Note: Descriptions are shown in the official language in which they were submitted.
2 1 -t~8
Attorney Docket No. 442-175
IMPROVED BASIC ALUMINUM HYDROXYCHLOROSULFATE PROCESS
AND PRODUCT THEREFROM
FIELD OF THE INVENTION
This invention relates to an improved process for
preparing basic aluminum hydroxychlorosulfates. In particu-
lar it relates to the product therefrom and its use in water
treatment.
BACKGROUND OF THE INVENTION
It is well known that various aluminum compounds can
be used as a coagulant in the treatment of water. The most
common of these compounds is alum. Notwithstanding the fact
that they are more expensive, basic aluminum chlorides
("BAC") have found acceptance as coagulating agents because
of their improved efficiency over alum. BAC has several
advantages over alum. The BAC coagulants are effective in
lower alkalinity water where alum is relatively ineffective,
and BAC has a lesser impact on pH reducing the need for lime
or caustic treating of water to bring it within the potable
range. The coagulating plant operation is improved since with
BAC there is a longer period between backwash. See for
example U.S. Patent Nos. 2,858,269, and 3,270,001 incorporat-
ed herein by reference. A more recent development has been
the introduction of basic aluminum hydroxychloride sulfates
("BACS") for use as coagulating agents in water treatment.
BACS solutions are prepared by introducing di-valent
sulfate ion into the BAC structure. Prior art methods for
21 7&6~8
producing BAC are disclosed in U. S. Patent Nos. 3,497,459;
3,544,476 and 4,981,673 all of which are incorporated herein
by reference.
U.S. Patent No. 3,544,476, discloses a method for
preparing BACS by introducing an anion (Y) into the struc-
ture of a basic salt compound having the general formula
Mn(OH)mX3n-m
M is a metal of tri or higher valency, X is an anion capable
of forming a monovalent acid, 3n is greater than m and the
basicity, defined as m/3nxlOO, is in the range of about 30 to
83%. Y is an anion capable of forming a di or greater valent
acid. M can be aluminum, chromium or iron. Where M is
aluminum and X is chlorine the basic compound is a BAC.
The anion, Y, is chemically introduced into the basic
salt structure in the form of an acid or its soluble metal
salt. Examples of Y are the anions of sulfuric, phosphoric,
polyphosphoric, chromic, bichromic, carboxcylic and sulfonic
acids. X is preferably Cl, but can be I, N03 or CH3COO. In
this process the production of BAC is not an intermediate
step along the route to the formation of a BACS.
The range of the ratio Y/M is about 0.015 to about
0.4. A BACS is formed by conducting the BACS forming reac-
tion in the presence a multivalent acid ion in an acid hy-
drolysis solution, e.g hydrochloric acid of Al. The BACS may
be obtained by the separation of an insoluble sulfate pro-
duced by the addition of the hydroxide, oxide or carbonate of
calcium or barium to a solution of a normal salt of aluminum
containing hydrochloric acid and sulfuric acid. the result-
ing product stream contains at least 10% or more by weight ofthe insoluble sulfate salt by-product.
U.S. patent No. 3,497,459 discloses and claims a
method for preparing a basic salt compound having the formula
2 1 76688
Rn(OH)mX3n-m
whèrein R can be aluminum and X can be Cl, which comprises
the digestion of an oxide ore, e.g. bauxite, with a mixed
acid system comprising sulfuric acid and hydrochloric acid.
The resulting product solution is treated with an insoluble
sulfate forming compound, e.g. calcium carbonate, to neutral-
ize the sulfuric acid used. The reaction solution is fil-
tered to remove the insoluble sulfate precipitate. The
mother liquor is alleged to be stable.
The prior art has recognized that BAC may be reacted
with sulfuric acid to form a basic aluminum sulfate precipi-
tate for ratios of S04/Al greater than 0.08. The '459 patent
suggests that their process inherently passes through that
reaction mechanism, but in the process of the '459 patent no
such precipitate is formed.
U.S. Patent No. 4,981,673 discloses a method for
preparing a BAC which comprises reacting a solution of alumi-
num sulfate with a slurry comprising calcium carbonate and
calcium chloride. The process stream is filtered to remove
precipitate. The filtrate comprises a solution of a BACS of
the formula
Aln(OH)m(S04)kC13n-m-2k
having a basicity, m/3nxlOO, of about 40~~ to about 60% and an
Al/Cl equivalent ratio, 3n/3n-m-2k of about 2.85 to 5.
While the prior art recognizes that a BACS can be
prepared from a previously prepared BAC by introducing a
sulfate ion into the bAC structure, it is uniformly agreed
that these compositions are not effective in water treatment
processes. The processes which do produce effective BACS
result in the formation of byproduct precipitate the disposi-
tion of which reduces the cost effectiveness of the process
as well as creating environmental problems.
2 1 76688
S~MMARY OF THE INVENTION
An aluminum hydroxychlorosulfate (BACS) is prepared by
reacting a solution of a basic aluminum halide with a sulfate
ion derived from sulfuric acid or aluminum sulfate. The
resulting product solution remains clear and no precipitate
is formed. While the products formed have some utility in
water treatment, they lack sufficient effectiveness in cold
water or low alkalinity waters to be commercially acceptable.
An improved product effective for the treatment of cold water
or low alkalinity water is prepared by introducing a calcium
ion in the form of calcium sulfate dihydrate, calcium carbon-
ate, calcium chloride, calcium hydroxide, or a mixture there-
of into the reaction mixture in an amount effective to im-
prove product efficacy while not producing calcium sulfate
precipitate by product.
DETAILED DESCRIPTION OF THE INVENTION
- The initial step in producing the BACS of this inven-
tion is to prepare a basic alurninum chloride by any suitable
known technique. In one prior art method a solution of
aluminum chloride is reacted with aluminum to form the basic
aluminum chloride. In another method of preparation of
aluminum chlorhydrates, aluminum is reacted with HCl in
water, the aluminum being in excess. While the concentration
of basic aluminum chloride in the solution in which it is
formed is not critical, generally it is made at concentra-
tion of 50~ w/w for practical reasons.
In the practice of this invention, the initial basici-
ty of the BAC solution is not critical. BAC solutions having
a basicity of 1/2 to 5/6 have been used successfully. Howev-
er, the Al/Cl atomic ratio of the BAC solution must be ad-
justed to about 1.2/1 to about 0.70/1 before sulfate ion
addition. The BACS of this invention has the general formu-
la:
Aln(OH)mC13n-mts04)p
21 7~8
wherein 3n > m and the percent basicity, m/3nxlOO, is about
50% to about 73%. The value of p is selected such that the
mole ratio S04/Al is about 0.05 to about 0.20. In carrying
out the process of this invention the concentration as Al 3
is about 4.0 to about 12.5%. It will be appreciated by those
skilled in the art that the source of Al+3 can be both the
BAC and the alum. Where the source of sulfate ion is sulfur-
ic acid, however, all of the aluminum is supplied by the BAC.
The S04/Al ratio may range from about 0.05 to about
0.20, preferably about 0.122 to about 0.150. The preferred
BAC is 1/2 basic BAC. The preferred S04/Al molar ratio for
this starting material is about 0.10 to about 0.15. Prefera-
bly, the sulfate bonding reaction is carried out using a 1/2
basic BAC adjusted to an Al/Cl atomic ratio of about 1.0/1 to
about. 0.70/1.
In carrying out the process of this invention a solu-
tion of basic aluminum chloride is heated to about 75 to
about 98~ C. with mixing. While a reflux condenser is uti-
lized to return any water evaporated back to the system to
maintain the concentration of reactants constant, true reflux
conditions, per se, that is boiling, need not occur. The
concentration of the hot solution or its basicity may be
adjusted by the addition of water, aluminum chloride hexahy-
drate, hydrochloric acid or other basic aluminum chloride
solutions of different concentrations or basicity as re-
quired. Methods of adjusting basicity are well known to
those skilled in the art.
After adjustment the Al~Cl atomic ratio of the solu-
tion can range between 0.70/ to about 1.2/1; typically about
0.75/1 to about 1.0/1, e.g., about 0.78/1 to about 0.90/1.
If adjustment is necessary it is preferred that the solution
be maintained at about 90 to about 95~ C. for about 10 to
about 60 minutes after adjustment to ensure that the reaction
is completed; preferably about 20 to about 50 minutes, e.g.,
40 minutes. The solution is then preferably cooled to about
2 1 766~û
75 to about 90~ C before sulfating, more preferably about 75
to about 85~ C., e.g., about 80 to about 85~C. Theoretical-
ly, adjustment oE basicity occurs as soon as the required
amount of HCl, aluminum chloride hexahydrate or other materi-
al used to make the adjustment is added. Stoichiometrically,
this is correct. Not wishing to be bound by theory, however,
it appears that there is some reconfiguration or rearrange-
ment of the BAC polymer or the structural distribution there-
of upon heating to a temperature of about 60 to about 98~ C.
This rearrangement or reconfiguration apparently has a bene-
ficial effect on the sulfate bonding reaction. Therefore, it
is preferred that the basicity adjustment be carried out at
these elevated temperatures. While the material added to
make the adjustment can be added at room temperature with
subsequent heating to the elevated temperatures, it is pre-
ferred that the temperature of the BAC solution be raised to
about 60 to about 85~ C. prior to such addition. The pre-
ferred temperature at which to complete this rearrangement or
reconfiguration is about 90 to about 95~ C. It will be
appreciated by those skilled in the art having access to this
disclosure that where adjustment of basicity of a BAC solu-
tion is concerned, adjustment in basicity necessarily results
in an adjustment of the Al/Cl atomic ratio by virtue of the
fact that the materials used to adjust basicity are aluminum
and/or chlorine containing compounds.
It will be appreciated by those skilled in the art
having access to this disclosure that if no adjustment of the
basic aluminum chloride solution is required it is not neces-
sary to heat the solution to 90-95~ C, and the solution can
be heated directly to about 75 to about 98~ C, e.g., about 80
to about 85~ C. After cooling (or heating directly as the
case may be) to about 75 to about 98~ C. sulfate ion is
introduced either as sulfuric acid or aluminum sulfate.
Where aluminum sulfate is used, for convenience, the aluminum
sulfate is added from a solution containing about 48% by wt.
of the aluminum sulfate, a commercially available product.
21 i~8~
While concentration is not critical, sulfuric acid is prefer-
ably added at concentrations of 66~ Baume or less, e.g. 60~
Baume'.
The sulfate anion should be added at a temperature of
about 75 to about 98~ C, preferably at a temperature of about
80 to about 85~ C. The sulfate anion may be added as the
acid, the aluminum salt and mixtures thereof with the follow-
ing constraints:
1. The addition rate must not result in temperature
excursions of greater than 5~;
2. The addition rate must not destabilize the system.
Too rapid an addition rate will result in the formation of
insoluble basic aluminum sulfate, evidenced by precipitate
formation. The addition rate will depend on the concentra-
tion of the BAC solution as well as the concentration of the
anion solution. The rate required to avoid precipitation is
readily determined without undue experimentation for a prede-
termined reaction mixture. Generally, addition of the anion
over at least a one half hour period will avoid precipita-
tion. However, where the anion addition is carried out
utilizing the acid, the addition is preferrably carried out
over a time interval of at least one hour.
3. The total amount of sulfate anion added is such
that the ratio of anion to total aluminum in the final reac-
tion mixture is about 0.05/1 to about 0.20/1, preferably,
about 0.122/1 to about 0.150/1
As used in the specification and claims with respect
to sulfate iOIl addition, the term "controlled rate" means
that the constraints described in numbered paragraphs 1 & 2
above are met.
It will be appreciated by those skilled in the art
that where the anion is added as the acid, the heat of solu-
tion will result in a temperature increase. Conversely, the
21 ;166~B
addition of an aluminum salt solution will result in a tem-
perature decrease unless the solution is heated before addi-
tion to the reaction mixture. However, even where the solu-
tion is brought up to temperature to avoid a temperature
excursion. it is necessary to add the solution at a con-
trolled rate to avoid the effect described in paragraph 2,
above.
After addition of the sulfate ion solution the system
is maintained at 75-98~ C, preferably 75-85~ C., for about 60
minutes to about 24 hours; typically two to twenty-four
hours, e.g., si~ to 12 hours. Not wishing to be bound by
theory, it is believed that this extended heating period
after sulfate ion addition, is required in order to form
sulfate ligands bonds. Mixing should be maintained throughout
the heating period. The solution is preferably then cooled
to about 40~ C. over about a twelve hour to twenty four hour
period. While the solution can be diluted to any desired
concentration at this point, it is preferred that the solu-
tion be aged for about 2 to 18 hours after its temperature
has been reduced below 40~ C. before dilution. Dilution
below an Al 3 concentration of 4.0 wt. may result in clouding
of the solution, and ultimately to precipitation of insolu-
bles. Preferably, the solution is not diluted below an Al 3
concentration of 4.5 wt.~.
The solution of product of this invention will be
clear, and depending on its characteristics can remain clear
indefinitely. Under certain conditions of concentration,
basicity and S04/Al ratio, failure to dilute may result in
the generation of solid precipitate after the cooled solution
has been standing for 24 hours or longer. These solutions
must be diluted to remain stable. Where the aluminum content
of the solution measured as Al 3 is greater than 8.4%, the
Al/Cl atomic ratio is in the range of about 0.8 to about 1.0
and S04/Al ratios of greater than 0.12 dilution of the solu-
tion may be required. Generally, dilution to reduce the
21 7Ç~8~
solids concentration by about 10 to 20 wt.% of its original
value will be sufficient to promote long term stability.
While it is possible to determine empirically which
solutions must be diluted by carrying out the process under
fixed conditions, waiting at least 24 hours, preferably,
about 2 to about 5 days, to determine whether or not clouding
occurs, and if so, rerunning the reaction with different
dilutions until stable solutions are achieved, it is more
practical to dilute to the Al 3 concentrations found to
promote stability regardless of the reaction conditions
selected. In carrying out the dilution process the water
should be added at a moderate rate with adequate mixing to
ensure that the solution is homogeneous without stratifica-
tion or areas of high concentration. In general, where the
source of sulfate ion is alum, it is preferred that the
product stream be diluted to an Al 3 concentration oE less
than 7Ø Where the sulfate ion source is sulfuric acid it
is preferred that the solution be diluted to an Al 3 concen-
tration of less than 8.0g6, preferably less than 7.5 wt.~6.
The advantages of the instant invention may be more
readily appreciated my reference to the following examples.
EXAMPLE 1
350.6 grams of a 50 wt.g~o, 5/6 basic BAC analyzing
12.39% aluminum and 8.27 wt.g~ chlorine was placed into a one
liter flask fitted with a stirrer and reflux condenser. The
solution was heated to 80~ C. prior to the drop-wise addition
of 136.8 grams of 20~ Baume HCl over a seven minute period.
The temperature was increase to 95~ C. and held there for one
hour with continuous mixing. The temperature was then re-
duced to 80-85 degrees.
31.3 grams of 60~ Baume sulfuric acid was then added
over a 12 minute period. The temperature was maintained at
about 80-85~ C. for an additional 30 minutes. Then heating
was discontinued. The solution passively cooled to a temper-
ature of 40~ C. over a two hour period. Mixing was continu-
ous over the entire reaction time.
2 1 76688
-.~
281.2 grams of room temperature water was added to the
reaction mixture, with continuous mixing, after the reaction
mixture had cooled to below 40~ C. The finished solution was
clear, and no precipitation occurred over a thirty day peri-
od. The solu-tion analysis was as follows:
Aluminum - 5.49% Chloride - 8.84%
Sulfate - 2.93Yo Al/Cl (atomic) - 0.82
S04/Al molar ratio - 0.150
EXAMPLE 2
The procedure of Example 1 was repeated using 431.5
grams of a 50% solution of BAC (Al = 12.35%, Cl=8.27~) and
204.48 grams of HCl. The HCl addition was carried out over a
ten minute period at a temperature of 60~ C. The reaction
temperature then was increased to 90-95~ C., and held there
for about 20 minutes. After reducing the reaction tempera-
ture to 80-85~ C., 164.0 grams of 48,~~ w/w of commercial grade
aluminum sulfate solution (Al = 4.45%) was added drop-wise
over a 40 minute period. After an additional 30 minutes at
80-85~ C., with continuous mixing, heating was discontinued.
The reaction mixture was allowed to cool passively with
continuous mixing for 16 hours until the temperature dropped
to about room temperature, i.e., 24~ C. 131.3 grams of water
at room ternperature was then added while mixing was contin-
ued. The solution concentration was reduced to 85.9% of its
original concentration by the addition of water. The fin-
ished solution was clear and free of precipitates, and ana-
lyzed as follows:
Al = 6.50~ Cl = 10.69% Sulfate = 4.18% A1/Cl = 0.80
S04/Al = 0.181
_l ~
2 1 16688
--I ~
EXAMPLE 3
569.44 grams of a 50~ solution of 5/6 basic BAC was
added to a one liter beaker fitted with a stirrer and a
reflux condenser. The solution was heated to 60~ C. with
mixing, and 176.4 grams of 20~ Baume HCl was then added,
drop-wise, over a twenty minute period. The reaction mixture
temperature was then increased to 90-95~ C. and maintained at
that temperature for about 45 minutes. The temperature was
decreased to 80-85~ C. and 54.08 grams of 60~ Baume sulfuric
acid was added drop-wise over a 30 minute period. The tem-
perature was maintained at 80-85~ C. for an additional 60
minutes. Heating was then discontinued, and the system was
allowed to cool passively over an 18 hour period to a about
room temperature. Aliquots of the solution were taken and
each diluted to a different concentration. Dilution was made
by the addition of water at room temperature, with mixing.
Prior to dilution the solution was clear and had the
following stoichiometry:
Al=8.79% Cl=12.83% Sulfate=5.00% Al/Cl=O.90
S04/Al=0.16
The effect of dilution is shown in Table I.
TABLE I
DILUTION Al (%) 30 DAY STABILITY AT ROOM TEMPERATURE
Neat 8.79 5-10% precipitated solids
90% 7.91 trace solids, less than 0.5%
80% 7.03 clear solution
70% 6.15 clear solution
62% 5.45 clear solution
While the BAC solutions were adjusted with HCl in the
foregoing examples, it will be appreciated by those skilled
in the art that the adjustment could have been made utilizing
aluminum chloride hexahydrate or a BAC solution having a
different Al/Cl atomic ratio than the BAC reactant to be
2 1 ~68~
-1 ~
utilized. A significant advantage of this invention is that,
unlike prior art methods of producing BACS, there is no
significant amount of insoluble byproduct produced. Such
byproduct not only increases production cost, but creates
environmental problems from the need to dispose of these
insoluble materials.
It will be noted that the times utilized in the forego-
ing examples do not conform strict~y to the disclosure. This
is not an inconsistency. The discrepancy is a result of the
fact that small batches are more susceptible to control of
parameters such as mixing. The disclosure and claims on the
other hand are directed toward a process which has commercial
application on a large batch scale.
While the process of this invention produces a BACS
solution substantially free of precipitate, it will be appre-
ciated by those skilled in the art that in production runs
minor fluctuations of process conditions from the intended
values may occur, resulting in the formation of precipitate.
These variations must be controlled so that precipitate
formation does not exceed 1% by weight of the total batch.
Preferably, reaction conditions are controlled to maintain
the level of precipitate, if any, to about 0.5 wt.% or less.
At levels significantly greater than 1 wt.% of precipitate
the process begins to become uneconomical, and sufficient
precipitate is produced to begin to create the environmental
problems the process of this invention see~s to avoid.
In another embodiment of the invention the process may
be carried out under modified conditions. These conditions
include carrying out the sulfating reaction at a temperature
of about 90-95~C and al 3 concentration less than 7Ø It
will be appreciated that this temperature range is above the
range previously described as preferred. In this particular
embodiment of the invention, in order to utilize this higher
temperature range effectively at the lower concentrations, it
is preferred that a double adjustment of the BAC be used.
The first adjustment is carried out prior to the sulfation
2 1 ~6~88
-I ~
step, and the subsequent adjustment is carried out at the
conclusion of the anion addition and prior to the addition of
calciurn ion. In this particular embodiment, unless the
adjustment is split into two steps precipitation may occur.
Additionally, only a part of the required water is added
initially, the remainder being added later in the reaction
process. A production run utilizing this modified process is
illustrated for a product having the following specifica-
tions:
Aluminum 5.42 wt.%
Chloride 9.00 wt.%
Sulfate 2.90 wt.~,~
Al/Cl 0.80i 0.03
S04/A1 0.148-0.153
S.G. 1.200iO.01 @ 25~ C.
Materials utilized for the process were:
5/6 Basic conventional aluminum chloride prepared
as a 50% solution; (BAC)
20~ Baume' HCl
60~ Baume sulfuric acid
. Process water
Since the sulfate ion is supplied by sulfuric acid the total
aluminum is supplied by the BAC. Initially 100% of the BAC
and 40% of the total water requirement was added to the
reactor. The diluted BAC solution is heated to 70~ C. with
slow, non-aerating mixing. 75% of the calculated HCl require-
ment is added over a one hour period. After thorough mixing,
the temperature is increased to about 90-95~ C. and all of
the required sulfuric acid is added over a seven to eight
hour period. Since plant reactors need not be run with
reflux condensers in place, water loss will occur through
vents, and water must be made up by addition. After comple-
2 1 16688
,~
tion of the sulfuric acid addition, additional water is addedslowly and continuously until the specific gravity is within
specification.
During the heating period, the batch is analyzed for
Adjustments that are required to attain product specifica-
tions are preferably made over the first 10-12 hours of
heating after completion of the sulfate ion addition. A
final adjustment of the specific gravity is made after the
heating period and prior to cooling the batch.
If adjustment of S04/Al ratio is required care must be
taken not to add an excess of sulfate, since precipitation
will result. The remaining 20~ Be HCl should then be added.
After thorough mixing, heating is terminated and the batch is
allowed to cool to about 60~ C. A suspended solids content
of 1~ of the total batch size by weight or less is accept-
able. If any suspended solids are present filtration without
a filter aid can be carried out after the batch has cooled
below 60~ C.
An effective water treatment coagulant should destabi-
lize and precipitate the maximum amount of suspended matter
in the water utilizing hte least amount of hydrolizable
cationic metal ion, e.g., aluminum. Furthermore, it is de-
sirable to produce a high density floc to ensure rapid set-
tling. Additionally, it is desirable to have rapid floc
onset. Since the floc is removed by filtration hte floc must
have a high shear strength or cohesiveness. It has been
surprisingly found that these objectives can be achieved and
the effectiveness of the BACS improved by controlling the
iron content of the BACS solution. The total iron content
should be about 75 to about 250 ppm, preferably about 160 to
about 190 ppm. Those skilled in the art will appreciate that
both BAC and aluminum sulfate can contain iron in varying
amounts. It is therefore, necessary to first confirm the
iron content of the raw materials of the reaction before
making additions of iron ion to the reaction system. When
required the addition of iron can be accomplished by the
-1~
~ 1 /668B
-
1~
addition of a water soluble iron salt. Illustrative, non-
limiting examples of such iron salts are ferric chloride and
ferric sulfate.
The additional iron is introduced prior to the sulfate
addition and preferably prior to Al/Cl atomic ratio adjust-
ment. Ferric chloride forms a yellow solution. If the
solution is added prior to sulfate anion addition, the yellow
color dissipates. If on the other hand the solution is added
to the BACS solution after anion addition is completed, the
solution remains yellow, evidencing the fact that the iron
has not been incorporated into the polymer formed. Such an
addition has no utility for the purpose of this invention.
It has been found that while the product of the process
disclosed is useful in water treatment, it is not as effica-
cious as desired for cold water treatment, e.g., water tem-
peratures of below 10~ C, and low alkalinity water. In order
for the BACS formed from BAC to be effective in cold water it
has been found necessary to introduce calcium ion into the
system. The addition of calcium as ion results in overall
floc formation efficiency and improved cold water efficien-
cy. It will be appreciated by those skilled in the art
having access to this disclosure, that calcium sulfate dihy-
drate, calcium hydroxide and calcium carbonate are sparingly
soluble in water. They are, however, slightly more soluble
in the BACS solution. In ordcr that the addition of calcium
ion be effective for its intended purpose and to avoid any
precipitate formation it is necessary to add calcium ion in a
very limited concentration range. The total calcium ion
concentration in the BACS should be about 0.1 to about 0.4
weight percent, typically, about 0.20 to about 0.25 weight
percent. Where the sole source of calcium is calcium sulfate
dihydrate, the calcium content of the BACS is limited to the
range of about 0.10 to about 0.15 because of the limited
amount of the calcium sulfate which can be incorporated into
the system. In one embodiment the calcium ion is added in
the form of a slurry of the sulfate and carbonate in the
2 1 /6688
-
1 ~
predetermined amounts to achieve the desired concentration.
Calcium hydroxide can be prepared from the oxide by slaking
to form a slurry.
As used in the specification and claims the term
"calcium carbonate" is intended to include all grades of
calcium carbonate including dolomitic grades which con-tain
minor amounts of magnesium carbonate, magnesium hydroxide or
mixtures thereof. We prefer to utilize USP grade of calcium
carbonate because some commercial grades contain impurities
which are insoluble, and add to filtration requirements which
it is preferred to avoid. We preferably incorporate a minor
amount of magnesium carbonate, e.g., Ca/Mg mole ratio of
about 3/1 to about 4/1, e.g., about 2/1 to about 3/1, which
is reflective of the ratios of calcium to magnesium found in
nature, to the USP grade of calcium carbonate. While there
is no conclusive evidence, not wishing to be bound by theory,
it appears that magnesium may be involved in the formation of
additional ligand bonds. The magnesium can also be added as
the hydroxide.
It has also been found that water soluble calcium
chloride can be utilized as a calcium source. It has addi-
tionally been found that by using the combination calcium
chloride and calcium sulfate dihydrate, these compounds can
contribute a portion of the anion for the purpose of achiev-
ing the desired sulfate ion concentration as well as to
adjust the Al/Cl atomic ratio using the calcium chloride as a
minor source of chloride ion. It will be appreciated by
those skilled in the art having access to this disclosure
that a mixture of calcium carbonate and calcium sulfate
dihydrate, or calcium chloride and calcium sulfate dihydrate
can be utilized.
Notwithstanding the use of calcium sulfate dihydrate
and calcium chloride in the process of this invention, the
primary source of sulfate ion for the sulfation process is
the acid or aluminum salt, and the primary source of chloride
is HCl, aluminum chloride, or a ~AC having a different Al/Cl
-1 ~
~1 /6688
t ~
atomic ratio which is utilized in adjusting the Al/Cl atomic
ratio.
In calculating the sulfate anion concentration to be
contributed by the acid or aluminum salt it is necessary to
take into account the sulfate ion contributed by the calcium
sulfate so as not to exceed the range specified in numbered
paragraph 3 above. Similarly in adjusting the Al/Cl atomic
ratio the amount of chloride contributed as calcium chloride
must be considered in order to maintain the Al/Cl atomic
ratio within the desired range, as described above.
When the calcium ion is added in the form of a slurry,
the calcium slurry typically has a solids content of about 5
to about 10 weight percent. Direct addition of the powdered
calcium salts are preferably avoided since it will result in
insoluble particles. Additionally, the slurry must be added
at a controlled rate to avoid insoluble particle formation in
the BACS solution. Typically, the slurry is added over at
least a one hour interval, e.g., one to two hours, with good
mixing. Mixing is continued until substantially all of the
calcium salts are dissolved, e.g., for about an additional
two hours to insure that all of the calcium salts have been
solublized. Further mixing may be desirable if it appears
that solublization is not complete. Not wishing to be bound
by theory, it is believed that solublization occurs as a
result of reaction of the calcium salts with the anionic
residuals of the BACS. Whenever the calcium slurry contains
calcium carbonate the slurry is preferably added at tempera-
tures between about ambient and about 45~ C. Higher tempera-
tures may result in undesirable precipitation reactions.
Where the slurry contains only calcium sulfate dihydrate or
the dihydrate in combination calcium chloride the slurry
addition can be made at the temperature at which the sulfate
anion is added using the acid or aluminum salt. However, such
a slurry can be added at a reduced temperature.
_l ~
~ 1 /6688
Where the BAC solution used in the process is a 5/6
basic BAC, it is necessary to adjust the Al/Cl atomic ratio
to about 1.2 to about 0.70. The BACS solution can be fin-
ished by the addition of water to adjust the concentration of
BACS in solution. The specifications for the improved BACS
of this invention are:
Broad Range Preferred Range
( % w/w ) ( % w/w )
Al = 4.5 to 8.00 % Al = 5.30 to 5.60 %
Cl = ~.8 to 11.00 % C1 = 8.25 to 9,25 %
S04 = 2.20 to 3.80 % S04 = 2.60 to 2.90 %
Ca = 0.1 to 0.4 % Ca = 0.15 to 0.25 %
Fe = 0.01 to 0.03 ~ Fe = 0.015 to 0.020 %
S.G.= 1.18 - 1.26 @ 25~ C S.G. = 1.19 - 1.22 @ 25~ C
Preferred A1/C1 atomic ratio = 0.8100/1 to 0.8225/1
Preferred S04/Al atomic ratio = 0.1375 to 0.1500/1
As noted above where the calcium carbonate compound contains
no magnesium, a magnesium compound is preferably added. The
specific gravity ranges shown apply whether or not calcium
and iron are included in the BACS.
The following example illustrates the invention utiliz-
ing aluminum sulfate as the sulfate ion source.
EXAMPLE 4
A one kilo batch of improved BACS was prepared in the
following manner:
TABLE II
Quantity
Com~onent wt. %qrams
5/6 Basic BAC
50% wt.solution 40.21 402.1
20~ Be' HCl 17.30173.0
Alum 48% soln.10.98109.8
CaS04.2H20 0.45 4.5
-I ~
2 1 ~ a 8
-I ~
TABLE II
Quantity
Component wt. %qrams
CaC03 0.25 2.5
FeC13 0.12 1.2
(42.9% w/w soln.)
Water 30.69306.9
A one-liter glass reaction flask was fitted with a
reflux condenser a stirrer and a heating mantel. 100 grams
of water was charged to the flask together with the 402.1
grams of 5/6 BAC. With mixing at room temperature the 1.2
grams of ferric chloride solution was added. Mixing was
continued for about thirty minutes to ensure complete inte-
gration of the iron into the system. The temperature of the
reaction mixture was then increased to 60~ C and 95~ of the
total HCl was added (164 grams) over about 30 to 45 minutes
to adjust the basicity of the BAC. The temperature was then
increased to about 82--85~ C. The aluminum sulfate solution
(109.8 grams) was then added at a rate of approximately 1.4
ml/min., the total addition time being approximately one
hour. The temperature was maintained with continuous mixing
for about 12 hours. Then the remaining HCL (8.6 grams) was
added. The temperature was reduced to 40~ C. slurry com-
prising 4.5 grams of calcium sulfate dihydrate and 2.5 grams
of calcium carbonate in one hundred grams of water. The
slurry was added to the reaction mixture at a rate of about 1
ml/min. with continuous mixing. The slurry addition was
completed in about two hours. After addition of the calcium
slurry was completed, heat was discontinued and mixing was
maintained for about two hours. The balance of the water
(106.9 grams) was then added to complete the batch.
The HCl addition was made in two parts to avoid over-
shooting the desired Al/Cl atomic ratio. Generally, the
ratio will be determined by analysis before addition of the
remaining acid, or other material utilized to adjust the
_1~
21 76688
-2
ratio.
EXAMPLE 5
This example illustrates the use of sulfuric acid as
the sulfate anion source. A one kilo batch was prepared
using the following materials:
TABLE III
Quantity
Component wt. ~qrams
5/6 BAC 50% 44.23442.3
20~ Be' HCl 16.31163.1
60~ Be' H2S04 3.35 33.5
FeCl3 soln. 0.12 1.2
CaS04.2H20 0.45 4.5
CaC03 0.25 2.5
Water 35.29352.9
A one liter glass lined reaction vessel was fitted with
a mixer, heating mantel and reflux condenser. 100 grams of
water and 442.3 grams of BAC were charged into the vessel.
With mixing, 1.2 grams of ferric chloride solution (42.9%
FeCl3 w/w) was added at ambient temperature . Stirring was
continued for an additional 30 minutes. The reaction mixture
was then heated to 60~ C, and 95% of the total HCl was added
(154.9 grams) over a 30-45 minutes time interval with con-
stant stirring. The temperature was then increased to 82-85~
C. The sulfuric acid (33.51 grams) was then added at approx-
imately 0.35 ml/min., the total amount being added over a one
hour interval. The temperature was maintained for 12 hours
with continuous mixing, after which the remaining HCl (8.16
grams) was added. The temperature was then lowered to 40~ C.
A slurry comprising 4.5 grams of calcium sulfate dihydrate
and 2.5 grams of calcium carbonate in 100 grams of water was
prepared. The slurry was added to the reaction mixture at a
rate of about 1.0ml/min. with continuous mixing, addition
time being about two hours. After addition of the slurry,
heating was discontinued and mixing continued for about two
-2~
21 ~68~
-
-21-
hours. The reaction mixture was then diluted by the addition
of 152.9 grams of water.
While the above examples illustrates the invention
there are certain parameters which should be met in order to
achieve the objectives of the invention. The BAC concentra-
tion in the initial reaction mixture should be about 4.0 to
about 12.5% as Al 3, preferably about 9.0 to about 12.5%. At
the time of addition of the sulfate ion the Al/Cl atomic
ratio should be about 1.2/1 to about 0.70/1, preferably
about 1.00 to about 0.70 to 1. The method of preparation of
the BAC is not critical, the Al/Cl atomic ratio can be
achieved directly or by adjustment.
As has been stated above the Al/Cl atomic ratio can be
adjusted using HCl, aluminum chloride hexahydrate or a BAC of
a different Al/Cl atomic ratio than the starting material.
In one embodiment of the invention the adjustment of Al/Cl
atomic ratio is accomplished in two steps. This is a partic-
ularly advantageous method where the BAC concentration is
such that the Al 3 is about 7.9% or greater. In this modifi-
cation of the process the BAC is adjusted to an initial Al/Cl
atomic ratio of about 1.2 to about 0.91. After the sulfate
anion addition is made and before the calcium salt addition
is made a further adjustment is made to reduce the Al/Cl
atomic ratio to about 0.9 to 0.70.
As used in the specification and claims the term
"substantially free" as used in reference to precipitate
content of the process product stream, means the product
stream contains less than about 1.0 wt. % of such precipi-
tate. Typically, in a well controlled reaction the product
stream will contain less than about 0.03 wt.~ precipitate.
