Metal Exchangeability in the REE-Enriched Biogenic Mn Oxide Birnessite from Ytterby, Sweden

A black substance exuding from fractures was observed in 2012 Ytterby mine, Sweden, and identified 2017 as birnessite with the composition Mx[Mn(III,IV)]2O4∙(H2O)n. M is usually calcium sodium, x around 0.5. The unique, being calcium, magnesium, also rare earth elements (REEs) constituting up to 2% of total metal content. biogenic origin established 2018. Analysis microbial processes leading formation REE enrichment has continued since then. process fast dynamic, indicated by depletion manganese other metals fracture water during passage over precipitation zone mine tunnel. Studies exchangeability structure are main objective present program. Exposure solutions lanthanum, iron led exchanges altered distribution birnessite, however, generating phases almost identical structures after exchanges, no new mineral were detected. Exchangeability more efficient for trivalent (REE) divalent (calcium) monovalent (sodium) a similar size (ionic radii 90–100 pm).