Effect of alkali regeneration on pore characteristics and performance of ferric oxyhydroxide and akaganéite sorbents

This study focused on the regeneration of iron sorbents and the investigation of sorbent properties after exposure to four sorption-desorption cycles. Batch regeneration tests with sodium hydroxide were conducted on two commercial sorbents (CFH-12 and GEH 101) saturated with vanadium. CFH-12 is ferric oxyhydroxide that also contains some gypsum and goethite (Kemira Oyj). GEH 101 is ferric hydroxide containing akaganéite (ß-FeOOH) and ferrihydrite (GEH Wasserchemie). Both materials displayed similar performance in sorption and desorption studies despite their mineralogical difference. Both materials can be reused but the sorption efficiency decreased from 95–97% to about 53–55% after the first sorption (initial V 50 mg/L, dosage 10 g/L) and then remained at the same level. NaOH desorbed 84–86% of vanadium in the first cycle. X-ray photoelectron spectroscopy confirmed that the surface did not contain vanadium after regeneration. Thus the desorption-resistant fractions were located in the pores of the materials. Subsequent desorption stages provided the same or higher recovery of vanadium. Both materials showed some wider pore size distribution, whereas pore volume increased significantly only with CFH-12. This study confirmed that regeneration with alkali and reuse of iron sorbents is a viable option although the sorption and desorption efficiency are affected by the treatment.