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Adsorption of sodium dodecylsulfate (SDS) onto chrysotile from aqueous solutions was investigated along with varying temperature, ionic strength and surface treatments. Commercial chrysotile fibers were treated by sonication or extensive washings. The ratio of adsorbed SDS per gram of chrysotile is approximately constant with varying chrysotile masses. A steady state is reached after about 2 h of contact between SDS and chrysotile. In general, less surfactant is adsorbed on the sonicated chrysotile than on the extensively washed chrysotile. For the sonicated chrysotile, isotherms presented an adsorption maximum in the region of the surfactant critical micelle concentration, when the experiments were carried out without ionic strength control. The adsorption maximum is due to the presence of magnesium ions in the solution, which can form complexes with dodecylsulfate ions. For the extensively washed chrysotile, the isotherm behavior is similar to that obtained with sonicated chrysotile in the presence of an inert electrolyte. No significant difference in adsorption of SDS on the extensively washed chrysotile was observed when varying temperature or ionic strength. The adsorption of SDS was found to be dependent on the prior surface treatment. |
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