Interactions of Chromium Ions with Starch Granules in an Aqueous Environment

Abstract

In this study, interactions of dichromate ions with potato starch granules in highly acidic aqueous solutions and at different temperatures were investigated. It was found that the process underwent a reduction of Cr(2)O(7)(2-) to Cr(3+) accompanied by the formation of intermediate Cr(5+) ions detected by electron paramagnetic resonance (EPR) spectroscopy. The reactions took place after the attachment of dichromate anions to the granules and resulted in a lowering of the Cr(2)O(7)(2-) initial content in the solution. The newly formed Cr(3+) ions were both accumulated by the granules or remained in the solution. It was observed for the first time that the quantity of such ions taken by the granules from the solution was noticeably higher than that delivered by trivalent chromium salt solution. It was revealed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) that the chromium ions were not only adsorbed on the granule surface but also introduced into the granule interior and evenly distributed there. An activation energy of the reduction reaction equal to 65 kJ·mol(-1) and the optimal parameters of the process were established. The proposed mechanism could be useful for the bioremediation of industrial effluents polluted by hexavalent chromium compounds.

Effect of Starch Phosphorylation on Interaction With Chromium Ions in Aqueous Solutions

“…The results of the zeta potential measurements are shown in Figure . An increase of zeta potential with the lowering of pH value, as stated previously for native potato starch, is also observed for phosphorylated starch and reference sample. However, in the case of modified starch, as well as the reference, the isoelectric point is shifted toward the higher acid region.…”

“…Figure A illustrates the number of Cr(III) ions created by the reduction of Cr(VI) ions or by dissolution of Cr(NO 3 ) 3 · 9H 2 O. At pH = 1, 5.68 · 10 19 Cr(III) ions were produced in the reduction of Cr(VI) and adsorbed on phosphorylated starch (Figure A), which is 12 times higher than the amount obtained at the same conditions for native potato starch (0.48 · 10 19 ) . It should be noted that adsorbed amount of Cr(III) on the phosphorylated starch is very close to the number of PO 4 3− groups (6.6 × 10 19 ).…”

“…It was shown previously that native potato starch is effective in decreasing of Cr(VI) concentrations in aqueous solutions. In the present work, the influence of starch phosphorylation on the effectiveness of this process was examined.…”

“…The broad signal from Cr(III) species was characterized by g≌1.89, a typical EPR spectrum for chromium ions in this valence state, whereas the sharp signal was assigned to the Cr(V) species . In the case of Cr(III) ions adsorbed on phosphorylated starch, the signal consists of multiple overlapping lines, suggesting the presence of adsorption centers differing in the local environment.…”

“…The interactions of transition metal ions with natural and synthetic polymers are a globally important research focus in terms of managing environmental pollution . We previously demonstrated that acidic aqueous Cr(VI) ions solutions can be treated with starch to considerably lower the concentration of these hazardous ions . Furthermore, the reduction of Cr(VI) – primarily to Cr(III) – and the sorption on starch granules was documented.…”