Enhanced removal of Cr(III)-EDTA chelates from high-salinity water by ternary complex formation on DETA...

A novel amino-functionalized magnetic adsorbent (Fe₃O₄@C@DETA) was developed for adsorption of Cr(III) and Cr(III)-EDTA from wastewater. Fe₃O₄@C@DETA were successfully prepared by modification of Fe₃O₄@C with diethylenediamine (DETA), which exhibits a core-shell structure and sufficient saturation magnetization. Fe₃O₄@C@DETA exhibits much better adsorption performance for Cr(III) and its chelates than the Fe₃O₄@C because of newly introduced amino active sites. The enhanced adsorption capacity of Fe₃O₄@C@DETA for Cr(III) is 44.74 mg g^-1 (at 25 °C and pH 3.0), which is due to the surface coordination with the newly introduced amino functional sites. The Cr(III)-EDTA anions as a whole was adsorbed through the electrostatic interaction with protonated amino species of the Fe₃O₄@C@DETA and have maximum adsorption capacity of 47.27 mg g^-1 (at 25 °C and pH 3.0). The adsorption data of free and EDTA coordinated Cr(III) were followed the Langmuir equation, while the adsorption dynamics was well explained by pseudo second order model indicating the chemical nature of adsorption process. The higher concentration of Ca²⁺ ions in the wastewater compete for adsorption sites and inhibit the Cr(III) removal, while on other hand Ca²⁺ ions promotes the adsorption of Cr(III)-EDTA, because of electrostatic interaction with adsorbent active sits. Furthermore, the adsorbent can be easily separated by external magnetic field and regenerated in acidic solution. The adsorbent is stable, recyclable and have more than 75% regeneration efficiency and can be repeatedly used in the adsorption process.