ABSTRACT
Systematic adsorption tests were carried out to determine the efficiency of organo-zeolite (OZ) for removal of atrazine, lindane and diazinone from water. The hydrophobic character of OZ-pesticide interactions was confirmed by measuring the amount of pesticides sorbed on zeolite samples modified with 25, 50, 75 and 150 mmol of stearyldimethylbenzylammoniumchloride (SDBAC)/kg of zeolite. The effects of adsorbent particle size, solid content in the suspension and the initial pesticide concentration in the solutions were also investigated. For effective adsorption of diazinone onto an OZ, it is necessary for the SDBAC/diazinon ratio to be higher than 25. The adsorption capacities, calculated by fitting the experimental data to the Langmuir-Freundlich equation, were 2.0 micromol/g (atrazine), 4.4 micromol/g (diazinone) and 3.4 micromol/g (lindan). At lower initial concentrations of pesticide solution, a linear dependence existed between the amount adsorbed and the equilibrium concentration of pesticide. Column experiments showed that at volumetric flow of 6 cm3/ min, the breakthrough points (at C/C0 = 0.1) were 560 bed volume (BV) for lindane and 620 for diazinone.
Subject(s)
Atrazine/chemistry , Atrazine/isolation & purification , Diazinon/chemistry , Diazinon/isolation & purification , Hexachlorocyclohexane/chemistry , Hexachlorocyclohexane/isolation & purification , Water Purification/methods , Zeolites/chemistry , Adsorption , Herbicides/chemistry , Insecticides/chemistry , Molecular StructureABSTRACT
Adsorption of zearalenone (ZEN), ochratoxin A (OCHRA) and aflatoxin B1 (AFB1) on natural zeolite, clinoptilolite, modified with different amounts of octadecyldimethylbenzyl ammonium (ODMBA) ions was investigated. Results showed that adsorption of hydrophobic ionizable ZEN on unmodified zeolite tuff was very low and that adsorption on organozeolites increased with increasing hydrophobicity of the zeolitic surface. The adsorption was independent of the form of ZEN in solution and the solution pH, indicating that hydrophobic interactions with ODMBA are responsible for ZEN adsorption. Adsorption of low polar ionizable OCHRA on organozeolites also increased with increasing hydrophobicity of the zeolitic surface, however, OCHRA showed moderate adsorption on unmodified zeolitic tuff at pH 3. OCHRA adsorption on unmodified zeolite as well as on lower surface coverage of organozeolite was dependent on the form of OCHRA in solution; there was a decrease of adsorption at high pH, where OCHRA is in the anionic form. It indicated that at acidic pH, low surface coverage allows some combination of hydrophobic interaction with ODMBA and interactions with the surface of the zeolite. At higher surface coverage, the OCHRA adsorption was higher and practically independent of pH, indicating that the hydrophobic interactions of OCHRA with ODMBA are responsible for its adsorption. Nonionizable low polar AFB1 had a high affinity for the unmodified zeolitic tuff and the adsorption of AFB1 was greatly reduced for organozeolites, indicating that AFB1 does not have high tendency for hydrophobic interactions with ODMBA. pH dependence of AFB1 adsorption, while AFB1 has the same form at all pHs, demonstrated that the surface modification of the zeolite depends on pH and that these modifications have influence on its adsorption. The calculated dipole moments of neutral mycotoxin molecules: AFB1-9.5D, OCHRA-6.9D and ZEN-2.2D are in qualitative agreement with adsorption experimental data.
Subject(s)
Adsorption , Mycotoxins/chemistry , Aflatoxin B1/chemistry , Benzalkonium Compounds/chemistry , Dose-Response Relationship, Drug , Hydrogen-Ion Concentration , Ions , Models, Chemical , Molecular Conformation , Ochratoxins/chemistry , Quaternary Ammonium Compounds/chemistry , Surface Properties , Surface-Active Agents/chemistry , Zearalenone/chemistry , Zeolites/chemistryABSTRACT
This study was aimed at elucidating the mechanism of adsorption of quaternary amines, stearyldimethylbenzylammoniumchloride (SDBAC), as monomers and as micelles, distearyldimethylammoniumchloride (DDAC) and hexadecyltrimethylammoniumchloride (HTAC), on the surface of sepiolite. The adsorption capacity for these surfactants onto sepiolite, calculated by fitting the experimental data to the Langmuir-Freundlich equation, were 324% (SDBAC), 278% (DDAC), and 258% (HTAC) of the cation exchange capacity of sepiolite. The Mg(2+) ions released during the exchange process were higher than the CEC value of sepiolite because of the simultaneous dissolution of the present minerals. The water adsorption decreased with the increasing surfactant loading up to 250 mmol/kg of sepiolite, which can be ascribed to an intensification of the hydrophobic properties. With loadings above 250 mmol/kg, the water adsorption increases. Simple kinetic analysis of SDBAC adsorption was performed. The properties and the type of bonding between the surfactants and sepiolite were investigated by DT, TG, and DTG analysis. During the gradual heating in oxidizing atmosphere, the adsorbed organic material is oxidized giving rise to significant exothermic peaks. The exothermic peak temperatures in the range 200-500 degrees C depended on the surfactant loadings and provided evidence of the formation of multilayers on the sepiolite surface.
