Recovery of antimony compounds from alkaline sulphide leachates

• Antimony and arsenic were selectively extracted from a lead silicate slag through alkaline sulphide hydrometallurgy.
• Dissolution of arsenic and antimony was slightly influenced by NaOH concentration and temperature.
• Sodium thioantimonate and sodium hydroxyl antimonate were precipitated from synthetic NaOH-Na2S-Sb2S3 solutions.
• Precipitation of NaSb(OH)6 was strongly dependent on time and H2O2 dosage.
• Sodium thioantimonate was recovered from the leachate through crystallization and elemental sulphur addition.

In copper metallurgy, antimony impurities usually form alloys and compounds with the transition metals to make up the basic building blocks of a speiss phase. This speiss phase is generally rich in copper and precious metals, which are desirable to recycle and recover at the smelter. The presence of this impurity unfortunately creates a build-up of this metal in the copper circuit, leading to problems during copper refining processes. Therefore, a removal or reduction of the antimony impurity to an acceptable level is a necessary step before the speiss can be recycled at the smelter for the recovery of its valuable metals. A lead silicate slag that was obtained after smelting a copper speiss admixed with silica, soda and lead oxide, was leached in alkaline sulphide solution to selectively dissolve its antimony content. Furthermore, the pregnant sulphide leachate was purified by precipitation and crystallization techniques to recover antimony as sodium thioantimonate and sodium hydroxyl antimonate using synthetic Na2S-NaOH-Sb2S3 solutions. The leaching results indicate that the highest amount of antimony and arsenic extracted from the material after 24 h at 100 °C and reagent concentration of 30 g/L NaOH + 30 g/L S2 − was 83% and 90%, respectively. In the precipitation process, the addition of hydrogen peroxide to the alkaline sulphide leachate prompts the precipitation of antimony as NaSb(OH)6. The result also implies that < 100% of stoichiometric hydrogen peroxide is required to completely oxidize the total amounts of both Sb3 + and S2 − in the solution and to quantitatively precipitate > 90% of the antimony in solution. The influence of catalytic agents and temperature on the process was not clearly reflected in this investigation due to the exothermic reaction with hydrogen peroxide. Moreover, the addition of elemental sulphur to the sulphide leachate also influences the precipitation of antimony as sodium thioantimonate.

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