CS231030B1 - Process for the treatment of magnesium sulphite - Google Patents

Abstract

The aim of the invention was to develop a technology for processing the product from the magnesite flue gas desulfurization process. This aim is achieved by reacting magnesium sulfite with phosphoric acid under stirring in a molar ratio of MgSOj : PoOc = 1 to 1.1. The sulfur dioxide formed in the reaction is forcibly desorbed, the liquid phase can be used as a highly concentrated PMg fertilizer.

Description

The invention relates to a process for the treatment of magnesium sulfite.

Magnesium sulphite tri- or hexahydrate is an intermediate in the flue gas desulfurization by the magnesite method. However, magnesium sulphite can also be the final product from the desulfurization point of view since it is a suitable raw material for the so-called magnesium bisulfite process for the production of cellulose, for the production of magnesium nitrate and sulfuric acid and for the production of magnesium oxide and sulfuric acid. Of note are those methods of treating magnesium sulfite, which can be advantageously carried out in chemical plants without calcination of magnesium sulfite.

For a desulphurization plant to work in this way, it must be able to dispose of all sulphite production, which cannot be achieved by cellulose and magnesium nitrate production. Therefore, other economically advantageous methods of treating magnesium sulfite are sought.

One of the novel processes is the process for treating magnesium sulphite according to the invention, which comprises reacting magnesium sulphite tri- or hexahydrate under intensive stirring with β phosphoric acid, obtained for example by decomposing natural phosphates with nitric acid and adjusting the lime / phosphorus ratio , in a molar ratio of MgSO4: PgOg = 1 to 1.1, and the sulfur dioxide formed is at least partially forced to be desorbed from the reaction mixture and the liquid phase is treated as necessary.

The advantage of this new technology is that magnesium sulphite can be processed in one chemical plant at the same time to form a magnesium phosphate fertilizer and sulfuric acid. Together with the consumption of magnesium sulphite for the production of cellulose and magnesium nitrate, it creates a sufficient outlet basis for all magnesium sulphite produced at one desulphurization station, so there is no need to build a plant for its treatment including thermal decomposition of sulphite and sulfuric acid production.

When carrying out the process according to the invention, it is important that the mixing of the reactants does not even result in local heating, as this may initiate the exothermic oxidation of the sulphite with calcium nitrate, which is present in considerable concentration in the precipitated phosphoric acid. For this reason, hexahydrate is preferable to trihydrate because the temperature decreases by about 12 ° C when mixing hexahydrate with frozen phosphoric acid, while for magnesium sulphite trihydrate only by about 6 ° C. Overall, the reaction temperature should not exceed 30 ° C, from an optimal ee of 20 ° C.

When the reactants are mixed, approximately half of the total chemically bound sulfur dioxide is released. The reaction mixture foams strongly. Subsequent desorption is carried out by air bubbling in the amount required to process the sulfur dioxide into sulfuric acid by a tower or chamber process. After forced air desorption, 1 to 4% by weight of the initially present sulfur in the form of magnesium sulphite remain in the liquid phase. This residue of sulfur dioxide is subsequently heated, respectively. thickening converts the liquid phase to a sulphate anion by oxidation with a nitrate anion to form an appropriate amount of nitrogen oxides. The formation of a sulfate anion then leads to the formation of a calcium sulfate precipitate.

Example

21.1 g of magnesium sulphite hexahydrate was rapidly mixed with 67.1 g of frozen phosphoric acid, which contained 21% by weight of ^{P 2} ® 5 ⁸ 5% by weight of N in form (NOj) g. The mixture was foamed to 40 ml with stirring. 5.6 liters of air were then bubbled through the reaction mixture at 20 ° C. 81.6 g of a slightly turbid liquid product was obtained with a content of? 2θ5 * 7.27 55 by weight and a SOg content of 0.25 55 by weight. 96% of the total amount of sulfur present in the magnesium sulphite was recovered.

Claims (1)

Process for the treatment of magnesium sulphite, characterized in that the magnesium sulphite tri- or hexahydrate is reacted with vigorous stirring with phosphoric acid obtained, for example, by decomposing natural phosphates with nitric acid and adjusting the calcium / phosphorus ratio in a molar ratio MgSO4: PgO4 = 1 to 1.1 and the resulting sulfur dioxide is at least partially forced desorbed from the reaction mixture.