Abstract

Vanadium was recovered successfully from spent iron sorbent (ferric oxyhydroxide, CFH-12) using a two-step process including alkaline leaching and precipitation with CaCl₂. The spent CFH-12 was collected from a field study in which a filter system was used to remove vanadium from mining-influenced water (referred to as MIW-treated CFH-12). Fresh CFH-12 was treated with synthetic vanadium solution (SVS-treated CFH-12) to compare the recovery process with the field study. First, a full factorial design was performed to optimize the precipitation process using synthetic leaching solution. The optimal conditions were found to be two times the theoretical dosage of CaCl₂, a precipitation temperature of 60°C, and a precipitation pH of 12.7. Vanadium desorption from the spent sorbents was conducted using 1 M NaOH, a contact time of 30 minutes and a CFH-12 solid-to-liquid ratio of 0.15 kg/L. The results revealed that vanadium could be efficiently precipitated from the leaching solution of MIW-treated CFH-12 and SVS-treated CFH-12. A higher dosage of CaCl₂ was required to recover vanadium from MIW-treated CFH-12 due to the complexity of the leaching solution, which resulted in a lower vanadium content in the product. XRD analysis showed that the product recovered from SVS-treated CFH-12 mainly contained Ca₅(VO₄)₃OH and a small amount of CaCO₃. TEM images revealed that the calcium vanadate hydroxide particles were round in shape, about 0.2–0.4 µm in size and formed aggregates. The product recovered from MIW-treated CFH-12 contained amorphous calcium vanadate and crystalline Ca(OH)₂. XPS analysis confirmed that vanadium existed as V⁵⁺ in all of the recovered products.