CS232711B2 - Parting method of ferrous,clayey and manganous impurities from magnesium chloride solution in hydrogen chloride - Google Patents

Abstract

For separating ferrous, aluminous and manganous contaminations from hydrochloric magnesium chloride solutions the ferrous and aluminous contaminations are precipitated together with optionally present silicic acid and boron compounds at a temperature of 60 to 110 DEG C and a pH-value of 3 to 5.2 by gassing the solution with air and/or oxygen and subsequently the precipitation of manganese is carried out at a pH-value of /4,5, bivalent manganese being oxidised, too. After the precipitation step, the deposit is separated.

Description

The present invention relates to a process for separating ferrous, aluminum and manganese impurities from a solution of magnesium chloride in hydrochloric acid.

Methods are known for producing pure magnesium from magnesium-containing minerals such as magnesite, dolomite, serpentine, chlorite, talc and other or industrial intermediates such as flakes from the treatment of these minerals, which consists essentially of the said materials they decompose with hydrochloric acid, resulting in sludges that are weakly acidic due to the hydrochloric acid content. These sludges contain a proportion of the undissolved starting material and solutes, in particular magnesium chloride, iron chloride, aluminum chloride, manganese chloride and dissolved silicic acid.

Neutralization of these sludges after possible separation of the undissolved fraction precipitates hydrated iron, manganese dioxide and alumina by oxidation of ferrous chloride and manganese chloride, chlorine, hydrogen peroxide or other oxidizing agent. With them, the silica in solution and other impurities such as boron are entrained. After the precipitate is filtered off, a neutral magnesium chloride solution is obtained which practically contains only calcium chloride as an impurity. After precipitation of calcium chloride and its separation, a pure magnesium chloride solution is obtained which is pyrolytically cleaved according to the equation

MgCl 2 + H 2 O - MgO + 2 HCl in a suitable furnace, for example, a spray-fired furnace, a fluidized bed furnace, or a cylindrical rotary furnace, can convert to pure magnesium oxide and flue gases containing hydrogen chloride formed in the reaction. The flue gases are purified from the magnesium oxide drift, for example with a magnesium chloride solution, then the hydrogen chloride contained in the flue gases is separated by water, for example in so-called adiabatic columns. When using an adiabatic column, hydrochloric acid flows from its bottom, which can reach a maximum azeotropic concentration.

In the literature relating to this process, precipitation of said hydrated oxides is not discussed in detail. The references are limited to stating that the contaminated solution obtained from said sludge after separation of the undissolved fraction is neutralized by aerating or introducing chlorine or another oxidizing agent by the end product of the process, i.e. magnesium oxide, magnesium industry or calcium oxide, coagulation occurs by an unspecified mechanism.

To date, the problems of precipitation of the hydrated oxides mentioned above, in particular by oxidation with air oxygen, have been unresolved. Unexplained losses of magnesium often result from the exact balance of the starting materials and the products obtained, which of course is economically disadvantageous. It has also been found that precipitation is often incomplete or is associated with an extremely long aeration time of the precipitated solution. Another unfavorable phenomenon is the sedimentability or filterability of the obtained clot quality of the precipitate, which often leads to pronin. Here, there are significant fluctuations in vehicle problems.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved process for oxidizing a ferrous and manganese moiety in solution and precipitating the corresponding hydrated oxides from a solution of magnesium chloride in hydrochloric acid.

The above-mentioned drawbacks have no method of separating ferrous, aluminum and manganese impurities from a solution of magnesium chloride in hydrochloric acid, which consists in the precipitation of iron at a temperature of 60 to 110 ° C, preferably at a temperature of 80 to 90 ° C, by adding at least one pH-enhancing agent, preferably by the addition of magnesium oxide, calcium oxide, magnesium hydroxide, calcium hydroxide or mixtures thereof, under intense air and / or oxygen blowing at a pH of up to 5.2, preferably 4 to 5, as hydrated iron oxide, optionally together with aluminum hydroxide, silicic acid and boron compounds, whereupon manganese precipitates at a solution pH greater than or equal to 6 when introducing air and / or oxygen to oxidize divalent manganese, or manganese precipitates at a pH solution greater than or equal to 4.5 when chlorine introduced oxidation of divalent manganese, whereupon it is eliminated Measured precipitate collected, optionally together with solid impurities present in the starting solution of magnesium chloride, sedimentation and / or filtration.

preferably, the precipitation is carried out batchwise in the mixing zone. The precipitation can also be carried out continuously in a cascade of stirred zones, wherein the precipitation of iron is carried out in the first or several zones maintained at a pH of 3 to 5.2, preferably up to 5, and then manganese precipitation in one or more other zones a pH of greater than or equal to 4.5.

Preferably, magnesium oxide with a particle size of at most 1 millimeter is used for neutralization, which is optionally hydrated and is in the form of a solid or an aqueous suspension.

It is also advantageous to use a powder containing magnesium oxide and / or calcium oxide for neutralization.

In the process according to the invention, the iron is precipitated as hydrated magnesium oxide free of magnesium, predominantly in the form of δ-FeO (OH); this structure was verified by X-ray ^examination

It is clear from the above that two processes are used to precipitate manganese in the process of the invention. . The pH may be raised to a value greater than or equal to 6 and the divalent manganese is oxidized by introducing air and / or oxygen; this procedure is preferable because of the easier availability of the oxidizing agent. However, the pH can also be maintained at greater than or equal to 4.5 and the divalent manganese is oxidized by introducing chlorine gas; in this process the oxidation proceeds very quickly.

The precipitation according to the invention can be carried out both discontinuously in a stirred vessel and continuously in a cascade of stirred boilers. When using a cascade, the precipitation of iron takes place in one or more containers maintained at a pH of 3 to 5.2, preferably 4-5, and the precipitation of manganese is then carried out in one or more containers in which the pH is kept greater than or equal to 4, 5.

An advantage of the process according to the invention is that it purifies the magnesium chloride solution without significant magnesium losses.

The process according to the invention essentially consists in appropriately maintaining the pH during the precipitation. As mentioned at the outset, the starting material is an impure solution of magnesium chloride which contains hydrochloric acid and which is optionally free of solids. The pH of this solution increases with the intensive introduction of air or oxygen. Magnesium oxide, magnesium hydroxide, oxide can generally be used for this purpose. calcium and / or calcium hydroxide. Sodium hydroxide, potassium hydroxide and ammonium hydroxide can also be used, for example. It goes without saying that the use of all substances other than the magnesium compounds leads to contamination of the magnesium chloride solution, with the result that the solution must then be further purified from the added substances. Magnesium oxide, which is preferably in powder form and has a particle size of at most 1 mm, is therefore particularly preferred for said neutralization; the magnesium oxide may optionally be hydrated and may be in solid or aqueous suspension form. Due to availability, a suitable precipitating agent is a drift comprising magnesium oxide and / or calcium oxide.

It should be noted that iron precipitation occurs in air oxidation prior to manganese precipitation, meaning that the precipitation of manganese occurs only when all the iron is present in the form of hydrated ferric oxide.

It has now been found that, depending on the pH, iron precipitation may produce two types of hydrated oxide: hydrated type 1 oxide and hydrated type 2 oxide. Hydrated type 1 oxide is formed when the pH of the magnesium chloride solution rises rapidly to greater than 5 , 2. Hydrated type 2 oxide is formed when the precipitation of iron is carried out in the pH range of 3 to 5.2, preferably 4. to 5, with vigorous aeration or oxygen introduction.

In both types of hydrated oxides, iron is trivalent at the end of the precipitation, but the X-ray structure of both types of hydrated oxides is different. The x-ray spectrum of the hydrated type 1 oxide corresponds to the maximum extent of pyroaurite (Mg6Fe2'CCOi (OH 16.4H2O) or brugnatelite (Mg6FeCO3 (OH) 13.4H2O). On the other hand, the structure of S-FeO (OH) is predominantly demonstrated in hydrated type 2 oxide.

It has been shown that the precipitation of hydrated type 2 oxide results in minimal loss of magnesium, while the precipitation of hydrated type 1 oxide co-precipitates a large amount of magnesium, which is then removed from the solution following separation of the precipitate from the magnesium chloride solution.

It should further be noted that the structure of the once formed hydrated oxide of type 1 or 2 no longer changes by increasing the pH. This means that further magnesium no longer passes into the precipitate.

The subsequent precipitation of manganese is known to be enhanced. pH. When iron precipitates in the form of hydrated type 2 oxide, the addition of magnesium oxide is considerably lower in order to adjust the set end pH than when iron precipitates in the form of hydrated type 1 oxide. 2 creates conditions that improve the precipitation of manganese.

After precipitation of the precipitate, the precipitate must be separated; it separates in the form of an almost neutral sludge. Surprisingly, it has been found that iron precipitates as hydrated type 2 oxide in favor of separating the precipitate. This precipitate provides in the sedimentation apparatus a substantially dense sludge as well as a denser filter cake for subsequent filtration. The sedimentation rate is approximately the same for both types of hydrated oxides.

Furthermore, it has surprisingly been found that the precipitation resulting in hydrated type 2 oxide significantly reduces the silica and alumina contents in the end product. For example, oxide. Magnesium, which is made from magnesium chloride solution after precipitation of iron in the form of hydrated type 1 oxide, contains on average 0.11% silica and 0.12% alumina, while magnesium oxide, produced from magnesium chloride solution after precipitation of iron in the form of % hydrated oxide type 2, contains 0.02% silica and 0.01% alumina.

In summary, the precipitation of hydrated type 2 oxide results in a reduction of magnesium loss, an increase in oxidation rate and yield to manganese precipitation, an improvement in the sedimentation and filtration properties of the precipitate, and a reduction in the silica and alumina content of magnesium oxide produced from the final magnesium chloride solution. .

In a batch process, the pH is raised to 4.5 as soon as possible and as fast as possible, and the solution is maintained at this value while introducing air or oxygen until complete. precipitation of iron. Finally, the pH can be further increased, preferably to a value higher than 6, and the manganese precipitates. In the case of continuous precipitation in a cascade of stirred boilers, the conditions in the first vessel ¹ can be maintained downstream, for example, such that the pH is 4.5 and the residence time is determined so as to quantitatively precipitate iron in the vessel. In other containers, the pH may be gradually increased in order to achieve a total precipitation of manganese, but not yet form magnesium hydroxide. This requires a pH of at least 6.

The use of chlorine for the oxidation of iron is also possible, although not necessary, since this oxidation also takes place with air or oxygen relatively as rapidly as with the use of chlorine. However, a reaction time of 2 to 3 hours is required for the precipitation of manganese in air oxidation. When the oxidation of divalent manganese is carried out with chlorine, the reaction time required for this is reduced to 10 to 15 minutes. In addition, less magnesium oxide is consumed since it is possible to rapidly oxidize divalent manganese with chlorine already at a lower pH, i.e. greater than or equal to 4.5, than that required by air oxidation. If the manganese content of the starting solution is not too high, the costs of chlorine are negligible in view of the advantages achieved.

In the following, the process of the invention will be explained in more detail by way of examples of a specific embodiment.

The starting solutions used in the examples are prepared by dissolving natural magnesite in 19% hydrochloric acid and filtering off the solid residue. These solutions have the following composition:

MgCl2 260 g, 1-1 (G.1 110 ^_ 1 MgOj Fe 2.8 g. 1 “1 Mn 0.2 g.1’1 Si 0,04 g.1-1 AI 0,03 g.1-1 free HCl 4,1 g.11

The pH of this solution, determined at ambient temperature, is 1.2.

For neutralization, an aqueous suspension of technical ground magnesium oxide containing 100 g of magnesium oxide per liter of suspension is used.

Comparative Example A A liter of magnesium chloride solution was heated to 85 ° C in a rapidly stirred glass flask equipped with a reflux condenser. The air was introduced into the solution at a rate of 16.7 liters per hour and then 3.38 g of magnesium oxide was added all at once. First, a black precipitate is formed which gradually turns reddish-brown. The pH rises - up to 6, but to the end - the precipitation drops again to 5.4. - Iron precipitation is complete after -15 minutes. After two additional hours at 85 ° C, during which the manganese precipitates, the precipitate is filtered off, washed, and dried at 120 ° C. The results of the measurements made in connection with the precipitation of the suspension, the filter cake and the dry residue are summarized in Table IV below.

Example 1 1 liter of magnesium chloride solution was heated to -85 ° C in a vigorously stirred glass flask equipped with a reflux condenser. Air is introduced into the solution in an amount of 16.7 liters through the gas frit. and 1.126 g of magnesium oxide are added. This raises the pH to -4.6. Over the next 30 minutes, the pH is maintained between 4.4 and 4.6 by the addition of magnesium oxide. For this purpose, 1.198 g of magnesium oxide are consumed. A red-brown precipitate is formed, and after -30 minutes the iron precipitation is complete. Additional magnesium oxide was then added in an amount of 1.054 g. The pH rose to 66.3 and dropped to ,26.2 by the end of the precipitation. After two hours at -85 ° C, when manganese precipitates, the precipitate is filtered off, washed and dried at 120 ° C. The results of measurements taken in conjunction with suspension precipitation, filter cake and dry residue are summarized in Table IV below.

Examples - 2 and 3

Comparative Examples B and -C

The precipitation of iron is carried out in an intensively stirred glass flask equipped with a reflux condenser and an overflow neck. The magnesium chloride solution and the magnesium oxide slurry are fed continuously and a frit is used to aerate. The reaction mixture was heated to 85 ° C; the reaction volume is 1 liter. The slurry continuously leaving the glass flask was collected and the precipitate was then filtered, washed and dried at 120 ° C. Four experiments were performed at different pH values. Examples 2 and 3 are methods of the invention, while Comparative Examples -B-and -C refer to the prior art method. As can be seen from the following Table I, the hydrated iron oxide predominantly has a < 5-FeO ((1H)) structure and the desired lower sediment volume. This hydrated oxide only at a pH of less than or equal to 5. At a higher pH, the consumption of oxide / magnesium increases very strongly.

Table I

Example 2 3 В C Temperature (° C) 85.0 85.0 85.0 85.0 pH [measured at 85 ° C] 4,5 5/0 5.5 5.0 MgO (g · ml MgCl solution) 2.1 2.6 6.0 12.5 Mean delay time (Ir) 0.49 0.43 42 0.42 Air (Ί, r * MgClcí solution) 16.7 14.7 14, « 15.0 Excluded iron j%) 97.0 100.0 100., 0 100.0 Sediment volume after greater than or equal to 24 h (cm ³ .1 &lt; -1 &gt; of M-gdj solution) 29.0 40.0 96.0 172.0 Impurities in the filtrate (MW ^{1 1} ): Fe 77.0 <5.0 <5.0 <5.0 Mn 100.0 100.0 100.0 100.0 X-ray structure of dry filter cake (specified amount): pyroaurite little little predominantly m n Л most of them п йс t> v í α-FeO (OH) very very Mg (OH) 2 many many little

Example 4

Precipitation is carried out in a four-stage stirred boiler cascade. The operating conditions are given in Table II below.

Table II

Container no. Reaction volume (1) Mean delay time (h) Aeration of the solution (1 air per 1 MgCl2 solution) Temperature ( ⁹ , С) 1 ’ 3.76 0.476 5.19 85 ’ 2 5.8 0,718 2.07 85 3 7.9 0,978 0.91 85 4 8.1 1,002 0.91 85 1—4 25.6 3,174 9.08 85

.1 The vessel is equipped with a impeller stirrer perforated basket with a rotational speed of 2000 rpm for ^one to better air distribution in the solution; this better air distribution results in lower air consumption. Other vessels are equipped with a paddle speed of 700 min ^-1. Air is introduced into the first vessel through a glass tube that terminates vertically below the stirrer, and air is introduced into the remaining vessels through a gas frit.

The magnesium chloride solution and the magnesium oxide slurry are simultaneously added to the first column, the magnesium oxide being metered so as to maintain the pH at 4.5. This requires 2.15 g of magnesium oxide per liter of magnesium chloride solution. In a second vessel, the pH was adjusted to 6.1 by the addition of 1.30 g of magnesium oxide per liter of magnesium chloride solution.

99.6% of the iron is precipitated in the first vessel. Containers 2 to 4 serve to precipitate manganese.

The results of measurements taken in conjunction with the evaluation of slurry precipitation, filter cake and dry residue are also shown in Table IV.

Example 5

The start of the precipitation of the iron is carried out as in Example 1, but after 30 minutes the air supply is interrupted. 0.5 g of magnesium oxide is then added to precipitate manganese and 0.25 g of chlorine is introduced. After a total precipitation time of 45 minutes, the precipitate is filtered off. Less than 0.5 mg was found in the filtrate. ^_1 1 and 22 mg of iron, manganese l ^_1 7.

Example 6

The precipitation is carried out continuously in one two-stage boiler cascade. The operating conditions are given in Table III below.

Table III

Container Reaction Medium time Gas introduction Temperature C. volume (1) delay (h) (1 air (g chlorine (° C) per solution per solution MgClž) MgClž)

3,760,465

2,520,311 + 2 6,280,776

The vessel 1 is equipped with a impeller stirrer having a perforated basket speed 2000 min ^-1; container 2 is equipped with a paddle speed of 700 min ^-1. Air is introduced into the first vessel through a glass tube which terminates vertically below the stirrer. The introduction of chlorine into the vessel 2 is carried out by a gas frit. The magnesium chloride solution and the magnesium oxide slurry are simultaneously introduced into the first vessel, with the magnesium oxide being added at 5.05-85-0.2585.

5.05 0.2585 forged to a pH of 4.5. This requires 2.15 g of magnesium oxide per liter of magnesium chloride solution. 0.5 g of magnesium oxide per liter of magnesium chloride solution was added to the second vessel. The slurry leaving the second vessel was cooled to less than 40 degrees C and filtered. Less than 0.5 mg was determined in the filtrate. 1 “! iron and 25 mg. .I ^-1 manganese.

Table IV

Example

MgO consumption (g. L ¹ of MgCl2 solution) pH value of precipitation of Fe

Sediment volume after more than 24 hours (cm ³ .1 - ¹ MgCl 2 solution)

Wet filter cake (g. 1 ^_1 MgCl2 solution)

Filter cake dried at temperature

120 ° C

- X-ray structure: pyroaurite 5-FeO (OH) - weight (g. 1 ^_1 MgClCl solution) Fe content (%) Mn content (%)

Magnesium oxide removed from filter cake solution (g. 1 - ¹ MgCl2 solution)

Impurities in the filtrate;

Fe (mg. 1 ^_1)

Mn (mg. 1 ^_1)

AND 1 4 3.38 3.38 3.45 6.0 4,5 4,5 144.0 60.0 58.0 59.4 16.6 16.4 predominantly little little amount very much very much 10.1 5.29 5.18 27.7 52.7 53.5 14.3 5.3 5.5 2.39 0.46 0.47 0.5 0.5 0.5 101.0 66.0 155.0

OBJECT OF THE INVENTION

Claims (5)

Method for separating ferrous, aluminum and manganese impurities from a solution of magnesium chloride in hydrochloric acid, characterized in that the iron is precipitated at a temperature of 60 to 110 ° C, preferably at a temperature of 80 to 90 ° C, by adding at least one pH-increasing substance, preferably by the addition of magnesium oxide, calcium oxide, magnesium hydroxide, calcium hydroxide or mixtures thereof, with intensive air and / or oxygen purging at a pH of 3 to 5.2, preferably 4-5, as hydrated ferric oxide, optionally together with aluminum hydroxide, silicic acid and boron compounds, whereupon manganese precipitates at a solution pH greater than or equal to 6 when introducing air and / or oxygen to oxidize divalent manganese, or The manganese precipitates at a pH of the solution greater than or equal to 4.5 by introducing chlorine to oxidize divalent manganese, whereupon the precipitate formed is optionally separated together with the solid impurities present in the starting magnesium chloride solution by sedimentation and / or filtration. 2. Method according to claim 1, characterized in that the precipitation is carried out discontinuously in the mixing zone. 3. The process according to claim 1, wherein the precipitation is carried out continuously in a cascade of mixing zones, wherein the precipitation of iron is carried out in the first or several zones maintained at a pH of 3 to 5.2, preferably 4 to 5, and precipitation of manganese in one or more other zones maintained at a pH greater than or equal to 4.5. 4. A process as claimed in any one of claims 1 to 3, characterized in that magnesium oxide having a particle size of not more than 1 mm, which is optionally hydrated and in solid or aqueous suspension form, is used for neutralization. 5. Method according to claim 1, characterized in that a powder containing magnesium oxide and / or calcium oxide is used for neutralization.