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

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.

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.