Uranium Adsorbents Based on Hypercross-Linked Asphalt Polymers via a Cyanide-Free Strategy

The preparation of highly selective and cost-effective uranium adsorbents still remains challenging. Amidoxime-based adsorbents are well known for their targeting effects on uranyl ions. However, the formation of amidoxime groups requires the use of toxic cyanides. In this work, a family of amidoxime-based uranium adsorbents derived from asphalt has been prepared successfully with a cyanide-free strategy. Hypercross-linked asphalt polymers (HAPs) were prepared by using formaldehyde dimethylacetal as the external cross-linker. Then, cyano groups were grafted onto HAPs via the reaction with dichloromethyl methyl ether, followed by the treatment with aqueous ammonia and iodine. Eventually, the cyano groups were converted into amidoxime groups with hydroxylamine to obtain uranium adsorbents (HAP-AOs). The optimum cyanation reaction parameters and HAPs have been screened, and the optimal HAP-AO exhibits a maximum absorption capacity of 485 mg g–1 with high selectivity and excellent recyclability. It should be noted that this preparation procedure of uranium adsorbents can be further extended to other raw materials containing aromatic rings, including coal tar, coumarone-indene resin, and toluene. This work not only provides a cyanide-free strategy for preparing amidoxime-based adsorbents but also sheds light on the value-added utilization of massive byproducts of the petrochemical industry in a sustainable development protocol.