Interactions in Ternary Mixtures of MnO^sub 2^, Al^sub 2^O^sub 3^, and Natural Organic Matter (NOM) and the Impact on MnO^sub 2^ Oxidative Reactivity

• Published in: Environmental science & technology Vol. 50; no. 5; p. 2345
• Main Authors: Taujale, Saru, Baratta, Laura R, Huang, Jianzhi, Zhang, Huichun
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 01-03-2016
• Subjects: Acids; Adsorption; Chemical compounds; Chemical reactions; Dissolution; Ions; Oxidative stress
• ISSN: 0013-936X

Our previous work reported that Al...O... inhibited the oxidative reactivity of MnO... through heteroaggregation between oxide particles and surface complexation of the dissolved Al ions with MnO... (S. Taujale and H. Zhang, "Impact of interactions between metal oxides to oxidative reactivity of manganese dioxide" Environ. Sci. Technol. 2012, 46, 2764-2771). The aim of the current work was to investigate interactions in ternary mixtures of MnO..., Al...O..., and NOM and how the interactions affect MnO... oxidative reactivity. For the effect of Al ions, we examined ternary mixtures of MnO..., Al ions, and NOM. Our results indicated that an increase in the amount of humic acids (HAs) increasingly inhibited Al adsorption by forming soluble Al-HA complexes. As a consequence, there was less inhibition on MnO... reactivity than by the sum of two binary mixtures (MnO...+Al ions and MnO...+HA). Alginate or pyromellitic acid (PA) -- two model NOM compounds -- did not affect Al adsorption, but Al ions increased alginate/PA adsorption by MnO... The latter effect led to more inhibition on MnO... reactivity than the sum of the two binary mixtures. In ternary mixtures of MnO..., Al...O..., and NOM, NOM inhibited dissolution of Al...O... Zeta potential measurements, sedimentation experiments, TEM images, and modified DLVO calculations all indicated that HAs of up to 4 mg-C/L increased heteroaggregation between Al...O... and MnO..., whereas higher amounts of HAs completely inhibited heteroaggregation. The effect of alginate is similar to that of HAs, although not as significant, while PA had negligible effects on heteroaggregation. Different from the effects of Al ions and NOMs on MnO... reactivity, the MnO... reactivity in ternary mixtures of Al...O..., MnO..., and NOM was mostly enhanced. This suggests MnO... reactivity was mainly affected through heteroaggregation in the ternary mixtures because of the limited availability of Al ions. (ProQuest: ... denotes formulae/symbols omitted.)