Effect of organic ligands on the removal of Cr(III) from water by coagulation process

The existence of Cr(III) complexes in water has become the key problem posed for the standard discharge of Cr-containing wastewater. Coagulation is the most common method for the treatment of chromium wastewater. However, little information has been collected regarding the effect of organic matters on Cr(III) removal by the coagulation process. In this study, the removal of Cr(III)acetate (Cr-ace) complexes with the molar ratio of 1: 1, 1:2 and 1:3 by coagulation were systematically investigated. Fe(III) salts were more efficient than Al(III) in Cr(III) removal. Approximately 95% removal rate of Cr-ace (1:1) was obtained with Fe(III) dosage of 0.8 mM, while about 70% and 35% removal efficiency of Cr(III)-ace (1:2 and 1:3) were achieved, respectively. With the increase of carboxyl contents, Cr removal efficiencies were decreased due to the enhanced stable structure of the Cr(III) complex. When Fe(III) concentration was 0.8 mM, the removal rate of Cr- ace (1:1, 1: 2, 1:3) by Fe(III) flocs were 61.5%, 61.47%, 48.15%, respectively. Under the same condition, the removal efficiency of Cr-ace with Al(III) adsorption were 74.99%, 53.67%, 36.85%, respectively. Such results indicated adsorption played an important role in Cr removal, especially at high dosage coagulants. The growth of flocs was inhibited accompanied by acetate in high concentration. Furthermore, Ca2+ has limited influence on Cr removal, while short complexation time was beneficial to Cr removal. This paper provided some theoretical support for the influence parameters of Cr(III) removal from wastewater through coagulation.

Automated summary

This study demonstrated that Fe(III) salts were more efficient in removing Cr-ace complexes compared to Al(III) salts. The removal efficiency of Cr(III) complexes decreased with an increase in the carboxyl content. Additionally, high concentrations of acetate inhibited the growth of flocs.