Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
" 1201~2~
The present invention concerns a process for the
recovery of aluminum and iron salts from acidic waste waters.
It was previously usual practice either to neutralize
such acidic waste waters and to direct them to the river, or
to discharge them into the sea.
These methods, however, are risky on the grounds of
environmental protection. They have ~he further disadvantage
that the materials contained in the acidic was~e waters,
especially aluminum and iron, can be no longer used.
Other possible methods, therefore, have been sought.
For example, the acidic waste waters accumulating with the
production of clay are being used for the treatm~nt of indus-
trial and community waste waters, along with active bentonite
as an inor~anic precipitation-, flocculation-, separation and
absorbtion means.
This utilizes only a comparatively small frac~ion of
the accumulated acidic waste waters.
The inven~ion is based on the problem of finding a
process for the recovery of aluminum and iron salts from acidic
waste waters, whereby not only can the previous environment-
ally harmul practices be eliminated, but the substances con-
tained in the waste waters can also be transformed into in-
dustrially useful products.
The subject of the invention is thus a process for
the recovery of aluminum and iron salts from acidic waste
waters, characterized in that:
A. the acidic waste waters are neutrali~ed with calcium
oxide and/or calcium hydroxide or the precipitation of
aluminum hydroxide and iron (III) oxide hydrate;
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~.201gL~Z
B. the aluminum hydroxide-iron (III) hydroxide precipitate
obtained is treated with sodium hydroxide until the aluminum
hydroxide dissolves as sodium aluminate;
C. the remaining iron (III) oxide hydrate precipitate is
separated from the sodium aluminate solution, washed, and
dried, the iron (III) oxide hydrate is pellated for use as
a gas purification substance or converted by thermal treat-
ment to an iron (III) oxide suitable for use as a pigment;
D. and the sodium aluminate solu~ion is trans~ormed into a
crystalline zeolite by conversion with a water-glass solution.
With the recoverable acidic waste waters, according
to the invention, the first concern is with waste waters
accumulating with the clay extration. Such waste waters
usually contain small quantities of colloidal silicic acid.
These particles of colloidal silicic acid evidently act as
crystallization nuclei in the zeolite formation (step D).
Since it is seen surprisin~ly, that the æeolite formation
proceeds more slowly when the sodium aluminate solution is
free of silicic acid.
The reasons for the improved crystal formation arc,
however, still not known exactly. The fact is that zeolite
formation is improved to a surprising degree if silicic acid
is present.
In general, the acidic waste waters used (from the
clay production) have the following analytic composition:
A13~ 12 - 16 g/liter
Fe3+ 4 _ 6 g/liter
c~2+ 2 _ ~ g/liter
Mg2~ 2 - 4 g/liter
SiO2 0.2 _ 0.4 g/li~er
~z~ z
Cl- ~5 - 90 g/liter
fr~e HGl 4 - 6 g/liter
The acidic waste waters in step A are neutralized
to a pH value of 3-8, preferably 6.6 - 6.7.
In the case where the iron salt or a part of the iron
salt in the waster water is present in the divalent condition,
the precipitation in step A occurs in a suitable manner when
the waste water is brought into contact with a gas containing
oxygen. In general, air is blown through the solution to
achieve this; the iron (III) oxide hydrate thus obtained is
especially well suited as a gas purification substance.
The preferred waste waters used contain aluminum and
iron (and sometimes other metals) in the form of the corres-
ponding chlorides. They also contain some free HCl.
The starting materials can, however, be waste waters
containing sulfuric acid, in which case a preneutralization
is carried out before step A with calcium oxide and/or cal-
cium hydroxide, by adjusting the pH to a value of about 3.
Then the separated calcium sulfate is filtered off.
The scope of the invention includes additionally the
use of the iron (III) oxide hydrate produced according to
step C as a gas purification substance, or the use of the
iron (III) oxide produced thereby as pigment. The scope of
the invention includes also the use of the ziolite produced
according to step D as a molecul.ar sieve or as an adsorption
material.
The zeolite obtained is primarily a Y-zeolite, which,
as previously explained, evidently as formed because of the
presenc~ of the so-called "nucleus formation substances" in
a well-crystallized form. With the same resulting materials,
zeolites of the A- and Y- types are also produced.
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The precipitation of aluminum hydroxide and of iron
(III) oxide hydrate in step A is, in general, carried out
as follows:
The waste waters containing hydrochloric acid, alum-
inum chloride, and iron chloride are first heated by a blast
of superheated steam, to just below the boiling point. With
further blasts of steam, the pH is adjusted to about 6.6,
whereby a mixture of aluminum hydroxide and iron (III) oxide
hydrate precipitates.
The treatment of the aluminum hydroxide-iron (III)
oxide hydrate precipitated with sodium hydroxide in step B
is generally carried out as follows:
After filtering and washing the hydroxide precipitate,
sodium hydroxide is added to the hydroxide mixture, and the
aluminum hydroxide is converted into sodiu~ aluminate.
The further treatment of the iron (III) oxide hydrate
in step C is as follows:
The iron (III) oxide hydrate is filtered from the dis-
solved aluminate and washed to be free of all aluminates.
The drying of the materials for the gas purification takes
place at 60-llO~C. In industrial use, the iron (III) oxidP
hydrate is formed into pellets with the addition of a pres-
sing aid ~or removal of hydrogen sulfide from gas mixtures.
The iron (III) oxide to be used as pi~ment is obtained
by calcining the oxide hydrate at 600~C.
The iron (III) oxide hydrate obtained according to
the invention is especially well-suited for gas purification,
i.e., for the removal of hydrogen sulfide from diverse gas
mixtures.
For the gas purification, the gases containing H2S
are led over the pelleted iron (III) o~ide hydrate substances
lZ0~42~
placed in the reactors. The more or less strongly hydrated
iron oxide reacts with the hydrogen sulfide according to the
following equation:
Fe2O3 + 3H2S = Fe2S3 + 3H2O + 14.9 kcal
The conversion of the sodium aluminate solution obtained
in step D into a crystalline Y-zeolite is carried out, in
general, as follows:
Following known procedures, a crystallized Y-zeolite
is obtained by producing a suspension of nuclei for crystal
formation is produced by the reaction of sodium aluminate
with sodium silicate with an excess of caustic soda; the
suspension is then ~onverted with sodium silicate to a zeolite
having a SiO2/ A1203 mole ratio of abou~ 5:1.
Through the "SiO2-contamination" in the aluminate ob-
tained from the acid waste water, the crystal nucleus forma-
tion seems to be improved, so that the time necessary for
the crystallization of the zeolite can be greatly shortened.
The same is true for the production of zeolites of
the A- and X types.
The invention is in no way limited by the following
examples:
EXAMPLE 1
1500 liters of clay-deco~pensation solution, contain-
ing hydrochloric acid, (17.7 g/liter A12O3, 8.6 g/liter Fe23)
are stirred strongly with 66 kg CaO to a pH of 6.7. Then
50g of flocculating agent, dissolved in 5 liters of water,
is added to improve the filterability of the resulting hydro-
xide [Al (OH)3 or Fe(OH)3].
After a reaction time of 4 hours, the hydroxide mixture
is filtered off in a filter pr~ss.
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1;2~)~9~2~
The filter cake (512 kg hydroxide mixture witn 90%
H2O) is added to 30 kg NaOH flakes, which are contained in a
container of corrosion-resistant steel. The liquefying mix-
ture is then heated and held for one hour at 90-95C.
After cooling to 80C, the sodium aluminate solution
is separated from the iron oxide in the filter press.
631 kg of sodium aluminate solution (3.3% A12O3,
3.55% Na2O) is mixed with 169 kg NaOH (50% solution) and
29 kg NaOH flakes, so that 830 kg of a solution with 2.5%
A12O3 and 14.5% NaOH results.
The aluminate solution (830 kg) cooled at 20-25C,
is then added to 265.6 kg of sodium water glass (41 Be~
28.6% SiO2) wi~h intensive stirring. From the clear solu-
tion the suspension of nuclei for the ~rystal formation is
formed after a short time. After 20 minutes of stirring and
warming to 40~C~ the substance is filtered and washed.
301 kg of this filtered substance (dry substance
26%) is stirred with 421 kg sodium water glass (41Be), 145
kg NaOH (7.5% solution), and 90 kg of water, heated to 98C
and held at this temperature for 4 hours.
After this reaction time, a crystallized Y-zeolite
with a crystallinity of 100% is formed.
EXAMPLE 2
1500 liters of clay-decompensation solution contain-
ing sulfuric acid 517.7 g/liter A1~03, 8.6 g/liter Fe2O3) is
adjusted by the addition of calcium oxide under strong stir-
rin~ to a pH value of 3. The precipitated calcium sulfate is
then separated o~er a filter press, and the filtrate is
brought up to a pH of 6.6 by the further addition of CaO.
T~e hydroxides of aluminum and iron are filtered
after the addition of 50 g of flocculating agents dissolved
~ Z~ ~2~
in 5 liters of water, and processed further as in Example 1,
with a reaction time of 4 hours.
The accumulated iron (III) oxide hydrate still con-
tains some calcium sulfate, which, however, does not impair
the efficacy for H2S-removal.
The Y-zeolite obtained by this prscess has, in any
case, a crystallinity of 100% ater a reaction time of 4
ours.
EXAMPLE 3
1 liter of a sodium aluminate solution with 33 g/li-
ter A12O3 and 47 g/liter Na2O is stirred strongly into 1
liter of an 80C sodium silicate solution with 81 g/liter
SiO2 and 24 g/liter Na2O. The sodium aluminate solution is
produced as described in Example 1 and increased to the de-
sired Na20 content with sodium hydroxide.
After 8 hours of reaction time at 80C, while it is
stirred s~owly, the resulting A-zeolite is filtered, washed
and dried (to about 20% water of hydration). A crystallized
A-zeolite with calcium bonding capacity of 130 g Ca/g of
water-free product is obtained.
EXAMPLE 4
For the synthesis of a zeolite of the Y-type, a
sodium silicate solution with 83.5 g Na2O/liter and 62 g
SiO2/liter is heated to 95C and mixed intensively with a
sodium aluminate solution containing 71 g Na2O/liter, or
66 g A12O3/liter, and also heated to 95C. The sodium alum-
inate solution obtained according to Example l ~33 g A12O3/
liter or 35.5 g Na2O/liter) must be evaporated by half in
order to obtain the necessary Na20/A12O3 ratio. The mole
ratio of SiO2tA12O3 of the component mixture amounts to 2.5.
lZ01~22
Also, the mole ratio of Na20/SiO2 is 2, and the mole ratio
of Na20/A1203 is 5.
After a reaction time of 2 hours twithout stirring),
the crystallized zeolite is iltered, washed and dried.
EXAMPLE OF APPLICATION
To demonstrate the effectiveness of the iron (III)
oxide hydrate, obtained according to the invention, as a gas
purification substance, a gas composed of 4 vol.% hydrogen
sulfide, 42 vol.% CO2, 52 vol.% methane, and 2 volO% water,
at room temperature, with a space velocity of about 9G0/hr,
is passed over 500 ml of the iron ~III) oxide hydrate, ob-
tained according to Example 1, which is in a stationary
reactor; after 5 hours, the sulfur content of the substance
is analytic~lly determined.
The sulfur content amounts to 35%. In comparison
thereto, about 30% is measured with known gas purification
substances.
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