Phosphogypsum and clay mineral/phosphogypsum ceramic composites as useful adsorbents for uranium uptake

Abstract

We analyzed the sorption capacity of phosphogypsum and clay mineral-based ceramic composites. Phosphogypsum is a waste by-product generated from apatite in the production process of phosphoric acid and phosphate fertilizers. On the one hand, the chemical composition of phosphogypsum poses a considerable problem to production plants due to its acidic properties. On the other hand, phosphogypsum can constitute an excellent sorbent material for cations that prospectively create insoluble phosphoric mineral phases. To examine and study the above issues, a series of ceramic composites with differing phosphogypsum content were prepared and examined to evaluate their uranyl sorption capacity. The isotherms of uranyl adsorption onto the composite surface were determined and kinetic experiments were conducted to determine the sorption properties and kinetic parameters. Experiments were conducted under both static and dynamic conditions. Furthermore, diffraction studies and chemical composition analyses were carried out using a scanning electron microscope with an energy dispersive spectrometry feature. We found that the maximum uranium (VI) adsorption reached nearly 0.09 mol kg−1, which equaled 21 g of uranium adsorbed per 1 kg of phosphogypsum at 298 K. The results indicated efficient uranyl ion chemisorption onto the examined composites. In addition, the occurrence of phases corresponding to the composition of autunite group minerals were observed. The composites have potential application in water treatment technologies and hazardous waste landfills.