WO2002061158A1

WO2002061158A1 - Fluidized bed chloride method for obtaining metal oxide concentrate, especially titanium dioxide

Info

Publication number: WO2002061158A1
Application number: PCT/EP2002/000841
Authority: WO
Inventors: Wendell E. Dunn; Reinhard Marx
Original assignee: Colour Ltd.
Priority date: 2001-01-30
Filing date: 2002-01-25
Publication date: 2002-08-08
Also published as: CN1273627C; DE10103977C1; AU2002226423B2; CN1489635A

Abstract

Disclosed is a method for obtaining metal oxide concentrate from an ore containing metal and iron. The ore is subjected to the effects of chlorine in a fluidized bed reactor in the presence of carbon and optionally other additives at a temperature of over 900 DEG C. The reaction is carried out in batches in the fluidized bed reactor and a gas containing oxygen, and chlorine are fed to the fluidized bed reactor as a fluidizing gas. More than 5 wt. % excess carbon is present, in relation to the required amount for the reaction, in order to remove the iron as chloride. A product enriched with metal oxide is removed. A valuable reaction product can thus be obtained by the inventive method in a simple, economical way.

Description

FLUID BED CHLORIDE METHOD FOR PRODUCING METAL OXIDE CONCENTRATE, ESPECIALLY ERE TITANIUM DIOXIDE

The invention relates to a process for obtaining metal oxide concentrate from an ore containing the corresponding metal and iron, the ore being exposed to the action of chlorine in a fluidized bed reactor in the presence of carbon and optionally further additives at a temperature of more than 900 ° C. ,

The most commonly used raw material for the extraction of titanium dioxide pigment is mineral ilmenite. This is essentially a chemical compound of TiO ₂ and FeO with Fe ₂ O ₃ components, the titanium dioxide content of which is between 30 and 70%. Ilmenite also contains various impurities in the molecular lattice, plus a small proportion of gangue minerals. Commercial titanium dioxide is currently obtained using either the sulfate or chloride process. It is available as anatase or rutile type, which differ in the crystal structure. The operators of the sulfate process alone can currently produce anatase. The rutile, which is thermodynamically more stable, can be obtained by both methods. More than 56% of the world market (US $ 8 billion / a) requirement for titanium dioxide is covered by plants that operate on the basis of the chloride process.

Over the past 20 years, the net increase in titanium dioxide capacity has been largely due to the chloride process. The iron of the starting material is removed as iron chloride. The large amount of iron chloride produced poses waste problems. Therefore, most manufacturers of titanium dioxide require a raw material with a minimum titanium dioxide content of around 85%. Natural ilmenite, the titanium dioxide content of which has been increased, is known as synthetic rutile. This is usually obtained from an ilmenite that contains 45 to 60% titanium dioxide. The higher the content of titanium dioxide in the starting material, the lower the proportion of undesirable waste. The average titanium The dioxide content of the starting material in the chloride process has been continuously increased due to the stricter requirements for environmental protection. In the past, efforts have therefore always been made to meet these requirements.

Previously known processes for the production of an artificial or "synthetic" rutile, which separate the impurities of the precursors, essentially ilmenites, by chlorination, require several fluid bed reactors which operate continuously and are connected in series. There are different exhaust gas flows that are difficult to clean. In the last stage in particular there are noticeable losses of titanium dioxide, which is also volatilized as TiCk. A corresponding method is shown in US 4,332,615 (from 1982). A titanium-containing ore is then worked up to essentially pure titanium dioxide, which is used for the production of pigments by continuously chlorinating the ore in a first fluidized bed reactor in the presence of carbon and at high temperature until the iron content has reached approximately 3.5% by weight. % is reduced. The resulting mixture is fed continuously to a second reactor in which the iron content can be reduced to about 0.1 to 1% by weight. Continuous processes for the extraction of titanium dioxide from titanium-containing ores are also described in US Pat. No. 4,211,755 (from 1980) and US Pat. No. 4,085,189 (from 1978).

It has been evident for a long time that the process for the extraction of titanium dioxide from the corresponding ores is carried out continuously from an overall point of view, although there are a number of complications when it is carried out. This applies in particular to the removal of toxic gases to remove solids and a certain loss of chlorine and titanium. In addition, a complex chain of reaction vessels must be used, often more than two chlorinators and several fluid bed separation devices. No. 3,699,206 considers it advantageous to carry out an additional treatment by alternately introducing carbon monoxide on the one hand and chlorine on the other hand into the fluidized bed reactor. It has surprisingly been found that, contrary to the prevailing technical opinion, a batch process leads to unexpected advantages, which are discussed in the following detailed description of the present invention.

The invention relates to a process for the production of metal oxide concentrate, which is characterized in that an ore containing titanium and iron is worked up, the reaction being carried out in batches in the fluidized bed reactor, an oxygen-containing gas and chlorine being fed to the fluidized bed reactor as fluidizing gas. the carbon is present in an excess of about 5% by weight in excess of the conversion amount required to remove the iron as chloride and a product enriched with titanium dioxide is removed.

It is therefore an essential feature of the present invention that the reaction is carried out in batches in a fluidized bed reactor, in which the raw material and added carbon form the solid part of the bed, and in which chlorine and an oxygen-containing gas, in particular air enriched with oxygen, are used for fluidization. be fed. By adjusting the process parameters described below, it is achieved that intermediate titanium tetrachloride is formed from rutile left in the reactor and this evaporates the impurities of the precursor as chlorides through an exchange reaction, with reduced titanium replacing the impurities in the oxide lattice.

The process according to the invention works in the manner mentioned if it is ensured that a reduction potential (= CO: CO 2 ratio) is constantly maintained by means of an excess of carbon, which enables the reduction and chlorination of rutile. Since the carbon is not only required for the chemical reaction, but also has to provide energy by combustion to CO, a large excess is required. The amount of carbon added, based on the amount of ore, must therefore be at least about 5% by weight. It is preferred if the excess is at least about 10% by weight and in particular about 20% by weight. An excess of more than about 25% by weight is very particularly preferred. An excess of about 40% by weight is generally of no benefit. AI however, higher amounts are not harmful. They only have to be separated and returned later.

The fluidized bed reactor is set up in such a way that additional carbon or ore can be metered into the running batch until the end of the process, including in the finished batch. As a result, the carbon is always available in the required amount. It may also be beneficial to add fresh ore towards the end of the reaction. The finished batch is worked up in the manner described below.

For the purposes of the invention, petroleum coke with a low ash content and a high fixed carbon content is preferably used as carbon. The particle size is preferably between about 1.5 and 4 mm, in particular between about 2 and 3 mm. A petroleum coke of the following composition is particularly suitable: fixed carbon 96 to 98%, volatile fractions 0.5 to 1%, moisture 0.1 to 0.5%, ash content 0.5%, sulfur maximum 1%. The carbon, in particular the petroleum coke, is used in the chlorination in such an excess amount that during the reaction in the fluidized bed reactor mainly iron (II) chloride and at most an insignificant amount of iron (III) chloride are formed. The process is preferably controlled so that no iron (III) chloride is removed.

Any titanium and iron-containing ores can be used within the scope of the invention. If one speaks subsequently of “titanium-containing ores”, then these should also contain other contaminating constituents, such as vanadium and chromium, in addition to titanium and iron. In this way, low-quality ores containing titanium can also be used. These include, for example, non-weathered ilmenites and weathered ilmenites, such as Orissa and even Telness, which contain magnesium, among other things. Ilmenites are preferred. The particle size of the titanium-containing ore is preferably between approximately 50 and 450 μm, in particular between approximately 70 and 350 μm and very particularly preferably between approximately 150 and 250 μm. An ilmenite, which is internationally referred to as "beach sand ilmenite", is of particular importance in the context of the invention as a starting material. This has the following typical composition: 50.2% titanium dioxide, 12.8% iron trioxide, 34.1% iron oxide, 0.6% aluminum oxide, 0.6% manganese oxide, 0.05% chromium oxide, 0.25% vanadium oxide, 0 , 6% magnesium oxide, 0.03% P2O5, 0.01% Zrθ2, 0.8% silicon dioxide and traces of rare earths. The particle size already mentioned is also preferred here. A bulk density of approximately 2.4 to 3.0 g / cm ³ , in particular approximately 2.6 to 2.8 g / cm ³ , leads to a particularly advantageous procedure and to a particularly cheap product.

To successfully carry out the method according to the invention, it is necessary to maintain a minimum temperature in the main reaction range of about 900 ° C. It is very particularly preferred that the reaction temperature is set to more than about 1000 ° C., in particular to about 1030 to 1100 ° C. The best results are achieved when the temperature in the fluidized bed is around 1040 to 1070 ° C.

The advantageous temperature conditions when carrying out the chlorination are maintained in particular by using an oxygen-containing gas, in particular an oxygen-enriched gas, in addition to the chlorine, preferably a gas of nitrogen and oxygen with a high oxygen content, in particular a mixture, as the fluidizing gas from about 90% oxygen and about 10% nitrogen. Pure oxygen can also be used. The desired reaction temperature can be set by the amount of oxygen in the fluidizing gas which is fed to the fluidized bed reactor in the lower part through a special distributor plate. The fluidizing gas can contain the chlorine necessary for chlorination. However, this can also be introduced into the system in isolation from the oxygen-containing gas.

The gas entry conditions of the fixed bed (for example entry pressure and fluidization speed) can be readily determined by a person skilled in the art. Typically, the inlet pressure is dependent on the fluid bed depth and is equal to the fluid bed pressure at the initial fluidization point plus the gas outlet pressure. Preferably the inlet pressure is maintained at at least about 50 kPa and not more than about 150 kPa. The fluidization rate also depends on the density of the material to be fluidized and is necessarily below the exit rate, which is well below the minimum flow rate that ensures the fluidization. The gas velocity in the bottom region of the fluidized bed is preferably between approximately 70 mm / s and 140 mm / s.

The main reaction is generally preceded by drying of the starting material, preferably in a fluidized bed reactor at a temperature of at least about 110.degree. The starting material is advantageously introduced in portions. At the start of the process, the temperature is generally about 600 ° C. In addition, the fluidized bed reactor can also contain unreacted ilmenite, artificial rutile and coke from a previous production cycle. The new cycle then advantageously begins with feeding the ore, preferably in portions, while maintaining the temperature at no less than about 600 ° C by fluidizing the bed with air and burning residual carbon. Additional carbon is then added. This is followed by a heating phase, the temperature preferably being set to approximately 1000 ° C., in particular to the preferred ranges mentioned. At this point, the actual chlorination begins based on the chlorine fed into the bottom area (expediently from a container with compressed liquid chlorine). The process product is transferred to a central collecting container in order to then be sent to the further processing measures, which will be discussed in the following.

When a batch has ended, the fluidized bed is expediently freed of chlorine and carbon monoxide by blowing in air and / or nitrogen and then emptied into a vigorous stream of water which serves to deter the hot material. The discharge opening is located at a height such that a sufficiently high rutile fluid bed remains in the reactor for the start of the next batch. In order to obtain a rutile of the desired purity, the quenched material must be subjected to mechanical wet processing. This is expediently carried out in three steps: sieving off coarse excess coke, separating by density on a setting stove and magnetic separation of unreacted ilmenite, recirculating the separated products, whereby they are dried beforehand. Only at the setting hearth is there a fraction with the gait of the ore, which must be discarded. The titanium dioxide content of the process product is preferably at least 96% by weight or in particular significantly higher. A typical analysis of this "rutile 96" is as follows with regard to the remaining impurities: about 0.5% by weight of aluminum oxide, about 0.1% by weight in each case of calcium oxide, magnesium oxide, vanadium oxide, chromium oxide and phosphorus pentoxide, about 0, 3% by weight of iron (IΙI) oxide, about 0.2% by weight of magnane oxide, about 0.9% by weight of silicon dioxide.

The gases leaving the fluidized bed reactor are cooled to condense the iron (II) chloride, which is separated in a cyclone. Furthermore, carbon monoxide and carbon dioxide, together with various other volatile chlorides, in particular vanadium (V) and chromium (III) chloride, are passed through a gas scrubber with the chlorides being eliminated. These can be worked up in a suitable manner. The remaining carbon monoxide can be used as a heating gas for drying measures within the process according to the invention.

Almost all of the chlorine used in the main reactor of the process according to the invention is found in the iron (II) chloride obtained. This is stored in an intermediate bunker.

A special feature of the process according to the invention is the further treatment of the separated iron (II) chloride. This is oxidized in the usual form with oxygen to form iron (III) oxide and chlorine gas, which is advantageously returned to the fluidized bed reactor during the chlorination. The oxidation reaction is carried out in a combustion chamber at a temperature of preferably about 650 to 800 ° C. Although the reaction is slightly exothermic, it can be advantageous to use a secondary heat source consisting of a carbon monoxide gas burner. The iron (III) oxide obtained is a valuable by-product. It is separated from the chlorine stream in a cyclone, rinsed with carbon dioxide and quenched with water. Due to its purity of around 95% Fe ₂ O ₃ , it can be used in a steel mill.

The essential processes of the method according to the invention in connection with the implementation in the fluidized bed reactor can be illustrated with the aid of the attached FIG. 1. An ilmenite concentrate is dried at 110 ° C in a fluid bed. The same happens with the petroleum coke used. The dried ilmenite is then introduced into the fluidized bed for chlorination, in which the temperature is above about 900 ° C. Petroleum coke is also fed to the fluidized bed reactor. The fluidizing conditions are adjusted by the addition of chlorine and air enriched with oxygen. Gaseous iron (II) chloride is removed from the fluid bed. After deposition in solid form, it is oxidized to iron (III) oxide in a facility at about 700 ° C. This is isolated and removed. The chlorine is drawn off and returned to the fluidized bed reactor. A solid mixture of unreacted ilmenite, remaining petroleum coke and the desired rutile is obtained. This is subjected to various processing measures, e.g. wet processing, sieving, treatment on a wet setting stove and magnetic separation of unreacted ilmenite. The unreacted ilmenite is returned to the fluidized bed reactor, the gait is derived and the desired rutile is dried at 110 ° C. The rutile has a titanium dioxide content of more than about 96%. It is superior to natural rutile in many ways. They are hard, non-friable, high-density particles. This leads to a minimal loss due to abrasion or carryover in the fluid bed reactor compared to e.g. a product using the chloride process. In addition, it is more reactive with chlorine than natural rutile or rutile, e.g. is obtained by the cup method. This means higher throughput for a given chlorination plant.

Of particular economic advantage in the work-up according to the invention is the recovery of the chlorine from the iron (II) chloride formed by this is reacted with oxygen to form iron (III) oxide and chlorine. In a continuous process, this is done by oxidizing gases drawn from the fluidized bed. Here, the chlorine is difficult to separate from the carbon oxides. So far, the liquefied chlorine has been separated from the low-boiling gases (carbon dioxide, carbon monoxide and nitrogen) by distillation. This requires complex compression of the mixture to liquefy the chlorine. The invention eliminates these problems. The iron (II) chloride is quickly cooled and concentrated in solid form. It can be easily separated from the gases formed. The chlorine is present in iron (II) chloride in a quasi-stable intermediate form. This can be easily oxidized with oxygen to solid iron (III) oxide, producing chlorine which can be easily recovered and fed to the chlorination stage.

There are a host of other advantages which appear when the method according to the invention is carried out: the invention thus enables easier operation while saving on components, leads to better heat transfer efficiency, good heat balance, easy regulation of the method and to use a single separate fluid bed reactor. The solids are expediently preheated in the fluidized bed reactor and remain there until the work-up is complete. After flushing out the resulting toxic gases, the solids can easily be removed. No further solid / gas isolation steps are required.

The proposal according to the invention does not produce any significant amounts of titanium tetrachloride. This precludes a significant loss of titanium. In the continuous process, the formation of titanium tetrachloride leads to a loss of titanium. Accumulated iron (III) oxide is contaminated and unusable for any other possible processing.

In the event that the titanium-containing ore used contains a noticeable amount of vanadium, especially if it is ilmenite, vanadium is removed as oxitrichloride. In the process conditions, it is a gas (boiling point 127 ° C). It goes through the stage in which the ferric chloride is condensed. Vanadium oxitrichloride that is removed can be reacted with water, resulting in non-volatile vanadium oxide or hydroxide that can be easily separated. If it is collected in large quantities, it is a valuable processing material.

The result of the process according to the invention is simple, economical and safe to operate and, moreover, it provides a valuable process product. Complicated additional measures, such as the alternating introduction of carbon monoxide and chlorine for pre-, intermediate and / or post-treatment, are not necessary.

The invention is explained in more detail below using an example.

example

In a fluidized bed reactor with an internal diameter of 2400 mm and an inside height of 2700 mm, after a batch has been emptied, a residual fluid bed of approximately 300 mm remains. It consists of a mixture of rutile and petroleum coke and is kept flowable by blowing air at a temperature of not less than 600 ° C. Before the new ore batch in a quantity of 14000 kg is fed over 35 minutes over a double rotary valve, the bed is heated up to 1050 ° C by entering the coke and supplying oxygen-enriched air. The batch requires a total of 1200 kg of petroleum coke. As soon as the specified temperature is reached and the coke is charged, the chlorine begins to be added. The chlorine is obtained from the oxidation reactor operated in parallel. The temperature is maintained by controlling the amount of oxygen. The amount of coke added causes the carbon to essentially burn to CO, which is necessary for the reduction and chlorination of the rutile. The overpressure at the bottom of the fluidized bed reactor is about 30 kPa at the start of the batch and about 50 kPa after the reactor has been filled. The entire gas flow flows through the fluidized bed at a speed of approximately 100 mm / s. The actual reaction time - heating and chlorination - is about 2.5 hours, while the cycle The time for a batch, which includes emptying and other ancillary work, should be specified at around 3.5 hours. The reaction gases (CO, CO2, N2 and volatilized chlorides) leave the reactor through an approximately 20 m high, vertical and water-cooled tube with a diameter of 350 mm. The iron (II) chloride condenses on its way through this tube and can then be separated off in a cyclone. The remaining gases then pass through a gas scrub to separate residual chlorides, especially the vanadium oxychloride, and then enter a combustion chamber in which the enthalpy of combustion of the CO gas is used for drying purposes.

The iron (II) chloride separated in the cyclone reaches an intermediate bunker and from there via a metering cellular wheel sluice into the oxidation reactor. This reactor has approximately the same dimensions as the chlorination reactor, but is connected at the bottom to a CO production plant - for example a small fluidized bed reactor in which a coke bed reacts with oxygen and carbon dioxide. The developed carbon monoxide is burned with oxygen. The heat developed is used to heat the reactor and to maintain the temperature at times when chlorine is not required. The required temperature is between 700 and 800 ° C. The iron (II) chloride is oxidized to iron (III) oxide by blowing the iron (II) chloride into the hot oxidation chamber with a stream of oxygen. The pressure of the oxygen is adjusted so that the chlorine that is formed and recycled at the bottom of the chlorination reactor still has a pressure of 50 kPa. The reaction product Fe ₂ O ₃ is separated from the chlorine stream by means of a cyclone.

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Claims

claims

1. A process for the extraction of metal oxide concentrate from an ore containing the corresponding metal and iron, the ore being exposed to the action of chlorine in a fluidized bed reactor in the presence of carbon and optionally further additives at a temperature of more than 900 ° C., thereby ge ^ indicates that an ore containing titanium and iron is worked up, the reaction being carried out in batches in the fluidized bed reactor, an oxygen-containing gas and chlorine being fed to the fluidized bed reactor as fluidizing gas, the carbon compared to the amount of reaction required to remove the iron as chloride in one Excess of more than about 5 wt .-% is present and a product enriched with titanium dioxide is removed.

2. The method according to claim 1, characterized in that the temperature in the fluidized bed is set to more than about 1000 ° C, in particular to about 1030 to 1100 ° C.

3. The method according to claim 2, characterized in that the temperature in the fluidized bed is set to about 1040 to 1070 ° C.

4. The method according to at least one of the preceding claims, characterized in that the excess of carbon is set to more than about 5 wt .-%, in particular to about 10 to 25 wt .-%.

5. The method according to at least one of the preceding claims, characterized in that the oxygen-containing gas is a mixture of nitrogen and oxygen with a high proportion of oxygen.

6. The method according to at least one of claims 1 to 4, characterized in that oxygen and chlorine are supplied as the fluidizing gas.

7. The method according to at least one of the preceding claims, characterized in that ilmenite is used as the ore containing titanium and iron.

8. The method according to claim 7, characterized in that the ilmenite has a particle size of approximately 50 to 450 μm, in particular approximately 70 to 350 μm, and / or a bulk density of approximately 2.4 to 3.0 g / cm ³ , in particular approximately 2.6 to 2.8 g / cm ³ .

9. The method according to at least one of the preceding claims, characterized in that petroleum coke, in particular low ash content and high fixed carbon content, is used as carbon.

10. The method according to claim 9, characterized in that the petroleum coke has a particle size of about 1.5 to 4 mm, in particular about 2 to 3 mm.

11. The method according to at least one of the preceding claims, characterized in that the carbon is used in such an excess that during the reaction in the fluidized bed reactor essentially iron (II) chloride and possibly only an insignificant amount of iron (III) chloride is developed.

12. The method according to at least one of the preceding claims, characterized in that the gases leaving the fluidized bed reactor are cooled to condense iron (II) chloride, which is separated off in a cyclone.

13. The method according to claim 12, characterized in that the gases remaining after separation of the iron (II) chloride, which contain carbon monoxide and carbon dioxide and other volatile chlorides, in particular vanadium and chromium chlorides, are removed and the chlorides are eliminated by a gas scrubber be performed.

14. The method according to claim 13, characterized in that the remaining carbon monoxide is used within the process as a heating gas for drying measures.

15. The method according to claim 12, characterized in that the separated iron (II) chloride is oxidized with oxygen to form iron (III) oxide and chlorine gas, which is returned to the fluidized bed reactor.

16. The method according to claim 15, characterized in that the iron (III) oxide is separated from the chlorine in a cyclone, rinsed with carbon dioxide or oxygen and quenched in water.

17. The method according to at least one of the preceding claims, characterized in that the product enriched with titanium dioxide is prepared for the isolation of the rutile by wet screening of excess carbon, separation of the gait on a setting hearth and by magnetic separation of unreacted ilmenite.

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