Method for Purification and Concentration of Mgcl2-Brines

Europâisches Patentamt

European Patent Office (H) Publication number: 0 038 381 Office européen des brevets Bl

@ Date of publication of patent spécification: 18.04.84 © IntCl.*: C 01 F 5/30 @ Application number: 80200797.1 @ Date offiling: 22.08.80

(§) Method for purification and concentration of MgCI2-brines.

(30) Priority: 1 8.04.80 NO 801 137 @ Proprietor: NORSK HYDRO A/S 11.06.80 NO 801737 BygdoyAlle2 N-Oslo 2 (NO)

@ Date of publication of application: 28.10.81 Bulletin 81/43 @ Inventor: Groenhof, Hendrik Cornelis Teglverksveien 116 N-1313 Voyenenga (NO) (45) Publication of the grant of the patent: 18.04.84 Bulletin 84/16 @ Representative: Urbanus, Henricus Maria, Ir. et al, c/o Vereenigde Octrooibureaux Nieuwe Parklaan @ Designated Contracting States: 107 DE FR GB IT NL IML-2587 BP 's-Gravenhage (NL)

(56) References cited: DE-C - 676 406 DE - C - 1 667 826 DE-C-2513947 DE-C-2613289 US - A - 2 479 001 00 US - A - 3 642 455 <0 US - A - 3 690 844 00 C9 o o Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall Q. be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. Background of the invention According to DE-PS 2613289 a highly con- Field of the invention centrated magnesium chloride solution can be The invention relates to a method for produc- obtained from dilute solutions by evaporation to ing purified and concentrated MgCl2-brine by 440-475 g/I magnesium chloride, separation evaporation and crystallization from brines con- of carnallite and sodium chloride, debromina- taining MgCl2, KCI, NaCI and MgS04. tion with chlorine, subsequent precipitation of sulphates by means of a lime- or dolomite sus- Description of the prior art pension, separation of the precipitate, followed Different methods for purification and con- by crystallization of a mixture of carnallite/- centration of magnesium containing brines are sodium chloride by cooling. It is claimed that the known from the patent literature. Large quanti- formation of sulphate containing double salts, ties of such brines are obtained as a by-product which would lead to loss of potassium values, is from the production of potassium chloride, prevented by this method. potassium sulphate and sodium chloride. Such In DE-PS 2513947 on the other hand the brines can be purified and concentrated in dif- formation of sulphate containing langbeinite is ferent ways in order to obtain a highly concen- desired. After evaporation of the solution the trated MgCl2 brine, with a low content of KCI, crystallization of langbeinite is promoted by NaCI and MgS04, which is suitable as a raw nucleation by addition of langbeinite crystals. material for the production of magnesium metal After further evaporation and subsequent or magnesium oxide. cooling crystallization carnallite is separated DE-PS 676406 shows how solutions with from the product brine and contacted with the less than 320 g/I magnesium chloride can be crude brine for decomposition. The sulphate evaporated until saturation with carnallite is salts are converted to potassium sulphate. reached. The sodium chloride-kieserite mixture which crystallizes due to evaporation is then Summary of the present invention separated, the hot brine is cooled and the The present invention involves recirculation carnallite which crystallizes due to cooling is of carnallite and part of the final product brine in separated from the product brine. However, the the process of purification and concentration of solutions obtained in this manner still contain MgCl2-brines. The improvement of the method about 1% potassium- and sodium chloride and of the present invention results from recyling of considerable quantities of magnesium sulphate. part of the final product brine to an evaporation The sulphate ions have to be removed by pre- step which is followed by a cooling crystalliza- cipitation with lime. After further evaporation tion step. additional mixtures of carnallite and kieserite It is therefore an object of the invention to have to be separated from the brine at tem- produce a concentrated magnesium chloride peratures up to 130°C, before a concentrated brine of a sufficient purity by a very simple brine of sufficient purity is obtained by cooling process for purification and concentration of and separation of a crystalline carnallite/- MgCl2-brines comprising only one evaporation sodium chloride mixture. step and without any addition of chemicals. In DE-PS 1667826 it is proposed to con- It is a further object of the present invention centrate magnesium chloride brines containing to produce a product brine of high purity with a sulphates by evaporation under vacuum at tem- low content of MgS04. peratures of 60-90°C, and subsequent It is still a further object of the present inven- heating of the solution at atmospheric or slightly tion to provide a method for purification and elevated pressure to 108-130°C, followed by concentration of MgC12-brines characterized by isothermal removal of the sulphate compound low potassium losses. No potassium containing and cooling of the solution obtained to 25°C. double salts, such as langbeinite or carnallite, The solution is then concentrated to 50 are formed in the evaporation step. weight % magnesium chloride hexahydrate by The foregoing and other objects of the vacuum evaporation at 60-90°C. After present invention will be described more fully in cooling crystalline Bischofite is obtained. the following more detailed description. From DOS 2613288 it is known that a highly concentrated magnesium chloride solution can Brief description of the drawings be obtained after debromination with chlorine, Fig. 1 is a schematic flow-sheet of the sulphate precipitation with calcium chloride, present method. increasing the magnesium chloride content to Fig. 2 shows a variant flow-sheet of the 270-330 g/I by carnallite decomposition, and method shown in Fig. 1. subsequent concentration by evaporation and cooling to ambient temperature, resulting in the Description of the preferred embodiments crystalization of carnallite. The solution which is The improvement in accordance with the obtained after removal of the crystals is the method of the present invention involves the required concentrated brine product. steps of: 1. Decomposition of carnallite in crude The slurry should be kept near its boiling brine, followed by filtration of a NaCI/KCI crystal point for several hours in order to secure the mixture. lowest possible MgS04 content in the brine 2. Mixing of recycled product brine with before filtration (2a). After filtration the kieserite brine from step 1, evaporation of the resulting by-product (C) can be utilized in the production brine and subsequent separation of a mixture of of potassium sulphate by means of known tech- kieserite and sodium chloride crystals. niques. 3. Crystallization, separation of carnallite 3. The clarified solution from evaporation and NaCl crystals and recycling of the crystal step 2 is cooled by vacuum cooling, indirect mixture to step 1. cooling, or a combination of these techniques, In case the crude brine is nearly saturated to 20-35°C in crystallization step 3. A sus- with carnallite it may be necessary to feed some pension is formed in this manner, containing water to step 1 in order to avoid saturation with carnallite and some sodium chloride. The carnallite. crystals are separated from the brine by filtra- In one alternative embodiment of the present tion (3a) and recycled to step 1. The highly con- invention only part of the crude brine is used for centrated MgCl2 brine (440-460 g/I) which is decomposition of the recycled carnallite in step obtained is partly recycled to evaporation step 1. This is done by means of a by-pass as shown 2. The main part of the product brine (B) is avail- in Fig. 2-stream A2. able for use as the raw material for the produc- The foregoing characteristic of the improved tion of magnesium products. method of the present invention will be described in more detail by reference to the Example 1 attached drawings, Fig. 1 and Fig. 2, and the Crude brine containing 275 g/I MgCl2, 23 g/I examples which are presented below. MgSO4, 54 g/l KCl, 35 g/l NaCl and impurities 1. A brine (A) containing magnesium has been concentrated and purified in accord- chloride, sodium chloride, potassium chloride ance with the present invention. and magnesium sulphate is mixed with a mixture of carnallite (MgCl2 . KCl . 6H2O) and Step 1 sodium chloride crystals from cooling step 3. Feed rate: 470 l/h of crude brine The carnallite is decomposed. The temperature Addition of 65 kg/h carnallite (MgCl2 . KCl of the suspension in this decomposition step 1 . 6 H2O) and 6 kg/h NaCl is kept in the range of 20 to 55°C. Normally it Decomposition temperature: 35°C will be advantageous to carry out the decom- After decomposition the slurry was cooled to position at a temperature in the range of 35 to 25°C. 55°C and then cool to 20-30°C in order to establish a low KCI concentration in the brine Brine composition: prior to filtration. The magnesium chloride concentration in the brine after carnallite decomposition should be less than 310-325 g/I, dependent on the temperature. The crystal mass in suspension, which is a mixture of potassium and sodium chloride (D), is separated from the brine in a filtration Crystal mixture separated from the brine: step 1 a and can then be converted to a com- mercial potassium chloride grade by means of known techniques. Step 2 2. Brine from step 1 is mixed with recycled Addition of 140 I/h of product brine. product brine in evaporation step 2 in order to achieve a favourable composition of the result- Brine composition prior to evaporation: ing brine prior to evaporation. The magnesium chloride content increases to 310-380 g/I. The sulphate concentration (MgS04) in the liquid phase is lowered due to mixing with product brine. By means of this recycle the formation of potassium sulphate or -chloride containing Evaporation at a temperature of 130°C. double salts during evaporation can be prevented. Brine comoosition: The resulting brine is concentrated to 430- 460 g/I by evaporation at a final temperature in the range of 125 to 135°C at approximately 1 bara. The evaporation is conducted in a manner known per se., e.g. multiple effect evaporation. Sodium chloride and kieserite crystals are Crystal mixture separated from the brine: formed. The evaporation is terminated before saturation with carnallite is reached. Step 3 Step 3 Brine from step 2 was subjected to: The brine from step 2 was subjected to: 1) Cooling under vacuum down to 80°C, and 1) Cooling under vacuum to 75°C, and 2) Indirect cooling to 25°C. 2) Indirect cooling to 30°C. Brine composition (B): Brine composition (B):

A mixture of carnallite and NaCI was filtered A mixture of carnallite and NaCI filtered off, washed and recycled to 1. Part of the was step off and recyled to step 1. Part of the product product brine was recycled to step 2. brine was recycled to step 2. Example 2 During this test run in the pilot plant only a of the crude brine part was used for the decom- 1. A method of and of the carnallite purifying concentrating a position recycled (Fig. 2). crude chloride brine Feed rate: 460 I/h of crude brine magnesium containing a also containing magnesium sulphate, potassium chloride and sodium chloride, which Crude brine composition (A): method comprises the steps of:

(1) mixing crude magnesium chloride containing brine with carnallite and sodium chloride from step (3) below and decomposing the Step 1 carnallite, Addition of 110 kg/h of a filter cake contain- (1a) separating crystals of potassium chloride ing 72 wt.% carnallite and 4,5 wt.% NaCI to and sodium chloride from the brine, 360 I/h of the crude brine. The decomposition (2) adding to the brine a quantity of purified and concentrated temperature was 45°C. After decomposiiton magnesium chloride contain- the slurry was cooled to 27°C. ing brine from step (3) below and evaporat- ing the brine to cause sodium chloride and Brine composition after cooling: kieserite crystals to form, (2a) separating the sodium chloride and kieserite crystals from the brine, (3) cooling the remaining solution to cause sodium chloride and carnallite crystals to form, Crystal mixture separated from the brine: (3a) separating the sodium chloride and carnallite crystals from the solution and recycling them to step (1) above and feeding part of the purified and concentrated magnesium chloride Step 2 containing brine product to step (2) Addition of 120 I/h of product brine (B) to the above. mixture of brine from step 1 (A 1) and by- passed crude brine (A 2). 2. The method of claim 1, wherein the said decomposition of recycled carnallite takes Brine composition prior to evaporation: place in a decomposition step (1), into which all the crude brine (A) is introduced. 3. The method of claim 1, wherein the decomposition of recycled carnallite takes place in a decomposition step (1) in part of the crude brine (A1), the remaining crude brine by-passing at of 129°C. Evaporation a temperature step (1). 4. The method of claim 2, wherein the said Brine composition: decomposition of carnallite takes place at a temperature in the range of 20 to 55°C. 5. The method of claim 3, wherein the said decomposition of carnallite takes place at a temperature in the range of 20 to 55°C and the Crvstal mixture separated from the brine: decomposition is conducted to obtain an increase of the MgCl2 concentration of the brine to 310-325 g/I. saumure brute contenant du chlorure de mag- nésium et contenant également du sulfate de 1. Verfahren zum Reinigen und Konzent- magnésium, de chlorure de potassium et du rieren einer rohen Magnesiumchlorid enthalt- chlorure de sodium, ce procédé comprenant les enden Sole mit zusätzlichem Gehalt an Mag- étapes consistant à: nesiumsulfat, Kaliumchlorid und Natrium- chlorid, mit folgenden Verfahrensstufen: (1) mélanger de la saumure brute, contenant du chlorure de magnésium, avec de la carnal- (1) Mischen von roher magnesiumchloridhal- lite et du chlorure de sodium provenant de tiger Sole mit Carnallit und Natriumchlorid l'étape (3) ci-après et décomposer la carnal- aus der unten folgenden Stufe (3) und Zer- lite; setzung des Carnallits, (1 a) séparer de la saumure les cristaux de (1 a) Abtrennen der Kaliumchlorid- und Natrium- chlorure de potasium et de chlorure de chloridkristalle aus der Sole, sodium; (2) Zugabe einer Menge der gereinigten und (2) ajouter à la saumure une quantité de konzentrierten magnesiumchloridhaltigen saumure purifiée et concentrée, contenant du Sole aus der unten folgenden Stufe (3) zu der chlorure de magnésium, provenant de l'étape Sole und Verdampfung der Sole, um die Bild- (3) ci-après et évaporer la saumure pour por- ung von Natriumchlorid- und Kieseritkri- voquer la formation de cristaux de chlorure de stallen zu bewirken, sodium et de kiésérite; (2a) Abtrennen der Natriumchlorid- und Kie- (2a) séparer les cristaux de chlorure de sodium seritkristalle von der Sole, et de kiésérite de la saumure; (3) Abkühlen der verbleibenden Lösung, um die (3) refroidir la solution restante pour provoquer Bildung von Natriumchlorid- und Carnallitkri- la formation de cristaux de chlorure de stallen zu bewirken, sodium et de carnallite; (3a) Abtrennen der Natriumchlorid- und Car- (3a) séparer de la solution les cristaux de nalliktristalle aus der Lösung und deren Rück- chlorure de sodium et de carnallite et les führung in die obige Stufe (1) und Zugabe recycler vers l'étape (1) ci-dessus et intro- eines Teils des gereinigten und konzentrier- duite une partie de la saumure purifiée et ten magnesiumchloridhaltigen Soleprodukts concentrée, contenant du chlorure de sodium in obige Stufe (2). et constituant du produit, dans l'étape (2) ci- dessus. 2. Verfahren nach Anspruch 1, bei dem die 2. Procédé selon la revendication 1, dans Zersetzung von rückgeführtem Carnallit in einer lequel la dite décomposition de la carnillite Zersetzungsstufe (1) stattfindet, in die die ge- recyclée se produit dans une étape (1) de samte Rohsole (A) eingeführt wird. décomposition dans laquelle on introduit la 3. Verfahren nach Anspruch 1, bei dem die totalité de la saumure brute (A). Zersetzung des rückgeführten Carnallits in einer 3. Procédé selon la revendication 1, dans Zersetzungsstufe (1) in einem Teil der Rohsole lequel la décomposition de la carnillite recyclée (A1) stattfindet, wobei die verbleibende Roh- se produit dans une étape de décomposition (1) sole an der Stufe (1) vorbeigeführt wird. réalisée sur une partie de la saumure brute (A1 ), 4. Verfahren nach Anspruch 2, bei dem die le reste de la saumure brute contournant l'étape Zersetzung von Carnallit bei einer Temperatur (1 ); im Bereich von 20 bis 55°C stattfindet. 4. Procédé selon la revendication 2, dans 5. Verfahren nach Anspruch 3, bei dem die lequel ladite décomposition de la carnallite se Zersetzung des Carnallits bei einer Temperatur produit à une température comprise entre 20 et in inem Bereich von 20 bis 55°C stattfindet und 55°C. die Zersetzung derart geführt wird, daß ein An- 5. Procédé selon la revendication 3, dans stieg der MgCl2-Konzentration der Sole auf 310 lequel ladite décomposition de la carnallite se bis 325 g/I erhalten wird. produit à une température comprise entre 20 et 55°C et l'on conduit la décomposition de façon à obtenir une augmentation, jusqu'à 310 à 325 g/I, de la concentration de la saumure en MgCl2. 1. Procédé pour purifier et concentrer une