FR2686524A1 - METHOD FOR THE EVAPORATION REDUCTION OF AQUEOUS SALT SOLUTION OR SUSPENSION, CONCENTRATED. - Google Patents

Abstract

a) Process for the reduction by evaporation of a concentrated aqueous saline solution or suspension. b) A process characterized in that borax is added to the solution or suspension before reduction by vaporization, in that the borax is added in an amount of 5 to 30 g per liter of solution or suspension.

Description

"Process for the evaporation reduction of a solution

  The invention relates to a process for the boiling reduction of a solution or a concentrated salt-water suspension. The term "evaporative reduction" is intended to mean the expulsion of water from the solution or

  suspension at elevated temperature until

  Crystalline paste or dry product Under reduced pressure the reduction by boiling can be done at

  a temperature reduced accordingly.

  In the laboratory and in the technical field there is often the problem of reducing by boiling

  aqueous solutions or suspensions, concentrated salt

Trees.

  In G Jander, E Blasius, a teaching book

  Analytical Chemistry and Mineral Preparations, Sixth Edition, S Hirzel Stuttgart (1966), the general basis of work on page 72 indicates the possible dangers in boiling concentration: particular is desired when reducing by boiling if a solid body separates furthermore it

  a violent projection occurs easily ".

  The projection in the last phase of the

  chage, that is to say during the passage of the solution

  line concentrated in the crystalline paste or in the product

  dry, is not only a risk for the

  but also causes significant deposits and encrustations in the upper part of the container.

  boiling point and possibly in

  exhaust or suction circuits

  which can lead to the clogging of these natural

  Projection is extremely undesirable, especially in the case of solutions or suspensions, toxic solutions or waste radioactive salts, because then there is the danger of contamination. Various tests have been made, to put under control the projection during the reduction by

  boiling solutions or suspensions while stirring

  tinually, using mechanical separators, baffles or others or by adding surfactants These tests only knew a result

  The continuous agitation requires an expenditure of

  importance, especially if we have to

  to work under partial vacuum Baffles cause a

  insufficient precipitation of droplets

  The effect of surfactants is only

limited.

  The object of the invention is to prevent or at least greatly reduce the projection during reduction by boiling or drying solutions or

  concentrated salt water suspensions, without

  be mechanically acting elements.

  The object is achieved according to the invention in that it is added to the solution or suspension, before the

  concentration by evaporation, from borax to

  from 5 to 30 g per liter of solution or suspension.

  Advantageous embodiments of the method according to the invention are characterized in that

  vaporization reduction is carried out at a time

  between 70 and 1500 C, preferably at

800 C and about 200 m / bar.

  According to another characteristic of the invention, the vaporization reduction is carried out at

reduced pressure.

  According to another characteristic of the in-

  the solution or suspension contains

radioactive salts.

  According to another characteristic of the in-

  vention, the reduction by vaporization is carried out

  in containers suitable for permanent storage.

  According to another characteristic of the in-

  the use of cast iron containers.

  Projection during vapor reduction

  drying or drying of solutions or suspensions

  to be considerably reduced by borax

  The evaporation and drying are carried out with the addition of borax at a temperature of between 700 ° C. and 150 ° C. It is particularly preferred to work below the temperature of 1000 ° C. and to maintain

  the solution or suspension in partial vacuum We consider

  re particularly favorable to carry out the

  vaporization at about 800 ° C and about 200 mbar. Borax should preferably be added in an amount of at least 5 g per liter or even more preferably 7.5 to 10 g per liter of solution or suspension to be used. Quantities greater than 30 g / l are

more often useless.

  The calculated amount of borax can also

  in charge operation

  continuous implementation, be put in place before the start

  concentration in the spray container.

  It is also possible to add borax to the

  lution or suspension already in the storage tank

age or reserve.

  If the solution or suspension contains radioactive salt waste, then the vaporization concentration is preferably carried out in containers supporting the final storage or in

  Shielded containers, may be cast iron.

  The action of borax during spray reduction of solutions or suspensions may not be fully understood.

  release of water of crystallization during the vaporization

tion plays a decisive role.

  From the Gmelin manual, 8 th edition, volume 28, part 7 (1975) pages 126132, it appears that during the

  keeping the temperature of an aqueous solution of

  At about 800 ° C. highly hygroscopic tincalconite occurs. Na 2 1B 405 (OH) 41-8H 2 O -> Na 2 1B 405 (OH) 4 J 3 H 20 + 5H 20 Borax Tincalconite chains of octahedra chains deformed, regularly arranged metastable, very hygroscopic

  The intermediate product may be

  very hygroscopic calconite binds water temporarily

  released in the last phase of the reduction by

  porisation or drying, that is to say during the passage

  concentrated solution or suspension of crystalline

  This mechanism could explain the significant reduction of the spurt as soon as the addition of small amounts

  from borax to the concentrated solution or suspension.

  An essential advantage of the process according to

  tion is that we can give up largely or completely constructive measures on the

  device to be used, measures intended to prevent

  expensive spray during concentration by vaporization Borax is a cheap chemical

  and nontoxic and it already acts in small amounts.

  The conduct of the process during the vapor reduction

  The upper part of the spray vessel and possibly the exhaust or suction

  connect are at least largely free of

warehouses.

  Other advantages of the process according to the invention

  exist when solutions-or suspensions

  aqueous, concentrated, saline

  radioactive waste Such solutions so far have been put into a solid form by magnetization, considerably increasing the volume But as in many countries, for example in Germany, there is no available immediate disposal, the cement packages had to be stored

  provisional for an indefinite time The need for

  space for intermediate and final storage can be

  significantly reduced if vapor reduction is

  Such waste solutions are carried out in shielded containers suitable for final storage, for example cast iron and if the dry residue is deposited in these containers. In the process according to the invention, the dry product remains in the spray reduction vessel. and is not transported in other

  parts of installation by spray droplets

  tion. The invention will be described in detail in

  following from examples of embodiment.

  Trials were carried out with two

  which corresponded to the composition of solu-

  concentrations of concentrated radioactive waste of medium activity (MAWC, Medium Active Waste Concentrate)

  solutions contained as the main component of the

  sodium, and besides that aluminum nitrates

  minium, calcium, magnesium, iron, tin, or other

  organic complexing agents such as EDTA, tartrates

  tributylphosphate, dibutylphosphate and kerosene. The proportion of dissolved salts amounted in one case to approximately 350 g / l,

  in the other case at about 130 g / l.

  The device used consisted essentially of

  of a closed vessel of 1.5 liters of capacity, of a collecting tank in which

  the solutions were adjusted to a p H of 9 and melange

  borax and exhaust gas section

with a vacuum pump in circuit.

  The spraying vessel was heated by an immersion bath The temperature of the solution or suspension or dried product was determined

  in the spray container by means of thermocou-

  ples. Spraying tests were carried out

  at about 80 ° C and at a pressure of about 200 mbar.

  The dried product was then warmed to about

1500 C.

  Without adding borax the projection in the

  last phase of drying during the suspension

  Concentrated crystalline paste or dry product was so strong that deposits occurred in the exhaust gas section. In addition it was of no importance to predispose the entire solution in the vaporizer vessel or to introduce the

  solution continuously in the container.

  A concentration of 5 g / l of borax in the solution used already reduced the projection very strongly during vaporization reduction. From borax additions of 7.5 g / 1 the projection was extremely low.

  place in the exhaust section of the

  test by adding borax to the solution.

Claims (4)

R E V E N D I C A T IO N S   1) Method for reducing by vaporization   an aqueous salt solution or suspension, concentrated   characterized in that borax is added to the solution or suspension prior to vapor reduction.   The process according to claim 1, wherein   in that the borax is added in a quantity   from 5 to 30 g per liter of solution or suspension.   30) Method according to claims 1 or 2,   characterized in that the vaporization reduction is carried out at a temperature of between 70 and 1500 C, preferably at 800 C and approximately at a pressure of of 200 m / bars.   40. The method of claim 3, wherein   in that the vaporization reduction is carried out alised at reduced pressure.   Method according to one of claims 1   at 4, characterized in that the solution or suspension   contains waste radioactive salts.   Process according to claim 5, characterized   in that the vaporization reduction is carried out   in containers suitable for permanent storage. tif.   70. The method of claim 6, wherein   in use by using cast iron containers.