Effect of alkaline precipitation on Cr species of Cr(III)-bearing complexes typically used in the tannery industry. (February 2018)

• Record Type: Journal Article
• Authors: Wang, Dandan; Ye, Yuxuan; Liu, Hui; Ma, Hongrui; Zhang, Weiming
• Is Part Of: Chemosphere. Volume 193(2018)
• Page Start: 42
• Page End: 49
• Publication Date: 2018-02
• Subjects: Alkaline precipitation -- Cr(III)-collagen -- Cr(III)-citrate -- Mechanism -- Polymeric Cr(III); Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2017.11.006
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Various organic compounds extensively used in the leather industry could influence the performance of alkaline precipitation with Cr(III). This study focused on two typical Cr(III)-bearing complexes (Cr(III)-collagen and Cr(III)-citrate) ubiquitous in tannery effluent yet with distinct treatment efficiencies, as Cr(III) was much more difficult to remove in the Cr(III)-citrate solution. Comprehensive analytical methods were employed to explore the intrinsic mechanism. It was found that a lower removal efficiency towards Cr(III) was significantly associated with higher oligomers. The molecular size of the Cr(III)-citrate complex continued to increase with rising pH, making it larger overall than Cr(III)-collagen species. The growing oligomer moiety of dissolved Cr(III)-complex species could persist in the stronger basic pH range, leading to the large amount of residual Cr(III) in the Cr(III)-citrate system. Combining this result with potentiometric titration and X-ray photoelectron spectroscopy data, it was believed that the polymeric species other than monomers facilitated resisting the attack from hydroxide ions, and the postulated Cr(III)-citrate species towards higher oligomers were discovered. Beyond that, both charge neutralization and sweeping effects were presented among the gradually emerging flocs in the Cr(III)-collagen system together with the electric double layer compression effect derived from salinity, thus resulting in a larger floc size and higher Cr(III) removal efficiency in saline solutions. Graphical abstract: Image 1 Highlights: The variation of Cr(III) speciation in typical tannery complexes during alkaline precipitation process was examined. Cr(III)-citrate complex grew into higher oligomers along with the rising pH. Both charge neutralization and sweeping effects were presented among flocs in the Cr(III)-collagen system. The electric double layer compression effect resulted in larger floc size and better Cr(III) removal in saline solutions. The variation mode of Cr(III)-citrate species from monomer to macrocyclic tetramer was proposed.