Note: Descriptions are shown in the official language in which they were submitted.
WO~ 097 2~96~ PCT/US91/~96~9
MAGNESIUM ~YDROXIDE ~AVING STAC~ED LAYER, C~YSTALLINE
STRUCTURE AND PROCESS THEREFOR
Magnesium hydroxide can be produced by adding a
water-soluble alkaline ~a~erial to an aqueous solution
of a magnesium salt at atmospheric pressure or slightly
above and temperatures fro~ slightly above room
temperature to about lOO degrees centigrade (C) or
slightly higher. The precipitate which forms on
standing forms small crystals whose largest dimension
does not exceed about 5 microns and whose thickness is
in the range of about 300 to about 900 angstrom units.
The use of i~organic fillers such as magnesium hydroxide
- to provide flame retardancy in thermoplastic resins is
known.
The prior art does not disclose magnesium
hydroxide particles structurally characterized by a
predominant mul~ilayered, stacked, crystalline ;
structure. The magnesium hydroxide of the invention can
be prepared by a batch or continuous mixing process, as
disclosed herein, wherein each layer of the multilayered
structure is a single crystal of magnesium hydroxide
that forms o~ ~he (000l) plane of brucite. The-stacked
layers form elongated particles where the plane of each
... .. . ... .. ...... ... .
WO 92/12097 P'Cr/lJS91/096~,
~7'
~3~ 2-
layer is perpendicular to the long axis of the
cylindrical particle.
The particulate magnesium hydroxide of the
invention is particularly suited for use in conjunction
- with thermoplastic synthetic resins to provide flame
retardancy thereto. In this application, the solid
particles of magnesium hydroxide can be utilized
subsequent to coating with a surfactant or can be
utilized without any coating thereon.
Figures 1 and 2 are reproductions of
photographs taken magnified 30,000 times of a sample of
magnesium hydroxide produced respectively in a batch
process and in a continuous process. The multilayered,
stacked~ crystalline structure is evident.
Figure 3 is a graph showing the particle size
distribution of two sa~ples of a magnesium hydroxide
produced by the continuous process of the invention~ as
shown in lines labeled "A" and ;'B". The particle size
distribution of a prior art magnesium hydroxide is shown
in the line identified as "C".
Figures 4 and 5 are rep~oductions of
2~ photographs taken magnified 10,000 and 30,000 ~imes,
respectively, of a sample of magnesium hydroxide
produced in the continuous process of the invention.
The present invention includes a batch or
3 continuous method for the production of a magnesium
hy~droxide having a particulate, crystalline structure
with a fine plate-like form, characterized by:
(a) mixing a concentrated aqueous mixture of an
alkaline material and a magnesiu~ containing salt,
WO92/12097 PCT/US91/09629
--3--
wherein the mixture comprises 20 to 60 percent by weight
of a mixture of reactants comprising an alkaline
~aterial and a magnesiu~ containing salt and said
alkaline material is used in a stoichiometric excess of
the amount present of said magnesium containing salt and
(b) heating the mixture at ambient pressure to
convert said magnesium containing salt to magnesium
hydroxide with a plate-like form 30 to 200 Angstrums
thick and a median particle size of up to l micron.
The method of preparing the novel particulate,
crystalline structure magnesium hydroxide characterized
predominantly as multilayered and stacked, comprises
mixing an aqueous solution of a magnesiu~ salt,
described in examples 6 through 9, with an alkaline
material and heating ~he mixture at ambient pressure and
elevated temperature to precipitate the magnesium
hydroxide. The temperature used for heating the mixture
is between 40C and 120C, preferably, 50C to 1~0C, and
most preferably~ 65C to 80C. At temperatures of less
than 40C, the reaction time is unsatisfactorily slow.
In the process of the invention, less than an
equivalent amount of an alkaline material is mixed in an
aqueous medium with a magnesium containing salt and the
mixture reacted by-heating at ambient pressure to
precipitate magnesium hydroxide. Alternatively, in the
process of the invention, less ~han an equivalent amount
of a magnesium containing salt is mixed in an aqueous
medium with an alkaline material and ~he mixture heated
at ambient pressure to convert the magnesium containing
salt to magnesium hydroxide. Generally, the alkaline
material and the magnesium salt reactants are combined
.. . : ., . . ~.~ . . .: . .... . . . . . .... . .
... . . ~ . . . . . . : . . , ; : .
WO92/12097 PCl/US91/09629
q~ 4 ~
in the proportion of 0.7 to 1.30 equivalen~ of one of
said reacta~ts per equivalent of the other of said
reactan~s, preferably, a proportion of 0.85 to 1.15
equivalent, and most preferably, 0.95 to 1.05
equivalent. In the processes of the invention, the
reactants (alkaline material and magnesium containing
salt) are present in a high concentration. Generally,
the reactants are present at a ~otal solids content of
20 to 60 percent by ~eight based upon the total weight
of reactants and aqueous medium preferably7 the total
solids of reactants is 20 to 45 percent by weight, and
most preferably, 25 to 35 percent by weight.
Generally, the precipitation reaction at
elevated temperature is continued for 1 to 4 hours,
preferably, 1 to 3 hours, and, ~ost preferably, 1 to 2
hours. Thereafter, the precipitated magnesium hydroxide
is separated by filtration or other convenient means
from the aqueous medium and fro~ the soluble salts
dissolved therein. Washing the precipitate with water
and subsequent re-filtration may be necessary to
appropriately reduce the concentration of residual salts
associa~ed with the precipitated ~agnesium hydroxide.
Generally, the residual soluble salt concentration is
reduced to 0.05 percent by weight to 5 percent by
weight, preferably 0.2 percent to 3 percent by weight
and, most preferably, 0.1 percent to 1 percent by
weight.
3 Should it be desirable to reduce the specific
surface area of the particulate ~agnesium hydroxide of
the invention, the magnesium hydroxide, subsequent to
reaction, filtration, and washing, may be redispersed in
water a~d further reacted in a post reac~ion by heating
at elevated te~perature. The reaction mixture concen-
W092/12097 PCT/US9l/09629
~ 2 ~ 9 ~
tration, temperature, and time for reaction are the same
as previously indicated for the initial precipitation
reaction. A substantial reduction in specific surface
area is obtained by this post reaction, provided the -
magnesium hydroxide is post-reacted in an aqueous medium
which is substantially free of dissolved salts.
Generally, a soluble salt concentra~ion of 0.05 percent
to 5 percent by weight, preferably, 0~2 percent to 3
percent by weight, and, most preferably, 0.1 percent to
1 percent by weight is required in the reactant mixture
during the post reaction. The preferred particulate
magnesium hydroxide of the invention is characterized by
a predominane distinctive multi-layered, stacked,
crystalline structure, a median particle size produced
in the batch process of about l micron, and a particle
size distribution in which 70 percent of the magnesium
hydroxide par~icles are within 0.6 to 3.9 microns or a
continuous process in which about 80 percent of said
particles are within 0.3 to 1.6 microns.
Any magnesium salt which is soluble in water
can be used for making the Mg(OH)2 of this invention by
the procedure defined above. Representative inorganic
magnesium salts are MgF2, MgC12, MgBr2, MgI2, MgBrO3,
MgBrO4, MgC103, MgC104, MgCrO4, MgFeO4, MgS04, MgSo3,
MgS203, Mg(MnO4)2, MgMoO4~ Mg(N03)2. Magnesium salts of
organic acids can also be used, provided they are watér
soluble. Representative salts of orga~ic acids include
those of fatty acids having from l to about 6 carbon
atoms, such as magnesium formate, ace~ate, propionate,
butyrate, pentanoate, hexa~oate, citrate or a salt of an
aromàtic acid such as magnesium benzoate, salicylate and
phthalate.
:,
.. ~ .. . , .. ., . . , ~ . . . .
, i . . . . . ~ , .
,. . ,. ~
W092/12097 PCT/US~1/09629
~ 6- -
The preferred magnesium salts are those of
sulfuric7 nitric and hydrochloric acid, the most
preferred salt being MgC12, because of its ready
availability from sources all over the world.
Preferably, the magnesium salt is a brine
comprising an aqueous solution of an alkali metal or an
alkaline earth ~etal halide salt including magnesium
chloride. More specifically, both natural and synthetic
brines which contain at least about 15 total weight
percent of the chlorides of magnesium and calcium are
preferred. The brine usually contains at least 2
percent by weight of magnesium chloride.
The alkaline material can be an amine or a
slaked calcined dolo~ite or an alkali or alkaline earth
metal hydroxide or mixtures thereof.
The use of calcined dolomite in the production
of magnesium hydroxide has certain inherent advantages
over the use of calcined limestoneO Among such
advantages are the high yield of magnesium hydroxide
when dolomite is employed since, when calcined, it
contains about 1 mole of MgO per mole of CaO and,
therefore, when reacted with a magnesium chloride-
containing brine and the magnesium oxide becomes
hydrated, it yields substantially two times the a~ount
of magnesium hydroxide which would be produced from the
reaction of calcined limestone with an equal quantity of
the brine. Dolomite is relatively plentiful, being
found in a substantially high degree of purity, and is
often located conveniently near natural brine sources~ -
as for example, in the state of Michigan, U.S.A.
~ 92/12097 2 ~ L p~r/us9l/o9629
_7_
Disadva~tages, however, have heretofore been
associated with the production of magnesium hydroxide as
a precipitate employing dolomite as a raw ~aterial,
salient among which have been its poor fil~erability
when separating it as a filter cake from the mother
liquor and when dewatering it folLowing washing or
following reslurrying of the washed cake. The low
solids, i.e., the low density of the filter cake
produced during filtration (often as low as 30 to 35
percent solids) is also undesirable and particularly
undesirably is the high contamination of the product
produced from water-slaked dolime unless promptly used,
pareicularly calcium contamination, which has also been
associated wi~h contamination of the magnesium hydroxide
precipitate from ingredients present in the brine,
especially chlorides and borates. De~atering refers to
the step of concentrating an aqueous slurry of magnesium
hydroxide, this step being commonly carried out by
employing a rotary vacuum filter.
Among the larger uses of magnesium hydroxide is
the manufacture of periclase-type refractory products
which cannot tolerate an appreciable contamination of
the magnesium hydroxide. Difficulties arising from
contamination by calcium ha~e been particularly
troublPsome. As much as 1.5 percent calcium oxide in
the ignited ~agnesium hydroxide product is generally
con-idered a maximum contamination for commercial
acceptance and not more than 1 percent CaO is preferred.
A number of large deposits of dolomite are substantially
pure, e.g., ~he Cedarville quarries of Michigan, which
by analysis shows this deposit to consist of about 1.03
moles of CaC03 per mole of MgC03 with a small percent of
iner~s. The only concern regarding contamination in the
, " , ; ,., . . . , i . : !."' ' " ' ~: ' ~ '
WO92/12097 PCT/~S91/09629~
N ~ ~ 8-
use of such dolomite as a source material is calcium
co~tamination of the magnesium hydroxide.
In addition to a conventional batch process of
precipitation, the magnesium hydroxide of the invention
can be prepared utilizing ultrasollic mixing means
preliminary to heating the mixture to complete the
conversion reaction or precipitation of magnesium
hydroxide. Precipitation of magnesium hydroxide
utilizing ultrasonic vibration produced with a wave
direction coinciding with the direction of precipitation
of the salts is kno~mi. These waves increase rapidity of
precipitation owing to the fact that the waves are
propaga~ed in the same direction as that in which the
precipitates fall. It is well kno~n that the device for
producing the ultrasonic or supersonic waves can be
disposed on, for example, a pipeline for discharging
water from a decanting reactor.
If desired, the magnesium hydroxide of the
invention may be treated with an anionic surfactant to
form solid particles of magnesium hydroxide coated with
the surfactant. This form of the magnesium hydroxide of
the invention is more preferred when using it as a flame
retardant or flame-retarding filler for thermoplastic
resins or in water-soluble paints. The coating process
can be performed by contacting the magnesium hydroxide
with an anionic surfactant or by contacting e;ther or
both the reactan~s with an anionic surfactant prior to
3 the productio~ of the magnesium hydroxide of the
invention. For example, an aqueous solution of a
desired amou~t o~ an anionic surfactant is mixed with
solid particles of the magnesium hydroxide under -
co~ditions such that they contact each other i~timately,
for example, by agi~ating them sufficie~tly9 or by
WOg~/12097 PCT/lJS91/09629
2 ~ ~ ~3 ~
thermal treatment of an aqueous slurry at 120 to 250C.
A solid powder of magnesium hydroxide coated ~ith the
anionîc surfactant is formed upon removal of water. The
surfactant is chemically adsorbed onto the surface of
the solid particles of the magnesium hydroxide. This
can lead to improved properties (as co~pared to uncoa~ed
magnesium hydroxide) when the magnesium hydroxide i5
incorporated in thermoplastic synthetic resins or in
water-soluble paints.
The amount of the anionic surfactant to be
applied as a coating can be adjusted for opti~um
results. Solid magnesium hydroxide powder of this
invention coated by using an aqueous surfactant solution
containing 5 millimoles to 30 milli~oles per liter of
water, of the surfactant is preferred. For example, the
a~ount of the anionic surfactant adsorbed onto the solid
particles of the magnesium hydroxide of this invention
is preferably 1/4 to 3 times, more preferably 1 to 2.5
times the amount (X in millimoles) required to coat the
entire surface of the solid particles (one gram) with a
monolayer of the surfactant molecules. The amount X
(millimoles) can be calculated in accordance with the
following equation.
y
X = _ (millimoles)
6.0Z X C
wherein C is the absolute value of the adsorption cross-
sectional area [(A)2] per molecule of the anionic
surfactant used and Y is the absolute value of the
specific surface area (~2/g) Of the magnesium hydroxide
o~ this inventionr
According to this inventi~n, there can be
provided a composition containing uncoated magnesium
hydroxide of this invention or the magnesium hydroxide
.. . . .
. : : . ,. . 1' ~ - ,
'
W092/12097 PCT/US~1/09629
of this invention coated with an anionic surface active
agent. For example, compositions having improved
properties, es~ecially those useful fcr melt shapingl
can be provided by incorporating the coated or uncoated
magnesium hydroxide of this invention in a thermoplastic
synthetic resin, preferably those having great
hydrophobicity and great non-polarity, as a flame
retardant or flame-retarding filler in an amount of 50
to 250 parts by weight (pbw) per 100 pbw of the resin.
Examples of the thermoplastic synthetic resin include
styrene resins such as a homo- or co-polymers of
styrene, olefin resins such as homo- or co-polymers of
olefins, polyester resins9 polycarbonate resins, nylon
resins, acetal resins, and blends of these resins.
These compositions may be provided in the form of melt-
shaped articles. Furthermore, by incorporating the
coated or uncoated magnesium hydroxide of this invention
in paints or lacquers in an amount of 5 to 150 pbw per
100 pbw of the resin vehicle, paint compositions having
improved properties can be obtained. ;~
Various conventional additives may further be
incorporated in the thermoplastic synthetic resin
composition or in paint compositions in accordance with
thi s inven t i on . ,
Examples of these additives are coloring agents
(organic and inorganic pigmen~s) such as isoindolinone,
cobalt aluminate~ carbon black, or cadmium sulfide,
other fillers such as calcium carbonate, alumina7 zinc
oxide or talc; antioxidants such as 2,6-di-t-butyl-4-
methylphenol, 2,2'-methylenebis (4-methyl-6-t-butyl-
phenol), dilauryl thiodipropionate or tridecyl
phosphite; ultraviolet absorbers such as 2-hydroxy-4-
meehoxy ben~ophenone, 2(2'-hydroxy-5'-methylphenyl)
WO92/12097 PCT/US91/0~62~
2~9l3~1 ~
benzotriazole, 2-ethylhexyl-2-cyano-3,3-diphenyl
acrylate, phenyl salicylate or nickel-bisoctyl phenyl
sulfide; plasticizers such as di-2-ethyl hexyl
phthalate, di-n-butyl phthalate, butyl stearate, or
epoxidized soybean oil; and lubricants such as zinc
stearate, calcium~ aluminum and o~her metal soaps, or
polyethylene wax.
These additives can be used in customary
amountsO For example, the amount of the coloring agent
1~ is 0.1 to 3 pbw; the amount of the other filler is up to
20 pbw; the amount of the antioxidant or ultraviolet
absorber is 0.00l to ~ pbw; the amount of the
plasticizer is up to 20 pbw; and the amount of the
lubricant is up to lO pbw. All these amounts are based
on 100 pbw of the resin component.
The anionic surface active agent (surfactant)
used to coat the magnesium hydroxide of this invention
includes, for example, alkali metal salts of higher
fatty acids of the formula
RCOOM
wherein R is an alkyl group containing 8 to 30 carbons
atoms, and M is an alkali metal atom, alkyl sulfate
salts of the formula
ROSO3M
wherein R and M are the same as defined above,
alkylsulfonate salts of the formula
RSO3M
.... .. . .. .. . ...... .
W092~12097
PCTJUS91/0~6
-12-
wherein R and M are the same as defined above, alkylaryl
sulfonate salts of the formula
R-aryl-S03M
wherein R and M are the same as defined above, a~d
sulfosuccinate ester salts of the formula
ROCOCH2
ROCOCHS03M ;
wherein R and M are the same as defined above. These
anionic surfactants can be used either alone or in :
admixture of two or more.
Specific examples of the surface active agent
are sodium stearate, potassiu~ behenate, sodium
montanate, potassium stearate, sodium oleate, potassium
oleate, sodiu~ palmitate, potassium palmitate, sodium
laurate, potassium laurate, sodium dilaurylbenzene-
sulfonate, potassium octadecylsulfate, sodium lauryl-
sulfona~e or disodium 2-sulfoe~hyl Q-sulfostearate.
Alternatively, the magnesium hydroxide of the :
invention can be coated with a fatty acid ester of a
polyhydric alcohol. For some purposes, such coating is
superior to the use of a coating of an anionic surface
active agent such as an alkali metal salt of a higher
fatty acid. The polyhydric alcohol can have 2 to 6
hydroxyl groups and is represented by such compounds as
ethylene glycol, propylene glycol, glyceryl,
trimethylolpropane, pen~aerythritol and .
dipentaerythritol. Of these polyhydric alcohols 9 those
of the neopentyl series such as dipentaery~hritol,
pe~taerythritol, and trimethylolpropane, are preferably
in view of their stability at high temperatures. A
sa~urated fatty acid having 4 to 24 carbon atoms,
WO92/l2097 PCT/US91/09629
2 ~ 9 ~ Q!,~
-13-
preferably, a saturated straight chain fatty acid having
8 to 18 carbon atoms or a mixture of acids having the
above defined carbon atoms on ~he average can
advantageously be used as the fatty acid constituent.
The fatty acid ester of the polyhydric alcohol can be a
completely esterified compound wherein all hydroxyl
groups in the starting polyhydric alcohol are esterified
or a partial ester, wherein only a part of the hydroxyl
groups are esterified.
The use of magnesium hydroxide in thermoplastic
polymer materials has replaced the prior use of a
mixture of antimony trioxide and a halide compound such
as a vinyl chloride resin as additives useful for
incorporating flame retardancy in thermoplastic
materials. This is because the use of magnesium
hydroxide in thermoplastics as a flame retardant results
in thermoplastic composites which emit less smoke and
less toxic smoke as compared to thermoplastic composites
containing halogenated flame retardant additives. The
prior art use of a combination of antimony trioxide and
a halide as flame retardant additives in a thermoplastic
material also results in the evolution of a halogen gas
during the molding operation utilized to form specific
objects from the thermoplastic resins so compounded for
flame retardancy. The evolution of halogen gas leads to
the corrosion of molding machines and metal molds and
results in a toxic environment for workers involved in
the moldi~g operation. The incorporatio~ of magnesium
hydroxide in thermoplastic materials to provide flame
retardancy is superior in accomplishing the desired
result without the deleterious effect of the evolution
of a halogen gas during the molding operation.
- . .. : ~ .: .,
. . ~
. . ~
W092/l2~97 PCT/US91/0962
~ 14-
Suitable thermoplastic resins for use with the
magnesium hydroxide of this inve~tion include: poly- - -
propylene, propylene-ethylene copolymer, polyethylene,
ethyle~epropylene copolymer, ethylenevinyl acetate
copolymer9 polystyrene, acryloni~rile-butadiene-styrene
copolymer, acrylonitrile-styrene copolymer. Especially
suitable are polyolefins such as polypropylene,
propylene-ethylene block or random copolymers, hi~h-
density or low-density polyethylene.
The following examples illustrate the various
aspects of the invention but are no~ intended to limit
its scope. Where not otherwise specified throughout
this specification and claims, temperatures are given in
degrees centigrade and parts, percentages, and
proportions are by weight.
Example l
An aqueous lime slurry containing 23 percent by
weight cal~ium hydroxide and 17 percent by weight
magnesium hydroxide and having a total solids content of
40.5 percent by weight was pretreated with an anionic
surfactant sold under the trade name Silwet 7604 at a
z5 ratio of 1.5 grams surfac~ant per liter of lime slurry
by mixing the lime slurry with the surfactant for 30
minutes. Silwet is sold by the Union Carbide
Corporation.
An aqueous brine solution containing 8.9
percent by weight magnesium chloride, 17 percent by -
weight calcium chloride, 009 percent by weight sodium
chloride, and lesser amoun~s of other salts including
those of strontium, lithium, boron, and iron having a
total solids content of 27.8 percent by weight was
W092/12097 PCT/US91/09629
similarly treated with Sil~et 7604 (an organo modified
polydimethyl siloxa~e) anio~ic ~;urfactant at a ratio of
0.42 grams of suractant per lit:er of brine solution
utilizing the process described above.
The anionic surfactant treated lime slurry was
heated in a vessel under agitation to 71C and,
thereafter the brine solution at ambient temperature was
pumped into said veqsel containing the lime slurry over
a period of 95 minutes. The pH of ~he mixture ~as 6.6
0 at the end of the brine addition. The temperature of
the vessel containing the mixture was mai~tained at
about 71~C. After all the brine had been added, the -
addition of heat to the vessel was terminated and the '
contents of the vessel were thereafter stirred for a
period of about 18 hours. A small additional volume of
brine was then added to adjust the pH of the slurry to
7~0. The amount of lime slurry utilized tu combine with
the brine was 0.9 equivalent. The slurry was
subsequently filtered and washed to remove calciu~
chloride. ,~
Upon analysisO the magnesiu~ hydroxide
particles recovered from this batch process were found
to have a median particle size of 0.87 micron, as
determined with a Micromeritics Sedigraph which combines
the principle of sedimentation ~ith X-ray detection in
order to obtain this measurement of particle si~e. The
particles consist of stacked layers, each of ~hich i5 a
3 single crystal of mag~esium hydroxide having a unit
layer thick~ess of 30 to 200 Angs~roms. Electron
diffraction patterns recorded from individual particles
show that,the crystal structure of this layered material
is brucite, a known form of magnesium hydroxide. There
are small crystallographic rotatio~s between adjoining
., , - . .
- ~, . . . .
WO92/12~97 PCT/US91/0962~_
~ ~16-
layers. The individual particles are ~ot single
crystals; rather they are highly--ordered stacks of thin
crystals. Each layer of brucite forms on the (0001)
plane, and the stacked layers form elongated particles
whose long dimension, normal to the (0001) plane, is the
brucite c-axis. The long dimension of the particle is
typically 0.25 to 1 micron, a~d t:he width of the
particle is typically about half the length. Whe~
viewed perpe~dicular to the c-axis, many of the
partieles are seen to taper to~ard the e~ds. The shape
of each magnesium hydroxide layer is irregular and
varies from triangular to hexagonal to circular. Hence,
the layer dia~eter within a single particle varies form
100 to 1700 Angstroms, and, therefore, the particle
diameter varies. This variation in particle diame~er
gives the particles a distinct layered corrugated
appearance when vie~ed perpendicular to the c-axis.
Exam~le 2
Example 1 ~as repeated except that the lime
slurry and the brine solution were not treated with an
anionic surfactant prior to combination and heating to
precipitate the magnesium hydroxide. The resulting
magnesium hydroxide particles upon determination of
particle size in accordance ~ith the method utilized in
Example 1, had a median particle size of 1.0 micron and
substantially similar morphology.
Example_3
., ., .: ~ v, ,.
Example 2 ~as repeated except that the li~e
solution was added to the brine solution. This was
heated to 71C u~der agitation and, ~hereafter, the lime
solution at ambie~t temperature was added to the
?
WO92/12097 _17_2~ PCT/US91/09629
vessel containing the brine slurry. The resulting
magnesium hydroxide had a median particle size of l.l
microns and substantially similar morphology.
Example 4
~ xample l was repeated except that a continuous
process was used and the li~e slurry of Example l was
pretreated with Silwet 7604 anionic surfactant at a
ratio of 2.6 grams surfactant per gallon of slurry in
accordance with the procedure described in Example l.
The brine solution described in ~xample l was similarly
pretreated with this anionic surfactant at a ratio of
2.6 grams surfactant per gallon of brine solution.
Thereafter, both the lime slurry and the brine ;
solution at ambient temperature were pumped
simultaneously into the ultrasonic ~ixing chamber of a
"Model A" Sonolator ho~ogeni~er manufac~ured by Sonic
Engineering Corporation, Norwalk, Connecticut. The
ratio of the speed of the pump utilized to pump the
brine solution into the ultrasonic mixing chamber over
that of the pump utilized to pump the lime slurry into
the ultrasonic mixing chamber was 3.5 which is
equivalent to providing a 14 percent excess of brine
solution over the stoichiometric ratio required to react
the brine solution with the lime slurry. In this
example, the brine solution and the lime slurry were
pumped into the ultrasonic equip~ent ~ixing chamber at
ambient temperature and at a pressure of 400 to 500
pounds per square inch. The mixed lime slurry and brine
solution were thereafter poQt-treated by placing the
~ix~ure in a tank fitted with an agitator and a steam
coil. Agitation and heating at the boili~g point were
, . . ,, . , . . ., .,, . ~
.,: -, ` ' . ~' ' ' ,,
W092/l~097
PCT/US91/0962~
~ .
continued for a period of two hours and7 thereafter9 the
mixture was filtered and washed ~7ith water.
The magnesium hydroxide product obtained ~as
found to have a median particle size of 0.61 micron with
90 percent by volume of the particles having a particle
size of less than 0.93 micron ancl 10 percent of the
particles having a particle size of less than 0.42
microns.
Exa~le 5
Example 4 ~as repeated except that no anionic
surfactant was used to pretreat the lime slurry and the
brine slurry. Substantially similar results are
obtained.
Example 6
An aqueous lime slurry containing 23 percent by
weight calcium hydroxide and 17 percent by weight
magnesium hydroxide and having a total solids content of
40.5 percent by weight was pretreated ~ith Silwet 7604
anionic surfactant at a ratio of 1.3 grams surfactant
per gallon of lime slurry by mixing the lime slurry with
the surfactant for 30 minutes.
An aqueous brine solution containing 8.9
percent by weight magnesium chloride, 17 percent by
~eight calcium chloride, 0.9 percent by weight sodium
chloride, and lesser amounts of other salts including
those of strontium, li~hium, boron, and iron having a
total solids content of 27.8 percent by weight was
si~ilarly treated with Silwet 7604 anionic sur~actant at
W O 92/12097 P~r/US91/09629
~ 20~6~
,9
a ratio of 1.3 grams of surfactant per gallon of brine
solution utilizing the process described above.
The anionic surfactant treated lime slurry was
pumped into the ultrasonic mixi~g apparatus described
above. Similarly, the anionic surfactant brine solution
was pumped fro~ a vessel containing the brine solution
to the ultrasonic mixing apparatus. The "Model A"
So~olator used as an ultrasonic mixing means was set at ~-
a pressure of 400 psi. The ratio of the speed of the
pump used to pump the brine solution into the ultrasonic
mixing cha~ber over that speed of the pump used to pump
the lime slurrg into the ultrasonic mixing chamber was
3.5, which is equivalent to providing a 14 percent
excess of brine solution to the lime slurry. The amount
of lime slurry utilized to combine with the brine was
0.9 equivalent. Subsequent to ultrasonic mixing, the
reaction mixture was transferred to a post treatment
mixing tank and heated for 2 hours at 105~G. The
precipitated magnesium hydroxide was recovered from the
aqueous medium by filtration and washing of the
precipitate to remove salts.
Upon analysis, the magnesium hydroxide
particles recovered from this continuous process were
found to have a median particle size of 0.7 micron, as
determined with a Micromeritics Sedigraph which combines
the principle of sedimentation with X-ray detection in
order to obtain this measurement of particle size.
3 About 80 percent of the particles were within 0.3 to 1.4
microns. The particles consist predominantly of
individual plate-like formed particles many of which are
0.25 to 0.3 micron in width. Each of the particles is a
single crystal of magnesium hydroxide having a unit
layer thickness of 30 to 200 Angstroms. Electron
.
,
.
- .;
WO92/12097 PCT/US91/096
6~ 20- .
diffraction patterns recorded from i~dividual particles
show that the crystal structure of these particles are
brucite, a known for~ of magnesium hydroxide.
Example 7
Example 6 was repe~ted except that the lime
slurry and the brine solution were not treated with an
anionic surfactant prior to mixing by ultrasonic means
and heating to precipitate the magnesium hydroxide. The
resulting magnesium hydroxide particles upon
determination of particle size in accordance with the
method utilized in Example 6, had a median particle size
of 0.8 micron and substantially similar morphology.
Example 8
Example 6 was repeated except that the lime
slurry and the brine solution were heated to 71C prior
to mixing by ultrasonic means. Substantially similar
median particle size and morphology are obtained in
comparison with that obtained in ~xample 6.
Exam~le 9 `
.:
~xample 8 was repeated except that the lime
slurry and the brine solution were not treated with an
anionic surfactant prior to mixing and heating to
precipitate the magnesium hydroxide. Substantially
similar median particle size and morphology are obtained
as compared to Example 8.
