Note: Descriptions are shown in the official language in which they were submitted.
;.3~2~
In the process of manufacturing magnesium nletal, the electrolysis of
anhydrous magnesium chloride in a molten salt eutectic is normally practiced.
The magnesium metal is separated from the bath and electrolysis cell by flo-
tation in molten baths that contain primarily MgC12, KCl, and NaCl along with
additional CaC12 salts. Other eutectic "mixed" salt baths used to recover
magnesium metal have included molten baths containing MgC12 - LiCl mixtures
with other salts such as KCl, BaC12, NaCl, and CaC12. Various types of trace
metal, such as vanadium, may be added to the mixed baths as salts to enhance
-their electrolysis characteristics.
One of the more profound difficulties found in operating an elec-
trolysis procedure to manufacture magnesium metal is the build up of cell
"smut", which is primarily magnesium oxides, in the salt bath. This "smut"
is not soluble in the eutectic molten baths and accumulates on electrodes, in
flow paths, and generally throughout the equipment in contact with the molten
salt bath. The presence of this "smut" is harmful to the electrolysis cell
operation. Its presence is caused primarily by insufEiciently dried magnesium
chloride being used as a cell feed during continued electrolysis.
Recentlyl new procedures have been developed to obtain high quality
anhydrous magnesium chloride. These processes are described in United States
Patent 3,983,22~ and in United States Patent 3,966,888 both issued to ~llain,
et al. The patents issued to Allain, et al, describe a process which success-
fully manufactures extremely high quality anhydrous MgC12 from MgC12 hydrate
salts or concentrated MgC12 aqueous solutions. These starting materials are
admixed with ethylene glycol and then exposed to temperatures sufficient to
distill from these admixtures all water initially present, thus leaving an
anhydrous ethylene glycol solution of MgC12. This anhydro~ls ethylene glycol-
MgC12 solution is treated with anhydro-ls ammonia forming the insoluble hexa
ammoniate complex o~ formula MgC12 6Nh3 which precipitates, and is then
;,~
.3;~
filtered from this glycol - MgCl2 6N~13 slurry. Subsequent unique washing
stepsJ solvent recovery steps, and a final roasting process which drives off
ammonia ~Eor recycle) and recovers high quality ~gCl2 (anhydrous) completes
the process.
One of the difficulties of the economic operation of the above pro-
cess is the source of the MgCl2 hydrate salts or concentrated solutions.
Brines, bitterns, and even sea water may be used to recover these hydrated
MgCl2 salts or concentrated aqueous solutions. It would be beneficial also
to use various types of naturally occurring mineral ores or mixed salts con-
taining magnesium values if a process could be found to simply and economical-
ly convert these mineral ores and mixed salts to anhydrous MgCl2.
We have discovered that we can easily achieve the beneficiation of
certain ores and mixed salts containing magnesium values, and by such bene-
ficlation open up many geographic locations to possible economic consideration
as sites to manufacture MgCl2 ~anhydrous) and possibly even magnesium metal.
We have particularly discovered a process which converts any common
magnesium containing sulfate or chloride salt, double salt, or mixture there-
of to anhydrous magnesium chloride o:E exceptionally high purity while simul-
taneously recovering either fertilizer grade potassium sulfate or recovering
anhydrous and economically valuable potassium chloride. We have also success-
fully discovered a combined process which can use the anhydrous potassium
chloride recovered from the beneficiation of a carnallite double salt to im-
prove the economics of recovering anhydrous magnesium chloride from a mîxed
salt containing magnesium sul-fate and potassium sulfate.
We have discovered a method of beneficiating a mixed salt mineral
ore containing potassium and magnesium values in either the sulfate or the
chloride form and in either their anhydrous or hydrated form which allows the
recovery of anhydrous magnesium chloride and the simultaneol1s recovery of
-- 2 --
either commercially accep-table potassium chloride or commercially acceptable
potassium sulfate. This beneficiation of these mixed salt mineral ores allows
the separation and isolation of several critical and economica]ly valuable
salts. These salts are anhydrous magnesium chloride, anhydrous potassium
sulate, and/or anhydrous potassium chloride.
We have simultaneously discovered that we may obtain anhydrous mag-
nesium chloride from either mixed chloride ores containing magnesiwn and
potassium values, such as carnallite, or independently from mixed salts or
magnesium sulfate and potassium sulfate which may also be found in various
locations throughout the world. Examples of the mixed sulfate salts contain-
ing both magnesium and potassium values are the mineral ores named Langbei-
nite, Leonite, Shoenite, and Picromerite. The Langbeinites are often given
the formula K2S04 2MgS04. Leonite, on the other hand, is a tetrahydrate
having the formula K2S0~ MgS04 4H20. The hexahydrate salt is referred to
as shoenite. Picromerite is another mineral name given to a magnesium-potas-
sium sulfate ore which is commercially mined.
The potassium-magnesium containing mixed salts which have chloride
ion concentrations are normally referred to as carnallites. These materials
are most often found containing water of hydration, for example, MgC12 KCl
The invention, therefore9 is a combination o~ a method of benefici-
ating a mixed salt mineral ore containing potassium chloride and magnesium
chloride and/or their hydrates which allows the recovery of anhydrous magne-
sium chloride and the simultaneous recovery of commercially acceptable potas-
sium chloride, a method of beneficiating a mixed salt mineral ore containing
potassium and magnesium sulfate and/or their hydrates which allows the recov-
ery of anhydrous magnesium chloride and the simultaneous recovery of commer-
cially acceptable potassiwn sulfate, and finally, the combination of these two
-- 3 --
~2~
methods of beneficiating magnesium ores of the type mentioned in such a manner
that a commercial facility may use either a carnallite ore as a feed material,
a mixed potassium/magnesium sulate ore as a feed material, or may use a com-
bination of these two mineral ores or types of ores as feed material to the
process.
The simplest way of describing our invention is to outline the sep-
arate processes involved and then demonstrate their mutual combination.
Toward that end, we initially will describe the process of beneficiating a
carnallite type ore primarily containing MgC12 KCl and its various hydrate
forms.
The method of beneficiating a mixed salt mineral ore containing
potassium chloride and magnesium chloride and/or their hydrates allows the
recovery of anhydrous magnesium chloride and the simultaneous recovery of
commercially acceptable potassium chloride. This beneficiation of these
carnallites allows the separation and isolation of two critical and economic-
ally valuable inorganic salts. These two salts are anhydrous magnesium chlo-
ride and potassium chloride. This method of beneficiation of these carnallite
mineral ores which contain potassium chloride and magnesium chloride comprise
the following steps:
(a) Dissolving the carnallite mineral ores in the minimum amount of water
required to obtain complete solubility, thereby obtaining a carnallite solu-
tion;
(b) Filtering from the carnallite solution of ~a) any residual precipitates
which are not soluble in said solution, thereby obtaining a filtered solution;
(c) Adding ethylene glycol to the filtered solution of (b) in sufficient
quantities to solubilize all magnesium chloride present in said filtered solu-
tion, thereby obtaining an ethylene glycol-water-carnallite solution;
~d) Dehydrating the ethylene glycol-water-carnallite solution of step (c) by
- 4 -
3~
distilling water there-frol~, thereby obtaining an anhydrous solution of mag-
nesium chloride in ethylene glycol which may contain up to about 2.0% potas-
si~ chloride (by weight) and a precipitate of cmhydrous potassium chloride,
said precipitate then being removed and recovered from said solution of mag-
nesium chloride in ethylene glycol;
(e) Adding anhydrous ammonia to the anhydrous solution of magnesium chloride
in ethylene glycol~ thereby forming a complex precipitate of MgC12 6NH3
which may contain small quantities of KCl, said precipitate being filtered
from the solution~ washed with a low molecular weight solvent for ethylene
glycol, said solvent having been saturated with anhydrous ammonia prior to
washing said precipitate and recovering said washed precipitate of anhydrous
MgC12 . 6NH3;
(f) Heating the MgCI2 6NH3 of (e) to temperatures sufficient to drive off
all ammonia, thereby recovering anhydrous magnesium chloride.
It is noted in step te~ that it is possible to remove trace quanti-
ties of potassium chloride from the MgC12 6NH3/glycol cake by washing it
with a low molecular weight solvent, for example methanol, saturated with
ammonia in quantities sufficient to remove the potassium chloride. This is a
surprising discovery since one would expect that the ammonia saturated solvent
would not sPlectively extract the potassium chloride from the magnesium chlo-
ride ammoniate-glycol filter cake.
The sequence of steps outlined in the previous paragraphs allows for
the production of anhydrous magnesium chloride of sufficient quality to be
used as cell feed in an electrolysis cell recovering magnesium metal. In ad-
dition, it also allows the recovery of potassium chloride of sufficient quali-
ty to be used commercially.
Another operation that is pre:Eerred in this invention is the simul-
taneous dissolution and precipitation reactions that occur when water-ethylene
-- 5 --
glycol solutions are added to the original carnallite mineral ores. This
mixture is then stirred and maintained at sufficient temperature to allow the
solubilization of the mixed potassium and magnesium chloride making up the
carnallite mineral ores. This solution, after treatment to remove any remain-
ing suspended solids, is then dehydrated by distilling water therefrom, there-
by obtaining an anhydrous solution of magnesium chloride in cthylene glycol
which may contain up to about 2% potassium chloride ~by weight). From this
point on the procedures outlined above are followed to recover both the anhy-
drous rnagnesium chloride, and the potassium chloride, as well as to recover
and recycle the ethylene glycol, anhydrous amrnonia, the low molecular weight
solvent which is used to recover the glycol that is entrained in the magne-
sium chloride ammonia complex precipitate, and to remove KCl from this complex
precipitate.
It has been found that the use of a carnallite which contains water
of hydration, for example MgC12 KCl 6H2O, allows the use of ethylene gly-
col without the addition of more water to solubilize the carnallite material
containing water of hydration. As an example of such a procedure, we present
the possibility of adding sufficient hydrated carnallite as described above
to ethylene glycol, such that a solution of magnesium chloride in the ethylene
glycol after dehydration and removal of precipitated KCl would be between 8-10
weight percent. This solution is then heated to temperatures sufficient to
distill from this solution the water of hydration contained in the original
carnallite. ~s this distillation proceeds, the potassiurn chloride precipi-
tates from the solution and may be recovered as described above. ~hen the
solution is totally anhydrous, the potassium chloride is removed by techniques
described or anticipated above, and the magnesium chloride-ethylene glycol
solution which may contain up to 2.0 weight percent potassium chloride is
treated with anhydrous ammonia to form the magnesium chloride/ammonia complex
-- 6 --
3~
precipitate and recovery steps are followed as described above. Subsequent
to the recovery steps mentioned, anhydrous magnesium chloride is recovered,
ethylene glycol is recovered and recycled, anhydrous ammonia is recovered and
recycled, and the low molecular weight solvent for ethylene glycol is also
recovered and recycled.
~ he processes developed for the beneficiation of the magnesium/
potassium sul-~ate ores are previously described as recovering economically
valuable salts. These two salts are anhydrous magnesium chloride and potas-
sium sulfate. This method of the beneficiation of these mixed salts contain-
ing potassium and magnesium sulfates comprise the following steps:
(a) Dissolving the mixed double salt containing magnesium and potassium sul-
fate in water at a temperature between 50C and 90C and then filtering the
insoluble residue from the soiution;
(b) Adding to and dissolving into the filtered solution of step ~a) a molar
equivalent to potassium chloride, the molar equivalent calculated on the basis
of the solublized magnesium cation requirement for chloride ion, thereby
forming a final solution;
(c) Heating the final solution of step ~b) to a temperature within the range
of 50C and 90C for a period of time sufficient to allow chemical equilibrium
to be established, thereby ~orming an equilibrated solution;
(d) Adding sufficient ethylene glycol to the equilibrated solution of step
~c) to fully dissolve all magnesium chloride calculated to be present in that
solution, then removing from the ethylene glycol-water solution the potassium
sulfate which precipitated on the addition of said ethylene glycol;
te) Distilling water from the solution of step (d) thereby forming an anhy-
drous magnesium chloride solution in ethylene glycol and an anhydrous precip-
itate of potassium sulfate, then removing said K2S0~ precipitate from said
solution;
- 7 -
3~ ~
~f) Combining the potassium sulfate precipita~es of steps (d) and ~e) and
washing said combined precipitates with sufficient water ~maintained below
70C) to remove entrained ethylene glycol, and recovering the washed potassium
sulfate~
(g) Treating the anhydrous magnesium chloride solution in ethylene glycol
formed in step (e) with anhydrous ammonia to form a magnesium chloride ammonia
complex which precipitates from the ethylene glycol solution;
~h) Removing the complex precipitate from the ethylene glycol and washing it
with a low boiling solvent for ethylene glycol to remove any ethylene glycol
entrained in the precipitate;
~ leating the magnesium chloride ammonia complex to drive off ammonia leav-
ing as a finished product completely anhydrous magnesium chloride.
The sequence of steps outline~ in the previous paragraphs also allows
for the production of anhydrous magnesium chloride of sufficient quality to
be used as cell feed in an electrolysis cell recovering magnesium metal. In
addition it allows for the recovery of potassium sulfate of sufficient quality
to be used in commercial grade fertilizers.
Another operation that is preferred in this invention is the simul-
taneous dissolution and exchange reactions that occur when the mixed magne-
sium and potassium sulfates mineral ores previously mentioned are added to amixture of water and glycol. This mixture is then stirred and maintained at
a temperature between 50C and ~0C for a period of time sufficient to dis-
solve the mixed double salt of magnesium and potassium sulfates.
To this mixture, after removal of any insoluble residues, either by
filtration, centrifigation, or any other technique commonly used to separate
solids from liquid solutions, is added sufficient potassium chloride to pro-
vide a molar e~uivalent of chloride ion for the solublized magnesiu~n cation
present in this mixed solution. The potassium chloride may be commercially
.3~'~
obtained or may be obtained from the previously outlined process for the bene-
ficiation of carnallite ores, if the two processes are operated simultaneously.
The rate of the dissolution of the added potassium chloride is enhanced by
increasing the temperature to at least 50C. A period of time sufficient to
allow chemical e~u;libration has been found to be at least 15 minutes at these
temperatures.
After chemical equilibration has been established in this solution
mixture, any residual precipitates are removed by common solid~ uid separa~
tion procedures. These precipitates contain primarily potassium sulfate. At -~
this point the mixture is dehydrated by a distillation process such that the
final solution derived following this distillatioll process is a mixture of an
anhydrous potassium sulfate solid precipitate in a solution of anhydrous MgC12
in ethylene glycol.
Again the anhydrous potassium sulfate is removed from this mixture,
washed with cold water to recover ethylene glycol, and isolated for sale as a
fertilizer. The remaining anhydrous magnesium chloride in ethylene glycol is
treated as above, that is, by addition of anhydrous ammonia, separation of the
magnesium chloride-ammonia complex from the ethylene glycol, washing the anhy-
drous magnesium chloride complex precipitate with a low boiling solvent for
ethylene glycol to remove the ethylene glycol entrained in this precipitate,
and finally heating the MgC12 ammonia complex to drive off and recover the
ammonia and leave as a finished product a completely anhydrous magnesium
chloride.
In the practice of this invention, the source of the mixed salts is
not particularly important. It is, however, important that the minerals used
as raw materials be somewhat free of impurities. ~lowever, it has been found
that by following the procedures outlined previously, even these impurities
can be precipitated and isolated from the products of these reactions. The
_ g _
. .
3~
impurities normally would be isolated either by initial filtration of a water
solution, by the second filtrations or solids isolation following the first
addition of glycol to the water solution, or finally isolated following the
total dehydration step leading to the magnesium chloride glycol solutions
mentioned above.
The reactions mentioned above are limited to those solutions that
contain water. A demonstration of this is found in an attempt to accomplish
the above reactions and the above beneficiation of the mixed salts containing
potassium and magnesium sulfates by the procedures outlined above in totally
anhydrous and non-aqueous solvent systems. Those solvent systems checked
included methanol, acetone, ethylene glycol, the diethylether of tetraethylene
glycol, and tetraethylene glycol. Without the presence of water, no metathet-
ical exchange reactions occurred that would be of more than nominal interest.
The organic solvent systems mentioned above were checked both as is and in the
presence of aqueous mixtures. There was no reaction between the potassium
chloride and the mine~als containing potassium and magnesium sulfate in the
organic solvents as is. Water had to be added for the metathetical exchange
reactions to occur. However, those reactions made using the solvent as an
aqueoussolution provided no additional benefit to the metathetical reactions
or their rates that occurred when using only an equivalent amount of water.
The presence of the organic compounds were not found to enhance the metatheti-
cal exchange reaction rates.
Various additives were used, and none used seemed to improve the
yield or the final brine concentration. The addition of small amounts of
polyacrylic acid, ammonium chloride, magnesium chloride, sodium chloride, and
calcium chloride had no effect on the extent of the metathetical reaction or
the rate of the metathetical reactions. Trace amounts of inorganic acids,
such as sulfuric acid and hydrochloric acid, seemed to depress the extent of
- 10 -
the reaction as well as the rate of the metathetical exchange reactions.
~ rom the work that we have completed, it would appear that ~he
potassium sul~ate ~ormed by the metathetical reactions outlined above or
initially present in the mixed salts must be removed from the solution as
the reaction proceeds to allow the maximum degree of this metathetical
reaction to occur.
~XAMPLES
50 Grams of carnallite ~MgC12 KCl 6~120) was added to 250 grams
of ethylene glycol. This solution was heated to the point at which water
began to distill from the solu~ion. This distillation was continued until
all of the water that had been contained in this precipitate was removed,
leaving behind an anhydrous solution which contained magnesium chloride,
potassium chloride and ethylene glycol. In this solution was suspended
anhydrous potassium chloride. This KCl was removed by filtration and the
remaining solution was then cooled to room temperature, and sufficient anllydrous
ammonia was added to precipitate from this solution all of the magnesium
chloride values obtained therein. After the precipitation of the magnesium
chloride/ammonia complex was complete? the complex precipitate was filtered
from the solution and washed with methanol saturated with ammonia. This
washing removed all of the entrained ethylene glycol contained in the mag-
nesium chloride ammonia complex precipitate. The precipitate cake also
contains some potassium chloride. Howevcr, this potassium chloride may
also be removed by washing with additional methanol saturated with amtnonia.
The potassium chloride recovered in the methanol wash as a solution in
methanol may be recovered from said solution by distillation procedures.
Table I presents the results o~ treating the original carnallite-
ethylene glyco] mixture mentioned above as outlined.
.
Z~
TABLE _
Complex Ethylene Glycol
Filter Cake Filtrate
-
Mg 8.75% Mg 0.05%
K0.86% K 1.04%
Cl ~7.26% Cl 2.22%
NH3 56.39%
After MeOH ~sat. NH~ Wash
Complex* Filtrate
10Filter Cake Wash Li~uor
Mg 11.27% Mg None Detected
K 0.43% K 0.09%
Cl 33.82% Cl 0.13%
NH3 ~remainder)
* Additional washing can rid the complex filter cake completely of KCl.
EXAMPLES
A typical example of the beneficiation of the mixed double salt con-
taining magnesium sulfate and potassium sulfate is outlined below.
2g.5 Grams of a double salt which analy~ed as containing 10.7% mag-
nesium and 18.2% potassium, the remainder being sulfate and trace quantities
o other salts, was added to 60 grams of water and heated to 80C. This mix-
ture was stirred and allowed to dissolve (approximately 5 min.). To this
mixture was added 14.9 grams of potassium chloride followed by additional
stirring and heating. A reaction time and equilibration time of rom 3 to 10
minutes was allowed. This mixture was then filtered to accomplish a removal
of insoluble salts. To the filtrate was added 90 grams of ethylene glycol.
This mixture was then heated until the water began to distill from these mixed
- 12 -
:
.~ ,
;3~(a
solutions. As the water is removed, anhydrous potassium sulfate precipitates
from the solution remaining. The distillation is complete when no further
water can be removed from the solution mixture remaining~ At that time the
entire amount of potassium sulfate initially present has precipitated and the
remaining solution is com~osed of anhydrous magnesium chloride in ethylene
glycol. This anhydrous solution of magnesium chloride in ~lycol is recovered
through a fi~tration or any solids~ uid separation technique of choice while
simultaneously recovering the glycol wetted potassium sulfate precipitate.
The potassium sulfate precipitate is given a cold water wash ~temperatures are
maintained below 70C) and analyzes at a sufficient quality to be sold as a
potassium sulfate fertilizer. The MgC12 solution in ethylene glycol is ex-
posed to anhydrous ammonium chloride which precipitates the MgCL2 as a complex
whose formula is thought to be MgC12 6NH3. This MgC12 ammonia precipitate
is removed from the glycol solu~ion, washed with a solvent for ethylene glycol
that is a low boiling solvent, and then heated to temperatures that are suf-
ficient to drive off the complexed ammonia. These reactions to isolate the
anhydrous MgC12 from the MgC12 ammonia complex are outlined in United States
patents 3~983,244 and United States 3~966,888.
Additional work was done which allowed the definition of reactions
which would lead to a higher concentration of MgC12 in both the initial brines
as well as the ethylene glycol-MgC12 brines. The summary of the reactions `
are given in Table II. This table will outline the amount of double salt
reaction with KCl, the amount of water and ethylene glycol used in the reac-
tion, the temperatures of the reaction, the extent of the metathetical ex-
change, and the effects of any added salts such as magnesium chloride, sodium
chloride and calcium chloride.
- 13 -
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~ xamination of Table II and observations made when at~empting to
work with more concen~rated solutions of the double salt containing MgS0~ and
K2S04 allow us to conceive of a process that would convert only a portion of
the double salt magnesium values to anhydrous MgC12 in glycol. The portion
of unreacted double salt, unreacted potassium chloride, and the potassium sul-
fate product derived from the metathetical excharlge reaction that would be
present in the precipitates in the previously described process steps could
be recycled back to earlier process steps and s~ill derive the benefits of
the invention.
The combination of the above techniques allows the recovery of anhy-
drous magnesium chloride by simultaneously treating carnallite ores, as pre-
viously described, and mixed sulfate ores containing magnesium and potassium
values. Figure I outlines in block diagram form a potential process for
accomplishing this benficiation and recovery of high purity, high quality,
anhydrous MgC12 suitable for use as electrolysis cell feed in the recovery of
magnesium metal. Either anhydrous KCl or anhydrous K2S0~ or a combination of
the two may be recovered by this process, depending on the relative amounts
of either type of mixed ores are being processed.
; The blocks in the process outlined in ~igure I are meant to repre-
sent each of the steps previously described in the separate detailed outline
of the individual processes. The benefits of the combined process are as
follows: First, only a single processing scheme is necessary to isolate MgC12
(anhydrous) from the MgC12 . 6NH~/glycol slurry formed in both processes.
This eliminates equipment duplication and has obvious economic adv~mtages;
Secondly, the KCl byproduct obtained from the carnallite beneficiation may be
used advantageously as a raw material in the initial metathetical exchange
reactions required for the beneficiation of the mixed Mg/K sulfate salts;
Lastly, the combination of the two processes allows technical, processing,
- 16 -
and economic variability which may be used to advantage depending on pricingand availability of all raw materials.
Although Figure I describes, in diagram form a combination, it is
not our intention to be limited by its particular schematic design. Many
flexabilities may be anticipated from the diagram as well as the previous
descriptions.
- 17 -
'
