Adsorption de surfactants sur le dechet lainier de carbonisage surfactant adsorption on the wool carbonizing waste

Although wool carbonizing waste is available in large amounts (8.000 tonnes per year, in France), no process has been developed for its valorization. Wool carbonizing waste is made up of chemically modified short-sized wool fibres and of plant material particles which are considered as sulphuric lignins. Owing to the physical structure as well as to the polar and apolar characteristics of its macromolecules, wool carbonizing waste was likely to be a suitable material for the adsorption of ionic organic solutes. The adsorption of various surfactants on wool carbonizing waste was therefore investigated so as to assess the optimal conditions of use of this substrate in water pollution control. The adsorption isotherms of anionic (SDS; Figs 1 and 2). cationic (CPC; Figs 3 and 4), and non-ionic (NPPO; Fig. 5) surfactants were drawn, for various pH and temperature conditions, so as to determine the adsorption mechanisms involved as well as the adsorption capacity of the carbonizing waste and the optimal adsorption conditions. The adsorption was shown to be enhanced by temperature as a result of changes in adsorbent structure. Wool carbonizing waste is therefore liable to be used for the purification of hot effluents. The processing of anionic surfactant solutions by wool carbonizing waste requires acidic media (pH < 3), whereas alkaline media are more suitable for effluents containing cationic surfactants. Ionic bonding is involved in both cases. The adsorption rates of SDS and CPC range from 15 to 26% and from 35 to 55%, respectively, depending on the temperature, and are thus markedly higher than that of NPPO (7%) of which adsorption proceeds mainly through hydrophobic bonding. Although these adsorption rates are lower than those of ion-exchange resins, they are higher than those of charcoals (Table 3). The L-shape of the adsorption isotherms corroborates the successive involvement of ionic and hydrophobic interactions in the case of ionic surfactants. The models of Langmuir and Freundlich (Tables 1 and 2) were used for the modelization of water processing units. Besides, the column processing of a SDS solution showed the effect of pH on the efficiency of the operation (Fig. 6) as well as the beneficial effect of temperature (Fig. 7). The processing of industrial effluents in a stirred reactor corroborated the outstanding ability of wool carbonizing waste to adsorb cationic surfactants (Table V). Furthermore, these tests showed that the removal of non-ionic surfactants is improved when they are mixed with anionic surfactants (Table 4).