DE1253253B - Process for the production of concentrated, aqueous, magnesium chloride-containing solutions - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

COIt

German class: 12 m-5/30

Number: 1 253 253

File number: T 26103IV a / 12 m

Filing date: April 28, 1964

Open date: November 2, 1967

The present invention relates to a process for the production of concentrated, aqueous, magnesium chloride-containing solutions by digesting to a grain size of less than 0.84 mm of crushed silica-containing magnesium minerals with concentrated hydrochloric acid in the Boiling heat.

Certain silica-containing magnesium minerals are suitable because of their acid solubility and Their high magnesium content makes them ideal as possible starting products for elemental magnesium and its connections. For the isolation of magnesium and its compounds from such Minerals have undergone many processes based on digesting and dissolving the mineral in hydrochloric acid suggested. A major disadvantage of the known methods that use hydrochloric acid is in that silica gels and colloidal silicas are formed at the same time. These gels build up the mineral particles a coating through which the further access of the acid to the mineral particles prevented or diminished, which means that the mineral can only be used to a limited extent. These gels also prevent rapid filtration and hold a significant proportion of the dissolved salts in the Filter cake back, which means that considerable amounts of washing water are required to remove the dissolved Sufficiently isolate solids. This undesirably gives a very dilute one Solution that eventually needs to be concentrated. The poor filterability requires high investments for the filter apparatus.

As is well known, the use of sulfuric acid as a leachate, presumably because of the great heat of reaction, the low volatility of this acid and the great chemical stability the metal sulfates, the gel formation of the silica can be avoided under certain circumstances. Unfortunately, for economic and technical reasons, magnesium sulfate is not preferred form in which the magnesium of a mineral is isolated. Also the use of nitric acid for the leaching of olivine and other silica-containing magnesium minerals is known. she however, it is also not preferred for economic and technical reasons.

Hydrochloric acid is largely preferred for leaching because the magnesium of the mineral is called magnesium chloride goes into solution, which at relatively low, economically interesting temperatures is decomposed to form magnesium oxide, which is an easily sold chemical product.

Process for the production of concentrated,
aqueous solutions containing magnesium chloride

Applicant:

Twin Sisters Magnesia & Chemical Corporation,

Richland, Wash. (V. St. A.)

Representative:

Dr.-Ing. W. Abitz and Dr. D. Morf,

Patent Attorneys, Munich 27, Pienzenauer Str. 28

Named as inventor:

Kermit B. Bengtson, Richland, Wash .;

James C. Almond,

Lennart N. Johanson, Seattle, Wash. (V. St. A.)

Claimed priority:

V. St. v. America May 21, 1963 (282 079)

In addition, gaseous hydrogen chloride is formed during thermal decomposition, from which the Originally used acid can be easily restored and leached further mineral can be used. Alternatively, by-product hydrochloric acid from other sources can be used and leaching can be combined with other chemical chloride processing methods thereby achieving considerable economic advantages.

Other researchers have also observed the gel formation of the silica when hydrochloric acid is used. Previous attempts to reduce or prevent gelation of silica, such as by progressive digestion and burning of the mineral to improve its reactivity limited success.

In the process according to the invention, silica-containing magnesium minerals are mixed with hydrochloric acid leached and the gel formation of the silica almost completely eliminated. A burning of the mineral is not required or desired. A practically complete one is obtained after a relatively short time Decomposition. The silica is in the form of chemically very reactive, loose aggregates of amorphous

709 680/364

3 4

phen silica particles with up to 50 microns or so contaminates the silica, whereby the value acquires more diameter, the elementary part of the latter is reduced,
particle size is in the millimicron range. These loose, because of the affinity of hydrochloric acid for water, form non-colloidal silica aggregates, this acid forms a structure in dilute chloride solutions, like filtration after leaching Constantly boiling mixture, as a result of which un-washing water passes through very easily, as a result of which it is possible to obtain a concentrated trenjjuig of the silicic acid from the dissolved metallic acid by distillation. In contrast, allow the er, ^ alzenT ^ hr to be facilitated. Compared to other concentrated solution processes according to the invention, such as the progressive digestion, working in a concentration range in which the mineral can be better utilized. Which the constant boiling mixture does not exist, after leaching, filtering and washing, which makes it possible for the hydrochloric acid to quickly and tene solution is relatively highly concentrated. This is easy to recover as a concentrated gas,
an important and notable advantage if the fact that the concentration of the magneman takes into account that almost everything in the solution of prenosium chloride evaporates before evaporation according to the invention must become. th procedure, constitutes an essential and not

According to the invention, these goals are achieved by only showing a gradual difference. B. a centigen hydrochloric acid, which is in relation to the conversion 20 18% solution and according to the invention a 35% solution of magnesium and other present metals, is preferably in a low stoichio- anhydrous basis per 100 kg of magnesium chloride on the chlorides Evaporation of 270 kg of excess water is present, mixed, after which water saved. This comparison of figures shows the temperature of the mixture at a speed borrowed the fundamental difference and simultaneity of about 10 ⁰ C per minute up to boiling 25 days also the advantages of the invention and driving after the heat of reaction has subsided.

is kept at this temperature until typical, silica-containing magnesium minerals

the reaction ended and the silica precipitated, which can be treated according to the invention,

len, which are then called by the:

Suspension is separated in a known manner. 30 olivine - magnesium orthosilicates with the all-

From the USA patent specification 2,549,798 the common formula is (Mg, Fe, Mn) ₂ SiO ₄ .

already a process for the production of ma serpentine - weathered olivine; hydrated

Magnesium chloride solutions by treating magnesium silicate (Mg ₃ Si ₂ O ₇ · 2 H ₂ O).

smaller siliceous maenesiummmerahen ". . ^ _τ ·,. · ·. ·,

known with HCl at the boiling point. According to the 35 garment - nickel magnesia

known methods, however, are substantially more encryption U ™, ^M gJ ^blO s ^{"n Η} 2 ^{υ λ}

process stages required than in the case of the inventive silicic acid-containing magnesite - magnesite, the process according to the invention, and, moreover, it does not contain any silica as an impurity,
Product with such a high magnesium chloride concentration - Silica-containing fraction - Fraction that reaches as tration in the filtrate as in the present 40 contamination contains silica.
Invention. But not so much magnesium chloride is transferred either. While the process generally consists of any difference between the process according to the invention or other silicic acid-containing marens compared to the known process, it is particularly suitable for midarin that all acid and mineral olivine and serpentine according to the invention are particularly suitable and all ore are mixed at the same time. When loading is described for olivine. Also the type of Kiekennen processes the acid and the ore selsäureeinclusions in the silicic acid-containing magnesite are mixed partially and the slurry from deposit to deposit vari-acid and ore partially digested from deposit to deposit. and thus the practical feasibility of the

In accordance with the present invention, we will pre-empt 50 processes.

preferably a low stoichiometric acid- The mineral is first ground with a suitable pre-excess, based on the amount of mineral in the ore, directions and applied to a particle size of, while according to the USA patent no more than 0.84 mm, the majority being 65 up to 95% of the stoichiometric amount of acid which the particles should be smaller than 0.84 mm. Then for the conversion of 85% of the total mine- 55 the mineral is mixed at ambient temperature with 25-ral amount in the chloride required, to 15 to 38% by weight hydrochloric acid, preferably in 35% of the total weight of the mineral, is added a slight stoichiometric excess and is mixed the remainder of the mineral and the acid from which it is particularly advantageous to add about 106% of the theoretical amount, in each case after the stoichiometrically required amount has ended the reaction of the preceding addition. 60 carries, and the mixture in a suitable digestion. In addition, according to the invention, the over device is brought, which is not neutralized with suitable stirring and liquid acid, it can rather be provided with heating devices. During the leaching separated and reused for further ore, the mixture will become permanent and gentle. The U.S. patent shows that stirring to keep the mineral particles in suspension so that the excess acid is neutralized. At 65 th and to allow the acid free access,
This neutralization also causes the iron that is not completely present in the solution to be precipitated from above. After filtering closed so that the process remains at atmospheres of the solution, the iron in the residue and pressure is carried out.

In the digestion vessel, the gently guided mixture, which is initially present as a thick slurry, is heated so that the temperature increases from about 25 to about 75 ° C within a few minutes whereupon the mixture begins to boil by itself due to the heat of reaction released. Now the heating from the outside is stopped, but the stirring is maintained so that the mineral can be removed remains in suspension and the acid continues to have easy access to any mineral particle. the Heat of reaction alone raises the temperature of the slurry to just over 100 ° C. The temperature the slurry will be closely watched and after about 5 minutes it will begin to fall off, and the boiling will stop. This is an indication that the reaction is coming to an end. Now it is heated again from the outside in order to keep the solution close to or at the boiling point, and about another 10 minutes to complete the reaction as much as possible.

While the mixture is still hot, the insoluble silica will come off the solution - preferably through a vacuum filter - filtered off and the filter cake washed with a relatively small amount of water. Although not essential to good filtration, the addition of a coagulant has been found as beneficial to a complete coagulation of the silica to loose aggregates guarantee.

Subsequently, metal ions other than magnesium are removed from the filtrate. Such Removal does not fall within the scope of the present invention and is not discussed in detail.

If the process described with a small stoichiometric excess or with about the theoretical, stoichiometric amount of acid is carried out, about 95% of the mineral reacts with the acid. This percentage is relatively high and is believed to be the greatest benefit ever achieved with a technically applicable process using hydrochloric acid became.

The ease with which solubles are isolated from the insoluble silica residue by filtration depends very much on the acid concentration that occurs during the leaching of the mineral was applied, namely it increases with increasing acid concentration. A mineral which leached by boiling with hydrochloric acid, the concentration of which is less than 25%, can only be filtered with difficulty, and washing out the dissolved salts from one so formed Residue requires a large amount of washing water. When using hydrochloric acid with a concentration of about 38 percent by weight can be compared to the dissolved salts from the silica residue be washed out in a very short time, and the required amount of wash water for removal a given percentage of adhering solutes is also much less. The application larger acid concentrations is impractical as those at ambient temperature and Atmospheric pressure are unstable. The application of acid concentrations that are at the high end of the The specified range increasingly favors the expulsion of some of the hydrogen chloride out of the solution before it can be consumed for the reaction with the mineral because the hydrogen chloride escapes more easily from a highly concentrated solution and because it is also easier to escape concentrated metal chloride solutions, which are formed when concentrated hydrochloric acid is used to decompose the mineral. This loss of hydrochloric acid from concentrated solutions somewhat diminishes the efficiency of using the mineral. On the other hand, the

ίο Amount of free acid in the finished leaching liquid reduced to very low values without having to be neutralized. The different amounts HCl, which is in vapor form from the reaction vessel when leached with acid of the specified concentration can of course be recovered in an acid cooler for reuse. A nominal loss of unconverted but cheap mineral is more than made up for by the value of the HCl recovered in the cooler, which when using dilute acid would remain in solution and would eventually have to be neutralized. An optimal acid concentration for the leaching, which is a very easily filterable residue, a concentrated solution of metal chlorides, gives high mineral utilization efficiency and low residual acidity, is 31 weight percent HCl.

The term "filterability" used generally refers to the ease with which the solubles by filtration from the silica and other insoluble materials that are after the treatment according to the invention of the silica-containing magnesium minerals with hydrochloric acid remains, can be separated. The filterability is specifically defined here as 100 times the reciprocal time in seconds that is required to pass 100 ml of wash water at 50 ° C. through a filter cake to pass through the leaching of 100 g of silica-containing magnesium mineral with Acid is obtained by passing the resulting slurry through a horizontal filter 9 cm in diameter is filtered. The filter cake to be tested should be washed, but not mechanically after filtration be whirled up. Furthermore, a good one should be obtained during the filtration as well as during the test Water jet vacuum can be applied. It is clear that the definition is empirical and arbitrary, them however, proves to be very useful for comparison purposes in the present case.

For a better understanding, the invention is described in the following description with reference to FIG the drawings further explained.

F i g. Fig. 1 shows a flow diagram of an embodiment of the method according to the invention; in

Figure 2 is the filterability of the residue plotted against the concentration of the acid used for leaching.

In Fig. 1, an olivine ground to a size of 0.84 mm or smaller arrives by means of a transport device 12 in the mixing tank 10, in which it is cold with hydrochloric acid, which is supplied via line 14 is supplied, is mixed. According to the invention, the hydrochloric acid is in a concentration of 25 to 38 weight percent HCl applied in an amount that is preferably a low stoichiometric Excess for the mineral equals. The cold slurry exits the mix tank via line 16 and enters the reaction

I 253 253

vessel 18, which has a suitable stirring device 20 and a heating device, such as. B. steam coils 22, contains. The inside of the reaction vessel 18, the blades of the stirrer 20 and the heater 22 are made of a corrosion-resistant material. The cold slurry is in such a Tank introduced intermittently.

The heat introduced into the reaction vessel 18 via the heating device 22 is regulated in such a way that that the cold slurry comes to the boil after about 5 minutes of heating. At the start of boiling the heating is stopped and the reaction is allowed to take place with the liberated heat of reaction continue running until the temperature of the slurry begins to drop and the boiling subsides. Well will continue heating so that the solution boils for about an additional 10 minutes in order to maximize the reaction to be carried out completely. The hot slurry is then fed into the Filter 26 brought and the process in reaction vessel 18 with a fresh batch of cold slurry repeated. The reaction vessel 18 has a collecting device 28 for collecting the released Acid vapors which are sent to an acid cooler for recovery of this acid.

The filtration and washing of the silica take place in the filter 26. The concentrated filtrate and some of the washing water go via line 30 to a further cleaning apparatus (not shown), while the remainder of the wash water is returned to the filter 26 via line 32 and for washing of the next batch is used. Some of the wash water can also be used for others Purposes.

To explain the influence of the acid concentration on the gel formation of the silicon dioxide and the silica and the filtration are given the following examples, in which the acid concentration differentiate:

example 1

100 g of olivine (grain size 0.71 mm, containing 49.1% MgO and 8.0% FeO) were in one 800 ml beaker mixed with 496 ml 20 weight percent HCl in the cold. The resulting slurry was hand stirred intermittently with a glass rod while the beaker was heated over a gas flame. The heating rate was adjusted so that the slurry began to boil after about 5 to 11 minutes. If the slurry is due to the released heat of reaction boiled by itself, the gas flame was removed, and when the temperature began to fall, a smaller flame was placed under it according to the procedure described above. The reaction was continued for about 15 minutes after the start of boiling, whereupon 10 ml of a coagulant solution was added

ao the. The hot solution was poured in using a Buchner funnel (9 cm diameter) Water jet vacuum filtered immediately. After the completion of the filtration, the cake was washed on the filter and filterability characterized by the time taken for 100 ml to pass through Water at 50 ° C was required by the washed but not stirred cake. Of the The reciprocal of seconds, multiplied by 100, was used as a point for recording the curve in Fig. 2 used.

Example 2, 3 and 4

Examples 2, 3 and 4 are exact repetitions of Example 1, only different amounts were used Acid used in various concentrations to leach the mineral. The used Acid volumes were chosen so that in all examples the same amount by weight of hydrogen chloride was used.

Table 1

example acid
concentration
Vo acid
volume
ml Gram
HCl
total 100 l / filter time
for
100 ml of water mineral
conversion
Vo Gram
free HCl in the
Leaching
liquid Grams of HCl
boiled away Vo MgCl ₂
in the
liquid 1
2
3
4th 20.0
25.0
31.0
37.9 496
365
290
227 99
99
99
99 0.238
0.417
0.98
1.08 80.3
81.7
71.6
63.3 14.3
9.7
0.06
0.62 6.7
11.1
29.4
37.0 21
29
34
35

These examples show that the filterability when using 31% hydrochloric acid compared with 20% hydrochloric acid increases noticeably, but increases only slightly if 37.9% hydrochloric acid is in place of 31% hydrochloric acid is applied. The total amount of wash water used to remove the dissolved salts from the silica required to a given value changes roughly the other way around to filterability, and the concentration of dissolved metal chlorides in the leaching liquid increases with the concentration of the acid used for the leaching, so that the concentration of the with Leaching liquid combined in the washing solutions noticeably as the concentration of the acid increased increases. However, the residual acidity will be in leachate fluids obtained by the application of As can be seen from Table 1, concentrated acid is very easily brought to very low values. In Fig. 2 the filterability is plotted against the concentration of the acid. The values of the four examples in Table 1 were used to establish the curve in FIG. 2 among many other experimental ones Values are also used. The curve shows that the filterability increases sharply when in place of 20 or 25% acid 31% acid is used, while the further increase between 37.9 and 31% acid is low. Taking into account all factors including cooking away the acid, the optimal acid concentration is about 31 percent by weight HCl.

All of the foregoing discussion relates to a leaching process in which digestion takes place under atmospheric pressure. Indeed, the filterability and mineral utilization in the case of leaching under atmof spherical pressure sufficiently large to make such a process economical to design. However, it has been found that in addition to the improved filterability through application certain further advantages can be achieved by hydrochloric acid in the concentration range from 25 to 38% if the digestion is preferably carried out under pressure. The main benefit is a reduction the loss of acid by boiling away and an associated increase in the usefulness in mineral recovery. When this procedure is carried out with the method according to the invention the reaction vessel is equipped for work under pressure and has the same instructions as for work under atmospheric pressure devices for stirring and heating. The same slurry as above is placed in the reaction vessel, which, however, is closed at the top while heating is. The mineral particles are kept in suspension by stirring to keep the acid in has free access to the individual mineral particles. The heating is adjusted so that the temperature of the enclosed slurry from ambient temperature to about 80 ° C within a few minutes increases. At this temperature the exothermic heat of the silica decomposition starts a large amount To provide heat, which increases both the temperature of the slurry and the pressure in the vessel rise rapidly. Due to the limitations of the apparatus, it may be necessary to use pressure as a preference to be regulated by cooling or by blowing off steam. When regulating by blowing off only a small amount of steam will need to be vented of steam if the heat input is so it is set so that the temperature of 80 ° C is reached in about 8 minutes and is interrupted, when the temperature begins to rise rapidly. After reaching a temperature of for the first time 80 ° C the decomposition reaction is practically complete within 5 minutes. The end of Reaction can be recognized by a rapid drop in pressure when the acid content of the solution drops and no more heat is released. However, if the slurry is drained at this point it would be extremely difficult to nitride. The slurry will therefore held near the maximum pressure and temperature for another approximately 10 minutes by adding if necessary further heat is supplied from the outside. The heating is then ended and the pressure equalized rapidly made with the atmosphere. A coagulant is then added to the slurry and hot filtering the slurry as in the atmospheric pressure process. These The type of method according to the invention is also illustrated in the following example.

Example 5

358 parts by weight of hydrochloric acid (specific weight 1.155) were mixed with 100 parts by weight of olivine (grain size up to 0.074 mm) and placed in a glass apparatus with a stirrer, manometer, thermometer and drain valve. The apparatus was carefully heated from the outside to 40 ^° C., whereupon the drain valve was closed. The following values were obtained during the execution of the experiment:

5 Time, minutes J-TUCK Tempe Remarks after this kg / cm ² rature Beginning 0 ⁰ C Closed drain 0 40 valve, supplied IO Heat decreased 0.21 5 0.56 60 7th 1.75 74 9 1.97 113 ¹ p 10 2.11 120 HV ₂ 1.97 133 Reaction apparently 13th 131 ended, fed Heat decreased 20th 1.83 14th 1.97 130.5 14V ₂ 2.39 133 17th 2.76 138 «5 21 1.40 140 25th 0 131 End of heat supply 30th 112 Drain valve open

The reaction products were removed from the apparatus and 300 parts of water were added. the entire reaction mass was poured onto a vacuum filter (9.9 cm diameter) and 507 parts of liquid Sucked off in 30 seconds while 215 parts remained in the cake. A total of 0.27 equivalents or 9.9 g HCl present in total liquid. The filter cake was 3.0 cm thick, and after washing and drying 45.5 parts by weight remained. The conversion of the olivine was therefore 95.6%>. The filterability according to the specified Definition was about 16 on a scale corresponding to FIG. 2.

The method according to the invention thus results both at atmospheric pressure and at elevated pressure Print out an economical method for the extraction of magnesium and its compounds Olivine and other silica-containing magnesium minerals. The procedure is such that it easily performed in an apparatus composed of readily available components can be. The required temperature is achieved by utilizing the exothermic heat of reaction largely maintained by itself and reduces the amount of heat required from outside. About that in addition, the magnesium chloride formed is obtained in a relatively concentrated form and the costs sellable for evaporation in manufacture Magnesium compounds from the chloride are largely reduced. The inventive method is thus for the technical exploitation of the deposits, the olivine and other silica-containing magnesium minerals and are available in large quantities, well suited.

Claims (4)

Patent claims: 1. Process for the preparation of concentrated, aqueous, magnesium chloride-containing solutions by digesting to a grain size of 709 680/364 Less than 0.84 mm of crushed silica-containing magnesium minerals with concentrated hydrochloric acid at the boiling point, characterized in that the ore is treated with a 25 to 38 percent strength by weight hydrochloric acid which, with regard to the conversion of magnesium and other current metals to the chlorides, preferably in a low stoichiometric Excess is present, mixed, after which the temperature of the mixture is increased to boiling at a rate of about 10 ° C per minute and, after the heat of reaction has subsided, is kept at this temperature until the reaction has ended and the silica has precipitated, which is then removed by the still hot suspension is separated in a known manner. 2. The method according to claim 1, characterized in that before being separated from the a coagulant is added to insoluble silica to further precipitate the silica will. 3. The method according to one or more of claims 1 and 2, characterized in that the hydrochloric acid in an amount of about 106% of the theoretical, stoichiometrically required Amount is applied. 4. The method according to claims 1 to 3, characterized in that the method under Printing is carried out. Considered publications:
U.S. Patent No. 2,549,798. 1 sheet of drawings 709 680/364 10.67 © Bundesdruckerei Berlin