Removal of aliphatic amino acids by hybrid organic-inorganic layered compounds

Amino acids have been extensively used in several processes of the pharmaceutical and food industries. Treatments for the recovery and reuse of the wastewaters generated from these processes are few and little known. This work aims at studying the influence of variables like temperature, pH and ionic strength on the adsorption of the amino acids Asp and Glu, contained in aqueous solutions, on layered double hydroxides of the Mg-Al-CO3-LDH system. The adsorption experiments were performed at two different temperatures (298 and 310 K), two different pH values (7.0 and 10.0), and two ionic strength conditions (with or without the addition of NaCl). The adsorption isotherms exhibited similar profiles under the various conditions studied: an increase in temperature as well as an increase in the pH value decreased the amount of adsorbed amino acid while an increase in the ionic strength increased Asp and Glu adsorption. The PXRD analysis showed that the diffractograms obtained before and after the adsorption of amino acids have a similar pattern. The FT-IR spectra of the adsorbed material presented specific bands, which are related to the amino acids. The concentration range varied up to the anion solubility product and the extraction rate lay between 2.7 and 23.4% at higher equilibrium concentrations, showing that Mg-Al-CO3-LDH is efficient at removing the amino acids from the aqueous medium.