Binding and Oxidation State of Uranium in Recent Phytogenic Sediments, Peats, and Lignites of Selected Areas, Influenced by Physico‐Chemical Parameters

Abstract

AbstractThe high bog plateau “Drei Horste” at Lake Oderteich in the Upper Harz Mountains (Western Germany) shows uranium(VI) being dissolved from a granitic bedrock and transported by oxidizing waters containing humic and fulvic acids. Uranium(VI) is deposited in phytogenic sediments and in peat layers. In the sediments the concentration of uranium correlates with the content of functional acid groups. The binding between the organic substance and uranium is based on ion exchange, as shown by experiments with fractions of different isolated humic substances. – Uranium in lignites from “Date Creek”, Arizona, USA shows a significant correlation to organic carbon. The proceeding coalification from peat to lignite causes a change in the binding of uranium: uranium in organic binding is to be observed in low grade ores (<0.1% U) only. High grade ores (>0.1% U) have uranium in inorganic binding mainly. The oxidation state in organic low grade ores is controlled by their contents of organic reductants and of humic acids. Prerequisites for the formation of high grade ores in “Date Creek” were a low E vs. SHE‐level (formation of coffinite) and an availability of organic (humic acids) and inorganic (zeolites) exchange sites for the remaining portion of uranium(VI).