Synthesis, Characterization, and Sorption Capacity of Layered Double Hydroxides and Their Complexes with Polymerin

Mg-Al layered double hydroxides (LDHs) containing chloride (LDH-Cl) or carbonate (LDH-CO3) in the interlayer were obtained at room temperature and after calcitation at 450 degrees C (LDH-Cl-450 and LDH-CO3-450) and were characterized by X-ray diffraction and Fourier transform infrared analyses. Sorption isotherms of a humic acidlike fraction naturally occurring in olive oil mill waste waters, named polymerin, on these LDH minerals were carried out. Because LDH-CO3 showed the highest capacity to sorb polymerin among the four LOH minerals synthesized, two organo mineral complexes named LDH-CO3 LP (low polymerin) and LDH-CO3 HP (high polymerin) were prepared by coprecipitation (LDH-CO3 LP) and sorption onto a preformed LDH-CO3 mineral (LDH-CO3 HP). These complexes were characterized chemically and physicochemically, and their stability to pH and after thermal treatment at 80 degrees C were evaluated. The diffuse reflectance infrared Fourier transform and X-ray analysis of the complexes indicated that polymerin was sorbed only on the external surfaces of LDH -CO3 and no intercalation occurred. The LDH polymerin complexes appeared to be more stable than LDH-CO3 at pH 4.0 and showed that they were able to sorb both As(V) and Zn. Because the waste waters are usually contaminated with mixtures of pollutants in cationic and anionic forms, the LDH-polymerin complexes appear more suitable than the sorbents in a potential water remediation process.