Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED BASIC ALUMINUM HYDROXYCHLOROSULFATE PROCESS
AND PRODUCT THEREFROM ~ ~
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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 ls 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"j 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
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.
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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
33%. 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, carboxylic and sulfonic
acids. X is preferably Cl, but can be I, N03 or CH3COO.
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-
tlon in the presence a multivalent acid ion in an acid hydro-
losis solution, e.g hydrochloric acid of Al. The BACS may be
obtained by the separation of an insoluble sulfate produced
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-
lng product stream contains at least lOX or more by weight of
the 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
Rn(OH)mX3n-m
wherein 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.
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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 preclpitate is formed.
U.S. Patent No. 4,981,673 discloses a method for
preparlng 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(so4)kcl3n-m-2k
having a basicity, m~3nxlOO, of aboùt 40% to about 60% and an
Al/Cl equivalent ratio, 3n/3n-m-2k of about 2.85 to 5.
The disadvantage of prior art processes is that they
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.
SUMMARY OF THE INVENTION
An aluminum hydroxychlorosulfate (BACS) is prepared by
reacting a solution of a basic aluminum halide with a sulfate
lon derived from sulfuric acid or aluminum sulfate. The
resulting product solution remalns clear and no precipitate
is formed. An improved product effective for the treatment
of cold water is prepared by introducing calcium sulfate
dihydrate in combination with calcium carbonate or calcium
chloride, or a mixture thereof into the reaction mixture in
amount effective to improve product efficacy while not pro~
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ducing calcium sulfate precipitate by product. Utilizing
calcium carbonate as the calcium salt improves floc formation
effectiveness but does not impart cold water effectiveness to
the ~ACS.
DETAILED DESCRIPTION OF THE INVENTION
The initial step in producing the BACS of this inven-
tion is to prepare a basic aluminum chloride by any suitable
known technique. In one prior art method a solution of
aluminum chloride is reacted wlth 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 50X w/w for practical reason6.
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 HAC solution must be ad-
~usted to about 1.2/1 to about 0.70/1 be~ore sulfate ion
addition. The BACS of this invention has the general formu-
la:
..;. . ,
Aln(OH)mCl3n-m(s04)p
wherein 3n > m and the percent basiclty, m/3nxlO0, is about
50% to about 73X. The value of p is selected such that the
mole ratlo SO /Al is about 0.05 to about 0.20. In carrylng
out the process of thls lnventlon the concentratlon as Al 3
18 about 4.0 to about 12.5X. It wlll be appreclated by those
skllled ln the art that the source of Al+3 can be both the
BAC and the alum. Where the source of sulfate ion is sulfur-
lc acld, however, all of the aluminum ls supplled by the BAC.
The S04/Al ratlo may range from about 0.05 to about
0.20, preferably about 0.122 to about 0.150. The preferred
BAC ls 1/2 ba~lc BAC. The preferred SO4/Al molar ratlo for
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thls starting materlal 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 thls invention a solu-
tion of baslc aluminum chlorlde is heated to about 75 to
about 98 C. with mixing. While a reflux condenser is uti-
llzed to return any water evaporated back to the system to
maintaln the concentratlon of reactants constant, true reflux
condltlons, per se, that ls bolling, need not occur. The
concentratlon of the hot solution or lts baslclty may be
ad~usted by the addltlon of water, alumlnum chlorlde hexahy-
drate, hydrochlorlc acld or other baslc alumlnum chlorlde
solutlons of dlfferent concentratlons or baslcity as re-
gulred. Methods of ad~ustlng basiclty are well known to
those skilled ln the art.
After ad~ustment the Al/Cl atomic ratlo of the solu-
tlon can range between 0.70/ to about 1.2/1; typlcally about
0.75/1 to about 1.0/1, e.g., about 0.7~/1 to about 0.90/1.
If ad~ustment 18 necessary it is preferred that the solutlon
be malntalned at about 90 to about 95 C. for about 10 to
about 60 mlnutes after ad~ustment to ensure that the reactlon
19 completed; ~referably about 20 to about 50 minutes, e.g.,
40 mlnutes. The solution is then preferably cooled to about
75 to about 90 C before sulfatlng, more preferably about 75
to about 85 C., e.g., about 80 to about 85C. Theoretlcal-
ly, ad~ustment of basiclty occurs as soon as the requlred
amount of HCl, alumlnum chlorlde hexahydrate or other materi-
al used to make the ad~ustment 1~ added. Stolchlometrlcally,
thls ls correct. Not wlshlng to be bound by theory, however,
it appears that there ls some reconflguratlon or rearrange-
ment of the BAC polymer or the structural dlstrlbutlon there-
of upon heatlng to a temperature of about 60 to about 95 C.
Thls rearrangement or reconflguratlon apparently has a bene-
flclal effect on the sulfate bondlng reactlon. Therefore, lt
ls preferred that the baslcity ad~ustment be carrled out at
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~ Attorney Docket No. 442-154
these elevated temperatures. While the material added to make
the ad~ustment can be added at room temperature with subse-
quent heating to the elevated temperatures, it i8 preferred
that the temperature of the BAC solution be raised to about
60 to about 85 C. prior to such addition. The preferred
temperature at which to complete this rearrangement or recon-
figuration is about 90 to about 95 C. It will be appreclat-
ed by those skilled in the art having access to this disclo-
sure that where ad~ustment of basicity of a BAC solution ls
concerned, ad~ustment in basiclty necessarily results in an
ad~ustment of the Al~Cl atomic ratio by virtue of the fact
that the materials used to ad~u~t baslcity 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 ad~ustment of the
baslc aluminum chlorlde solutlon ls requlred lt ls not neces-
sary to heat the solution to 90-95 C, and the solution can
be heated dlrectly to about 75 to about 98 C, e.g., about 80
to about 85 C. After coollng (or heatlng dlrectly as the
case may be) to about 75 to about 98 C. sulfate lon ls
lntroduced either as sulfuric acld or aluminum sulfate.
Where aluminum sulfate is used, for convenience, the aluminum
sulfate is added from a solution containing about 48X by wt.
of the aluminum sulfate, a commercially available product.
While concentration is not critical, sulfuric acid is prefer-
ably added at concentrations of 66 Baume or less, e.g. 60
Baume'. At above 66 Baume'the sulfation reaction is too
aggressive and may have a detrimental effect on the 8ACS.
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
acld, the alumlnum salt and mixtures thereof with the follow-
ing constraints:
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1. The addition rate must not result in temperature
excurslons of greater than 5;
2. The addition rate must not destabilize the system.
Too rapid an additlon rate will result in the formation of
insoluble basic aluminum sulfate, evidenced by precipitate
formation. The addition rate will depend on the concentra-
tlon of the BAC solution as well as the concentration of the
anlon 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 hour period will avoid precipitation.
3. The total amount of sulfate anion added is such
that the ratio of anion to total aluminum in the final reac-
tlon mlxture 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 lon addltlon, the term "controlled rate" means that
the con6traints descrlbed in numbered paragraphs 1 & 2 above
are met.
It will be appreciated by those skllled in the art
that where the anlon ls added as the acid, the heat of solu-
tlon will result ln a temperature lncrease. Conversely, the
addltlon of an aluminum salt solutlon wlll result ln a tem~
perature decrease unless the solution ls heated before addl-
tlon to the reactlon mlxture. However, even where the solu-
tlon ls brought up to temperature to avoid a temperature
excurslon. lt is necessary to add the solution at a con-
trolled rate to avold the effect descrlbed in paragraph 2,
above.
After addition of the sulfate ion solution the system
is malntained at 75-98 C, preferably 75-85 C., for about 60
minute~ to about 24 hours; typlcally two to twenty-four
hours, e.g., slx to 12 hours. Not wlshlng to be bound by
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theory, it i8 belleved that this extended heating period
after sulfate ion additlon, is required in order to form
sulfate llgands as evldenced by HPLC size excluslon chroma-
tography. Mixing should be maintained throughout the heatlng
perlod. The solution is preferably then cooled to about 40
C. over about a twelve hour to twenty four hour period.
Whlle the solution can be diluted to any desired concentra-
tion at this point, it is preferred that the solution be aged
for about 2 to 18 hours after its temperature has been re-
duced below 40 C. before dilutlon. Dilutlon below an Al 3
concentratlon of 4.0 wt. may result in clouding of the solu-
tion, and ultlmately to precipitation of insolubles. Prefer-
ably, the solution is not dlluted below an Al 3 concentratlon
of 4.5 wt.X.
The solutlon of product of thls invention wlll be
clear, and dependlng on its characteristics can remaln clear
lndefinitely. Under certaln condltlons of concentratlon,
baslclty and S04/Al ratlo, fallure to dllute may result ln
the generatlon of solld preclpitate after the cooled solutlon
has been standlng for 24 hours or longer. The6e solutions
must be dlluted to remain stable. Where the aluminum content
of the solution measured as Al 3 i9 greater than 8.4X, the
Al/Cl atomic ratio is in the range of about 0.8 to about l.0
and S04/Al ratios of greater than 0.12 dilution of the solu-
tlon may be requlred. Generally, dilutlon to reduce the
sollds concentration by about 10 to 20 wt.X of lts orlglnal
value wlll be sufflclent to promote long term stablllty.
Whlle it i8 po6~ible to determine empirically whlch
solutlons must be dlluted by carrylng out the process under
flxed conditlons, waitlng at lea6t 24 hours, preferably,
about 2 to about 5 days, to determine whether or not cloudlng
occurs, and lf 90, rerunning the reactlon wlth dlfferent
dllutions untll stable solutions are achieved, it 18 more
practical to dilute to the Al+3 concentrations found to
promote stability regardless of the reaction condltions
selected. In carrylng out the dllution process the water
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should be added at a moderate rate with adequate mixing to
ensure that the solutlon is homogeneous wlthout stratifica-
tion or areas of hlgh 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 of le~s
than 7Ø Where the sulfate ion source ls sulfuric acid it
is preferred that the solution be diluted to an Al 3 concen-
tration of less than 8.0%, preferably lese than 7.5 wt.X.
The advantages of the lnstant invention may be more
readily appreciated my reference to the following examples.
EXAMPLE 1
350.6 grams of a 50 wt.X, 5/6 basic BAC analyzing
12.39X aluminum and 8.27 wt.% 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.
281.2 grams of room temperature water was added to the
reactlon mixture, with continuous mixing, after the reaction
mixture had cooled to below 40 C. The finished solution was
clear, and no precipltation occurred over a thirty day peri-
od. The solution analysis was ae follows:
Alumlnum - 5.49% Chloride - 8.84X
Sulfate - 2.93X Al/Cl (atomic) - 0.82
S04/Al molar ratlo - 0.150
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EXAMPLE 2
The procedure of Example 1 was repeated using 431.5
grams of a 50X solution of BAC (Al = 12.35%, Cl=8.2~X) and
204.4B 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 lncreased 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 = 4.45X) 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 reactlon 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 temperature was then added while mixing was contin-
ued. The solution concentration was reduced to 85.9X of its
orlginal concentration by the addition of water. The fin-
ished solution was clear and free of precipltates, and ana-
lyzed aB follows:
Al - 6.50X Cl = 10.69% Sulfate = 4.18% Al/Cl = 0.80
S04/A1 ~ 0.181
EXAMPLE 3
569.44 grams of a 50X solution of 5/6 ba~ic BAC was
added to a one liter beaker fitted with a stirrer and a
reflux condenser. The solutlon 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 perlod. The tem-
perature was maintained at 80-85 C. for an additional 60
minutes. Heating was then discontinued, and the system wa~
allowed to cool passively over an 18 hour period to a about
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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 mixlng.
Prior to dilution the solution was clear and had the
following stoichiometry:
Al=8.79X Cl=12.83% Sulfate=5.00% Al/Cl=O.90
S04/Al=0.16
The effect of dilutlon i8 shown in Table I. ~.
"
TABLE I
pILUTION Al (%) 30 DAY STABILITY AT ROOM TEMPERATUR~
Neat 8.~9 5-10% precipitated solid~
90% 7.91 trace sollds, less than 0.5X `
80% ~.03 clear solutlon
~OX 6.15 clear solution
62X 5.45 clear solutlon
Whlle the BAC solutions were ad~usted with HCl in the
foregoing examples, it will be appreciated by those skilled
ln tho art that the ad~ustment could have been made utilizing
aluminum chloride hexahydrate or a BAC solution having a ~ `
dif~erent Al~Cl atomic ratio than the BAC reactant to be
util$zed. 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 strictly to the disclosure. This
is not an inconsistency. The di~crepancy 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.
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Whlle the process of this invention produces a BACS
solutlon substantially free of precipitate, it will be appre-
ciated by those skilled in the art that in production runs
minor fluctuations of proces~ conditions from the intended
values may occur, resulting in the formation of precipitate.
These variations must be controlled so that preclpitate
formation does not exceed 1% by welght 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 t and sufficient
precipitate is produced to begin to create the environmental
problems the process of this invention seeks 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 90-95C and Al 3 concentration less than 7Ø It
will be appreciated that this temperature range is above the
range previously descrlbed as preferred. In order to utilize
this higher temperature range effectively at the lower con-
centrations, it is preferred that a double ad~ustment of the
BAC be used. The first ad~ustment is carried out prior to
the sulfation step, and the subsequent ad~ustment is carried
out at the conclusion of the anion addition and prior to the
addition of calcium ion. Unless the ad~ustment 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 uti-
lizing this modified process is illustrated for a product
having the following specification~:
Aluminum 5.42 wt.%
Chloride 9.00 wt.X
Sulfate 2.90 wt.%
Al/Cl 0.80~ 0.03
S04/Al 0.148-0.153
S.G. 1.20010.01 @ 25 C.
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Materlals utillzed for the proce6R were:
5~6 Baslc conventional alumlnum chloride prepared
as a 50X solutlon; (BAC)
20 Baume' HCl
60 Baume sulfuric acid
. Process water
Slnce the sulfate lon ls supplled by sulfuric acld the total
alumlnum ls supplled by the BAC. Inltially lOOX of the BAC
and 40X of the total water requirement was added to the
reactor. The diluted BAC solutlon is heated to 70 C. wlth
slow, non-aerating mixing. 75% of the calculated HCl requlre-
ment is added over a one hour perlod. After thorough mlxlng,
the temperature 18 increased to about 90-95 C. and all of
the required sulfurlc acld is added over a seven to elght
hour period. Since plant reactors need not be run wlth
reflux condensers in place, water loss wlll occur through
vents, and water must be made up by additlon. After comple-
tlon of the sulfurlc acld addltlon, additlonal water 18 added
slowly and contlnuou~ly untll the speclflc gravlty i9 wlthln ~ -
speclflcatlon.
Durlng the heatlng perlod, the batch ls analyzed for
Ad~ustments that are requlred to attain product speciflca-
tlons are preferably made over the flrst 10-12 hours of
heatlng after completlon of the sulfate lon addltlon. A
flnal ad~ustment of the speclflc gravlty is made after the
heatlng perlod and prlor to coollng the batch.
If ad~ustment of S04/Al ratlo is requlred care must be
taken not to add an excess of sulfate, slnce preclpltatlon
wlll result. The remalnlng 20 Be HCl should then be added.
After thorough ~lxlng, heating ls termlnated and the batch i9
allowed to cool to about 60 C. A suspended sollds content
of lX of the total batch slze by welght or les~ ls accept-
able. If any suspended sollds are present flltratlon wlthout
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a filter aid can be carried out after the batch has cooled
below 60 C.
It has be~n surprisingly found that the effectiveness
of the BACS can be improved by controlling the iron content
of the BACS solutlon. 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 appreclate 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
lron can be accompllshed by the addition of a water soluble
lron salt. Illustratlve, non-llmiting examples of such iron
salts are ferric chloride and ferric sulfate.
The additional lron is introduced prior to the sulfate
addition and preferably prior to Al/Cl atomic ratio ad~u6t-
ment. Ferric chloride forms a yellow solution. If the
solutlon is added prior to sulfate anion addition, the yellow
color dissipates. If on the other hand the solution is added
to the BACS solutlon after anion addition ls completed, the
solutlon remains yellow, evldencing the fact that the iron
has not been lncorporated lnto 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 i8 useful in water treatment, it i8 not as effica-
clouc as desired for cold water treatment, e.g., water tem-
peraturec of below 10 C. 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 calcium carbonate results in overall floc forma-
tion efficiency. For improved cold water efficiency, howev-
er, it is necessary to add calcium ion as calcium sulfate
dihydrate. It will be appreciated by those skilled in the
art having access to this disclosure, that both calcium
sulfate and calcium carbonate are sparingly soluble in water.
They are, however, slightly more soluble in the BACS solution.
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.
In order 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 concen~
tration range. The total calcium ion concentration in the
BACS should be about 0.1 to about 0.4 weight percent, prefer-
ably about 0.20 to about 0.25 weight percent. In the prac-
tice of this invention in order to produce a BACS having
improved cold water effectiveness, it is necessary that the
calclum sulfate contribute about 0.04 to about 0.15 weight
percent calcium, preferably about 0.08 to about 0.12 weight
percent. The balance of the calcium content of the finished
product is derived from calcium carbonate or calcium chlo-
ride. 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 ln
the form of a slurry of the sulfate and carbonate in the
predetermined amounts to achieve the desired concentration.
It has also been found that water soluble calcium
chlorlde can be utilized as a calcium source. It has addi-
tionally been found that by using the combination calcium
chloride and calcium sulfate, these compounds can contribute
a portion of the anion for the purpose of achieving the
desired sulfate ion concentration as well as to ad~ust 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 or calcium
chloride, and calcium sulfate can be utllized. To ensure
that the product is effective in cold water the calcium
sulfate must be included, contributing calcium ion in the
range ~pecified above. Calcium carbonate and chloride uti-
lized in the absence of the calcium sulfate results in im-
proved efficiencies over the prior art. However, the calcium
sulfate is essential to produce a suitable water treatment
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BACS with cold water effectiveness as is required in the
northern latitudes of thls country and Canada.
Where the calclum sulfate and calcium chloride are
used, the primary source of sulfate ion is the acid or alumi-
num salt, and the primary source of chloride is HCl, aluminum
chloride, or a BAC having a different Al/Cl atomic ratio
which i5 utlllzed in ad~ustlng the Al/Cl atomlc ratio.
In calculatlng the sulfate anlon concentration to be
contributed by the acid or aluminum salt it ls 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 ad~usting 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 descrlbed above.
Preferably the calcium slurry has a solids content of
about 5 to about 10 weight percent. Direct addition of the
powdered calcium salts should be avoided since it will result
in lnsoluble partlcles. Additionally the slurry must be
added at a controlled rate to avoid lnsoluble particle forma-
tlon ln the BACS solution. Typlcally, the slurry i8 added
over at least a one hour interval, e.g., one to two hours,
with good mixing. Mixlng i8 continued until all of the
calclum salts are dlssolved, e.g., for about an additional
two hours to lnsure that all of the calclum salts have been
solubllzed. Further mixing may be desirable lf it appears
that solublization i9 not complete. Not wishing to be bound
by theory, it i9 believed that solublization occurs as a
result of reaction of the calcium salts wlth the anionic
residuals of the BACS. Whenever the calcium slurry contains
calcium carbonate the slurry should be added at temperatures
between ambient and 45 C. Higher temperatures can result in
undesirable preclpltatlon reactions. Where the slurry con-
talns only calcium sulfate dihydrate or the dihydrate in
.
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combination calcium chloride $he 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.
Where the BAC solution used in the process is a 5/6
basic BAC, it is necessary to ad~ust the Al/Cl atomic ratio
to about 1.2 to about 0.70. The BACS solution can be fln-
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
(X w/w) (X w/w)
Al = 4.5 to 8.00 % Al = 5.30 to 5.60 %
Cl = ~.8 to 11.00 % Cl - 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 X
Fo = 0.01 to 0.03 X Fe = 0.015 to 0.020 X
S.G.= 1.18 - 1.26 @ 25- C S.G. = 1.19 - 1.22 @ 25- C
Preferred Al/Cl atomic ratio = 0.8100/1 to 0.8225/1
Preferred S04/Al atomic ratio ~ 0.13?5 to 0.1500/1
The specific gravlty 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:
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TABLE II
Quantity
Component wt. X qrams
5/6 Basic BAC
50X wt.solution 40.21 402.1
20 Be' HCl 17.30 173.0
Alum 48% soln.10.98 109.8
CaS04.2H20 0.45 4.5 ~ ~
CaC03 0.25 2.5 ;
FeC13 0.12 1.2
(42.9X w/w soln.)
Water 30.69 306.9
A one-liter glass reaction flask was fitted with a
reflux condenser a ~tirrer 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
reactlon mixture was then increased to 60 C and 95X of the
total HCl was added (164 grams) over about 30 to 45 minutes
to ad~ust the basicity of the BAC. The temperature was then
increased to about 82-85 C. The aluminum sulfate solutlon
(lO9.B 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 mlxlng
for about 12 hours. Then the remaining HCL (8.6 grams) was
added. The temperature was reduced to 40 C. slurry com-
prlsing 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 ~lurry addition was
completed in about two hours. After addition of the calcium
slurry was completed, heat was discontinued and mixing was
maintalned for about two hours. The balance of the water
(106.9 gram~) was then added to complete the batch.
. ~:
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The HCl addition was made in two parts to avoid over-
shooting the desired Al/Cl atomic ratio. Generally, the
ratlo will be determined by analysis before addition of the
remaining acid, or other material utilized to adjust the
ratio.
~XAMPLE 5
Thls example illustrates the use of sulfuric acid as
the sulfate anion source. A one kilo batch was prepared
uslng the following materials:
TABLE III
Quantitv
Component wt. Xqrams
5/6 BAC 50X 44.23442.3
20 Be' HCl 16.31163.1
60 Be' H2S04 3.35 33.5 ;
FeC13 soln. 0.12 1.2
CaS04-2H20 0.45 4.5
CaC03 0.25 2.5
Water 35.29352.9
A one llter glass llned reactlon vessel was fitted with
a mixer, heating mantel and reflux condenser. 100 grams of
water and 442.3 grams of BAC were charged lnto the vessel.
Wlth mixlng, 1.2 grams of ferric chlorlde solutlon (42.9X
FeCl3 w/w) was added at amblent temperature . Stlrrlng was
continued for an addltlonal 30 mlnutes. The reactlon mixture
was then heated to 60 C, and 95X 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-B5
C. The sulfurlc acld (33.51 grams) was then added at approx-
imately 0.35 ml/mln., the total amount belng added over a one
hour interval. The temperature was maintalned for 12 hours
with continuous mixing, after whlch the remainlng HCl (8.16
gram~) was added. The temperature was then lowered to 40 C.
A slurry comprising 4.5 grams of calcium sulfate dlhydrate
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and 2.5 grams of calcium carbonate in 100 grams of water was
prepared. The slurry was added to the reactlon mixture at a
rate of about l.Oml/min. with continuous mixing, addition
time belng about two hours. After addition of the slurry,
heatlng was discontinued and mixing continued for about two
hours. The reaction mixture wa~ 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 ob~ectives of the invention. The BAC concentra-
tion ln the lnitial reaction mixture should be about 4.0 to
about 12.5X 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 ad~ustment.
As has been stated above the Al/Cl atomic ratio can be ~ -
ad~usted using HCl, aluminum chloride hexahydrate or a BAC of
a different Al/Cl atomic ratlo than the starting material.
In one embodiment of the invention the ad~ustment of Al/Cl
atomic ratio is accompllshed in two steps. This is a partic-
ularly advantageous method where the BAC concentration is
such that the Al 3 is about 7.9X or greater. In this modifi-
catlon of the process the BAC is ad~usted to an lnltial Al/Cl
atomic ratio of about 1.2 to about 0.91. After the sulfate
anion addltlon ls made and before the calcium salt addition
ls made a further ad~ustment i8 made to reduce the Al/Cl
atomlc ratlo to about 0.9 to 0.70.
As used in the specification and claims the term
"substantlally free" as used ln reference to precipitate
content of the process reaction stream, means the product
stream contalns about 1.0 wt. X or less of such precipltate.
Typically the product stream will contain less than 0.5 wt.%
preclpitate. ~-~
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