DE564059C - Manufacture of clay - Google Patents

Description

It is known, alumina-containing raw materials, which are known to always be iron and silica Contained as an impurity, wet with caustic alkalis at high temperature and to open up increased pressure and the obtained and possibly cleaned Further processing of alkali aluminate solution on alumina.

It is also known to use low levels of silicic acid in this process Apply amounts of lime alongside the alkali carbonate or hydroxide. It was already proposed to dig up alumina-containing substances with alkali or alkaline earth bases alone. In this way, soluble alkali or alkaline earth silicates and free alumina are obtained, the latter then by means of caustic soda or caustic potash is to be made soluble. The unclear ones made about this in the literature However, information has so far not led to any practical use.

According to the invention, very pure alumina is obtained if the halogen-free starting materials are used (ζ. Β. bauxite or clay) initially moist in the autoclave with such a large Amount of alkaline earth base, e.g. lime and water, treats all of the aluminum as certain alkaline earth aluminate containing water of crystallization, e.g. B. insoluble calcium aluminate, and the silica as an insoluble alkaline earth silicate, e.g. B. calcium silicate, is bound, then the alkaline earth aluminate formed with alkali carbonate or alkali sulfate solution in converts the heat and from the alkali aluminate solution thus obtained and separated the clay falls in a known manner.

The reactions are facilitated by the fact that the material before or during the Treatment in the autoclave is ground very finely.

The alkaline earth base and the mineral are ground together and the add required amount of water; you can also proceed with advantage in such a way that the base and the mineral are comminuted in the presence of water, for example in a colloid mill. The process can be further improved by keeping the colloid mill inside the autoclave itself is arranged so that intimate mixing and heating occur simultaneously can be made, whereby the duration of the treatment in the autoclave and the fuel consumption can be reduced.

If the mineral contains alumina compounds in addition to free alumina, these are expediently broken down in advance by roasting. If, for example, clay is to be processed, heating to around 650 to 750 ^{0 will make} the aluminum 6c

nium silicate is destroyed, making the clay much more vulnerable to attack. At a Bauxite is roasted at around 500 or 600 ° C, but some give it Bauxite has better alumina yields when used unannealed. When the Digestion of the mineral used alkaline earth base gives a soluble alkaline earth aluminate (when using barite), this soluble aluminate can be converted into insoluble alkaline earth aluminate implement, for example, by treating it with lime. This gives a precipitate of insoluble calcium aluminate, which is then treated with an alkali salt and thereby an alkali aluminate and a solution of barium oxide hydrate can be obtained, which is used to digest a new amount of clay mineral can be used.

As already stated, it is important that the digestion of the clay mineral is present a sufficient amount of water is carried out so that a certain crystal water-containing Alkaline earth aluminate is obtained.

When using lime, the aluminates containing water of crystallization have one or any of the following formulas:

Al ₂ O ₃ -2 CaO-7 H ₂ O;

Al ₂ O ₃ -3 CaO-21 H ₂ O; AUO ₃ -4 CaO-12 H ₂ O.

It follows that when lime is used as the base for the digestion, a Amount of water applied must be at least 50% of the weight of the reaction stepping clay and lime amounts.

Example i

Treatment of a bauxite of the following composition with lime:

This bauxite is mixed with lime in the ratio of 180 kg slaked lime per 100 kg Grind bauxite (or the equivalent amount of quicklime) and then with 150 liters of water are added to every 300 kg of bauxite and lime.

Incidentally, one could also use the bauxite and the lime together very advantageously The presence of the water.

The mixture prepared in this way is then placed in the autoclave for about 3 hours boiled at 10 atmospheres to form calcium aluminate.

Al ₂ O ₃ 56.95 TiO ₂ 3.06 SiO ₂ 2.56 H ₂ O 12.20 Fe ₂ O ₃ 25.23

To form a calcium aluminate of the type Al ₂ O ₃ · 4 CaO 12H ₂ O for 100 kg of the present bauxite of the above composition, 170 kg of the slaked lime used are consumed, while the rest is reacted with the existing silica, etc.

The product obtained is allowed to settle, whereupon it is separated from the liquid and ^{leached with 10% sodium carbonate solution at 80 °} C. with stirring.

The sodium aluminate is then stripped off and the residue is washed with a 5 ^o / o * § ^en liquor at said temperature door.

The alumina is then processed in a known manner from the alkalis obtained in this way Carbon dioxide precipitated.

In this way, a yield of 90% of the Al ₂ O ₃ contained in the mineral is obtained with a silica content of 0.05 per 100 kg of Al ₂ O ₃ , ie the alumina obtained has the composition:

85 Al ₂ O ₃ 99.85

SiO ₂ 0.05

Example 2

The same raw material can also be opened up with barite by using for the digestion 400 kg of barium hydroxide, 100 kg each Bauxite and 8000 l of water used.

Similar to the formation of CaO-Al ₂ O _3, these quantities correspond to the substance quantities that are necessary for the formation of compounds of the Al ₂ O ₃ '4 BaO type. _{The excess Ba (OH) 2} , which is no longer required for the formation of aluminate, is used to form barium silicates, etc.

After the mass has been boiled for about 3 hours at 8 atmospheres in the autoclave it is separated from the liquid, barium aluminate being obtained in solution will; the residue is then washed out.

The withdrawn filtrate and the leaching water are treated separately with lime, whereby calcium aluminate precipitates - which is then treated further as in Example 1. The filtrates, which contain the barium hydroxide, are returned to the plant immediately back, the leaching waters return to there only after they have reached the initial level have been concentrated.

The calcium aluminate recovered is treated with sodium carbonate as above.

A yield of 87% is obtained, i.e. a slightly lower yield than when using Lime.

According to the procedure described, you can

Sodium aluminate liquors can be produced with very small amounts of impurities.

The fuel consumption is limited to the utmost as the applied Temperatures are low and the usual dilutions and concentrations are avoided can be.

Finally the use of the alkaline earth bases is much more economical than that of the alkali bases, and the losses from silicoaluminate formation are at the low levels used Temperatures and the low value of the base bound by the silica are insignificant, so that also high-silica minerals, such as low-quality bauxite or clays, according to the claimed process can be processed.

Claims (1)

Claim: Process for the production of alumina by wet digestion of raw materials, z. B. bauxite and the like, preferably in an autoclave, with an alkaline earth base, e.g. B. lime, characterized in that that the digestion with at least ι mol. Alkaline earth base, z. B. lime, per ι mol. Alumina and about 2 to 3 mol. Alkaline earth base per mol. Silica to form one alkaline earth aluminates containing water of crystallization is carried out and the alkaline earth aluminates formed before the known Further processing with a solution of alkali carbonate or alkali sulfate to alkali aluminate implemented.