Recovery of vanadium and gallium from solid waste by-products of Bayer process

• Recovery of V and Ga from vanadium sludge and electrofilter dust was investigated.
• Recovery of V2O5 from purified solution via precipitation of ammonium metavanadate.
• Two-stage of carbonisation was demonstrated to produce a Ga-rich precipitate.
• A flowsheet was proposed for treatment of vanadium sludge and electrofilter dust.

In this study, recovery of vanadium and gallium from solids waste by-products (vanadium sludge and electrofilter dust of calcination plant) of Bayer process was investigated. An efficient purification process was developed based on the removal of impurities such as phosphate by water leaching, neutralisation using CO2-enriched air and addition of aluminate solution. Recovery of V2O5 from the purified solution via the precipitation of ammonium metavanadate, its conversion into polyvanadate by the addition of ammonium sulphate and sulphuric acid, respectively, and then the ignition of the latter at 560 °C was demonstrated. Effects of various parameters on the purification and precipitation processes were shown. A treatment process involving sintering and two-stage of carbonisation was also demonstrated to produce a Ga-rich precipitate. A gallate solution suitable for electrolysis of Ga was also shown to be prepared from this precipitate. A complete flowsheet was proposed for the treatment of vanadium sludge and electrofilter dust.