US3870506A - Beneficiation of ores - Google Patents

Abstract

A method for the beneficiation of an ore containing titanium and iron oxides to produce a beneficiate containing a reduced proportion of iron oxide, which comprises forming a mixture containing the ore and carbon, the carbon content of such mixture being in the range 20 to 40% by weight, and treating such mixture in a fluidized bed reactor at a temperature in the range 800*1000*C with a treatment gas which comprises 20 to 50% by volume of chlorine and 0 to 10% of oxygen.

Description

United States Patent [191 Robinson et al.

[ BENEFlClATlON OF ORES [75] Inventors: Michael Robinson, Grimsby; Harry Brian Wilson, North Thoresby; David Antony Gray, Grimsby, all of England [73] Assignee: Laporte Industries Limited, London,

England [22] Filed: Jan. 24, 1972 [21] Appl. No.: 220,243

[30] Foreign Application Priority Data Jan. 27, 1971 Great Britain 03241/71 [52] US. Cl. 75/1, 423/75 [51] Int. Cl C22b 1/00 [58] Field of Search 75/1, 1 T, 112; 423/75, 423/149 [56] References Cited UNITED STATES PATENTS l2/l939 Muskat et al. 423/75 Mar. 11, 1975 2,l84,885 l2/l939 Muskat et al. 423/75 2,852,362 9/1958 Daubenspeck et al. r. 75/2 2,933,373 4/l960 Love et a1 75/l Primary E xaminerAnth0ny Skapars [57] ABSTRACT A method for the beneficiation of an ore containing titanium and iron oxides to produce a beneficiate containing a reduced proportion of iron oxide, which comprises forming a mixture containing the ore and carbon, the carbon content of such mixture being in the range 20 to 40% by weight, and treating such mix ture in a fluidized bed reactor at a temperature in the range 800-1000C with a treatment gas which comprises 20 to 50% by volume of chlorine and O to 10% of oxygen.

10 Claims, 4 Drawing Figures PATENTED NARI 1 I975 sum 1 or z PATENTEU MRI 1 5 SHEET 2 OF 2 BENEFICIATION OF ORES The present invention relates to the beneficiation of ores and more particularly relates to the beneficiation of ores which contain titanium and iron values. The most common of such ores is ilmenite which contains titanium and iron oxide. If this ore is to be used in the manufacture of titanium tetrachloride, which is an intermediate in metal or titanium dioxide pigment production, then it is desirable to benftciate the ore and remove at least a proportion of the iron content whilst substantially not removing any of the titanium content.

Intheory such beneficiation can be effected by controlled chlorination of the ore under such conditions that the iron content is converted to iron chloride whilst the titanium content is unaffected; Unfortunately however it is difficult to control the reaction in such a way that this is achieved without either substantial loss of the titanium content or insufficient removal of the iron content.

Prior proposals to this end have been made in U.S. Pat. Nos. 2,184,884 and 2,184,885 (which correspond to British Pat. Nos. 533,378 and 533,379). The essential disclosure in U.S. Pat. No. 2,184,884 is that using a chlorine-air mixture as the reactant gas the proportion of iron and titanium removed from the ore depends upon the percentage of carbon in the reactant mass. Although the specification states that up to 20% by weight of carbon may be used, the detailed disclosure of the drawings makes it quite clear that more than 15% would be grossly uneconomic owing to high loss of titanium from the ore.

In U.S. Pat. No. 2,184,885, on the other hand, no oxygen is present in the reactant gas and although a diluent is mentioned in the specification no details are given as to the proportion of such diluent. Moreover, although the specification states that up to 15% by weight of carbon can be used, the detailed disclosure makes it clear that it is uneconomic to use more than about 5% of carbon.

in both these prior proposals control of the selectivity of the chlorination is effected by the control of the carbon content ofthe reactant mixture and whilst this may be relatively easy using briqueted carbon and ore in a shaft furnace as described therein, it is not practical in other forms of furnace now preferred in the industry e.g. fluidized bed.

We have now discovered that using a fluidized bed reactor and an excess of carbon over that considered practicable in the prior proposals, control can be effected by varying the effective partial pressure of the chlorine. Such a procedure is considerably easier to operate and control than the prior proposals and gives satisfactory results.

Thus according to the present invention there is provided a method for the beneficiation of an ore containing titanium and iron oxides to produce a beneficiate containing a reduced proportion of iron oxide, which comprises forming a mixture containing the ore and carbon, the carbon content of such mixture being in the range 20 to 40% by weight, and treating such mixture in a fluidized bed reactor at a temperature in the range 800-l000C with a treatment gas which comprises 20 to 50% by volume of chlorine and 0 to by volume of oxygen.

it should be noted that in the present invention it is essential to use a fluidized bed reactor and therefore it is necessary to use a loose and preferably welldispersed mixture of ore and carbon as the charge to the reactor. It will be noted that the minimum carbon content that we propose is 20% by weight and is therefore greater than that of the prior proposals. However this carbon content is not critical, provided that the content lies within the range specified and variations within this range do not materially affect the degree of beneficiation. it should further be pointed out that this range of carbon contents is considerably in excess of that required in the reaction and the product beneficiate is mixed with free carbon. Subsequently the product beneficiate will normally be mixed with excess carbon and preferably fed directly to a conventional fluid bed chlorination system to produce titanium tetrachloride.

The beneficiation reaction is temperature sensitive, but control is effected by the proportion of chlorine in the reactant gas. Similarly control of this proportion will affect the degree of removal of iron and also the degree of removal of titanium.

It will be appreciated that, if we neglect the carbon mixed with the beneficiate, it is possible to operate the process in such a way that the beneficiate contains any required proportion of titanium and any required proportion of iron. However for practical purposes it is necessary that the beneficiate should contain in excess of titanium dioxide and less than about 5% of iron, the remainder being oxides of other elements such as metals, silicon or phosphorus. Moreover for efficient operation it is necessary at least of the titanium dioxide originally present in the ore should be present in the beneficiate. Thus it will be understood that it is uneconomic to produce a beneficiate which contains, for example, in excess of 99% titanium dioxide and no iron, if the recovery of titanium dioxide is, for example, only 50% of that originally present in the ore.

Considered as an overall process including heat losses from the system, the reaction of chlorine with titanium ores is endothermic which means that heat must be supplied to keep the reaction going. As is well known this heat can be supplied from external sources either by direct heating of the reactor vessel or by-preheating of the reactant gas or charge, However, the preferred method of providing the necessary heat is by controlled reaction of the carbon content of the charge with oxygen. In accordance with the invention up to 10% by volume of the treatment gas can be oxygen and depending upon the other conditions this may or may not be sufficient to maintain the reaction as thermally self-sustaining. If this proportion of oxygen is insufficient, then additional oxygen may be injected into the reactor but this must be done at such a location and in such a way that the products of the reaction when mixed with the treatment gas do not take the total reactant gas composition outside the limits specified.

Thus according to a further feature of the invention, the process comprises separately injecting a heating gas into the reactor at a location below the point of injection of the treatment gas, such heating gas containing a proportion of oxygen such that the process is thermally self-sustaining and the point of injection being such that at the level of injection of the treatment gas the oxygen content of the combined gas flows is less than 10% by volume.

As has been indicated above it is necessary to overcome the endothermicity of the overall selective chlori- 3 nation reaction by supplying heat to the system. In order to minimize the amount of heat required to be added, several factors can be manipulated. Thus the reactor vessel may be located withina furnace and may be preheated by means of this furnace before passing any reactant gas into the system and it of course follows that the charge within the reactor vessel will'be preheated at the same time. A convenient temperature to which the reactor vessel is preheated is within the range from 850 to 950C and any further solid material supplied to the reactor vessel may conveniently be preheated to this temperature. It may also be desirable to preheat the reactant gases. The diluent gas is conveniently chosen so that it has a low specific heat and in consequence we prefer to use nitrogen rich mixtures rather than carbon dioxide rich mixtures as may be obtained for example from the recycle of exhaust gases produced in the reactor vessel. The volume of diluent gas required will of course depend on the desired partial pressure of chlorine but obviously the higher the proportion of chlorine the lower the proportion of diluent gas required and consequently the lower the amount of heat which has to be supplied to the diluent gas. The invention is particularly suited to the preferred range of 30 to 45% by volume of chlorine within the treatment gas.

To assist in heat economy it is convenient to preheat the treatment gas by extracting the heat from the solid product i,e. beneficiate coke mixture as by means of a counter current exchanger or contacting device. The fresh charge is conveniently pre-heated in a fluid bed contacting device in which some of the coke is combusted using air, additional coke being added to the feed for this purpose. It will be apparent that the need for heat economy is particularly important when a continuous process is being used.

The quantitative chemical reactions which take place in the reactor vessel are not known but although we do not wish to limit our invention by discussing what we believe to be the theory of reaction, we believe that the selectivity of attack affording preferential attack on the iron content of the ore is basically due to the fact that chlorination of iron values results in an increase in the volume of gaseous components whilst chlorination of titanium dioxide does not result in any increase in volume.

We have found, experimentally, that the relative proportions of ferrous chloride and ferric chloride depend upon the relative amount of gaseous chlorine and iron in the bed. We prefer to operate in such a way that the predominant product is ferrous chloride which, since it is volatile at the reaction temperature employed, is rapidly car'ried away from the system by the outlet gases. This lower chloride of iron is surprisingly obtained without prior reduction of the ore by using chlorine diluted to the extent specified herein. It will be appreciated that when the predominant product is ferrous chloride then the chlorine content of the'outlet gases will be small and perhaps undetectably small. Indeed one of the major advantages of operating so that ferrous chloride is the predominant product is the saving in the amount chlorine used.

The amount of oxygen in the reactant gases is normally controlled to be sufficient to ensure that the oxides of carbon are present mainly as carbon dioxide which is a preferable effluent gas to carbon monoxide 4 and which moreover makes maximum use of the carbon content of the charge for generating heat.

In order that the present invention may be more readily understood the same will now be described by way of example and with reference to the accompanying drawings wherein FIG. 1 is a diagrammatic representation of a first embodiment of reactor vessel,

FIG. 2 is a diagrammatic representation of a second embodiment of reactor vessel,

FIG. 3 is a graph showing TiO recovery plotted against chlorine content and FIG. 4 is a graph showing iron content of beneficiate as against chlorine content.

Referring now to the drawings and to FIG. 1 in particular the reactant vessel 10 comprises a generally cylindrical body having walls 11 made of a material which is resistant to heat and to chlorine such as, for example, fused silica. The reactor vessel 10 is located in a furnace (not shown). The base of the reactor vessel is closed by a perforated base plate 12 below which is a plenum chamber 13 with a gas inlet 14 for the treatment gas. A gas off-take 15 is provided near the top of the vessel. An inlet 16 is provided near the top of the reactor vessel 10 for the charge of ore and coke andan outlet 17 is provided near the base of the vessel for the product beneficiate.

Very conveniently the charge comprises by weight of ilmenite ore for example West Australian ilmenite which analyzes at 54.5% TiO and 30% Fe present as oxides together with 25% by weight of coke. Fludization of the bed of coke and ore, the components of the charge, is possible without grinding the mixture, the ore being in its natural size range of -l80u.

In use the charge is placed in the reactor vessel and is fluidized by a flow of nitrogen or other inert gases whilst the reactor vessel and charge are heated to a temperature of approximately 900C by means of the said furnace. When the reactor and its contents have reached the temperature of 900C the fluidizing gas is replaced by a treatment gas comprising 42% by volume of chlorine and 10% by volume of oxygen, the remainder being nitrogen and other inert gases. It is found that a time of between two and three hours is necessary for substantially complete reaction and at the end of this time the chlorine and oxygen feed are switched off and the bed cooled whilst the flow of inert gas was maintained. At the end of the cooling period the bed contents were analyzed as comprising coke with beneficiate of composition 92.7% by weight TiO and 1.4% Fe O The recovery of TiO was 96%. When the unit is operated continuously the ore and coke mixture is continuously added through a feeding device located at the inlet 16 and the beneficiated ore is withdrawn at frequent intervals through the outlet 17 with the excess coke. I

This apparatus may easily be adapted to function continuously by using as the initial bed a mixture of 80% by weight beneficiate and 20% by weight coke in which the beneficiate analyzes at 93.5% by weight of titanium dioxide. At 900C chlorine is admitted at the base of the reactor to give a 40% v/v concentration on the inert fluidizing gas stream while ilmenite ore and coke in the ratio of 80% to 20% by weight resepectively are continuously fed into the system. As shown'in Table I it can be seen that the beneficiate recovered from outlet 17 over a period of 4 hours has a high titanium diox- Table I Time (hours) %(by weight) of TiO in recovered beneficiate bum-.

In this steady operation no chlorine was detected in the efflux gases and analyses of samples of it showed that substantially all the iron chloride was ferrous chloride.

It should be remarked that the ore contains a certain measure of impurities some of which will be removed during this chlorination process but some of which will go through to the beneficiate. It is necessary for economical working to get a recovery of better than 95% of TiO that is to say not more than of the TiO should escape throught the gas outlet. For satisfactory working the beneficiate should analyze at better than 90% TiO or seen from another point of view should contain less than about 5% of Fe O It was found using the apparatus of FIG. 1 that it was difficult to obtain a satisfactory thermal balance without introducing an excessive amount of oxygen. The apparatus of FIG. 2 was therefore devised.

In the apparatus of FIG. 2 the reactor vessel is again of generally cylindrical form and is made of fused silica. It comprises an upper section 21 and a lower section 22 of smaller diameter than the portion 21. The base of the section 22 is provided with a perforated base plate 23 and a gas plenum chamber 24 with an inlet 25 for gases. At the junction between the portions 21 and 22 there is a generally annular portion 26 provided with a plurality of gas inlets 27.

The reactor vessel 20 is also provided with a gas offtake 28 and inlet 29 for the charge and an outlet 30 for the beneficiate. As before the reactor vessel is located in a furnace.

In one experiment using the apparatus of FIG. 2, a charge of 65 lbs of West Australian ilmenite was placed in the vessel together with approximately 22 lbs of coke. The reactor vessel was heated up to 900C in the furnace using a fluidizing flow of nitrogen and when it reached this temperature oxygen was admitted through the gas inlet 25 to the extent of 20% by volume of the fluidizing gas. This flow of oxygen was calculated to provide a steady temperature and at least 50% of the oxygen was consumed before reaching the upper section 21 of the reactor vessel. Chlorine was admitted through the gas inlet 27 to the extent of 28% by volume of the total gas flow. After a sufficient reaction period (approximately 2 hours l0 minutes) the chlorine and oxygen flows were stopped and the bed contents cooled and recovered. The beneficiate analyzed at 94.1% Ti0 and 1% Fe O with the recovery of TiO being in excess of 95%.

In order to demonstrate the criticality of the chlorine content of the treatment gas a series of experiments were carried out at-various volume percentages of chlorine and the results are plotted in FIGS. 3 and 4. In both FIGS. 3 and 4 the minimum recovery of Ti0 was 95% by weight, this being the minimum recovery which is economically satisfactory. It is seen quite clearly in FIG. 3 that the purity of the beneficiate remains better than TiO up to about 45% by volume of chlorine in the treatment gas. The reason for the sudden fall in purity of the beneficiate is clearly apparent from FIG. 4 where up to slightly more than 45% by volume of chlorine in the treatment gas gives an iron content of less than 4% but with the iron content increasing rapidly with higher percentages of chlorine in the treatment gas.

It will be apparent that in all cases and in contrast to the prior proposals hereinbefore mentioned, the charge to the reactor vessel contains in excess of 20% by weight of carbon and it is also clear that under the conditions of this invention the critical factor is the chlorine concentration in the treatment gas and not the carbon content of the charge. It should however be emphasised again that the carbon content must be in excess of that necessary for the reaction. The beneficiate is therefore mixed with carbon.

It will be appreciated that control of the chlorine content of the treatment gas is readily effected by controlling the amount of chlorine and/or oxygen and for diluent gases fed to the reactor. The effect of the control can be measured by monitoring the off gases for chlorine, ferrous/ferric chloride titanium tetrachloride and carbon oxides. It will be apparent that control of the reaction is much easier and more effective than by control of the carbon content.

We claim:

1. In a method for the beneficiation of an ore con taining titanium dioxide and a mixture of iron oxides to produce a beneficiate containing a reduced proportion of iron oxides, wherein the improvement comprises forming a mixture of the ore containing the said mixture of iron oxides and carbon, the carbon content of the mixture being in the range of from 20 to 40% by weight and said carbon content being in excess of that necessary for reaction, enclosing the mixture in a fluidized bed reactor, treating the mixture in a fluidized bed reactor at a temperature in the range of 800 to 1,000C. with a treatment gas essentially consisting of 20 to 50% by volume of chlorine, 0 to 10% by volume of oxygen and a diluent gas whereby control of the beneficiation reaction is effected by the proportion of chlorine in the reactant gas, and recovering the resulting beneficiate from the reactor.

2. A method according to claim 1 which includes separately injecting a heating gas into the reactor at a location below the point of injection of the treatment gas, such heating gas containing a proportion of oxygen such that the process is self-sustaining and the point of injection being such that at the level of injection of the treatment gas the oxygen content of the combined gas flows is less than 10% by volume.

3. A method as claimed in claim 1 in which the reactor is located in a furnace.

4. A method as claimed in claim 1 in which the reactor is pre-heated to a temperature in the range from 850 to 950C.

5. A method as claimed in claim 1 in which the treatment gas includes nitrogen.

6. A method as claimed in claim 1 in which the treatment gas comprises 30 to 45% by volume of chlorine.

7. A method as claimed in claim 1 in which the ferrous chloride is produced.

8. A method as claimed in claim 1 in which substantially no chlorine is detectable in the outlet gases.

9. A method as claimed in claim 1 wherein the fluidized bed reactor is operated continuously.

10. A method as claimed in claim 1 wherein the diluent gas is a nitrogen rich mixture.

Claims (10)

1. IN A METHOD FOR THE BENEFICATION OF AN ORE CONTAINING TITANIUM DIOXIDE AND A MIXTURE OF IRON OXIDES TO PRODUCE A BENEFICATE CONTAINING A REDUCED PROPORTION OF IRON OXIDES, WHEREIN THE IMPROVEMENT COMPRISES FORMING A MIXTURE OF THE ORE CONTAINING THE SAID MIXTURE OF IRON OXIDES AND CARBON, THE CARBON CONTENT OF THE MIXTURE BEING IN THE RANGE OF FROM 20 TO 40% BY WEIGHT AND SAID CARBON CONTENT BEING IN EXCESS OF THAT NECESSARY FOR REACTION, ENCLOSING THE MIXTURE IN A FLUIDIZED BED RECTOR, TREATING THE MIXTURE IN A FLUIDIZED BED REACTOR AT A TEMPERATURE IN THE RANGE OF 800* TO 1,000*C. WITH A TREATING GAS ESSENTIALLY CONSISTING OF 20 T0 50% BY VOLUME OF CHLORINE, 0 TO 10% BY VOLUME OF OXYGEN AND A SILUENT GAS WHEREBY CONTROL OF THE BENEFICATION REACTION IS EFFECTED BY THE PROPORTION OF CHLORINE IN THE REACTANT GAS, AND RECOVERING THE RESULTING BENEFICATE FROM THE REACTOR.

1. In a method for the beneficiation of an ore containing titanium dioxide and a mixture of iron oxides to produce a beneficiate containing a reduced proportion of iron oxides, wherein the improvement comprises forming a mixture of the ore containing the said mixture of iron oxides and carbon, the carbon content of the mixture being in the range of from 20 to 40% by weight and said carbon content being in excess of that necessary for reaction, enclosing the mixture in a fluidized bed reactor, treating the mixture in a fluidized bed reactor at a temperature in the range of 800* to 1,000*C. with a treatment gas essentially consisting of 20 to 50% by volume of chlorine, 0 to 10% by volume of oxygen and a diluent gas whereby control of the beneficiation reaction is effected by the proportion of chlorine in the reactant gas, and recovering the resulting beneficiate from the reactor.

2. A method according to claim 1 which includes separately injecting a heating gas into the reactor at a location below the point of injection of the treatment gas, such heating gas containing a proportion of oxygen such that the process is self-sustaining and the point of injection being such that at the level of injection of the treatment gas the oxygen content of the combined gas flows is less than 10% by volume.

3. A method as claimed in claim 1 in which the reactor is located in a furnace.

4. A method as claimed in claim 1 in which the reactor is pre-heated to a temperature in the range from 850* to 950*C.

5. A method as claimed in claim 1 in which the treatment gas includes nitrogen.

6. A method as claimed in claim 1 in which the treatment gas comprises 30 to 45% by volume of chlorine.

7. A method as claimed in claim 1 in which the ferrous chloride is produced.

8. A method as claimed in claim 1 in which substantially no chlorine is detectable in the outlet gases.

9. A method as claimed in claim 1 wherein the fluidized bed reactor is operated continuously.

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