Smelting Chromium Using Low Iron Chromium-containing Slag in Treatment of Vanadium Precipitation Wastewater with Low COD

Vanadium precipitation wastewater was treated separately using supernatant of sodium thiosulfate solution and sodium metabisulfite,but COD of the wastewater reduced by the former was as high as 2 878 mg/L,far exceeding the emission standards.Wastewater with a lower COD and chromium-containing slag with low iron content can be obtained by sodium metabisulfite reduction,neutralization and precipitation for the vanadium precipitation wastewater.Industrial operating conditions for treatment of vanadium precipitation wastewater with sodium metabisulfite are proposed as follows:addition amount of sodium metabisulfite is 3.1~3.2 times as much as Cr⁶⁺ content in the wastewater,with 15~30 min of reduction time.Through ammonia removal for the wastewater after the treatment mentioned above,no hexavalent chromium is detected in the water discharged to the sewage treatment plant with 65 mg/L of average COD value,satisfying the emission limits of Liaoning province local standard "Integrated Wastewater Discharge Standard"(DB21/1627-2008).Meanwhile,slag with low iron content(0.27%,calculated as Fe₂O₃) and high content of chromium(41.6%,calculated as Cr₂O₃) can be obtained.After roasting the chromium-containing slag,qualified chromium JCr95(Cr ≥ 95%) can be produced by outfurnace smelting.