ZA200306982B - Process for the extracting of metal oxide concentrate. - Google Patents

Description

PCT/EP 02/00841 26.06.2003

Colour Ltd. Dr.H/gm

PROCESS FOR THE EXTRACTION OF METAL OXIDE CONCENTRATE

The invention relates to 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.

The most frequently used raw material for the extraction of titanium dioxide pigment is mineral ilmenite. The latter is essentially a chemical compound of TiO, and FeO with

Fe,O3 fractions and whose titanium dioxide content is between 30 and 70%. In the molecular lattice ilmenite also contains various impurities, together with a small amount of gangue minerals. At present commercial titanium oxide is produced either by the sulphate process or the chloride process. It is obtainable as an anatase or rutile type, which differ with regards to the crystal structure. Only the sulphate process operator can at present produce anatase. The thermodynamically more stable rutile can be produced according to both processes. More than 56% of the world market needs for titanium dioxide (8 billion

US dollars per annum) is covered by plants operating on the basis of the chloride process.

Over the last 20 years the nett rise ot titanium dioxide capacity has largely been based on the chloride process. The iron of the starting material is removed as iron chloride. The large amount of iron chloride produced gives rise to waste problems. Therefore most titanium dioxide manufacturers require a starting material with a minimum titanium dioxide content of approximately 85%. Natural ilmenite, whose titanium dioxide content has been raised, is referred to as synthetic rutile. The latter is generally extracted from an ilmenite containing 45 to 60% titanium dioxide. The higher the starting material content of titanium dioxide, the lower the proportion of undesired waste. The average titanium dioxide content of the starting material in the chloride process is continuously being raised due to the ever stricter

Nd

PY L°. 2003/6982 environmental protection requirements. Therefore efforts have always been made in the past to meet these requirements.

Known processes for the production of "synthetic" rutile, which separate by chlorination the impurities in the starting substances, essentially ilmenites, require several fluidized bed reactors, which are operated continuously and in series. This leads to different waste gas flows, which are difficult to clean. Particularly in the final stage significant titanium dioxide losses occur and co-volatilization thereof takes place as TiCls. A corresponding process 1s disclosed by the 1982 US 4,332,615. According to the latter a titanium- containing ore is processed to substantially pure titanium dioxide, which is used for the production of pigments, in that the ore is continuously chlorinated in a first fluidized bed reactor in the presence of carbon and at a high temperature until the iron content has dropped to approximately 3.5 wt.%. The mixture obtained is continuously supplied to a second reactor, where the iron content can be reduced to approximately 0.1 to 1 wt.%.

Continuous processes for the extraction of titanium dioxide from titanium-containing ores . are also described in the 1980 US 4,211,755 and 1978 US 4,085,189.

It has clearly long been expert opinion that the process for extracting titanium dioxide from the corresponding ores can only be performed continuously, although such a performance gives rise to a number of complications. This more particularly relates to the separation of toxic gases in order to remove solids, as well as a certain loss of chlorine and titanium fractions. It is also necessary to use a complex chain of reaction vessels, e.g. more than two chlorinating apparatuses and several fluidized bed separating apparatuses. US 3,699,206 considers it advantageous to carry out an additional treatment by an alternate introduction into the fluidized bed reactor of carbon monoxide on the one hand and chlorine on the other.

It has surprisingly been found that, contrary to prevailing expert opinion, a batchwise process leads to unexpected advantages as can be gathered from the following, detailed description of the present invention.

Po ~ 2003/6982

The invention relates to a process for the extraction of metal oxide concentrate, which is characterized in that an ore containing titanium and iron is processed, the reaction being performed batchwise in the fluidized bed reactor, to which are supplied as the fluidizing gas an oxygen-containing gas and chlorine, the carbon being present in an excess of more than approximately 5 wt.% compared with the necessary reaction quantity for removing the iron as chloride and a titanium dioxide-enriched product is removed.

The essential feature of the present invention is consequently that the reaction is performed batchwise in a fluidized bed reactor, in which the raw material and added carbon form the solid fraction of the bed and to which, for fluidization purposes, are supplied chlorine and an oxygen-containing gas, particularly oxygen-enriched air. By setting the process parameters described hereinafter, it is possible to achieve that in intermediate manner titanium tetrachloride is formed from the rutile left in the reactor and it volatilizes the impurities of the starting substance by an exchange reaction in the form of chlorides and reduced titanium appears in the oxide lattice in the place of the impurities. .

The process according to the invention operates in the indicated manner if it is ensured that through a carbon excess a reduction potential (= CO:CO; ratio) is constantly maintained permitting the reduction and chlorination of rutile. A high excess is necessary because carbon is not only needed for the chemical reaction, but also must supply energy by combustion to CO. The added carbon quantity, based on the ore quantity, must consequently be at least approximately 5 wt.%. Preference is given to an excess of at least approximately 10 wt.% and in particular approximately 20 wt.%. In a more particularly preferred manner use is made of an excess of more than approximately 25 wt.%. Generally no advantage results from an excess of more than approximately 40 wt.%. However, higher quantities are not harmful, it merely being necessary to subsequently reseparate and recycle them.

The fluidized bed reactor is set up in such a way that in the current charge can be dosed, as desired, further carbon or ore up to the end of the process and even into the finished charge.

Thus, carbon is always present in the necessary quantity. Towards the end of the reaction it

° £0 2003/6892 can also be advantageous to add fresh ore. The processing of the finished charge takes place in the manner described hereinafter.

For the purposes of the invention the carbon is preferably constituted by petroleum coke having a low ash content and a high fixed carbon content. The particle size is preferably between approximately 1.5 and 4 mm, particularly between approximately 2 and 3 mm. A petroleum coke with the following composition is particularly suitable: fixed carbon 96 to 98%, volatile fraction 0.5 to 1%, moisture 0.1 to 0.5%, ash content 0.5%, max sulphur 1%.

The carbon, particularly petroleum coke, is used in such an excess quantity when performing chlorination that during the reaction in the fluidized bed reactor mainly iron(II) chloride and at the most only an insignificant quantity of iron(III)-chloride is produced. The process is preferably controlled in such a way that no iron(Ill)-chloride is removed.

Random titanium and iron-containing ores can be used in the present invention. When reference is made hereinafter to "titanium-containing ores", then in addition to titanium and iron, they can also contain other contaminating constituents such as vanadium and chromium. Thus, it is also possible to use low quality, titanium-containing ores. These include e.g. unweathered ilmenites and weathered ilmenites, such as Orissa and even

Telness, which inter alia contain magnesium. Preference is given to ilmenites. The particle size of the titanium-containing ore is preferably between approximately 50 and 450 um, particularly between approximately 70 and 350 pm and in particularly preferred manner between approximately 150 and 250 um.

Within the scope of the present invention particular significance is attached to an ilmenite starting material internationally known as beach sand ilmenite. The latter has the following typical composition: 50.2% titanium dioxide, 12.8% iron trioxide, 34.1% iron oxide, 0.6% alumina, 0.6% manganese oxide, 0.05% chromium oxide, 0.25% vanadium oxide, 0.6% magnesium oxide, 0.03% P,0s, 0.01% ZrO,, 0.8% silicon dioxide and traces of rare earths.

The already mentioned particle size is preferred. A bulk density of approximately 2.4 to 3.0 g/cm’, particularly approximately 2.6 to 2.8 g/cm’ leads to a particularly advantageous process performance and to a particularly favourable product.

® t°. 2003/6982 - S

For a successful performance of the process according to the invention it is necessary to maintain a minimum temperature in the main reaction area of approximately 900°C. In particularly preferred manner the reaction temperature is more than approximately 1000°C and more particularly approximately 1030 to 1100°C. The best results are obtained if the temperature in the fluidized bed is approximately 1040 to 1070°C.

Advantageous temperature conditions when performing chlorination are in particular maintained if as the fluidizing gas use is made of an oxygen-containing gas, particularly an oxygen-enriched gas, besides chlorine, preferably a gas formed from nitrogen and oxygen with a high oxygen percentage, particularly a mixture of approximately 90% oxygen and approximately 10% nitrogen. Pure oxygen can also be used. The desired reaction temperature can be set through the oxygen quantity in the fluidizing gas, which is supplied by a special distributor plate to the lower part of the fluidized bed reactor. The fluidizing gas can contain the chlorine quantity necessary for chlorination. However, the latter can be introduced in isolation into the system and separately from the oxygen-containing gas. :

The gas entry conditions of the fluidized bed (e.g. entry pressure and fluidizing rate) can be readily determined by the expert. Typically the entry pressure is a function of the fluidized bed depth and is the same as the fluidized bed pressure at the initial fluidizing point, plus the gas exit pressure. Preferably the entry pressure is kept at a minimum of approximately 50 kPa and a maximum of 150 kPa. The fluidizing rate is also dependent on the density of the material to be fluidized and is necessarily below the exit rate, which is well below the minimum flow rate ensuring fluidization The gas rate in the hottom area of the fluidized bed is preferably between approximately 70 and 140 mm/s.

The main reaction is generally preceded by a drying of the starting material, preferably in a fluidized bed reactor at a temperature of at least 110°C. The starting material is advantageously introduced portionwise. At the start of the process the temperature is generally approximately 600°C. In addition, the fluidized bed reactor can also contain unreacted ilmenite, synthetic rutile and coke from a preceding production cycle. The new cycle then advantageously begins with the feeding in of ore, preferably in portions, whilst the temperature is kept at no less than approximately 600°C through fluidizing the bed with air and burning residual carbon. Further carbon is then added. This is followed by a heating phase, the temperature being set preferably at approximately 1000°C and in particular at the aforementioned, preferred ranges. At this time chlorination starts as a result of the chlorine introduced into the bottom area (appropriately from a vessel with compressed, liquid chlorine). The process product is transferred into a central receiving tank for supplying to the further processing measures to be described hereinafter.

When a batch is ended, the fluidized bed is freed from chlorine and carbon monoxide, appropriately by blowing in air and/or nitrogen, and is then emptied in a strong flow of water, which ensures the quenching of the hot material. The emptying opening is at a level such that there remains in the reactor a sufficiently high rutile fluidized bed for starting the next batch.

In order to arrive at a rutile with the desired purity, the quenched material must undergo mechanical wet preparation. This appropriately takes place in three stages: screening. course excess coke, separating on the basis of density on a table, magnetic separation of unreacted ilmenite and recirculation of the separated products, which are dried beforehand.

Only on the table does a fraction, which has to be discarded, appear with the ore gangue.

The titanium dioxide content of the process product is preferably at least 96 wt.% or in particular well above this figure. A typical analysis of this "rutile 96" is, with respect to the remaining impurities, as follows: approximately 0.5 wt.% alumina, approximately 0.1 wt.% of in each case calcium oxide, magnesium oxide, vanadium oxide, chromium oxide and phosphorus pentoxide, approximately 0.3 wt.% iron(Ill)-oxide, approximately 0.2 wt.% manganese oxide and approximately 0.9 wt.% silicon dioxide.

The gases leaving the fluidized bed reactor are cooled for condensing the iron(Il)-chloride, which is separated in a cyclone separator. In addition, carbon monoxide and carbon dioxide, together with the various other volatile chlorides, particularly vanadium(V) and chromium(III)-chloride,, are passed through a gas washer, accompanied by the separation of the chlorides, which can be processed in an appropriate manner. The carbon monoxide

. ® 7 left behind can be used in the process according to the invention as a heating gas for drying measures.

Almost the entire chlorine content used in the main reactor of the process according to the invention occurs in the iron(Il)-chloride obtained and is stored in an intermediate bunker.

A special feature of the process according to the invention is the further treatment of the separated iron(ll)-chloride. The latter is oxidized with oxygen in order to form iron(Ill)- oxide and chlorine gas, which are resupplied to the tluidized bed reactor in advantageous manner during chlorination. The oxidization reaction is performed in a combustion chamber at a temperature of preferably approximately 650 to 800°C. Although the reaction 1s slightly exothermic, it can be advantageous to use a secondary heat source comprising a carbon monoxide gas burner. The iron(IlI)-oxide obtained is a valuable byproduct. It is separated from the chlorine stream in a cyclone separator, scavenged with carbon dioxide and quenched with water. As a result of its Fe;O; purity of approximately 95% it can be used in a smelting plant.

The essential sequences of the process according to the invention in conjunction with the reaction in the fluidized bed reactor are shown in the enclosed fig. 1. An ilmenite concentrate is dried in a fluidized bed at 110°C and the same takes place with the petroleum coke used. Subsequently for chlorination purposes the dried ilmenite is introduced into the fluidized bed, where the temperature is above approximately 900°C.

Petroleum coke is also supplied to the fluidized bed reactor. The fluidizing conditions are set by supplied chlorine and oxygen-enriched air. Gaseous iron(Il)-chloride is removed from the fluidized bed. Following separation in solid form it is oxidized to iron(Ill)-oxide at approximately 700°C in an apparatus, followed by its isolation and removal. The chlorine is drawn off and recycled to the fluidized bed reactor. A solid mixture of unreacted ilmenite, remaining petroleum coke and desired rutile is obtained. It undergoes various processing measures, €.g. a wet preparation, screening, treatment on a wet table and magnetic separation of unreacted ilmenite. The unreacted ilmenite is recycled to the fluidized bed reactor, the gangue is removed and the desired rutile is dried at 110°C. The rutile has a titanium dioxide content of more than approximately 96%, being superior in

® 8 many ways to natural rutile. The product is in the form of hard, non-crumbly particles having a high density. This leads to a minimum loss by abrasion or transfer to the fluidized bed reactor compared e.g. to a product obtained by the chloride process. It is also more reactive with chlorine than natural rutile or rutile e.g. obtained according to the bucket process. This means a higher throughput for a given chlorination plant.

In the case of the process according to the invention a particular economic advantage is the recovery of chlorine from the iron(II)-chloride formed, in that it is reacted with oxygen accompanied by the formation of iron(Ill)-oxide and chlorine. In a continuous process this takes place in that gases drawn off from the fluidized bed are oxidized. It is difficult to separate the chlorine from the carbon oxides. Thus, hitherto the liquefied chlorine was separated by distillation from the low boiling gases (carbon dioxide, carbon monoxide and nitrogen), which requires complicated compression of the mixture for liquefying the chlorine. Such problems are excluded by the present invention. The iron(II)-chloride is rapidly cooled and concentrated in solid form. It can easily be separated from the gases. formed. The chlorine is present in the iron(II)-chloride in a quasi-stable intermediate form.

This can easily be oxidized with oxygen to solid iron(III)-oxide, which leads to chlorine, which can be recovered without difficulty and supplied to the chlorination stage.

Numerous other advantages arise when performing the process according to the invention.

Thus, the invention makes easier operation possible whilst economizing on constituents, leads to a better heat transfer efficiency, good thermal balance, an easy regulating of the process and the use of a single, separate fluidized bed reactor. In the fluidized hed reactor the solids are appropriately preheated and remain therein until processing is at an end.

After the flushing out of the resulting toxic gases, the solids can be removed without difficulty and no more extensive solid/gas isolation stages are needed.

The proposal according to the invention does not lead to the production of significant titanium tetrachloride quantities, thereby preventing a significant titanium loss. When the process is performed continuously titanium tetrachloride formation leads to a titanium loss,

The iron(Ill)-oxide is contaminated and unusable for processing which would otherwise be possible.

In the case where the titanium-containing ore used contains a significant vanadium proportion, particularly if it is ilmenite, vanadium is removed in oxytrichloride form, Under the process conditions it constitutes a gas with a boiling point of 127°C. It passes through the stage within which the iron(Il)-chloride is condensed. The removed vanadium oxytrichloride can be reacted with water leading to non-volatile vanadium oxide or hydroxide, which can be easily separated. If collected in large quantities, it constitutes a valuable further processing material.

Thus, the process according to the invention can be easily, economically and safely performed and also leads to a valuable process product. Complicated, additional measures, such as e.g. the alternate introduction of carbon monoxide and chlorine for prior, intermediate and/or subsequent treatment, are unnecessary.

The invention is further illustrated by the following example.

Example

Following the emptying of a batch, an approximately 300 mm high residual fluidized bed remains in a fluidized bed reactor with an internal diameter of 2400 mm and a vertical clearance of 2700 mm. It consists of a mixture of rutile and petroleum coke and is kept fluid by blowing in air at a temperature of no less than 600°C. Before the new ore batch of 14000 kg is supplied over a 35 minute period using a double star feeder, the bed is heated by feeding in coke and supplying oxygen-enriched air at 1050°C. In total the batch requires 1200 kg of petroleum coke. As soon as the indicated temperature is reached and the coke has been charged, chlorine addition commences. The chlorine is drawn from the parallel- operated oxidizing reactor. The temperature is maintained by controlling the oxygen quantity. As a result of the added coke quantity the carbon essentially burns to CO, which is necessary for reduction and chlorination of the rutile. The overpressure on the bottom of the fluidized bed reactor at the start of the batch is approximately 30 kPa and after filling the reactor approximately 50 kPa. The total flow of gas flows through the fluidized bed at a rate of approximately 100 mm/s. The actual reaction time - heating and chlorination -

® 10 amounts to approximately 2.5 h, whilst the cycle time for a batch and which includes emptying and secondary activities, is approximately 3.5 h. The reaction gases (CO, CO,

N; and volatilized chlorides) leave the reactor through an approximately 20 m high, vertical, water-cooled pipe with a diameter of 350 mm. During the passage through this pipe the iron(Il)-chloride condenses and can consequently be subsequently separated in a cyclone separator. The remaining gases then pass through a gas washing system for separating residual chlorides, particularly vanadium oxychloride, and then pass into a combustion chamber, where the combustion enthalpy of the CO gas is utilized for drying purposes.

The iron(II)-chloride separated in the cyclone separator passes into an intermediate bunker and from there via a dozing star feeder into the oxidizing reactor. Said reactor has roughly the same dimensions as the chlorinating reactor, but is connected at the bottom to a CO production plant, e.g. a small fluidized bed reactor, in which a coke bed reacts with oxygen and carbon dioxide. The carbon monoxide generated is burnt with oxygen. The heat. evolved 1s used for heating the reactor and for maintaining the temperature at times when no chlorine is required. The necessary temperature is between 700 and 800°C. Oxidation of the iron(Il)-chloride to iron(Ill)-oxide takes place in that iron(II)-chloride is blown with an oxygen stream into the hot oxidation chamber. The oxygen pressure is set in such a way that the resulting, recycled chlorine at the bottom of the chlorinating reactor still has a pressure of 50 kPa. The reaction product Fe,Os is separated from the chlorine stream by means of a cyclone separator. * % %

Claims (17)

1. Process for extracting metal oxide concentrate from an ore containing the corresponding metal and also 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, characterized in that an ore containing titanium and iron is processed, the reaction being performed batchwise in the fluidized bed reactor, to which are supplied as the fluidizing gas an oxygen-containing gas and chlorine, the carbon being present in an excess of more than approximately 5 wt.% compared with the necessary reaction quantity for removing the iron as chloride and a titanium dioxide-enriched product is removed.

2. Process according to claim 1, characterized in that the temperature in the fluidized bed is - set at more than approximately 1000°C and in particular at approximately 1030 to 1100°C.

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

4. Process according to at least one of the preceding claims, characterized in that the carbon excess is set at more than approximately 5 wt.%, particularly approximately 10 to 25 wt.%.

5. Process 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 oxygen percentage.

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

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

® 12

8. Process according to claim 7, characterized in that the ilmenite has a particle size of approximately 50 to 450 pm, particularly approximately 70 to 350 pm and/or a bulk density of approximately 2.4 to 3.0 g/cm’, particularly approximately 2.6 to 2.8 g/cm’.

9. Process according to at least one of the preceding claims, characterized in that as carbon use is made of petroleum coke, particularly with a low ash content and a high fixed carbon content.

10. Process according to claim 9, characterized in that the petroleum coke has a particle size of approximately 1.5 to 4 mm, particularly approximately 2 to 3 mm.

11. Process according to at least one of the preceding claims, characterized in that the carbon is used in an excess such that during the reaction in the fluidized bed reactor essentially iron(Il)-chloride and at the most only an insignificant quantity of iron(Ill)- chloride is produced. :

12. Process according to at least one of the preceding claims, characterized in that the gases leaving the fluidized bed reactor are cooled for condensing iron(Il)-chloride, which is separated in a cyclone separator.

13. Process according to claim 12, characterized in that the gases remaining after the separation of the iron(Il)-chloride and which contain carbon monoxide and carbon dioxide, as well as other volatile chlorides, particularly vanadium and chromium chlorides, are removed and are passed through a gas washer, accompanied by chloride separation.

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

15. Process according to claim 12, characterized in that the separated iron(II)-chloride is oxidized with oxygen in order to form iron(IlI)-oxide and chlorine gas, which is recycled to the fluidized bed reactor.

16. Process according to claim 15, characterized in that the iron(Ill)-oxide is separated from the chlorine in a cyclone separator scavenging with carbon dioxide or oxygen and quenched in water.

17. Process according to at least one of the preceding claims, characterized in that the titanium dioxide-enriched product for rutile isolation purposes is prepared by wet screening of excess carbon, separating the gangue on a table and magnetic separation of unreacted ilmenite. * ok Xk