A novel method to synthesize scorodite using ferrihydrite and its role in removal and immobilization of arsenic

Arsenic is a highly toxic and carcinogenic element, which poses a huge threat to millions of people. The toxicity of arsenic links to its solubility. Therefore, the immobilization of arsenic is of great significance. Among a series of arsenic immobilization materials (include arsenate, arsenite and arsenide), scorodite is the most suitable one due to its excellent stability. In this study, we propose a novel method to synthesize scorodite using ferrihydrite as an in situ iron donator. The process occurs via the dissolution of ferrihydrite followed by the coprecipitation of iron and arsenic ions on the surface of ferrihydrite. A series of experiments were carried out to investigate the optimal reaction conditions and applicable scope of initial arsenic concentration for this process. The results indicated that 99.9% of arsenic was removed from aqueous solution and immobilized as stable scorodite at reaction time of 6 h, pH 1.5, Fe/As molar ratio of 1.1 and reaction temperature of 90°C. This process is applicable to the solution with initial arsenic concentration ranging from 1 to 10 g/L, which shows great potential for practical applications.