Method for removing aluminum by neutralizing sodium chromate alkali solution

Abstract

The invention discloses a method for removing aluminum by neutralizing a sodium chromate alkali solution. The sodium chromate alkali solution with the velocity of 6.9m<3> / h-20m<3> / h and the sodium bisulfate clear liquid with the velocity of 1.3m<3> / h-1.7m<3> / h flow to a reaction kettle simultaneously, the pH value of reaction slurry is always between 6.5-8.5, the reaction slurry is insulated and slaked for 1 hour-1.5 hours, a material is discharged, the discharge liquid is filtered and washed through a plate filtration machine, the chromium content measured by referring sodium chromate in filter cake can be reduced to less than 1%. The invention employs the novel method for removing aluminum by neutralizing the sodium chromate alkali solution, under the prerequisite condition that the pH value of sodium chromate neutral slurry is always between 6.5-8.5 and the temperature is controlled at 92-100 DEG C, the flow velocity of the sodium chromate alkali solution and the sodium bisulfate clear liquid can be controlled, so that the sodium chromate content in aluminum hydroxide mud can be reduced to less than 1%, the aluminum hydroxide mud can be directly used for producing aluminum hydroxide or cryolite, the processes of roasting, activating and removing hexavalent chromium are not required to produce the aluminum hydroxide or cryolite.

Description

technical field [0001] The invention belongs to the field of chromium salts, in particular to a method for neutralizing and removing aluminum in sodium chromate alkaline solution. Background technique [0002] The by-product of chromic anhydride is solid sodium bisulfate, its main components are 33% to 36% sulfuric acid, 48% to 50% sodium sulfate, 1% to 3.5% chromic anhydride, 0.2% to 0.5% (based on Cr 2 o 3 ) of water-soluble trivalent chromium, 8% to 11% of water-insoluble matter (its composition is sodium chromium sulfate). Plate and frame filtration removes water-insoluble matter, and its main component of gained sodium bisulfate clear liquid is as follows: (Na 2 Cr 2 o 7 .2H 2 O: 40g / L~50g / L, H 2 SO 4 :260g / L~320g / L). [0003] The existing sodium chromate alkaline solution neutralizes and removes aluminum. Slowly add sulfuric acid or sodium bisulfate into the sodium chromate alkaline solution, adjust the pH value to 7-8, and heat-preserve at 80°C-90°C for 45 ...

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Problems solved by technology

[0003] The existing sodium chromate alkaline solution neutralizes and removes aluminum. Slowly add sulfuric acid or sodium bisulfate into the sodium chromate alkaline solution, adjust the pH value to 7-8, and heat-preserve at 80°C-90°C for 45 minutes. After the aluminum hydroxide sludge filtered by the plate and frame filter is washed with hot water, the sodium chromate content is 28W% to 35W%. For this reason, the sodium hydroxide chromium removal process is added, and the chromium in the aluminum hydroxide sludge can be removed. The sodium chromate content is reduced to 3.0W%~3.5W%, and the aluminum hydroxide aluminum sludge produced not only has a serious loss of sodium chromate, but also has basically no use value

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