AU624980B2 - Recovery of tio2 concentrates from tio2-containing substances - Google Patents

Description

62 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Ir Application Number: Lodged: Frm nt. Class Complete Specification Lodged: Accepted: Published: S Priority *o Related Art 0 4 Name of Applicant Address of Applicant Actual Inventor: Address for Service METALLGESELLSCHAFT AKTIENGESELLSCHAFT Reuterweg 14, D-6000 Frankfurt/Main, Federal Republic of Germany RUDOLF HENG, WALTER KOCH and ALI-NAGHI BEYZAVI WATERMARK PATENT TRADEMARK ATTORNEYS.

LOCKED BAG NO. 5, HAWTHORN, VICTORIA 3122, AUSTRALIA Complete Specification for the invention entitled: RECOVERY OF TIO2 CONCENTRATES FROM TiO2-CONTAINING SUBSTANCES The following statement is a full description of this invention, including the best method of performing it known to us Recovery of TiO 2 Concentrates From TiO 2 -containing Substances

DESCRIPTION

0 49 This invention relates to a process of recovering a TiO 2 concentrate from TiO 2 -containing preo*o*0 cursors by a direct reduction of the iron content of the 9004 precursors to metallic iron, a magnetic separation of the reduced product into magnetic and nonmagnetic fractions, an oxidation of the metallic iron of the magnetic fraction in an acid aqueous medium with agitation of the suspension S"and a supply of oxygen-containing gas into the suspension 4 i at an elevated temperature and under a superatmospheric pressure, and a subsequent separation of the iron oxides from the TiO 2 concentrate.

Synthetic rutile is recovered as a TiO 2 concentrate from TiO 2 -containing substances, such as ilmentite, pseudorutile etc..

British Patent Specification 980,864 I iI -2discloses a process in which ilmenite is reduced at temperatures from 1000 to 1150 °C with an addition of carbon, the reduced ore is separated by sieving and magnetic separation from the gangue and surplus reducing agent, and the metallic iron is oxidized by an oxidation effected in an acid aqueous medium having a pH value of at least 4 but below 7 and is thus liberated from the reduced ilmeniteo The oxidation is effected with agitation and with a supply of oxygen-containing gases into the suspension either under atmospheric pressure and at a temperature in the range from 60 to 80 °C or under a pressure of about 7 bars and at a temperature in the range from 150 to 170 C. The oxygen-containing gas which is employed preferably consists of a mixture of air and C02o Mixtures of oxygen and CO2, SO 2 and NO 2 are also mentioned as well as mixtures of SO 2 and/or NO 2 with air, oxygen and CO2 individually or in combination. An oxidation under a pressure of 7 bars and with a supply of air or of mixtures of oxygen with C02, SO 2 or NO 2 will result in TiO 2 concentrates having poor properties. In Sthe practice of that process the oxidation is effected under atmospheric pressure and with a supply of air and an addition of NH CI. As that oxidation requires a long reaction time, that stage must be effected discontinuously and is highly expensive. The composition of the iron oxides cannot be controlled. If the ilmenite contains i 3 manganese, that process will require an afterleaching with sulfuric acid in a separate stage. The resulting acid filtrate must be subjected to a sewage treatment.

It is an object of the invention to avoid said disadvantages and to permit a fast oxidation with a high yield and a production of a high-grade synthetic rutile.

In accordance with the present invention there is provided a process of recovering a Ti0 2 concentrate from TiO 2 -containing precursors by a direct reduction of the iron content of the precursors to metallic iron, a magnetic separation of the reduced product into magnetic and nonmagnetic fractions, and oxidation of the metallic iron of the magnetic fraction in an acid aqueous medium with agitation of the suspension and a 1 0 supply of oxygen-containing gas into the suspension at an elevated temperature and under a superatmospheric pressure, and a subsequent separation of the iron oxides from the TiO 2 concentrate, characterized in that the iron content of the TiO 2 -containing precursors is reduced to effect a metallization of at least 90%, the oxidation of the 0 o°a separated magnetic fraction is effected in a sulfuric acid or hydrochloric acid medium at a pH value below 2, under a pressure of 12 to 24 bars, and at a temperature from 150 to 2100C and with a supply of an oxygen-containing gas which contains at least oxygen and is supplied at least at the rate which is stoichiometrically required to form hematite, and the resulting hematite is separated from the Ti02 concentrate which is o o° contained in the suspension after the latter has been pressure-relieved.

20 The term "metallization" as used in the foregoing paragraph and throughout the 4# 4 present specificstion including the accompanying claims is defined as metailization Fe metallic 100 Fe total The direct reduction of the iron content, i.e. a reduction in a solid state below the 2 5 melting point of the charge, may be effected in a rotary kiln, an orthodox fluidized bed or a circulating fluidized bed. The reducing agents employed may consist of solid carbon, or of a gas or of combinations thereof. The direct reduction is preferably C_ I i -4carried out in a rotary kiln in a countercurrent operation, in which coal is used as a reducing agent. If the TiO 2 precursors which are employed contain manganese, sulfur or sulfur-containing substances will be added so that the manganese content is transformed to manganese sulfide, which is leached in the acid medium employed to effect the succeeding oxidation. To prevent a reoxidation of metallic iron the material discharged from the rotary kiln is cooled under conditions under which metallic iron will not be oxidized. A magnetic separation is subsequently performed. The magnetic fraction contains metallic iron and Ti0 2 The nonmagnetic fraction con- Ssists of surplus reducing agent, gangue and coal ash.

The surplus reducing agent may be recycled to the rotary kiln. The exhaust gas from the rotary kiln is preferably afterburnt and is supplied to a gas purifier. The magnetic I fraction is charged together with water into a tank. A >i suspension is produced by stirring and is withdrawn at a controlled rate from the tank and supplied to the autoclave. Acid at the rate required to adjust a pH value below 2 is then directly pumped into the autoclave when the same has been closed and is being supplied with oxygen. The 02 partial pressure in the autoclave will prevent a formation of H2 and/or H2S. The autoclave may be equipped with stirrers or may consist of a tumbling autoclave. The required residence time of the suspension in the autoclave is empirically determined for each material r.l i. 1 and generally amounts to 10 to 30 minutes. The oxygencontaining gas which is employed consists of commercially pure oxygen which contains at least 90% and pre- I ferably 94 to 96 oxygen. The total pressure in the autoclave is composed of the water vapor pressure corresponding to the temperature and of the pressure of the oxygen-containing gases which are supplied. The oxygencontaining gas is supplied at a rate which is at least as high as the rate which is stoichiometrically required to oxidize the metallic iron to hematite. In batch operation, oxygen is used only in a small surplus. Whereas a larger surplus of oxygen would not be disturbing, it would involve a corresponding loss of oxygen. But the autoclave is preferably operated continuously because that mode of operation is more economical. In continuous operation oxygen is always supplied in a large surplus related to the flow rate of the suspension. But that surplus oxygen is not consumed so that it will not be lost.

The quality of the synthetic rutile and the yield are virtually the same in case of an oxidation under pressure in a sulfuric acid or hydrochloric acid medium. But the use of a sulfuric acid medium is preferred because it involves lower corrosion problems. The suspension may contain up to 60 g sulfuric acid per liter. The suspension which has been discharged from the autoclave is pressurerelieved in a plurality of stages. The pressure is prei. i i -6ferably relieved in two stages. A pressure relief to i about 6 bars is effected in the first stage and to I about 1.5 bars in the second. The pressure-relieved suspension is separated into TiO 2 concentrate and hematite by a multistage hydrocyclone treatment. The TiO 2 concentrate is filtered, on a belt filter iiand is washed with water and is subsequently dried and Sdelivered as synthetic rutile. The residual suspension, which contains hematite, is also subjected to a solidliquid separation. The moist residue is dumped or is processed further.

In accordance with a preferred feature the iron conteut of the precursors is reduced to effect a metallization above 93%. That metallization results i in a product of high purity.

In accordance with a further feature the magnetic fraction is continuously oxidized under pressure. If the autoclave is provided with stirrers, i the autoclave is preferably divided on the liquid side into a plurality of compartments by partitions. A stirrer and lines for supplying the oxygen-containing gas into the suspension are provided in each compartment. The suspension is supplied at one end of the autoclave into the first compartment and flows from compartment to compartment over the partitions aid is withdrawn from the last compart- I ment at the other end of the autoclave. A continuous oxidation under pressure will resiit in considerable savings relative to a batch oxidation under pressure.

In accordance with a preferred feature the suspension has a pH value from 0.9 to 1.2 during the oxidation under pressure. A pH value in that range will result in particularly good operating conditions.

In accordance with a preferred feature, the suspension contains 5 to 50 g/1 sulfuric acid and to 35 by weight solids. Good results will be produced in that case.

In accordance with a preferred feature the suspension contains 8 to 12 g/1 sulfuric acid and 20 to 27% by weight solids. Particularly good results will be produced by an operation under such conditions.

In accordance with a preferred feature the oxidation under pressure is effected under a pressure of 13 to 18 bars.

Particularly good results will be obtained in that range.

In accordance with a preferred feature Sthe oxidation under pressure is effected under an 02 partial pressure which is 3 to 6 bars higher than the water vapor pressure that corresponds to the prevailing temperature. This will result in a highly effective i lioeration of the oxidized iron content from the reduced solids. That 02 partial pressure is constantly maintained particularly in continuous operation. In a batch operaion the 02 partial pressure will be much lower at the end of the treatment.

In accordance with a preferred feature the oxidation under pressure is effected under an 02 partial pressure which is 4 to 5 bars above the water vapor pressure which corresponds to the prevailing temperature. A particulaly effective liberation of the -8oxidized iron content will thus be effected. That 02 partial pressure is constantly maintained particularly in continuous operation. In a batch operation the 02 partial pressure will be much lower at the end of he i treatment.

iIn accordance with a preferred feature the oxidation under pressure is effected at a tempera- 0 Sture from 170 to 190 Particularly good results will i be produced at that temperature.

In accordance with a preferred feature the filtrates obtained by the separation of the hematite and the Ti0 2 concentrate from the pressure-relieved suspension are recycled for the preparation of the suspension which contains the magnetic fraction. The evaporation of water during the pressure relief may be compensated by the washing waters. As a result, I there will be no waste water or waste waters will be obtained only at low rates when enriched impurities must be withdrawn i from the circulation.

ii Example 1 kg ilmenite was reduced by means of i 0.6 kg coal, which contained about 1% sulfur, and by means of 10 kg sulfur in a Salvis furnace at 1100°C, below the melting point. The reduced material was then cooled in a nitrogen stream and was sieved at 0.7 mm. The coarses consisted of surplus coal. te undersize was suujected c I -9to magnetic separation. The magnetic product can be described as reduced ilmenite and had the following chemical 1 analysis: iTi as TiO 2 66.4 by weight Fe total 31.5 i Fe metallic 30.3 Mn i S 0.58 Metallization 96.0 i The reduced ilmenite had a particle size range from 0,3 to 0.032, which is virtually the same S.particle size range as that of the ilmenite charged into the furnace.

A suspension of 450 cm3 water and the reduced ilmenite was prepared and was supplied to a stirrable autoclave. 12.2 liters of pure oxygen under a pressure of jI bars and 50 cm 3 of dilute sulfuric acid (5 g H 2 S0 4 corresponding to a pH value of about 1, were supplied to the closed autoclave. The suspension was heated to 80°C by external heat. Then the supply of external heat was discontinued and the stirrer was operated at its full speed so that the supply of oxygen to the suspension was initiated.

As soon as the aeration had been initiated, the reaction started; this was indicated by a strong temperature rise.

The maximum temperature of 2070C was reached after 3 minutes. During that time the 02 partial pressure was always i- -L.

kept 5 bars above the water vapor pressure corresponding to the prevailing temperature.

j, The water vapor pressure amounted to 18 bars so that the total pressure as 23 bars. After a total time of 15 minutes the autoclave was cooled with water to a temperature below 100 0 C. After the cooling the suspension was filtered off and the filter cake was slurried in water and by repeated decanting was separated into synthetic rutile and hematite.

SThe chemical analyses were as follows: Synthetic Hematite rutile TiO 2 98.70/ by weight 1.8% by weight Fe total 1.1 66.8 I Fe metallic 0.16 (0.05 j Mn 0.7 N0.05 S total 0.08 0.9 i The advantages afforded by the invention reside in that the oxidation is effected within a very short time and with a very high conversion so that the plant is operated at a very high specific output. Owing to the relatively short agitation time during the oxidation, the particle size of the charged material is substantially preserved and there is no strong disintegration. Besides, the oxidation may be effected continuously.

-IF

4 -llii The oxidation under pressure eliminates the need for 1 an acid afterleaching of the rutile in a separate t stage. Waste water can be avoided or minized.

i.i iii i'{ i 1 ;i i

Claims (6)

1. A process of recovering a Ti0 2 concen- trate from Ti0 2 -containing precursors by a direct reduction of the iron content of the precursors to metallic iron, a magnetic separation of the reduced product into magnetic and nonmagnetic fractions, and oxidation of the metallic iron of the magnetic fraction in an acid aqueous medium with agitation of the suspen- sion and a supply of oxygen-containing gas into the sus- pension at an elevated temperature and under a superatmos- pheric pressure, and a subsequent separation of the iro, oxides from the Ti0 concentrate, characterized in that the iron content of the TiO 2 -containing precursors is reduced to effect a metallization of at least 90%, the oxidation of the separated magnetic fraction is effected in a sulfuric acid or hydrochloric acid medium at a pH value below 2, under a pressure of 12 to 24 bars, and at a temperature from 150 to 210 0C and with a supply of an oxygen-containing gas which contains at least oxygen and is supplied at least at the rate which is stoichiometrically required to form hematite, and the resulting hematite is separated from the Ti0 2 concen- trate which is contained in the suspension after the lat- ter has been pressure-relieved.

2. A process according to claim 1, character- ized in that the iron content of the precursors is reduced i !f -13- i to effect a metallization above 93%. j 5. A process according to claim 1 or 2, characterized in that the magnetic fraction is conti- nuously oxidized under pressure.

4. A process according to any of claims i :o 1 to 3, characterized in that the suspension has a pH i value of 0.9 to 1,2 during the oxidation under pressure. A process according to any of claims 1 to 4, characterized in that the suspension contains to 30 g/l sulfuric acid and 15 to 35 by weight solids.

6. A process according to any of claims 1 to 5, characterized ih that the suspension contains 8 to 12 g/l sulfuric acid and 20 to 27 by weight solids. S7 A process according to any of claims 1 to 6, characterized in that the oxidation under pres- sure is effected under a pressure of 13 to 18 bars. S8. A process according to any of claims 1 to 7, charactEized in that the oxidation under pressure Sis effected under an 02 partial pressure which is 3 to 6 bars higher than the water vapor pressure that corres- ponds to the prevailing temperature.

9. A process according to claims 1 to 8, characterized in that the oxidation under pressure Is effected under an 02 partial pressure which is 4 to bars above the water vapor pressure which corresponds to L -14- the prevailing temperature. A process according to any of claims 1 to 9, characterized in that the oxidation under pressure is effected at a temperature from 170 to 190 0 C.

11. A process according to any of claims 1 to 10, characterized in that the filtrates obtained by the separation of the hematite and the TiO2 concentrate from the pressure-relieved suspension are recycled for the preparation of the suspension which contains the magnetic fraction. DATED this 25th day of July 1990. METALLGESELLSCHAFT AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS "THE ATRIUM" 290 BURWOOD ROAD HAWTHORN. VIC. 3122. L I ii