Layered double hydroxides for remediation of industrial wastewater containing manganese and fluoride.

Abstract

This work describes an environmentally-friendly procedure for the removal of manganese and fluoride from industrial wastewaters (IW) using layered double hydroxides (LDHs) and calcined layered double oxides (LDOs). Ternary Mg-Mn-Al LDHs (LDH-IW) were produced from IW containing a high concentration of manganese, which decreased from (99.420 ± 3.110) mg L 1 to (0.003 ± 0.001) mg L 1 after the synthesis procedure. Synthetic Mg-Al LDH was also produced for comparison purposes. Both materials were calcined and the resulting oxides (LDO and LDO-IW) were used for the removal of fluoride present in the same IW. The materials were characterized by X-ray diffraction, electron energy-loss spectroscopy, thermal analysis, Raman spectroscopy, and electron microscopy. The kinetics and adsorption isotherms for fluoride removal from aqueous solutions were studied in batch mode. For both LDO and LDO-IW, the adsorption of fluoride followed pseudo-second order reaction kinetics. Langmuir-type adsorption was observed for LDO, while adsorption by LDO-IW was according to the Freundlich model. The results showed that the oxides were able to remove 94% of the fluoride present in the IW at an initial concentration of 162 mg L 1. The procedure reduced the concentrations of the pollutants (manganese and fluoride) to levels that complied with Brazilian effluent standards.