Metal‐complex Formation by Lichen Compounds

Abstract

The formation of soluble complexes, frequently coloured, when solid lichen compounds were shaken with water suspensions of biotite, granite, and basalt indicated that chemical weathering had occurred. The formation of colourless complexes and the adsorption of the dissolved lichen compound or complex by the silicate phase complicate the interpretation of the spectrophotometric analysis data. Lichen compounds invariably released greater amounts of Ca than of Mg, Fe, and A1 from the silicates and, for each lichen compound, the release of Ca was usually greater from biotite than from granite or basalt. Release of cations from the silicate materials resulted largely from metal-complex formation rather than from reactions directly involving hydrogen ions. Citric, salicylic, and p-hydroxybenzoic acids and EDTA, used as control organic acids, usually released considerably greater amounts of cations from the silicates than did the lichen compounds, consistent with the higher water solubility of the control organic acids. Similar amounts of Fe, All Ca, and Mg were released from the silicates by solutions of the lichen compounds and by solid lichen compounds. Lichen compounds are sufficiently soluble in water to form soluble metal complexes and to effect chemical weathering of minerals and rocks.

A Biomimetic Approach to the Chemical Inactivation of Chrysotile Fibres by Lichen Metabolites

“…[22] Lichen secondary metabolites, the "lichen substances", which comprise aliphatic, cycloaliphatic, aromatic and terpenic compounds, [24,25] may also contribute to the weathering processes, by chelating transitionmetal ions. [26][27][28] In a previous study, we reported that lichens also degrade chrysotile fibres (serpentine asbestos). [29] Chrysotile [Mg 3 Si 2 O 5 (OH) 4 ] is composed by the association of a tetrahedral silicate sheet of composition (Si 2 O 5 ) n 2nÀ with an octahedral brucite sheet of composition [Mg 3 O 2 (OH) 4 ] n 2nÀ .…”

Morphological and Chemical Features of Bioweathered Granitic Biotite Induced by Lichen Activity

“…Few works have investigated the morphological and chemical features affecting biotite during biochemical weathering induced by lichens. Iskandar and Syers (1972), in laboratory experiments studying metal-complex formation by lichen acids with aqueous suspensions of biotite, granite and basalt observed release of Fe, A1, Ca and Mg from silicates. Chelating properties of lichen acids were investigated later by and who reacted mica and other minerals with suspended lichens.…”

Heavy Metal Behavior in Lichen-Mine Waste Interactions at an Abandoned Mine Site in Southwest Japan

“…Several lichen compounds such as depsides and depsidones are slightly soluble and have the ability to chelate in conjunction with the presence of polar groups such as OH, CHO, and COOH [34]. Although the dissolution and decomposition of rock-forming minerals by lichen acids has been demonstrated in laboratory experiments [35,36], the dissolution and decomposition processes have not been conclusively proven in previous field studies [37,38].…”