Transformation of Ni-containing birnessite to tectomanganate: Influence and fate of weakly bound Ni(II) species

Abstract

The geochemical behavior of nickel, an essential trace metal element, strongly depends on its interactions with Mn oxides. Interactions between the phyllomanganate birnessite and sorbed or structurally incorporated Ni have been extensively documented together with the fate of Ni along the transformation of these layered species to tunnel Mn oxides (tectomanganates). By contrast, interactions of phyllomanganates with weakly bound Ni species (hydrated Ni, Ni (hydr)oxides), that possibly prevail in natural Ni-rich (>10% NiO) manganates received little attention and the influence of these Ni species on the phyllomanganate-to-tectomanganate transformation remains essentially unknown. Within this framework, a set of phyllomanganate precursors with contrasting contents of Ni were prepared and subjected to a reflux process mimicking the natural phyllomanganate-to-tectomanganate conversion. Layered precursors and reflux products were characterized with a combination of diffractometric, spectroscopic, thermal, and chemical methods. Ni is essentially present as hydrated Ni(II) and Ni(II) (hydr)oxides in layered precursors with no detectable Ni sorbed at layer vacancy sites or structurally incorporated. Despite the high content (~1/3) of Jahn-Teller distorted Mn(III) octahedra in these layered precursors, which is known to be favorable to their conversion to tectomanganates, polymerization of Ni(OH) 2 in phyllomanganate interlayers is kinetically favored during reflux process. Asbolane, a phyllomanganate with an incompleteisland-likeoctahedral layer of metal (hydr)oxides, is thus formed rather than todorokite, a common tectomanganate with a uniform 3×3 tunnel structure. A nitric acid treatment, aiming at the dissolution of the island-like interlayer Ni(OH) 2 layer, allows an easy and unambiguous differentiation between asbolane and todorokite, which is unaffected by the treatment. Both compounds exhibit indeed similar periodicities and can be confused when using X-ray diffraction, despite contrasting intensity ratios. Ni(OH) 2 polymerization hampers the formation of tectomanganates and likely contributes to the prevalence of phyllomanganates over tectomanganates in natural environments. Most Ni is retained during the reflux process, part of Ni (~20%) being likely structurally incorporated in the reaction products, thus enhancing the sequestration of Ni in Mn oxides.

Understanding the role of manganese oxides in retaining harmful metals: Insights into oxidation and adsorption mechanisms at microstructure level

“…1 ) [ 16 , 20 , 59 , 76 , 77 ]. Charge defects in birnessite layers arise from vacancies, the substitution of layer Mn 4+ with lower valence cations like Mn 3+ , Ni 2+ , and Co 3+ , and edge sites [ 35 , 78 ]. The defects can be neutralized by Mn 3+ , Mn 2+ , H + , interlayer alkaline/alkaline earth metals, and other cations [ 79 , 80 ].…”

“…The MnO 6 octahedra connect via edge-sharing to form single chains, producing Mn oxides with diverse structures through edge- and/or corner-sharing [ 33 ]. Based on the stacking arrangement of MnO 6 octahedra, the Mn oxides are typically classified into two categories: layered structure (i.e., phyllomanganate) and tunneled structure (i.e., tectomanganate) [ [34] , [35] , [36] ]. The layered structure comprises layers of edge-sharing MnO 6 octahedra, with symmetry dependent on the Mn(III) octahedra distribution.…”

“…The layered structure comprises layers of edge-sharing MnO 6 octahedra, with symmetry dependent on the Mn(III) octahedra distribution. The tunneled structure, however, involves edge-sharing MnO 6 octahedra forming tunnel walls or floor/ceiling [ 35 ]. Heterovalent Mn ions and/or foreign transition metal cations may be present in both layered and tunnel-structured Mn oxides, either replacing Mn(IV) structurally or acting as charge compensators in phyllomanganate interlayers or tectomanganate tunnels [ [37] , [38] , [39] , [40] ].…”

The important role of the interaction between manganese minerals and metals in environmental remediation: a review

“…Co(II) and Fe(II) are immobilized on birnessite by replacing Mn(III) and Mn(IV); however, only the replacement of Mn(III) has been found in the Ni(II) immobilization process. The grain boundary coordination radius (CR) determines the substitution of metals with Mn(III)/Mn(IV) in the birnessite layer: the smaller the difference between CR of metals and Mn(IV) or Mn(III), the more compatible they are with the Mn layer (Wu et al, 2020).…”

Transformation of the phyllomanganate vernadite to tectomanganates with small tunnel sizes: Favorable geochemical conditions and fate of associated Co

“…For Me/(Me+Mn) ratios higher than 20 at.% (Me = Co, Ni), Co forms, often in association with Ni, an octahedral sheet sandwiched in between MnO2 layers leading to the minerals asbolane or lithiophorite, depending on the Al content (Chukrov et al, 1987;Manceau et al, 1987;Llorca and Monchoux, 1991;Roqué-Rosell et al, 2010;Lambiv Dzemua et al, 2013;Ploquin et al, 2019). The presence of this octahedral sheet has also been shown to impede the transformation of layered Mn oxides to tectomanganates (Wu et al, 2020).…”