Hexagonal birnessite, a typical layered Mn oxide (LMO), can adsorb and oxidize Mn(II) and thereby transform to Mn(III)-rich hexagonal birnessite, triclinic birnessite, and/or tunneled Mn oxides (TMOs), remarkably changing the environmental behavior of Mn oxides. We have determined the effects of co-existing cations on the transformation by incubating Mn(II)-bearing δ-MnO2 at pH 8 under anoxic conditions for 25 d (dissolved Mn < 11 μM). In the Li+, Na+ or K+ chloride solution, the Mn(II)-bearing δ-MnO2 first transforms to Mn(III)-rich δ-MnO2 and/or triclinic birnessite (T-bir) due to the Mn(II)-Mn(IV) comproportionation, most of which eventually transform to a 4 × 4 TMO. In contrast, Mn(III)-rich δ-MnO2 and T-bir form and persist in the Mg2+ or Ca2+ chloride solution. Yet, in the presence of surface adsorbed Cu(II), Mn(II)-bearing δ-MnO2 turns into Mn(III)-rich δ-MnO2 without forming T-bir or TMOs. The stabilizing power of the cations on the δ-MnO2 structure positively correlates with their binding strength to δ-MnO2 (Li+, Na+ or K+ < Mg2+ or Ca2+ < Cu(II)). Since metal adsorption decreases the surface energy of minerals, our result suggests that the surface energy largely controls the thermodynamic stability of LMOs. Our study implies that the adsorption of divalent metal cations, particularly transition metals, can be a prime cause of the high abundance of LMOs, rather than the more stable TMO phases, in the environment.
Yang, Peng, Post, Jeffrey E., Wang, Qian, Xu, Wenqian, Geiss, Roy, McCurdy, Patrick R., & Zhu, Mengqiang (2019). Metal Adsorption Controls Stability of Layered Manganese Oxides. Environmental Science and Technology, 53(13). https://doi.org/10.1021/acs.est.9b01242
@article{osti_1559537,
author = {Yang, Peng and Post, Jeffrey E. and Wang, Qian and Xu, Wenqian and Geiss, Roy and McCurdy, Patrick R. and Zhu, Mengqiang},
title = {Metal Adsorption Controls Stability of Layered Manganese Oxides},
annote = {Hexagonal birnessite, a typical layered Mn oxide (LMO), can adsorb and oxidize Mn(II) and thereby transform to Mn(III)-rich hexagonal birnessite, triclinic birnessite, and/or tunneled Mn oxides (TMOs), remarkably changing the environmental behavior of Mn oxides. We have determined the effects of co-existing cations on the transformation by incubating Mn(II)-bearing δ-MnO2 at pH 8 under anoxic conditions for 25 d (dissolved Mn +, Na+ or K+ chloride solution, the Mn(II)-bearing δ-MnO2 first transforms to Mn(III)-rich δ-MnO2 and/or triclinic birnessite (T-bir) due to the Mn(II)-Mn(IV) comproportionation, most of which eventually transform to a 4 × 4 TMO. In contrast, Mn(III)-rich δ-MnO2 and T-bir form and persist in the Mg2+ or Ca2+ chloride solution. Yet, in the presence of surface adsorbed Cu(II), Mn(II)-bearing δ-MnO2 turns into Mn(III)-rich δ-MnO2 without forming T-bir or TMOs. The stabilizing power of the cations on the δ-MnO2 structure positively correlates with their binding strength to δ-MnO2 (Li+, Na+ or K+ 2+ or Ca2+ < Cu(II)). Since metal adsorption decreases the surface energy of minerals, our result suggests that the surface energy largely controls the thermodynamic stability of LMOs. Our study implies that the adsorption of divalent metal cations, particularly transition metals, can be a prime cause of the high abundance of LMOs, rather than the more stable TMO phases, in the environment.},
doi = {10.1021/acs.est.9b01242},
url = {https://www.osti.gov/biblio/1559537},
journal = {Environmental Science and Technology},
issn = {ISSN 0013-936X},
number = {13},
volume = {53},
place = {United States},
publisher = {American Chemical Society (ACS)},
year = {2019},
month = {05}}
Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 286, Issue 1336, p. 283-301https://doi.org/10.1098/rsta.1977.0118