Adsorption of Cr(III) by EGTA modified magnetic microsphere: Effect of high salinity and organic chelating acids

EGTA functionalized magnetic microsphere (Fe 3 O 4 @SiO 2 @EGTA) was prepared for the removal of Cr(III) from highly saline organic wastewater environment. The synthesized adsorbent was characterized with Fourier transform infrared (FTIR), powder x-ray diffraction (XRD), thermogravimetric analysis (TGA) and x-ray photoelectron spectrometry (XPS). The characterization techniques depicted the successful surface modification of magnetic particles (Fe 3 O 4 @SiO 2 ) with the functional groups of EGTA without changing its crystal structure. The maximum adsorption amount of Cr(III) was 25.25 mg ⋅ $\cdot$ g −1 at pH 4.0. The Langmuir isotherm was well fitted on the adsorption data, while adsorption equilibrium was achieved in first 15 min, and the equilibrium data well explained by pseudo second order model. The smaller concentrations of inorganic cations (Na + ${}^{+}$ , Ca 2＋ , Mg 2 + ${}^{2+}$ ), organic acids (EDTA, Citric acid , Formic acid) and complexing agent with high salt system reduce the adsorption capacity to some extent, but after that the higher concentrations of these competing species have no apparent effect on the adsorption performance. According to the XPS analysis, the carboxyl and amino groups were responsible for the adsorption of Cr(III), while the main mechanism of adsorption were coordination complex and electrostatic interaction. The prepared adsorbent can be readily isolated by external magnetic field and regenerated for several times and still possess higher adsorption performance.