NO831323L - PROCEDURE FOR THE PREPARATION OF ALUMINUM AND IRONIC ACID WASTE WATER - Google Patents

Abstract

1. A process for the treatment of acid waste water containing aluminum and iron, wherein (a) the acid waste containing small amounts of colloidal silicic acid is heated to just below boiling point so as to precipitate aluminum hydroxide and hydrated iron (III) oxide and is neutralized with calcium oxide and/or calcium hydroxide ; (b) the resultant aluminum hydroxide iron (III) hydroxide precipitate is trated with sodium hydroxide until dissolution of the aluminum hydroxide as aluminate ; (c) the remaining hydrated iron (III) oxide precipitate is separated from the sodium aluminate solution, washed dried and the hydrated iron (III) oxide is pelletised for use as a gas-purifying medium or is converted by thermal treatment into iron (III) oxide suitable for use as pigment ; (d) and the sodium aluminate solution is converted into a crystalline zeolite by reaction with a water glass solution.

Description

The present invention relates to a method for processing aluminium- and iron-containing, acidic waste water.

Until now, it was common to either neutralize such acidic waste water and carry it into the rivers or to empty it into the sea,

However, such discharge methods are questionable for environmental reasons. It also has the disadvantage that the substances in the acidic waste water, especially aluminum and iron, can no longer be used.

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One has/therefore already searched for other application possibilities, whereby e.g. the acidic waste water produced by afInrvemensdtt ilsliom ng uoav rgbanleiksje word feslalminmegn s-m, ed floakkktiinv gbse-n, tsonepitat rabsljoens-

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and absorbents for the treatment of industrial and

municipal wastewater. "In this way, however, only a small fraction of the formed acidic waste water can be utilised.

The task for the present invention was therefore to find a method for the processing of aluminum and iron-containing acidic waste water, whereby not only the previous, environmentally harmful emptying was eliminated, but also the waste water's contents could be transferred into technically valuable products.

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oGipjepnasrbteanidd infog r of opalfuimnnineilusmen - eog r djeerrnfhor oledn ig frseumrt ganavgslmöpostve anvnd, which is characterized by (a) the acidic wastewater is neutralized with calcium oxide pg/or calcium hydroxide to precipitate aluminum hydroxide and iron (III) oxide hydrate; (b) the aluminum hydroxide-iron (III) hydroxide precipitate obtained is treated - with sodium hydroxide until dissolution

of the aluminum hydroxide as aluminate; (c) the remaining iron (III) oxide hydrate precipitate is separated from the sodium aluminate solution, washed and dried and the iron (III) oxide hydrate is pelletized for use as a gas scrubber or transferred by thermal treatment into iron (III) oxide suitable for use as a pigment; (d) and the sodium aluminate solution is transferred into a crystalline zeolite by reaction with a water glass solution.

The four wastewaters that can be processed according to the invention are primarily wastewaters that are formed by pale earth mining, which normally contain small amounts of colloidal silica<y>re<.>These silicic acid particles obviously act as crystallization seeds during the zeolite formation (d), as it over- - it was quickly established that zeolite formation occurs more slowly when the aluminate solution is silicic acid-free.

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—What is the reason for the improved crystal formation in steps

'(d) really is, is not yet entirely clear. One fact, however, is the surprising improvement of the zeolite formation in the presence of the silicic acid.

In general, the acidic waste water used from bleached earth manufacture has the following analytical composition: 3+

Fe 4 to 6 g/litre;

Al3+ 12 to 16 g/litre;

About 2 to 4 g/liter;

Mg<2+>2 to 4 g/liter; SiO 2 O.2 to 0.4 g/liter;

Cl" 65 to 90 g/litre; free HC1 4 to 6 g/litre.

The acidic waste water in step (Ia) is preferably neutralized to a pH value of from 3 to 8, preferably from 6.6 to 6.7.

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If the iron or part of the iron in the waste water)

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__exists in a divalent state, the precipitation occurs in steps

(a) appropriate by bringing the waste water into contact with an oxygen-containing gas. In general, air is then blown through the solution, and the iron (III) oxide hydrate thus formed is particularly well suited as a gas cleaning mass. I • i

The acidic waste water used preferably contains aluminum and iron (and possibly the other metals) in the form of the corresponding chlorides. Furthermore, they also contain some free HC1.

M; however, it is also possible to start from sulfuric acid waste water, where before step (a) a pre-neutralization is carried out with calcium oxide and/or calcium hydroxide to a pH value of less than approx. 3.0 and filter out the separated calcium sulphate.

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Object of the invention by further use of the iron (III) oxide hydrate produced according to step (c) as a gas cleaning mass or the iron (III) oxide produced therefrom as a pigment. Furthermore, the subject of the invention is the use of the zeolite produced according to step (d) as a molecular sieve or as an absorbent.

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Herein, it primarily concerns Y-zeolites, which, as indicated above, are obviously formed in the presence of the aforementioned "nucleating substances", in a good crystalline form. With the same starting materials, one can also produce;

sI to A- and Y-type zeolites. jI

The precipitation of aluminum hydroxide and the iron (III) oxide hydrate in step (a) is generally carried out as follows: j

The hydrochloric acid aluminum chloride and ferric chloride-containing wastewater is heated by blowing in superheated steam first to i j just below the boiling point. The neutralization is then carried out under further steam blowing to approx. pH 6.6, whereby a mixture of aluminum hydroxide and iron (III) oxide hydrate is precipitated. ! I 1 I _The treatment of aluminum hydroxide-iron (III)-oxide hydrate-mfi einlnleinlighen emt ed as naphthoyl ilugmehr:droxide in step (b) is carried out in allI<->

E! After filtering and washing the hydroxide precipitate, sodium hydroxide is added to the hydroxide mixture, and the aluminum hydroxide is transferred into the sodium aluminate.

The further treatment of the iron (III) oxide hydrate in step [c) proceeds generally as follows: The iron (III) oxide hydrate is filtered from dissolved aluminate and washed aluminate-free. The drying of the material to be used for the gas purification takes place at 60 to 110 C. For in the plant for removing hydrogen sulphide from a gas mixture, the iron (III) oxide hydrate is pelletised with the addition of a pressing aid.

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The iron (III) oxide hydrate produced according to the invention

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is particularly suitable for gas purification, i.e. for the removal of hydrogen sulphide from various gas mixtures.

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Thus, the P^S-containing gas was passed through the pelleted iron (III) oxide hydrate masses placed in reactors; for gas purification. Underneath, hydrated iron oxide reacts more or less strongly with hydrogen sulphide according to |i

The transfer of the sodium aluminate solution obtained in step (d) into a crystalline Y-zeolite is generally carried out as follows:

' By a method known per se, a crystalline Y-zeolite is produced by reacting sodium aluminate

.. with, sodium silicate with an excess of caustic soda produces

' a slurry of crystal nucleation centers and then convert these sodium silicate into a zeolite with a molar ratio SiO2/Al2O3 of approx. 5.

Through the "SiO2 contamination" in the aluminate produced from the effluent, crystal nucleation appears to be improved, so that the time required for crystallization of the zeolite can be greatly shortened.

The same applies to the production of zeolites of A and

The X type.

In the following, the invention is illustrated by examples: Example 1

1500 liters of hydrochloric acid bleaching solution (17.7 g/l A1203; 8.6 g/l Fe203) is brought to pH 6.7 with 66 kg CaO under vigorous stirring. 50 g of flocculant dissolved in 5 1 of water are then added to improve the solubility of the precipitated hydroxides (Al(OH) ^ respectively Fe(OH) 3 ).

After a reaction time of 4 hours, the hydroxide precipitate is filtered in a filter press.

The filter cake (512 kg of hydroxide mixture with 90% H„0) is added to 30 kg of NaOH pieces which are placed in a container of corrosion-resistant steel. The mixture that becomes liquid is then heated and held for one hour at 90 - 95 C.

"Without<r>cooling to 80 C, the sodium aluminate solution separates

:L the filter press from the iron oxide hydrate. !

""631 kg of sodium aluminate solution (3.3% Al-O.,; 3.55 NaoO)' is mixed with 169 kg of NaOH (50%ig) and 29 kg of NaOH (pieces), so that 830 kg of solution with 2, 5% Al 2 O 3 and 14.5% NaOH.

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Now the aluminate solution (830 kg) is cooled to 20 - 25 C h! il sodium water glass (41° Be, 2 8.6% SiO~) with vigorous stirring. From the initially clear solution, the slurry of the crystallization formation center is formed after a short time.! One more 20 min. stirring and heating to 40 o C, filter and wash the mass.

301 kg of this filtered mass (TS 26%) is stirred with 421 kg of sodium water glass (41° Be), 145 kg of NaOH (7.5%) and 90 kg of water is heated to 9 8 C and kept at this temperature for 4 hours trip.

i After this reaction time, it has formed crystallized;

Y-zeolite with a crystallinity of 100%.

Example 2

1500 liters of sulfuric acid pale earth leaching solution (17.7 g^l A12C>3, 8.6 g/l Fe203) are neutralized with calcium oxide under vigorous stirring to a pH value of 3. The precipitated gypsum is then separated through a filter press, and the filtrate brought to pH 6 by further addition of CaO.

As in example 1, the hydroxides from aluminum and iron are filtered after the addition of 50 g of flocculant dissolved in

in 5 1 water and a reaction time of 4 hours and treated further accordingly.

DI a formed iron (III) oxide hydrate still contains some gypsum, which, however, does not affect the efficiency of H2S removal

However, the Y-zeolite obtained by this method also has a crystallinity of 100% after a reaction time of 4 hours. j

Example 3 j

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In 1 1 liter of 80 oC hot sodium silicate solution with 81 g/l SiOn in 1 liter of hot sodium silicate solution with 81 g/l in 2 and 24 g/l Na90, 1 liter of a sodium aluminate solution is vigorously stirred in with 33 g/l Al-jO^and 47 g/l Na2O. The sodium aluminate solution was prepared as described in example 1 and brought to the desired Na~0 content with NaOH. '

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After a reaction time of 8 hours at 80 o C with slow stirring, the A-zeolite formed is filtered off, and washed and dried (to approx. 20% water of hydrate). A crystalline A-zeolite with a calcium binding capacity of 130 g Ca/g of the anhydrous product is obtained. j j

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i<!>For the synthesis of a Y-type zeolite, a sodium silicate solution with 83.5 g Na20/1 and 62 g SiO2/1 is heated to 95°C and mixed vigorously with a sodium aluminate solution containing

hoi popldvear rme7t 1 g tiNl a2905/°C 1 hi en3h0 omldinsv. iDs en 66 ig foAlgle 20e3/ks1 emopg el lik1 edleanandenes .deer

sodium aluminate solution (33 g A190 /l respectively 35.5 g N1 a^O/1) is evaporated to half and to achieve the necessary Na20/Al2O2 ratio. The molar ratio SiO-^rAl-jO^ of the component mixture is 2.5. In addition, the molar ratio of Na20:SiO2 is 2 and the molar ratio of Na20:Al203 is 5.

After a reaction time (without stirring) of 2 hours, the crystallized zeolite is filtered off, washed and dried.

UseIce example

In order to determine the effectiveness of the iron (III) oxide hydrate produced according to the invention as a gas cleaning mass, a gas consisting of 4% by volume hydrogen sulphide, 42% by volume C02, 52% by volume methane and 2% by volume water is passed at room temperature at a room velocity of approx. 900 h over 500 ml of the iron (III) oxide hydrate prepared according to example 1, which is in a standing reactor, and after 5 hours the sulfur content in the mass is determined analytically.

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The sulfur content is 35%. In comparison with this is measured

in in approx. 30% on well-known gas cleaning compounds

Claims (8)

1. Procedure for processing aluminum and iron-containing acidic waste water, characterized by in ij[a)- neutralizes the acidic wastewater to precipitate aluminum hydroxide and iron (III) oxide hydrate with calcium oxide and/or calcium hydroxide; (b) treating the obtained aluminum hydroxide iron (111) 1 - hydroxide precipitate with sodium hydroxide until dissolution of the aluminum hydroxide as aluminate; (c) separating the remaining iron (III) oxide hydrate precipitate from the matrix aluminate solution, washing it, drying it and pelleting the iron (III) oxide hydrate for use in gas scrubbers or transferring it by thermal treatment in iron (III) oxide suitable for use as a pigment; (d) and transfers the sodium aluminate solution by reaction'with ! : e' In a water glass solution in a crystalline zeolite. ■ 2. Method according to claim 1, characterized: by using iron (III)-containing wastewater in water, the precipitation in step (a) is carried out in contact with one oxy-| gaseous gas. IN 3. Method according to claim 1 or 2, character-! ! i s e r t by starting from acidic waste water that contains small amounts of colloidal silicic acid.. i IN j 4. Method according to one of claims 1-3, characterized in that one starts from an acidic waste water in water with the following average composition: J i i 1 3+ i i Al° 12 to 16 g/litre; ' .. L .... -Fe3+ 4 to 6 g/liter; 'Ca<2+>2 to 4 g/litre; Mg<2+>2 to 4 g/liter; SiO 2 O.2 to 0.4 g/liter; Cl" 65 to 90 g/litre; free HC1 4 to 6 g/litre. 5. Method according to one of claims 1-4, characterized in that the acidic waste water in step (a) is neutralized to a pH value of from 3 to 8, preferably 6.6 to 6.7. 6i. Method according to one of claims 1-3. characterized in that by using sulfuric acid: av--l1 øp" of water before step (a) a pre-neutralization is carried out with calcium oxide and/or calcium hydroxide until a pH value of no more than approx. 3 and from reduces the excreted calcium sulfate. 7. Use of the iron (III) oxide hydrate prepared according to I; - claim 1 [step (c)] as gas cleaning mass or the iron (III) oxide produced therefrom as pigment. I I 8. Use of the zeolite produced according to claim 1 [step (d)] as a molecular sieve or as an absorption material. ; IN 'I