Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFICATION
The present invention relates to a method for
producing polynucleate basic trivalent metal hydroxysulfate
in solid form which when dissolved in water produces posi-
tively charged polynucleate complexes possessing charge
neutralizing propertie~ in systems that contain suspended or
colloidal negativel~ charged particles.
The objective of the present invention is to
provide a rational method for industrial production of
polynucleate, basic aluminum sulfate in solid form.
BACKGROUND OF THE INVENTION
There are known to the art a number of aluminum
products which contain polynucleate aluminum ions in solu-
tion. These products have been produced in response to the
demand for more effective chemicals for use in water puri-
fication, paper sizing and plant dewatering processes. The
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products exhibit considerably improved properties for use
within these technical fieldq, due to the higher electrical
charge of the polynucleate metal ions in comparison with the
earlier simple compounds.
The aluminum products that have been developed are
principally of two kinds: chloride-based basic aluminum
compoundq, and sulfate-based basic aluminum compounds. With
regard to the first group, there was initially developed a
polyaluminum chloride (PAC) of the general formula
[ AlClX~O~)3-X ]n
where x is <3, normally 1-2. Such compounds and methods for
their manufacture are described, for example, in SE-B-
7201333-7, SE-B-7405237-4, SE-B-7412965-1, SE-B-7503641-8,
and DE-A-2630768.
The other type of aluminum chloride solutions
(PALC) which are also based on the same polynucleate com-
plexes, have general formulas which can be written as:
[ AlC13 x AOH ]n
where A signifies an alkali metal, and
[ AlC13 2 B(OH)2 3n
where B signifies an alkali earth metal, n is a positive
integer, and x is a number in the range 1 to 2.7. Poly-
nucleate aluminum chloride solutions of the PALC-type are
described in FR-Al-7512975, according to which the solutions
are prepared by alkalizing aluminum chloride solutions with
solutions of alkali hydroxide. According to this reference,
however, it has not been possible to produce clear, stable
solutionq other than in a highly diluted state.
The term "stable solution" means a solution which
will not change significantly with regard to its composition
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and properties, even when stored for long periods of time.
It is stated in the FR-Al-7512975 that a solution containing
up to 0.40 moles of aluminum per liter can be obtained under
certain circumstances. The stability of the solution,
however, is greatly limited and the solution must be injected
directly into the water to be treated. It is clearly evident
from the reference, and in particular from the working
examples, that the known PALC solutions which have aluminum
concentrations above about 0.1 mole/liter cannot be expected
to be effective and stable.
Sulfate-based basic aluminum compounds have been
described in EP-A-79850039-3, EP-A-80850033-4 and SE-
A8101830-1. These products contain polynucleate metal ions
in solution, to a greater or lesser extent, and are thus
effective water cleansing agents. The sulfate-based products
can also be used for purposes other than for cleansing water
in which the presence of polynucleate metal ions favors the
effects desired. In certain cases, however, it is highly
desirable, and even necessary, to restrict the supply of
sulfate ions to the smallest possible amount.
Low sulfate is particularly important when using
the product to produce drinking or tap water. Sulfate
reduction is also important in the case of systems which are
used and cleansed repeatedly in order to eliminate the risk
of sulfate accumulations in tissue and in water. This
applies to water purifying systems used in areas where there
is a water deficiency, necessitating the repeated use of
available water for as long as possible, with intermediate
cleansing of the water. In water such as this, after
cleansing the water ten times with conventional aluminum
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sulfate, or compositions having corresponding sulfate con-
tents, the sulfate content of the water may reach such high
levels as to result in a corrosive attack on the water-
carrying conduit systems, resulting in troublesome leakage.
The problem of enrichment of sulfate-ions has ncw also become
manifest in the manufacture of paper, where the water trans-
portation system is, to a large extent, completely closed for
environmental purposes. The manufacturing processes are
seriously affected by excessively high salt concentrations in
the paper stock.
U.S. Patent No. 4,238,347 discloses a method of
producing sulfate-lean basic aluminum sulfate of the formula:
Al (OH)X (S04)y (H2P4)z (H2)w
where x is 0.75 to 1.5;
y is 0.7 to 1.07;
z is 0 to 0.2 and
is 2.0 to 4.2, wherein
x + 2y + z is equal to 3.
The compounds are prepared by reacting aluminum sulfate with
the comminuted calcium carbonate, optionally in the presence
of phosphoric acid, and passing the reaction mixture through
a filter to isolate the gypsum formed. It has been found,
however, that the carbon dioxide leaving the reaction process
from the calcium carbonate, together with the gypsum create
certain technical problems.
SE-A-8104149-3 describes an improved method for
producing sulfate-lean polynucleate aluminum hydroxide
complexes of the formula:
[ Al (OH)X (S04)y (H20)z ]n
3Q where n is an integer;
--4--
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x is 0.75 - 2.0;
y is 0.5 - 1.12;
x + 2y is 3;
z is 1.5 - 4 when the product is in solid ~orm, and
z is ~>4 when the product is in solution, wherein
aluminum sul~ate is reacted with one or more compounds taken
from the group CaO, Ca(OH)2, BaO, ~a(OH)2, SrO, Sr(OH)2 in
aqueous solution to form the aforesaid compound, whereafter
the resultant alkali earth metal sulfate precipitate is
isolated and the residual solution optionally evaporated.
The resultant solution has excellent properties and can be
obtained with a high basicity, OH/Al < 2Ø Manufacture is
complicated, however, since isolation of the alkali earth
metal sulfate is difficult to achieve and places specific
demands on the technical equipment used.
Still a further method of producing these complexes
is described in SE-A-8206207-6, in which a solution of an
aluminum salt is neutralized to pH 5-7 to precipitate amor-
phous aluminum hydroxide, which is isolated and thereafter
contacted with sulfate-ions in the form of aluminum sulfate
and/or sulfuric acid to a "y" value of 0.5 - 1.12, preferably
0.5 - 0.75, this product being optionally converted to a
solid form.
Another method of producing polynucleate aluminum
hydroxide sulfate complexes is described in SE-A-8206206-8.
This method comprising cooling a solution containing a
polynucleate hydroxide sulfate complex of the formula:
Alm ( OH ) n
in which the anion is (SO4) (3m-n)-(3m-n)/2
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where m and n are integers. These materials are prepared by
alkalizing aluminum sulfate with NaO~ or Na2C03, so as to
crystallize out Na2S04 lOH20 which is then separated out
and the rjesidual solution optionally concentrated or dried to
solid form by evaporation.
The conversion of solutions of polynucleate alumi-
num complexes to a solid form in order to maintain the
stability of the complex in those instances when the presence
of costly stabilizing agents is not desired, is both compli-
cated and expensive, such that the final product is not trulycompetitive with standard aluminum sulfate (BOLIDEN~ ALG) or
aluminum-ferrisulfate (BOLIDEN~ AVR), for use in water
cleansing processes. Water cleansing processes, drinking
water, and domestic sewage purification processes require the
presence of large ~uantities of flocculating agents for
precipitating out the impurities present, such as, inter
alia, phosphorous, and the cost of the water cleansing
chemicals re~uired in sewage purification in particular is
very high. Demands have therefore been made for more effec-
tive and relatively inexpensive chemicals.
SUMMARY OF THE INVENTION
It has now surprisingly been found possible toeliminate these technical problems in a simple and an effi-
cient manner with the aid of the produc~ ~roduced according to the
method of the present invention, which produc-t contains a sulfate-
lean basic metal hydroxysulfate of the general formula.
[ M (OH)X (S04)y (H20)Z ]n
where n is an integer;
M is a trivalent metal ion
x is 0.75 - 2.0
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y is 0.5 - 1.12;
x + 2y is 3;
z is 1.5 - 4 when the product is in a solid form and z
is >~4 when the produc-t has the form of an aqueous solution, and
calcium sulfate hemihydrate. The mole ratio of Ca, expressed as
Ca(OH)2, to M, expressed as M2(S04)3, is at most 2, and -the
amount of water in the product, expressed as the water of
crystallizatJon per mole M2(S04)3, is at most 6 H20- The mole
ratio of Ca(OH)2 to M2(S04)3 is suitably 1.0 to 2.0, although
preferably 1.5 to 2Ø
The invention therefore provides a me-thod for producing,
in a simple and practical manner, a polynucleate basic metal
hydroxysulfate product in solid form which, when dissolved in
water, will provide a positively charged polynucleate complex
possessing charge neutralizing properties in systems containing
suspended or colloidal negatively charged particles. The method
comprises mixing a molten aluminum or iron III sulfate and a
calcium compound taken from the group consisting of Ca(OH)2, CaO,
CaC03 and CaMg(C03)2 and allowing the mixture to react to form a
product. The product is cooled to ambient temperature to form a
comminutable or grindable solid product containing polymetal
hydroxysulfate complex and calcium sulfate hemihydrate.
Optionally a molten aluminum sulfate, A12(S04)3 ' 14H20 and
aluminum sulfate-ferrisulfate, A12(S04)3 14H20; Fe2(S04)3 9H20 is
mixed with the calcium compound. Also optionally, water may be
removed from the mixture. The product optionally contains
polyferrihydroxy sulfate complex.
DETAILED DESCRIPTION OF THE INVENTION
Solid compositions produced by the me-thod according to
the invention are mixtures of calcium sulfate hemihydrate with a
metal hydroxysulfate complex of the genera] formula:
[ M (OH)X (S04)y (H20)z ] n
wherein M is a trivalent metal ion;
n is an integer;
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x is 0.75 to 2.0;
y is 0.5 to 1.12; and
z is 1.5 to 4.
Particularly preferred solid compositions are those
in which
x is -~ ol -1.8 '~ 3
y is 0.6 to 0.7; and
z is 2.0 to 2.5.
The compound exists in the form of a polynucleate complex in
aqueous solution and has the same form when solid.
For use as a water treatment chemical, the solid
product of the invention will generally be redissolved in
water. The solid product obtained in accordance with the
invention dissolves relatively quickly in water (<2 minutes),
even when ground or comminuted to a relatively coarse par-
ticle size. The gypsum (calcium sulfate hemihydrate) present
is suspended in the resultant solution, while the metal
hydroxysulfate complex is dissolved therein. The water
cleansing properties of such a suspension have been found to
2Q be far superior to those of conventional aluminum sulfate
products (BOLIDEN~ ALG, AVR). The reason why the respective
constituents of the product rapidly suspend and dissolve in a
water phase is probably due to the fact that the gypsum
present, which has a hemihydrate form in the solid product is
rearranged to a dihydrate, therewith causing an increase in
volume and temperature such as to accelerate the dissolution
reaction.
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The present invention will now be described in more
detail with reference to a number of working examples.
Example 1
A product having a basicity (OH/M) of 1.7 was
prepared from 100 9 of molten aluminum sulfate-ferrisulfate
' A12 (SO4)3 14~2O; Fe2 (SO4)3 9H2O, 7~ Al
3% Fe). The temperature of the melt was 115C and the melt
was held at this temperature while mixing 15.0 9 CaO with the
melt over a period of 2 minutes. The resultant reaction
mixture was then cooled to room temperature, and the molten
product gradually transformed into a solid, comminutable
product.
The final product was analyzed and found to contain
water in an amount corresponding to 6 H2O per mole (Al, Fe)2
(SO4)3. The polynucleate aluminum sulfate-ferrisulfate
complex present in the product contains 1.7 OH per mole M
~Al, Fe). The product contained CaSO4 12 H2O~ calcium
sulfate hemihydrate.
Example 2
100 9 A12(SO4)3 14H2O having a temperature of
115C were admixed with 15.5 9 CaO, in accordance with the
procedure of Example 1 to yield an end product having an
OH/Al ratio of 1.65 in the resultant polyaluminum hydroxy-
sulfate complex.
If calcium hydroxide is used in place of CaO, it i5
necessary to evaporate off larger quantities of water, in
order to obtain a comminutable product. This can be affected
by maintainin~ the product at an elevated temperature for
some few minutes prior to cooling the product to room
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temperature, or by reacting the product in a vessel of large
sur~ace area so as to rapidly evaporate the water present.
It should be noted that it has not been possible
previously to pre2are polymetal hydroxy complexes at temper-
atures higher than 70C when practicing the known methods,due to decomposition of the complex at said higher temper-
atures. It is therefore particularly surprising that the
product can be produced successfully by means of the
method according to the present invention.
It has been found that with a dry solids content of
69~ or above of M2(SO4)3 ~ xH2O measured by expelling water
in a conventional domestic microwave oven for five minutes at
maximum power, it is not necessary to expel water during the
reaction between ~2~SO4)3 and CaO.
In order to obtain a comminutable or grindable
product, the M2O3 content oE the polymetal hydroxy complex of
the end product is preferably in excess of 14~ by volume, the
calcium sulfate being precipitated out as hemihydrate. This
means that the crystallization water present per mole of
ingoing A12(SO4)3 or ~Al,Fe)2 (SO4)3, about 14 H2O, is
reduced to 6 82O in the end product.
A product according to Example 1 (PAV) above was
tested with regard to its ability to clarify turbid sewage
water. The test also included a comparison test using
standard aluminum suleate-ferrisulfate (AVR). The starting
turbidity was >100 FTU. As will be seen from the following
table, the product produced according to the present invention
gave a far better result than the standard product.
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Table
Dosage Turbidity FTU
mmole/l Metal PAV AVR
140 3.5 35
160 3.5 35
180 3.0 35
200 3.0 37
220 3.0 38
240 4.0 42
260 5.0 47
2~0 5.0 Sl
A5 shown in the Table, the product according to the invention
exhibits a highly linear, flat register and overdosing does
not increase the turbidity in any way.
