Chromas oksidas is pagamintas pagal šlifavimą chromitą to 160-200 mesh, pridėjimas soda pelenai ir dolomitas, oksidavimas ir skrudinimas at 1050-1150 degree , and tada išplovimas su vandeniu in priešprieša (žr. išplovimas) ir filtravimas to gauti a Na2CrO4 content of more than 200 g/ litrai of tirpalas.
Add sulfuric acid to neutralize the sodium chromate solution to a pH of 7 to 8. Filter out impurities such as aluminum hydroxide and then evaporate until the Na2CrO4 content is greater than 450 g/L. Filter out Na2SO4 crystals. Adjust the pH of the solution to 4±0.2 with sulfuric acid, then filter out the Na2SO4 crystals to obtain sodium dichromate (Na2Cr2O7) solution. When the solution is concentrated to approximately 1100 g/L of Na2Cr2O7, cool and filter out the Na2SO4 crystals. Then concentrate the solution to a concentration of 1500 to 1550 g/L of Na2Cr2O7, and keep it at 90 to 100 degree for 8 hours, then cool to below 35 degree , and the heavy crystals will form. Sodium chromate. Sodium chromate can also be converted into sodium dichromate using the carbonic acid method, that is, gas containing 50% CO2 is introduced at 15 to 16 atmospheres, and the precipitated precipitate is sodium bicarbonate: 2Na2CrO4+2CO2+H2O─→Na2Cr2O7+2NaHCO3 bicarbonate Sodium can be recycled and reused. This method can recycle half of the soda ash added during roasting, which is more advantageous than the sulfuric acid method for obtaining sodium sulfate, but sodium chromate cannot be completely converted into sodium dichromate.
Electrolytic production generally uses carbon ferrochromium as raw material and adopts the chromium ammonium vitriol electrolysis process. Crush the carbon ferrochromium, dissolve it in the mixed solution of electrolytic anode return liquid, crystallization mother liquor and sulfuric acid, filter to remove silicate and other residues, and treat the filtrate with ammonium sulfate to remove iron. After the pure chromium ammonium solution is aged (kept at {{0}} degree for 15 days), pure chromium ammonium vitriol Cr2(SO4)3·(NH4)2SO4·24H2O crystallizes. Pure chromium ammonium vitriol is dissolved in hot water and sent to the diaphragm electrolytic cell for electrolysis. Stainless steel is used as the cathode, lead-silver alloy (1%Ag) is used as the anode, the current density is 753 A/m2, the cell voltage is 4.2 volts, and the electrolyte temperature is 52~54 degree . The flow rate of the electrolyte into the anode chamber should be controlled, and the pH of the solution should be accurately controlled to 2.1 to 2.4. The average current efficiency is 45%, and the power consumption is about 18.5 kW·h/kg. The product purity is 99.2~99.4% flake metal chromium, containing 0.3~0.5% oxygen, and is brittle. In order to improve the purity of metallic chromium, the oxygen content can be reduced through vacuum treatment or hydrogen reduction. Using +6-valent chromium solution electrolysis (current density 9500 A/m2, temperature 84~87 degree ), high-purity metallic chromium (containing oxygen 0.01~0.02%) can be obtained, but the current efficiency is very low (6~87 degree ). 7%).
