JPS6086021A - Granulation of red mud cake - Google Patents

Abstract

PURPOSE:To produce easily handleable granular red mud easily forming tough crust on the surface, by granulating the water-containing cake of red mud with a granulator, adding the ash of a coal-fired fluidized bed boiler to the granulator when the growth of the granule is almost completed, and mixing the mixture. CONSTITUTION:The red mud slurry discharged from the aluminum production process is filtered and concentrated to obtain a hydrated red mud cake having a water-content of about 30%, and the cake is granulated with a granulator. The cake is mixed with about 15wt% ash of a coal-fired fluidized bed boiler, based on the supplied red mud, when the growth of the granule in the granulation stage is almost completed. A firm crust is formed on the surface of the granule by the combined effect of (i) the evaporation of water from the surface of the granule by the heat of the slaking reaction of CaO contained in the discharged ash, (ii) the hardening action caused by the adsorption of the red mud, (iii) the absorption of water from the surface of the red mud to the fine ash powder, and (iv) the coating effect of the ash to the granule, etc. Strong granules of red mud free from adhesivity can be produced by this process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for granulating a red mud cake, and more specifically, the method for granulating a red mud cake according to the present invention involves f-filtering red mud slurry discharged from an aluminum manufacturing process. The resulting water-containing red mud cake is granulated using a granulator, and when the growth of the granules in the granulation process is almost completed, discharged ash from a coal-fired fluidized bed boiler is added and mixed to form granules. It is characterized by the formation of a strong shell on the surface of its body.

Red mud, that is, the residue obtained by alkali extraction of alumina from bauxite in the so-called Bayer process alumina production process, usually contains 30 to 50% by weight of FetOs and AJx.
Os 15-25% by weight, 5ift 8-15% by weight,
Ti (h 5-10% by weight, Nano 3-10% by weight
, Ig, Loss 8 to 12% by weight, and the constituent particles are very fine.

Traditionally, red mud was disposed of as industrial waste, such as by ocean dumping or landfill, but it can also be used as a source of iron in cement production, as a raw material for artificial aggregates and refractories such as bricks, as a catalyst carrier, as a soil conditioner, etc. has found many uses.

Such red mud is discharged in the alumina manufacturing process as a slurry containing a large amount of water, so no matter what purpose it is used for, it must be made into a form that is easy to handle by removing the water. For this purpose, dewatering and drying are usually carried out, but the constituent particles of red mud are very fine, making it difficult to dehydrate, and they settle in storage hoppers and belt conveyor transfer areas, making them difficult to handle. As moisture on the surface evaporates over time, dust is generated, worsening the working environment. As described above, dehydrated red mud cake has the trade-off drawbacks of adhesion and dust generation.

As methods for treating red mud having such properties, for example, there is a method of granulating it while applying heat from the outside, as shown in Japanese Patent Application Laid-Open No. 52-3596, and a method of granulating it while applying heat from the outside, as shown in Japanese Patent Application Laid-Open No. 48-45.
As shown in Publication No. 494, a method has been proposed in which red mud is sufficiently dehydrated in advance to form a pellet, and then an expensive chemical is added to dehydrate it, but these methods do not completely solve the problem. It has not been resolved since then.

The present invention relates to a method for making the above-mentioned red mud into a form that is easy to handle. However, when the granules are generated and grown, and the growth is almost complete, ash from a coal-fired fluidized bed boiler is added to the granules for granulation.

That is, in the present invention, by adding discharged ash from a coal-fired fluidized bed boiler to the grain surface of the granulation formation gap to the filtered cake of red mud slurry, granulation is performed by heat generation due to the slaking reaction of CaQ contained in the discharged ash. Due to the evaporation of surface water, the hardening effect due to the adsorption of red mud, the moisture absorption on the surface of red mud grains by most of the fine ash, and the coating effect, a strong shell is formed on the surface of the grains, and there is no adhesion. Since it can be made into strong granules, the conventional problems have been completely solved.

An embodiment of the present invention will be described below.

The red mud slurry discharged from the alumina manufacturing process was overconcentrated to 29.3% by weight of attached moisture using a press filter to obtain a red mud cake consisting of particles having the particle size distribution shown in Table 1.

This red mud cake was processed by operating a dish-type granulator with an inner diameter of 5.0 m and a depth of 1.05 m at 6-4 rpm and a % inclination angle of 49''.
Granulation was carried out by adding 15% by weight of ash discharged from a coal-fired fluidized bed boiler to the amount of supplied red mud. The discharged ash added in this case was added so as to be mixed with the red mud just before the red mud was granulated and taken out from the granulator.

The ash discharged from a coal-fired fluidized bed boiler is added just before the end of granulation because a red mud cake with a water content of 18 to 20% by weight is used, so these powders are added from the early stages of granulation. However, if the waste ash is added at the stage where the granules are formed and grown, and the growth is finished, a small amount can be produced. This is because by adding , a strong shell is efficiently formed on the surface of the granules.

Next, a crushing test was carried out on the granulated product thus granulated, and the number of times a steel ball weighing 438 tons was dropped from a height of 10 degrees until it was crushed was measured. The number of falls until crushing of the red mud granules to which the ash discharged from the coal-fired fluidized bed boiler was added was calculated in the same way as the red mud granules to which lime factory dust was added.゛It is shown in the table. A large number of times means a high curing strength.

In the present invention, red mud slurry containing a large amount of water is kept in a red mud cake with a water content (25 to 35% by weight) that can be easily achieved industrially, and then heated to reduce the water content below that level. It can be made strong and easily removable by the simple operation of adding the above-mentioned discharged ash, such as discharged ash from a coal-fired fluidized bed boiler, just before the completion of granulation, without adding any dehydrating agents. As described above, according to the present invention, red mud, which is difficult to handle, can be made into non-adhesive and strong granules, which makes it easy to handle when used for various purposes. The granulation used here is not limited to transfer granulation, but may also be vibration granulation.

Claims (1)

[Claims] The red mud cake discharged from the aluminum manufacturing process is overconcentrated, the resulting water-containing red mud cake is granulated using a granulator, and when the growth of the granules in the granulation process is almost completed, coal is A method for granulating red mud cake, which is characterized by adding and mixing ash discharged from a fired fluidized bed boiler to form a strong shell on the surface of the granules.