This invention relates to a process for the production of pellets comprising red mud and also to pellets formed using that process. This invention seeks to address the problems associated with red mud disposal by producing pellets which can be used for other purposes.

Red mud (sometimes referred to as "bauxite residue") is a bi-product of the aluminium extraction "Bayer" process. Due to its high level of alkalinity it is a hazardous waste product which cannot be disposed of easily. Red mud can be dried but the energy required to do so is vast and thus drying to solve the disposal issue is a non-economical option. Moreover, drying does not completely resolve the problem since the alkalinity of the red mud remains unchanged. Conventionally, red mud is distributed into dedicated "ponds" which are essentially areas of land solely for the purposes of containment; this thereby renders the land toxic and unsuitable for other uses.

In an attempt to reduce the negative impact of red mud and eliminate the problem of its disposal, there is an increasing need for a process which enables red mud to be recycled and used for alternative purposes such as to treat waste contamination.

The problem of waste contamination affects many industrial processes. Such problems include, the presence of phosphate in waste water which leads to difficulty in environmental disposal; the presence of high levels of sulphuric acid in water affected by acid mine drainage; and odour emitted from industrial effluent. It would be highly beneficial to produce a product utilising red mud which can be used in the treatment of waste contamination caused by such industrial processes.

It is a principle aim of the present invention to provide pellets incorporating red mud and a process for the production of such pellets which addresses some or all of the above problems associated with waste contamination.

According to a first aspect of this invention, there is provided a process for the production of red mud pellets comprising the steps of: (a) forming a slurry comprising a mixture of red mud, clay and optionally water;

(b) adjusting the water content of the slurry to achieve a desired level;

(c) forming pellets of the adjusted mixture; and

(d) heating the pellets until solidified.

Clay serves as a binding agent for the red mud base media. Various types of clay can be used, but brick clay, which is a mix of clay and shale has been found to be highly suitable. The use of the red mud waste material benefits the environment as it serves to lower the level thereof that is sent to dedicated ponds for storage.

The optional requirement for the addition of water in step (a) and/or the amount thereof may depend on the level of water contained in the red mud. If the moisture content of the red mud is high it may be unnecessary to include water as an optional process in step (a) in order to form slurry of sufficient viscosity. In a preferred arrangement the moisture content of the slurry may be within the range 12-16% and ideally 15%. The adjusting of the water content of the slurry in step (b) may comprise drying the slurry to a particular level to enable pellets to be formed. This may be achieved by applying heat to the slurry.

The red mud may be treated to ensure that it is chemically neutral. Such treatment could take place prior to the mixing of the red mud with other components in step (a). In this way the process may further comprises an additional step, prior to step (a), of neutralising the red mud. Alternatively, treatment of the red mud could be effected simultaneously with the mixing in step (a) or thereafter - prior to formation of the pellets in step (d).

Neutralisation may be carried out using any suitable process. Preferably neutralisation is carried out chemically by, for example, adding an acidic substance to the red mud. In one arrangement, the step of neutralising may comprise treating the red mud with chlorides. Alternatively, the step of neutralising preferably comprises mixing the red mud with gypsum. Gypsum is more cost effective than chlorides and has been shown not adversely to affect the performance of the resultant pellets. In some cases, the Applicants have discovered that the use of gypsum as a neutraliser has improved the quality of the resultant pellets, particularly when used in the treatment of waste water to recover phosphate.

The process may require an additional step of adjusting the pH of the slurry. This is because the slurry may be too alkaline due to the nature of red mud or because the slurry may be too acidic, possibly as a result of neutralisation of the red mud, if such a step is carried out. The pH may be adjusted prior to the adjusting the water content of the slurry in step (b) and may be carried out together with the mixing of the components in step (a) or indeed after step (a) has been performed. The pH may be adjusted by mixing the slurry with an acidic or alkaline substance. Where the slurry is too alkaline, preferably the substance used to adjust the pH is citric acid. The citric acid may be in powdered form as this could assist with the solidification of the mixture. Where the pellets are intended for use in the water industry a pH of 7.5 is preferably the target level in order effectively to treat waste water. When the pellets are intended for using in treating acid mine drainage ideally the pH is about 9.5.

The size of the pellets formed will depend, in part, on the desired use. Generally, it has been found that smaller pellets provide greater effectiveness in waste contamination treatment. For most applications, it is suitable to form pellets which are generally 1 cm ³ in size. Preferably, the pellets are less than 1 cm ³ in size.

It is believed that an irregular shape enhances performance. The pellet may be any shape but is desirably generally cuboidal. The pellet size and/or shape can change when the pellets are heated in step (d) depending on the particular heating technique employed or other factors (e. g., the pellets can be broken). Thus, the pellet sizes and shapes referred to above relate to the pellet sizes and shapes after the pellets have been heated in step (d). Preferably, the pellets have a size after being heated in step (d) that is around the same as the size of the pellets prior to such heating.

Heating of the pellets may be carried out in step (d) by a refractory sagger. Alternatively, and preferably for large scale production the pellets are heated in step (d) by a rotary kiln or a tunnel kiln such as a single brick tunnel kiln. The Applicants have discovered that pellets formed using the process of the present invention may be used for different purposes if they are subjected to different temperatures in the heating process of step (d).

In a first arrangement, for forming a first type of pellet for use in the treatment of acid mine drainage, the pellets need to be heated to a very high temperature. Investigations have shown that for this purpose a suitable temperature for heating the pellets in step (d) is between 1030 - 1050°C. Most preferably, the pellets are heated to a temperature of 1030°C [, as this has been shown to provide the most reliable and effective results.

In a second arrangement, a second type of pellet may be produced for use in the treatment of waste water for phosphate recovery. In this arrangement a lower temperature of heating of the pellets is required as compared to that discussed above. Preferably, in this arrangement the pellets are heated in step (d) to a temperature between 790°C and 810°C. More preferably the pellets are heated to a temperature of 800 °C as this has been shown to produce effective results.

A third type of pellet can be produced which is effective in deodorising industrial effluent. This type of pellet ideally requires heating at a relatively low temperature. Preferably, the pellets are heated in step (d) to a temperature of between 790°C and 810°C. The pellets may be heated to a temperature of 800 °C as this has been shown to be most effective.

The optimum quantities of each component are dependant greatly on the end use of the pellets. In a particularly preferred process, the mixture, prior to any addition of water in step (a), may comprise a set of components, within the following ranges:

- 76% - 80% by volume of red mud; and

- 20% - 24% by volume of clay.

Of course, the quantities of each component can vary significantly from those figures defined herein, and this would not depart from the scope of the invention.

According to a second but closely related aspect of this invention, there is provided red mud pellets formed using the process described hereinbefore. The process of the present invention uses a sustainable raw material in the form of red mud to produce products which can be used in the treatment of contaminants generated by industrial processes. The process reduces contamination levels and provides a permanent solution to the problem of waste contamination.

By way of example only, processes for forming red mud pellets and pellets formed from such a process will now be described in detail, reference being made to the accompanying drawings in which:-

Figure 1 is a figurative representation of a process of forming red mud pellets according to the present invention.

A method according to the present invention is described with reference to the formation of three types of pellets for use in three distinct waste contamination treatments. The method differs for each type of pellet only in the temperature required to heat the pellets; as such, like reference numbers have been used for the common steps carried out in each process.

Red mud 10 is to be used as a constituent of each type of pellet. In step (a) the red mud 10 is treated in order, at least partly, to neutralise and thus reduce its alkalinity. This is achieved by adding a substance to the red mud 10. In one arrangement, as shown in step (a1 ) chlorides 1 1 are added to the red mud 10 to reduce the alkalinity. In an alternative neutralising treatment, as shown in step (a2), the red mud 10 is mixed with gypsum 12.

In step (b) the neutralised red mud 10 is mixed with brick clay 13 and water 14 in order to form a slurry 15. The quantity of red mud 10 is between 76- 80% and the quantity of brick clay 13 is between 20-24%, prior to the addition of water 14. The addition of water 14 may not be necessary in step (b) if the moisture content of the red mud 10 is sufficiently high.

Depending on the type of pellet to be formed the target pH may differ; for the water industry the target pH is approximately 8.5. The pH of the slurry 15 may need to be adjusted and this can be achieved by mixing powdered citric acid 18 into the slurry 15. As indicated by step (d ), the addition of the citric acid 18 could be to the red mud 10 at the same time as the mixing of the red mud 10, brick clay 13 and water 14 in step (b) or, as shown in step (c2) it may be carried out after the slurry 15 has been formed. In this embodiment, the slurry 15 should have a moisture content of 6- 9%. If this is not the case then it may be necessary to adjust the moisture content by either heating the slurry 15 or adding more water 14. Ideally the slurry 15 is heated in step (d) in order to dry it slightly and thus harden it to make it more suitable for forming into pellets. Any suitable heating means may be employed for this purpose.

In step (e) pellets 19 are formed; this can be carried out manually but preferably an industrial pellet maker is used. The pellets 19 are ideally irregular, but generally square in shape. The size of the pellets 19 should be less than 1 cm ³ in order to achieve the best results in reducing contamination levels.

Once pellets 19 of appropriate size and shape have been formed the next step is to heat the pellets 19, as indicated in step (f) in order to form a hardened product for use in treating waste material. Heating can be carried out using a refractory sagger. Alternatively, as shown in Figure 1 , the heating may be carried out using a rotary kiln 20.

At least three different types of pellet 19 can be formed using the process of the present invention and these may be used respectively to:

1 . Remove/recover phosphate from waste water;

2. treat acid mine drainage; and

3. deodorise industrial effluent.

As discussed above, the formation of these different pellets differs predominately in the temperature to which the pellets 19 are heated in step (f) although other parameters such as the ratio of red mud to clay can vary.

For the recovery of phosphate in water the pellets 19 must be heated to a temperature of approximately 800 °C; the dwell time for phosphate is around 2 hours. The treatment of acid mine drainage will require firing the pellets 19 at a high temperature between 1030-1050°C. This will provide a very hard pellet 19 that is able to withstand being submerged in acid mine water with a pH in the region of 4 for a period of up to 3 year. The temperature required to heat pellets 19 for the purpose of deodorising industrial effluent is in the region of 800 ^Q C.