Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B34/00—Obtaining refractory metals
  • C22B34/10—Obtaining titanium, zirconium or hafnium
  • C22B34/12—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08
  • C22B34/1204—Obtaining titanium or titanium compounds from ores or scrap by metallurgical processing; preparation of titanium compounds from other titanium compounds see C01G23/00 - C01G23/08 preliminary treatment of ores or scrap to eliminate non- titanium constituents, e.g. iron, without attacking the titanium constituent

Definitions

• the invention relates to a process for obtaining a TiO2 concentrate from TiO2-containing materials by direct reduction of the iron content of the materials to metallic iron, magnetic separation of the reduced product into a magnetic and a non-magnetic fraction, oxidation of the metallic iron of the magnetic fraction in an acidic aqueous medium with agitation of the suspension and supply of oxygen-containing gas into the suspension at elevated temperature and pressure, and subsequent separation of the iron oxides from the TiO2 concentrate.
• Synthetic rutile is obtained as a TiO2 concentrate from TiO2-containing substances such as ilmenite, pseudorutile, etc.
• ilmenite is reduced with the addition of carbon at temperatures of 1000 to 1150 ° C
• the reduced ore is separated from the gangue and excess reducing agent by sieving and magnetic separation
• the metallic iron is oxidized by oxidation in an acidic aqueous medium with a pH of at least 4 but below 7 and is thereby released from the reduced ilmenite.
• the oxidation takes place with agitation and supply of oxygen-containing gases into the suspension either at atmospheric pressure and a temperature in the range from 60 to 80 ° C or under a pressure of about 7 bar and at a temperature in the range from 150 to 170 ° C.
• a mixture of air and CO2 is preferably used as the oxygen-containing gas.
• Oxidation under 7 bar pressure and introduction of air or mixtures of oxygen with CO2, SO2 or NO2 give TiO2 concentrates with poor properties.
• this method is used in such a way that the oxidation takes place under atmospheric pressure, introduction of air and addition of NH4Cl.
• This oxidation requires a long reaction time, ie this step must be carried out batchwise and is very complex.
• the composition of the iron oxides cannot be controlled. If the ilmenite contains manganese, this process must be followed up with sulfuric acid in a separate step. The resulting acidic filtrate must be subjected to wastewater treatment.
• the invention has for its object to avoid these disadvantages and to enable rapid oxidation with high output to produce a high quality synthetic rutile.
• the iron content of the TiO2-containing precursors is reduced to a metallization of at least 90%, the oxidation of the separated magnetic fraction in sulfuric acid or hydrochloric acid medium at a pH below 2, a pressure of 12 to 24 bar, a temperature of 150 to 210 ° C with the supply of oxygen-containing gas with at least 90% oxygen content in an at least stoichiometric amount for the formation of hematite, and the hematite formed is separated from the TiO2 concentrate from the relaxed suspension.
• the direct reduction of the iron content ie a reduction in the solid state below the melting point of the feed, can take place in a rotary kiln, a classic fluidized bed or a circulating fluidized bed.
• Solid carbon, gas or combinations can be used as reducing agents.
• the direct reduction is preferably carried out in a countercurrent rotary kiln using coal as the reducing agent. If the TiO2 materials used Containing manganese, sulfur or sulfur-containing substances are added. As a result, the manganese content is converted into manganese sulfide, which is leached out in the acidic medium during the subsequent oxidation.
• the rotary kiln discharge is cooled to prevent reoxidation of metallic iron under conditions not oxidizing with respect to metallic iron. A magnetic separation then takes place.
• the magnetic fraction contains the metallic iron and the TiO2.
• the non-magnetic fraction consists of excess reducing agent, gait and coal ash.
• the excess reducing agent can be returned to the rotary kiln.
• the exhaust gas from the rotary kiln is passed into the gas cleaning, preferably after post-combustion.
• the magnetic fraction is charged in a tank with water.
• a suspension is produced by stirring and this is withdrawn from the tank in a controlled amount and introduced into the autoclave.
• the amount of acid required to adjust to pH ⁇ 2 is then pumped directly into the closed and oxygenated autoclave, whereby H2 or H2S formation is avoided by the O2 partial pressure in the autoclave.
• the autoclave can be designed with stirrers or can be designed as a rolling autoclave.
• the required residence time of the suspension in the autoclave is determined empirically for each material and is generally 10 to 30 minutes.
• oxygen-containing gas Technically pure oxygen containing at least 90%, preferably 94 to 96%, oxygen is used as the oxygen-containing gas.
• the total pressure in the autoclave is made up of the water vapor pressure corresponding to the temperature and the pressure of the oxygen-containing gases introduced.
• the oxygen-containing gas is introduced in an amount which corresponds at least to the amount which is stoichiometrically required for the oxidation of the metallic iron to hematite.
• the excess of oxygen is kept low. A larger excess of oxygen does not interfere, but it does corresponding oxygen loss.
• the autoclave is preferably operated continuously because this mode of operation is more economical. In continuous operation, a large excess of oxygen - based on the amount of suspension used per unit of time - is always used.
• the quality of the synthetic rutile and the yield are practically the same in the case of pressure oxidation in a sulfuric or hydrochloric acid medium.
• working with a sulfuric acid medium is preferred because it causes fewer corrosion problems.
• the sulfuric acid content in the suspension can be up to 60 g / l.
• the TiO2 concentrate is, for example on a belt filter, filtered and washed with water, then dried and removed as a synthetic rutile. The remaining hematite-containing suspension is also subjected to a solid-liquid separation. The damp residue goes to the landfill or for further processing.
• a preferred embodiment is that the iron content of the precursors is reduced to a metallization of over 93%. This metallization results in a very pure product.
• a preferred embodiment is that the pressure oxidation of the magnetic fraction takes place continuously.
• the autoclave is equipped with stirrers, the autoclave is preferably divided into several compartments on the liquid side by partitions. In each compartment there is a stirrer and supply lines for the arranged oxygen-containing gas in the suspension.
• the suspension is fed into the first compartment at one end of the autoclave, flows from compartment to compartment over the partitions and is withdrawn from the last compartment at the other end of the autoclave. Continuous pressure oxidation results in considerable savings compared to discontinuous pressure oxidation.
• a preferred embodiment is that the pH of the suspension during the pressure oxidation is 0.9 to 1.2. This pH range results in particularly good working conditions.
• a preferred embodiment is that the sulfuric acid content in the suspension is 5 to 30 g / l and the solids content is 15 to 35% by weight. This ensures good operating results.
• a preferred embodiment is that the sulfuric acid content in the suspension is 8 to 12 g / l and the solids content is 20 to 27% by weight. In most cases, this results in particularly good operating results.
• a preferred embodiment is that the pressure oxidation is carried out at a pressure of 13 to 18 bar. This area gives particularly good results.
• a preferred embodiment is that the pressure oxidation is carried out with an O2 partial pressure of 3 to 6 bar above the water vapor pressure corresponding to the temperature. This results in a very good release of the oxidized iron content from the reduced solid.
• This O2 partial pressure is constantly maintained, especially in a continuous mode of operation. In the case of a batch operation, the O2 partial pressure at the end of the treatment are much lower.
• a preferred embodiment is that the pressure oxidation is carried out with an O2 partial pressure of 4 to 5 bar above the water vapor pressure corresponding to the temperature. A particularly good release of the oxidized iron content is achieved.
• This O2 partial pressure is constantly maintained, especially in a continuous mode of operation. In a batch operation, the O2 partial pressure at the end of the treatment can be significantly lower.
• a preferred embodiment is that the pressure oxidation takes place at a temperature of 170 to 190 ° C. Particularly good results are achieved at this temperature.
• a preferred embodiment consists in that the filtrates obtained in the separation of the hematite and TiO2 concentrate from the relaxed suspension are recycled to produce the suspension with the magnetic fraction.
• the amount of water evaporated by relaxing can be compensated for by the wash water. This means that there is no waste water, or only small amounts, when enriched impurities have to be removed from the circuit.
• the grain size of the reduced ilmenite was between 0.3 and 0.032 mm. This grain practically corresponded to the grain of the ilmenite used in the furnace.
• a suspension of 450 cm 3 of water was prepared and placed in a stirred autoclave.
• 12.2 l of pure oxygen at a pressure of 10 bar and 50 cm3 of dilute sulfuric acid (5 g of H2SO4) corresponding to a pH of about 1 were introduced.
• the suspension was heated to 80 ° C. by external heat, the external heat supply was switched off and the stirrer was set to full speed, and thus the gassing of the suspension with oxygen was initiated.
• the reaction started immediately after fumigation began - evident from the sharp rise in temperature. After 3 min. the maximum temperature was reached at 207 ° C. During this time, the O2 partial pressure was always kept 5 bar above the water vapor pressure of the corresponding temperature.
• the water vapor pressure was 18 bar, so that the total pressure was 23 bar.
• the autoclave was cooled to a temperature below 100 ° C. by water cooling. After cooling, the suspension was filtered off, the filter cake slurried in water and separated into synthetic rutile and hematite by repeated decanting.
• the chemical analyzes were as follows: Synthetic rutile Hematite TiO2 98.7% by weight 1.8% by weight Fe total 1.1 66.8 Fe metallic 0.16 ⁇ 0.05 Mn 0.7 ⁇ 0.05 S total 0.08 0.9
• the advantages of the invention are that the oxidation takes place in a very short time with a very high degree of implementation and a very high specific system performance is thereby achieved. Due to the relatively short agitation time during the oxidation, the grain size of the material used is largely preserved and there is no strong comminution. Furthermore, the oxidation can be carried out continuously. The pressure oxidation eliminates the acidic post-leaching of the rutile in a separate stage. Wastewater can be avoided or reduced to a minimum.

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• Chemical & Material Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Compounds Of Iron (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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Citations (8)

• 1989
  • 1989-07-27 DE DE19893924796 patent/DE3924796A1/de not_active Withdrawn
• 1990
  • 1990-06-23 EP EP90201674A patent/EP0410496A1/fr not_active Withdrawn
  • 1990-07-26 PT PT9483190A patent/PT94831A/pt not_active Application Discontinuation
  • 1990-07-26 AU AU59814/90A patent/AU624980B2/en not_active Ceased

Patent Citations (8)

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