Formation, aggregation, and transport of NOM–Cr(iii) colloids in aquatic environments

Abstract

The complexation of natural organic matter (NOM) with chromium (Cr) represents an integral part of the Cr cycling in nature. To date, most studies on the interaction of NOM with...

NOM-Induced Dissolution of CrxFe1–x(OH)3 Precipitates and Formation of Cr(III)-NOM-Fe Colloids under Oxic and Anoxic Conditions

“…The formation of Cr(III)-NOM-Fe colloids is dominantly owing to the complexation of Cr(III) and Fe with NOM, which inhibits the hydrolysis of Cr(III) and Fe ions and thus favors the smaller particle sizes. 21,50,51,72,73 Particle size and zeta potential measured by DLS support the dispersion of Cr(III)-NOM-Fe colloids. The hydrodynamic diameters of Cr(III)-NOM-Fe colloids formed under both oxic and anoxic conditions ranged from 79 to 167 nm (Figure 4a).…”

“…The zeta potential results show that Cr­(III)-NOM-Fe colloids possessed strongly negative surface charges (i.e., −40––17 mV, Figure b), further ensuring the particle stability of colloids. Under anoxic conditions, the particles have a higher surface negative charge compared to the particles formed under oxic conditions, which may be ascribed to the more reduced functional groups in AHA red than AHA ox . ,,, Altogether, the stability of Cr­(III)-NOM-Fe colloids formed under both oxic and anoxic conditions can be attributable to the enhanced electrostatic and steric stabilization imparted by NOM adsorbed on the particle surfaces. ,, …”

“…At high NOM concentration, the similar colloidal behaviors between Cr­(III) and Fe­(III/II) suggest their close associations in colloidal fractions during the NOM-induced dissolution of Cr x Fe 1– x (OH) 3 precipitates. The formation of Cr­(III)-NOM-Fe colloids is dominantly owing to the complexation of Cr­(III) and Fe with NOM, which inhibits the hydrolysis of Cr­(III) and Fe ions and thus favors the smaller particle sizes. ,,,, …”

“…Aldrich humic acid (AHA, 1415-93-6, Sigma-Aldrich) was chosen as a representative of NOM, owing to its well-characterization and wide application in colloid chemistry research. ,,, The AHA stock solution was prepared by dissolving aliquots of dried powder in 1 L ultrapure water at pH 10.5 ± 0.1 in the dark with constant stirring. After 3 days of rotation, the AHA suspension was filtered through 450 nm nitrocellulose membranes (Millipore).…”

“…32,33,38,39 Altogether, the stability of Cr(III)-NOM-Fe colloids formed under both oxic and anoxic conditions can be attributable to the enhanced electrostatic and steric stabilization imparted by NOM adsorbed on the particle surfaces. 26,51,74 3.3. Characterization of Cr(III)-NOM-Fe Colloids and Large Particles.…”