DE1583944B2 - METHOD OF REMOVING UNWANTED ZINC OXIDE FROM IRON OXIDE FLIGHT DUST - Google Patents

Description

The invention relates to a method for removing undesired zinc oxide from iron oxide fly ash by mixing the fly ash with a used, weakly hydrochloric or weakly sulfuric acid Pickling liquid and subsequent treatment at elevated temperature.

Many attempts have already been made to remove the undesired zinc oxide from fly iron oxide dust and to recycle the iron oxide contained therein for beneficial use. For example, US Pat. No. 2,3 05,829 describes a process for recovering the zinc oxide and iron oxide contents from fly ash, in particular from the dust from blast furnace gas cleaning. The flue dust cleaned by this known process contains 20 to 30% zinc oxide and 20 to 40% iron oxide. For the cleaning in the known process chloride ions and sulfate ions are used containing pickle liquors, processed with the fly ash to form a paste, 1 to 2 hours are then heated to a temperature of 177 ⁰ C and 149 to 232 ° C, wherein from the the resulting mixture of iron oxide and zinc chloride is extracted with water, the zinc chloride. However, this known method has the disadvantage that on the one hand it is relatively cumbersome, on the other hand it is not suitable for the processing of flue dust which contains at least 50% by weight of iron oxide.

The object of the invention is therefore to provide an improved method for removing undesired zinc oxide from iron oxide fly dust, which is also applied to the processing of iron oxide fly dust containing at least 50 wt% iron oxide.

This object is achieved in a method for removing unwanted zinc oxide from iron oxide fly ash by mixing the fly ash with a used, weakly hydrochloric or weakly sulfuric acid Pickling liquid and subsequent treatment at elevated temperature solved in that the Flue dust contains at least 50 wt .-% iron oxide and zinc oxide in undesirable amounts and that the Mix at a temperature of about 66 to 121 C to convert most of the zinc oxide is converted into a zinc salt, the effluent from the reaction having a pH of 1 to 5.5, the iron oxide from the reacted mixture in the form of a solid filter cake, which is no more than Containing 0.50 wt .-% zinc oxide, is separated that the zinc salt-containing filtrate to concentrate the Salt is evaporated and from the evaporator water, which is suitable for draining into rivers or lakes is withdrawn.

According to the process according to the invention, it is possible in a technically simple and economical manner the fly ash, such as is obtained, for example, in a basic steelmaking process to work up that the iron oxide contained therein is recovered and used again for steel production can be, while at the same time the undesirable zinc oxide contained in the fly ash, which is preferably is contained therein in an amount of 0.25 to 4%, separated and in the form of a zinc salt is recovered. According to the method according to the invention, it is also possible to use weakly hydrochloric acid or weakly sulfuric acid pickling liquids to a technically useful recovery., wherein after completion of the invention. Process only those end products are obtained that are harmless to the environment in Rivers or lakes can be discharged.

According to a preferred embodiment of the method of the invention, the concentrated zinc salt is roasted to obtain zinc oxide, HCl or SO _{3 being} driven off in gaseous form, and these gaseous components are passed through an absorption tower to obtain hydrochloric acid and sulfuric acid.

In the practical implementation of the process according to the invention, the flue dust produced in a basic steelmaking process, which contains zinc oxide as well as iron oxide, is mixed with a used pickling liquid with a weak hydrochloric or weak sulfuric acid which has a pH of about 3 to about 5.5 . Subsequent heating of this mixture to a temperature of about 66 to about 121 ^° C. Zinc oxide is converted into a zinc salt, which is removed from the mixture in the manner described above, whereby a zinc oxide practically free fly dust is obtained.

The separated zinc salt, which can be in the form of zinc chloride or zinc sulfate, is then Continuously roasted to obtain zinc oxide.

The invention is described below using an exemplary embodiment with reference to the drawing explained in more detail. The drawing shows a flow diagram showing the removal of undesirable

3 4

Zinc oxide from airborne dust explained, in which the

, deadened with a used pickling liquid are worked up according to the invention

, vird. can is as follows:

The one from a basic steelmaking process

originating fly dust, which contains at least about 50% by weight 5 iron 61-62% by weight

Iron oxide and about 0.25 to about 4.5% by weight zinc oxide sulfur 0.23% by weight

contains, is stored in a dust container 3, from the zinc oxide 2.5-4.5 wt .-%

he by means of a fan 4 in a large dust layer - water 10-15 wt .-%

tion tank 6 is transferred. The tank 6 has such a silicon dioxide 2.4 wt .-%

Capacity that it can hold 2501 dust. Then 10 manganese 0.36% by weight

the dust is continuously fed into a reactor - phosphorus 0.4% by weight

which belongs to a group of reactors 10. Chromium 0.24% by weight

In this reactor the zinc oxide is made by means of a

spent, dilute, hydrochloric acid pickling solution, such as when leaching the zinc oxide from the fly ash

it accrues during pickling, leached from the fly ash. 15 must in order to achieve economically justifiable

The acidic pickling solution is from the storage tank 12 tion speeds and results the pH

pumped into the reactor 10. Instead of the hydrochloric acid of the diluted pickling liquid in the effluent

Pickling liquid can also be a sulfuric acid pickling reactor between 1 and 5.5, preferably between

fluids are used that are 1 and 1.5 or between 3 and 5.5 from the supply,

container 14 is pumped into the reactor 10. 20 with a pH of 4.5 to 5 being particularly preferred

In each of the reactors 10 there is a reaction. At such a pH, the zinc oxide becomes

temperature between about 66 and about 121 ⁰ C continuously transferred into the zinc salt, so that it

keep. After the end of the reac- tion that occurs, it is possible to remove the airborne dust from a technical one

tion between the zinc waste material contained in the fly ash, the considerable disposal problems

oxide and the ChIo- 25 contained in the pickling liquid, to be converted into a technically valuable material.

Ride or sulfate ions, a zinc salt is obtained (zinc conversion.

chloride, if the used pickling liquid is salty The temperature of the reaction between the flight is slurried together with the iron oxide in the pickling dust and the diluted used acidic pickling liquid. This slurry liquid must be between about 66 and about 121 ⁰ C is transferred to a thickener 15 and then 30, with a temperature of 80 to 105 ⁰ C fed to a filter 17 in which the iron oxide is preferred. It has been shown that then, formation of a solid cake, which contains about 65 wt .-% when the reaction ^{temperature is below 66 0} C, iron and about 15 wt .-% water, the reaction rate is so slow that a will. The filtrate from the filter 17 contains the zinc salt required long residence time in the reaction vessel (zinc chloride or zinc sulfate), some iron salt (iron 35 is borrowed, which is no longer economically viable. Chloride or iron sulfate) and an acid (hydrochloric acid The reaction temperature should but also not 121 ⁰ C or sulfuric acid) and water. exceed. The implementation is generally at

The filtrate is continuously transferred to an evaporator below the normal boiling point of the solution 20 introduced, in which the filtrate is concentrated. "Operating pressure carried out inside the reactor. The concentrated filtrate is then poured into a 40 The boiling point depends on the salt concentration Roaster 25 transferred and used for the production of zinc oxide of the used pickling liquid. Pass roasted around 132 ° C. In this case, gaseous chlorine is added, atmospheric pressure is used, the circulating hydrogen or gaseous sulfur trioxide can, however, also be carried out under pressure They are drifted off and by a gas absorption tower that is higher or lower than the atmosphere tower 27, which are 45 pressure with a sulfuric acid supply.

container 28 or a hydrochloric acid storage container 29 in To leach out the unwanted zinc oxide

Connected to the fly dust is a used, weakly salty

As from the left part of the enclosed hydrofluoric acid or weakly sulfuric acid pickling liquid

diagram shows, the product is turned from the. If a used, sulfuric acid pickling

Roaster mixed with water in a washer 31. 50 liquid is used, the acid concentration should

The resulting slurry is an ion within the range of 0.5 to 6 wt .-%

thicker 32 and the contained therein are kept concentrated, so that the effluent from the reactor

trated slurry is then passed through a filter to a pH of about 3 to about 5.5. Will

33 supplied, in which the zinc salt in the filtrate, on the other hand, uses a hydrochloric acid pickling liquid,

Zinc salt storage containers, namely a zinc chloride 55 then their content of HCl should be about 0.5 to about

storage container 34 or a zinc sulfate storage container 35, 4 wt .-%, so that the effluent from the

is fed. Reactor preferably has a pH of about 3 to

_{The ZnCl 2} or approximately 5 collected in the storage container 34.

_{the ZnSO 4} collected in the storage container 35 is The pH of the effluent from the reaction must periodically be introduced into an evaporator, for example 60 have a value between 1 and 5.5. If the value is wise over the weekend, in which case it is less than 1, then the effluent acts on the damper used, the water is removed from it, so that a system is too corrosive, while if solid salt remains. The pH of the evaporator 20 is more than about 5.5, the removed water passes through a cooler 37 in the range of the neutral point and the conversion of the storage container 39. The in the container 39 he 65 zinc oxide in zinc sulfate or Zinc chloride required holding water can then be reused. Reaction time is generally too long. With one, since it is clean and free of larger salt pH values of less than 5.5, only minimal amounts of the iron oxide in the fly ash are converted into

Iron sulfate (FeSO ₄ ) or iron chloride (FeCl ₂ ). The conversion of iron into iron sulfate or iron chloride is undesirable because it results in a loss of iron, which is to be reused as an oxide in steel production.

It has been found that it is very useful to thoroughly clean the filter cake obtained in the filter 17 to wash. This cake contains iron oxide particles, each of which is obviously made up of a coating Has zinc chloride or iron chloride. This coating must be removed so that a non-contaminated Iron oxide is obtained, which can be used again in steel production.

The invention is illustrated by the following example in which all percentages are based on weight are explained in more detail.

Reaction # 1 - 15 minutes, 82 ° C

example

Two different fly ash samples were taken in compliance with the different ones given below Treatment times and temperatures with a used, hydrochloric acid pickling liquid. Flue dust sample No. 1 contained 63.1% iron and 0.8% zinc. The fly dust sample no. 2 contained 63.3% iron and 0.78% zinc.

The results obtained in these reactions are summarized below. The following The tabular compilation also shows the percentage of iron and zinc in the fly ash Carrying out the reaction and the pH of the liquid effluent used.

% Iron

before after% zinc
before

later

pH of the

Downstream

liquid

Airborne dust No. 1 63.1 61.7 0.8 0.5 Airborne dust No. 2 63.31 62.2 0.78 0.45 Pickling liquid 9.3 -

Reaction # 2 - 30 minutes, 82 ° C

% Iron before

after »/“ zinc
before

later

pH of the

Downstream

liquid

Airborne dust No. 1 63.1 60.6 0.8 0.2 Airborne dust No. 2 63.3 61.1 0.78 0.18 Pickling liquid 9.3 -

about 2

Reaction # 3 - 45 minutes, 82 ° C

% Iron before

afterwards% zinc
before

later

pH of the

Downstream

liquid

Airborne dust No. 1 63.1 60.9 0.8 Airborne dust No. 2 63.3 60.7 0.78 Pickling liquid 9.3 -

0.1

4.5

Reaction # 4 - 15 minutes, 93 ° C

% Iron
before later %Zinc
before later pH of the
Downstream
liquid Airborne dust No. 1
Airborne dust No. 2
Pickling liquid
Response No. 5 - 63.1
63.3
9.3
30 minutes, 93 ⁰ C 82.7
61.8 0.8
0.78 0.46
0.42
track 1 % Iron
before later %Zinc
before later pH of the
Downstream
liquid Airborne dust No. 1
Airborne dust No. 2
Pickling liquid 63.1
63.3
10.1 61.6
61.2 0.8
0.78 track
0.01
track 2

7th
Response No. 6 - 1
45 minutes, 93 ° C 5 83 944 later 8th pH of the
Downstream
liquid % Iron
before later %Zinc
before track
0.01
0.01 4th Airborne dust No. 1
Airborne dust No. 2
Pickling liquid 63.1
63.3
10.4 61.3
60.9 0.8
0.78

From the above it can be seen that using the method according to the invention Considerable amounts of zinc from the fly ash samples under the time and temperature conditions given above could be separated.

1 sheet of drawings

Claims (2)

Patent claims: 1. Method of removing unwanted zinc oxide from iron oxide fly ash by mixing the fly dust with a used, weakly hydrochloric acid or weakly sulfuric acid pickling liquid and subsequent treatment at elevated temperature, characterized in that the fly ash contains at least 50% by weight of iron oxide and zinc oxide in undesirable amounts and that the mixture is at a temperature of about 66 to 12TC to convert the major part the zinc oxide into a zinc salt, the effluent from the reaction having a pH of 1 to 5.5, is converted, the iron oxide from the converted mixture in the form of a solid filter cake, containing not more than 0.50 wt .-% zinc oxide, is separated that containing the zinc salt The filtrate is evaporated to concentrate the salt and from the evaporator water that is suitable for draining into rivers or lakes, is withdrawn. 2. The method according to claim 1, characterized in that the concentrated zinc salt is roasted to obtain zinc oxide, wherein HCl or SO _{3 is} driven off in gaseous form, and these gaseous components are passed through an absorption tower to obtain hydrochloric acid or sulfuric acid.