Composition containing modified chromate-deficient red mud and method for producing same

Abstract

The invention relates to a composition which contains modified chromate-deficient red mud, comprising a mineral composition of10 to 50 wt. % of iron compounds,12 to 35 wt. % of aluminum compounds,5 to 17 wt. % of silicon compounds,2 to 10 wt. % of titanium dioxide,0.5 to 6 wt. % of calcium compounds,0 to 1 ppm of chromium (VI) compounds, andoptionally additional unavoidable impurities. The composition, in particular the modified chromate-deficient red mud, contains a poorly soluble reducing agent for Cr(VI). In this manner, an inexpensive chemical composition is provided in particular as an iteratively functioning long-term adsorbent for pollutants in liquid, gaseous, and solid milieu. The invention further relates to a method for producing same and to uses thereof.

Claims

1. A composition comprising modified, chromate-deficient red mud with a mineral composition of: 10 to 50% by weight of iron compounds; 12 to 35% by weight of aluminium compounds; 5 to 17% by weight of silicon compounds; 2 to 10% by weight of titanium dioxide; 0.5 to 6% by weight of calcium compounds; and 0 to 1 ppm of chromium (VI) compounds; wherein the modified, chromate-deficient red mud comprises a poorly soluble reducing agent for Cr(VI); wherein the composition further comprises a pH buffer system which is configured for stabilising a pH range in which the poorly soluble reducing agent for Cr(VI) and a resulting Cr(III) have a solubility in water at 25 C. of less than 1 g/l; and wherein the composition further comprises at least one of: an agent for removing nitrate and nitrite which is selected from the group consisting of urea and amidosulfonic acid; and an agent which is configured for removing pollutants by means of the formation of poorly soluble salts.

2. The composition according to claim 1, wherein the poorly soluble reducing agent for Cr(VI) comprises a poorly soluble Fe(II) compound.

3. The composition according to claim 1, wherein the poorly soluble reducing agent for Cr(VI) comprises iron(II) carbonate (FeCO.sub.3).

4. The composition according to claim 1, wherein a combination of readily soluble and poorly soluble Fe(II) compounds are contained therein.

5. The composition according to claim 1, wherein the modified, chromate-deficient red mud comprises a modified chromate-deficient, carbonised red mud comprising Fe(II) carbonate and oxides of iron, and in which the weight ratio of Fe(II) carbonate to the oxides of iron is at least 1.

6. The composition according to claim 5, wherein the modified chromate-deficient, carbonised red mud further comprises iron hydroxide and iron oxide hydrate, and in which the weight ratio of the sum of iron hydroxide and iron oxide hydrate to the oxides of iron is at least 1.

7. The composition according to claim 1, wherein the composition also contains at least one of the following agents: a further reducing agent for Cr(VI); an agent for removing nitrate and nitrite; an agent which is configured for removing pollutants by means of the formation of poorly soluble salts; and an organic substance, which forms activated carbon on a surface of the modified, chromate-deficient red mud during thermal treatment.

8. The composition according to claim 1, wherein the modified, chromate-deficient red mud has a specific surface area in the range from 2 to 250 m.sup.2/g (measured according to BET).

9. The composition according to claim 1, wherein the modified, chromate-deficient red mud has a specific weight of 4.5 g/cm.sup.3.

10. The composition according to claim 1, wherein the modified, chromate-deficient red mud is present substantially in the form of a granulate.

11. The composition according to claim 1, wherein the modified, chromate-deficient red mud is provided at least partially with a surface coating.

12. The composition according to claim 1, wherein the composition comprises a further reducing agent for Cr(VI)) which is selected from the group consisting of Fe, Al and Zn.

13. The composition according to claim 1, wherein the composition further comprises an organic substance, which forms activated carbon on a surface of the modified, chromate-deficient red mud during thermal treatment.

14. A method for producing a composition comprising modified, chromate-deficient red mud with a mineral composition of 10 to 50% by weight of iron compounds, 12 to 35% by weight of aluminium compounds, 5 to 17% by weight of silicon compounds, 2 to 10% by weight of titanium dioxide, 0.5 to 6% by weight of calcium compounds, and 0 to 1 ppm of chromium (VI) compounds, wherein the method comprises the following steps: a) providing neutralised red mud, b) adding a poorly soluble reducing agent for Cr(VI) to the red mud and mixing of the poorly soluble reducing agent for Cr(VI) with the red mud, c) reducing chromium(VI) compounds contained in the red mud by means of the poorly soluble reducing agent for Cr(VI) to chromium(III) compounds in aqueous systems producing a modified, chromate-deficient red mud, and d) adding a pH buffer system which is configured for stabilising a pH range in which the poorly soluble reducing agent for Cr(VI) and a resulting Cr(III) have a solubility in water at 25 C. of less than 1 g/l; and wherein the method further comprises at least one of the following steps: rehydrating by oxidation of Fe(II) compounds to Fe(III) compounds in aqueous solution; tempering the modified, chromate-deficient red mud at a temperature in the range from 450 C. to 700 C.; treating the modified, chromate-deficient red mud with acid; thermally treating the modified, chromate-deficient red mud at a temperature in the range from 150 C. to 350 C.; granulating the modified, chromate-deficient red mud; and applying a surface coating to the modified, chromate-deficient red mud.

15. The method according to claim 14, wherein the method further comprises adding at least one of the following agents: a further reducing agent for Cr(VI); an agent for removing nitrate; an agent which is configured for removing pollutants by means of the formation of poorly soluble salts; and an organic substance, which forms activated carbon on the surface during thermal treatment.

16. The method according to claim 14, wherein the method further comprises a drying step carried out in a substantially non-oxidising atmosphere under inert gas.

17. A composition comprising modified, chromate-deficient red mud with a mineral composition of: 10 to 50% by weight of iron compounds; 12 to 35% by weight of aluminium compounds; 5 to 17% by weight of silicon compounds; 2 to 10% by weight of titanium dioxide; 0.5 to 6% by weight of calcium compounds; and 0 to 1 ppm of chromium (VI) compounds; wherein the modified, chromate-deficient red mud comprises a poorly soluble reducing agent for Cr(VI); wherein the composition further comprises a pH buffer system which is configured for stabilising a pH range in which the poorly soluble reducing agent for Cr(VI) and a resulting Cr(III) have a solubility in water at 25 C. of less than 1 g/l; and wherein the composition further comprises an organic substance, which forms activated carbon on a surface of the modified, chromate-deficient red mud during thermal treatment.

18. The composition according to claim 17, wherein the poorly soluble reducing agent for Cr(VI) comprises one of: a poorly soluble Fe(II) compound; and iron(II) carbonate (FeCO.sub.3).

19. The composition according to claim 17, wherein a combination of readily soluble and poorly soluble Fe(II) compounds are contained therein.

20. The composition according to claim 17, wherein the modified, chromate-deficient red mud comprises: a modified chromate-deficient, carbonised red mud comprising Fe(II) carbonate and oxides of iron, and in which the weight ratio of Fe(II) carbonate to the oxides of iron is at least 1; and iron hydroxide and iron oxide hydrate, and in which the weight ratio of the sum of iron hydroxide and iron oxide hydrate to the oxides of iron is at least 1.

21. The composition according to claim 17, wherein the composition also contains at least one of the following agents: a further reducing agent for Cr(VI); an agent for removing nitrate and nitrite; an agent which is configured for removing pollutants by means of the formation of poorly soluble salts; and an organic substance, which forms activated carbon on a surface of the modified, chromate-deficient red mud during thermal treatment.

22. The composition according to claim 17, wherein the modified, chromate-deficient red mud has one of: a specific surface area in the range from 2 to 250 m.sup.2/g (measured according to BET); and a specific weight of 4.5 g/cm.sup.3.

23. The composition according to claim 17, wherein the modified, chromate-deficient red mud is present substantially in the form of a granulate.

24. The composition according to claim 17, wherein the modified, chromate-deficient red mud is provided at least partially with a surface coating.

25. The composition according to claim 17, wherein the composition comprises a further reducing agent for Cr(VI)) which is selected from the group consisting of Fe, Al and Zn.

26. The composition according to claim 17, wherein the composition further comprises at least one of: an agent for removing nitrate and nitrite which is selected from the group consisting of urea and amidosulfonic acid; and an agent which is configured for removing pollutants by means of the formation of poorly soluble salts.

Description

EXAMPLES OF APPLICATIONS

(1) Nitrate Removal from Aqueous Systems

(2) First of all the freshly introduced granulate bed is equilibrated with a column volume of demineralised water. Next the nitrate solution is pumped through the column at 0.1 L/minute. A sample is taken from the overflowing eluate at the head of the column at intervals of 10 minutes and is examined for nitrate by means of AAS. Even after 200 minutes no nitrate can be found in the eluate.

(3) For nitrate removal from an aqueous solution, shaped bodies according to the invention, which contained 10% by weight of amidosulfonic acid (p.a.), were used in a second test.

(4) The test setup corresponds to the above, with the difference that the nitrate concentration was now 800 mg/l (ground water nitrate value in California, USA) and the quantity of nitrate solution was 1000 l. Here too, no nitrate was found at any time in the samples taken, i.e. conversely, all nitrate had been removed. The check for sulfate ions also did not produce any positive findings.

(5) Purification of Gaseous Substances

(6) Air which has previously been bubbled through manure (pig manure from a fattening farm) by means of a fine nozzle flows through a granulate bed of 100 mm diameter and 1000 mm length in a vertical glass tube. In the olfactory test of the air a heavy odour pollution was detected. If this test air is drawn at 50 l/minute through the granulate bed of the composition according to the invention, no odour nuisance can be detected any more at the end of the test section (after the column) by the olfactory test.

(7) Ammonia is withdrawn from a cylinder and by means of a pressure reducer and an air bypass valve an air/gas mixture with 200 ppm NH.sub.3 was produced in the total gas stream. The flow meter shows a flow rate von 50 l/minute. The exhaust air coming out of the filter tube (dimensions as previously described) is subjected to an olfactory test for a pungent odour of ammonia. The detection limit/perception limit of humans ranges from 0.03 to 0.05 ppm ammonia. The limit value is 20 ppm. In order to increase the adsorption power, the system can be supplied with water.

(8) For the removal of fine dust/very fine dust filter cartridges were used as in the case of air purification (1000 mm long and 100 mm internal diameter). The entire system was operated at 12 000 L/h.

(9) The test system for the air washing with fine/very fine dust pollution of 10 mg/m.sup.3 comprises the provision of a test medium, wherein through permanent air turbulence, controlled by air turbidity (extinction) by means of lasers, it is ensured that during the test the dust distributed in the test air remained constant over the entire volume flow. Interestingly it has been determined that the cartridge packing which is kept wet by injection of water (through four laterally arranged nozzles by means of hose pumps in each case) has an approximately twenty times filter action.

(10) Geopolymers

(11) The production of geopolymers from potassium water glass takes place so that the alkali/silicon ratio is varied from 1-4. The geopolymer bound to potassium water glass as described below preferably operates with the K/Si ratio 1 to 2, wherein in this example fly ash or tailings are used as a component supplying Si. The material in the form of its individual components, together with the composition according to the invention loaded by adsorption, is introduced into a high-speed mixer and agitated at maximum rotational speed until the heating of the material mixture by the friction reaches 100 C. 80 C. are sufficient in order to accelerate the polymerisation reaction. Next the geopolymer raw material is discharged and compressed in corresponding moulds for production of the standard testpieces so that as far as possible no cavities ensue. The shrinkage of the shaped bodies is minimised here, so that no cracks occur in the shaped bodies arriving for final disposal and so the integrity of the shaped bodies is maintained. Studies of the eluate of the geopolymer (broken granulate) show that no pollutants from the geopolymer enter the aqueous phase.

(12) The implementation of the invention is not limited to the preferred exemplary embodiment se out above. On the contrary, a plurality of variants is conceivable which makes use of the described solution even for fundamentally different embodiments.