CS258178B1 - Method of ferrochromium dissolving in sulphuric acid - Google Patents

Abstract

Semi-continuous or continuous method dissolving ferochrome in acid The sulfuric acid according to the invention is carried out such that: the ferro-chromium in the reaction space acts sulfuric flow or circulating sulfuric acid, eventually content chromium and iron ions at a certain temperature and initial sulfuric acid concentration. It is preferred that the level of the reaction solution is at least at the height of the reacting ferochrome.

Description

SUMMARY OF THE INVENTION The present invention provides a semi-continuous or continuous process for dissolving ferochrome in sulfuric acid for the purpose of producing potassium chromite sulfate.

The present dissolution methods are carried out by heating the reaction mixture at a temperature of 90-135 [deg.] C. throughout the dissolution, with a larger amount of sulfuric acid added to the ferochrome. The ratio of the weight of dilute acid to the weight of ferochrome is always greater than one and has a value of 4 to 6.5, with a concentration of 40-60%.

The initial passivity of ferochrome is overcome by heating above 100 ° C or by the addition of iron (nickel) at concentrations of about 0.001% based on the amount of ferochrome. The presence of metals may be short-lived, for the time required for activation.

Such dissolution requires long-term heating of the reaction mixture, and after the initial rapid reaction phase, a very slow reaction occurs, especially in the higher degree of conversion of the sulfuric acid. Therefore, in order to obtain a solution of the desired parameters, the ferochroin needs to be dissolved for several days so that the specific power of the device is then very low, practically 0.75 kg of dissolved ferochromine per hour and 1 m of reactor.

Another dissolution method utilizes a lower ratio of the weight amount of sulfuric acid to ferochrome.

Under the conditions of said lower weight ratio, which is less than one, a rapid reaction occurs, which may be self-sustaining in a particular configuration.

In this procedure, the technological times are significantly shortened and the specific performance of the device rises to about 20 kg of dissolved ferochrome per hour, per 1 m ^{3 of} device.

The methods used are, in terms of mass exchange, in a static arrangement with an unforced flow of reacting acid, all of which is used together with the ferochrome in the reaction space. Thus, in the real arrangement of most of these processes, mass and heat fluxes are difficult to define in the reaction, which in turn results in a lower ferochrome dissolution rate and furthermore that the reaction is not well controlled. Due to the lower dissolution rate to achieve the necessary capacities, the volume of the equipment used is large and hardly allows the further utilization or eventual disposal of the gases produced containing toxic phosphines.

These deficiencies are eliminated by the method of dissolving ferro-chrome with a rectified flow according to the invention. It is a method of semi-continuous or continuous dissolution of ferochrome in sulfuric acid, characterized in that ferrochromium in the reaction space is treated by a rectified flow of sulfuric acid and / or circulating sulfuric acid or sulfuric acid containing chromium and iron ions at 80 to 140 ° C; an initial sulfuric acid concentration of 30 to 80% by weight. Preferably, the level of the reaction solution is at least at the level of the reacting ferochrome.

The process according to the invention achieves the maximum possible stoichiometry of the ferochrome, the maximum mass and heat exchange in the reaction space, resulting in a high dissolution rate of up to 200 kg of dissolved ferochrome per hour and 1 m of reactor. The flowing reaction acid avoids the formation of concentration equilibrium and local overheating in the reaction space during this exothermic reaction. Achieving a high dissolution rate allows the use of a structurally small, closed apparatus from which reaction gases can be removed for recovery or disposal. The rectified flow of the reaction acid can be further thermally influenced so that the course of the reaction is more favorable, especially in the phases of a higher degree of conversion of sulfuric acid. Another indisputable advantage of the capability of the closed apparatus is that the reaction proceeds in a reducing atmosphere which does not allow oxidation of the Cr ions formed, which have been shown to catalyze the crystallization of chromium alum. With a bulk density of 4.5 to 5 kg of ferochrome. dm &^lt; ³ > and a free volume of 40 to 60%, the ferrochrome overstoichiometry in the reaction space is 33 to 56 times higher than the theoretical amount, using 40% sulfuric acid and ferochrome containing 70% Cr and 20% Fe. The directed flow of the reaction acid is preferably conducted in the flow direction of the evolving reaction gas.

Example 1

Determination of the dissolution rate was carried out in a glass closed apparatus with reaction gas withdrawal through a water seal, further designed to allow the reaction acid to flow unidirectionally through the reaction space completely filled with ferochrome under the conditions described in the proposed dissolution method.

The ferro-chromium used thus filled the reaction space, while another ferro-chrome filled the storage space, from which it gradually fell into the reaction space as ferro-chromium declined. The reaction gases were disposed of by incineration. The raw material used was 2,780.0 g of ferro-chromium and 200 ml of 40% sulfuric acid. Periodically, a solution with the following average parameters, which meet the needs of the production of the alum, was discharged in a semi-continuous manner:

Specific weight:

Amazing Concentration:

Iron concentration:

Sulfuric acid concentration:

Dissolution rate:

1.58 G -3 . cm -3 143.66 G . dm ^J 58.1 G , sod ^{2 3} 63.3 G . dm ³ 4,5 g · . min

It follows that, while maintaining the microkinetic parameters of the device, the dissolution rate of the process reactor will be 270.0 kg. hours m

Example 2

Dissolution was carried out under the same conditions as in Example 1, except that the sulfuric acid concentration was 44%.

Achieved values:

Specific weight: 1.52 G Amazing Concentration: 144.3 G Iron concentration: 50.1 G Concentration of sulfuric acid: 42.2 G Dissolution rate: 5.0 G

The device again operated semi-continuously, ferrochromium in the reaction space compared to the present specification.

dm ^J dm ^-3 dm ^-3 dm ³ min ^-3 . dm ^-3 'of both examples, the above-stoichiometry of the acid was maximal and in the range indicated in

Claims (2)

OBJECT OF THE INVENTION Process for dissolving ferro-chromium in sulfuric acid, characterized in that ferro-chromium in the reaction space is treated with a rectified flow of sulfuric acid and / or circulating sulfuric acid or sulfuric acid with a content of ions and iron at 80 to 140 ° C and an initial acid concentration sulfuric 30 to 80% by weight. 2. The process according to claim 1, wherein the level of the reaction solution is at least at the level of the reacting ferrochromium.