DD290862A5 - METHOD FOR THE JOINT PRODUCTION OF SULFUR SULFATE AND MAGNESIUM HYDROXIDE FROM MAGNESIUM SULFATE - Google Patents

Abstract

The invention relates to a production process for sodium sulfate and magnesium hydroxide from magnesium sulfate. The aim and task is to effectively convert a concentrated solution of magnesium sulfate into a concentrated solution of sodium sulfate, producing as a by-product high-purity magnesium hydroxide. According to the invention, the object is achieved by continuously adding equimolar amounts of highly concentrated MgSO4 solution and at least 40% sodium hydroxide solution to a stirred magnesium hydroxide suspension and then separating the suspension by solid-liquid separation into magnesium hydroxide and sodium sulfate solution. magnesium hydroxide; Magnesium sulfate; Production method; Solid-liquid separation; Suspension}

Description

From this hot saturated Na ₂ SO ₄ solution, the dissolved Na ₂ SO _{4 can be} obtained by a salting out process by solid rock salt is dissolved to saturation, whereupon anhydrous sodium sulfate crystallized out.

Another possibility is displacement crystallization with organic water-miscible liquids, such as acetone.

Such a method is previously known from DD WP 87771.

Since this method presupposes the presence of a concentrated Na ₂ SO ₄ solution, acetone precipitation is not a possibility for the Na ₂ SO ₄ recovery from MgSO ₄ , but can be used if a Na ₂ SO ₄ solution is otherwise prepared from MgSO _{4 4 was} produced.

The production of sodium sulfate from magnesium sulfate is in Serowy: "The processing methods of Kalirohsalze", W.-Knapp-Verlag Halle 1952, pp. 128-133 and Matthes-Wehner: "Inorganic-technical process" German publishing house for basic industries, Leipzig 1964 p .345-347.

All processes starting from MgSO ₄ introduce the sodium component as sodium chloride and cause the magnesium to be separated from the sulfate by a crystallization process of Glauber's salt at low temperature and subsequent melting of the Glauber's salt. All previously known production methods adhere to the disadvantages that

1. a multistep polythermal process is required with Glauber's salt as an intermediate,

2. Both cold energy for a freezing process and heat energy for the Glauber's salt melting process are required,

3. the yield of the sulfate is only 65-70%,

4. the yield of sodium is only about 50%,

5. the magnesium component is completely lost,

6. The magnesium must be carried out as worthless magnesium chloride solution of low concentration from the process. The state of the art in the field of Mg hydroxide production is characterized in that MgSO ₄ has hitherto not been considered for Mg (OH) r production, especially not for the production of a particularly high grade product.

Magnesium hydroxide of high purity, which gives a> 99% MgO, can hitherto be produced industrially only from magnesium chloride. A preferred method is therefore the thermal cleavage to an impure MgO (Sprühöstoxid) and its hydration and subsequent calcination according to DD WP 220951 results in a pure hydroxide and oxide with> 99% MgO and <0.4% chlorides, directly in the pulp industry and after briquetting and sintering is used as the highest quality MgO sinter in the refractory industry.

A precipitation process for Mg hydroxide according to DD WP 256505 is previously known, after which MgCl ₂ solution can be reacted with a suitable basic precipitant, such as NaOH-containing bath liquor or Ca (OH) ₂ slurries, in such a way that a well-filtered and washable precipitate results and avoids the known slimy nature of magnesium hydroxide.

The prior art is characterized in that there is no common production process for sodium sulfate and Mg hydroxide, which converts both the Mg component of the raw material MgSO ₄ - and the sulfate component into a useful product.

Nor has hitherto been known a Na ₂ SO ₄ or Mg (OH) ₂ production process which manages without the presence of a salt solution (rejection solution).

Object of the invention

The invention has the aim of eliminating the disadvantages of the previous manufacturing processes for the products sodium sulfate on the one hand and Mg hydroxide on the other hand and to create a common manufacturing process for both products, which is characterized by a high economy, full utilization of Mg and SO ₄ component of the raw material and complete avoidance of a forced attack of repelling solution and a minimum number of process stages.

Presentation of the veson of the invention

The invention is based on the technical object of converting a concentrated magnesium sulphate solution into a concentrated sodium sulphate solution without significant loss of concentration and expenditure of energy, and thereby to produce a usable magnesium compound in the form of high-purity Mg hydroxide as a usable by-product. This problem is solved according to the invention in that the sodium component required for Na ₂ SO ₄ -BiIdUtIg from MgSO ₄ is introduced in contrast to known methods not in the form of sodium chloride, but in the form of concentrated NaOH solution while simultaneously precipitating sparingly soluble magnesium hydroxide. It was surprisingly found that from a concentrated MgSO ₄ solution by suitable choice of the precipitation conditions by the addition of MaOH in equimolar amounts in the form of at least 40% sodium hydroxide solution at precipitation temperature of about 70 to 95 ⁰ C readily filterable Mg hydroxide precipitates and as a byproduct Na ₂ SO ₄ -saturated Na ₂ SO ₄ solution suitable for Na ₂ SO ₄ production by known method suitable Na ₂ SO ₄ solution can be produced. The precipitation conditions according to the invention are, in addition to the use of a very high concentration of both reactants of both the MgSO ₄ solution (> 250 g / l MgSO ₄ ) and the sodium hydroxide solution (> 40% NaOH), the following additional conditions:

- Reaction must be carried out continuously in the almost complete absence of free Mg ²⁺ and free 0H "--ones in a highly concentrated Na ₂ SO ₄ solution whose concentration must be> 200 g / l Na ₂ SO ₄ and in the presence of suspended, solid magnesium hydroxide ,

- The precipitation temperature must be> 7O ⁰ C.

- The precipitation must be carried out continuously in such a way that introduced into the pre-swept Na ₂ SO ₄ ~ solution MgSO ₄ solution tied immediately continuously supplied sodium hydroxide solution and is converted to Mg (OH) _2, where both a OH ~ ions excess and an excess of free Mg ²⁺ ions> 1 g / l must be avoided.

- Another necessary condition is the maintenance of a solids content of Mg (OH) ₂ in the precipitation vessel> 80g / l suspension, which results from the precipitation in this amount by itself.

- The throughput of the two reactants should be limited so that s 25kg Na ₂ SO ₄ per m ³ vessel volume and hour arise. Under these reaction conditions, both a highly concentrated Na ₂ SO ₄ solution as a liquid phase and a readily washable and filterable Mg hydroxide as solid phase, the separation of which is possible easily and without loss of concentration. The inventive method provides in a single reaction step of undiluted at least 40% sodium hydroxide solution and also undiluted MgSO ₄ solution with a MgSO ₄ concentration> 250g / l MgSO ₄ in a single continuous reaction step a precipitation suspension containing both target products and solid by Liquid separation into usable products can be separated.

The liquid phase consisting of a highly concentrated Mg ₂ SO ₄ solution can easily be worked up to give anhydrous sodium sulphate, it being possible to use known processes. The previous complicated and energy-consuming process stages of freeze-crystallization of Na ₂ SO ₄ 10H ₂ O and its subsequent melting are completely eliminated. Likewise, the precipitate Mg hydroxide after washing the adhering liquid phase of the highest quality and, above all, virtually free of chloride.

It has also been found that it is also possible to react commercially available, about 50% sodium hydroxide solution and a cold-saturated MgSO ₄ solution with about 300g / l MgSO ₄ , without the filtration capacity of the precipitate is lost. This results in such a highly concentrated sodium sulfate solution with 300 to 320g / l Na ₂ SO ₄ , as was previously accessible only over the lengthy preparation route via Glauber's salt crystallization and melting of this crystallizate. The concentration of MgSO ₄ determines, in addition to the addition of water with the sodium hydroxide, the Na ₂ SO ₄ concentration of the filling solution and the forming Na ₂ SO ₄ solution can be obtained highly concentrated, if both hc: h concentrated MgSO ₄ solution and highly concentrated Sodium hydroxide solution is used and further addition of water is largely avoided.

Compared to the previous multi-stage and both cold energy and heat of fusion requiring production route for the product sodium sulfate results in a significant simplification, and saving almost all energy previously required. Of importance is also the achievable increase in recycling. Compared to the previous manufacturing process, which has a yield of about 68% for sulfate and a yield of 0% for magnesium, the sulfate yield increases to> 90% and the Mg yield to almost 100%. In addition, eliminates the need for seizure MgCI ₂ -containing process solutions that are to be repelled from the process.

L> apparatus implementation of the method according to the invention is simple. In principle, all types of stirred tanks can be used. The two reactants are continuously added at spatially separated locations of the vessel. The present in the stirred vessel suspension of precipitated magnesium hydroxide and concentrated Mg ₂ SO ₄ solution is thoroughly mixed by a stirrer, thereby achieving the distribution of the reactants in the total volume and the sedimentation of the precipitated product is prevented.

The inventive mixing of the reaction components in the most concentrated form possible without additional dilution before or during the precipitation process provides an already strongly solids-containing hydroxide suspension, which is either in the original form filtrierfähl ^ or with little additional effort by known forms of thickeners before filtration can be further thickened.

Surprisingly, it is possible without difficulty in the process according to the invention to obtain a readily filterable and washable Mg hydroxide. While customary precipitation processes for MgCl ₂ solutions and seawater usually give magnesium hydroxide in forms which are difficult to filter, which sometimes have to be converted into filterable forms with great difficulty in thickening apparatuses and flocculants, it is possible to precipitate the magnesium hydroxide from MgSO ₄ solutions high concentration under the specified conditions flawless to precipitate so good filterable magnesium hydroxide without the addition of other auxiliaries, that when filtering a thick, friable filter cake, which may have up to 2cm thickness, is not thixotropic and only about 28 to 35% water content (in Form adhering Na ₂ SO ₄ solutions) and also aiese good filterability when washing with hot water maintains.

The process according to the invention is based on a concentrated MgSO ₄ solution having MgSO ₄ contents of from 280 to 360 g / l of MgSO ₄ , which is prepared in known manner from the kieserite (MgSO ₄ .H ₂ O) present in potassium salt or from epsom salt ( MgSO ₄ 7 H ₂ O) can take place. Low NaCl contents of <50 g / l NaCl do not disturb the process according to the invention, so that customary MgSO ₄ solutions can be used in the potash industry. As caustic soda, any commercially available highly concentrated NaOH quality can be used.

Because of the intended lowest possible dilution of the Na ₂ SO ₄ reaction solution, as little water as possible should be introduced into the process via the sodium hydroxide solution, which is the case when commercially available 50% strength sodium hydroxide solution is used. As an apparatus continuously operable stirred vessels are used, which work in combination with known types of thickeners and drum or Bandfiltom. The preparation of the target products sodium sulfate from the liquid phase and Mg hydroxide from the solid phase of the precipitation suspension is possible after phase separation according to the respective known methods per se, for example by evaporation. Owing to the high Na ₂ SO ₄ concentration, Na ₂ SO ₄ recovery poses no particular difficulties, and even salting-out methods can be used. On the one hand, in a manner known per se, as in the present production process, this solution can be saturated with solid sodium chloride and the sodium sulfate salted out and recovered.

In this case, a Mg-free NaCl-Na ₂ SO ₄ solution and anhydrous sodium sulfate in solid form. On the other hand, the dissolved sodium sulfate can be salted out by displacement crystallization with acetone in a manner known per se from the reaction solution. High-purity Na ₂ SO ₄ qualities and a particularly high SO ₄ yield can be achieved by this process. After distillative recovery of the acetone leaves the process only small amounts of Na ₂ SO ₄ -containing water. However, this form of Na ₂ SO ₄ extraction requires more effort than salting out with NaCl.

The preparation of pure Mg hydroxide and, based on it, of high-purity MgO is likewise possible by known processes because of the good washability and filterability of the precipitate produced in the process according to the invention. The invention will be explained in more detail by exemplary embodiments.

Embodiment 1 For this figure 1

5m ³ / h MgSO ₄ solution with 320 g / l MgSO _{4 and} 47 g / l NaCl content are mixed with 1.08 t / h NaOH in the form of commercial 50% sodium hydroxide solution in a stirred vessel 1. In the mixing vessel 1 is a saturated Na ₂ SO ₄ solution and submitted Mg-Hydroxld in the form of an intensively mixed suspension at about 85 ⁰ C, which is mixed turhulent by a stirrer. The supplied reaction components are to be fed in continuous stream to separate locations of the reactor. The average residence time of the reaction mixture should be adjusted so that S 25 kg of newly formed Na ₂ SO ₄ / m ³ h are not exceeded. Of crucial importance is the maintenance of the concentration of free Mg ²⁺ and OH ions in the reactor. By continuous sampling and titration of the Mg ^{J +} ion concentration in the liquid phase and adjustment of the supply of reactants is to ensure that the Mg ²⁺ ion concentration is 5 1 g / l, possibly <0.3 g / l, on the other hand, no higher OH The excess of iron is removed from the reactor 1 and fed to a thickener 2 and a belt or drum filter 3. The filter cake consists of 0.78 t of Mg (OH) ₂ and 0 The filtrate from the filter 3 and the thickener 2 overflow are combined to give a sodium sulfate solution in an amount of 6.0 m ³ / h with an average composition of 295 g / l Na ₂ SO ₄ and 43 g / l NaCl , 0.5 to 1.0 g / l MgSO _4. The Mg hydroxide is pure with water by repeated filtration and washing in countercurrent pure and obtained in a conventional manner high purity MgO products whose purity to> 99% MgO The wash filtrate w either in the preparation of the MgSO ₄ solution, used or discarded. In the approximately 60 to 70 ° C hot Na ₂ SO ₄ -Lösun {i are added in a stirred vessel 4 1.6t / h solid rock salt, which dissolve and salt out 1.38 t Na ₂ SO ₄ (thenardite). The crystallized thenardite is separated from the NaCl-saturated solution on a filter and washed chlorine-free in a known manner and dried. The filtrate of the filter 5 with about 300g / l NaCl and 60 to 65% Na ₂ SO ₄ is repelled.

Embodiment 2 For this figure 2

The precipitation of the magnesium hydroxide and its separation from the concentrated Na ₂ SO ₄ solution are carried out according to Example 1. Deviating from this process control, the sodium sulfate solution is stirred with 6t of 93% acetone, wherein the precipitator 6 described in WP 87771 can be used. Crystallize 1650 kg of anhydrous sodium sulfate, which are separated from the solution. The acetone solution containing about 7% of the sodium sulfate in addition to the NaCl and MgSO ₄ from the Na ₂ SO ₄ solution is prepared by distillation in a distillation column 7 by known method and the acetone is recycled to the crystallization process, while the acotonfreie solution with residues on dissolved Na ₂ SO ₄ , NaCl and MgSO ₄ leaves the process.

The inventive method has the advantage that "in a common manufacturing process, both sodium sulfate in the form of concentrated solution and Mg hydroxide in l-orm easily filterable and washable form can be continuously produced and both all precursors of a conventional Na ₂ SO ₄ preparation MgSO ₄ as well as all precursors of Mg (OH) ₂ production, including their energy and apparatus requirements.

Claims (4)

1. A process for the co-production of sodium sulfate and magnesium hydroxide from MagnesiumulfatlöGung and sodium hydroxide solution, characterized in that in a stirred magnesium hydroxide whose liquid phase is a concentrated, at least 200c, Λ Na ₂ SO _4- containing solution and their solid phase precipitated magnesium hydroxide, continuously concentrated equimolar amounts , At least 40% sodium hydroxide solution and highly concentrated MgSO ₄ solution with 250 to 340g / l MgSO _{4 are} reacted at precipitation temperatures of 70 to 95 ° C so that the content of free Mg ²⁺ ions and free OH ~ ions in the solution S 1 g / l and a specific Na ₂ SO ₄ -BiIdU igsrate § 25 kg Na ₂ SO ₄ / m ³ h are maintained, then the Mg (OH) ₂ suspension formed by solid-liquid separation in magnesium hydroxide and Na ₂ SO ₄ -LOsUrIg is separated, followed by the preparation of Mg products by washing the sodium sulfate with water and the production of sodium sulfate done by known methods. 2. The method according to claim 1, characterized in that commercially available 50% sodium hydroxide solution is used as precipitant without further dilution. 3. The method according to claim 1 and 2, characterized in that the recovery of the sodium sulfate is carried out from the separated from the Mg hydroxide solution by Aufsättigen with solid NaCl. 4. The method according to claim 1 and 2, characterized in that the recovery of the sodium sulfate from the separated from the Mg hydroxide solution by addition of acetone by displacement crystallization. For this 2 pages drawings Field of application of the invention The invention relates to a process for the preparation of sodium sulfate and magnesium hydroxide from magnesium sulfate in a common manufacturing process, wherein in addition to the sulfate component and the magnesium component can be obtained as a high-quality useful product and the magnesium sulfate used as raw material is completely recycled material, üurch the inventive method will hitherto necessary complex process steps of Na ₂ SO ₄ production from MgSO ₄ solution Glauber's salt cooling including cooling and Glauber's salt melt process superfluous and the previous high apparatus, electrical energy and heat energy expenditure is eliminated. In addition, by dig utilization of the Mg component to a Nutzprodukt- Mg Hydroxld - both a high-quality cost-bearing coproduct recovered and avoided the previously unavoidable MgCl ₂ -containing conversion solution. The magnesium hydroxide obtained by precipitation from MgSO ₄ after washing the adhering Na ₂ SO ₄ solution and calcination yields a pure, CaO, SiO ₂ and chloride-free about 99% MgO, its use in both the pulp industry and in the Refractory industry to produce a top quality MgO sinter. Characteristic of the known state of the art The production process for sodium sulfate from magnesium sulfate which has remained essentially unchanged for decades is based on the double reaction between MgSO ₄ and NaCl in the aqueous salt system Na, Mg, S (VCI / H ₂ O according to US Pat MgS ₄ + 2NaCl * ± Na ₂ SO ₄ + MgCl ₂ Because of the high solubility of the anhydrous sodium sulfate in water, sodium sulfate does not crystallize out of the solution at ordinary temperature. In order to achieve a reaction in the direction of sodium sulfate, the strongly different solubilities of the sodium sulfate in the form of the anhydrous salt at room temperature and its decahydrate (Glauber's salt) must be exploited at low temperatures, so that a total polythermer process with multiple process stages at different temperatures results. Usually, MgSO ₂ solution obtained primarily from the salt mineral kieserite (MgSO ₄ H ₂ O) is converted into an MgSO ₄ -NaCl solution (so-called caustic soda) by addition of sodium chloride and cooled to 0 to 5 ° C. from this solution Glauber's salt and a MgCl ₂ -NaCl-MgSO ₄ solution (so-called Ε-lye) won. This solution must be repelled from the process after reheating. In addition to the MgCl _{2 formed} , a significant proportion of MgSO ₄ and NaCl are contained in this solution, giving a sulfate loss of 33-35% and a NaCl loss of about 50%. The recovered Glauber's salt is melted after separation from the solution by adding it to a hot Na ₂ SO ₄ solution with continuous heating. This forms solid sodium sulfate (thenardite) and a hot saturated Na ₂ SO ₄ solution (hot melt).