Enhanced removal of Cr(III)-EDTA chelates from high-salinity water by ternary complex formation on DETA functionalized magnetic carbon-based adsorbents

Abstract

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.