Uranium, extraction finishing processes

Silver is usually found in extremely low concentrations in natural waters because of its low crustal abundance and low mobility in water (USEPA 1980). One of the highest silver concentrations recorded in freshwater (38 pg/L) occurred in the Colorado River at Loma, Colorado, downstream of an abandoned gold-copper-silver mine, an oil shale extraction plant, a gasoline and coke refinery, and a uranium processing facility (USEPA 1980). The maximum recorded value of silver in tapwater in the United States was 26 pg/L — significantly higher than finished water from the treatment plant (maximum of 5.0 pg/L) — because of the use of tin-silver solders for joining copper pipes in the home, office, or factory (USEPA 1980). 

The uranium is extracted into the oil phase as shown in Eq. (19.4-5). The function of TOPO is not known precisely but it is essential to the process. In a second operation, the uranium first is stripped into strong aqueous acid by reversing Eq. (19.4-5) and then reduced to U4> by ferrous ion Eq. (19.4-6)]. This is to prevent reexuaction by the D2EHPA-TOPO. The process then proceeds to a finishing step wherein the U4 is reoxidized, extracted, concentrated, and precipitated as (NRhllOjCOj (AUT or yellow cake ). The finishing step is the same for both the solvent extraction atid liquid-membrane processes. 

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