Showing papers on "Sodium dichromate published in 2021"

Novel Method for Producing Chromic Oxide without Hexavalent Chromium Pollution by Acid Leaching

Abstract: Chromic oxide (Cr2O3) is one of the most important chromic salts and is widely used in industrial applications. Traditionally, Cr2O3 is prepared from chromium trioxide (CrO3) or sodium dichromate (Na2Cr2O7), both of which are manufactured from chromite ore. However, traditional manufacturing processes are time-consuming, inefficient, and energy-consuming, and they can catheuse severe environmental pollution by discharging large quantities of solid residues containing Cr in the form of Cr(VI) compounds. These compounds are also harmful to human health. Therefore, developing an environmentally friendly production process is of great concern to the chromic oxide industry. In this study, a new method for producing Cr2O3 without hexavalent chromium pollution was investigated. In this novel process, 97% of the total Cr—in the form of chromium sulfate (Cr2(SO4)3)—and Fe are leached from ferrochrome alloy using sulfuric acid. The concentration of Fe in the Cr2(SO4)3 solution can be reduced to 2 mg/L after precipitating with oxalic acid and extracting with di (2-ethylhexyl) phosphate. Cr2O3 is then produced by precipitating Cr from the Cr2(SO4)3 solution with sodium hydroxide, followed by calcination of the precipitated Cr(OH)3 at 500°C. Using this method, Cr2O3 with a purity of up to 99.3% was obtained in this study. Throughout the process, Cr existed only in the form of Cr(III); thus, the pollution caused by hexavalent Cr was eliminated, and environmentally friendly production of Cr2O3 was achieved.