SU148036A1 - Method for isolating pure sodium rosinate from waste solutions mouse-soda cleaning of coke oven gas - Google Patents

Description

A known method for separating pure rhodium sodium from spent MUSHIAK-SODA purification of coke oven gas is based on using different solubilities of thiosulphate and sodium rhodanide contained in them by evaporation of these solutions at boiling point with crystallization of thiosulphate and subsequent separation of sodium rhodanide from the resulting mother liquors.

The proposed method for the isolation of pure rhodium sodium in comparison with the known method allows: 1) to obtain the final product with a lower content of sodium thiosulfate, for which crystallization of thiosulfate is carried out in two stages at temperatures of about 25 and 0 °. respectively; 2) reduce the anhydrous salt content in the final product, which is achieved by crystallization of sodium rhodanide dihydrate at temperatures below 30.4 ° by introducing a solution of this salt, which is concentrated but not saturated at a given temperature, into a cooled saturated working solution.

Isolation of pure rhodium sodium by the proposed method is carried out in three stages:

a) obtaining technical roganous sodium,

b) alcohol crystallization,

c) water crystallization.

The spent mouse solution for purification of coke oven gas with a pH of 8-9 from the tank enters the evaporator, where it is evaporated at boiling at an appropriate temperature and vacuum.

No. 148036-2 (or at 120-125 ° at atmospheric pressure) to a density of 1.6 g / sl at 50 °; a substantial portion of the sodium sulphate is emitted from the solution as an anhydrous salt. The one stripped off solution is cooled in the crystallizer to a temperature of 25 °, as a result of which the main quantity of thiosulfate contained in it (up to 85%) in the form of a hydrofluoric salt crystallizes from the solution. To reduce the thiosulfate content in the solution, the latter, after separating the crystals from it in the centrifuge, is cooled to a temperature of about 0 ° in the crystallizer. With a decrease in temperature, the solubility of thiosulfate decreases significantly more than that of rhodanide with their joint presence; the solution becomes saturated, with respect to thiosulfate and rhodanide, at the crystallization temperature (eutonic point).

The salt recovered from the solution by crystallization at a temperature of 0 ° is pressed in a centrifuge; the resulting solution is evaporated to a thiosulfate content to a value corresponding to the eutonic point at the crystallization temperature of rhodanide. To clarify the solution, activated carbon is added to it and then filtered: the clarified solution is cooled to an appropriate crystallization temperature, for example, to obtain anhydrous rohanide, to a temperature higher than 31 °. Rodanide is released from the cooled solution in the crystallizer. The rhodanide crystals are pressed in a centrifuge, and the mother liquor is used partly for recirculation during crystallization and for separating thiosulfate from it at 0 °.

Next, the obtained sodium rodanide and previously dried (100-120 °) is subjected to alcohol crystallization, for which it is dissolved, for example, in methanol or ethanol when heated to 70-80 °; the solution is separated from the insoluble impurities by filtration or centrifugation and is partially evaporated, thus the main part of the genus P1 sodium is released. The solution is then cooled to 20-30 ° or less, and the remaining amount of sodium rohanide, which is separated from the liquid in a centrifuge, is released from it. The solution and the condensed vapors are again used for repeated operations, and the resulting anhydrous sodium rodanide is dried to recover the solvent. Periodically, if the solvent is watered or contaminated, the latter is completely evaporated. Solvent vapors are fed to the distillation column. The pure solvent obtained as a result of this operation is used for the second time, and the solid salt is used as technical sodium rodanide.

The preparation of sodium rhodanide standard dihydrate is produced by dissolving the product (from alcohol crystallization) in an aqueous working solution. Rhodanide is added to the solvent and an equivalent amount of water is added to form the dihydrate. Dissolution occurs at a temperature of 80 °, and if necessary (to clarify the solution) activated carbon is added to it and then filtered. The clarified hot solution is fed into the crystallizer, into which a part of the circulating uterine saturated solution is pre-poured, cooled to a temperature below 20-25 °, and the dihydrate crystals are seeded. Thus, the crystallization of sodium rhodanide dihydrate is carried out at a temperature below 30.4 ° (transition point) to prevent the formation of anhydrous sodium rhodanide. Pure roganous sodium is obtained, which meets the technical conditions.

When impurities are accumulated in the mother liquor in quantities exceeding the norms for obtaining a conditioned product, the mother liquor is transferred for processing to a technical product.

Subject invention

Claims (2)

1. A method for separating pure sodium rhodium sulphate from waste solutions of mouse-for-soda purification of coke oven gas, based on the use of different solubilities of the thiosulphate and sodium rhodanide contained in them, by evaporation of these solutions at boiling point with crystallization of sodium thiosulphate and subsequent isolation from the resulting rohanide mother solutions sodium, characterized in that, in order to reduce the sodium thiosulfate content in the final product, the crystallization of sodium thiosulfate is carried out in two stages at mperaturah about 0 and 25 °, respectively. 2. A method according to claim 1, characterized in that, in order to reduce the anhydrous salt content in the final product, the crystallization of sodium rhodanide dihydrate is carried out at temperatures below 30.4 °. By introducing a solution that is concentrated but not saturated at this temperature this salt in cooled saturated working solution. - 3 148036