Recovery of uranium from seawaters by ultra/nano filtration assisted by complexation

Uranium extraction from unconventional sources such as seawater is an important complementary source for nuclear fuel production. A common method for separating ions in aqueous solutions is ultra/nano filtration (UF/ NF), which employs both electrical and steric effects. While commercial inorganic UF/NF membranes have been used to separate uranium from other salts in natural or synthetic seawater, the high ionic strength of seawater tends to reduce the electrical effect. To overcome this, hydrophilic polymers with high selectivity towards uranium have been introduced into seawater to assist the filtration by complexation. This allows uranium to be rejected by the steric effect while allowing other metal ions to pass through the membrane. The performance of different hydrophilic polymers containing complexing functional groups, including alendronic acid, bis(phosphonic acid), and catechol, was evaluated to assist in the filtration process to separate uranium from other competitive metal ions (Na, K, Ca, Mg). The results show that two hydrophilic polymers, based on N-acryl-oylalendronate, demonstrate the best performance for the separation of uranium, achieving a sorption capacity of over 200 mg U/g polymer and an extremely high separation factor of U to salts (SF(U/Na) > 6000 for a (poly (NAM-co-ALNAm)). By using filtration assisted by complexation with polymers, uranium can be effectively rejected while maintaining low rejections for other salts in high salinity seawater of at 35 g L-1. Uranium can be released from the complex by spiking the seawater by concentrated nitric acid or sulfuric acid. These laboratory-scale filtration experiments have significant industrial applications for the recovery uranium from seawater.