Sinorhizobium meliloti 1021 Exopolysaccharide as a Flocculant Improving Chromium(Ⅲ) Oxide Removal from Aqueous Solutions

摘要

Chromium(Ⅲ) oxide is an amphoteric, dark green solid. This most stable dye is widely used in construction and ceramic industries as well as in painting. In this study, the attempt is made to determine flocculating properties of exopolysaccharide (EPS) synthesized by the bacteria Sinorhizobium meliloti 1021, which would increase the efficiency of chromium(Ⅲ) oxide removal from sewages and wastewaters. The conditions under which EPS is the most effective destabilizing component of chromium(HI) oxide suspension have been determined too. In order to characterize the structure of electric double layer formed at the solid/supporting electrolyte (EPS) solution interface, electrokinetic potential measurements and potentiometric titration were performed. The EPS amount adsorbed on the chromium(Ⅲ) oxide surface as a solution pH function was also measured. Moreover, the stability of Cr_2O_3 suspension in the absence and presence of S. meliloti 1021 EPS was estimated. The pooled analysis of all obtained results showed that EPS causes chromium(Ⅲ) oxide suspension destabilization in the whole examined pH range. The largest change in the system stability before and after the polymer addition was observed at pH 9. It is probable that under these conditions bridging flocculation occurs in the examined system.