DE1905674C - Process for the preparation of anhydrous from hydrated magnesium chloride - Google Patents

Description

The present invention relates to a process for the preparation of anhydrous from hydrated magnesium chloride which contains 1 to 5 percent by weight H ₂ O and 1 to 5 percent by weight magnesium-oxygen compounds.

The invention relates in particular to the production of anhydrous magnesium chloride from magnesium chloride salts, obtained from naturally occurring sources.

Although magnesium chloride and / or sulfate salts, from which the chloride is easily obtained by desulfation, are widely used on earth in aqueous salt solutions together with other salts, such as e.g. B. the chloride and / or sulfate salts of sodium, potassium, lithium, calcium, such as those found in seawater, inland seas, salt lakes and springs and also in the crystalline state in the past due to solar radiation from inland seas, lakes and the like are found, raises the isolation and recovery of practically pure and anhydrous magnesium chloride from such deposits problems, the solution of which causes considerable difficulties. Although the magnesium salts are compared to various other salts with which they are usually found together in aqueous solutions or in solid 2'ustand, such as. B. the sodium, potassium, calcium salts are completely soluble and can therefore be isolated from their aqueous solutions and obtained in an impure state by first precipitating these other salts selectively to form a mother liquor, which consists largely of magnesium chloride and magnesium sulfate salts , which can be desulphated, for example, by treatment with calcium chloride and the mother liquor, from which they can then be evaporated practically to dryness, for example by spray drying, the impure magnesium chloride salt thus obtained precipitates in hydrated form and is also normally, if not carefully was desulfated, contaminated to a lesser extent with sulfate salts, so that the end product, as explained in more detail below, various oxygen-containing compounds, such as. B. H ₂ O and any one or more compounds from the group consisting of MgO, MgOHCl, Mg (OH) ₂ and sulfates.

The oxygen-containing impurities retained in the impure salt thus obtained are, however, involved in the production of metallic magnesium from molten salts by electrolysis most harmful. If the magnesium chloride used for these purposes has a significant amount of water of crystallization contains, the electrolysis leads to the development of HCI, according to the amount of existing Water, by implementing the

ίο Electrolysis of released chlorine with the hydrogen of the water, whereby its oxygen content in turn reacts with magnesium to form MgO and also with the carbon anodes of _{the electrolysis cell to form CO 2 gas.} As a result, the carbon

fuel anodes eroded and corroded. In addition, the magnesium oxide forms one in the cell Sludge that reduces their operational efficiency and thus the yield of metallic magnesium. on in a similar way,

impurities that contain another oxide on the carbon anodes, while especially those in them The sulfates contained in them also attack the refractory lining of the electrolytic cell. This leads to a ver shortened service life of the cell, loss of electrical current and leads to surface tension problems related to coalescence and expediency Interfere with the extraction of the magnesium metal produced. It is therefore essential that the one used for the production of metallic magnesium by electrolysis

Magnesium chloride practically free from oxygen-containing compounds or other oxygen-containing ones Impurities is.

Completely anhydrous magnesium chloride, which is practically free from oxidic impurities, can be obtained by chlorinating pure magnesium oxide at an elevated temperature in the presence of carbon or carbon-yielding compounds, such as. B. carbon monoxide, carbon tetrachloride, are obtained, however, this process is expensive and the sources of pure magnesia are limited.

Another process for the production of anhydrous magnesium chloride is known from Austrian patent 91 927, in which magnesium oxide is reacted with sulfur chlorides at temperatures at which the starting material and the end product are at least predominantly in solid form. If, however, one assumes impure MgCl ₂ in the hydrated form, which comes from naturally occurring sources, then a purification of oxidic constituents including the water of crystallization is necessary. Is a derived from an aqueous salt solution, containing essentially magnesium chloride mother liquor slowly evaporated to dryness, then the resulting crystalline hydrate, the hexahydrate, MgCl ₂ ■ 6HJ ₁ O. From this, four molecules of water by drying at elevated temperature at about 204 ° C removed with formation of the dihydrate MgCl ₂ · 2 H _{2 O.} However, on further heating to remove the remaining water, decomposition and hydrolysis occurs, forming anhydrous chloride and the basic magnesium hydroxychloride MgOHCl. When spray-drying a highly concentrated aqueous solution or slurry of the dihydrate at about 482 to 538 ° C, some of the MgCl _{2 is} converted into HCl and any one or more compounds from the group MgO, MgOHcI and Mg (OH) _{2 by the hot, moisture-laden gases} , all of which in the following are equivalents of

MgO treated, decomposed. The spray-dried product thus obtained consists essentially of magnesium chloride _{powders which contain about 1 to 5 percent by weight H 2} O and 1 to 5% MgO or an equivalent thereof.

The present invention now provides a process in which anhydrous magnesium chloride can be prepared from such a product. The process according to the invention for producing anhydrous from hydrated magnesium chloride is characterized in that hydrated magnesium chloride, which contains 1 to 5 percent by weight H ₂ O and 1 to 5 percent by weight magnesium-oxygen compounds, is ^{melted at temperatures above 710 °} C. and treated with sulfur chloride gas will.

In contrast to the above-mentioned process of the Austrian patent, for which working below the melting point of anhydrous magnesium chloride is necessary in order to achieve a useful result, according to the invention it is carried out in the melt. Furthermore, according to the invention, the starting point is a material which contains 1 to 5 percent by weight H ₂ O, while according to the method of the Austrian patent it is necessary to work in the free or bound state in the absence of water. Furthermore, the method of the Austrian patent is based on magnesium oxide, which is contained in the starting material according to the invention only as an impurity.

The sulfur chloride compound used according to the invention comprises S ₂ Cl ₂ , SCl ₂ and SCl ₄ or sulfur monochloride, sulfur dichloride and sulfur tetrachloride. In the treatment with these sulfur compounds, the sulfur either combines with the oxygen present in the magnesium chloride melt to form SO ₂ gas, which escapes as such from the bath, or it escapes in the form of sulfur vapor, while this escapes from the sulfur chloride compound released chlorine gas, the MgO or equivalent compounds are chlorinated again to form MgCl ₂ .

Without being bound to any specific theory with regard to the reactions occurring during the sulfur _{chloride treatment, some reactions appearing to be possible in which SCl 4 or 3Cl 2 is} used as the sulfur chloride compound are given below.

(1) 2MgO + SCl ₄ -> 2MgCl ₂ + SO ₂

(2) Mg (OH) ₂ + SCl ₄ - ^ MgCl ₂ + 2HCl + SO ₂

(3) 2Mg (OH) (Cl) + SCl ₄

- ♦ 2MgCl ₂ + 2HCl + SO ₂

(4) 2H ₂ O + SCl ₄ - »■ SO ₂ + 4HCl

(5) Mg (OH) ₂ + 2SCl ₂

- »MgCl ₂ + SO ₂ + 2HCl + S

With regard to the above equations, it was found experimentally that, depending on the sulfur chloride compound used, in some cases, as in equation (5) above, free sulfur was precipitated from the melt. It has also been found that as the sulfur _{chloride is added to the bath containing sulfates as an impurity, the SO 4} content increases to a certain point and then decreases as the sulfur chloride continues to be added as discussed above.

According to a preferred embodiment in which the hydrated magnesium chloride contains sulfates and other oxygen-containing impurities after the sulfur chloride treatment to remove some of these impurities, the molten bath treated with activated carbon to remove sulphate impurities in gaseous form.

To carry out the process according to the invention, the spray-dried magnesium chloride, the

ίο Magnesium oxide or an equivalent thereof, water of crystallization, Contains sulphates and possibly other oxidic impurities, in a closed, brought with a flue pipe and melting furnace until the molten state.

»5 heats by sticking to those at a distance from each other attached carbon electrodes, which protrude into the loading, applies an alternating current. If so the feed is melted, sulfur chloride is passed through until the oxide impurities are in the are substantially removed.

The following examples are intended to illustrate the present invention.

example 1

5 27.2 kg of spray-dried magnesium chloride obtained in the manner described above from the Great Salt Lake in Utah, analysis showed, contained 1.4 weight percent magnesium oxide, based on the equivalent, and 0.07 weight percent SO ₄ . It was melted by slightly ie it heated to about 760 ⁰ C, above its melting point of 710 ⁰ C. The melt was treated with 2000 ml of SCI ₂ , corresponding to 12.5 percent by weight of magnesium chloride. The SCl ₂ was passed through the molten feed. After completion of the SCl ₂ treatment, the molten salt was treated with Ve percent by weight activated carbon. The following table shows the treatment results:

40 With
With 6 ° / o SCI ₂
12V.7o Weight
percent
MgO SO, 0.07
0.23
0.35
<0.01 Molten MgCl ₂
45 After treatment
After treatment
SCI ₂ With 7e ° / o 1.40
1.00
0.42
0.55 After treatment
Activated carbon

From this experiment it is apparent that the addition of sulfur chloride from a gradual increase in Sulphate content was accompanied, which was practically removed by post-treatment with activated carbon.

From the above experimental results further show that the treatment of the molten salt with 12V ₂ weight SCl ₂ reduced the MgO content to 30% of its initial value, while the activated carbon after treatment the SO decreased ₄ content to less than ¹ I ₇ of its initial value . The above treatment corresponds to a weight ratio of SCl ₂ initial MgO content of 9: 1.

Example 2

^δ 5 Another sample of spray-dried MgCl ₂ from the same source as in Example 1 contained 1.2% MgO and 0.016% SO ₄ when analyzed. The sample was melted and _{treated with SCl 2} , and after

treatment with activated charcoal gave the following results:

Molten MgCl ₂

After treatment with 4 g SCI / 100 g MgCl ₂

After treatment with 5g SClj / 100g MgCl ₂

After treatment with 0.5 g activated carbon / 100 g MgCl ₂

Weight percent MgO! SOj

0.4

This treatment corresponds to a weight ratio of SClj / initial MgO content of 4: 1 It should be noted that in this experiment the addition of sulfur chloride reduces the initial sulfate content not noticeably increased.

Example 3

Another sample of MgIC ₂ from the same source containing 1.4% MgO and 0.006 ¹ V ₀ SO ₄ was treated in a similar manner with the following results:

1.2 0.016

Ό, 5! 0.019

0.4 I 0.017

Molten MgCl ₂

After treatment with 67 ₂ g SCl ₂ /

100g MgCl ₂

After treatment with 137-g SCl ₂ /

100g MgCl ₂

Weight percent MgO! SO ₄

1.4
0.4
0.15

It was found that with the further addition of sulfur chloride the sulfate content was reduced to a negligibly small value, although the sulfate content initially increased with the addition of sulfur chloride. Therefore, no final treatment with activated charcoal was carried out in this test. The final treatment corresponded to a weight ratio of. SCljj / initial MgO content of about 10: 1, and the SCl ₂ was added over a period of 1 hour.

Claims (2)

Patent claims: 1. A process for the preparation of anhydrous from hydrated magnesium chloride, characterized in that hydrated magnesium chloride containing 1 to 5 percent by weight H ₂ O and 1 to 5 percent by weight magnesium-oxygen compounds is melted at temperatures above 710 ° C and treated with sulfur chloride gas will. 2. The method of claim 1 wherein the hydrated magnesium chloride is sulfates and other oxygen containing impurities, characterized in that after the sulfur chloride treatment the molten bath of activated carbon to remove some of these contaminants is treated to remove the sulphate impurities in gaseous form.