Rapid sequestration of chelated Cr(III) by ferrihydrite: Adsorption and overall transformation of Cr(III) complexes

Purification of various types of industrial wastewater containing chelated heavy metals (CHMs) remains a challenging task due to the easy dissolution, poor biodegradation and extremely high stability over a wide pH range. Compared with the common CHMs, the attention of Cr(III) complexes is greatly insufficient. Especially, Cr(III) of the wastewater is easily reoxidized and converted into Cr(VI) with high biotoxicity during the transferring process, so the treatment of Cr(III) complexes needs to be treated more strictly. Obviously, compared with previous advanced oxidation and replacement-coprecipitation technologies, adsorption method could directly remove Cr(III) complexes in one step, thus avoiding the accumulation of secondary toxic Cr(VI). Considering that ferrihydrite (Fh) materials are widely distributed on the nature, excellent adsorption performance, low cost, and environmentally friendly, this paper proposes a novel strategy that uses the common Fh as an efficient adsorbent to realize one-step elimination of typical EDTA-Cr(III) complexes without introducing secondary pollution. Batch experiment results illustrated that more than 93% of EDTA-Cr(III) was removed at pH = 3 or 6 (a final concentration of <1 mg/L EDTA-Cr(III) was detected in the residual solution within one hour). In particular, Fh retained good performance for the removal of EDTA-Cr(III) after desorption reactions in 2 g/L Na 2 SO 4 solution. A series of experiments and characterization results suggested that EDTA-Cr(III) was adsorbed on Fh materials mainly through electrostatic interactions and surface complexation. In general, this study also demonstrated Fh for the outstanding remediation of various Cr(III)-organic complexes from multicomponent environment.