Uranium adsorption by iron modified zeolite and zeolite composite membranes.

Abstract

Composite membranes incorporated with high-performance adsorbents are promising for uranium removal. The impact of speciation and ionic strength on uranium adsorption by zeolites was investigated in both static adsorption and composite membrane filtration. Zeolites with high Si/Al ratios exhibited the highest uranium adsorption capacity. Iron-modified zeolite, BEA-Fe30 completely removed uranium at a concentration of 0.6 g/L in static adsorption, with uranium uptake ranging from 125 to 130 μg/g at pH values between 6 and 12. At lower pH values, uptake decreased, dropping to 3 μg/g at pH 2. The increased uranium uptake between pH 6 and 12 is attributed to the formation of a ternary complex involving U(VI), carbonate, and Fe oxide surface (hydr)oxo sites. High ionic strength did not impact the adsorption of uranium. Additionally, PHREEQC modeling was employed to simulate uranium speciation and adsorption behavior under varying pH and ionic strength conditions, further validating experimental findings. Zeolite-loaded microfiltration/ultrafiltration (MF/UF) membranes achieved the WHO guideline of 30 μg/L uranium in the permeate, using less zeolite compared to static adsorption. With 0.25 g of zeolite, the MF/UF process achieved a uranium uptake of 699 μg/g, significantly higher than the 256 μg/g observed in static adsorption. However, uranium removal decreased with increased flow rates, suggesting mass transfer limitations during filtration. The study highlights the potential of composite membranes with high-performance zeolites for efficient uranium removal, contributing to advancements in water purification technologies and addressing environmental contamination.