Adsorption of surfactants by a chelating resin: Effects of floatability and metal loading.

摘要

The objective of this work was to investigate a new concept for the treatment of dilute waste effluents based upon the adsorption of surfactants onto a fine-sized chelating resin. As adsorption of surfactants increases the hydrophobicity of the resin, flotation can be used to separate the resin from solution.; Kinetics of ion removal improved substantially with fine-sized Dow XFS4195 resin ({dollar}>{dollar}150 {dollar}mu{dollar}m diameter) as compared to conventional-sized XFS4195 resin (300-1000 {dollar}mu{dollar}m diameter). The effect of pH, initial ion concentration, and counter ions on copper and chromium(VI) uptake were studied. Studies involving simultaneous removal of copper and chromium indicated that neither ion had a deleterious effect on the other's removal.; Adsorption isotherms were generated for fine XFS4195 with four surfactants, sodium dodecylsulfonate, tetradecylsulfonate, hexadecylsulfonate and dodecylbenzenesulfonic acid. Using a Langmuir-type equation, the monolayer coverage for each surfactant was estimated to range from {dollar}1.71cdot10sp{lcub}-3{rcub}{dollar} to {dollar}2.04cdot10sp{lcub}-3{rcub}{dollar} mol{dollar}cdot{dollar}g{dollar}sp{lcub}-1{rcub}.{dollar} As the specific surface area of the fine-size resin was determined by para-adsorption to be 1390 {dollar}pm{dollar} 30 m{dollar}sp2{lcub}cdot{rcub}{dollar}g{dollar}sp{lcub}-1{rcub},{dollar} the average monolayer coverage corresponded to an area of 126 A{dollar}sp2{dollar} per surfactant molecule. The Gibbs free energies of adsorption for SDSn, STSn, SHSn and DBSnA, calculated from the Langmuir isotherms, were {dollar}-{dollar}27.2, {dollar}-{dollar}28.5, {dollar}-{dollar}32.1 and {dollar}-{dollar}31.5 kJ{dollar}cdot{dollar}mol{dollar}sp{lcub}-1{rcub},{dollar} respectively. The average increment associated with each additional -CH{dollar}sb2{dollar}- group in the alkyl chain was found to be approximately {dollar}-{dollar}1.2 kJ{dollar}cdot{dollar}mol{dollar}sp{lcub}-1{rcub}.{dollar} Using the excess Gibbs free energy approach, the data indicated that the surfactant molecules were primarily adsorbing onto the surface in a flat configuration.; Desorption studies of surfactant-conditioned resin in distilled water showed little hysteresis from the adsorption isotherm. Desorption studies were also performed in H{dollar}sb2{dollar}SO{dollar}sb4{dollar} and NH{dollar}sb4{dollar}OH. While not much deviation from the adsorption isotherm occurred for desorption into H{dollar}sb2{dollar}SO{dollar}sb4,{dollar} studies using NH{dollar}sb4{dollar}OH indicated substantial desorption.; Metal loading studies of conditioned resin showed that adsorption of surfactants did not appear to affect metal uptake. While the metal loading kinetics of the resin conditioned with the alkylsulfonates were similar, the initial kinetics of copper uptake by DBSnA-conditioned resin were slower. However, similar copper levels were reached at equilibrium.; Film flotation and bubble-particle induction-time measurements indicated that after surfactant conditioning, the hydrophobicity of the resin surface was increased. A new flotation technique was developed to evaluate the floatability of the fine resin, which used the resin's low density and small particle size to its advantage. While a good flotation response ({dollar}<{dollar}94%) was found for resin conditioned with SDSn, STSn and DBSnA, using SHSn resulted in poor separation of the resin by flotation ({dollar}<{dollar}23%). As no collector was added during flotation, it appears that surfactant desorbing from the resin surface played a role in the process by acting as a frother and affecting froth stability.