Hydrothermal oxidation method for production of alkali metal dichromate from carbon ferrochrome

摘要

The present invention provides a hydrothermal oxidation method for producing alkali metal dichromate from carbon ferrochrome, and the method comprises the following steps: formulating an initial reaction liquid by mixing carbon ferrochrome, an alkaline substance and water, in which the actual addition amount of the alkali is controlled smaller than the theoretically required amount; adding the initial reaction liquid into a reaction kettle, charging an oxidizing gas into the reaction kettle, and allowing the reaction to proceed for 0.5 to 3 h at a temperature of 150° C. to 370° C. and a pressure of 2 Mpa to 24 MPa; carrying out solid-liquid separation, cooling the resultant filtrate to a temperature of −12° C. to −20° C. to precipitate crystals, and carrying out separation by centrifuge to obtain alkali metal dichromate solution; adding CrO3 to the alkali metal dichromate solution until the degree of acidification reaches 100% or greater, concentrating the solution by evaporation, and cooling it to precipitate crystals, so as to afford alkali metal dichromate. The method has a simple process, is easy to control, and can directly produce sodium dichromate under hydrothermal conditions.

主权项

1. A method for producing alkali metal dichromate from carbon ferrochrome as the raw material through a hydrothermal process, the method comprising the steps of
(1) formulating the raw material carbon ferrochrome together with an alkali and water into an initial reaction liquid, in which the actual addition-to-theoretical-requirement ratio of the alkali in oxidizing chromium in the carbon ferrochome to form alkali metal chromate is 55% to 80%; (2) adding the initial reaction liquid formulated in step (1) into a reaction kettle, charging an oxidizing gas into the reaction kettle, and allowing a reaction to proceed for 0.5 to 3 h at a temperature of 150° C. to 370° C. and a pressure of 2 MPa to 24 MPa, wherein CO2 generated during the reaction exerts a catalytic function which directs the reaction to produce a mixed solution of alkali metal chromate and alkali metal dichromate with the latter being predominant, wherein alkali metal bicarbonate generated during the reaction is used as a further alkali source for further alkaline oxidation of chromium (III) to alkali metal chromate, and the alkali metal bicarbonate further releases CO2 to further acidify the alkali metal chromate to alkali metal dichromate, thereby resulting in an oxidation ratio of chromium, defined as a percentage of chromium(VI) out of the total chromium in the carbon ferrochrome, greater than the actual addition-to-theoretical-requirement ratio of the alkali, and a degree of acidification greater than 50%; and (3) subjecting the reaction products from the reaction in step (2) to solid-liquid separation, cooling the resultant filtrate to a temperature of −12° C. to −20° C. to precipitate crystals, and separating the solution therefrom which is an alkali metal dichromate solution.