Adsorption Of Cationic Dyes Onto Organic Sepiolite From Single And Multisolute Systems

Dyeing wastewater has complicated constituents, and usually contains variouskinds of dyes which with high concentrations of deep color, high toxicity,biodegradable characteristics, and it is one of the industrial wastewater which isdifficult to be degraded. Sepiolite is a natural clay mineral, it has low prices andexcellent adsorption properties which is widely used in dyeing wastewater treatment.In this thesis, the adsorption of Malachite green(MG), Methylene blue(MB) andSafranine T(SF) onto organic sepiolite modified by the organic sueface sodiumdodecyl benzene sulfonate from single and multisolute syetems was studied.It hasgreat significance to expand sepiolite applications on dyeing wastewater treatment.The static experiment results showed that along with increase of pH thedecoloring rates of Malachite green and Methylene blue rised slightly but Safranine Twas just the opposite.Different systems’ decolorization rates rised with the increasingoscillation rate. The adsorption capacity of malachite green, methylene blue,safranineT in single system were702.5μmol/g,146.9μmol/g and86.0μmol/g under thecondition of25℃, pH4.5, oscillation rate170r/min, dosage of adsorbent2g/L,adsorption time4h. Competitive and synergy absorption was observed in themultisolute systems’ adsorption experiments. Malachite green and Safranine T showedcompetitive absorption at low concentration, while synergy adsorption at highconcentration. However methylene blue and Safranine T was manifested in a strongcompetitive adsorption.In the case of adsorption from single and multisolute systems，the total adsorptionisotherms were fitted well by Langmuir model but the isotherm of each dye haddifferent shapes. All of the systems exhibited a monolayer adsorption process on theuniform adsorbent surface. The isotherm of the competitive adsorption system aboutMethylene blue and Safranine T followed expanded Langmuir isotherm model, and thedye was adsorbed more easier when the Langmuir adsorption equilibrium constant waslarger. The reaction enthalpy changes Hin the processes of adsorption were greaterthan zero, Gibbs free energy changes G were from-37.30kJ/mol to-19.58kJ/mol,entropy changes ΔS were greater than zero,which showed that the adsorptionprocesses were entropy-driven and spontaneously physical chemistry endothermicreaction. The adsorption of every system could be well fitted by a pseudo-second model.The fore60min of the adsorption process followed the particle diffusion kineticsmodel, but diffusion step could not controll the adsorption rate.The equilibrium timeof malachite green and methylene blue in multisolute system was longer than singlesystem,but the equilibrium adsorption capacity were the same.SEM results showed that the sepiolite surface was smoother after adsorptionsaturation and the gap was smaller. The specific surface area and pore size werereduced to varying degrees, and the reducing scope followed the order of adsorptioncapacity which was Malachite green> Methylene blue> safranine T. XRD, FT-IR andXPS analysis showed the adsorption was dominated by ion exchange，namely the Na+on the organic-modified sepiolite was replaced by the dye cation.Meanwhile, theadsorption process might be affected by the van der Waals forces, electrostatic forcesand hydrogen bonding forces.