Enhanced removal of chromium(III) for aqueous solution by EDTA modified attapulgite: Adsorption performance and mechanism.

Ethylenediaminetetraacetic acid modified attapulgite (EDTA-ATP) was developed as a novel and promising adsorbent for removal of aqueous Cr(Ш). The structure and surface properties of EDTA-ATP were characterized and the results indicated that EDTA moieties have been successfully anchored on the surface of ATP. Adsorption of Cr(III) on EDTA-ATP and aminopropyl-modified attapulgite (APTES-ATP) monotonously reduced with decreasing pH, and Cr(III) adsorption on EDTA-ATP is substantially higher than APTES-ATP in tested pH range, especially at lower pH. Presence of citric acid and gelatin had no obvious influence on Cr(III) adsorption to EDTA-ATP, but significantly reduced Cr(III) adsorption on APTES-ATP. Coexisting cations resulted in decreased Cr(III) adsorption on EDTA-ATP by competition with Cr(III) for surface-bound EDTA groups of the adsorbent. Adsorption isotherm of Cr(III) on EDTA-ATP followed the Langmuir model and the maximum adsorption capacity of the adsorbent for Cr(III) was 131.37 mg/g at 25 °C and pH 3.0. Cr(Ш) loaded adsorbent could be regenerated easily in HCl solution and the regenerated adsorbent still exhibited high adsorption capacity for Cr(III). XPS analysis confirmed that the enhanced Cr(III) adsorption on EDTA-ATP was ascribed to form the stable complexes between Cr(III) and surface-bound carboxyl and amino groups of the adsorbents.