How is pure chromium produced by electrolysis?

Pure chromium is produced through the electrolysis of trivalent chromium solutions. The process involves several key steps:1

• Leaching and Purification: Milled high-carbon ferrochromium is leached using a mixture of sulfuric acid, recycled anolyte, and a chrome alum mother liquor containing ammonium sulfate. After filtering out silica and crude ferrous ammonium sulfate, the chromium is precipitated as ammonium chrome alum.1
• Electrolytic Deposition: The chrome alum crystals are dissolved in hot water and fed into the cathode portion of an electrolytic cell. A diaphragm separates the cell to prevent mixing with the anode's acidic products. As electric current passes from a lead anode to a stainless-steel cathode, chromium plates onto the cathode.1
• Refining: Every 72 hours, the chromium is stripped, heated to remove water and hydrogen, and further processed at high temperatures under vacuum to reduce oxygen content, achieving a purity of over 99.9 percent.1