BE450280A

BE450280A -

Info

Publication number: BE450280A
Authority: BE
Priority date: 1942-05-23
Also published as: FR894739A; CH234778A

Description

       

  Procédé de précipitation d'alumine des solutions d'aluminates alca-lins en travail-continu.

  
L'alumine est obtenue général suent à partir de matières brutes renfermant de l'alumine, respect! valent d?s composés d'alu-

  
 <EMI ID=1.1> 

  
on s'est déjà efforcé de réaliser en -continu le processus de précipitation de l'alumine, sans que les essais les plus divers dans

  
ce sens aient conduit à un -succès, parce qu'on ne parvenait pas à obtenir 1 -'alumine sous une forme suffisamment grenue. Des difficultés particulières ont été rencontrées spécialement lorsque la précipitation était exécutée à partir de solutions étendues, ou lorsqu'on employait pour la-précipitation un gaz à faible teneur en an-

  
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cipient de réaction était vidé et rempli d'une nouvelle charge de

  
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cipité alors -on une phase'subséquente du processus. De même, la proposition d'Employer des produits provenant de précipitations anté'rieures comme amorce n'a pas permis de réaliser la précipitation en continu. Cette mesure apporte seulement une plus grande facilité du

  
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Or, on a fait la constatation surprenante qu'on parvient

  
à réaliser une précipitation continue d'alumine sous une forme suffisamment grenue lorsqu'on a soin d'avoir présentes de grandes quantités de produits précipités. Suivant l'invention le- liquide doit .renfermer, dans la partie du récipient dans laquelle a lieu le processus de précipitation proprement dit, une quantité relativenent <EMI ID=6.1> 

  
quantité de liquide par précipitation. On est arrivé ainsi à de bons résultats avec la quantité quadruple.

  
Pour l'exécution de ce procédé on se sert d'un dispositif qui permet d'accumuler la quantité du produit précipité et de la maintenir'à un niveau déterminé. A cet effet le récipient, garni d'un agitateur et agencé pour une admission et une évacuation continues

  
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  Process for the precipitation of alumina from solutions of alkaline aluminates in continuous work.

  
Alumina is generally obtained sweat from raw materials containing alumina, respect! are valued at aluminum compounds

  
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efforts have already been made to carry out the process of precipitation of alumina continuously, without the most diverse tests in

  
this meaning led to success, because it was not possible to obtain 1 -'alumina in a sufficiently coarse form. Particular difficulties have been encountered especially when the precipitation is carried out from bulk solutions, or when a low-carbon gas is employed for the precipitation.

  
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reaction vessel was emptied and filled with a new charge of

  
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then a subsequent phase of the process is initiated. Likewise, the proposal to use products from previous precipitation as a primer failed to achieve continuous precipitation. This measure only brings greater ease of

  
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However, we have made the surprising observation that we have

  
in carrying out a continuous precipitation of alumina in a sufficiently coarse form when care is taken to have present large quantities of precipitated products. According to the invention the liquid must contain, in the part of the vessel in which the actual precipitation process takes place, a relative quantity <EMI ID = 6.1>

  
quantity of liquid per precipitation. We have thus obtained good results with the quadruple quantity.

  
For the execution of this process a device is used which allows the quantity of the precipitated product to be accumulated and to be maintained at a determined level. For this purpose, the container, fitted with a stirrer and arranged for continuous admission and discharge

  
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Claims

or liquid and for continuous discharge of the precipitated product. <EMI ID = 8.1>

cross section is variable. In this chamber the precipitated product separates from the laundry. By the variation of the. cross section the rate of rise of the liquid is regulated, so that a greater or lesser part of the precipitated material remains

Variation can be carried out in the most different ways. If part of the reaction product is precipitated in the form of grains so large that it cannot come out through the chamber

tion in fine-grained products in the stirring chamber, it is evaluated in the lower part of the container by pumping and this in an adjustable amount, then being fed into a device

which can in this case be returned to the container together with the solution, as required.

With this working mode, the precipitation can be carried out at: if relatively low temperatures, so for example at

carbon dioxide. The content of products already precipitated is adjusted

increased pressure in the precipitation vessel, as a result of the circulation of the liquid the introduced carbon dioxide gas is always covered again by quantities of liquid raised from below, hence. this results in a very uniform distribution and a

is found only for a fraction of the time of its stay in the precipitation vessel in contact with the carbon dioxide gas.

The processes known heretofore, operating with intermittent precipitation, require reaction vessels of a large capacity and require that the carbon dioxide be introduced into the lowest layers of the liquid. The compression work required for this is considerable.

With the working method according to the invention, which can be produced industrially in a simpler and more economical manner, a coarse alumina is obtained, easily separable from the lye.

It goes without saying that the precipitation can be executed

under other conditions and also in the most diverse devices.

CLAIMS * ..

tions of alkali aluminates, in continuous work, characterized in that, in the part of the precipitation vessel in which the actual precipitation takes place, the liquid contains a. large quantity of products * already precipitated, this quantity being at, less equal to, but better still multiple of the quantity obtained

2. A method according to claim 1, characterized in that the. precipitation is carried out in the presence of the quadruple quantity of products already precipitated.

rush.

se in that, in the case of the use of a gas as a precipitant, the latter is introduced into the liquid under low compression,