US1976564A - Process for the treatment of silicates with acids in order to obtain their soluble salts - Google Patents

Description

Oct. 9, 1934. F. JOURDAN 1,976,564

PROCESS FOR THE TREATMENT OF SILICATES WITH ACIDS IN ORDER TO OBTAIN THEIR SOLUBLE SALTS Filed March 10, 1933 Patented Oct. 9, 1934 PROCESS FOR THE TREATMENT OF SILI- CATES WITH ACIDS IN ORDER TO OBTAIN THEIR SOLUBLE SALTS Flix Jourdan, Rome, Italy Application March 10, 1933, Serial No. 660,252

In Italy March 18, 1932 1 Claim.

It is known that many silicates, mainly those containing alkali metals (potassium, sodium, lithium) may be attacked at high temperature and under pressure by the vapours of volatile acids,

5 such as hydrochloric or nitric acid. When the attack is efiected with the vapours at high temperature of these acids, which may also be mixed with water steam, a liquid condensate is obtained which contains in solution the soluble salts resulting from the reaction, the concentration of the said solution being however slight, which renders in practice the process very costly and consequently unsuitable, as it would require to be repeatedly applied or prosecuted by renewing continuously the vapours of the acid used in order to exhaust completely the minerals subjected to the treatment.

The present invention has for its object a new method for effecting the above said treatment, which allows to obtain with a small expense and in a practical and very convenient way, highly concentrated solutions of the salts resulting from the attack of rocks such as leucite, and other similar silicates, even with the condensable vapours of active liquids, which in consequence of the attack are but slightly charged with the soluble salts formed or dissolved.

The principle on which the working of the process according to the present invention is based, 3 is the following: After the attack at high temperature and pressure of the rock under treatment, either alone or in the presence of other substances capable of facilitating the reaction, and after collecting the liquid condensate or the liquid dropping down mechanically, instead of attacking the rock with the vapour from another liquid, the vapour obtained by re-evaporating the condensed liquid, is used; such vapour being pure as it consists only of vapour of acid and water steam, the dissolved substances in the liquid, in the case considered, being all fixed substances, so that the second attack has the same effect as if fresh vapours and steam were used. The condensed vapour contains other substances dissolved in it which increase the concentration of the liquid, the said operation being continued thus enriching successively the liquid until the complete exhaustion of all the useful components of the rock has been reached.

In. practice, it has been found convenient to use a quantity of liquid which is sufficient to extract from the rock and to transfer into the solution all the salts obtainable from the rock under treatment, to maintain the liquid always at the boiling temperature and under pressure, and the charge of rock to be treated at a temperature either equal (when wet vapours are used) or slightly lower, so that the vapour coming in contact with it may condense, both the liquid and the mineral being enclosed in the same closed container, having such dimensions that the liquid may not reach or come in contact with the material placed above it.

Under the said operating conditions, the process can be carried out in a continuous manner, and when good care is taken for thermally insulatfng the whole apparatus, in order to prevent heat losses, the consumption of combustible will be very small, viz: just the quantity which is sufl'lcient to replace the heat lost owing to the slight decrease of the temperature of the charge under treatment, whenever it is necessary to decrease the temperature of the said charge.

The annexed drawing shows schematically a vertical section of the apparatus used for carrying the invention into practice.

Supposing, by way of example, that it is desired totreat the leucite with nitric acid so as to obtain potassium and aluminium nitrates, the operation 0 is carried out asfollows:

The leucite is firstly ground or granulated and then placed in a container 1 perforated at the bottom and uncovered at the top. The said container is then introduced into the higher portion a of an autoclave formed by a vertical tube 2 capable of withstanding the pressure. The height of the autoclave must be sufficient to allow that, upon having poured into it the liquid required for the reaction, which collects at the bottom and which in the present case is nitric acid, in a quantity slightly less than that indicated by theory, the said liquid does not reach the vessel containing the charge of leucite, which is placed into the upper portion of the tube 2. The tube must be made with a material capable to withstand the action of the reagents used and of the reaction products, or it must be eventually lined with a. material which is not attacked by the said reagents and reactionproducts, such as for example grit sandstone. V

Theqautoclave is provided in its lower part with a discharge cock 4 for the exit of the saturated liquid. The fresh liquid is introduced from the top cover 3 through a suitable inlet.

Afterthe autoclave has been charged as described, it is closed, and the liquid, which is collected at its bottom, is heated in any convenient way, such for example, by means of an electric through a pipe having an inlet '7 and an outlet 8,

which causes the condensation of the vapour, which condensed vapour drops through the underlying layer of leucite from which it drops again to the bottom of the autoclave where it rejoins "described, is introduced into the apparatus, the

the boiling liquid.

In practical working the cooling above mentioned is not required when the steam is already saturated with moisture as is the case in the apparatus now described. I As nitric acid boils at a temperature which is lower than the boiling point of water, there will? be produced, under pressure and at hightemperature, vapours rich in nitric acid andwater, which will pass through the mass of leucite from the bottom to the top or conversely and the salts formed'remain dissolved in the condensed liquid, falling to the bottom of the autoclave where the nitric acid is collected. I II I I If the temperature of the attack is kept above 100 0., the silica is no longer dissolved and does not assume the gelatinous form which causes the obstructions occurring in the masses of theattack when operating with no pressure apparatuses. In addition, the heat, developed during the reaction of the attack in a closed apparatus, may be utilized wholly or in part for the heating required after-starting the operation. I i

.Moreover, if the temperature iskept' higher than 125 0., the following additional advantage is obtained: it is known that iron nitrate decom poses at a temperature .oiri25" C., while the aluminiumnitr'ate requires for its decomposition a a temperature of at least 140 C. Thereforaby Working at an intermediate convenient'temperature, between the two limits above mentioned, it will thus be possible to'eliminate' the greater por- I tion of the iron present in the form of iron oxide which precipitates with the insoluble residue. The above described result could not be obtained boiling temperature is a function of the concen' trationof the solution in acid and in salts, which varies continuously and consequently the temperature cannot be regulated, The boiling action agitates the maSsQwhile with the operation made under pressure with the acid in vapour form, the desired ,efiect'of dissolving rapidly the potash and the alumina is obtained directly and in a very simple mannenby operating'atv s'ucha temperature that neither the iron nor the silica may pass into solution. 1

' If a small quantity of iron, coming from the leucite or from the eventual corrosiori'of the ma- 'terial of the apparatus, should pass into the solution, there maybe added in the solutionfkept under pressure, a precipitant for the iron, such for example potassium ferrocyanide, or any other suitable reagent. The precipitate is separated from the liquid by filtration, for'example iby passing the solution through a layer 'o'f'silica formed with the exhausted leucite, which latter thus serves no'longer to eliminate the silica, which with the process described is produced in the insoluble form, but it eliminates the iron which has passed inthe; solution in the form of nitrate.

ldrawingthe c'oncentratedliquid free from-acid,

The iron precipitate may on the other hand be eliminated by using any other of the methods of filtration generally known, or by means of a centrifugal machine, or by any other method known and used in the industry for separating solid substances held in suspension in liquids.

When'theattack'has been completed, the exhausted leucite is removed from the hot apparatus, and another quantity of fresh leucite contained in .another container similar to that above autoclave is then" closed, and the heat is maintained by producing vacuum in it, so that the water in excess may be distilled up to the amount I which is considered necessary, passing the water vapour through the leucite. By operating in this way the last-traces of free acid which may still be presentin the solution become fixed, while the distilled water exhausted is free from acid solution of potassium and aluminium nitrates,

free from iron and from silica, from which the said two'nitrates can be separated by any known methods, subsequently admitting a fresh charge of acid into the autoclave. I 1

The operation carriedout as above described allows toleiiect the rapid attack of the leucite, to obtain the complete fixing of the acid without any loss, and also the'complete purification of the liquid whichis free from silica and from iron, as well asits. concentration by eliminating from ft'the pure water without the .use of pumps or of other costly and complicated distilling apparatuses. I V

I claim; I The process of treating silicates with acid vapours at high temperature for extracting therefrom the corresponding'salts, comprising charging the silicateinto a cage having a perfor at ed bottom and open at the top, disposed in the upper portionof a closed container, while charging the liquid, consisting of an aqueous solution of acid,'into the lower portion of the said container and heating it in order to obtain wet satu-',

rated acid vapour, permitting the same to pass throughthe mineral, which is at a slightly lower temperature, the vapour thus condensed and sat :urated with the soluble s'alt'abstracted from the mineral dropping into the hot liquid at the botexhausted or the underlying liquid has reached saturation of thesaid substances, including the furtherstep of introducing at the-end of the from said distillation to pass through the said fresh charge of; material, thereby utilizing the acid distilled from the liquid, and finally withiron and silica from said-container.

' jFitL JOURDANI tem of the'container, the cycle above described beingcontinued until the material is completely I

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