Effect of different anode materials on electrolysis of Cr from synthetic Cr-alum solution

The production of chromium metal begins with the mining of chromite ore. Chromite ore is then converted either into ferrochromium by smelting or into sodium dichromate by roasting and leaching. Chromic oxide (made from sodium dichromate) is converted into chromium metal by the aluminothermic process. Ferrochromium is converted into chromium metal by the electrolytic method. Turkey is one of the countries which possess the richest chromite ore reserves in the world. Although no metallic chromium production is carried out in Turkey, various chromium chemicals, along with ferrochromium are produced. High purity chromium metal is used in the making of heatresistant and high efficiency gas-turbine engines of the planes, and heat-resistant superalloys. In this research, effect of various anode types on the electrolysis of chromium from synthetically prepared chrome-alum solution in a specially-designed laboratory-scale electrowinning cell was investigated. The parameters of the electrolysis operation were: 52±1°C, pH = 2.1-2.4, 750 A/m ² current density, electrolyte composition: 40 g/L Cr, 90 g/L NH ₄⁺, 350 g/L SO₄^2-. Moreover, the head between the catholyte and anolyte levels (Δh) was optimized. Cathode morphologies were also determined through SEM analysis under the conditions of electrolysis experiments. In the first part of experimental studies where the current density was 750 A/m², the optimum Δh value was found to be 1,0 cm. The cell potential values, obtained at the optimum Δh, and by utilizing different anode materials such as; pure lead, Pb-Ca-Sn alloy, carbon, pressed and sintered graphite, and IrO₂ coated titanium, were 4,78 V, 4,85 V, 5,63 V, 4,99 V and 4,95 V, respectively. The Cr(III) to Cr(VI) oxidation occurs at its highest level when Δh is 1,0 cm, and thus, at the end of 72 hours, the Cr(VI) concentration in the anolyte is around 20 g/L. Surface quality of the chromium seems to be very compact when sintered graphite anode was utilized at the optimum experimental conditions.