q000302:isolation & purification; D012822:Silicon Dioxide / Q000737:chemistry*; D013816:Thermodynamics; D014873:Water Pollutants / Q000302:isolation & purification; D018508:Water Purification / Q000379:methods*
chemical_list: D000538:Aluminum Silicates; D002412:Cations; D004396:Coloring Agents; D014873:Water Pollutants; C121089:kyanite; D012822:Silicon Dioxide; D008751:Methylene Blue