ADSORPTION OF SODIUM DODECYL-SULFATE ON CASSITERITE SURFACE

Measurements of the adsorption of sodium dodecyl sulphate (SDS) onto c assiterite were made. It was found that at SDS concentrations below 10 (-3) mol/L the adsorption depended on the manner of preparation of the cassiterite and the pH of solution. However, the adsorption isotherms showed a point of inflection at 10(-3) mol/L corresponding to an occu pied area per molecule of about 0.8 nm2. This value is close to the su rface area covered by one dodecyl sulphate ion (DS-) as evaluated from the molecular structure of SDS. Near the critical micelle concentrati on (cmc), a plateau was found which corresponded to the adsorption of two statistical monolayers of DS- ions vertically oriented to the surf ace.