FR2721535A1 - Method and device for purifying sodium chloride. - Google Patents

Abstract

By the combination of leaching and flotation, using a wide variety of processing solutions, high-value NaCl having a purity of over 99% is prepared. The purification process is carried out in a conical reaction vessel (1) which is provided with a draw-off tube (2) of variable height, vertical. This withdrawal tube (2) is used at the same time for the preparation of the product, the classification and the flotation, while the leaching operation and the stilling zone for the separation of impurities are assigned to the main reaction vessel (1) .

Description

! Method and device for purifying sodium chloride The present

  The invention relates to a method and a device for purifying sodium chloride. The purification process according to the invention and the

  device according to the invention are also suitable for the purification of natural products as well as residual substances appearing during the treatment of crude potassium salts.

  Of the amount of raw salt prepared in Germany from potash deposits, only around 25% is used for the preparation of potassium and magnesium products. The remainder, mainly sodium chloride, is separated electrostatically, by flotation or by hot dissolving, and must either be used as backfill in deposits, or deposited in surface stocks. Residues outcropping the heap consist of approximately 90% sodium chloride. The remainder consists of potassium chloride, calcium sulfate, magnesium sulfate, clay minerals and various double salts of the Na +, K +, Mg2 +, Ca2 +, Cl- and SO42- ions. Treatment of these residues to obtain industrial salt has the effect of not only reducing the environmental loads from storage, but also

  also to conserve resources and, as this salt is already brought to light anyway, to save energy.

  According to the state of the art, there is already a whole series of proposals for purifying the rock salt obtained by miners, or the residues of rock salt are

forming during the operation.

  The preparation of sodium chloride during which it is first completely dissolved and then recrystallized by evaporation, involves a high expenditure of energy and is expensive (see Ullmann's Enzyklopâdie der Technischen Chemie, 4th revised and enlarged edition, Verlag Chemie, Weinheim , New York 1979, Vol. 18, p. 179 et seq.). In addition, sulfated and clay minerals can be separated by direct or indirect flotation,

  but this generally only leads to modest success.

  A partial solution is provided for example by DE 40 25 371, in which, after electrostatic treatment, an average fraction obtained by sieving is suspended in a solution of NaCl, and the solid impurities are separated by flotation with the addition of a flotation agent.20 Simple washing processes do move the adherent detergents, which lower the quality but only lead to limited increases in quality. On the other hand, an improvement can be obtained by leaching. According to DE 28 11 889, a mineral acid is added to the washing solution and the mixture is stirred for several hours. However, the efficiency of this process is limited and requires the neutralization of residual solutions. In patent DD 290 405, a leaching process for the purification of sodium chloride is recommended, in which the salt is leached in brine of pure NaCl free of hardness agents. In a potash workshop, there is usually no pure NaCl brine available, so it must be freshly prepared. This leads to a clear overload35 of the laundry budget in the corresponding workshops, which in many cases can only be managed with difficulty. In addition, for the preparation of pure brine, as long as there is no sodium chloride of adequate cleanliness, part of the purified product

  must be separated and is therefore lost for yield.

  The object of the invention is to prepare, by a combination of leaching and flotation, in a process

  simple purification and using a wide range of treatment solutions, a high value NaCl having a purity greater than 99% NaCl.

  As starting material, it is possible to use, in addition to rock salt, lower quality residues from the potash industry, such as they occur for example in electrostatic separation, flotation15 and hot dissolution of salts. crude potassium. In the case of using the process, it is advantageous to be able to use as a treatment solution a detergent already present in the workshop. For example, it is formed in various operations of covering solutions which2) are saturated with sodium chloride, but which still have a sufficient dissolving capacity for potassium chloride, magnesium chloride and magnesium sulfate, and even for calcium sulfate. The invention provides the possibility of using these recovery solutions as treatment solutions by combination of selective dissolution and pneumatic flotation. In addition, selective dissolution is accelerated by controlled disintegration (disintegration) of the sodium chloride matrix. Consequently, this partial operation will be designated in what follows under the name of "active leaching". The two partial operations, leaching and flotation, are carried out simultaneously

in the same device.

  The process according to the invention combines in particular the following characteristics: - Mixing of kneaded muddy water, added with a flotation agent, with an excess of several times of recycled solution. - Rapid introduction of this muddy water into the annular space at the foot of a conical container, without agitator, which is provided with a vertically movable central tube. - Dissolution and disintegration of the coarsest parts per stay in the lower part of the

conical container.

  - Ascent of medium and finer particles in the turbulent zone in the middle part of the

container.

  - Clarification, i.e. separation of the solid substance from the solution in the upper part of the conical container and exit from the solution clarified by

a withdrawal tube.

  - Descent of the pre-purified particles into the vertical inner tube, from which finely divided air bubbles rise which adhere to the grains of anhydrite or kieserite, and entrain them upwards, where they

  are removed with a layer of foam.

  - Extraction of the purified grains at the lower end of the vertical inner tube, a small part of the recycled solution entering this place and rising

  opposite direction of the descending particles.

  It is advantageous to heat the recycled solution drawn off by the drawing-off tube (upper) using a heat exchanger and to divide it, so that most of it enters the bottom of the conical container in the annular space and a small part of it enters the inner tube.35 Preferably:

2721535

  - the recycling solution used for treatment in the reaction space has a KCl content

  less than 30 g / l, an MgS04 content less than 50 g / 1 and a CaS04 content less than 2 g / l.

  - the recycling solution used for treatment in the reaction space has a concentration below saturation with regard to NaCl, which can allow a dissolution rate of the treated grains up to 40% .10 - used as an agent flotation of fatty acids and sulfated or sulfonated fatty acids, supplemented as necessary by agents promoting adhesion. The invention also relates to a device in which a conical reaction vessel without agitator is provided with a vertical product withdrawal tube, which has a variable height by means of extensions and is introduced into the flotation air stream, and that the reaction vessel is connected, by a circuit which is assigned to it to support the bed of solid substance and for the withdrawal of the solution from the reaction vessel, with a heat exchanger assigned to it and with the

  mixing container by the pipes and for the introduction of the mixture to be purified and with the withdrawal tube by a pipe for the classification of the grains in the product withdrawal tube.

  The device according to the invention consists of a conical container 1 at the tip of which is incorporated a product elimination tube 2 adjustable in height. The crude crystallization product kneaded with the treatment solution 7 and 13 is introduced at the conical end of the apparatus by a pump 4, coming from the

  mixing 9. An internal circulation current 4 has the function of keeping the raw material to be purified in suspension in a fluidized bed.

  The crude crystallization product to be purified is generally a heterogeneous mixture as regards the particle size. It has been observed that the impurities are distributed to a greater extent between the coarsest and finest fractions. In the purification operation, we must therefore take care that the

  coarser grains require a longer residence time than medium grain fractions. The fine fractions, which have a higher specific surface area, should if possible be disaggregated.

  In accordance with the invention, this is obtained by an internal classification. The coarsest grains are retained longer in the machine due to their higher falling speed. A partial stream separating from the circulation stream 4 is sent from below into the product elimination tube 2, whereby the finest particles are again brought back to a large extent in the floating bed. Air 3 is also introduced into the product withdrawal tube 2, which therefore also serves as a flotation domain. Insoluble and insoluble impurities

  19, separated by flotation, are discharged at the upper end of the reaction vessel.

  The device according to the invention is subdivided into three areas: - a floating bed, in which the leached raw material and the soluble impurities are separated, - a flotation and classification space, in which the alkaline earth sulfates and the constituents insolubles are eliminated, and the finest grain is returned to the main reactor, - and a tranquilization zone in the upper part of the reactor, which allows better

  separation of the flotation concentrate.

  As the treatment solution, all the sodium chloride solutions which still have a dissolving capacity for potassium chloride and magnesium sulphate can be used. It has been found that the execution of the process according to the invention takes place in a more satisfactory manner when the treatment solution is at a concentration slightly lower than saturation with regard to sodium chloride. This promotes the disintegration of impurities and accelerates leaching due to the partial disintegration of the coarsest grains. For this purpose, it is possible to add to the water treatment solution 11. In order to obtain efficient leaching and a short residence time, the hot purification process is carried out,

preferably at 30 to 80 C.

  In the examples, the invention will be explained in more detail. As a flotation agent,

  each time the Praestabitôl HSO W 46453 from Stockhausen in the form of a 1% solution. The addition of the flotation agent was carried out continuously in the mixing vessel 9.

EXAMPLE 1

  In Example 1, the device according to the invention was supplied with approximately 0.5 kg / h of a crude NaCl having the following composition: NaCl 94.1% KCl 1.9% MgSO4-H20 2.5 % CaSO4 1.5% and with about 0.5 l / h of pure NaCl brine. The

  two constituents were introduced continuously. The purification operation was carried out at approximately 60 ° C., the dissolution rate being approximately 10%.

  Quantity of flotation agent: 100

  The product was received at the lower end of the product disposal tube, it was filtered and dried.

  The following final quality was thus obtained: 5 NaCl 99, 5% KCl 0.2% MgSO4-H2O 0.2% CaSO4 0.06%

EXAMPLE 2

  In Example 2, approximately 5 kg / h of crude NaCl having the following composition was continuously introduced into a larger device: NaCl 92.3% KCl 2.8% MgSO4-H2O 3.0 % CaSO4 1.9% and approximately 15 1 / h of a treatment solution having the following composition: 20 NaCl 313 g / 1 KCl 11i g / 1 MgSO4-H2O 5 g / l CaSO4 2 g / l Quantity of agent flotation: 200 The purification was carried out at 50 to 60 ° C. with a dissolution rate of approximately 10%. The filtered and dried product had the following composition: NaCl 99.6% KCl 0.1% MgSO4-H20 0.03% CaSO4 0.3%

EXAMPLE 3

  In this example, approximately kg / h of a raw material having the following composition was introduced again: NaCl 92.4% KCl 2.6% MgSO4-H2O 3.1% CaSO4 1.9% and approximately 15 1 / h of the following treatment solution: NaCl 294 g / l KCl 23 g / l MgSO4-H20 42 g / l CaS04 2 g / l Quantity of flotation agent: 200

  The purification was carried out here again at 50-

  60 C, but with a dissolution rate of around 20%. The following product was thus obtained: NaCl 99.2% KCl 0.1% MgSO4-H20 0.05% CaS04 0.6%

Claims (7)

  1. Process for carrying out an additional concentration of a salt already present at a high percentage, which still contains impurities in soluble and insoluble form, the fragmented salt below a particle size of 1 mm being brought into contact with a solution of concentration below saturation, a flotation agent and finely divided air, characterized by the combination of the following characteristics: - Mixture of kneaded muddy water, added with a flotation agent, with an excess of several times of recycled solution.   - Rapid introduction of this muddy water into the annular space at the foot of a conical container, without agitator, which is provided with a vertically movable central tube. - Dissolution and disintegration of the coarsest parts per stay in the lower part of the conical container.   - Ascent of medium and finer particles in the turbulent zone in the middle part of the container. - Clarification, i.e. separation of the solid substance from the solution in the upper part of the conical container and outlet of the solution clarified by a withdrawal tube.   l! - Descent of the pre-purified particles into the vertical inner tube, in which rise the finely divided air bubbles which adhere to the grains of anhydrite or kieserite, and entrain them upwards, where they are eliminated with a layer of foam. - Withdrawal of purified grains at the lower end of the vertical inner tube, a small part of the recycling solution entering this place and rising   in the opposite direction of the descending particles.   2. Method according to claim 1, characterized in that the recycling solution drawn off by the tube   racking is heated using a heat exchanger and subdivided, the main part entering at the foot of the conical container in the annular space and a smaller part entering the inner tube.   3. Method according to claims 1 and 2, characterized in that the recycling solution used   for treatment in the reaction space has a KCl content of less than 30 g / l, an MgSO4 content of less than 20 g / l and a CaSO4 content of less than 2 g / l.   4. Method according to claims 1 to 3, characterized in that the recycling solution used   for treatment in the reaction space has a concentration below saturation with regard to NaCl, which can allow a dissolution rate of the treated grains up to 40%.   5. Method according to claims 1 to 4, characterized in that the temperature in the container   reaction is between 30 and 80 C.30 6. Method according to claims 1 to 5, characterized in that one uses as a flotation agent   fatty acids and sulfated or sulfonated fatty acids, supplemented as necessary by adhesion promoting agents.   7. Device for carrying out the method according to claims 1 to 6, characterized in that a container   conical reaction without agitator (1) is provided with a vertical product withdrawal tube (2), which has a variable height thanks to extensions and is introduced into the flotation air stream (3), and in that the reaction vessel (1) is connected, by a circuit (4) assigned to it to support the bed of solid substance and for the withdrawal of the solution from the reaction vessel (1), with a heat exchanger (5) assigned to it and with the kneading container (9) through the pipes (7) and (15) for the introduction of the mixture to   purify and with the withdrawal tube (2) through a pipe (17) for the classification of the grains in the product withdrawal tube.