DD291066A5 - METHOD FOR THE PRODUCTION OF HIGH-PURITY, FILTRATING MAGNESIUM HYDROXIDE AND CHLORINE - Google Patents

Abstract

The invention relates to a production process of high-purity, filterable magnesium hydroxide and chlorine from magnesium salts by indirect electrolysis. The aim and object of the invention is to produce a suitable alkaline precipitate by electrolytic means and its reaction with magnesium salts to magnesium hydroxide. According to the invention, this object is achieved by electrolytically decomposing a potassium chloride solution into chlorine, hydrogen and caustic soda (KOH-KCl solution), reacting the caustic solution in a loop reactor with concentrated magnesium salt solution and using the resulting potassium salt solution either to form potassium fertilizers or to return it to the electrolysis . {magnesium hydroxide; Chlorine; Electrolysis; Potassium chloride; Loop reactor; Magnesium salts; Baederlauge}

Description

For this 3 pages drawings

Field of application of the invention

The invention relates to a process for the production of magnesium hydroxide and chlorine from magnesium salts by indirect electrolysis while avoiding the precipitation processes occurring in the direct electrolysis of magnesium chloride solution in the diaphragm electrolysis cells. The resulting magnesium hydroxide is very pure and readily filterable after a washing process. It can be worked up by known calcining and sintering processes to high-quality magnesia quality and sintering. The resulting chlorine has the purity known from chloralkali electrolyses.

Characteristic of the known state of the art

The conversion of magnesium salt solutions into MgO and chlorine has great technical interest, since these can be obtained as by-product of the carnallit production of the potash industry in sufficient quantities and there is a high demand for high-purity MgO grades and chlorine. The direct electrolysis of aqueous magnesium salt solutions was

edited many times. Of technical interest is the direct electrolysis of aqueous, MgClj-containing solutions using separation systems. Diaphragmal cells as described in OE PS 1010954, are not suitable for the production of Mg (OH) ₂ due to high specific electrical energy consumption and contamination of the solid. Methods for electrolysis in cells with diaphragm are described in the patents DE PS 719169, DD WP 60295, DE PS 2060066 and SU PS 48219. The technical implementation of all previously proposed methods failed for the following reasons:

1. There are no reliable large-scale industrial cell designs that would allow the problems associated with the solids in the cathode compartments to be safely controlled.

2. It is not possible reliably to produce pure Mg (OH) ₂ in a readily filterable and thus leachable form. The additions to the electrolyte proposed to improve the filterability of the Mg (OH) ₂ complicate the processes.

3. There are site problems in the coupling of electrolysis plants (at the same time sites of chlorine processing) and potash processing (bound to deposits) in order to be able to economically design the overall process.

Methods for indirect electrolysis with NaOH or NaOH-NaCl baths as an intermediate, as described by the patents DD WP 200737, DD WP 154061 and DD WP 256505, are economically disadvantageous because:

- The processes are energetically very expensive;

- A variety of process stages must be coupled to achieve the process objective position;

- must meet favorable site conditions in order to avoid unwanted waste products.

ZInI the invention

The object of the invention is a process for the production of magnesium hydroxide from magnesium salt solutions by indirect electrolysis, which solves the problems of a direct electrolysis process and avoids the disadvantages of the previously proposed indirect electrochemical processes.

Explanation of the essence of the invention

The object of the invention is the discovery of a solution for the preparation of a suitable alkaline precipitating agent by electrochemical means and its chemical reaction with magnesium salt solutions to a pure, readily filterable magnesium hydroxide and suitable for direct processing alkali metal salt solution. This object is achieved in that a concentrated potassium chloride electrolysed in a known manner in a Diaphragmazelle while initially chlorine, hydrogen and a KCl-KOH bath liquor is recovered, then a reaction of these baths with alkaline chloride magnesium salt solutions from the potash processing to Mg (OH) ₂ takes place and enriched with potassium ions, largely magnesium-free alkali salt solutions are recycled at a suitable point in the potash processing. A Sondorfall the process according to the solution is that from the KOH-KCI bath liquor a purified KOH solution is prepared and that the magnesium salt solutions of purified concentrated MgCl ₂ - or MgSO ₄ solutions exist. It was surprisingly found that both KCl-KOH baths and concentrated pure KOH solutions as they can be prepared by known technology in addition to chlorine and hydrogen (Matthes, Wehner: "Inorganic-technical process", p.409, Verlag für Grundstoffindustrie , Leipzig 1964) with pure concentrated MgCl ₂ or MgSO ₄ solutions as well as with alkali chloride containing MgCl ₂ -MgSO ₄ mixed solutions lower Mg ^ total concentration to a readily filterable leachable magnesium hydroxide implement and that the resulting enriched with potassium ions largely Mg ^{2 +} -free implementation solutions without additional concentration steps can advantageously be integrated into the Kaliverarbeitungsprozeß in many ways the precipitation reaction proceeds at process pulp density in heatable large-volume loop reactors from, the following process and process parameters are adhered to.:

homogeneous mixing of the entire reaction space by means of six-slanted-blade stirrers, which bring about an internal volume flow directed against the container bottom,

pH value in the range from 8.5 to 10.0, measured at the reaction temperature, by controlled metering of one of the two reaction parameters, specific reaction range in the range from 5 to 100 kg Mg (OH) ₂ Mv ¹ reaction space h,

- reaction temperature 65 to 95 ° C.

The resulting suspension of solid Mg (OH) ₂ and the alkali metal salt solution can be thickened in technically relevant times and

filter.

The specific filter kuchon resistance is 1 × 10 ¹⁰ m / kg. The product is thus well filtered on vacuum filters and

dewatered. The further processing of the washed magnesium hydroxide is carried out in a known manner by drying,

Calcining and sintering. Depending on the composition and concentration of the precipitant and the magnesium salt solution are formed in concentration

and composition various conversion solutions that are widely used in the potash processing process. Without restricting the possibilities of use, according to the invention there are the following technologically and economically preferred

uses:

Fällungemittel reaction solution • -3- 291 J66 • Decomposing artificial No. konz.KOH solution pure conc. MgClj solution Umeetzungslöeung Use in the potash process carnallite 1 conc.KCI solution · Blankets of KCI-NaCl vacuum crystals • Reduction of NaCl release divorce at the vacuum • crystallization Blankets of crude potassium sulfate   conc. KOH-solution pure conc. MgSO ₄ solution Use as process water at 2 conc. K ₂ SO ₄ solution · the K ₂ SO ₄ production • as under 1. KOH-KCl baths lye pure conc. MgCl ₂ solution Decomposition of Schönitzu K ₂ SO ₄ 3 KOH-KCl baths lye pure conc. MgSO ₄ solution conc.KCI solution · 4 conc. KCIZK ₂ SO ₄ - · Blankets of KCI-NaCl vacuum KOH-KCl baths lye Shock solution mixed solution crystals 5 salt processing NaO-KO-K ₂ SO ₄ -LUSURI · Reduction of NaCl deposition KOH-KCl baths lye Kalimagnesialösung in the case of the vacuum crystal 6 from the K ₂ SO ₄ production (NaCl) -KCl-KjSO ₄ - sation solution Decomposing artificial KOH-KCl baths lye Push-off solution Car · carnallite 7 nallititverarbei- (NaCl) -KCl-K ₂ SO ₄ - Washing the Carnallitzer tung solution reduction product

In favorable site conditions, the KCI diaphragm electrolysis in cases 1 and 3 can again be charged with the resulting reaction solution. Otherwise, as in all other cases, solid KCl from the potash processing process is supplied to the electrolysis plant.

This provides both direct and indirect linkage of KCI electrolysis plants to Mg (OH) ₂ precipitation plants. Location-related restrictions of the coupling of both processes are eliminated. The entire chain of the material conversion processes is free of waste products, the waste products from the potash processing are reduced or eliminated by the plant.

The invention is explained in more detail by the following exemplary embodiments: Exercise booklet 1 From a concentrated KCl solution containing 375 g / l KCl, in a KCI diaphragm electrolysis plant, chlorine, Hydrogen and 15m ^{3 of} a KCl-KOH bath liquor containing 165g / l KOH produced. The bath liquor is mixed with 4.8m ^{3 of} concentrated MgC! ₂ solution of the composition 435 g / l MgCl ₂ , 1.5 g / l KCl, 3 g / l NaCl, 0.5 g / l CaCl ₂ , 860 g / l H ₂ O reacted. It produces 1.72 t of magnesium hydroxide (filter wet) and 18.2 m ^{3 of} a Reaction solution of the composition 294 g / l KCl, 0.7 g / l NaCl, 0.1 g / l CaCl ₂ , 862 g / l H ₂ O. The magnesium hydroxide

mashed twice with 2 m ^{3 of} water and filtered. The wash solution is combined with the reaction solution and added to the

Covering a KCl-NaCl-containing vacuum crystals used in the potash processing. 18.5t vacuum salt with a content

of 40% K ₂ O (63.3% KCI) and 36% NaC! can be worked up to a salable end-product 60% K, 0 with this 22.2 m ³ topcoat solution.

Exemplary Embodiment 2 For this, FIG. 1 and FIG. 2

In a precipitation reactor 1 are at 80 to 90 ⁰ C1 m ³ bath liquor with 160kg KOH and 165kg KCI continuously reacted with 0.41 m ³ Carnallitzersetzungslauge with 25 kg KCl, 140 kg MgCl ₂ , 11 kg NaCl to the reaction. There are formed 85 kg of Mg (OH) ₂ , which are obtained in readily filterable form, if the conditions mentioned in Example 1 are met. From the KCl content of the introduced bath liquor and from the KCl formed in the reaction, a concentrated KCl solution is formed, which also receives the KCl from the carnallite mother liquor. Overall, a KCl solution with 409 kg KCl and 11 kg NaCl and less than ₂ g / l MgCl ₂ , which leave the reactor as a suspension together with the precipitated hydroxide. In a thickener 2, the Mg hydroxide suspension is thickened. The thickened suspension is dehumidified by a drum filter 3. The magnesium hydroxide is recovered as a filter-wet intermediate with about 38% H ₂ O in the form of adherent KCl solution. The overflow of the thickener 2 and the iltrat of the filter 3 are combined. 1.25m ^{3 of} potassium chloride solution are formed, the concentration of which is about 300 g / l KCl, since some water is introduced during filtration.

This solution is suitable for decomposing carnallite crystal lysate instead of water, wherein the dissolved potassium chloride additionally crystallizes and increases the amount of decomposition KCl obtained. 3,15t Carnallitkristailisat (602 kg KCI, 984kg MgCl _2, 14 kg MgSO _4, 175kg NaCl, 1379kg H ₂ O) and 1.25 m ³ KCl solution (300g / l KCI) in a decomposition reactor 4 under stirring at 55 ⁰ C implemented. A suspension of 2.89 m ^{3 of} decomposition liquor (340 g / l MgCl ₂ , 65 g / l KCl, 27 g / l NaCl, 5 g / l MgSO ₄ , 860 g / l H ₂ O) and 795 kg KCl and 97 kg is formed NaCl as a solid. By thickening by means of a thickener 5 and filtration by means of a drum filter 6, the decomposition crystallizate is separated from the solution. Compared with decomposition with water, the decomposition crystallizate contains a higher KCl content, which substantially facilitates its further processing into high-percentage potassium chloride.

From the decomposition crystals, potassium chloride can be obtained in electrolyte quality in a top reactor 7 with water

which, in turn, gives KOH brine and chlorine by electrolyzing.

The decomposition liquor goes without further purification in the required amount in the precipitation reactor 1, since the KCl content in In contrast to other MgO recovery processes in the process according to the invention does not bother. The rest of Decomposition liquor can be further processed by known method to MgClj products, which is characterized by the low Sulfate content is greatly facilitated. Alternatively, it is possible to decompose only as much carnalite as carnallite replacement liquor for Mg (OH) ₂ precipitation

is needed. In this case, a KCI solution excess is formed by the known method in the covering process of

Potassium chloride production can be used instead of water. The modified process control can be seen in FIG.

Exemplary Embodiment 3 FIG. 3

1000 kg of Epsom salt are dissolved in 1.0 m ^{3 of} water to a 24.5% MgSCv solution. This is reacted with 895 kg of 50% potassium hydroxide solution and K ₂ SO ₄ -containing washing water from the washing stage of the Mg hydroxide in a precipitation reactor 1 continuously at 9O ⁰ C in a Mg (OH) ₂ suspension. The suspension in the precipitation reactor 1 consists of magnesium hydroxide and an approximately 15% potassium sulfate solution. The hot precipitation suspension is clarified in a thickener 2 to 85 to 9O ⁰ C, wherein the main amount of K ₂ SO ₄ solution flows out at the overflow of the thickener 2. The thickened Mg hydroxide suspension is filtered with a belt filter 3 and washed with 2.40 m ^{3 of} water, which takes place by mashing in a stirred vessel 4 and again filtering on a further bandpass filter 5. The washed magnesium hydroxide contains 37 to 41% H ₃ O. The K ₂ SO ₄ -containing wash filtrate is returned to the precipitation reactor 1. The potassium sulfate solution formed by the reaction is reacted with KCl and schoenite by a known method to potassium sulfate fertilizer. The potassium sulfate contained in the solution crystallizes in addition and increases the K ₂ SO ₄ yield of the Schönitumsetzung. If KOH-KCl-containing bath liquor is used instead of 50% potassium hydroxide solution, a K ₂ SO 4 -KCl solution is formed which is likewise usable for the conversion of schistite to potassium sulfate. The contained KCl is also used in the reaction of potassium sulfate formation by reacting with schistite to form K ₂ SO ₄ .

Claims (8)

1. A process for the preparation of high purity, filterable magnesium hydroxide and chlorine from magnesium salt solutions and concentrated potassium chloride solution by indirect electrolysis, characterized in that the Kaliumchloridlösüng in a Diaphragmazelle electrolytically decomposed into chlorine, hydrogen and a bath liquor (KOH-KCl-sol .mg) and this Bath liquor directly or after working up to a pure KOH solution with a stoichiometric amount of magnesium salts in the form of concentrated magnesium salt solutions continuously in loop reactors at a temperature of 65 to 95 ⁰ C within a pH range of 8.5 to 10.0 with a specific conversion rate of 5 to 100 kg of Mg (OH) ₂ per m ^{3 of} reaction space and hour to magnesium hydroxide and a concentrated potassium salt solution is reacted, the Mg (OH) ₂ obtained by thickening, filtration and washing pure and the potash solution used in the potash processing or in the case of KCI Solution in the Ele ktrolyse is recycled. 2. The method according to claim 1, characterized in that the magnesium salt solution is a highly concentrated purified of sulfate MgCl ₂ solution and as an alkaline precipitant a concentrated KOH solution, wherein a reaction solution is formed, fed directly to the process stage brine purification of KCI electrolysis becomes. 3. The method according to claim 1, characterized in that as magnesium salt solution, a highly concentrated MgSO ₄ solution and as an alkaline precipitant a concentrated KOH solution are used, wherein a pure K ₂ SO ₄ solution is formed as the reaction solution, instead of water of reaction in the double conversion of MgSO ₄ and KCl to potassium sulfate, while the KCI electrolyte is made with solid KCl from potash processing. 4. The method according to claim 1, characterized in that as magnesium salt solution, a largely MgSO ₄ -free Carnallitzersetzungslösung and as an alkaline precipitant KCI-KOH bath liquor are used, the resulting weakly NaCl-containing concentrated KCl solution for the decomposition of carnallite and Ceiling of the resulting Carnallitzersetzungsproduktes is used to potassium chloride with electrolytic salt quality, which in turn is used to produce the KCI electrolyte. 5. The method according to claim 1, characterized in that are used as the magnesium salt solution MgSO ₄ - and MgCl ₂ -containing solution of Kalirohsalzverarbeitung and as alkaline precipitating a KOH-KCl-bath liquor, wherein a KCl-NaCl-K ₂ SO ₄ -containing conversion solution arises, which can be used in a variety of ways in the potash processing process instead of water of reaction, wherein the KCI electrolyte with solid KCl from the potash processing is produced. 6. The method according to claim 1 and 5, characterized in that the reaction solution is used instead of water for covering a NaCl KCl crystallizate. 7. The method according to claim 1 and 5, characterized in that the reaction solution is used instead of water or NaCl-unsaturated salt solutions in the vacuum crystallization stage to reduce NaCl crystallization. 8. The method according to claim 1 and 5, characterized in that the reaction solution is used instead of water of reaction in the production of potassium sulfate by the process of the double reaction of MgSO ₄ and KCl.