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Home , Titanium dioxide, Titanium oxide

United States Patent (19) 11 4,120,694 Elger et al. 45 Oct. 17, 1978

54) PROCESS FOR PURIFYING A 56) References Cited TTANUMBEARING MATERIAL AND U.S. PATENT DOCUMENTS UPGRADING ILMENTE TO SYNTHETIC RUTLE WITH TROXIDE 1,819,770 8/1931 D'Ans ...... 423A21 1,820,455 8/1931 Hooey ...... 75/116 1964,747 7/1934 Sweet et al...... 75/116 75) Inventors: Gerald W. Elger; Ruth A. Stadler; 2,098,050 11/1937 McBerty ...... 423/154 Philip E. Sanker, all of Albany, Oreg. 2,804,384 8/1957 Armant ...... 75/1 T

2,818,347 12/1957 Brickenkamp ...... 75/121 2,919,982 1/1960 Fetterolf ...... 75/1 T 73) Assignee: The United States of America as represented by the Secretary of the Primary Examiner-L. Dewayne Rutledge Interior, Washington, D.C. Assistant Examiner-Michael L. Lewis Attorney, Agent, or Firm-William S. Brown; Donald A. Gardiner 21 Appl. No.: 830,523 57 ABSTRACT A process for removing impurities from an of 22 Filed: Sep. 6, 1977 -bearing material such as a titania by treat ing the material with SO3 gas and subsequently leaching (51) Int. Cl’...... C22B 1/06; C22B 7/04 with a liquid. In particular a process for upgrading an 52 U.S. C...... 75/1 T; 75/24; by preparing a titania slag therefrom and 75/97 R; 75/116; 423/69; 423/170; 423/554; purifying the slag such that it may be used as a synthetic 423/555 suitable for use in a fluidized-bed chlorination 58) Field of Search ...... 75/1 R, 1 T, 3, 4, 5, reactor to produce which can be 75/24, 97 R, 97 A, 101 R, 104, 15, 116, 121, reoxidized to TiO, 84; 423/82, 83, 85, 86, 150, 69, 155, 166, 170, 554, 555; 106/300 13 Claims, No Drawings 4,120,694 1. 2 the pre-reduction of ilmenite followed by reoxidation of PROCESS FOR PURFYING A metallic in a slurry and separation of the TITANUMBEARNG MATERAL AND hydrated iron and, finally, a process based upon UPGRADING LMENTE TOSYNTHETCRUTLE the selective chlorination of iron in ilmenite to separate WITH SULFUR TRIOXDE iron chloride leaving rutile as the residue. However, such processes have not been particularly successful in BACKGROUND OF THE INVENTION utilizing the more abundant low grade ilmenite to The invention relates to a process for removing impu produce a substitute chlorination feed stock which ap rities from an oxide of titanium-bearing material and, in proaches natural rutile in TiO, content. Most of these a preferred embodiment, a process for upgrading ilmen O processes are applicable to the use of high grade ilmen ite ore to synthetic rutile by the action of . ite ores from deposits of limited reserves. Titanium ores having commerical importance pres Thus, various processes for the upgrading of ilmenite ently include rutile, which contains about 95% by to synthetic rutile employ the initial conversion of the weight (TiO2), and ilmenite ore which ilmenite into a titania slag, see especially U.S. Pat. Nos. is nominally ferrous containing about 45 to 65% 15 3,860,412 and 3,996,332. However, commercially pro by weight TiO2. These two ores can be used in the duced titania slag contains associated alkaline production of TiO, suitable as and fillers in impurities. These alkaline earth impurities form high and with lesser amounts being used in chloride mixtures which can accumulate metal production. and cause defluidization of the bed in the subsequent Production of TiO, can be carried out by the chlorination reaction of the synthetic rutile to give tita sulfate process, in which ilmenite or titania-enriched nium tetrachloride. In addition, these alkaline earth smelter slag is reacted with concentrated , chloride mixtures form a liquid on the surface of or by the chloride process in which rutile or ilmenite is the particles to be chlorinated, thus causing impeaded chlorinated to produce titanium tetrachloride which is chlorination of the TiO, and an inefficient use of the reoxidized to TiO. The second process is preferred in 25 . that chloride plants employing rutile feed stock are less It is therefore an object of the present invention to expensive and less waste problems are encountered as remove impurities, particularly alkaline earth impuri compared with production plants using the sulfate pro ties, from an oxide of titanium-bearing material. cess. However, increased consumption of rutile in chlo It is a further object of the present invention to up ride-process pigment manufacture has placed increased 30 grade ilmenite in order to produce a synthetic rutile. demands upon the limited reserves of rutile, thereby An additional object of the present invention is to increasing costs and rendering the process less economi upgrade ilmenite ore to produce a feed stock suitable for cal. use in a chlorination reactor for the conversion of rutile Thus, there has been considerable interest in upgrad to titanium tetrachloride. ing ilmenite to produce a synthetic rutile which can be 35 An additional object of the present invention is to substituted as the feed stock in existing fluidized bed directly convert a titania slag to a feed stock suitable for chlorinators employing the chloride process for the use in a chlorination reactor for the conversion of rutile production of titanium tetrachloride from rutile. to titanium tetrachloride. In U.S. Pat. No. 3,996,332, of which one of the pres ent inventors was an inventor, a process is described SUMMARY OF THE INVENTION whereby ilmenite is smelted to produce a slag which is It has been found that impurities such as alkaline then oxidized, with a titanium pyrophosphate flux in earth oxides present in materials can be order to produce a synthetic rutile. selectively sulfated and subsequently leached out by the U.S. Pat. No. 3,560,153 describes a process whereby action of sulfur trioxide gas. In a particularly important ilmenite is reacted with and a reductant in 45 aspect, titania slag from the smelting of ilmenite is re order to convert the present into the corresponding acted with sulfur trioxide gas whereby the and sulfide. The thus-treated ilmenite can then be leached, oxide impurities are converted to double leaving behind the titanium dioxide. sulfates which can then be leached out of the slag with In U.S. Pat. No. 3,860,412, a process is described a liquid such as water. Further, the addition of where by a titaniferous material is upgraded into a feed 50 to the sulfur trioxide gas results in a concurrent trans stock suitable for the preparation of titanium tetrachlo formation of the titanium-bearing phases to rutile. That ride by the direct chlorination method whereby the is, the action of oxygen can be utilized concurrently in titaniferous material is communinuted, mixed with sul order to convert the lower valence titanium oxides to furic acid and heated. titanium dioxide in the form of rutile. U.S. Pat. No. 3,252,787 covers a process for the pro 55 Removal of the alkaline earth impurities by this pro duction of a high quality titanium dioxide concentrate cess can result in a superior feed stock for the chlorina from a titaniferous ore, particularly ilmenite, by roast tion of synthetic rutile. ing the ore in air to convert the iron to the ferric state, reducing the ferric iron to metallic iron with a reducing DETAILED DESCRIPTION OF THE agent and leaching out the metallic iron. INVENTION Further, titanium sulfide can be produced from The titanium-bering material which can be used in "black sands” by heating with sulfur dioxide and a hy the reaction with sulfur trioxide is preferably a titanifer drocarbon gas as described in U.S. Pat. No. 3,313,601. ous slag. The titaniferous slag may be produced by Generally, research on the upgrading of ilmenite smelting titanium ores such as ilmenite or titaniferous involves the removal of iron by hydrometallurgical, 65 magnetite. Smelting conditions can be as described in pyrochemical or pyrometallurigical methods. These U.S. Pat. Nos. 3,860,412 and 3,996,332. Generally, the processes include the prereduction of ilmenite followed smelting conditions are conventional although the slag by 2-stage sulfuric acid leaching of the iron therefrom, produced should preferably have a low concentration 4,120,694 3 4. of chlorine consumers other than titanium. Thus, the The reaction times can be suitably varied in order to iron content of the slag, reported as Fe0, should be kept maximize the formation of the alkaline earth sulfate below 10% by weight since high iron , e.g., 10 to impurities. Thus, by monitoring the sulfur content of 13%. FeC), do not respond effectively to rutile synthesis. the slag during the reaction, the reaction can be termi More preferably, the iron content should be in the range nated upon the disappearance of increases in sulfur of about 3 to 5% by weight of Fe0. content of the slag. The titania slag may be produced from ilmenite con Concentrations of sulfur trioxide can very widely in centrates by electric furnace smelting using coke or the reaction but suitable concentrations can be from other forms of as the reductant. Preferably, the about 50 to 100 cc/minute flowing over 25 grams of slag ilmenite concentrate is blended with carbon in a small 10 sample. If oxygen is added to the gas flow, a suitable amount of flux which is then pelletized amount can be about 100 cc/minute. using appropriate binders. Carbon requirement are In a particularly preferred embodiment of the inven about 125 to 150% of the stoichiometric amount based tion, the titania slag is heated in the reactor with sulfur upon the total reduction of iron oxides contained in the trioxide and oxygen flowing thereover, the bed being concentrate to give elemental iron with carbon going to 15 heated at a temperature of about 600 to 1100 C as the monoxide and on the saturation of the iron product monitored by a thermocouple. In this embodiment, the with 3.5 to 4% by weight carbon. The calcium oxide or cooling of the bed after the reaction is in an atmosphere lime flux is added in an amount equivalent to about 2 to of sulfur trioxide whereby the sulfur trioxide influences 5% by weight of the ilmenite charged. The purpose of the equilibrium of the sulfates in their reconversion back the flux is to increase the slag fluidity so that the smelt 20 to SO, so that the sulfates are not decomposed during ing step can be performed at lower temperatures and in this cooling stage. The sulfur trioxide can be present order to facilitate the later processing of the slag. The during cooling as a flow of gas or a static presence of slag liquidus temperatures will usually range from about the gas and sulfur dioxide can be substituted during this cooling stage. 1300 to 1400° C when flux is used. It is possible to 25 Although the particle size of the slag to be reacted reduce residual iron oxides to levels substantially below can vary widely, the slag is preferably ground so that 3%, but such a severe reduction also results in the reduc the particles can pass through an 80 mesh sieve. It has tion of titanium dioxide to lower valent titanium oxide been found that if the particles are ground too finely, causing a significant increase in the slag liquidus tem the particles may have a tendency to sinter. Further, the perature. A more detailed description of the electric 30 ground slag can be agglomerated with a binder, such a furnace smelting of ilmenite concentrates may be found sugar added in an amount of 2 to 3 pct. The agglomer in the Bureau of Mines Report of Investigations 5170 ated pellets can be to inch in diameter. Such pellets (1955). are preferrably used in large scale operations in order to The reactor to be used can be any suitable device minimize dust formation. capable of achieving the proper temperatures and 35 Although the leaching of the reacted slag can be contact between the slag and the sulfur trioxide gas. accomplished at various temperatures, room tempera Thus, a fixed bed vertical reactor can be used for batch ture is most convenient. Leaching with water at consid reactions or a rotary kiln can be used in a continuous erably higher temperatures is not advantageous since operation. calcium sulfate is not as soluble in water at such higher The sulfur trioxide can be commercially obtained or 40 temperatures. Preferrably, the leaching liquid is water. can be produced at the plant site by the reaction of The off-gases from the reactor can suitably be neu sulfur dioxide with oxygen over a suitable catalyst such tralized with a scrubber solution such as an aqueous as V2O5 or platinum. If the sulfur trioxide is produced lime solution. from sulfur dioxide, the catalyst is preferably VOssince In general, the ilmenite ore materials used to produce this catalyst is less subject to poisoning. However, the 45 the slag can comprise about 45 to 65% by weight tita conversion of sulfur dioxide can be accomplished by nium dioxide with higher concentrations being found in any conventionally known means. the slag. The titanium in the slag is generally present as Oxygen can be added to the sulfur trioxide feed a pseudobrookite-type structure illustrated by the fol stream in order to convert titanium oxides to the desired lowing formulas: titanium dioxide state. Since oxygen is taken up by vari 50 ous reactants, principly carbon to produce CO2, lower (Mn+, Mg, Fet, Tit)0.2TiO, titanium oxides to produce TiO, and Fe0 to produce Fe2O3, the oxygen is preferably added in an amount of and/or about 150 equivalent percent of these three oxygen consumers. That is, although most of the iron is re 55 (Fe, Al, Ti",), o, . Tio, moved in the smelting of the ilmenite, some iron is transferred to the slag and sufficient oxygen should be After treatment with the sulfur trioxide and oxygen, added to be certain that all titanium oxide forms are X-ray diffraction data indicated that the treated slag converted to titanium dioxide. contained rutile as a primary phase and a double sulfate The temperature of the sulfur trioxide treatment can CaSO4.3MSO, as a minor phase. range from about 600 to about 1100° C. However, the The following examples illustrates specific embodi particular temperature will depend somewhat upon the ments of the invention and are not to be taken as limit particular composition of the slag. Generally, tempera 1ng. tures higher than the about 600 to 1100 C range may EXAMPLE 1. result in the instability of the double sulfate of calcium 65 and magnesium. Further, temperatures below this range A sample of a rock-type ilmenite from New York may result in the formation of the sulfates of iron and state was smelted under highly reducing conditions to titanium. produce a pig iron fraction and a reduced titania slag. 4,120,694 5 6 This titania slag was found to have the following com temperature in the sulfur trioxide and oxygen atmo position by chemical analysis: sphere. Chemical analysis of the thus-treated slag indicated % by weight that the slag had 4.65% by weight sulfur. Ferrous Iron 5.3 The slag was then ground to pass through a 65 mesh (as ferrous oxide) sieve and covered with water in a beaker with stirring at TiO, 70,6 room temperature for 1 hour. After removing the wa SiO, 6.8 MgO 4.1 ter, the treated slag was dried and analysis indicated a CaO 8.2 54% by weight reduction in MgO and a 45% by weight Al2O3 4.5 6ief 0.5 10 reduction in CaO. (including V and Cr) 100.0 EXAMPLE 4 A sample of slag treated according to the present 5-gram samples of the ground reduced slag contain invention was chlorinated in order to produce titanium ing pseudobrookite-type material as a primary phase 15 and calcium as a minor phase were treated with tetrachloride. SO and O2, the SO, being formed by passing a mixture A slag sample was treated with sulfur trioxide and of SO, and Oover a VOscatalyst bed heated to 400 C. oxygen as in Example 3 and, after cooling to room The reactor utilized was a 1 inch vertical tube furnace temperature, was found to have 4.5% by weight sulfur. having a length of 18 inches. 20 The pellets were then ground, leached with water and Various temperatures of about 600 to 1100° C were dried as in Example 3. used in the runs with sulfur analysis of the slag being A sample of 833 grams of the dried slag treated ac taken periodically. cording to the present invention was then reag A slag sample treated at 900 C and cooled under a glomerated with 17 grams of sugar and 319 grams of sulfur trioxide atmosphere was found to have a sulfur 25 coke in preparation for a chlorination reaction. The content after treatment of 5.6% by weight. After cool pellets were about to 178 inch in diameter. ing to room temperature, the sample was allowed to sit 1107 grams of the pellets prepared from treated slag in water at room temperature after which the sample were then loaded into a 2 inch diameter vertical shaft was dried. About 60% by weight of the MgO and 40% reactor, 36 inches in length. The reactor was heated to by weight of the CaO were removed in the water leach 30 900' C and room temperature chlorine gas was passed of the treated slag samples as determined by chemical through the reactor at a flow rate of about 2800 cc/mi analysis. nute. Thus, titanium tetrachloride gas is present in the off-gases of the reactor and the TiCl is condensed from EXAMPLE 2 which TiO, is produced. The reduced titania slag utilized in Example 1 was 35 The off-gases of the reactor are monitored in order to divided into 100 grams samples and agglomerated with determine the percentage of chlorine therein. During 2% by weight sugar on a disc pellitizer to form to actual chlorination, the chlorine is present in an amount inch diameter pellets. The slag pellets were placed in a of about 5%. When the percentage of chlorine in the 2-inch vertical tube furnace having a length of 36 inches gases rises to about 60 to 70%, the chlorination is essen and were treated with SO and oxygen mixtures for 8 to tially finished. Thus, the reaction proceeded for about 16 hours. The sulfur trioxide flowed from a VO cata 175 minutes after which the reactor was allowed to lyst reactor with nflows of sulfur dioxide at 300 cc/mi cool. nute and oxygen at 300 cc/minute. Additionally, runs Elemental analysis of the pellets in the chlorination were made with sulfur dioxide and oxygen flow rates at reactor before and after chlorination indicated that 150 cc/minute each. By chemical analysis, it was deter 45 85.9% of the titanium originally in the pellets was ex mined that the maximum sulfur pick-up in the treated tracted and removed in the form of titanium tetrachlo slag material occurred at about 900' C using the 150 ride. cc/minute flow rates into the V.O. catalyst reactor. COMPARISON EXAMPLE 1 EXAMPLE 3 50 A chlorination reaction was conducted in a manner A sample of the untreated slag described in Example similar to that in Example 4 with the exception that the 1 was ground to pass through an 80 mesh sieve and pellets utilized were not treated according to the pres agglomerated with 2% by weight sugar on a disc pellet ent invention. izer to form to inch diameter pellets. Slag pellets were prepared as in Example 4 above About 1000 grams of the thus-produced pellets were 55 with the exception that the slag utilized was the un introduced into a 2 inch diameter vertical shaft reactor treated slag described in Example 1 having 70.6% TiO. as in Example 2. The reactor was heated to 900 C while The pellets were prepared with slag, sugar and coke in a flow of was passed therethrough. Upon reach the proportions set forth in Example 4. ing the temperature of 900 C, a flow of sulfur trioxide 1000 grams of the pellets were introduced into the and oxygen was passed through the reactor from the 60 chlorination reactor described in Example 4 and after bottom. The two gases introduced were from a VO heating to 1050 C, chlorine gas was passed there catalyst reactor into which was passed 300 cc/minute of through in the flow rate described in Example 4. sulfur dioxide and 250cc/minute of oxygen, the oxygen During the chlorination, it was observed that the being in excess of that required to convert all of the outside of the pellets became as caused by the sulfur dioxide. The VOscatalyst was obtained from the 65 formation of liquid salts of alkaline earth oxides. The Baker Chemical Company. reaction was terminated after 105 minutes in view of the After the reaction proceeded at 900 C for 16 hours, significant rise of chlorine in the off gases of the reactor. the reactor was sealed and allowed to cool to room When the cooled pellets were broken, it was observed 4,120,694 7 8 that significant amounts of titanium dioxides were left sion of lower valence titanium oxides to titanium diox ide. unreacted. 7. A process for upgrading ilmenite ore to a syn Analysis of the pellets before and after chlorination thethic rutile ore comprising the steps of: indicated a removal of only 55% of the titanium present a producing a titania slag containing alkaline earth therein. While not wishing to be bound by theory, this impurities from ilmenite ore; is believed to be caused by the inability of the chlorine b. reacting said titania slag with sulfur trioxide gas at gas to penetrate the liquid salt coating caused by high 600 to 1100 C; and subsequently percentages of alkaline earth oxides in the pellets. c. leaching said alkaline earth impurities from the What is claimed is: O titania slag with water. 1. A process for removing alkaline earth oxide impu 8. The process of claim 7, wherein step a) comprises rities from a titania slag consisting essentially of reacting smelting ilmenite ore to produce a titania slag fraction. said slag with sulfur trioxide gas at a temperature of 9. The process of claim 8, wherein said ilmenite ore about 600 to 1100 C to form a reaction product con comprises about 45 to 65% by weight titanium dioxide. taining alkaline earth sulfates, and subsequently leach 15 10. The process of claim 7, wherein in step c), at least ing said sulfates from the reaction product with water. one alkaline earth sulfate is removed from the titania 2. The process of claim 1, wherein said slag comprises slag by said leaching. 11. The process of claim 10, wherein said at least one a titanium slag produced by the smelting of ilmenite ore. alkaline earth sulfate comprises the double sulfate 3. The process of claim 2, wherein said ilmenite ore 20 CaSO4. 3MgSO4. comprises about 45 to 65% by weight titanium dioxide. 12. The process of claim 7, wherein in step (b), said 4. The process of claim 1, wherein said impurities reaction comprises the reaction of sulfur trioxide with at comprise calcium oxide and . least one alkaline earth oxide to produce the corre 5. The process of claim 1, wherein said reacting com sponding sulfate. prises the reaction of sulfur trioxide with at least one 25 13. The process of claim 7, wherein said reacting is in alkaline earth oxide to produce the corresponding sul the presence of gaseous oxygen resulting in the conver fate. sion of lower valence titanium oxides to titanium diox 6. The process of claim 1, wherein said reacting is in the presence of gaseous oxygen resulting in the conver ide. k k k k h 30

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