CS199133B1 - Method for the reduction of calcium and magnesium content in saltpeter solution from nitrate technology of magnesium oxide production - Google Patents

Description

The present invention relates to a process for reducing the calcium and magnesium content of nitrate solution of nitrate magnesium oxide technology.

Magnesite is an important magnesium raw material, especially for the production of magnesium oxide and for the preparation of base, refractory linings. In nature, magnesite is present in large quantities, but in addition to the basic component, magnesium carbonate, it contains significant amounts of undesirable impurities, especially calcium, iron, silicon and aluminum compounds · Ealcinating yields magnesium oxide, which preferably contains about 10% by weight .

Recently, the demands on high-quality, refractory material have increased and magnesia with a content of over 97.1% by weight is considered to be of high quality. magnesium oxide. Therefore, several chemical processes have been proposed to convert magnesite into very pure magnesium oxide.

One of the real processes for producing very pure magnesium oxide is the nitrate process and its variants. So according to MS. of the certificate No. 16149 * is based on kaloinised magnesite, which is gently puddled in nitric acid. This dissolves only the magnesium and calcium, while the other impurities remain in the solid phase and are separated by filtration. A very pure solution of magnesium nitrate is thus obtained, which contains only calcium from the impurities in the form of calcium nitrate.

A similar solution can be obtained according to MS. of magnesite decomposes the ammonium nitrate solution according to the equation

163638, when PaloMgO + 2NH ₄ NO ₃ = Mg (NO ₅ ) ₂ + 2HH 3 + H ₂ 0/1 /,

CaO + 2NH ₄ NO ₃ and Ca (NO ₃ ) ₂ + 2ΝΗ _? + H ₂ O (2).

Separation of calcium from magnesium occurs during the precipitation of the resulting solution of magnesium nitrate and calcium nitrate with ammonia according to CS. No. 164318, where ee precipitates only magnesium according to the equations

Mg (N0j) ₂₊ + 2H ₂ 2NHj 0 = Mg (0H) ₂ + 2NH ₄ N0 _3/3 /.

After the magnesium hydroxide has been filtered off, there remains a solution containing the original calcium nitrate, the reaction-formed ammonium nitrate and the residues of non-precipitated magnesium nitrate. After evaporation of the water, this solution is worked up to fertilizer saltpeter or according to MS. No. 163638 reverts to the decomposition of burnt magnesite. In both cases, however, the presence of calcium nitrate and, to some extent, magnesium nitrate in processing into fertilizer deteriorates its physical properties, in particular its wettability.

When the solution is returned to decomposition by calcined magnesite, the concentration of calcium nitrate in the solution increases, and therefore some of the calcium must be removed from the solution by precipitation to maintain its concentration at a certain level.

According to MS. 163638 and 164318, the addition of sulfuric acid or magnesium sulfate is used to remove the calcium, and the resulting gypsum is separated by filtration. However, this precipitation reaction proceeds slowly and incompletely so that it is associated with considerable technological difficulties (large reactor volumes, gypsum incrustation).

These drawbacks are largely eliminated by the method of reducing the calcium and magnesium content of the nitrate solution of the nitrate magnesium oxide production technology of the present invention, wherein the nitrate solution containing 8 to 70 wt. % ammonium nitrate, 0.3 to 6 wt. % magnesium nitrate, 0.3 to 20 wt. % calcium nitrate and optionally up to 12 wt. Ammonia is precipitated by the addition of ammonium carbonate or ammonia and carbon dioxide or carbon dioxide and ammonia already present in the nitrate solution, in amounts corresponding to 0.3 to 6 times the eteohiometric content of calcium and magnesium according to equations.

189132/4 /,

Mg (NO ₅ ) ₂ + (NH ₄ ) ₂ CO ₃ = MgCO ₃ + 2NH ₄ NO ₅ Ca (NO ₃ ) ₂ + (NH ₄ ) ₂ CO ₅ = CaCO 3 + 2NH ₄ NO ₅ (5), or

Mg (H0j) ₂ + NH 3 + CO ₂ + H ₂ 0 = MgCO 3 + 2NH ₄ NO ₃ Ca (NO ₃ ) ₂ + NH 3 + CO ₂ + HgO = CaCO _? + 2NH ₄ N0 _5/6 / / 7 /.

whereupon the precipitate formed is separated from the liquid phase.

An advantage of the process according to the invention is that the degree of calcium and, if necessary, magnesium is very high, the reaction proceeds rapidly and the resulting precipitate has good filtration and sedimentation properties. Any excess precipitant can easily be converted to the desired ammonium nitrate according to the equation:

(NH ₄ ) ₂ CO ₃ + 2 _? = 2 ΝΗ ₄ Ν0 ₃ + C0 ₂ + H ₂ 0/8 / and the resulting carbon dioxide is easily expelled by heating. This results in an ammonium nitrate solution free of undesirable impurities, so that incrustations and fouling of the pipeline paths due to continued precipitation, as is the case with sulfate ions, are avoided.

Also, the raw materials required for the precipitation of calcium and magnesium according to the invention do not present problems. Both ammonia and nitric acid are usually available, or? they form the basis of nitrate technology for the production of magnesium oxide and carbon dioxide is a waste product in most fertilizer plants that is emitted into the atmosphere without any benefit.

A further advantage is that in the operation of the process according to the invention, highly desirable, precipitated calcium carbonate can be produced, which is used as a filler in the paper, rubber and fat industry. Water-soluble ammonium nitrate is easily washed out with water from the calcium carbonate during filtration and the addition of magnesium carbonate is not a problem, or? in terms of fillers, it has the same properties as calcium carbonate.

We have experimentally found that the precipitation according to the present invention preferably produces calcium carbonate with an addition of magnesium carbonate, and only when the precipitant is used in a stoichiometric amount according to equation (5) or (7) ee, predominantly precipitates magnesium carbonate. It is therefore possible, by selecting the stoichiometric ratio between the precipitant and the magnesium and calcium present, to vary within quite wide limits, on the one hand, the calcium-magnesium ratio in the precipitate and, on the other hand, the residual calcium and magnesium content in the solution. Using a precipitant in an amount below 0.3 times the steohiometry according to equations (4) and (5) or (6) and (7) leads to insufficient decalcification. By using more than 6 times the required amount of precipitant, the degree of precipitation is practically not increased and means only inconvenient expense of the precipitant.

197133

Equations (4) to (7) express only stoichiometric ratios at precipitation. Solid precipitation products, i.e. magnesium carbonate and calcium carbonate, can also be formed in hydrated form or as double compounds in varying molar ratios.

Example 1

877 kg of the composition solution were fed into the miohane reactor

1.9 wt. Mg (NO2) ₂ ,

3.0 wt. Ca (H2O) _{2 >.}

25.3% wt. NH ^ Oj,

1.3 wt. HHj,

68.5% wt. HgO, and then carbon dioxide was added to the bottom of the reactor, and ee captured 7.4 kg. A white Buepenze was formed which was filtered on a filter press. The alkaline reaction of the filtrate was dulled by the addition of 54% HNO4 to pH 6.9 and carbon dioxide was expelled by heating to boiling. The obtained solution contained

1.7 wt. Mg (NO _? ) ₂ ,

0.3 wt. Ca (NOj) ₂ ,

30.0 wt. NH 4 NO 3 a

68.0% wt. HgO, the precipitate in the filter press was washed with water and after drying ee obtained 11.4 kg of a 90% by weight carbonate precipitate. CaCO 3, 10 wt. MgCO3.

Example 2

The stirred reactor was charged with 865 kg of the composition solution

1.9 wt. Ug (K0 _? ) ₂ ,

3.0 wt. Ca (R0j) ₂ ,

25.6% wt. % NH ₄ NO, _x 69.5 wt. HgO, and then carbon dioxide and ammonia gas were introduced to the bottom of the reactor. Carbon dioxide was captured in solution by 7.5 kg and ammonia then 11.5 kg. The resulting suspension, which was practically different from the suspension in Example 1, was further processed in the same manner.

Example 3

To the stirred reactor was charged 877 kg of a solution as in Example 1, after which an aqueous solution of 20% by weight ammonium carbonate was added. in an amount of 80 kg. The resulting suspension was further processed as in Example 1.

Claims (1)

SUBJECT OF THE INVENTION A process for reducing the calcium and magnesium contents of a nitrate solution from nitrate magnesium oxide production technology, characterized in that the nitrate solution containing 8 to 70 wt. % ammonium nitrate, 0.5 to 6 wt. % magnesium nitrate, 0.5 to 20 wt. % calcium nitrate and optionally up to 12 wt. Ammonia is precipitated by the addition of ammonium carbonate or ammonia and carbon dioxide or carbon dioxide and ammonia already present in the nitrate solution in amounts corresponding to 0.5 times the stoichiometric content of calcium and magnesium, whereupon the resulting precipitate is separated from the liquid phase.