GB2145401A - Aluminium chloride production - Google Patents

Abstract

A process for the production of aluminium chloride from an iron-containing aluminous material such as, for example, bauxite comprises chlorinating the bauxite in a fluidised bed in the presence of excess carbon and diluted chlorine to selectively remove iron in the form of iron chloride and to produce a beneficiate, chlorinating the beneficiate to produce aluminium chloride, contacting the aluminium chloride in the vapour form with metallic aluminium to further reduce the iron chloride content, condensing iron chloride, and selectively condensing the purified aluminium chloride. The iron chloride removed at various stages of the processes is condensed from unwanted gases, revolatalised and oxidised to generate chlorine of a purity suitable for direct re-use. A number of further features such as the selective chlorination of the iron values in the presence of water vapour and the electrostatic treatment of the vaporous aluminium chloride are applicable to the process.

Description

SPECIFICATION Aluminium Chloride Production This invention relates to a process for the production of aluminium chloride.

It has been proposed to produce aluminium metal by the electrolysis of aluminium chloride. United States Patent No. 3956455 assigned to Aluminium Company of America acknowledges the possibility of producing aluminium chloride from bauxite and describes the difficulties associated with the separation and recovery of aluminium chloride values from the hot reaction effluent from the chlorination of bauxite because of the presence of multiple impurities derived from the bauxite in the effluent, and because of the inherent characteristics of aluminium chloride during separation operations.Because of these difficulties the invention described in US Patent No.3956455 utilises Bayer process alumina in preference to bauxite as the initial reactant despite its content of sodium impurities and despite the formation of sodium/aluminium/chlorine complexes in the course of chlorination. Since Bayer process alumina typically contains less than about 0.5% by weight in total of iron, silicon and titanium oxides it is relatively more practicable to produce an extremely pure aluminium chloride from it and contents of 0.054% and 0.068% by weight in total of iron, silicon and titanium chlorides are obtained.

Bayer process alumina is becoming increasingly expensive due to the growing cost of energy. There is also growing concern over the red mud effluent generation. As a result, there is increasing interest in developing processes for the direct use of iron-containing aluminous materials such as available bauxites, which may be of relatively low grade and themselves unsuitable for use as raw material in the Bayer process, in the production of aluminium chloride for use in aluminium metal producing electrolysis cells.One such process is described in United States Patent No. 4363789 assigned to Reynolds Metals Company which process involves chlorinating such a material in a two stage process to produce aluminium chloride and then absorbing the aluminium chloride with alkali chloride to form a complex which is thereafter oxidised at a temperature of above about 500"C in a fluidised bed pebble reactor to form alumina, which alumina is purified of chlorides by washing. However, the use of aluminium chloride offers potential energy savings over the use of alumina, as is acknowledged in United States Patent 4363789, but its production is subject to the problems first outlined above. It is commercially desirable, therefore, to alleviate those problems.

Australian Patent No. 488695 granted to Comalco Limited relates to the production of aluminium chloride of low iron content from iron-containing aluminous material such as, for example, bauxite by initially reacting the material with sulphur dioxide and carbon monoxide to convert the iron content of the material to iron sulphide, chlorinating the iron sulphide-containing material to remove the iron in the form of ferric chloride and chlorinating the remaining aluminous material, depleted in iron, to produce gaseous aluminium chloride. This product has an iron content of the order of 0.05% calculated as Fe although at the expense of the complication of the extra chemical conversion to the sulphide.

The present invention relates to the production of aluminium chloride from an iron-containing aluminous material containing, for example, from 0.5% to 20% by weight of iron oxide before dehydration such as, for example, bauxite, bauxitic clays, kaolinite or koalinite clays or the like.

According to the present invention there is provided a process for the production of aluminium chloride comprising the following combination of features: a. providing a mixture of particles of an iron-containing aluminous material with a quantity of particles of carbon theoretically in excess of that required to react with the oxygen content of the iron component of the said material and with any oxygen added in following step (b) in the form of molecular oxygen the mixture having a temperature of at least 500or, b. fluidising the mixture and passing through the mixture a gas containing from 20% to 85% by volume of molecular chlorine while maintaining the temperature of the mixture at a sufficient level to allow iron oxide in the material to react with the chlorine and to be removed from the material in the form of iron chloride vapour entrained in the fluidising gas stream, c. providing a mixture of particles of the iron-depleted aluminous material resulting from step (b) with particles of carbon including, or consisting of, the excess defined in step (a) above, d. fluidising the mixture provided in step (c) above and passing through the mixture a gaseous chlorinating agent while maintaining the temperature of the mixture at a sufficient level to allow the aluminium oxide in the material to react with the chlorinating agent and to be removed from the material in the form of aluminium chloride vapour entrained in the fluidising gas stream, e. passing the aluminium chloride vapour through a bed of particles of metallic aluminium having a temperature of at least 400"C thereby to reduce the quantity of iron chloride present in the aluminium chloride vapour by reaction of the iron chloride with the metallic aluminium to form metallic iron and aluminium chloride, f. condensing residual iron chloride from the aluminium chloride, g. condensing the aluminium chloride thereby depleted of residual iron chloride from chlorides of yet lower boiling point and, if desired, condensing the chlorides of yet lower boiling point, h. condensing the iron chloride vapour removed entrained in the fluidising gas stream in step (b) above from the fluidising gas and separating the condensed iron chloride, j. re-vaporising iron chloride which has been condensed and oxidising the re-vaporised iron chloride so as to regenerate free chlorine in a form suitable for re-use in step (b) above.

A process defined by the combination of features (a) to (j) above provides a particularly efficient route to the production of aluminium chloride because it consumes its own waste chlorides and involves no gaseous chlorine purification stages. The product of the process can be at least comparable to that of Australian Patent No. 488695 with respect to iron content.

The chlorination reaction described in steps (a) and (b) is designed to give a particularly selective removal of iron from the iron-containing aluminous material by virtue of its use of excess carbon together with diluted chlorine. By the use of excess carbon that factor is removed as a possible controlling factor and the reaction is controlled instead by the degree of dilution of the chlorine resulting in a particularly efficient separation of iron values from the aluminous material. The residual solids, comprising a mixture of residual excess carbon and iron depleted aluminous material present in a fluidised bed in which iron is selectively removed by chlorination may, under some circumstances, absorb some iron chloride, particularly ferrous chloride, and other chlorides.In this case it may be desired to remove iron and other chlorides absorbed onto the solids by suitably treating them to remove said chlorides for example by water-washing free of soluble salts and thereafter drying. Alternatively solids may be contacted at an elevated temperature with a stream of non-reactive gas to strip absorbed iron chloride from the mixture.A controlled quantity of oxygen may be included in the non-reactive gas said controlled quantity being sufficient to react with a proportion only of the carbon present to maintain the temperature at least at the temperature of the preceding chlorination, or at least not more than 50"C below that temperature, and preferably at not more than 200"C above that temperature without being sufficient to react with any substantial proportion of the iron chloride present since the production of free chlorine at this stage in the process would be undesirable. Chlorides recovered from the carbon as above described are preferably treated to regenerate chlorine therefrom, according to step (j) above.

Inevitably, it is found that a small proportion of the alumina values in the material are chlorinated despite the excellent selectivity in favour of chlorination of iron values provided by the present invention. According to a further feature of the present invention the selectivity of removal of iron from the iron-containing aluminous material according to steps (a) and (b) may be further enhanced by the presence of a small proportion of water vapour. The watervapour may suitably be included in the non-chlorine gaseous input into the fluidised bed, for example in the stream of air or of oxygen and inert gases used to dilute the chlorine and to supply oxygen for bed temperature control purposes.The quantity of water vapour is preferably as low as is found to give an appreciable enhancement of selectivity as shown by a reduction in the quantity of aluminium removed from the bed with the iron chloride. Preferably the reduction is equivalent to at least 0.5%, for example from 1% to 5% or more, based on the weight of alumina remaining in the bed. The quantity of water vapour is preferably at least 0.01 g, for example at least 0.02 g per 1 Cl2 fed to the bed and, for example up to 0.1 g per 1 Cl2 or even more.At its broadest this feature is advantageously applicable to any process for the selective removal of iron values from an iron containing aluminous material by chlorination using diluted chlorine, i.e. chlorine having a concentration not more than 85% v/v, in the presence of excess carbon, in a fluidised bed whether or not the remaining alumina or the iron chlorides are further treated as defined in steps (a) of (j) herein.

It is also possible to supply the water vapour required by this feature by allowing a small quantity of water to remain in the aluminous material during the dehydration described hereafter although this is not as satisfactory method of operation as the inclusion of the water vapour in the fluidising gases. In this case the residual water vapour of the dehydrated aluminous material be suitably at least 0.002%, for example more than from 0.003% by weight.As an example of the effect of the presence of water vapour it was found that the use, as 45% by volume of the fluidising gas, of nitrogen which has been bubbled through water at 35 C and which was therefore saturated with water, in contrast to the use of a similar quantity of dry nitrogen, in the fluidised bed chlorination beneficiation of Ghanian bauxite in the presence of an excess of carbon resulted, after the same reaction time, in a residual iron oxide content in the bed solids of 2.0% wt in contrast to a content of 4.8% by weight.

The aluminium chloride produced by the chlorination of the iron-depleted aluminous material will still contain a small proportion of residual iron chloride and it is the object of the treatment with metallic aluminium to remove that residue.

According to yet a further feature of the present invention the aluminium chloride which has been treated with the metallic aluminium particles may be maintained at a temperature controlled to be above the desublimation point of the aluminium chloride, but such that any minute residual amounts of iron chloride still present therein are in condensed form and treated to remove such solid particles, for example by techniques known for the removel of dust from air. It is found that this achieves, in the context of the present process, the removal of an appreciable proportion of an extremely fine dust from the still vaporous aluminium chloride which dust comprises a mixture of iron chloride and aluminium chloride. The resulting aluminium chloride may have a content of iron chloride of below 0.1% by weight. At its broadest, however, this feature is independently applicable to the removal of metal chloride traces from a desired metal chloride vapour, provided that the metal chloride trace is solidifiable at a temperature at which the desired metal chloride is still a vapour, for example ZrCl4from TiCI4.

The iron-containing aluminous material, besides iron, has a content of values of other metals, for example, oxides of one or more of titanium, manganese, magnesium, together with silicon dioxide, all of which will tend to chlorinate in step (b) of the process. The manganese and magnesium chlorides, present in relatively small quantities, will tend to be absorbed onto the carbon with the ferrous chloride and to be removed from it as taught above. The silicon and titanium chlorides have lower boiling points than the aluminium chloride product and will remain with that product which may be recovered therefrom by selective condensation according to step (g) of the process.

The operation of the present invention will now be more specifically described.

If the iron-containing aluminous material contains bound water as does bauxite in a considerable quantity it is necessary to drive off the great majority of this water before the chlorination of the material is conducted. This dehydration step also achieves any necessary preheating. It is preferred to mix the carbon intended to be used in the first chlorination step, as such or as a suitable carbonaceous material convertible to carbon during the dehydration step, with the aluminous material before dehydration so that the whole chlorination charge is preheated. If desired, the dehydration and preheating may be accomplished by the combustion of a part of the carbon, by the use of a controlled quantity of oxygen which may be in the form of air.Preferably, however, the carbon is formed from coal and dehydration is accomplished by combustion of its volatile content in, for example, a rotary kiln. Preferably the dehydration/preheating step is conducted at a temperature of from 800"C to 1050 C.

The conditions used in step (b) may be selected to avoid the formation of undesired alumina phases.

Certain types of aluminous material, for example kaolinitic materials, have a lesser tendency to form undesired alumina phases that others for example bauxitic materials. Some aluminous materials may therefore be satisfactorily chlorinated at temperatures below about 1 1 OO"C. When chlorinating a material of this type the carbon is preferably, for example, a petroleum coke and the chlorination may be above about 775"C and up to 1100 C, being desirably controlled only to ensure that the temperature remains above the dew point of ferrous chloride in the system. If the aluminous material has a greater tendency to form undesired alumina phases it may not be desirable to operate at above the dew point of ferrous chloride.In this case it may be preferred to operate at below the melting point of ferrous chloride of about 670"C and to enable this to be achieved, the carbon may be active carbon or, preferably, a form of reactive coke derived by heating a non-caking or weakly caking coal in the substantial absence of oxygen until its surface area is at least 3m2/g.

The mixture of aliminous material and carbon, each of a fluidisable particle size for example from 200 to 24 mesh BSS, and preferably containing more than 20% and suitably up to 50% by weight of the mixture of the carbon to provide the essential excess required for the successive chlorination stages, is fluidised and contacted with chlorine-containing gas in order to chlorinate the iron-content of the aluminous material selectively. The chlorine concentration is controlled by the inclusion of inert gases and is preferably from 20% to 80% by volume of the gases introduced into the chlorination bed. In addition, preferably the expanded bed depth used is at least 2.75 metres in depth for example, suitably from 3 to 4.5 metres in depth thereby enabling a substantially chlorine-free zone to be maintained near the surface of the bed.The effect of these conditions is to maximise the selectivity of the chlorination, with respect to iron values. The chlorination is peferably controlled to give substantially no chlorine slip, for example a chlorine concentration in the gases leaving the fluidised bed of below 0.5% by volume. Preferably, a zone of at least 0.25 m, measured from the surface of the expanded bed, in depth has a chlorine concentration in the gases therein below 0.5% by volume.

There have been proposals for the direct oxidation of gaseous iron chloride in the gas space above the fluidised bed to regenerate chlorine at that point. However, this is disadvantageous since it causes further dilution of the effluent gases and the regeneration of gaseous chlorine at this point in the process makes the installation of a gaseous chlorine purification plant necessary to provide chlorine suitable for recycle.

According to the present invention the gaseous effluent from the fluidised bed from which at least some of the carbon has been allowed to disentrain or has been separated, is cooled to condense the iron chloride which is then separated from the remaining gases comprising inert gases and carbon oxides. A suitable temperatu re to achieve condensation is from 1 OO"C to 200"C, for example, and a suitable means for separation of the condensed particles is a cyclone. The condensed iron chloride may then be heated to, for example, from 800"C to 11 000C to revaporise it and is contacted with molecular oxygen to release chlorine from the iron chloride by converting it to iron oxide.The dilution of the chlorine may be controlled by the inclusion of a controlled quantity of non-reactive gas, for example by using a suitable combination of air and pure oxygen, so that the chlorine is suitable for recycling for use in the selective iron chlorination. This is a particularly advantageous feature of the present invention. It is within the scope of this invention to alter the form of the iron chloride or of some of it, e.g. from the ferrous to the ferric form to ease the processing of the bed effluent gases, provided that no chlorine, or no substantial quantity of chlorine, is evolved at this stage.

As a result of the removal of iron values from the iron-containing aluminous material by the selective chlorination reaction above described, there is produced a material suitable for chlorination of the aluminous values to produce aluminium chloride.

The mixture of aluminous material and excess carbon is fluidised for the chlorination of the aluminous material according to step (d). Suitably, the excess of carbon already present is in a sufficiently large proportion which proportion is preferably from 15% to 40% of the aluminous material and carbon although, if not, further carbon may be included. Since selectivity is no longer the object the nature and quantity of the chlorinating agent is not critical although, preferably, molecular chlorine is again used. Preferably the concentration of this chlorine in the fluidising gases introduced into the bed is from 40% to 100% by volume.

This chlorination may be conducted generally, in the temperature range 500"C to 1 100C although, if the preceding chlorination has been a relatively low temperature chlorination to avoid the formation of undesired alumina phases, for example, at a temperature below 775 C, the remaining bed material may suitably be further chlorinated at a temperature below about 775 C, for the same reason, to produce aluminium chloride vapour.If, however, the preceding chlorination has been at a temperature above about 775 C, for example at 950 C, the remaining bed material may be further chlorinated at a temperature of above 850 C, for example, from 850"C to 1100 C, to aluminium chloride.If despite precautions, or as a deliberate result, alpha-alumina has been generated in the course of the selective chlorination of the iron chloride, for example in at least 0.5%, or in at least 5.0%, the further chlorination is preferably conducted using as the carbon or a portion thereof active carbon, or a reactive coke formed by heating a coal having a British Standard Swelling Number (BSS 1016 Part 12) of below 6 1/2 preferably from 1/2 to 3 1/2 in the substantial absence of oxygen until it has a surface area of at least 3m2/g, e.g. up to 50m2/g, using a chlorination expanded bed depth of more than 2.5m preferably more than 3m and using a chlorinator temperature above 775"C.

The gases containing the chlorides of aluminium and of other impurities including iron issuing from this fluidised bed are then cooled somewhat and treated with metallic aluminium, to enable the iron values to be removed before condensing the bulk of the aluminium. Iron tri-chloride vapour present in the aluminium chloride vapour stream will react with aluminium metal to give a deposit of metallic iron and generate tsfurtheraluminium chloride.

The aluminium chloride from which residual iron chloride has been removed may be cooled to a temperature such that any further iron chloride remaining in it is in solid form and such that the majority of the aluminium chloride itself is in vapour form, which temperature is below that of the bed of reductive metal particles, for example, suitably from 250"C to 300 C, and treated to remove the solid particles. Electrostatic methods may be used to achieve this. A single stage negative polarity electrostatic precipitator may be used although the use of other types of precipitator is not excluded. The voltage drop across the precipitator plates may be from 8 to 12 kviinch. The iron chloride recovered in this manner represents material which would normally contaminate the aluminium chloride product.It inevitably contains some aluminium chloride. This material is preferably treated with the main body of iron chloride to regenerate chlorine therefrom in Step (h) above.

The aluminium chloride may be selectively condensed.

The residual gases remaining after the aluminium chloride condensation step comprise the gaseous products of the chlorination reaction being CO2, SiCI4, TiCI4, some remaining AICI3 and any non reactive gas such as N2 added to the system as purge gas.

The CO2 and N2 may eventually be passed to atmosphere after suitable cleaning. Were such cleaning by water or other liquid scrubbing agents the other constituents would be lost although operation by this means is not precluded. However it is preferable to condense as much as conveniently possible of the remaining chloride vapours for recovery for use either as intermediate chemicals for other purposes or, by means of feeding them via the chlorine regeneration stage (j) referred to above, to regenerate chlorine from them for recycle to the process.

The present invention enables a remarkable economy in chlorine utilisation to be maintained by virtue of the preferred use of a deep bed for the selective removal of iron values from the aluminous material having a zone containing no substantial chlorine content near its surface, thus avoiding chlorine slip, and by the use of the particular iron chloride processing steps set out herein including the particular sequence of treatment of the iron chloride to recover chlorine from it. This scheme for the processing of iron chlorides is new and enables substantially complete recovery of chlorine of that used to chlorinate the iron values in the ore to be achieved with 90% or more recovery of aluminium values fed to the chlorinator and with overall a Cl2 make up requirement of typically only 3 1/2 to 4% of the circulating Cl2 flow.

The entire process is particularly susceptible to continuous operation, continuous flows of the bed materials being taken for further treatment at an appropriate rate. While fluidised chlorination techniques are preferred, it is preferred to establish a progression of movement of the fluidised material through the bed from a solids input end to a solids output. By this technique the bed material removed may be fully reacted before removal.

According to a further aspect thereof the present invention may be operated as two separate processes, if desired at different localities, each separate process being novel and advantageous in its own right. Thus, the solid bed residue from the selective iron chlorination, together with the associated chlorine recovery stages may be operated as a unit. The excess carbon in the bed residue may be separated and used to fuel the revaporisation of the iron chloride. The remaining aluminous material is a useful article of commerce in its own right as a raw material for aluminium production. The remaining portion of the present process may also be operated separately, and may utilise such a last mentioned raw material mixed with fresh carbon in suitable quantity. The relatively smaller quantity of iron chloride recovered in this succeeding part of the process will, in this case require to be suitably treated, independently, to recover the chlorine.

This invention will now be illustrated by the following Example.

Example Ghanaian bauxite of particle size 0.1 to 1.0 mm diameter was mixed with anthracite coal of particle size < 2.0 mm diameter in such a ratio that after raising the temperature of the mixture to 1000 C so that the bauxite was dehydrated and calcined and the coal was dried and devolatilised, the resultant mixture was three parts by weight of calcined bauxite and one part by weight of a coke product. This calcination operation was carried out in a rotary cylindrical calciner in a non-oxidising atmosphere, and during the operation the surface area of the coal-derived coke product increased to about 20m2/gm and the analysis of the bauxite product was 70% Al203, 16.5% Fe2O3, with smaller quantities of SiO2 and Tri 02.

The main reactor assembly comprised a fluidised bed reactor consisting of a vessel 180 mm in inside diameter and 3.66 m in height made of fused silica enclosed in a gas fired furnace, a cyclone and a gas sampling device. Gasesforfluidisation and reaction entered the base of the reactor from metering equipment via a fused silica conical distributor which also carried means of removing the bed solids.

Gaseous products of reaction passed along a horizontal duch to the cyclone and then to the gas sampling device before disposal via a caustic scrubber to aatmosphere. Solids could be fed to the reactor from a pipe at the reactor top.

The bauxite/coke material was fed to the reactor, 60 kg of the material being initially fed to form an initial bed. The charge was fluidised with nitrogen and heated to 950 C. The fluidisation gases were then changed to the composition 14 1/min. chlorine, 12 1/min. air, and 21 1/min. nitrogen. Fluidisation was continued for four hours. At the end of four hours the pressure drop across the bed was noted and 2.5 kg of the feed mixture was added to the bed every 10 minutes of further operation, bed being withdrawn to maintain the original pressure drop reading. This was continued for 24 hours during which no free chlorine was detected at the gas sampling point. To assist the cooling of the gases as they passed along the horizontal duct a flow of 100 1/min. of nitrogen was added at the duct entrance.The material removed from the cyclone was found to be predominantly ferrous chloride with some aluminium chloride and particles of dust derived from the feed mixture. The material withdrawn from the bed and the material contained in the bed at the close of the run were both mixtures of beneficiated bauxite and excess coal-derived coke product. The ore fraction of th is mixture was 91.0% Al203 and 1.7% Fe2O3 with smaller quantities of SiO2 and TiO2 and was found to contain 70% alpha-AI2O3. The carbon fraction of the mixture had a surface area of 60 m2/gm.

Re-using the main reactor assembly the chlorides of iron and aluminium recovered from the cyclone were fed onto a bed of inert sand and carbon in the reactor and fluidised with a mixture of air and oxygen, at 1000"C, which caused them to volatilise. Upon the addition of further oxygen above this fluid bed at the entry of the horizontal duct, the volatilised chlorides oxidised to form a chlorine-containing gas and iron oxide which together with aluminium values and unreacted iron chloride could be removed from the cyclone and returned to the reactor for further reaction. A mixture of inert solids, carbon and oxides of iron and aluminium was withdrawn from the bed. The concentration of Cl2 containing gases at the gas sample point was found to be 37% v/v Cl2 which was suitable for recycle to the chlorination of further bauxite/coke mixture.

The pipework of the reactor was then modified so that immediately afterthe cyclone a further cyclone was added, the two cyclones and the horizontal duct preceding them being heated in a gas fired furnace operating at 500 C.

Again using the main reactor assembly a portion of the mixture of beneficiated bauxite and carbon was fed to the reactor to form a bed 2.6 m deep whilst fluidised with nitrogen, and heated to 9500C. The pressure drop across the bed was noted. The gases were then changed in composition to 35 1/min, chlorine and 12 1/min.

air. From time to time additions of the mixture of beneficiated ore and carbon were made to maintain the original pressure drop and hence bed depth. At the gas sample point no Cl2 slip was detected. The gases were conducted through the two cyclones which removed blowover dust derived from the bed.

Following the two cyclones the gaseous stream was then led via a sample point to an aluminium chloride purification unit. This unit was made up of two 155 mm diameter reactors 2.0 m long and arranged so that the gases flowed into the first at its lowest point, then from the first to the second at their uppermost points, then from the second at its lowest point. These reactors were filled with aluminium pellets in the form of 1/4 inch to 3/8 inch (6.35 mm - 9.5 mm)spheroidal pellets mixed with granular anthracite which had been devolatilised and leached with dilute hydrochloric acid so as to form granules of carbon-rich material approx. 1/4 inch to 3/8 inch (6.35 mm - 9.5 mm) in diameter in a 1:1 volume ratio.This mixture was introduced via a preheating unit to the uppermost points of the contactors and was withdrawn from their lowest points in a controlled fashion at a rate of 2 litres per 10 minutes per bed so as to maintain the presence of a bed of pellets at all times. Removal and addition of the mixture from hoppers was by means of pairs of plug valves so as to maintain gas tight conditions during these operations. The further reactor unit was enclosed in a furnace at400 C.

The gaseous purified aluminium chloride issuing from the second reactor was led to a cyclone operated at 180"C and thence to a large empty condensing vessel operated at 70"C. The gas exit of the condensing vessel led via a water scrubber to the atmosphere and the solids exit led to a bagging point.

Pellets led from the base of the contactor were found to bear metallic iron on their surfaces, and dust led from the base of the further cyclone was found to contain ferrous chloride.

The material collected in the final condenser contained 490 ppm Fe in AICI3 on average, and reaching thereafter 240 ppm Fe in AICI3 peak quality value and took the form of a pale yellow free-flowing powder which fumed on contact with moist air.

The gases discharged to atmosphere via the recirculating water-fed scrubber which was found to produce dilute hydrochloric acid by virtue of its absorption and hydrolysis of chlorides of lower boiling point than aluminium chloride e.g. of silicon and titanium which are separated from the aluminium chloride at this point.

Claims (11)

1. a process for the production of aluminium chloride characterised by the following combination of features: a. providing a mixture of particles of an iron-containing aluminous material with a quantity of particles of carbon theoretically in excess of that required to react with the oxygen content of the iron component of the said material and with any oxygen added in following step (b) in the form of molecular oxygen the mixture having a temperature of at least 500"C.

b. fluidising the mixture and passing through the mixture a gas containing from 20% to 85% by volume of molecular chlorine while maintaining the temperature of the mixture at a sufficient level to allow iron oxide in the material to react with the chlorine and to be removed from the material in the form of iron chloride vapour entrained in the fluidising gas stream.

c. providing a mixture of particles of the iron-depleted aluminous material resulting from step (b) with particles of carbon including, or consisting of, the excess defined in step (a) above, d. fluidising the mixture provided in step (c) above and passing through the mixture a gaseous chlorinating agent while maintaining the temperature of the mixture at a sufficient level to allow the aluminium oxide in the material to react with the chlorinating agent and to be removed from the material in the form of aluminium chloride vapour entrained in the fluidising gas stream, e. passing the aluminium chloride vapour through a bed of particles of metallic aluminium having a temperature of at least 400"C thereby to reduce the quantity of iron chloride present in the aluminium chloride vapour by reaction of the iron chloride with the metallic aluminium for form metallic iron and aluminium chloride, f. condensing residual iron chloride from the aluminium chloride.

g. condensing the aluminium chloride thereby depleted of residual iron chloride from chlorides of yet lower boiling point, h. condensing the iron chloride vapour removed entrained in the fluidising gas stream in step (b) above from the fluidising gas and, separating the condensed iron chloride, j. re-vaporising iron chloride which has been condensed and oxidising the re-vaporised iron chloride so as to regenerate free chlorine in a form suitable for re-use in step (b) above.

2. A process as claimed in claim 1 wherein the iron-containing aluminous material contains from 0.5% to 20% by weight of iron, calculated as the oxide, before dehydration and is a bauxite, bauxitic clay, kaolinite or kaolinitic clay.

3. A process as claimed in claim 2 wherein the aluminous material contains bound water and the said material is heated at a temperature of from 800"C to 1050 C to drive off at least a majority of the bound water.

4. A process as claimed in any preceding claim wherein the condensed iron chloride vapour is oxidised according to step (j) in the presence of molecular oxygen or of a mixture of molecular oxygen and air having a concentration of molecular oxygen such that chlorine having a concentration of at least 20% by volume is generated.

5. A process as claimed in any preceding claim wherein the chlorination of the iron-depleted aluminous material is conducted in the presence of from 15% to 40% by weight of carbon, based on the weight of the said material and the carbon, at a temperature of from 500"C to 1100 C.

6. A process as claimed in any preceding claim wherein the chlorination of the iron-containing aluminous material and of the iron-depleted aluminous material is conducted in the presence of carbon at least some of which is active carbon or a coke having a surface area of at least 3m2/g.

7. A process as claimed in any preceding claim wherein the chlorination of the iron-containing aluminous material is conducted in a fluidised bed having an expanded depth of 3 to 4.5 m and a zone of at least 0.25 m in depth is maintained, measured from the surface of the bed in which the chlorine concentration is below 0.5% by volume.

8. A process as claimed in any preceding claim wherein the chlorine containing gas used in step (b) contains water vapour.

9. A process as claimed in claim 8 wherein the water vapour is present in the gas in from 0.01 to 0.1 g/l of chlorine.

10. A process substantially as described and illustrated in the Example herein.

11. Aluminium chloride the product of a process as claimed in any one of claims 1 to 10.