Method for producing sodium chromate by roasting chromium ore and small amount of soda

Abstract

The invention discloses a method for producing sodium chromate by roasting chromium ore and a small amount of soda. The method is characterized in that chromium ore and calcined soda are mixed, wherein the added quantity of the calcined soda is 35% to 45% of theoretical required amount for complete reaction with dichromium trioxide in the chromium ore; then the mixture is added to a rotary kiln for first roasting, the temperature of materials at a hot space in the kiln is 1000 DEG C to 1050 DEG C, wrought materials are cooled and leached to obtain a sodium chromate leaching solution and first chromium dregs; the first chromium dregs are dried and crashed for second roasting with newly added calcined soda, the use amount of the calcined soda is 30% to 50% of theoretical required amount for complete reaction with the dichromium trioxide in the first chromium dregs; the sodium chromate leaching solution and second chromium dregs can be obtained through roasting and leaching processes, the second chromium dregs, limestone and newly added calcined soda are roasted for the third time, the use amount of the calcined soda in the third roasting is 35% to 75% of theoretical required amount for complete reaction with the dichromium trioxide in the second chromium dregs, and the use amount of the limestone is 2% to 5% of the sum of weight of three raw materials of the second chromium dregs, the calcined soda and the limestone; and the sodium chromate leaching solution and third chromium dregs are obtained after leaching. By adopting method of the invention, the utility ratio of the calcined soda is also enhanced greatly.

Description

technical field [0001] The invention relates to a method for producing sodium chromate by roasting chromium ore with less alkali. Background technique [0002] When roasting chrome ore with a rotary kiln, if the liquid phase amount (i.e. melt) in the charge is greater than 30%, the charge will be severely sintered so that the production cannot proceed normally. Therefore, the production methods of chromium salt mainly include calcium roasting process (chrome ore and soda ash roasting with calcium filler added) and calcium-free roasting process (chrome ore and soda ash roasting, returning slag as filler). Calcium roasting is to use the method of adding calcium filler to increase the roasting temperature and control the melt content. Calcium-free roasting uses the addition of roasting slag to increase the temperature and control the content of the melt. The above two roasting methods are all carried out under the condition of sufficient alkali amount, that is, the amount of ...

AI Technical Summary

Problems solved by technology

If the amount of soda ash is insufficient, the oxidation rate of chromite will decrease, which will directly affect the yield of chromium

But above-mentioned method, owing to have added the filler that contains a large amount of calcium oxide, will generate the insoluble solid of hexavalent chromium and a large amount of hydratable calcium silicate and calcium aluminum ferrite during roasting, when leaching, form a large amount of acid Dissolved chromium (calcium chromium aluminate, etc.), during leaching, acid-soluble chromium and sodium chromate are leached at the same time, which reduces the leaching rate of sodium chromate, and it is difficult to filter and wash, and the chromium slag is seriously damaged. Reduce the utilization rate of chromite ore

Under the action of carbon dioxide in the air and sunlight, the acid-soluble chromium in these slags will turn into water-soluble chromium, which is easily dissolved by rainwater or surface water, causing serious pollution of the environment by chromium slag.

Due to the large amount of slag, it is difficult to detoxify this chromium slag thoroughly, and the treatment cost is quite high

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