RECOVERY OF CHLORINE

Abstract: Chlorine may be recovered from residues from the fluidised bed chlorination of iron-containing metalliferous oxidic materials, such as ilmenite, bauxite, chromite, wolfra­ mite, scheelite, tantalite or columbite, the residues contain­ ing condensed iron chloride and blow-over bed solids, by heating the residue to revolatalise the iron chloride and reacting it with oxygen. The quantity of iron chloride in the oxidic material is controlled relative to the quantity of blow-over carbon so that the quantity of carbon is sufficient on combustion to provide the required heat but is insufficient to cause undue dilution of the chlorine produced by virtue of its combustion products. Chlorine of a concentration suitable for direct recycle to a chlorination process, e.g. of 30% to 50% volume concentration is produced.

Description: This invention relates to the recovery of chlorine from oxidisable metal chlorides. Metal values may be recovered from iron-containing metalliferous oxidic materials by chlorination processes. Such processes may involve the selective chlorination of the iron values in the material and the removal of iron chloride from the metal oxide-containing residue, generally referred to as beneficiation or 'partial chlorination' processes, or the chlorination of both the iron values and the metal values in the material and the subsequent separation of iron chloride from the metal chloride so produced, generally referred to as 'total' chlorination processes. In either type of process it is desirable to recover chlorine for recycle from the possibly substantial quantity of iron chloride, usually also accompanied by chlorides of other minor constituents, or even a proportion of the chloride of the major metal constituent other than iron, of the oxidic material. Hereafter reference to iron chloride includes a reference to other chlorides accompanying it unless the context requires otherwise. One process for the recovery of chlorine in a directly recyclable form is described in the Journal of Metals Vol 27 No 11, 1975 pages 12 to 16. In the referenced paper there is described the dechlorination of solid iron chloride by vapourising it and introducing it into contact with preheated oxygen in an externally heated bed of iron oxide particles. Extremely high concentration chlorine is obtainable by this means but at very considerable energy costs. A further process for the recovery of chlorine from iron chloride produced by means of a selective or 'partial' ore chlorination process is described in United States Patent No. 4094954 of SCM Corp. In that process the iron oxide content of a titaniferous ore, for example Australian Ilmenite having the composition 54% TiO₂ and 30% total iron oxides calculated as the metal, is chlorinated in the presence of petroleum coke and the vaporous stream containing the iron chloride in the vapour form is contacted with pure oxygen to obtain iron oxide and chlorine gas which is discharged from the system. Since this gas contains the combustion products of the coke used in the ore chlorination it cannot be at a concentration suitable for direct recycle to the chlorination reaction for which purpose a separate feed of chlorine is used. Yet a further process for the recovery of chlorine from iron chloride which may have been produced as a by-product stream from an ilmenite chlorination process for manufacturing titanium dioxide such a stream typically having the composition FeCl₃ 87% wt FeCl₂ 5% wt TiCl₄ 3% wt AlCl₃ 2% wt MnCl₃ 2% wt MgCl₂ 0.6% wt Miscellaneous 0.4% wt Total 100.0% is described in United States Patents No 4174381 and 4282185 of DuPont. According to that process a multistage recirculating fluidised bed reactor giving initial dense and downstream dilute fluidised zones and having specified dimensions is employed. The bed materials comprise recirculated iron oxide, sodium chloride as a catalyst and a carbonaceous fuel which is added to provide combustion heat to vaporise the iron chloride which is thereby enabled to react with an excess of oxygen added to the reactor. In this process the carbonaceous fuel is preferably a dry pulverised lignite char and represents an appreciable process cost. A process for beneficiating a titaniferous ore by chlorination of a fluidised bed of titaniferous ore mixed with coke is described in Patent Specification No. US-A-3865920. Gaseous iron chlorides above the fluidised bed are contacted with oxygen to form a gaseous cloud of a partially oxidised mixture of iron chlorides, iron oxide, oxygen and chlorine which is passed to a flue and cooled to complete the oxidation. US Patent No. 4060584 describes a two stage process for the recovery of chlorine from chlorinator dust which is a by-product of the chlorination of titaniferous materials. The present invention provides a process for treating an iron-containing metalliferous oxidic material which comprises chlorinating the oxidic material in a fluidized bed chlorinator unit with a chlorine-containing gas in the presence of an excess of carbon at a temperature Of 500 - 1050 o C to chlorinate said metal oxide material including at least a portion of said iron oxide and to combust a portion of the carbon and regenerating chlorine from the effluent stream by reaction with an oxygen-containing gas, characterised in that: (a) an effluent stream containing vaporous iron chloride and blow-over carbon is removed from the chlorinator unit; (b) the weight ratio of the iron oxide in the metalliferous oxidic material to the carbon is adjusted so that the effluent stream from the chlorinator unit contains about 1 to 3 parts by weight of blow-over carbon to 1 to 14 parts by weight of metal chlorides (including iron chloride); (c) the iron chloride and blow-over carbon are removed front the effluent stream from the chlorinator unit; and (d) the removed iron chloride and blow-over carbon are fed to a chlorine regenerator where they are reacted with an oxygen-containing gas that provides an excess of oxygen for combustion of the blow-over carbon and oxidation of at least a portion of the metal chlorides to produce chlorine gas for recycling to the chlorination step. This invention has the advantage of requiring no additional source of heat for the regeneration of chlorine from the iron chloride and enables the direct production of chlorine of recyclable concentration by control of the feed materials to the chlorination stage in a manner not previously taught. Thus the regeneration step can be effected without the addition of carbon beyond the blow-over carbon. The fluidised bed chlorination of iron-containing metalliferous oxidic materials, such as suitable ores, refined ores, sands, slags or industrial by-products, or mixtures of one or more of the above, in the presence of excess carbon is well known. The function of the carbon is to combine with the oxygen content of the iron or metal oxides to be chlorinated and, to provide reaction heat as a result of the combustion process. If the carbon is not in excess there will be a tendency for reoxidation of the chlorides formed. Additionally, there are a number of "partial" chlorination processes which obtain selectivity of chlorination by the use of diluted chlorine, the use of carbon in excess removing of carbon as a process controlling factor. The present process is illustrated hereafter by reference to the chlorination of oxidic iron-containing titaniferous materials, but is equally applicable to the chlorination of other iron-containing oxidic materials, since the critical feature relevant to the operation of the invention is the quantity of iron chloride produced. Thus, in one particular embodiment, the invention may be utilised in relation to the "total" chlorination of an oxidic iron-containing titaniferous material to produce an effluent stream containing titanium tetrachloride in addition to iron chloride, the iron chloride being selectively condensed from the titanium tetrachloride vapour. Equally, the invention may be applied to the "partial" chlorination, or beneficiation, of an oxidic iron-containing titaniferous material by means of an iron chloride selective chlorination process provided that the quantity of iron chloride in the effluent gas is controlled as taught herein. Other iron-containing metalliferous materials to which the present invention is also applicable are, for example, bauxite, chromite, wolframite, scheelite, tantalite or columbite. The fluidised bed chlorination of iron-containing metalliferous oxidic materials may be conducted to minimise the blow-over of bed solids. European Patent Specification No. 0034434, for example, where iron chloride in a fluidised bed effluent is contacted with oxygen in order to conduct a partial oxidation reaction in the top of a tall chlorination reactor containing the fluidised bed in the lower portion of the reactor discloses that the oxygen is introduced at such a point above the bed surface that carbon entrained in the effluent, or a proportion if it, has first become disentrained by virtue of a relatively low upward gas velocity, the disentrained carbon thereby being prevented from reacting with the oxygen. That patent teaches the use of a reduced cross-section in the reactor, to ensure the entrainment of solids formed, but only above the point of disentrainment of blow-over bed solids. Despite these precautions, of course, there will always be a loss of carbon due to the blow-over of the finer particles. In the process of United States Patent No. 4094954, referred to above, for example, such particles would be lost with by-product solids removed by means of a cyclone. According to the present invention it is not necessary to go to the expense of a modified reactor design as taught in European Patent Specification No. 0034434, nor in other way to take precautions to reduce the quantity of blow-over carbon, although processes which embody such precautions are not excluded from the invention. What is relevant to the practice of the invention is that the quantity of blow-over carbon is known and the quantity of iron chloride formed is adjusted relative to it, for example by selecting the composition of the particular iron-containing metalliferous material. The quantity of blow-over carbon and of iron chloride in the gaseous effluent from the fluidised bed is readily determined by sampling and basic analytical techniques applied either to the gaseous effluent or to the iron chloride condensate recovered from it. It is preferred that the content of carbon in the iron chloride condensate is greater than 7.5% by weight although it is, particularly preferably, at least 8.5% by weight. The concentration of the chlorine evolved is dependant on the quantity of carbon oxides produced by the combustion of the carbon. Preferably, therefore, the quantity of carbon is controlled to avoid any unacceptable dilution of the chlorine evolved and/or the quantity of chlorides are controlled to the same purpose. It is generally preferred that the quantity of carbon in the condensed iron chloride product is less than 20% by weight; particularly preferably less than 15% by weight and very suitably not more than 12.5% by weight. The condensed iron chloride product will usually contain chlorides of minor constituents of the material chlorinated or even a proportion of other major constituents thereof, some of which, such as chlorides of titanium zirconium, chromium, niobium, vanadium, tungsten are oxidisable with the iron chloride and therefore represent recoverable chlorine, and others of which, for example chlorides of calcium and manganese are not oxidisable under these conditions. Analysis of the condensate readily reveals the content of oxidisable and non-oxidisable chlorides and, therefore, the quantity of oxygen required to react with the oxidisable chlorides and to combust the carbon. An undue excess of oxygen acts to dilute the chlorine produced. If acceptable from the dilution standpoint a mixture of oxygen and air may be used to conduct the oxidation. The dilution of the oxygen may reduce the efficiency of the oxidation so that a greater excess of oxygen may be necessary where an oxygen/air mixture is used. Preferably the excess of oxygen, with reference to pure oxygen or oxygen/air mixtures not containing substantially more than 50% of air, is from 5% to 75%, particularly preferably from 5% to 50% with reference to the quantity required to combust the carbon and to react with the oxidisable chlorides. The present invention is preferably put into practice by introducing the condensed iron chloride, containing blow-over solids, into a bed, suitably a fluidised bed, of particles of an inert material into which bed oxygen-containing gas is introduced. The inert material may suitably be particulate iron oxide although other inert material, such as silica or spent chlorinator bed, may be used. It has been found to be particularly advantageous to utilise more than one input stream of oxygen or oxygen-containing gas. Preferably a first stream is introduced as the fluidising gas in a suitable quantity to react with the carbon content of the feed to the bed and to maintain the bed temperature. This stream may also be used if desired to preheat the bed by the combustion of an initial charge of carbon. The bed is preferably preheated to a temperature of at least 500 o C and temperatures of up to 1000 o C, or even higher, for example up to at least 1050 o C may suitably be maintained in the course of the process. Preferably the temperature is maintained at at least 550 o C particularly preferably at, at least, 600 o C. It has been found that it is not necessary to preheat this first stream. Preferably a second stream of oxygen or oxygen-containing gas, or more than one such further stream, is introduced above the bed surface and into contact with the revaporised iron chloride. If a large excess of oxygen over that theoretically required is used at this point in the process it may be considered desirable to preheat the second and/or further streams of oxygen-containing gas to some extent although this is not necessary in all cases. The preferred excess of oxygen indicated above relate to the total quantity of oxygen used and may be split between the various streams of oxygen or oxygen-containing gas used. Preferably, however, not more than a 25% excess, and particularly preferably not more than a 15% excess, of oxygen over that required to attain the desired temperature is used in the first stream. As a result of the reaction between the revolatilised iron chloride and the oxygen the gases leaving the oxidation zone contain iron oxide particles which may be recovered after any suitable temperature adjustment by usual means such as, for example, a cyclone. Such recovered iron oxide may contain a proportion of unoxidised iron chloride and is therefore preferably recycled to the bed from which a corresponding proportion of the inert solids is preferably purged. While the quantity of carbon blow-over can be varied within limits these limits are somewhat narrow under acceptable fluidised bed chlorination conditions. The iron oxide content of the material being chlorinated, however, may be varied by blending different grades of the material. If the flow of chlorine is sufficient the proportion of iron chloride and other oxidisable chlorides in the condensate recovered from the chlorination effluent will vary proportionally to the proportion of the oxides in the material. Thus it is possible to control the ratio of blow-over carbon to iron chloride (and other chlorides and materials) in the chlorination effluent. A suitable such ratio is preferably from 1:3 to 1:14 particularly preferably from 1:4 to 1:12. The present invention is advantageously applicable to the recovery of chlorine from iron chloride produced in the course of the chlorination of iron-containing titaniferous oxidic materials and requires a modification of normal practice in the chlorination of such materials. The chlorination of iron-containing titaniferous oxidic materials has tended to fall into two categories which are the "total" chlorination of materials, such as rutile or synthetic rutile, containing greater than about 85% by weight of titanium oxide and less than about 5% by weight of iron oxide and the "partial" chlorination or beneficiation of materials, such as ilmenite, containing generally less than about 50% by weight of titanium oxide and up to about 60% of iron oxide. In the latter category the product beneficiate containing not more than about 5% by weight of iron oxide has usually been used as a raw material for a 'total' chlorination process. Neither process produces an iron chloride condensate suitable for the application of the present invention since, in the context of a carbon blow-over, from reactions not specifically designed to reduce this, of about 0.075 to 0.125 parts per part by weight of titanium dioxide chlorinated, the first category produces an iron chloride condensate containing relatively too little iron chloride so that the application of the invention would result in an unduly high dilution of the chlorine evolved by carbon combustion products, and the second category produces an iron chloride condensate containing relatively too little carbon so that expensive additional carbon would have to be added in a substantial quantity. According to the present invention, as applied to the chlorination of iron-containing titaniferous oxidic materials, the iron oxide content of the material may suitably be from greater than about 10% to 35%, preferably from about 12% to 30% and particularly preferably from about 15% to 30% by weight of the material. The content of titanium dioxide in the material may suitably be from about 70% to 85% by weight of the material. A suitable material containing such proportions of constituents is not readily available and, in consequence, the invention is suitably put into effect by chlorinating blends of materials giving such proportions. Preferably such a blend is of ilmenite with, either, rutile or a mixture of rutile and slag. A suitable slag is produced by the Richards Bay Company and contains typically above about 85% by weight of titanium dioxide and about 10% of iron oxide although titanium dioxide-rich slags containing up to about 96% of titanium dioxide and down to about 2% of iron oxide may be used if obtainable. Sources of rutile and ilmenite ores or sands are well known to those in the art. One suitable range of blends of rutile, slag and ilmenite for use according to this invention is as follows. Rutile For example Australian Rutile and/or Sierra Rutile in respective proportions for example of 20-30 parts to 5-15 parts. Iron oxide content about 0.5-3%. Titanium oxide content about 95%-98%. Ilmenite For example Australian Ilmenite. Slag Richards Bay Slag for example having an iron oxide about 5-15% and a titanium oxide about 80-90%. Proportions on a TiO₂ basis :- (a) Rutile:Slag = 70 to 55:30 to 45 preferably = 68 to 58:32 to 42 for example = 63:37 (b) Rutile+Slag:Ilmenite = 50 to 60:50 to 40 preferably = 52 to 57:48 to 43 for example = 55:45 The particular sources of ores as stated above is not critical. The ranges given above contemplate the use of an ilmenite containing about 50% to 55% titanium dioxide and about 45% to 40% iron oxides. If an ilmenite containing markedly more iron oxides is used the proportions may have to be altered accordingly if it is required to obtain an iron chloride-containing condensate containing the proportions of oxidisable chlorides to carbon indicated above as preferred, in view of the wide variation in the content of iron oxides found in ilmenite. The process of this invention is based on the fluidized bed chlorination of an iron-containing metalliferous oxidic material with a chlorine containing gas in the presence of excess carbon at fluidized bed temperatures above 500°C The metalliferous oxide materials ordinarily comprise a blend of two or more metal oxide containing ores to provide between 10% and 35% iron oxide content by weight of the oxide material blend. The chlorination step chlorinates at least a portion of the iron values in the oxide material blend while the heat combusts at least a portion of the carbon to produce an effluent stream containing vaporous iron chloride and a quantity of blow-over carbon along with combustion gases. The vaporous iron chloride is condensed and removed from the effluent stream along with blow-over carbon particles to provide a residue wherein the quantity of condensed iron chloride is controlled relative to the quantity of blow-over carbon. In this regard, the relative quantities of condensed iron chloride and blow-over carbon are controlled by controlling the iron oxide content between 10% and 35% in the starting blend of metal oxide containing ores. Thus, the iron oxide content in the starting blend of oxide material is controlled to produce certain quantities of iron chloride and blow-over carbon as residues from the chlorination step. In accordance with this invention, the residues contain a quantity of blow-over carbon in combination with a quantity of condensed iron chloride in a weight ratio of 1 to 3 parts of blow-over carbon to 1 to 14 parts of condensed iron chloride (including minor amounts of other oxidizable metal chlorides). On a weight-basis, the content of blow-over carbon in the iron chloride condensate is between about 7.5% and 20% blow-over carbon based on the weight of blow-over carbon plus iron chloride. The quantity of condensed iron chloride along with the given quantity of blow-over carbon is then reheated in a recycle combustion step to an elevated temperature above 500°C. whereby the carbon and iron chloride react with excess oxygen to produce chlorine gas, carbon monoxide or dioxide gas, and iron oxide solids in gaseous stream containing between 30% and 50% by volume chlorine gas. This gaseous stream can be recycled to the initial chlorination step in the process. The excess oxygen in the recycle combustion step preferably is between 5% and 75% beyond the equivalents required to combust the carbon and react with the oxidizable chlorides. In this regard, the quantity of blow-over carbon combines with the oxygen content of the iron and other metal oxides to provide reaction heat in the recycle combustion step. The condensed iron chloride containing blow-over carbon can be heated in the recycled combustion step in a fluidized bed of inert materials into which the oxygen containing gas is introduced. The fluidized bed can be preheated to above 500°C. up to about 1050°C. for the recycle combustion step and regeneration of chlorine. Accordingly, the quantity of iron-chloride is controlled relative to the quantity of blow-over carbon whereby the quantity of blow-over carbon in the recycle combustion step is sufficient to provide the required heat in the recycle combustion step and yet avoid undue dilution of chlorine evolved from the recycle combustion step. The concentration between 30% and 50% by volume chlorine can be directly recycled to the initial fluidized bed chlorination step. In accordance with the process of this invention, no additional source of heat is required in recycle combustion step for regenerating chlorine from the condensed iron chloride. The process of the invention will be illustrated by the following examples and experimental runs. All of these runs used apparatus as shown in the accompanying drawing. The apparatus used in the examples and experimental runs comprises a fluidised bed chlorinator unit 1 comprised a silica tube 200mm internal diameter and 3.6m long, mounted vertically in a gas fired furnace provided with means 2 to admit fluidising gas at the base and to withdraw gaseous products from the top 3 along a horizontal cooling duct 4 provided with rodding points to a cold cyclone 5, with provision 6 to discharge solids from the cyclone base and gases from its vortex finder to a scrubber (not shown) for disposal. The base of the tube is also provided with means 7 for withdrawing bed without interrupting the flow of fluidising gases and with means for measuring the temperature of the bed. The fluid bed pressure drop could be measured. Means 8 are provided for introducing at a controlled rate, mixed ore and coke conveyed in to the said fluidising gases flow fed into the furnace through means 2. The unit thus described forms a means for producing a flow of freshly made iron trichloride from ores by the total or partial chlorination of these ores, the salt being accompanied by impurities present in the ores and by blow-over particles of ore and coke. In the event that the chlorinator is acting as a total chlorinator the flow of gases to its base is substantially neat chlorine gas although lower concentrations can also be used, and the chlorides more volatile than iron trichloride which remain in the gaseous phase, which pass out of the vortex finder of the cold cyclone, and which in a full scale plant are recovered for use, are here led away to the scrubber for disposal. In the event that the chlorinator is acting as a partial chlorinator the flow of gases to its base is chlorine diluted to 30-50% with gases inert to the reaction taking place, and bed material beneficiated in substances less reactive to chlorine than iron oxide is removed from time to time via the bed removal means at the base of the unit. The gases exiting the cold cyclone in this instance are substantially inert but contain small traces of chlorine slipping past the fluid bed which are removed in the scrubber. In operation the stream containing iron trichloride falls from the base of the cold cyclone 5 via its solids removal valve being a pocket valve, star valve, or similar mechanically driven continuous valve, and into a vertical feed tube 9 (75mm i.d.) which passes the material into a chlorine regenerator 10 now described. The experimental chlorine regenerator unit 10 is constructed of a high nickel alloy (Nimonic or Inconel) tube 180mm internal diameter 2.4m long mounting this vertically in a gas fired furnace and provided with means to admit fluidising gas at the base 11, and to withdraw gaseous products from the top along a horizontal cooling tube 12 provided with rodding points to a cold cyclone 13, with provision 14 to discharge solids from the cyclone base and provision 15 to release gases from its vortex finder to a scrubber (not shown) for disposal. The base of the tube is provided with means 16 for withdrawing bed without interrupting the flow of fluidising gases and with means for measuring the temperature of the bed. The base of the unit is provided with an insert 17 also of high nickel alloy, 125mm internal diameter and 450mm in length mounted vertically so as to form a fluid bed of this diameter within the unit thus restricting the volume flow rate of gases needed to fluidise the bed. The vertical feed tube 9 (75mm i.d.) terminates 100mm above this insert 17, and on oxygen gas inlet 18 to the nickel alloy tube is disposed 1100mm above the insert 17. The fluid bed pressure drop can be measured. In practice the annular space between the insert 17 and the reactor 10 vessel was allowed to fill with bed material, unfluidised, the pressure drop data providing data on the bed height to accomplish this initially and to allow the bed to be run at the top of the insert thenceforward. Materials, fine sand and coke, needed to initially form this bed and to replenish the bed withdrawn from the base of the unit were added from a hopper into the chlorinator cold cyclone whence they descended via the mechanical valve and feed tube to the regenerator fluid bed. The materials used in the Examples and experimental runs are described with respect to titaniferous ores but it is to be noted that the invention also applies to other ores e.g. aluminiferous ores. Ilmenite - 55% TiO2 West Australian ilmenite having a particle size distribution spreading from 90 micrometers to 220 micrometers or similar with weight mean size 170 micrometers or similar. Slag - 85% TiO2 S. African slag of a particle size range of 100 micrometers to 500 micrometers or similar, weight mean size 230 micrometers or similar. Petroleum Coke A - Substantially pure carbon, c.99% and a typical particle size 90 micrometers to 2000 micrometers, being ground coke, and containing approx. 10% w/w material finer than 200 micrometers. Petroleum Coke B - Substantially pure carbon, c.99%, and of typical particle size 100 micrometers to 3500 micrometers, being ground coke, and containing approx. 4% material finer than 200 microns. A and B purchasable from Conoco or PMC. Petroleum Coke C - Substantially pure carbon, c.99%, and of typical particle size 500 micrometers to 4000 micrometers, being ground coke, and with a weight mean size of 1500 micrometers. C purchasable from Great Lakes Carbon. Experimental runs will now be described which do not fall within the invention. Experimental Run 1 A fluid bed of ilmenite and coke B was previously chlorinated and this bed was used to form the starting bed in the chlorinator, being approx. 80% w/w ore sand and 20% w/w coke, being 1 metre deep. A selective chlorination was then carried out. The bed was heated by means of the furnace to 950°C. whilst fluidised with nitrogen and then the gases were changed, being 60 l/min chlorine, 15 l/min air, and 70 l/min nitrogen, the air being adjusted so that the bed temperature ran at 950-1000°C. with the furnace temperature also being 950-1000°C., meanwhile feeding 3.2 kg of ilmenite along with 0.8 kg of coke B, evenly every 10 minutes. Under these conditions c.2% chlorine slippage occurs and the iron chloride formed is iron trichloride. Slippage at 2% is controllable by altering the bed depth to suit using the pressure drop as an indicator and removing bed materials (beneficiated ilmenite and coke) at a greater or a lower rate of removal to diminish or increase the bed depth, the Cl₂ slippage being measured ex cyclone by means of a gas chromatograph. Iron trichloride etc and blow-over materials condense in the cooling duct and are recovered in the cyclone, falling through the mechanical valve and down the feed tube. A fluid bed of sand and the same coke was established in the chlorine regenerator also at 950-1000°C. with the furnace temperature being at 950-1000°C. and fluidised with 45 l/min of 0₂/N₂ mixture, the proportions of which can be varied to give control of the fluid bed temperature. Oxygen was also added via the oxygen addition tube 1m above the base of the feed tube in the regenerator, the quantity of this was controlled to give a Cl₂/O₂ molar ratio of about 10/1 in the exit gas as measured by gas chromatograph. In this case typically 35% Cl₂ v/v in the product was found and 20 l/min of 02 was required. Under these conditions with a low O₂/Cl₂ molar ratio an excess of iron trichloride is present in the system condensing in the cyclone of the second unit and available for recycle to the unit in order to achieve substantially 100% conversion efficiency overall. Running as above it is found that unless additional coke is added to the fluid bed of the second unit, eventually it is found to be impossible to control the temperature within the second unit, as insufficient carbon is coming forward from the first unit to sustain it. Adding such coke, however, is a possible means of running the unit although not within the scope of the invention at present disclosed. Experimental Run 2 In this, the material added to the first unit is 10 kg slag and 2.5 kg coke B per 10 minutes, all other quantities being the same. In this instance it is found that it is not possible to control the unit, as it is not possible to obtain a Cl₂/O₂ molar ratio of 10:1 with a Cl₂ concentration above 25% v/v as a large excess of coke is coming forward from the first unit and with which the oxygen flows preferentially react, diluting the Cl₂ in the product gas and giving an unwanted rise in temperature in the second unit so as to put in jeopardy the life of the equipment. The following examples illustrate the process of the invention. Example 1 Equal parts by weight of the ilmenite and the slag were fed to the unit at the rate of 4.8 kg mixed ore with 1.2 kg coke B fed evenly every 10 minutes. In this instance it is found possible to achieve 35% Cl₂ v/v with Cl₂/O₂ molar ratio of 10:1 without additional coke being added and with steady operating temperatures being obtained. Example 2 West Australian ilmenite was fed at 3.2 kg every 10 minutes to the first rig as before, but, instead of also feeding 0.8 kg of coke B every 10 minutes, a mixture of coke A and coke C was fed so that while 0.8 kg of the mixture were fed every 10 minutes the proportions of the mixture varied so that the run could be sustained without separately adding coke to the second unit. It is found that adding coke C only in minor amounts effected a reduction in the coke blowing over from the first unit to the second unit and coke A which is a cheap and economical source of supply is used almost exclusively.

Claims: A process for treating an iron-containing metalliferous oxidic material which comprises chlorinating the oxidic material in a fluidized bed chlorinator unit with a chlorine-containing gas in the presence of an excess of carbon at a temperature of 500 - 1050 o C to chlorinate said metal oxide material including at least a portion of said iron oxide, and to combust a portion of the carbon and regenerating chlorine from the metal chloride by reaction with an oxygen-containing gas, characterised in that: (a) an effluent stream containing vaporous iron chloride and blow over carbon is removed from the chlorinator unit; (b) the weight ratio of the iron oxide in the metalliferous oxidic material to the carbon is adjusted so that the effluent stream from the chlorinator unit contains about 1 to 3 parts by weight of blow-over carbon to 1 to 14 parts by weight of metal chlorides (including iron chloride); (c) the iron chloride and blow-over carbon are removed from the effluent stream from the chlorinator unit; and (d) the removed iron chloride and blow-over carbon are fed to a chlorine regenerator where they are reacted with an oxygen-containing gas that provides an excess of oxygen for combustion of the blow-over carbon and oxidation of at least a portion of the metal chlorides to produce chlorine gas for recycling to the chlorination step. A process according to Claim 1, characterized in that the regenerating step is effected without the addition of carbon beyond the blow-over carbon. A process according to either of the preceding claims, characterized in that the concentration of recycled chlorine gas to the blend chlorination step is between about 30% and 50% by volume. A process according to any one of the preceding claims, characterized in that at least one of the blended metal oxide materials is a titaniferous material. A process according to claim 4, characterized in that the blended metal oxide materials comprise ilmenite and rutile ores and optionally rutile slag. A process according to any one of claims 1 - 3, characterized in that the blended metal oxide material comprises bauxite. A process according to any one of claims 1 - 3, characterized in that one of the blended metal oxide materials comprises chromite, wolframite, scheelite, tantalite or columbite. A process according to any one of the preceding claims, characterized in that the blended oxide material contains between about 10% and 35% by weight iron oxide. A process according to claim 4 or 5, characterized in that the titanium oxide content is between 70% and 85% by weight. A process according to any one of the preceding claims, characterized in that the chlorination process is a total chlorination process. A process according to any one claims 1 - 9, characterized in that the chlorination process is a partial chlorination process. A process according to any one of the preceding claims, characterized in that the effluent stream from the chlorinator unit comprising vaporous metal chlorides including iron chlorides is condensed to remove iron chlorides from the effluent stream along with said blow-over carbon. A process according to claim 12, characterized in that the content of carbon in the iron chloride condensate is between 7.5% and 20% by weight based on the condensed iron chlorides and the blow-over carbon. A process according to any one of the preceding claims, characterized in that the excess oxygen in the regeneration step is between 5% and 50% excess required to combust the blow-over carbon.

Inventors: ROBINSON, MICHAEL
Applicants: SCM CHEMICALS LIMITED
Application year: 1985
Main classification: C01B7
IPC codes: C22B1, C01B7, C01G49