NO885057L - PROCEDURE FOR THE PREPARATION OF GROUP IVB TRANSITION METAL-ALKALIMETAL FLUORIDE SALTS AND PURIFICATION OF THESE. - Google Patents

Description

Field of the invention

The present invention relates to a method for the production and purification of group VIb transition metal-alkali metal fluoride salts, such as sodium fluorotitanate and sodium fluorozirconate, from group IVb transition metal oxide ores, such as ilmenite and zircon, by fluorinating the ore with an alkali metal fluoride salt, such as sodium silicofluoride and the like. in a furnace reactor at an elevated temperature between approx. 650° C and 1000° C.

The background of the invention

Titanium metal has been of significant importance to the aerospace industry since the early 1950s because it combines a high strength-to-weight ratio with the ability to perform at much higher temperatures than aluminum or magnesium. Titanium has also seen increasing use in the chemical process industry due to its excellent resistance to chloride corrosion.

In the United States, primary titanium is imported from

Japan, Europe and the USSR. The main amount of titanium metal is produced by the "Kroll" process which involves magnesium reduction of titanium tetrachloride which is produced from rutile (Ti02) or synthetic rutile. Titanium metal is also made from titanium tetrachloride by sodium reduction and electrowinning. The product of the Kroll process is metallic sponge which is consolidated using a high temperature arc melting process.

The most important consideration in titanium production is the avoidance of contamination of the titanium with metallic and non-metallic impurities because the presence of impurities, even in very small quantities, can make the product brittle and unworkable. Precautions are typically taken to prevent contamination of titanium metal with oxygen, nitrogen, alkali metals, alkaline earth metals, iron, manganese, carbon halides, silicon dioxide and the like. However, controlled amounts of oxygen, nitrogen and carbon can be added to titanium to give reinforced titanium alloys.

US Patent No. 2,550,447 teaches a process for producing titanium metal from titanium oxide ores, such as rutile, anatase and ilmenite, which comprises reduction of the ore with aluminum metal followed by iodination of the product obtained by such reduction. The iodinated product is then reacted with potassium iodide to give titanium tetraiodide. After removal of the potassium iodide, the titanium tetraiodide is converted into titanium metal either by thermal decomposition or reduction. This is a very expensive method for producing titanium metal.

US Patent No. 2,781,261 describes the process for converting titanium dioxide to titanium by fluorinating the titanium dioxide, neutralizing the fluorotitanium acid product and reducing the neutralized fluorotitanium product with aluminum.

US Patent No. 2,837,426 describes a process for converting ilmenite to an alkali metal fuortitanate by reacting ilmenite with sulfuric acid to form titanium sulfate, removing a portion of the iron contained with the titanium sulfate, by reduction and precipitation of the reduced iron compound and converting the titanium sulfate filtrate to an insoluble fluorotitanate with ammonium and/or alkali fluoride solution.

US Patent No. 2,857,264 teaches a method for producing an alkali metal chlorotitanate by digesting ilmenite ore in a mixture of sulfuric acid and hydrochloric acid. The iron present is precipitated as divalent iron sulphate and then further recovered by the addition of hydrochloric acid to precipitate a divalent iron chloride. After removal of the solid divalent ferric chloride, potassium chloride is added to the titanium-containing liquor to salt out the potassium chlorotitanium which can be reduced by a Group I metal to titanium.

US Patent No. 3,012,878 describes a process for reducing titanium halide to titanium metal using sodium metal.

US Patent No. 3,825,415 describes a method which is similar to the method described in US Patent No. 3,012,878, except that the method is carried out in the vapor phase.

US Patent Nos. 4,127,409 and 4,072,506 deal with the extraction of zirconium and hafnium by reduction of the corresponding potassium chlorozirconates and hafniates by means of

an alloy of aluminum and zinc.

US patent no. 4,390,365 relates to a method for producing titanium metal from ilmenite ore by fluorinating the ore with an alkali metal fluorosilicate at a temperature of from approx. 600° C to approx. 1000° C to form titanium fluorides optionally in the presence of carbon and/or silica tetrafluoride, leaching of the titanium fluoride to provide an aqueous solution of titanium fluoride, crystallization of the titanium fluoride from solution and reduction of the titanium fluoride to titanium metal with a reducing alloy of aluminum and zinc . The leaching solution optionally contains hydrogen fluoride, and the leaching solution is optionally oxidized and hydrolysed to form insoluble iron hydroxide which is separated from the leaching solution before crystallization of the titanium fluoride.

US Patent No. 4,468,248 relates to a process for reducing titanium halides to titanium metal by reducing the titanium halides with a molten alloy of aluminum and zinc at elevated temperatures to produce a titanium and zinc alloy. The titanium metal is extracted by distilling off the zinc.

US Patent No. 4,470,847 relates to a process for producing titanium, zirconium and hafnium metal and alloy particles suitable for powder metallurgy from the corresponding Group IVb transition metal zinc alloy by distilling off the zinc to form a corresponding sponge, sintering the sponge, hydrogenation of the sponge, grinding of the hydrogenated sponge, dehydrogenation of the hydrogenated particles obtained and passivation of the dehydrated particles.

Summary of the invention

The present invention relates to a method for producing a +4-valent Group IVb transition metal alkali metal fluoride salt (also referred to as "+4-valent salt") from a Group IVb transition metal oxide ore, which comprises the steps of fluorinating a Group IVb transition metal oxide ore by contacting the ore in an unsealed reactor with an alkali metal fluorosilicate (also known as "alkali metal silicofluoride") and alkali metal fluoride salt at a temperature of from about 600° C to approx. 1000° C to convert the Group IVb transition metal oxides in the ore to +3 and +4 worthy Group IVb transition metal-alkali metal fluoride values (also referred to as "+3 and +4 worthy values"). For each mole of Group IVb transition metal oxide present in the ore, the ore is contacted with at least approx. 0.8 molar equivalent of an alkali metal fluorosilicate and with at least approx. 1.6 molar equivalents of an alkali metal fluoride salt to minimize the loss of fluorine as silicon tetrafluoride gas from the reactor.

It has been found that during a furnace reactor operation, one mole of silicon tetrafluoride gas escapes in the exhaust gases for every two moles of alkali metal fluorosilicate introduced into the furnace. This gas, which has a residence time of less than 30 seconds in the furnace, comes out together with the exhaust gas from the furnace, and reacts very little with the ore. Stoichiometrically, one mole of Group IVb transition metal oxide should react with one mole of an alkali metal fluorosilicate to form one mole of a +4 worthy Group IVb transition metal alkali metal fluoride salt and one mole of silicon dioxide. In practice, however, if a mole of a Group IVb transition metal oxide is introduced together with a mole of an alkali metal fluorosilicate in a furnace reactor, only half of the silicon tetrafluoride formed from the cleavage of the fluorosilicate reacts to form Group IVb transition metal fluoride salts.

One third of the fluoride in the alkali metal fluorosilicate escapes from the furnace as silicon tetrafluoride. The loss of fluorine is an economic disadvantage for the process because the fluorine-containing reactants are the most expensive reactants used for the process. Theoretically, in consideration of the silicon tetrafluoride loss, 1.5 mol of alkali metal fluorosilicate is needed to fluorine the metal oxide in the ore, but for most ores an excess is needed to react with impurities, lime, carbonates and the like in the ore.

It has unexpectedly been found that if at least 0.8 mol of an alkali metal fluorosilicate, at least 1.6 mol of an alkali metal fluoride salt and 1 mol of a Group VIb transition metal oxide are introduced into the furnace, essentially all of the Group IVb transition metal oxide is converted to +3 and +4 worthy Group IVb transition metal-alkali metal fluoride values and little, if any, silicon tetrafluoride is released during the process which may escape with the furnace exhaust (see Reaction (6) below). This method of converting metal oxides into metal fluoride salts is a great improvement over the processes according to the state of the art.

It has also been found that alkali metal non-fluoride salts (basic alkali metal salts) can be used in place of alkali metal fluoride salts to achieve substantially complete conversion of the metal oxide to the corresponding metal fluoride salt with little, if any, production of silicon tetrafluoride gas. If, however, a basic alkali metal salt is present, an additional amount of an alkali metal silicofluoride salt sufficient to convert the alkali metal non-fluoride salt to an alkali metal fluoride salt is required. This improved process for preparing Group IVb transition metal-alkali metal fluoride values from Group IVb transition metal oxide ores comprises fluorinating a Group IVb transition metal oxide ore by contacting the ore in an unsealed fluorination zone with an alkali metal fluorosilicate at a temperature of from about 600°C to approx. 1000° C to convert the metal oxide to +3 and + 4 worthy Group IVb transition metal-alkali metal fluoride values. For each mole of metal oxide present in the ore, the ore is contacted with at least 1.07 molar equivalents of an alkali metal fluorosilicate and with at least 1.07 molar equivalents of an alkali metal in the form of a basic alkali metal salt. The basic alkali metal salt is preferably a carbonate salt, bicarbonate salt or oxide salt, such as sodium hydroxide.

This method has the further advantage that basic alkali metal salts can be used instead of the more expensive alkali metal fluoride salts. In this embodiment, basic alkali metal salts are converted to alkali metal fluoride salts which can react with the metal oxide in the ore to fluorine the metal oxide.

Alternatively, for each mole of

Group IVb transition metal oxide in an ore that is fluorinated with at least 1.6 molar equivalents of an alkali metal fluorosilicate to fluorinate substantially all of the ore and produce approx. 0.8 molar equivalent of silicon tetrafluoride gas. The gas comes out of the furnace together with the exhaust gas. The exhaust gas can be washed with water to capture the silicon tetrafluoride and convert this into fluorosilicic acid and silicon dioxide. It is difficult to use fluorosilicic acid as an additional fluorinating agent for ore fluorination because fluorosilicic acid decomposes at elevated temperature into silicon tetrafluoride and hydrofluoric acid. However, the fluorosilicic acid can be contacted with an alkali metal halide salt, such as sodium chloride, to produce an alkali metal fluorosilicate and a hydrogen halide, such as sodium fluorosilicate and hydrochloric acid. The alkali metal fluorosilicate is separated from the acid and used in the ore fluorination reaction.

This alternative process for the production of +3 and

+4 worthy Group IVb transition metal-alkali metal fluoride values from a Group IVb transition metal oxide ore include the steps that: a) a Group IVb transition metal oxide ore is fluorinated by contacting the ore in an unsealed fluorination zone with an alkali metal fluorosilicate at a temperature of from approx. 600° C to approx. 1000° C to form a fluorinated ore containing +3 and +4 worthy Group IVb transition metal-alkali metal fluoride values, the ore being contacted with at least 1.6 molar equivalents of the alkali metal fluorosilicate for each mole of Group IVb transition metal oxide present in said ore, being 0, 5 moles of silicon tetrafluoride gas are formed and released for each mole of alkali metal fluorosilicate introduced into the fluorination zone.

Plus 4 (+4) worthy Group IVb metal-alkali-metal-fluoride materials can be recovered by the additional steps of: b) the fluorinated ore is removed from the fluorination zone and introduced into a leaching zone in which the fluorinated ore

leached with an aqueous hydrochloric acid solution to convert the +3

and +4 worthy Group IVb transition metal-alkali metal fluoride materials to +4 worthy Group IVb transition metal alkali metal fluoride salt and to dissolve in the leach liquid at least 95% by weight of the Group IVb transition metal alkali metal fluoride salt,

c) the leachate is separated from the insoluble solids to form a leachate free of solids

substances,

d) the separated leachate is introduced into a crystallization zone in which the leachate is cooled to a temperature of at least 60°C to precipitate at least 99% by weight of the silicon impurities, such as Na2SiFg, and a portion of the +4-valued Group IVb transition metal-alkali metal fluoride salt from the leach liquor as solids, and e) the solids formed in the crystallization zone are separated from the leach liquor to give an aqueous solution which

contains +4 Group IVb transition metal alkali metal fluoride salt substantially free of silicon dioxide.

The silicon tetrafluoride gas formed and released in the fluorination zone can optionally be extracted for the production of alkali metal fluorosilicate and hydrochloric acid, which can be recycled; in the further steps that: f) the silicon tetrafluoride gas from the fluorination zone is introduced into a hydrolysis zone in which the silicon tetrafluoride is contacted with water to convert the silicon tetrafluoride into fluorosilicic acid and silicon dioxide , g) the fluorosilicic acid is introduced into an alkali metal fluorosilicate production zone in which the fluorosilicic acid is contacted with an alkali metal chloride. for the formation of an alkali metal fluorosilicate and aqueous hydrochloric acid, h) the aqueous hydrochloric acid solution is separated from the alkali metal fluorosilicate,

i) the separated hydrochloric acid solution is introduced into the leaching zone, and

j) the separated alkali fluorosilicate is introduced into the fluorination zone.

This method offers the advantage that it does not require the use of alkali metal fluoride salts or basic alkali metal salts in the fluorination step, and it avoids the loss of fluoride from the overall reaction scheme in the form of silicon tetrafluoride.

The +3 and +4 valence Group IVb transition metal-alkali metal fluoride materials formed from the above-described fluorination processes are a mixture comprising +3 transition metal fluoride material and +4 transition metal fluoride material, such as Na^TiF^ and Na2TiOF4. These materials can be converted to a +4 worthy Group IVb transition metal-alkali metal fluoride salt, such as sodium fluorotitanate or sodium fluorozirconate.

This conversion is carried out in the leaching step in the presence of aqueous hydrochloric acid. This conversion requires the presence of trivalent iron which is converted to divalent ferric chloride. The conversion requires at least approx. 1.75 mol of hydrogen chloride per Group IVb metal present as +3 and +4 worthy materials. Under the correct leaching conditions, time, temperature and agitation, at least 95% by weight of the +3 and +4 worthy materials are rendered soluble. The leaching liquid is separated from the insoluble component in the leaching step and cooled to a temperature of at least approx. 60° C to precipitate silicon impurities. Silicon impurities have a very low solubility in the leach liquid at temperatures of 60° C or lower, and essentially all silicon impurities precipitate. It is inevitable that a part of the +4 valuable salt, depending on the HCl concentration and generally below 10% by weight, also precipitates together with the silicon impurities. In general, strong hydrochloric acid concentrations favor a better splitting by maximizing the leaching of dt +4 worthy salt. However, strong acid concentrations favor a back reaction between silicon dioxide and the +4 valence salt. These solids are separated from the cooled leach liquor and can be recycled into the leach zone to recover the +4 worthy salt. The leaching liquid in the leaching zone is saturated with respect to dissolved silicon contaminants. The recycled solid silicon impurities cannot thus cause an accumulation of silicon impurities in the leach liquid.

The +4 valuable salt falls out of the leach liquid

by cooling the leach liquor to a temperature not exceeding 30° C. Preferably, sodium chloride (solid) and/or hydrogen fluoride are added to the leach liquor to aid the salting out of the +4 valuable salt. The +4 valuable salt crystallizes out essentially in pure form, but it contains small amounts of dissolved iron-manganese compounds. Surprisingly, the iron and manganese compounds or impurities can be easily removed from the product crystals by washing the crystals one or more times with dilute aqueous hydrochloric acid. This is a

important trade-off when the +4-valent Group IVb transition metal-alkali metal-fluoride salt is to be used to prepare a Group IVb transition metal by reducing the +4-valent salt as described here. The preferred means of reducing the +4 valence salt is by adding the salt to a molten aluminum-zinc alloy and agitating it to achieve intimate contact between the alloy and the salt. The +4 valuable salt is reduced to Group IVb metal which is soluble in zinc,

and the aluminum is oxidized to an aluminum fluoride salt.

This type of reduction can also be used to

purify the Group IVb transition metal. Impurities that are not soluble in the molten zinc or the molten Group IVb transition metal-zinc alloy are recovered towards the top of the molten alloy or fall to the bottom of the molten alloy depending on the respective densities of the alloy and the impurities. It is very difficult to

clean Group IVb metal scrap, such as titanium metal scrap, containing insoluble impurities, such as halide salts, alkali metal salts, alkaline earth metal salts, tungsten carbide and nitrides. Such metal scrap can be cleaned by adding it to molten zinc which will dissolve the Group IVb transition metal, but not the insoluble impurities. The insoluble impurities, i.e. for example halide salts, alkali metal salts, alkaline earth metal salts and nitrides, due to their insolubility and density, will be found towards the top of the molten Group IVb transition metal zinc alloy (referred to as the "molten alloy") forming a separate phase and/or slag., Other insoluble impurities heavier than the molten alloy, such as tungsten carbide, will settle to the bottom of the molten alloy. If the Group IVb transition metal zinc alloy contains unacceptable amounts of impurities that are soluble in the molten alloy ("soluble impurities"), a high purity Group IVb transition metal can be added to the molten alloy to dilute the concentration of the soluble impurities to give a Group IVb transition metal-zinc alloy that has an acceptable level of contamination. Alternatively, a +4 worthy Group iv transition metal alkali metal fluoride salt and a molar equivalent

of aluminum is added to the molten alloy in which the +4 valency salt will be reduced to a Group IVb transition metal to dilute the soluble impurity content. The insoluble impurities on top of the molten alloy are skimmed off, and the molten alloy is stripped of the heavier insoluble impurities which fall to the bottom of the molten alloy, to provide a molten alloy substantially free of insoluble impurities. The zinc is removed by sublimation either under a vacuum or using an inert gas purge to give a Group IVb transition metal sponge which can be converted to a Group IVb transition metal powder suitable for powder metallurgical use as described in US Patent No. 4 470 847.

Description of the drawings

Fig. 1 is a schematic illustration of the method according to the present invention for the production of sodium fluorotitanate, Fig. 2 is a schematic representation of the cleaning steps according to the present invention for removing silicon, iron and magnesium impurities from a sodium fluorotitanate product, Fig. 3 is a schematic illustration of a cleaning process of the present invention for cleaning Group IVb transition metal scrap to produce a metal sponge, and

Fig. 4 is a curve showing the effect of washing

of sodium fluorotitanate crystals with 1 wt% HCl washes.

Detailed description of the invention

With reference to fig. 1 illustrates the process for producing sodium fluorotitanate using ilmenite ore. However, the method can be used for other ores that contain titanium dioxide or zirconium oxide,

to prepare alkali metal fluorotitanate or alkali metal fluorozirconate, respectively. The fluorination zone 10 is in an unsealed furnace in which the ore and, where appropriate, additives are added through the feed end 12. Hot gas is introduced through

product end 14 in countercurrent to the ore flow. The oven is preferably heated by indirect means, such as oven wall heating devices. The ore is preferably ground, mixed with the other feed materials and formed into agglomerates with a diameter of less than 5.1 cm. It has been found that the addition of carbon in conjunction with the iron present in the ore or iron, as divalent iron oxide, which has been added to a low-iron ore, has a synergistic effect on the subsequent recovery of the Group IVb transition metal From about 1 to about 10, and preferably from about 1.2 to about 4, wt% carbon may be mixed with the ferrous ore to enhance the recovery of titanium. It has been found that ores with a low iron content or even substantially free of iron benefit from the addition of iron, as trivalent iron oxide, to the ore. The ore should contain at least 14 wt. % iron The ore preferably contains from about 14% to about 36% by weight iron and from about 25% to about 50% by weight Group IVb transition metal.

In the embodiment of the present invention where the ore is fluorinated in the presence of an alkali metal fluoride salt or a basic alkali metal salt, the salt, carbon and iron are formed with the ore to form an integral component of the feed agglomerate. In this embodiment, the ore is mixed with at least 1.6 molar equivalents of alkali metal fluoride, such as sodium fluoride, or basic alkali metal salt, such as sodium carbonate, for each mole of Group IVb transition metal in the ore.

The feed agglomerates are also mixed with the fluorinating agent, an alkali metal fluorosilicate, preferably sodium fluorosilicate. If the fluorosilicate is the only fluorinating agent, at least 1.6 molar equivalents of fluorosilicate are mixed with the ore for each mole of Group IVb transition metal in the ore. If the feed is also mixed with an alkali metal fluoride salt, the feed agglomerates are mixed with at least 0.8 molar equivalents of an alkali metal fluorosilicate and at least 1.6 molar equivalents of an alkali metal fluoride salt for each mole of Group IVb transition metal in the ore. If the feed agglomerates are mixed with a basic alkali metal salt, the feed agglomerates are mixed with at least approx. 1.07 molar equivalents of an alkali metal fluorosilicate and with at least 1.07 molar equivalents of an alkali metal in the form of a basic alkali metal salt for each mole of Group IVb transition metal in the ore. The additional alkali metal fluorosilicate is required to fluorine the basic alkali metal salt.

The ore, iron (if any), carbon, fluorinating agent and basic alkali metal salt or fluoride salt (if any) are ground to a particle size of approx. 0.59 to approx. 0.038 mm, preferably from 0.15 to 0.038 mm, and is thoroughly mixed and then formed into agglomerates for supply to the furnace fluoridation zone.

The feed agglomerates are heated in the fluorination zone to a temperature between approx. 600° C and 1000° C, preferably from approx. 750° C to approx. 950° C, to convert the Group IVb transition metal oxide to +3 and +4 worthy Group IVb transition metal-alkali metal fluoride materials. The fluorination is believed to proceed via the series of reactions reproduced below. The reactions are illustrated using sodium salts

+4

and Group IVb transition metal compounds (M and M ).

However, the same reactions occur with other alkali metal salts.

Reaction (1) takes place at elevated temperatures, such as 600°C or higher, in which the alkali metal fluorosilicate decomposes to form 2 moles of an alkali metal fluoride and silicon tetrafluoride gas. Reactions (2) to (4) are reactions between silicon tetrafluoride and basic alkali metal salts, which give an alkali metal fluoride salt, carbon dioxide, silicon dioxide and water as the case may require. Reaction (5) is the reaction between a Group IVb transition metal oxide (MO^) and 1 molar equivalent of an alkali metal fluorosilicate and 2 molar equivalent of an alkali metal in the form of a basic alkali metal salt, such as sodium carbonate. In this fluorination reaction, the Group IVb transition metal oxide is fluorinated to form a +4-valent Group IVb transition metal alkali metal oxide fluoride material Na2M0F^.

Reaction (6) shows that if reaction (5) is carried out

in the presence of at least two molar equivalents of an alkali metal fluoride salt instead of a basic salt, 2 molar equivalents of the metal oxide are fluorinated. Reaction (7) is a reaction that takes place between the carbon starting material and the iron oxide in the ore, forming divalent iron oxide and carbon monoxide.

The divalent iron oxide reacts with the alkali metal fluorosilicate to give an alkali metal iron(II) fluoride as shown by reaction (8). The alkali metal-iron(II) fluoride reacts with the alkali metal fluorosilicate and the Group IVb transition metal oxide MC>2 to form a +3-valent Group IVb transition metal-alkali metal fluoride bond, trivalent iron oxide, silicon tetrafluoride and silicon dioxide as shown by reaction (9).

If a basic alkali metal salt is present, the silicon tetrafluoride will react with the salt to form an alkali metal fluoride salt (see reactions (2) and (4)). A portion of the Group IVb transition metal oxide (M02) reacts directly with the alkali metal fluorosilicate as shown by reaction (10) to form a +4-valent Group IVb transition metal-alkali metal oxide-fluoride compound, silicon tetrafluoride and silicon dioxide. If a basic alkali metal salt is present, the silicon tetrafluoride will react with the salt to form an alkali metal fluoride salt.

As shown in reaction (11), part of the trivalent iron oxide reacts directly with the alkali metal fluorosilicate to form an alkali metal iron(III) fluoride salt, silicon tetrafluoride and silicon dioxide. The silicon tetrafluoride can react with the basic alkali metal salt to form an alkali metal fluoride salt. Reaction (12) is a combination of reactions (8) to (11) in which for each mole of Group IVb transition metal oxide in the ore this is contacted with

1.6 molar equivalents of an alkali metal fluorosilicate and 0.48 molar equivalents of divalent iron oxide.

The carbon and the trivalent iron oxide which are assembled in the feed agglomerates react to form divalent iron oxide and carbon monoxide. The +3 and +4 valenced Group IVb transition metal-alkali metal fluoride materials comprise a mixture of a +3 valence Group IVb transition metal-alkali metal fluoride material (Na^MFg) and a +4 valence Group IVb transition metal-alkali metal oxide fluoride material ( Na2MOF4). Part of the divalent iron oxide is converted into an alkali metal iron(II) fluoride salt (Nao .FeFb,). About. 1 molar equivalent of silicon tetrafluoride is formed for each mole of alkali metal fluorosilicate present in the feed agglomerates.

As explained above, the addition of 2 molar equivalents of an alkali metal fluoride salt or the addition of one molar equivalent of an alkali metal in the form of a basic alkali metal salt per moles of alkali metal fluorosilicate eliminate the formation of free silicon tetrafluoride gas in the reaction (12).

The +3 and +4 valued Group IVb transition metal-alkali metal fluoride products (Na^MFg and Na2MOF4) from reaction (12) are converted to the desired +4 valued Group IVb transition metal-alkali metal fluoride salt, namely alkali metal fluorotitanates and alkali metal fluorozirconates. The conversion is achieved by contacting the +3 and +4 valence Group IVb transition metal-alkali metal fluoride materials with an aqueous hydrogen chloride solution in the presence of trivalent iron oxide and an alkali metal iron(III) fluoride salt as shown.

The feeding mixture should contain at least 0.24 molar equivalent iron per mol Group IVb transition metal oxide, preferably as iron oxide, to supply sufficient fluoride in the form of an alkali metal iron(III) fluoride salt (Na^FeFg)

during the formation of Na„MF, during the leaching step. The feeding mixture can also contain more than 1.6 molar equivalents of alkali metal fluorosilicate per mol Group IVb transition metal oxide. However, only 1.6 molar equivalents of the fluorosilicates are necessary when at least 0.24 molar equivalents of iron are present.

Again with reference to fig. 1, fluorinated ore 16, which comprises the solid products from the reaction (12) and other solid contaminants, is transferred from the producing end 14 of the furnace to a leaching zone in which the fluorinated ore is leached with aqueous hydrochloric acid. The leaching solution has an HC1 concentration of less than 10% by weight HC1, preferably from approx. 1% to approx. 3% by weight. Conventional leaching equipment can be used in the leaching zone to solubilize the +3 and +4 valence Group IVb transition metal-alkali metal fluoride material (Na3 0MFo, or Na^MF^) identified in reaction (12). The solubilized salts are converted to the desired +4 valency Group IVb transition metal-alkali metal fluoride salt ( Na^ MF^ ), namely alkali metal fluorotitanates and alkali metal fluorozirconates.

It is believed that the chemical reactions responsible for this transformation are those indicated by reaction (13).

Reactions (12) and (13) illustrate the importance of iron compounds for the fluorination and conversion reactions to form the desired +4 valence Group IVb transition metal alkali metal fluoride salt. The Group IVb transition metal compounds according to reaction (12) are found in the aqueous leaching liquid in the leaching zone. The leaching liquid is separated from the undissolved solids after the leaching, as these include iron-containing solids, silicon impurities (primarily silicon dioxide), clays and the like. The leaching operation is normally carried out at a temperature between approx.

60° C and the boiling point temperature of the leaching solution, preferably between approx. 100° C and 110° C. The leaching is normally carried out continuously instead of batchwise, with a residence time between approx. 1 minute and approx. 3 hours, preferably for approx. 4 to approx. 10 minutes.

The hot leach solution 20 containing the desired +4 valence Group IVb transition metal-alkali metal fluoride salt is transferred to a crystallization zone 22 in which the leach is cooled to a temperature from approx.

60° C to approx. 25° C, preferably between approx. 27° C and 23° C,

in which a portion, generally less than 10% by weight, of the desired +4-valued Group IVb transition-metal-alkali-metal-fluoride salt is crystallized and substantially all silicon impurities precipitated. Conventional crystallization equipment, such as that described in The Chemical Engineer's Handbook, 5th Edition, R.H. Perry and C.H. Chilton, McGraw-Hill Book Co,

New York, N.Y. (1973), can be used in the crystallization zone. The solids are removed from the cooled leachate to give a substantially pure dissolved +4 Group IVb transition metal-alkali metal fluoride salt"(Na A "TiFb,).

In the embodiment of the invention where alkali metal fluorosilicate is the only fluorinating agent used in the fluorination zone, silicon tetrafluoride is formed and leaves the fluorination zone together with the exhaust gases 30. The exhaust gases are passed through a conventional gas scrubber (t^SiFg production zone) 32 in which the gases are washed with water to capture the silicon tetrafluoride to form fluorosilicic acid and silicon dioxide as shown by reaction (14). Silicon dioxide solids are separated from the fluorosilicic acid. The fluorosilicic acid 34 is transferred to a sodium fluorosilicate production zone 36 in which the fluorosilicic acid is reacted with sodium chloride 38 or another alkali metal chloride to form sodium or other alkali metal fluorosilicate and an aqueous hydrochloric acid solution, as shown by reaction (15).

In the fluorosilicic acid production zone, the hot off-gas containing the silicon tetrafluoride is rapidly cooled by the scrubbing water, thereby eliminating the need to cool the off-gas before scrubbing. However, if desired, the exhaust gas can be pre-cooled before scrubbing. The amount of fluorosilicic acid formed in the fluorosilicic acid production zone is insufficient to provide the required amount of alkali metal fluorosilicate needed in the fluorination zone. Additional fluorosilicic acid 40 is therefore preferably added to the alkali metal fluorosilicate production zone to produce at least 1.6 moles of alkali metal fluorosilicate for each mole of Group IVb transition metal oxide introduced into the fluorination zone. The alkali metal fluorosilicate produced in the alkali fluorosilicate production zone and which is slightly soluble in the aqueous hydrochloric acid solution is separated from the hydrochloric acid solution, preferably after the entire mixture has been cooled to a temperature of at least 30° C. The separated alkali metal fluorosilicate is dried and mixed with the ore and additives, which described above, forming the feed mixture for the fluorination zone. After separation, the hydrochloric acid solution 42 is introduced into the leaching zone to leach and convert the +3 and +4 valuable Group IVb transition metal-alkali metal-fluoride materials as described above. In the preferred embodiment of the present invention, the leached solution contains less than 10% by weight of HC1, preferably from approx. 1% to approx. 3 wt% HC1.

Fig. 2 shows a preferred embodiment of the present process for providing a +4-valent Group IV transition metal-alkali metal fluoride salt with improved purity for a very high salt recovery. The leached zone 18 shown in fig. 2 is operated in the same way as the leached zone shown in fig.

1. The leaching liquid 20 is led to a first crystallization zone 50 in which the leaching liquid is cooled to a temperature between approx. 25° C and approx. 60° C, preferably between approx. 27° C

and approx. 33° C. A portion of the salt product and essentially all of the silicon impurities (primarily alkali metal fluorosilicate) precipitate as insoluble solids 52 and are separated from the cooled leach liquid. The separated solids are recycled back to the leach zone to recover the +4 valued Group IVb transition metal-alkali metal fluoride salt which is made soluble in the leach liquor.

Some of the silicon impurities are also made soluble by the leaching liquid. However, since the leaching liquid in the leaching zone is essentially saturated with silicon impurities, most of the silicon impurities from the first crystallization zone precipitate together with the other insoluble substances 54 in the leaching zone. Recycling of the silicon impurities from the first crystallization zone back to the leaching zone thus does not result in a concentration or accumulation of silicon impurities in the leaching liquid. The leaching liquid 54 from the first crystallization zone is led to a second crystallization zone 56 in which the leaching liquid is cooled to a temperature between approx. -10° C and approx. 30° C, preferably from approx. -10° C to approx. 0° C, to essentially excrete all the +4-valued Group IVb transition-metal-alkali-metal-fluoride salt.

The rate of crystallization can be increased by salting the mother liquor in the second crystallization zone with sodium chloride 58. Small amounts of hydrofluoric acid can also be added to improve yields. However, hydrofluoric acid is relatively expensive and quite corrosive. Its use can be minimized or omitted by performing the leaching step under optimal conditions. The salting out is carried out by adding between approx. 50 and approx. 150 g of sodium chloride per liters of leaching liquid.<*>From 0 to approx. 10 g hydrofluoric acid (48% solution) per liters of leaching fluid can be added to improve the titanium yield. The crystallized solids 58 which contain the desired fluoride salt product and are substantially free of silicon impurities are separated from the leachate from the second crystallization zone and transferred to a multi-stage countercurrent washing zone 60. The spent leachate 62 can be disposed of in an environmentally acceptable manner or it can be recycled as the salting out medium for the sodium silicon fluoride crystallization zone.

In wash zone 60, the +4 valued Group IVb transition metal-alkali metal fluoride salts are counter-currently washed in one or more stages with dilute hydrogen chloride solution to remove substantially all iron and manganese and all minor impurities soluble in dilute hydrochloric acid. At each wash, the crystals are washed with at least an equal amount by weight of dilute HC1. The dilute hydrochloric acid contains less than 5% by weight of HCl, preferably less than 2% by weight. The washing is carried out at a temperature below 30° C, preferably at the ambient temperature. A single washing desalted with the dilute hydrochloric acid solution reduces the iron content and manganese content in the salt product to below 100 parts per million (ppm). The washing liquid with the soluble contaminants is deposited using normal environmentally acceptable methods.

After the Group IVb transition metal alkali metal fluoride salt has been washed, the salt is dried to remove moisture. The salt can then be reduced by conventional methods for preparing titanium metal or advantageously reduced with a molten aluminum and zinc alloy, as set forth in US Patent Nos. 4,390,365 and 4,468,248, to produce a molten Group IVb transition metal zinc alloy . The molten alloy can, after the separation of the insoluble impurities, be converted into a pure Group IVb transition metal by sublimation of the zinc, preferably under a vacuum or by sweeping an inert gas stream, such as an argon gas stream.

The dried crystals of the fluorides of the Group IVb metal can be reduced in a reducing zone in which they are contacted in the molten state with a molten zinc-aluminum alloy. The alloy may comprise from 1:99 to 20:80 parts by weight of aluminum in relation to zinc. The molten salt and the alloy are mutually immiscible. Agitation of the molten salt and molten alloy to ensure intimate contact is therefore preferred. Reduction takes place at a temperature from at least 650 C to approx. 1000° C, preferably from approx. 850° C to approx. 950° C. The contact time between the molten alloy and the molten salt can be varied to ensure that the Group IVb metal present in the salt is converted to a Group IVb metal-zinc alloy. The aluminum present in the aluminum-zinc alloy during the reduction is converted to the corresponding fluoride salt and can be isolated as the pseudocryolite.

After the agitation of the mixture has been stopped, the reduced mixture separates as the molten salt rises to the top from which it can be poured off from the molten alloy. Alternatively, the molten Group IVb metal-zinc alloy can be separated from the bottom of the vessel and transferred to a reducing zone where the zinc is separated from the Group IV metal. The removal or reduction of the zinc must take place under inert conditions due to the tendency of the Group IVb metal to take up oxygen and nitrogen. It is suitable that an argon atmosphere is present during the sublimation step or that the sublimation is carried out under a vacuum. A suitable vessel for carrying out the sublimation, as well as other of the various high temperature operations described herein, is a graphite-lined reactor. It has been shown that during the salt reduction step it is advisable that both the salt and alloy basins are maintained above the liquidus temperature in order to avoid the formation of solids which may be abrasive both to the agitator and the reactor walls.

It is desirable to have the molten zinc nearly saturated with dissolved Group IV metal, if possible, to minimize the amount of zinc to be distilled in the subsequent sublimation step. The salt reduction step can advantageously take place under an elevated pressure to increase the boiling point temperature of the molten Group IVb metal-zinc alloy, which increases the solubility of the Group IVb metal in molten zinc. For example, a titanium-zinc alloy boils at approx. 915° C at atmospheric pressure. At this temperature, only approx. 15% by weight of titanium metal is dissolved in molten zinc before solid formation. If the reduction is carried out under an elevated pressure (about 1.5 atmospheres), however, the molten titanium-zinc alloy boils at about 950°C, and approx. 25% by weight of titanium metal can be dissolved in the zinc before solid formation begins.

At elevated pressures, the main limitation of the reduction temperature is determined by the construction materials of the reactant vessel. For example, at temperatures approaching 1000° C, there is a significant increase in the contamination of the Group IVb metal with carbon from graphite from the graphite reactor wall. The degree of carbon pollution becomes serious above 1100°C.

In the sublimation step, the sublimation is carried out under vacuum or in an inert gas atmosphere, such as an argon gas atmosphere, to prevent oxygen and nitrogen contamination of the Group IVb metal. The zinc is distilled off at a temperature of approx. 800° C to approx. 1000° C so that a Group IVb metal sponge is left behind. When the distillation is carried out under a vacuum, the distillation can take place at a somewhat lower temperature.

The Group IVb metal sponge can be sintered to reduce its surface area. After sintering and cooling, the sponge can be passivated by exposure to a controlled amount of oxygen-containing gas to provide a thin (monomolecular) protective coating of the Group IVb transition metal oxide on it before the sponge is exposed to the air or another non-inert atmosphere. The sublimated zinc can be recovered and recycled for use in subsequent salt reduction steps.

With reference to fig. 3, Group IVb metal scrap is contaminated with impurities soluble in molten Group IVb metal and molten zinc, added to a molten aluminum-sich alloy in a zinc alloy zone 70 to dissolve the metal scrap. A Group IVb transition metal fluoride salt is added to the zinc alloy zone 70, which is reduced by the molten aluminum metal to a Group IVb metal that is found again in the zinc to dilute the soluble impurities in the molten Group IVb metal-zinc alloy. The aluminum is reduced to form an aluminum fluoride salt which is insoluble in the molten Group IVb metal-zinc alloy. The reduction is preferably carried out with agitation to ensure intimate contact between the molten metal salt and the molten aluminium-zinc alloy. The zinc and aluminum separately or as an aluminum alloy and the metal salt can optionally be melted simultaneously in the zinc alloy zone. By the above methods, the purity of the scrap metal can be increased by diluting the soluble impurities in the metal with pure Group IVb transition metal produced from the metal fluoride in the presence of the scrap, so that the metal obtained can satisfy industrial and/or military specifications.

In an alternative embodiment of the present invention, Group IVb metal scrap can be added to the zinc alloy zone in which the zinc is not alloyed with aluminium, in order to remove insoluble impurities, such as carbon, halide salts, alkali metal salts, alkaline earth metal salts, aluminum salts, silicon dioxide and nitrogen, which are insoluble in molten zinc and molten Group IVb transition metal. These latter contaminants will float to the surface of the molten Group IVb metal-zinc alloy and can be poured off. If the metal scrap contains heavy insoluble impurities, such as tungsten carbide, tungsten molybdenum or the like, these impurities will fall to the bottom of the zinc alloy zone after the agitation is finished, and the molten Group IVb metal-zinc alloy can be poured off from such heavy insoluble impurities. If the scrap metal contains undesirable amounts of soluble impurities, high-purity Group IVb transition metal can be added to the zinc alloy zone to dilute the soluble impurities in the scrap metal to provide Group IVb transition metal in the molten metal-zinc alloy that will pass industrial and/or military specifications.

In a further embodiment of the present invention, the Group IVb metal-zinc alloy produced in the zinc alloy zone may be alloyed with alloying agents, such as vanadium, aluminum, nickel and the like, to form a

Group IVb transition metal alloy after the removal of zinc. Alternatively, the scrap metal, the alloying agents, the pure metal and/or the metal salt can be melted together with zinc_and/or aluminum and zinc.

After the formation of the molten Group IVb transition metal zinc alloy optionally containing alloying agents, the molten alloy is transferred to a sublimation zone in which the zinc is removed by sublimation to give a Group IVb transition metal sponge. If it is carried out under an inert gas atmosphere, the sublimation can be carried out at a temperature between approx. 800° C and approx. 1000° C. If the sublimation is carried out in a vacuum, the sublimation can be carried out at a temperature below 800° C. To prevent oxygen and nitrogen contamination of the Group IVb metal during the sublimation, the sublimation is carried out under an inert gas atmosphere unless it is carried out in a vacuum. The metal sponge can be sintered to reduce its surface area and then passivated with an oxygen-containing gas so that the sintered Group IVb metal sponge can be further processed to produce Group IVb metal powder that can be used for metallurgical powder purposes in accordance with the methods described in US patents no. .4 470 847 and 4 595 4513.

The present invention is further described with reference to the following examples which are presented for the purpose of illustrating the invention. These examples are not intended to be a limitation of the invention.

Example 1

With reference to fig. 1, 1.5 mol of fluorosilicic acid 40 (in the form of a 23% by weight aqueous solution) is reacted with 3 mol of sodium chloride 38 to form 1.5 mol of sodium silicon fluoride crystals 39 and 3 mol of hydrochloric acid 42 (approximately a 10% by weight aqueous solution ). Sodium silicon fluoride is combined with ilmenite ore containing 1 mol of titanium dioxide, and heated in a fluorination zone opened in a furnace 10 to a temperature between approx. 700° C and 800° C. The sodium silicon fluoride is split in the oven to form sodium fluoride and silicon tetrafluoride. Half of the silicon tetrafluoride, 0.75 mol, reacts with the titanium dioxide in the ore to form +3 and +4 valuable titanium fluoride salts and silicon dioxide. The other half of the silicon tetrafluoride comes out of the reactor in the form of silicon tetrafluoride gas in the exhaust gases 30. The silicon tetrafluoride in the exhaust gas is transferred to the silicon tetrafluoride production zone where it is washed with water to form 9.25 mol of silicon dioxide and 0.5 mol of fluorosilicic acid 34 (about a 23 wt% aqueous solution). The fluorosilicic acid is recycled to the sodium fluorosilicate production zone. The fluorinated ore 16 is ground and then transferred to a leaching zone 18 in which the fluorinated ore is leached with aqueous hydrochloric acid to convert the +3 and +4 valuable titanium fluoride salts into titanium fluoride which is made soluble by the leaching liquid. The leach liquid is separated from the insoluble solids and transferred to the crystallization zone 22. In the crystallization zone, the leach liquid is cooled to form crystals of titanium fluoride and a spent leach liquid containing soluble impurities of iron, hydrochloric acid, sodium fluoride and the like.

Example 2

The method according to example 1 can be carried out in such a way that the loss of silicon tetrafluoride gas in the exhaust gas is eliminated. The ore containing 1 mol of titanium dioxide is combined with 1.6 mol of sodium fluoride and 0.8 mol of sodium silicon fluoride and introduced into the fluorination zone to form fluorinated ore containing the +3 and +4 valuable titanium fluoride salts, sodium fluoride, silicon dioxide impurities, iron oxide and iron salts and unreacted gangue. The fluorinated ore is transferred to a leach zone where it is leached with a hydrochloric acid solution obtained from an external source to form a leach liquor containing the desired +4 value sodium fluorotitanate for solubilization in the leach liquor and the insoluble solids separated from the leach liquor. The leach liquor is transferred to the crystallization zone to crystallize out the desired sodium fluorotitanate product, leaving a spent leach liquor containing soluble sodium chloride, soluble iron salts, other impurities, and excess hydrochloric acid.

Example 3

The method according to example 1 can be carried out in such a way that the loss of silicon tetrafluoride in the exhaust gases is prevented by putting the ilmenite ore containing 1 mol of titanium dioxide together with 1.07 mol of sodium silicofluoride and 1.07 mol of a basic sodium salt, such as sodium carbonate, sodium bicarbonate or sodium hydroxide . The feed material is passed through a fluorination zone 10 in which the feed material is heated to form +3 and +4 valuable titanium fluoride salts, sodium fluoride, silicon dioxide impurities, iron salts and carbon dioxide or water. Fluorinated ore is transferred to the gradient zone 18 in which the fluorinated ore is leached with hydrochloric acid solution obtained from an external source to solubilize titanium fluoride salts and form the soluble sodium fluorotitanate. The leach liquor is separated from the insoluble solids and transferred to a crystallization zone where it is cooled to crystallize out the desired sodium fluorotitanate.

Although methods according to examples 1-3 have been illustrated using sodium salts, other alkali metal salts, such as potassium salts or lithium salts, can also be used. However, the sodium salts are less expensive than the corresponding potassium salts and lithium salts and thus offer economic advantages.

Example 4

A mixture of finely ground ilmenite ore (36.8 parts by weight), sodium silicofluoride (61.5 parts by weight) and calcined petroleum coke (1.7 parts by weight) was intimately dry blended. The mixture contained 1.36 molar equivalents of sodium fluorosilicate per moles of titanium dioxide. Water (9.4% by weight) was mixed into the mixture and spheres with a diameter between +9.5 and -15.9 mm were prepared from the mixture in a sphere forming pan. The spheres were dried in a tray dryer. The dried spheres (2501.5 g) were placed in a pot; heated with an indirect heating device at a temperature between 750°C and 788°C for a total time of 4 hours to ensure that the charge was completely reacted with silicon tetrafluoride, and 256 g of silicon tetrafluoride were

measured into the pot during the last two hours of the reaction

after the emission of silicon tetrafluoride from the reaction i

the essential had ceased. Only a small amount (about 35 g) of this later added silicon tetrafluoride was consumed by the charge.

During the reaction, a total amount of 10.8 g of carbon, 28.8 g of oxygen and 646 g of silicon tetrafluoride was swept out of the pot with the nitrogen purge gas (200 cm 3 per minute), which was continued for the duration of the reaction. In addition, 126 g of water was collected from the exhaust gas in a dry ice-cooled trap.

The fluorinated ore from the reaction had its original shape, in the form of spheres, but the fluorinated ore had a smaller volume due to the weight loss that occurred during the reaction. The balls were crushable and were ground in a hammer mill to 90% -0.25 mm. A small sample of the milled fluorinated ore was leached in two steps with hydrochloric acid (3.6% by weight). 70% of the titanium in the ore was solubilized. The remainder of the fluorinated ore was leached in a single step with an aqueous hydrogen fluoride-hydrogen chloride solution (3 wt% HF and 7 wt% HCl) in a ratio of 1 part by weight of fluorinated ore to 5.1 parts by weight of a leaching solution. The titanium was solubilized, and sodium fluorotitanate crystals were recovered from the leach liquor (63.8% by weight).

This example showed that approx. half of the silicon tetrafluoride that was formed during heating from the sodium fluorosilicate incorporated in the balls reacts with the ilmenite ore. The other half of the silicon tetrafluoride did not react with the ore and left the reaction zone together with the purge gas. The amount of titanium extracted was not high due to reason

of the fluoride loss. Of the 1.1 mol Na2SiFg per moles of titanium in the spheres reacted only approx. 0.53 mol of Na2SiF6 with the ore, the remainder passing into the gas phase and being removed from the system with the nitrogen purge.

Example 5

A new ball composition comprising 33.1 parts by weight of ilmenite ore, 65.3 parts by weight of sodium fluorosilicate and 1.6 parts by weight of calcined petroleum coke was prepared in the same way as in example 4. The mixture was finely ground and shaped into balls and heated in accordance with the method according to example 4. The fluorinated ore, after it had been ground, was leached with a hydrochloric acid-fluoric acid solution (6 wt% HCl and 5 wt% HF). In this experiment, half of the silicon tetrafluoride that was formed from the sodium fluorosilicate in the balls passed into the gas phase and did not react with the ore. In a large-scale leaching of the fluorinated ore, 87% by weight of the titanium was solubilized when the fluorinated ore was leached with a hydrogen fluoride-hydrogen chloride solution (2.9% by weight HF and 6.9% by weight HC1).

Example 6

Another bullet composition was made which included

28.7 parts by weight of ilmenite ore, 69.9 parts by weight of sodium fluorosilicate and 1.4 parts by weight of calcined petroleum coke. The mixture was finely ground and shaped into balls as described in example 4 and was then farmed in accordance with the method according to

example 4. The fluorinated ore was ground and leached with an aqueous hydrochloric acid solution (9.5% by weight HCl), and 95% of the titanium was solubilized in the leaching liquid. Almost 96% of the titanium in the leaching liquid was recovered as sodium fluorotitanate crystals by cooling the leaching liquid to -7° C and adding 100 g of sodium chloride per liters of leaching liquid to salt out the sodium fluorotitanate.

Example 7

Moist sodium fluorotitanate crystals recovered from the leach liquors, such as the leach liquor of Example 6, were washed with successive batches of a 1% by weight hydrochloric acid solution. The iron and magnesium impurities in the sodium fluorotitanate crystals were reduced to low levels during the first few washes. The residual level of iron and manganese in the sodium fluorotitanate crystals is dependent on the quality and size of the grown crystals which in turn are dependent on the quality of the crystallization apparatus construction and on the working parameters. To facilitate the removal of these contaminants, the crystals are preferably allowed to grow to a small size, which is achieved by rapid cooling of the leach liquid at a temperature below 0°C.

The silicon impurities are not reduced by washing. As part of the sodium fluorotitanate crystals dissolve during the washing operation, the silicon contamination level increases because the sodium silicofluoride is not dissolved by the washing liquor.

The effectiveness of washing the sodium fluorotitanate crystals crystallized from the leach liquids and containing approx. 7% to approx. 10% by weight hydrogen chloride, with a 1% by weight aqueous hydrochloric acid wash is shown in Fig. 4. The first wash effectively lowers the concentration of iron to below 100 parts per million (Curve A). However, each washing with 1% by weight aqueous hydrogen chloride gradually increases the concentration of sodium silicofluoride impurities in the crystals (Curve B).

Example 8

The leach liquor obtained from leached fluorinated spheres according to Example 6 was cooled from the leaching temperature of 95° C. to 35° C. in a crystallizer. The titanium content in the leach liquid was reduced from 20.8 to 15.0 g per litres. The silicon content in the leach liquid was reduced from 0.23 to 0.001 g per litres. The leachate was filtered to remove the precipitated solids containing silicon and titanium. The filtered leachate was then cooled to -7°C in a crystallizer while 100g of sodium chloride for each liter of leachate and 5.0g of hydrofluoric acid (49% by weight) for each liter of leachate were slowly added. Sodium fluorotitanate crystals precipitated, and the titanium content of the leach liquor was reduced to 0.3

g titanium per liters of leaching liquid. The sodium fluorotitanate crystals were separated from the leach liquor by filtration and washed with 1% by weight aqueous hydrochloric acid as described in Example 7, to remove iron, manganese and other minor contaminants which are soluble in the leach liquor.

Example 9

The solids recovered from the leach liquor in Example 8 where the leach liquor is cooled to 35° C. can be recycled to the initial stage for leaching the ore. The sodium fluorotitanate is made soluble in the leaching liquid together with part of the silicon impurities. However, most of the silicon impurities are not solubilized and are removed from the leaching liquid by filtration. As the leach liquid at this stage is relatively saturated with respect to silicon impurities, this recycling step does not lead to an accumulation of silicon contaminant concentration in the leach liquid.

Claims (61)

1. Process for the production of Group IVb transition metal-alkali metal fluoride materials from a Group IVb transition metal oxide-containing ore, which includes the steps that: a Group IVb transition metal oxide containing ore is fluorinated by contacting the ore in an unsealed reactor with an alkali metal fluorosilicate and alkali metal fluoride salt at a temperature of from approx. 600° C to approx. 1000°C to convert the Group IVb transition metal oxides to +3 and +4 worthy Group IVb transition metal-alkali metal fluoride materials, and for each mole of Group IVb transition metal oxide present in the ore, the ore is contacted with at least 0.8 moles of an alkali metal fluorosilicate and at least 1.6 molar equivalents of an alkali metal fluoride salt to minimize the loss of fluorine in the form of silicon tetrafluoride gas from the reactor. 2. Method according to claim 1, where the ore is selected from the group consisting of ilmenite and zircon. 3. Method according to claim 1, where the alkali metal fluorosilicate is sodium fluorosilicate and the alkali metal fluoride is sodium fluoride. 4. Method according to claim 3, where the Group IVb transition metal oxide is titanium dioxide and the +3 and +4 valuable Group IVb transition metal-alkali metal fluoride materials are Na0 TiF, and Na„TiOF.. 3 6 2 4 5. Method according to claim 3, where the Group IVb transition metal oxide is zirconium dioxide and the Group IVb transition metal alkali fluoride materials are Na0 ZrF, and Na^ ZrOF.. 3 6^2 4 6. Process for the production of a Group IVb transition metal-alkali metal fluoride salt from a Group IVb transition metal oxide ore, which comprises the steps that: a Group IVb transition metal oxide-containing ore is fluorinated by contacting the ore in an unsealed reactor with an alkali metal fluorosilicate in the presence of a basic alkali metal salt at a temperature of from about 600° C to approx. 1000°C to convert the Group IVb transition metal oxides to +3 and +4 worthy Group IVb transition metal-alkali metal fluoride materials, and for each mole of Group IVb transition metal oxide present in the ore, the ore is contacted with at least 1.07 molar equivalents of an alkali metal fluorosilicate and at least 1.07 molar equivalents of an alkali metal in the form of said basic alkali metal salt. 7. Method according to claim 6, where the basic alkali metal salt is selected from the group consisting of an alkali metal carbonate, an alkali metal oxide, an alkali metal bicarbonate or mixtures thereof. 8. Method according to claim 7, where the alkali metal fluorosilicate is sodium fluorosilicate and the basic alkali metal salt is selected from the group consisting of sodium carbonate, sodium hydroxide, bicarbonate and mixtures thereof. 9. Method according to claim 8, where the Group IVb transition metal oxide ore is ilmenite and the +3 and +4 valuable Group IVb transition metal-alkali metal fluoride materials are Na^ TiFg and Na2 TiOF4 . 10. A method according to claim 8, wherein the Group IVb transition metal oxide ore is zircon and the +3 and +4 valuable Group IVb transition metal-alkali metal fluoride materials are Na3 ZRF6 and Na2 ZrOF4- 11. Process for the production of a Group IVb transition metal-alkali metal fluoride salt which is essentially free of silicon dioxide, from a Group IVb transition metal oxide ore, comprising the steps that: (a) a Group IVb transition metal oxide ore is fluorinated by contacting the ore in an unsealed fluorination zone with an alkali metal fluorosilicate at a temperature of from about 600°C to approx. 1000°C to obtain a fluorinated ore, gaseous silicon tetrafluoride M is formed, and the Group IVb transition metal oxide is converted to +3 and +4 worthy Group IVb transition metal-alkali metal fluoride materials, with for each mole of Group IVb transition metal oxides present in the ore being the ore contacted with at least approx. 1.6 molar equivalents of alkali metal fluorosilicate, (b) the fluorinated ore is removed from the fluorination zone and introduced into a leaching zone in which the fluorinated ore is leached with an aqueous hydrochloric acid solution to solubilize the +3 and +4 valency Group IVb transition metal-alkali metal fluoride materials and a portion of the iron salts and silicon dioxide and to converting the +3 and +4 valenced Group IVb transition metal-alkali metal fluoride materials into a +4 valenced Group IVb transition metal-alkali metal fluoride salt which is soluble in the leach liquor, (c) the leach liquor is separated from insoluble solids, (d) the separated leach liquid is introduced into a cry- stallisas ion zone in which the leaching liquid is cooled to a temperature of at least 60° C to precipitate solids containing silicon impurities and +4 worthy Group IVb transition metal-alkali metal-fluoride salt , and (e) the solids formed in the crystallization zone are separated from the leach liquor to provide an aqueous solution containing the +4 Group IVb transition metal alkali metal fluoride salt product substantially free of silicon impurities. 12. Method according to claim 11, including the steps that: (a) the gaseous silicon tetrafluoride from the fluorination zone is introduced into a hydrolysis zone in which the silicon tetrafluoride is contacted with water to convert the silicon tetrafluoride into fluorosilicic acid, (b) the fluorosilicic acid is introduced into an alkali metal fluorosilicate production zone in which the fluorosilicic acid is contacted with an alkali metal chloride to form an aqueous hydrochloric acid solution and a solid alkali metal fluorosilicate, (c) the solid alkali metal fluorosilicate is separated from the aqueous hydrochloric acid, and (d) the separated hydrochloric acid solution is introduced into the leaching zone. 13. Method according to claim 11, where approx. 2.0 molar equivalents of alkali metal chloride are introduced into the alkali metal fluorosilicate production zone for each mole of fluorosilicic acid introduced. 14. Method according to claim 13, where the alkali metal fluorosilicate produced in the alkali metal fluorosilicate production zone is introduced into the fluorination zone. 15. Method according to claim 13, wherein at least 1.5 molar equivalents of fluorosilicic acid are introduced from an external source into the alkali metal fluorosilicate production zone for each mole of Group IVb transition metal oxide in the ore introduced into the fluorination zone. 16. Method according to claim 15, where the alkali metal chloride introduced into the alkali metal fluorosilicate production zone is sodium chloride and the alkali metal fluorosilicate produced in the alkali metal fluorosilicate production zone and introduced into the fluorination zone is sodium fluorosilicate. 17. Method according to claim 11, wherein the Group IVb transition metal oxide ore is ilmenite and the +4-valent Group IVb transition metal-alkali metal fluoride salt is sodium fluorotitanate. 18. Method according to claim 11, wherein the Group IVb transition metal oxide ore is zircon and the +4-valent Group IVb transition metal alkali metal fluoride salt is sodium fluorozirconate. 19. Method according to claim 11, where at least 3 molar equivalents of hydrogen chloride in the form of the aqueous hydrochloric acid solution are introduced into the leaching zone for each mole of Group IVb transition metal oxide in the ore introduced into the fluorination zone. 20. Method according to claim 11, where the leaching of the fluorinated ore with an aqueous hydrochloric acid solution is carried out at a temperature between approx. 60° C and the boiling point temperature of the leaching liquid. 21. Method according to claim 11, where the leach liquid is crystallized in the crystallization zone at a temperature between approx. 27° C and approx. 33° C. 22. Method according to claim 12, where the fluorosilicic acid is contacted with the alkali metal chloride in the alkali metal fluorosilicate production zone at a temperature between approx. ambient temperature and approx. 1000°C. 23. Method according to claim 11, where the Group IVb transition metal oxide ore is mixed with a carbon source and the obtained ore-carbon source mixture is introduced into the fluorination zone, the mixture containing from approx. 1% to approx. 10%, based on weight, of carbon source. 24. Method according to claim 23, where the carbon source is selected from the group consisting of coal, coke, petroleum coke, charcoal, carbon black and activated carbon. 25. Method according to claim 11, where the Group VIb transition metal oxide-containing ore comprises from approx. 14% to approx. 36%, based on weight, iron and from approx. 25% to approx. 25, based on weight, titanium. 26. Method according to claim 11, where the Group IVb transition metal oxide-containing ore contains at least 14% by weight of iron as iron oxide. 27. Method according to claim 11, where the Group IVb transition metal oxide-containing ore is mixed with a carbon source and the obtained ore-carbon source mixture is introduced into the fluorination zone, the mixture containing from approx. 1.2% by weight to approx. 4 wt% carbon source. 28. Method according to claim 11, where the Group IVb transition metal oxide-containing ore is contacted with the alkali metal fluorosilicate at a temperature from approx. 750° C to approx. 950°C. 29. Process for producing a purified Group IVb transition metal fluoride salt from a fluorinated Group IVb transition metal oxide-containing ore, comprising the steps of: (a) a fluorinated Group IVb transition metal oxide containing ore containing +3 and +4 valence Group IVb transition metal-alkali metal fluoride materials is leached in a leaching zone with an aqueous hydrochloric acid solution under conditions to solubilize the +3 and +4 valence Group IVb transition metal-alkali metal -fluoride values to convert the +3 and +4 valenced Group IVb transition metal-alkali metal fluoride materials into a +4 valenced Group IVb transition metal-alkali metal fluoride salt which is soluble in said leaching liquid, (b) the leach liquor is separated from insoluble solids, (c) the separated leach liquid is cooled in a crystallization zone at a temperature between approx. 30° C and approx. 60° C to precipitate solids containing silicon impurities, the silicon impurity concentration in the leaching liquid being reduced to a concentration not exceeding approx. 0.001 g silicon impurities per liters of leaching liquid, d) the precipitated solids are separated from the leaching liquid, and the separated solids are recycled into the leaching zone, and (e) the leach liquor is introduced into another crystallization zone in which the leach liquor is cooled to a temperature not exceeding 30° C. to crystallize out a +4 worthy Group IVb transition metal alkali metal fluoride salt which is substantially free of silicon impurities. 30. A method according to claim 29, wherein the crystallized salt from the second crystallization zone is separated from the leach liquor and washed at least once with dilute aqueous hydrochloric acid to remove substantially all iron and magnesium impurities from the salt to give a +4 worthy of Group IVb transition metal alkali metal fluoride salt containing less than 100 ppm iron, less than 100 ppm manganese and less than 0.001% silicon. 31. Method according to claim 29, where the fluorinated ore is leached with an aqueous hydrochloric acid solution that has a hydrogen chloride concentration that is less than approx. 23% by weight. 32. Method according to claim 29, where the fluorinated ore is leached with an aqueous hydrochloric acid solution which has a concentration of from approx. 1% to approx. 3 wt% hydrogen chloride. 33. Method according to claim 29, where from approx. 50 g to approx. 150 g alkali metal chloride and from approx. 0 to approx. 1 g of a 49% solution of hydrogen fluoride is introduced into the second crystallization zone together with each liter of leaching liquid introduced. 34. Method according to claim 29, where approx. 100 g of alkali metal chloride and approx. 1.25 g of hydrogen fluoride is introduced into the second crystallization zone with each liter of leaching liquid introduced. 35. Method according to claim 34, wherein the alkali metal chloride is sodium chloride. 36. Method according to claim 29, where the fluorinated ore is fluorinated ilmenite ore and the +4 valuable Group IVb transition metal-alkali metal fluoride salt is sodium fluorotitanate. 37. Method according to claim 29, where the fluorinated ore is fluorinated zircon ore and the +4 valuable Group IVb transition metal-alkali metal fluoride salt is sodium fluorozirconate. 38. Method according to claim 30, wherein the dilute aqueous hydrochloric acid solution used in the washing step has a hydrogen chloride concentration of less than 2% by weight. 39. Method according to claim 28, where the fluorinated ore is contacted with at least approx. 1.7 molar equivalents of hydrogen chloride for each mole of +3 and +4 valuable Group IVb transition metal-alkali metal fluoride materials contained in the fluorinated ore. 40. Process for producing a purified Group VIb transition metal-dialkali metal hexafluoride salt from a fluorinated Group IVb transition metal oxide ore, comprising the steps of: (a) a fluorinated ore containing +3 and +4 valence Group IVb transition metal-alkali metal fluoride materials is contacted with an aqueous hydrochloric acid solution under conditions to convert said materials to a salt of the formula A„MF <g> and to solubilize A2 the MFg salt to form a leaching liquid, wherein A is an alkali metal, M is a Group VI transition metal and F is fluorine, (b) the leach liquor is separated from insoluble salts; (c) the separated leach liquid is cooled in a crystallization ion zone at a temperature between approx. 27° C and approx. 33° C. to precipitate solids containing silicon impurities, the concentration of silicon impurities in the leaching liquid being reduced to a concentration which is no greater than approx. 0.001 g silicon impurities per liters of leaching liquid, (d) the precipitated solids are separated from the leaching liquid, (e) the leach liquid is introduced into another crystallization zone together with an alkali metal chloride salt and hydrofluoric acid, in which the resulting mixture is cooled to a temperature not higher than 0° C., to crystallize out the A2 MFg salt, (f) The A„MF, salt is separated from the leach liquid, and (g) The A2 MFg salt is washed in a washing zone at least once with dilute aqueous hydrochloric acid to remove iron and magnesium impurities from the salt to give an A2 MFg salt containing less than 100 ppm iron, less than 100 ppm manganese and less than 0.001% silicon. 41. Process for producing a high-purity Group VIb transition metal zinc alloy from Group IVb transition metal scrap containing impurities insoluble in molten Group IVb transition metal and molten zinc, comprising the steps of: (a) dissolution in molten zinc of a Group IVb transition metal scrap containing impurities which are insoluble in molten Group IVb transition metal and molten zinc in molten zinc at a temperature between approx. 650° C and approx. 1000° C to form a molten Group IVb transition metal zinc alloy phase and a separate phase containing the aforementioned insoluble impurities, (b) separating the molten alloy phase from the phase containing insoluble impurities. 42. Method according to claim 41, where the impurities which are insoluble in molten Group IVb transition metal and molten zinc are halide salts, alkali metal salts, alkaline earth metal salts, nitrides, nitrogen and refractory carbides. 43. Method according to claim 41, where the impurities that are insoluble in molten Group IVb transition metal and molten zinc have a density that is less than the density of the said molten alloy phase, and that the said own phase containing the said insoluble impurities floats on .top of the molten alloy phase. 44. Method according to claim 41, where the impurities that are insoluble in molten Group IVb transition metal and molten zinc have a density that is greater than the said molten alloy phase, and that the said own phase containing insoluble impurities sinks to the bottom of the molten alloy phase. 45. A method according to claim 41, including the further step of sublimating the zinc from the separated molten alloy phase to produce a Group IVb transition metal which is substantially free of said insoluble impurities. 46. Process for producing a high-purity Group IVb transition metal from Group IVb transition metal scrap containing impurities that are insoluble in molten Group IV b transition metal and molten zinc, comprising the steps of: (a) a Group IVb transition metal scrap containing impurities insoluble in molten Group IVb transition metal and molten zinc is dissolved in molten zinc at a temperature between about 650° C and approx. 1000° C to form a molten group Group IVb transition metal zinc alloy phase and a separate phase containing the aforementioned insoluble impurities, (b) the molten alloy phase is separated from the phase containing insoluble impurities, and (c) the zinc is sublimed from the separated molten alloy phase at a temperature of at least 1000°C to provide a Group IVb transition metal sponge which is substantially free of zinc metal and said insoluble impurities. 47. Method according to claim 46, where the impurities which are insoluble in molten Group IVb transition metal and molten zinc are halide salts, alkali metal salts, alkaline earth metal salts, nitrides, nitrogen and heat-stable carbides. 48. Method according to claim 46, where the impurities that are insoluble in molten Group IVb transition metal and molten zinc have a density that is less than the density of the said molten alloy phase, and that the said own phase containing the insoluble impurities floats on top of the molten alloy phase. 49. Method according to claim 46, where the impurities that are insoluble in molten Group IVb transition metal and molten zinc have a density that is greater than the said molten alloy phase, and that the said separate phase containing the insoluble impurities sinks to the bottom of the said molten alloy phase. 50. Process for producing a high purity Group VIb transition metal zinc alloy from Group IVb transition metal scrap containing impurities soluble in molten Group IVb transition metal and molten zinc, comprising the steps of: (a) dissolution in molten zinc of a Group VIb transition metal scrap containing impurities soluble in molten Group IVb transition metal and molten zinc in molten zinc at a temperature between about 650° C and approx. 1000° C to form a molten Group IVb transition metal zinc alloy containing the soluble impurities, and (b) dissolving additional Group IVb transition metal having a low content of said soluble impurities, in the molten alloy, sufficient Group VIb transition metal having a low content of soluble impurities, in said molten alloy to produce a molten other Group IVb transition metal zinc alloy having a soluble impurity content not exceeding a predetermined value. 51. The method of claim 50, including the further step of sublimating the zinc from said second molten alloy at a temperature of at least 1000°C to provide a Group IVb transition metal sponge that is substantially free of zinc and has a soluble impurity content that does not exceeds a predetermined value. 52. Process for producing a high purity Group IV transition metal zinc alloy from Group IVb transition metal scrap containing impurities soluble in molten Group IVb transition metal and molten zinc, comprising the steps of: (a) dissolution in molten zinc of a Group IVb transition metal scrap containing impurities which are soluble in molten Group IVb transition metal and molten zinc, at a temperature between approx. 650° C and approx. 1000°C to form a molten Group IVb transition metal zinc alloy containing said soluble impurities, and (b) dissolving additional Group IVb transition metal having a low soluble impurity content by reducing a predetermined amount of a Group IVb transition metal salt by the following formula: A„MF, wherein A is an alkali metal, M is a Group IVb transition metal and F is fluorine, with a molar equivalent of aluminum metal dissolved in the molten zinc, sufficient Group IVb transition metal salt being introduced to obtain another molten alloy having a soluble impurity content which does not exceed a predetermined value. 53. A method according to claim 50, wherein the zinc is sublimed from said second molten alloy at a temperature of at least 1000°C to give a Group IVb transition metal sponge which is substantially free of zinc metal and has a soluble impurity content not exceeding a pre specific concentration. 54. Method according to claim 41, wherein the Group IVb transition metal scrap is titanium metal scrap. 55. The method of claim 41, wherein the Group IVb transition metal sponge is a zirconium metal scrap. 56. Method according to claim 46, wherein the Group IVb transition metal scrap is titanium metal scrap. 57. The method of claim 46, wherein the Group IVb transition metal sponge is a zirconium metal scrap. 58. Method according to claim 50, wherein the Group IVb transition metal is titanium metal scrap. 59. Method according to claim 50, wherein the Group IVb transition metal is a zirconium metal scrap. 60. Method according to claim 52, wherein the Group IVb transition metal scrap is titanium metal scrap. 61. The method of claim 52, wherein the Group IVb transition metal sponge is a zirconium metal scrap.