Process and plant for purifying red mud

Abstract

A process for purifying red mud including reduction of the red mud to reduced material, and traversing the reduced material with an oxygen-containing gas in the presence of a catalyst suitable for iron oxidation.

Claims

1. A process for purifying red mud, comprising the following steps: 1. reduction of the red mud to reduced material, and 2. at a temperature between 75 and 95 C., traversing the reduced material with an oxygen-containing gas in the presence of a catalyst suitable for iron oxidation creating an at least partially oxidated product.

2. The process according to claim 1, characterized in that step 1 takes place under continuous or discontinuous addition of a reducing agent, which contains hydrogen, at least one hydrocarbon, carbon monoxide and/or coal.

3. The process according to claim 1, characterized in that step 1 is carried out at a temperature between 800 and 1500 C.

4. The process according to claim 1, characterized in that in step 2 an amine compound is used as catalyst.

5. The process according to claim 4, characterized in that in step 2 the amine compound content lies between 0.5 and 3 wt-% based on the total mass of the mixture of reduced material and catalyst.

6. The process according to claim 1, characterized in that air is used as oxygen-containing gas.

7. The process according to claim 1, characterized in that in step 2 the oxygen-containing gas flows into the reduced material with a flow rate of 2 to 20 Nl/min.

8. The process according to claim 1, characterized in that before step 1 the red mud is washed with washing water, whereby washed mud is obtained.

9. The process according to claim 8, characterized in that drinking water or sea water is used as washing water.

10. The process according to claim 8, characterized in that the washing water has a temperature between 30 and 60 C.

11. The process according to claim 8, characterized in that the washing water is added in a ratio of 0.01 to 0.1 l(H.sub.2O)/kg(red mud).

12. The process according to claim 8, characterized in that washing is effected for a period of 1 to 5 hour(s).

13. The process according to claim 1, characterized in that before step 1, the red mud is subjected to drying.

14. The process according to claim 13, characterized in that the drying is carried out at a temperature between 80 and 130 C.

15. The process according to claim 13, characterized in that iron oxide is leached out from the at least partially oxidize product.

16. The process according to claim 15, characterized in that the iron oxide leached out is removed by a solid-liquid separation.

17. The process according to claim 1, characterized in that in step 2, water, or optionally a recirculated aqueous solution liberated from dissolved substances, or both is added.

18. The process according to claim 1, characterized in that after step 2 a product mixture is dried.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) In the drawing:

(2) FIG. 1 shows the schematic structure of the plant according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) In the plant according to FIG. 1, red mud is introduced into a washing apparatus 13 via a conduit 11. The washing agent, which preferably is water in drinking water quality or sea water, is introduced into the washing apparatus 13 via conduit 12. Via conduit 14 and conduit 15, the hydroxides Ca(OH).sub.2 and NaOH obtained due to washing are discharged together with the washing water.

(4) The red mud washed is removed from the washing apparatus 13 via conduit 16 and from there gets into a drying apparatus 17. It is dried there at temperatures between 95 and 105 C., preferably until the material is present in powder form.

(5) Via conduit 18, this powdery material subsequently is introduced into a reduction apparatus 19. Via conduit 20, the reduction apparatus 19 is charged with a reducing agent, which can be hydrogen, hydrocarbons, carbon monoxide or coal. The state of matter of the reducing agent depends on the type of reactor used. In a preferred aspect, there is used a rotary kiln with a solid reducing agent or a fluidized-bed reactor with a gaseous reducing agent.

(6) As a result of the reduction waste gases are obtained, which via conduit 21 can be guided into a waste gas treatment 22 and after their treatment can be blown off from there into the surroundings via conduit 23.

(7) After passing through these pretreatment stages, the reduced material is supplied to the actual chemical treatment via conduit 24. Said chemical treatment is effected in a reactor 30, into which on the one hand a suitable catalyst, particularly preferably ammonium chloride (NH.sub.4Cl), is introduced via conduit 31 and an oxygen-containing medium, preferably air, is introduced via conduit 32. In that the reduced material is traversed by the oxygen-containing gas, a selective oxidation of the contained iron to Fe.sub.2O.sub.3 occurs in the presence of the catalyst.

(8) The material 33 treated in this way subsequently is supplied to a wet separation 34. Via conduit 35, a washing agent, preferably water, is introduced into the same. This leads to a leaching out of the contained rust, which in the liquid phase is transferred into a solid-liquid separation 40 via conduit 39. The solid iron oxide separated there is discharged from the process via conduit 41 and either can be supplied to a further value chain or be dumped as environmentally harmless garbage. Via conduit 42, the liquid obtained is fed back into the aeration reactor 30.

(9) Via conduit 36, the remaining solid products are discharged from the wet separation 34. These products are dried in the drying apparatus 37, preferably likewise at temperatures between 90 and 110 C., before the finished product is discharged via conduit 38. The finished product can be used as feed for a Bayer process, for producing titanium oxide pigments or as solid heat carrier (SHC).

EXAMPLE

(10) Pretreatment

(11) Red mud with a composition of 50 wt-% Fe.sub.2O.sub.3, 11 wt-% CaO, 10 wt-% SiO.sub.2, 16 wt-% Al.sub.2O.sub.3, 2 wt-% MgO, 5 wt-% Na.sub.2O and 6 wt-% TiO.sub.2 is washed with water or sea water at 40 to 50 C. for 3 hours, wherein calcium oxide (CaO) and sodium oxide (Na.sub.2O) are transferred by reaction into the aqueous hydroxides Ca(OH).sub.2 and NaOH and are removed from the red mud together with the washing water.

(12) Due to washing, the alkaline red mud is neutralized, since still contained OH.sup. ions likewise are flushed out.

(13) The contained solid material subsequently is dried for 6 hours at a temperature between 95 and 105 C.

(14) The dried material then is reduced, wherein the reduction either is carried out in a fluidized-bed reactor with hydrogen (H.sub.2), methane (CH.sub.4) or carbon monoxide, or in a rotary kiln with coal (C) as reducing agent. The reaction temperature lies between 1000 and 1450 C., the mean retention time is 3 hours.

(15) The contained oxides silicon oxide (SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3) and magnesium oxide (MgO) are stable and are not reduced at these temperatures At temperatures above 1200 C., the contained titanium oxide is reduced to Ti.sub.3O.sub.5 and Ti.sub.2O.sub.3. Almost 6 wt-% TiO.sub.2 contained in the red mud is converted acid soluble oxides (Ti.sub.3O.sub.5 and Ti.sub.2O.sub.3) reduced to Ti.sub.3O.sub.5.

(16) Chemical Treatment

(17) In the actual chemical treatment, the material then is mixed with a catalyst, wherein the amount of the catalyst is approximately 1 wt-% of the total mixture of reduced material and catalyst. As catalyst, ammonium chloride is used.

(18) This mixture then is aerated with air at temperatures of about 85 C., wherein the flow rate with which the air enters into the reactor lies between 5 and 10 Nl/min. The iron obtained in the reduction thereby is oxidized, i.e. the iron rusts.

(19) This rust subsequently can easily be separated from the obtained solution. Separating is effected by leaching out with a washing liquid, preferably water. The product is obtained as solid. In the example given it contains 29.4 wt-% SiO.sub.2, 47.1 wt-% Al.sub.2O.sub.3, 5.9 wt-% MgO and 17.6 wt-% TiO.sub.2 with traces of Ti.sub.3O.sub.5. In principle, it is also possible to further process the iron oxide leached out and thus obtain it as valuable product.

(20) Part of the remaining solids, namely SiO.sub.2, Al.sub.2O.sub.3 and MgO, still are stable and are not reducible at temperatures between 1000 and 1450 C. In a further reduction, the contained titanium oxide partly can be converted into the Magneli phase, whereby Ti.sub.3O.sub.5 is obtained, which is very easily dissolved in acid. This means that this product is particularly suitable to be subjected to a further reduction, whereby the titanium compounds very easily can be processed to TiO.sub.2 pigments in a sulfate process.

(21) TABLE-US-00001 List of Reference Numerals: 11-12 conduit 13 washing apparatus 14 bedding 17 drying apparatus 18 reduction apparatus 20, 21 conduit 22 waste gas aftertreatment 23, 24 conduit 30 aeration reactor 31-33 conduit 34 washing apparatus 35, 36 conduit 37 drying apparatus 38, 39 conduit 40 solid-liquid separator 41, 42 conduit

SEQUENCE LISTING

(22) Not Applicable.