Arsenic removal from spent liquor generated during processing of vanadium sludge

Abstract

During production of ammonium meta-vanadate from vanadium sludge an arsenic containing (~2.2g/l) spent liquor is generated. Safe disposal of such liquor without arsenic contamination to the environment is essential. Therefore, various methods such as ion-exchange, adsorption, solvent extraction and precipitation were applied for recovery of arsenic from the spent liquor. Based on the Eh-pH diagram of As-H2O, the arsenic based species were delineated. For ion exchange Lewatit FO 36 and Amberlite IRA 400 Cl- resins were used to extract arsenic from the spent liquor. With Lewatit FO 36 a maximum of 20% arsenic was recovered at A/R ratio of 50. Amberlite IRA 400 Cl- on the other hand didn’t extract arsenic at all. A two stage solvent extraction process using TBP as an extractant, with a recovery of 97% arsenic from the spent liquor was developed. From the loaded TBP almost complete stripping of arsenic was obtained with 0.1 – 0.5M NaOH solution. Precipitation of arsenic from the spent liquor as copper arsenate or iron arsenate was also examined. During the fixation of arsenic with iron, 70% arsenic was recovered in the precipitate. This process needs to be evaluated further with the aim of using the iron hydroxide containing arsenic for different applications.