Upgradation of water hyacinth for decontamination of uranium-containing radioactive wastewater with double environmental benefit

Abstract

Water hyacinth is recognized as one of the top ten invasive weeds that pose significant environmental hazards globally. The resourceful utilization of water hyacinth offers substantial ecological benefits. In this work, water hyacinth is employed to synthesize a phosphorylated biochar for the efficient decontamination of uranium-containing radioactive wastewater, thereby achieving dual environmental benefits. The biochar with a large specific surface area of 1328 m2/g and a large pore volume of 0.94 cm3/g is obtained via carbonization of a freeze-dried water hyacinth-phytic acid composite. It possesses a high density of uranophilic phosphoric acid groups, with the surface phosphorus content reaching 0.78 at%. As anticipated, phosphorylated biochar demonstrates superior adsorption performance for uranium (VI) ions. The removal efficiency achieves 99 % in a uranium solution with an initial concentration of 100 mg/L at a dosage of 1.0 g/L within 30 minutes, while the maximum adsorption capacity reaches 478 mg/g. It is proficient in removing uranium across a pH range of 2.2–6.6 and exhibits tolerance under high ionic strength conditions. The distribution coefficient for uranium attains 28.5 L/g, which is significantly higher than that of many other metal ions. Moreover, the biochar is readily regenerated by elution with diluted HNO₃ and reused up to five times without any loss of efficiency. Delightfully, phosphorylated biochar effectively reduces the uranium concentration in actual nuclear wastewater from 16 μg/L to below 4 μg/L. The effective adsorptive decontamination of radioactive wastewater, followed by the incineration of spent biochar, significantly reduces the volume of radioactive waste.