Impregnation of smectite with layered double hydroxides of different chemistry for simultaneous removal of Cr(III) and acid blue dye

Abstract

Bifunctional adsorbents obtained by co-precipitation of anionic layered double hydroxides (LDH) on the surface of cationic montmorillonite (MMT) are considered to be more effective than the physical mixtures of the mentioned materials. This is due to high degree of dispersion of the materials and their mutual interactions which improve the rheological properties. Such hybrid composite enables a simultaneous removal of both cationic and anionic pollutants from aqueous solutions. This includes wastewaters from the tanning industry, which often contain chromium(III) from tanning processes and various dyes. In this work, an in-situ synthesis method at room temperature was developed. Four materials were obtained by LDH co-precipitation – Mg/Fe, Mg/Al, Ni/Al and Ni/Fe – in the presence of a smectite-rich sample from Wyoming (SWy). The mass ratio of smectite/LDH was 1:1. For comparison, four analogous physical mixtures of MMT/LDH, raw SWy and LDHs were used in the experiments. The materials were analyzed by XRD, FTIR, SEM/EDS analysis, thermal and textural analysis based on N2 adsorption/desorption. The effectiveness of removing pollutants was determined in adsorption experiments using Cr(III) cations and anionic dye Acid Blue 129. The conducted experiments showed a high removal capacity of both pollutants by the Mg/Al and Mg/Fe LDH-smectite composites, in single- (up to 100% for AB129 and 97% for Cr(III)), two- (up to 94% for AB129 and 91% for Cr(III)) and multi-component systems (over 62% for AB129 and 99.9% for Cr(III)). The synthesized materials show promising properties in terms of their use as adsorbents for treatment of complex industrial wastewaters.