Crystal Chemistry of Thallium in Marine Ferromanganese Deposits

Our understanding of the up to 7 orders magnitude partitioning thallium (Tl) between seawater and ferromanganese (FeMn) deposits rests upon two foundations: (1) being able quantify Tl(I)/Tl(III) ratio that reflects extent oxidative scavenging Tl by vernadite (?-MnO2), principle manganate mineral in oxic suboxic environments, (2) determine sorption sites bonding environments Tl(I) Tl(III) complexes on vernadite. We investigated these foundations determining oxidation state chemical form FeMn crusts nodules from global oceans at a concentration ranging several hundred ppm (mg/kg) down low level. Seventeen hydrogenetic eleven Pacific, Atlantic, Arctic, Indian Oceans Baltic Sea were characterized analysis, X-ray diffraction, Raman spectroscopy, Mn K-edge absorption near-edge structure (XANES) L3-edge high energy-resolution XANES (HR-XANES) extended fine (EXAFS) spectroscopy. The increases linearly 1.5 319 with Mn/Fe Fe-vernadite crusts, whereas percentage total varies 62 100% independent both Mn(III)/Mn(IV) ratios. data, complemented molecular modeling coordination calculations, suggest enrichment is driven uptake octahedrally coordinated above vacant Mn(IV) layer edges layers, crystallographic site Ba surface which an analogue K. Thus, has affinity for regardless its state, lack correlation explained site. 2 112 buried ratio, 0 100%. Nodules subjected sediment diagenesis replacement layered tunneled todorokite are depleted have more reduced thallium. Knowledge complex interplay mineralogy, processes, siting required understand variability concentrations, redox acquisition processes marine deposits.