[1]United States Patent Office 31625@645 3,625,645 PROCESS FOR THE RECOVERY OF VANADIUM FROM RAW TITANIUM CHLORIDE F'rancesco Ferrero and Giuseppe Sironi, Novara, and Angelo Garberi, Cilavegna, Italy, assignors to Monte. 5 catini Edison S.p.A., Mlan, Italy Filed May 16, 1969, Ser. No. 825,158 Claims priority, appheation Italy, May 20, 1968, 16,706A/68 Int. Cl. C22b 59100, COIG 31100 10 tJ.S. Cl. 23-17 8 Claims ABSTRACT OF THE DISCLOSURE A process is disclosed for recovering vanadium from 1 5 s olid TiClvfree residues obtained in the purification of r aw TiCI4 with H2S, wherein the solid residues are treated with oxygen or an oxygen-containing gas at temperatures b etween 150' and 200' C., thereby obtaining a VOC13- c ontaining gas from which the VOC13 is separated in a 2 0 p r4ctically pure state by rectification. The solid TiCI4-free r esidues are obtained from the purification sludges of the li quid raw TiCI4 by drying same at temperatures of 150'- 1 80' C., in a stream of inert gas, preferably nitrogen. 2 5 The present invention relates to a process for the recovery of vanadium from raw titanium chloride. More particularly, this invention relates to a process for recovering vanadium, in the form of practically pure VOC13, from 30 the'residues of the purification of TiCI4 from vanadium compound with hydrogen sulphide. ,As is already -known, the raw titanium tetrachloride obtained by chl(>rination of mineral rutile or other titaniferous ores (ilmenites, leucoxenes, etc.) is a yellow- 35 orange liquid containing as main impurities vanadium chlorides and oxychlorides and silicon, iron and aluminum chlorides; furthermore, it contains dissolved therein a ni@mber of gases such as CO, C02, COC12, HCI, C12- Hereinafter these gases will be referred to as "uncondens- 40 able gases." Rectification allows the separation of the uncondensable gases and the silicon tetrachloride as head products. The Fe, Al, Cr. etc. impurities are eliminated as highboiling tail products. The central fraction of the rectified product 45 is a clear, yellow-orange colored Equid consisting of TiCI4 and vanadium compounds. I The vanadium present in the raw titanium tetrachloride in the form of soluble chloride and/or oxychloride is only (tifficultly separable by rectification from the TiCI4, both r'O because of its low concentration in the latter, as well as for the closeness of the respective boiling temperatures. The elimination of the vanadium is, however, indispensable for obtaining titanium tetrachloride sufficiently pu7e for producing TiO2 pigment or metal titanium. 55 The known processes for the separation of the vanadium from raw titanium tetrachloride consist essentially of a chemical purification of the latter by the use of various agents such as hydrogen sulphide, oleic acid, 60 mineral oils, xanthic esters, soaps, etc. Treatment with these substances causes the vanadium to be precipitated in the form of insoluble and non-volatile compounds, whereupon it is then possible to achieve the desired Ti-V separation by simple distillation of the TiCI4- 65 Among the various purifying agents, hydrogen sulphide is one of the most frequently used, both for its tested effectiveness as well as for the ease of dosing and manipulation. T'he prior art purification processes with H2S consist 70 substantially in treating the raw TiCI4 in liquid phase with a sufficient amount of gaseous H2S at room temperaPatented Dec. 7, 1971 2 ture, thereby obtaining slurries relatively fluid and decantable in comparison with those obtained with the other above-mentioned agents. Although these slurries containi@g in suspension the solid reaction products may be distilled directly, it is nevertheless preferabie to first subject them to a decanting process and then to carry out the distillation or rectification on the clarified liquid in order to avoid serious drawbacks, due to the accumulation of the solid compounds in the boiler or pot of the distihationapparatus. The thickened sludges, since they contain a considerable amount of TiCI4 (about 80% by weight), must obviously be subjected to a process of vaporization in:order to recover the titanium tetrachloride contained in them, thereby obtaining a dry TiCI4- free product. According to another process described and claimed in Serial No. 822,1 1 0, filed May 1969, this dry product containing besides the vanadium compounds also the other impurities of the raw TiCI4, and which is free of TiCI4, may be obtained directly without having to pass through the above-described wet steps, by carrying out the purification of the raw TiCI4 by means of H2S in gaseous phase at a temperature between 130' and 180' C. By this process, in fact, the vanadium impurities separate as solid products at the same time as the solids dragged downstream of the chlorination reactor (titaniferous ore, coke, etc.) and with the volatile chlorides which desublimate or condense (FeCI2, FeCI3, ZrCl,,, etc.). This dry product, however obtained, contains prevailingly in the form of VOC13 and VOC12, practically all the vanadium which was present in the starting raw substance and may therefore be conveniently subjected to a process for the recovery of the vanadium itself. Thus, the object of this invention is to provide a process for the recovery, in the form of a practically pure compound, the vanadium contained in the above-mentioned dry TiCI4-free product obtained as a residue in the purification of the TiCI4- Another object of this invention is to recover the vanadium in the form of a valuable product such as VOC13 which, considering its substantial purity, may be used directly, for instance, as a component of polymerization catalysts for olefines. Still another object of this invention is to convert the dry solid coming from the vaporization of TiCI4, and containin.- hydrolizable products, into an inert mass which will not produce smoke when brought into contact with moisture, because it contains no more hydrolizable chlorides and, therefore, may be freely discharged into the air, thereby saving the cost of its elimination. A still further obj.-ct is to recover the vanadium by a simple and cheap system which may be directly inserted into an existing plant for the production of TiCI4- All these and still other objects are attained by the process of this invention, which consists in treating the solid TiCI47free residues, as obtained by the purification of the raw TiCI4 which H2S with oxygen or gases containing oxygen at temperatures of from 150' to 200' C., thereby obtaining a gas containing VOC13, and from which the VOC13 may be separated in a prac,tically pure state by rectification. If the antecedent purification of the TiCI4 with hydrogen sulphide has been carried out in the liquid phase, after the settling or filtering of the slurry one ob,tains a thickened sludge which is fed into a suitable vaporizer (for instance, of the screw type) where the evaporation of the TiCI4 takes place in a current of a dry inert gas (for instance nitrogen, C02, CO, argon, helium) at temperatures between 150' and 180' C. The TiCI4-vapors, free of vanadium but contaminated by small amounts of silicon tetrachloride, are sent either directly or after condensing, to a fractioning column from
[2]31625,645 3 which the uncondensable gases and the silicon tetrachloride (B.P. 57.6' C.) are separated as a head product, while the tail product (B.P., 136.4' C.) - constitutes the pure titanium tetrachloride which may be used directly for the desired industrial purposes. 5 The drying system for the thickened sludges may also include other apparatuses different from the screw-type, such as for instance heated mechanical mixers, rotary hearth furnaces, roller or rotary dryers and the like, for facilitatin.- the separation of the gases and vapors from the 10 solid particles and allowing the dischargi-ig of the latter. If the solids containing the vanadium are already free of TiC]4, one may then proceed directly to the treatment with the oxidizin,@ gas. The dry solid produ@t contains usually from about 5% 15 to 20% by weight of vanadium, calculated as metallic vanadium. The treatment of this dry solid at 150-200' C. with oxidizin.- -ases (oxygen, air or oxygen-enriched air in any ratio) may be carried out in the same apparatus as is used 20 for the recovery of the TiC'4 from the sludges, thus involving a discontinuous or intermittent process. Alternatively one may use apparatuses of the same type (that is, the above-mentioned screw-type mixers, rotary furnaces, etc.) or apparatuses of different type (for instance, of the 25 fluid-bed type). Preferred are apparatuses provided with means for indirect heating. When not using the same apparatus as is used for the recovery of the TiC]4 from the sludges, it is feasible to carry out the process in a continuous manner. 3( The amount of oxidizin- gas used in the oxidation treatment amounts to 1 to 2 kilos of oxygen for each kg. of vanadium to be recovered. The gases produced durin.- the oxidation consist Of VOC13, TiCI4 (formed by oxidation of the TiCI3 present in the solid before the oxidation), 35 and S02 (formed by oxidation of the sulphur introduced as H2S) - These gases contain (respectively) 2.5-1.5 k@-. Of VOC]3 per cubic meter of gaseous mixture when using oxygen, and 1.3-0.5 k@. Of VOC13 when usirig air. 40 The contact time of the oxidizing gas in the apparatus for the oxidation of the solids must be sufficiently long to ensure the most complete as possible transformation of the vanadium compounds into VOC13; this time depends on the partial pressure of the oxygen, on the temperatlii-e' on the kind of equipment employed, and on the contact ,, 45 face between the solid and the gas. The vapors produced during the oxidation reaction may be fractionated directly or they may be condensed at temperatures between O' C. and -30' C., thereby obtainin@ a dark red liquid essentially consisting of VOC13 nd a 5o little TiC]4. This product, rectified in a column of 10 to 30 plates, yields a head fraction boilin,a between 125' and 127' C. which is a red-orange colored product corisistin.- essentially of pure VOC'3, and a tail product which boils above 127' C. and which consists of VOC13 and TiCI4- 55 This latter fraction is preferably recycled back into the system involving the step of purification with H2SThe following examples (and corresponding figlires) are given in order to still better illustrate the inventive idea of this invention: 60 EXAAIPLE I With reference to the plant schematically represented in the accompanyin., FIG. 1, 100 kg. of liquid raw TiCI4 (containing 0.17% by weight of vanadium expressed as 65 metallic vanadium), after having been treated while stirring and at room temperature with 0.2 kg. of H?,S in 15 minutes, give place to a slurry which, de-gassed with a current of dry nitro,,en (600 liters) in 30, minutes while stirrin.-I is then discharged via line I into settling tank F, 70 where it is left to settle for 2 hours. In this way there were obtained 93.2 k.@. of clarified TiCI4 (which goes to a rectificat,,on step via line 2) and 6.80 kg. of thickened material (containing 85% by weight of TICII) which is conveyed throu.@li line 3 into 7 c, the screw evaporator A. Here, with the screw at rest, the thickened material is dried for 4 hours at 160- C. with a stream of dry nitrogen (65 liters/hr.) entering from line 4. The TiCI4-Vipors (5.8 kg.) leave through line 7, are condensed in B and by means of line 8, are re-united with the clarified TiCI4 leaving F on its way to rectification via line 2. in evaporator A remain 0.99 kg. of a solid showing the following composition in percent by weight: V=17.2%; Ti@13.8%; Cl@46.0%; elementary S= 10.3%; combined S=3.2%; Fe+Al<l%. An oxygen stream (60 liters/hr.) is passed through the solid product remaining iii A for a period of 3 hours. The oxygen flows in through line 5 at 170'-200, C., while th,- screw is at rest. The vapors leavin- A are thereupon conveyed directly through 9 into rectifi'cation column C, which has 16 plates and from which, by operating with a reflux of IO: 1, there are obtained (through I I-D12) 0.18 k,-. of gaseotis S02 via line 14, and 0.47 kg. of head products via outlet 13 (B.P. 125'-127' C.; strength in VOC13>98%; the residue being substantially TiCI4), @nd 0.21 kg. of tail product from the rectification column via line 10 (B.P. 127'-130' C.; having 70% of TiCI4, and 30% Of VOC13). The tail product from line 10 is recycled back inlo the H2S treatment system. The exhausted solid (0.20 kg.) is freely discharged into the air from A through 6, by putting the screw into motion. This solid contains predominantly TiO2 and titanium oxychlorides. The vanadium recovered with this dry solid amounts to 0.016 kg. from which one calculates a recovery of 90.6%. EXAMPLE 2 With reference -to the plant schematically illustrated in the accompanyin- F@TG. 2, 100 kg./hr. of slurry (0.17% by weight of vanadium) coming from the treatment of TiCI4 with H2S are continuously fed through I into the DORR decanter or classifier A. From A 93 kg./hr. of clarified TiCI4 are withdrawn via line 2. This is then rectified. 7 kg./hr. of thickened slurries are discharged continuously via line 3 into the screwevaporator B, heated at 170' C., where they are heated with 200 liters/ hr. of dry nitrogen introduced via line 4. 6.0 kg./hr. of TiCI4-vapors are, removed from B via line 5 and then condensed in D, the condensate being added to the clarified product leaving the system via line 2. The nitrogen flowing out of condenser D is then re-cycled by means of -the recycling pump E. Both screws, B and C, are kept in motion by carrying out the two treatments continuously. From screw B 0.99 kg./hr. of dry solids are discharg@-d via line 6 into screw mixer C kept at a temperature of 160' C., the dry solids meeting in their path of flow a counter-current strearn of air (800 liters/hr.) fed in via line 8. The vapors coming from line 7 are fractioned in F (a column with 16 plates, onrating with a reflux of 10:1) thereby obtaining (respectively) through 10 and condenser G, 0.18 kg./hr. of gaseous S02 in 13, and 0.43 k,,./hr. of head products in 11) B.P. 125'- 127, C.; contents in NOC13>98%, the residue consisting substantially of TiCI4) - From the bottom of the column F, there are discharged 0.24 k.-./hr. of tail product (32% Of VOC13+68% TiCl,) via outlet 10. This is recycled back into the H2S purification system. 0.22 k.@./hr. of exhai-isted solid material containingessentially TiO2, titariium oxychlorides and a little 'vanadium are discharged from C via outlet 9. The vanadium removed with the dry solid amounts to 0.022 kg./hr. Thus, the recovery of the vanadium equals 87%. 'yvhat is
