Recovery of uranium with bisphosphonate modified mesoporous silicon

Abstract

• Mesoporous silicon was functionalized with bisphosphonates for uranium adsorption. • The functionalization was highly stable in repeated adsorption/desorption cycles. • The adsorbent was exceptionally selective towards uranium. • The adsorbent was regenerated within less than a minute. • Desorbed uranium was enriched by 15-fold in comparison to initial solution. Anthropogenic activities such as mining and ore beneficiation generate large amounts of uranium-contaminated wastewater. The metal is radioactive and toxic; therefore, it needs to be removed to protect the environment and human health. Adsorption is a viable method to remove uranium from wastewater because of the low energy consumption and ability to remove even low concentrations of uranium. However, most adsorbents are not effective to selectively adsorb uranium and their stability is typically degraded in repeated adsorption/desorption cycles. Herein, we employed a novel nanostructured adsorbent to selectively remove uranium from a tailing obtained from processing of real ore sample by Knelson concentration method. The adsorbent consisted of bisphosphonate ligands grafted on highly stable carbonized surfaces of mesoporous silicon. The porous structure of the adsorbent enhanced its permeability allowing it to be used in a column setup where metal solutions were flown through the adsorbent. The adsorbent was capable of repeatedly adsorbing and desorbing uranium without significant reduction in the performance. Importantly, the adsorbent showed essentially higher selectivity towards uranium than towards other less harmful metal ions, and the material could be regenerated with an acid. Desorption was carried out with sulfuric acid resulting in 15-fold enrichment of uranium compared to the initial solution, while other metals did not concentrate efficiently. The adsorbent was capable of selectively capturing uranium from a solution with various other metals and the adsorbed uranium was rapidly desorbed and quantified with a reasonable purity, indicating the adsorbent as a potential candidate for industrial applications.