Chromium Removal and Sorption Mechanism from Aqueous Solutions by Wine Processing Waste Sludge

• Published in: Industrial & engineering chemistry research Vol. 45; no. 26; pp. 8891 - 8899
• Main Authors: Liu, Cheng-Chung, Wang, Ming-Kuang, Chiou, Chyow-San, Li, Yuan-Shen, Lin, Yu-An, Huang, Shu-Shan
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 20.12.2006
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology; General treatment and storage processes; Pollution; Wastes; Sorption; Waste treatment; Aqueous solution
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie060978q

Wine processing waste sludge (WPWS) has been shown to be an effective sorbent for the sorption of heavy metals (i.e., chromium and nickel), but the mechanism of removal of hexavalent chromium [Cr(VI)] by WPWS remains obscure. The aims of this study were to determine the effects of temperature, initial concentration of Cr(VI), and particle size on the removal Cr(VI) using WPWS. The characteristics of WPWS were determined, and sorption mechanism studies were also performed. The WPWS used was a deposit mixture containing considerable quantities of chemical coagulation as well as activated sludge precipitation from the settling basins of a wastewater treatment plant. Differential scanning calorimetry (DSC) analysis revealed that the WPWS comprised abundant labile carbohydrates and few aromatic structures. According to the IR spectrum, carboxylic groups were the most important functional group in WPWS, interacting with chromium species by protonation and redox reaction. All kinetic experiments were conducted at an initial pH of 2.0, and all of them had reached steady state within 240 min. The final pH values of the suspensions were approximately 4.2, and the increase of the pH caused low Cr removal. In addition, about 2−18% of the Cr(III) remained in the liquid phase. The Cr removal percentage increased with increasing temperature (i.e., 14−25%), but it was less affected by particle size (17−22%). All kinetic data obtained from different conditions showed good compliance with a pseudo-second-order model, and the rate constant k 2 was found to range from 0.032 to 0.074 g mg-1 min-1. Some of the Cr(VI) ions were reduced to Cr(III) ions as a result of oxidation of organic components in WPWS, as indicated by monitoring using the X-ray absorption near-edge spectroscopic (XANES) technique.