Aggregation Kinetics of Manganese Oxides Formed from permanganate activated by (Bi)sulfite: Dual Role of Ca 2+ and Mn II/III

• Published in: Water research (Oxford) Vol. 159; p. 454
• Main Authors: Cheng, Haijun, Ma, Jun, Jiang, Jin, Pang, Su-Yan, Yang, Tao, Wang, Panxin
• Format: Journal Article
• Language: English
• Published: England 15.05.2019
• Subjects: Aggregation; Nanoparticles; Manganese oxides; In situ; Cation-bridging

Aqueous aggregation kinetics of manganese oxides, the solid products formed during water treatment and subsurface remediation with permanganate, are crucial for its application. In this study, manganese oxides nanoparticles were in situ formed in a permanganate/(bi)sulfite system, which was found to have excellent oxidation ability. Aggregation kinetics of such manganese oxides (i.e., MnO -1.5, MnO -2.5 and MnO -5; the number represents the molar ratio of (bi)sulfite to permanganate) were evaluated by employing time-resolved dynamic light scattering under various aquatic conditions. In NaNO solution, the stability of manganese oxides decreased in the order of MnO -1.5 > MnO -2.5 > MnO -5, indicated by their critical coagulation concentrations (CCCs). X-ray photoelectron spectroscopy (XPS) and zeta potential measurements indicated that Mn were responsible for the decreased stability due to their charge neutralization effects. However, in Ca(NO ) solution, three manganese oxides had similar CCCs, probably due to the relatively great charge neutralization ability of Ca . Suwannee River fulvic acid (SRFA), through electrosteric interaction, suppressed the aggregation of MnO -1.5 in Ca(NO ) solution, but had no such effect in NaNO solution. Comparatively, the stability of MnO -5 was markedly enhanced with SRFA in NaNO solutions. It was proposed that Ca and Mn could increase the adsorption of SRFA through charge neutralization and cation bridging. This study highlights the dual role, dependent on either presence or absence of SRFA, of Ca and Mn in controlling the aggregation of manganese oxides nanoparticles.