Antimony Recovery from Lead-Rich Dross of Lead Smelter and Conversion into Antimony Oxide Chloride (Sb4O5Cl2)

Antimony was selectively leached from a lead-rich industrial process residue called "dross" and recovered as an antimony oxide chloride (Sb4O5Cl2), which can be used as a component in flame retardants or as an anode material in aqueous chloride batteries. The dross is a residue generated by a lead smelter and contained about 30 wt % lead and about the same concentration of antimony, along with some minor metals such as zinc, iron, and tin. Solutions of hydrochloric acid dissolved in organic solvents such as ethanol, 1-octanol, ethylene glycol, and Aliquat 336 chloride were compared for selective leaching of antimony. All investigated lixiviants leached comparable amounts of antimony (60-76%), but the lowest codissolution of lead (similar to 0.1%) was achieved by hydrochloric acid in ethanol or in 1-octanol. Only ethanol was chosen for further investigation since it is significantly cheaper than 1-octanol. Moreover, ethanol is classified as an environmentally preferable green solvent. Hydrochloric acid in ethanol leached much less lead than using water, and the former also required a lower chloride concentration to get high leaching yields of antimony. Leaching under optimized conditions was successfully upscaled in a 1 L batch leaching reactor, achieving an antimony leaching efficiency of 90% (28 000 mg L-1) and a lead leaching efficiency of only 0.4% (100 mg L-1). The dissolved antimony in the pregnant leach solution (PLS) was fully recovered by hydrolysis precipitation whereby high-purity antimony oxide chloride (Sb4O5Cl2) was obtained, by adding to the PLS an equivalent volume of water. The ethanol in the remaining PLS was distilled to be reused for more leaching. The valorization of an industrial process residue and the use of ethanol contribute to the sustainability and the greenness of the process.