Effects of CMC and Micelle Formation on the Removal of Sodium Benzoate or Sodium Stearate in a Sodium Aluminate Solution

Micelle formation over a critical micelle concentration (CMC) is related to the economic removal of organics in a sodium aluminate solution. In this research, removal of organics was investigated by adding activated alumina and red mud. The micelle formation of sodium benzoate and sodium stearate, together with enthalpy, Gibbs free energy and entropy, was discussed by detecting the surface tension. The removal rate of organics was > 21% with activated alumina or red mud in a concentrated sodium aluminate solution. Increasing benzoate (or stearate) concentration and elevating temperature decreased the surface tension. Furthermore, the concentrated sodium aluminate solution remarkably increased the cross-sectional headgroup area of sodium stearate compared with that of sodium benzoate and led to a strong depletion interaction and small organic assembly on the surface. The low CMC, large cross-sectional headgroup area and strong depletion interaction of micelles on the surface reduced the removal rate of organics in the sodium aluminate solution compared with that in water.