Effects of pH, temperature, and ionic strength on adsorption of sodium dodecylbenzenesulfonate into Mg-Al-CO3 layered double hydroxides

Layered double hydroxides (LDHs) can be structurally described by the stacking of positively charged layers with host anionic species in the interlayer domain. These materials can be used as an alternative adsorbent to remove pollutant anions from waste waters. In this work, we have studied the influence of the pH, temperature, and ionic strength on the adsorption of sodium dodecylbenzenesulfonate (SDBS) in Mg-Al-CO₃ LDH. The adsorption experiments were carried out using the batch method and the equilibrium suspensions were submitted to zeta potential measurements. The PXRD pattern with a basal spacing of 7.6 Å , characteristic of hydrotalcite (Mg-Al-CO₃ LDH), was maintained after adsorption, indicating that the interlayer anion was not exchanged. The FT-IR spectra of the adsorbed solid presented a new band assigned to the sulfonate group (1200 cm^-1) of the dodecylbenzenesulfonate anion. Adsorption experiments showed that an increase in the pH and in the temperature causes a decrease in the SDBS adsorbed amount, while an increase in the ionic strength of the medium causes an increase in the adsorbed amount. Electrokinetic potential measurements, as a function of equilibrium concentration, presented profiles in accordance with those of isotherms, in each case.