FI70562C - FOERFARANDE FOER FRAMSTAELLNING AV TITANSULFATLOESNING - Google Patents

Description

70562

The invention relates to a process for preparing a titanium sulphate solution, in which a titanium-containing material is reacted with dilute sulfuric acid in the presence of a reducing agent. The titanium sulfate solution prepared by the process of the invention can be used to prepare a titanium dioxide pigment.

Titanium dioxide is a well-known material with the desired pigment properties and is useful in paint and coating preparations and plastic materials. Several different processes are known for the production of titanium dioxide-15 material, for example the sulphate process and the chloride process.

In a conventional sulfate process for preparing titanium compounds, a titanium-containing material, such as ilemite ore, which includes massive ilmenite and ilmenite sand, and titanium-containing or furnace slag is reacted with concentrated sulfuric acid (e.g., 90-96% sulfuric acid). The reaction is sometimes referred to as "extraction" or "ore extraction". The extraction reaction of titanium-containing material and concentrated sulfuric acid is exothermic in nature and progresses very rapidly. Typically, the titanium-containing material and concentrated sulfuric acid are placed in a reaction vessel called an extraction tank. Water is usually added to the extraction tank to initiate and accelerate the acid-ore reaction by the heat generated, resulting in vigorous boiling of the aqueous-acid solution at about 100-190 ° C and the evolution of large amounts of water vapor with entrained particulate material. As the vigorous reaction progresses, water is removed and the reaction mass becomes solid.

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The reaction is completed in the solid phase at a temperature of about 180-215 ° C. The extraction operation is a batch process carried out in one and the same extraction tank. Use as many tanks as necessary according to the desired capacity of the production plant 5 to prepare the titanium sulphate solution.

The solid reaction mass obtained from the extraction, referred to as the "cake", is allowed to cool. The solid cake is then dissolved in water or dilute acid 10 to provide a solution of sulfate salts of iron, titanium, and other trace metals in the titanium-containing material.

The reaction mixture is then treated to convert ferric iron to ferrous iron in a reduction step. Unless the iron in the reaction-15 mixture is completely reduced to the ferrous state, ferric sulfate will pass through the process and possibly cause iron contamination of the final product.

In order to ensure that during the preparation of the reaction solution for hydrolysis, the iron remains in the ferroti-20 and does not oxidize, it is preferable to allow the reduction to proceed sufficiently far that the titanium solution contains a small amount of trivalent titanium. In this case, it is essential that the content of trivalent titanium is within a certain range. The reduction, which has gone too long, gives a poor yield in the hydrolysis step as a result of TiCl 4 losses. Too mild a reduction, on the other hand, makes it uncertain whether sufficient trivalent titanium is always present to prevent iron moieties from oxidizing to the Ferri state.

As described in U.S. Patent 2,309,988, in a commonly used method for reducing Ferri ion, a basket containing scrap iron is immersed in a reactor vessel containing a dissolved, unreduced extraction cake. In the second method, a sufficient amount of iron is poured into the reactor and the bulk of the solution is stirred or otherwise kept in contact with the iron until reduction occurs. These methods tend to cause local overheating of the titanium solution and local decrease in acidity due to the reaction of iron and solution. This tends to provide unstable solutions that vary from batch to batch. U.S. Patent No. 1,014,793 discloses the reduction of the iron component of ilmenite solutions to the ferrous state by the addition of metallic zinc, sulfuric acid or sodium thiosulfate. In addition, tinned iron, crystalline titanium (3) -10 sulfate, and sulfur dioxide have also been proposed as reducing agents. These known methods, although effective when used with previously extracted rivet ore solutions, could not be used during the extraction reaction due to loss of solution fluidity and solidification. In addition, in the subsequent dissolution of the reaction cake, such use would have resulted in an unstable solution that would self-clump, resulting in an uncontrolled hydrolysis reaction that prevents the formation of Pigment-grade titanium dioxide.

The iron and titanium sulphate salt solution obtained after separate extraction and reduction steps is further treated by known measures to remove ferrous sulphate (commonly referred to as "vihtrilli") to give a titanyl sulphate solution which, on hydrolysis, produces hydrated titanium dioxide. Titanium dioxide hydrate is usually subjected to a calcination treatment in a suitable incinerator to remove water of hydration and form an unhydrated titanium dioxide pigment. The above process is described in more detail in, for example, U.S. Patent Nos. 1,504,672, 3,615,204 and 3,071,439.

The present invention relates to a novel process for the preparation of a titanium sulphate solution which substantially avoids or eliminates the above-mentioned disadvantages typical of a conventional sulphate process. As used herein, the term titanium sulfate is used to denote compound titanium sulfate salts such as titanyl sulfate and titanium (3) sulfate.

The process of the invention is characterized in that a) a titanium-containing material in an amount of about 10-400% greater than the stoichiometry required to react with sulfuric acid to form titanium sulfate, and b) a dilute sulfuric acid solution having a concentration of about 25-60 wt%. %, based on the total weight of the solution, is reacted at about 140 ° C in the presence of a reducing agent which reduces ferric iron to ferrous iron, the resulting reaction mixture is cooled to below 110 ° C without precipitating reaction products to form a reaction mixture containing titanium sulfate and insoluble.

The titanium dioxide pigment prepared from the titanium sulfate solution prepared by the process of the present invention can be prepared by hydrolyzing the titanium sulfate solution to form titanium dioxide hydrate and calcining the titanium dioxide hydrate to form titanium dioxide, after which the titanium dioxide is recovered.

The accompanying drawing illustrates an embodiment of the process of the invention using a continuous process to produce titanium dioxide.

It has been found that a titanium-containing material can be reacted with dilute sulfuric acid completely in the liquid phase in the presence of a reducing agent to provide a stable hydrolyzable titanium sulfate solution that can be used to prepare titanium compounds and titanium dioxide dipigments. In particular, it has surprisingly been found that the presence of a reducing agent in the extraction step greatly accelerates the reaction rate between the titanium-containing material and dilute sulfuric acid to provide a hydrolyzable titanyl sulfate solution useful for the preparation of titanium compounds. Therefore, the use of a reducing agent in the Li-5 extraction step eliminates the prior art need for a separate and independent reduction step after extraction.

The extraction reaction is performed using a titanium-containing material. As used herein, the term titanium-containing material 10 means a material that contains recoverable titanium moieties when processed in accordance with the process of the invention. Exemplary materials include titanium-containing slag, kiln slag, ilmenite ores such as magnetic ilmenite and massive ilmenite, and ilmenite sand.

The extraction reaction is performed using a sufficient amount of titanium-containing material to provide an excess of said material in an amount of about 10-400% above the stoichiometric amount. This amount can also be shown to be 1.1-5 times the stoichiometric amount. The following formula shows the stoichiometry of the extraction reaction:

FeTiO 3 + 2H 2 SO 4 -> TiO 5 SO 4 + FeSO 4 + 2H 2 O The use of excess titanium-containing material in the extraction reaction is efficient and desirable to achieve a successful and useful process in accordance with this invention without excessive grinding of the ore. The surface area of the titanium-containing material is preferably between about 2 3 0.05 and 0.6 m / cm. Ore with a larger surface area may be used, but it does not provide any benefit due to increased grinding costs. As mentioned above, an excess of titanium-containing material in the range of about 10-400% above the stoichiometric amount required to react with sulfuric acid should be used in the process extraction reaction. The use of smaller amounts of material results in unacceptably low reaction rates and long processing times, making the process economically unattractive. The use of higher than recommended excesses of Mate-5 material is not desirable due to the greatly reduced flowability of the reaction mixture and the need to recycle large amounts of unreacted titanium-containing material to the extraction reactors. Unexpectedly, for example, it has been found that doubling the amount of titanium-containing material, such as Maclntyre-expression rivet ore, above the stoichiometric amount to react with dilute sulfuric acid increases the reaction rate by at least 10-fold in the last extractor. It should be noted that the reaction rates vary with the source of titanium-containing material used during the extraction.

The concentration of sulfuric acid used in the process of the invention should be between about 25-60% by weight based on the total weight of the acid solution. An acid concentration of less than about 25% by weight is undesirable because hydrolysis of titanium dioxide occurs during and in connection with the extraction reaction using such acids. Premature hydrolysis of titanium salt solutions prevents the formation of pigment grade titanium dioxide at a later stage in the process. Also, the use of an acid having a concentration greater than about 60% by weight is undesirable because (1) the resulting reaction solution is more viscous and more difficult to handle, (2) the economics of recycling the used acid cannot be realized unless the spent acid is concentrated, which unnecessarily raises operating costs and (3) the higher concentration of reaction products in solution promotes the precipitation of ferrous sulfate monohydrate and recoverable titanyl sulfate dihydrate. The presence of ferrous sulphate monohydrate makes the tare weight separation inefficient and difficult to remove by filtration.

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The operating conditions of the process for carrying out the extraction reaction can be easily adjusted depending on the concentration of dilute sulfuric acid and the particular amount of titanium-containing material used to achieve the optimum operation of the process. To illustrate this, the use of low concentration sulfuric acid, e.g., less than 40% by weight, initially requires the use of a process at the lower end of the recommended temperature range due to the lower boiling point of dilute sulfuric acid. It is desirable to increase the amount of titanium-containing material used to extract as much material as possible in the first extraction reactor, at which point the operating temperature and reaction rate are usually higher. As mentioned below, in subsequent extraction reactors, the temperature is kept at a lower level than in the first reactor and, ultimately, must be lowered to prevent or avoid premature hydrolysis of the titanium salt solution.

The temperature at which the extraction reaction takes place is below about 140 ° C and preferably from 55 ° C to the boiling point of the reaction solution, i.e. between about 55-140 ° C. The choice of temperature that is too low in the extraction reactor should be avoided because the extraction reaction proceeds too slowly and thus requires a longer residence time of the reagents in the extraction reactor. Extended residence times should also be avoided to prevent the undesirable risk of nucleation in the reaction solution due to premature hydrolysis of the titanium salt. The choice of a temperature above 140 ° C is not recommended because the titanium salt hydrolyzes at much higher rates at higher temperatures. Carrying out an extraction reaction below about 55 ° C should be avoided because the reaction products begin to precipitate from solution and the viscosity of the reaction mixture increases, making the removal of unreacted solids very difficult. The recommended operating temperature for carrying out the extraction reaction is between about 70-110 ° C.

It should be noted that the extraction reaction of the process of this invention can be carried out as a batch reaction, e.g., in a reaction vessel from which the reaction mixture, after the extraction reaction has progressed to the desired extent, is removed and further processed in other vessels. A preferred embodiment of the process 5 of the invention is one in which the digestion reaction is carried out continuously in at least two reaction vessels and in which the titanium-containing material and dilute sulfuric acid are made to flow in parallel.

When the process is carried out continuously, it is preferable to carry it out using two or more extraction reactors. The total number of extraction equipment depends on the ease of reaction control, the production capacity of the plant and the process. sin processing.

Recommended operating temperatures for carrying out the extraction reaction in the two extraction reactors or stages are those in which the first extraction apparatus is maintained below about 140 ° C and preferably below about 110 ° C and the second extraction apparatus is maintained below about 100 ° C and preferably below at about 75 ° C.

Preferred operating temperatures for performing the extraction reaction in the three extraction reactors or stages are those in which the first extraction apparatus is maintained below about 140 ° C and preferably below about 110 ° C The second extraction apparatus is maintained below about 110 ° C and preferably below about 100 ° C. And the third extractor is maintained below about 80 ° C, and preferably below about 75 ° C.

The preferred operating temperatures for carrying out the extraction reaction in the four extraction reactors or stages are those in which the first extraction apparatus is maintained below about 140 ° C 30 and preferably below about 110 ° C, the second extraction apparatus is maintained below about 110 ° C and preferably below about 90 ° C. C, the third extractor is maintained below about 100 ° C and preferably 36 ° C and the fourth extractor is maintained below about 90 ° C and preferably below about 75 ° C.

35 Recommended operating temperatures for carrying out the extraction reaction in the five extraction reactors or stages are those in which the first extraction apparatus is maintained below about 140 ° C and preferably below about 110 ° C, the second extraction apparatus is maintained below about 110 ° C, and preferably below 5 at about 90 ° C, the third extractor is maintained below about 100 ° C, and preferably below about 85 ° C, the fourth extractor is maintained below about 90 ° C, and preferably below about 80 ° C, and the Fifth the extractor is maintained below about 85 ° C, and preferably below about 75 ° C.

All of the above extractor temperatures can be varied depending on the desired yield and reaction times at each step. One of the essential and striking features of the invention in providing a useful process is that the temperature of the extraction reaction is lowered as the reaction progresses to prevent or avoid premature hydrolysis of the titanium salt solutions obtained. Premature hydrolysis of the titanium salt solution prevents the formation of a pigment grade or grade of titanium dioxide.

The duration of the extraction reaction in the extraction reactor is adjusted by the optimum degree of conversion or extraction of the 20 titanium-containing materials. stage. In general, it is recommended to extract or react as much titanium-containing material as possible in the first extraction reactor or stage, where the temperature is maintained at the highest level to prevent hydrolysis of the titanium sulfate in solution. For example, in a continuous multi-stage system using McIntyre ore as a source of titanium-containing material, it is sometimes possible to extract up to about 90% by weight of the stoichiometric amount of ore fed to the process in the first stage, excluding excess ore. Preferably about 30-80% and most preferably 60-80% by weight of the stoichiometric amount of ore is extracted in the first step, except for excess ore. The conversion is measured by the stoichiometric amount of titanium-containing material from the amount of reaction.

70562 10 The temperature is used to control the extraction reaction, preferably by controlling the ratio of active acid to titanium in the reaction solution. This ratio is an indication of the degree of conversion or extraction. The phrase "active acid" 5 means the total amount of free acid in the reaction solution plus the acid combined with the titanium in the reaction solution. The ratio of active acid to titanium dioxide (active acid: titanium dioxide) is calculated as the sum of both the free acid in solution and the titanium advanced in the solution divided by the titanium in solution (calculated as TiCl 2). The active acid content of the solution can be determined, for example, by titrating a selected sample (by weighing or pipetting technique) with a 0.5 N base solution (NaOH) to pH 4.0 in a barium chloride / ammonium chloride buffered solution. The titration gives the content of the free acid plus the combined acid TiO2, which is called the active acid.

To illustrate this, 60 ml of a buffer solution containing 75 g / l barium chloride and 250 g / l ammonium chloride are added to a beaker containing the sample in question and diluted to 250 ml with water and titrated with 0.5 N base to the methyl orange end point.

In the batch process, the concentration of active acid can vary widely and is not critical except to the extent that the extraction and reduction take place in the liquid phase. In a continuous process, the active acid is allowed to drop from infinity at the beginning of the reaction to 1.50-7.0 at the end of the reaction, depending on the extraction conditions. Typically, the level of the ratio of active acid to TiCl 4 ranges from 2.0 to 3.5. As the level of active acid decreases, the stability of the titanyl sulfate solution against hydrolysis deteriorates. In general, the temperature of the reaction solution should be kept below about 140 ° C, and preferably below about 110 ° C, when the ratio of active acid to titanium (calculated as titanium dioxide) drops to about 2.0. Thus, in order to obtain 70562 11 in a two-stage extraction process, the temperature of the reaction solution in the first stage of the extraction reaction or in the extraction apparatus should be kept below about 140 ° C until the ratio of active acid to titanium dioxide in the reaction solution drops to about 3.0. about 100 ° C, such as 70 ° C. In contrast, in the three-step extraction process, the temperature of the first step is maintained at about 110 ° C to obtain a reaction mixture having a ratio of active acid to titanium dioxide in the reaction solution of about 2.5-3.0, followed by a second step at about 100 ° C. to obtain a reaction mixture in which the ratio of active acid to titanium dioxide in the reaction solution is between about 2.2 and 2.5. The reaction can then be completed in a third step at a temperature below about 80 ° C to provide a reaction mixture having a ratio of active acid to titanium dioxide in the reaction solution of about 2.0.

The reducing agent can be added at any point in the extraction process. In a multiple extraction process, it is recommended to add a reducing agent to the first step to maximize ore extraction and ferric iron reduction initially.

Typically, the reduction of ferric iron 25 in the extraction mixture can be achieved using conventional sulfate process reducing agents. Such substances may be gaseous reducing agents, such as sulfur dioxide, which may be used alone or in combination with activated carbon. Other typical reducing agents include sulfuric acid, sodium thiosulfate, titanium (3) sulfate, reduced expression rivet, and mixtures thereof, as well as metallic materials such as tin, iron, zinc, zirconium, titanium, aluminum, magnesium, and mixtures thereof. alloys. These exemplary reducing agents are not intended to exclude other agents known in the art.

70562 12 These substances may be used in the form of solutions or solids. The preferred solid reducing agent is in the form of granules or powder.

The amount of reducing agent used is that amount which is at least stoichiometric for the amount of ferric iron present. A small excess of reducing agent, typically up to about 10% above that required to reduce all ferric iron, can also be used to reduce a small amount, typically less than 1% of tetravalent titanium to tri-10 trivalent titanium. The following chemical oxidation-reduction reaction equation shows the stoichiometry of the system using aluminum and iron reducing agents: a) Al ° + 3Fe + 3 = Al + 3 + 3Fe + 2 15 b) Fe ° + 2Fe + 3 = 3Fe + 2 When used the amount of reducing agent added to the reaction solution in the extraction equipment of a reducing agent such as powdered iron depends on the amount of ferric iron in the titanium-containing feedstock. In general, about 3 to 8% by weight of reducing agent, based on the total weight of the reacted titanium-containing material, is sufficient to provide satisfactory results in a process using 25 titanium-containing materials, such as ilmenite ore containing 5 to 13% Fe 2 O 2. The addition of a reducing agent such as powdered iron has another advantageous effect in that it accelerates the rate of the extraction reaction.

Coincidentally, the accelerating effect of iron on the extraction reaction rate increases as the particle size of the iron decreases.

After completion of the extraction reaction, the resulting reaction mixture containing titanium sulfate, ferrous sulfate and trace elements derived from a titanium-containing material can be treated to recover a titanium sulfate solution for the preparation of titanium compounds or treated according to conventional sulfate process oxide process techniques.

Referring to the diagram shown in the appended figure for the production of titanium dioxide in a multi-stage reactor system, reference numeral 10 shows an extraction reactor. A titanium-containing material such as ilmenite is adapted to be fed to the extraction reactor 10 from the ore storage tank 11. Dilute sulfuric acid having a concentration of 25-60% by weight based on the total weight of the acid solution is fed from a strong acid mixture (96% by weight) from a fresh acid source 12. combined with either recycled acid (15-45% by weight or water, directly in the extraction reactor 10. The ilmenite ore in the extraction reactor 10 and dilute sulfuric acid are continuously stirred at a temperature not exceeding the boiling point of the reaction solution in the reactor 15.

The reagents in the extraction reactor 10 are maintained at a temperature below about 140 ° C, and preferably between about 55-140 ° C. More specifically, the reagents in the extraction reactor 10 are preferably kept at 110 ° C. The extraction reactor 10 can be maintained at any suitable pressure; normal pressure is recommended for economic reasons.

When operating continuously in the three-stage extraction system shown, the reaction mixture is transferred from the extraction reactor 10 to a conventional separation device 13, e.g. a filter or cyclone separator, where part or all of the unreacted effluent ore is continuously separated and recycled from the recycle tube 14 to the extraction reactor 10. transfers from the extraction reactor 10 to the extraction reactor 15, thereby not involving the recycling of any unreacted ilmenite ore to the extraction reactor 10.

It is recommended to keep the reaction solution in the extraction reactor 15 at a temperature slightly lower than the temperature in the extraction reactor 10. The reaction mixture in the extraction reactor 15 70562 14 is maintained, for example, at about 100 ° C. Temperature control in the extraction reactor 15 can be achieved by adding recycled acid or water. The pressure in the extraction reactor 15 is preferably normal pressure, but higher pressures can be used if desired.

The reaction mixture can be continuously transferred from the extraction reactor 15 to a conventional extraction device 16, e.g. a filter or cyclone separator, where part or all of the unreacted ilmenite ore is separated and recycled through the recycle tube 17 to the extraction reactor 15. Alternatively, the reaction mixture can be continuously transferred , in which case it does not involve the recycling of unreacted ilmenite ore to the extraction reactor 15.

It is recommended that the reaction mixture in the extraction reactor 18 be maintained at about 70 ° C and normal pressure.

The reaction mixture from the extraction reactor 18 is continuously fed to a suitable separation device 19, e.g. a filter or a self-weight separator (or multiples thereof 20 arranged in series and / or in parallel), in which unreacted ilmenite ore is separated from the liquid reaction product. Excess or unreacted ilmenite is recycled through lines 21 and 21 'to one or both of the extraction reactors 18 and / or 10. The liquid reaction product 25 from the separation device 19 is passed to a settling device n 20, e.g. a conventional settling device or a LAMELLA the solid material is removed from the reaction product. The use of a LAMELLA landing gear is not considered part of this invention.

As mentioned above, the extraction reaction is carried out in extraction reactors 10, 15 and 18. It is not essential that the extraction reaction be carried out in three extraction reactors. In fact, the process can be carried out batchwise using only one extraction reactor. However, it is recommended to use two or more extraction reactors to carry out the process continuously. When only two extraction reactors are used, the temperature of the second extraction reactor, such as the extraction reactor 15, can be adjusted to a lower temperature, such as e.g. 70 ° C.

A suitable reducing agent from tank 22 is added to the extraction reactor 10 or the extraction reactor 15 or both reactors in order to reduce the trivalent ferric iron in the extraction solution to divalent ferrous iron. The presence of the reduced state prevents the contamination of the subsequently obtained titanium hydrate with ferric salts. In the extraction equipment, the amount of reducing agent added to the reaction solution depends on the amount of ferric iron in the ilmenite feed ore, as described above.

With this measure, it is possible to avoid a separate reduction step for the extraction solution, which would otherwise be necessary. The reducing agent can be added at any point in the extraction operation. The amount of reducing agent used is selected so that not only the trivalent iron in ilmenite ore is reduced to the divalent state, but also a portion of the titanium in the reaction solution is reduced to the trivalent state to obtain a titanium sulfate solution for hydrolysis containing sufficient trivalent titanium. The presence of trivalent titanium prevents the formation of ferric iron which would be adsorbed on the titanium dioxide particles at a later stage of the process.

A certain amount of metal sulfates, i.e. ferrous sulfate monohydrate, usually precipitates during the extraction reaction without any appreciable deterioration in the flowability of the reaction mixture. The ferrous sulfate monohydrate can be easily dissolved at the end of the extraction reaction by adding water. At least a portion of the water can be replaced with a titanium sulfate solution from which much of the ferrous sulfate has been removed (by crystallization and separation of ferrous sulfate heptahydrate at a later stage in the process described below). With this measure, the addition of excess water to the system can be minimized or avoided. Usually the excess water has to be removed at a later stage of the process, e.g. by evaporation.

Water or a solution of water and titanium sulphate may be added to the reaction solution in the last extraction reactor or at a suitable point between the last extraction reactor and the separation device 19 to provide cooling.

The addition of water or a solution of water and titanium sulfate is not considered part of this invention.

The resulting solution containing titanium sulfate, ferrous sulfate, and trace elements derived from ilmenite ore can be recovered and processed to produce titanium compounds. Alternatively, the solution may be processed to produce a titanium dioxide pigment, with the reaction solution being passed to a settling device 20 to remove solids from the solution.

When titanium dioxide is prepared, the reaction solution is then passed from the precipitator 20 to the crystallizer 23, where the vihtrill (i.e., ferrous sulfate heptahydrate) is crystallized and removed by known process steps. For example, the solution is cooled in a continuous or batch vacuum crystallizer to about 10-20 ° C by placing it under a vacuum of 23.5 mmHg to form large crystals of vihtrill (FeSO 4 .71 ^ 0) which can be easily filtered through a drum or table filter. Vihtrill cake can be washed to recover soluble titanium parts. The reaction solution from the filter can be concentrated by known measures, e.g. by evaporation before it is subjected to hydrolysis. The reaction solution can also be clarified either before or after crystallization and removal of ferrous sulfate heptahydrate. The clarification step before crystallization is preferred if it is desired to obtain high purity ferrous sulfate heptahydrate which can be further processed, e.g. to prepare reagents used for water and sewage purification.

it 70562 17

It is recommended that the reaction solution be subjected to a fine filtration step prior to hydrolysis. After removal of the ferrous sulphate heptahydrate and, if necessary, clarification and fine filtration, a titanium sulphate solution is obtained which has a preferred FejTiCl 2 ratio and which can be directly hydrolysed or optionally evaporated by known means in a vacuum evaporator to the desired TiO2 concentration, followed by hydrolysis.

The reaction solution from the crystallizer 23 consists of a solution of titanium 10 sulphate (TiOSO 2), which is fed to a hydrolysis apparatus 24, where the titanyl sulphate is hydrolysed by known process steps to obtain titanium dioxide hydrate. In particular, the titanyl sulfate solution is hydrolyzed to provide insoluble titanium dioxide dihydrate by diluting the titanyl sulfate solution with water at elevated temperatures. For example, a predetermined amount of titanyl sulfate solution, preferably with a titanium dioxide content of more than 200 g / l, is preheated to more than 90 ° C and added with stirring to 20 parts of clear water at substantially the same temperature and 3-4 1/2 parts of solution per part of water. . The solution is brought to a boil and titanium dioxide in the form of colloidal particles is precipitated, the colloidal particles flocculating to give filterable titanium dioxide oxide hydrate. The method and means for performing the hydrolysis step are well known in the art and are described, for example, in U.S. Patent Nos. 1,851,487 and 3,071,439.

After hydrolysis, the titanium dioxide hydrate is filtered through a filter device 25 such as a Moore filter and the resulting filter cake 30 is fed to a calciner 26 where it is heated in a known manner to remove hydration water and adsorbed sulfuric acid to give titanium dioxide of suitable pigment grade.

A significant advantage of the process of the present invention is that it can reduce or even eliminate the serious problem of "used 70562 18 acid" disposal characteristic of the conventional sulfate process for the production of titanium dioxide pigment. In particular, the spent acid from the extraction, crystallization and hydrolysis steps of the process is reprocessed or recycled for use in carrying out the extraction reaction with ilmenite ore. Thus, the process of the present invention may be free or substantially free of spent waste acid.

To illustrate this, the spent acid from the filter 25 is passed through a tube 27 and returned to the extraction reactor 10. If desired, the spent acid from the filter 25 can be concentrated, e.g., by evaporation in a known manner in the concentrator 28 before returning to the extraction reactor 10.

Another and significant advantage of the process of this invention is that the recycled spent acid can be fed directly to any or all of the extraction reactors to control the temperature in each extraction reactor. The above provides a suitable and efficient way to balance and control the reaction temperature between the reactors.

The principle and practice of the present invention are described in the following examples, which are merely illustrative and not intended to limit the invention thereto, as changes in the art and procedures will be apparent to those skilled in the art. All parts and percentages defined herein are by weight unless otherwise indicated. Conversions are measured by the amount of reaction to the stoichiometric amount of treated ore.

30 The procedures and tests defined in this and the examples below were performed as follows:

Area was measured by the sedimentation method described by Jacobsen A.E. and Sullivan, W.F.

"Method for Particle Size Distribution for the Entire 35 Subsieve Range" Vol 19, page 855 in Analytical Chemistry (November, 1947).

i9 70562

Example 1 800 g of ilmenite ore (Maclntyre ore) with a surface area of 0.39 m / cm was charged to an extraction reactor vessel. 1.16 liters of 43% by weight sulfuric acid was added to 5 reaction vessels. The temperature of the reagents was raised to 108 ° C by heating under constant stirring with a stirrer made of TEFLON material. After 50 minutes, a 3 15 cm sample of the reaction mixture was filtered by gravity through glass filter paper into a 100 ml polypropylene laboratory glass. The filtrate was analyzed for active acid content and titanium content (expressed as TiCl 4. The active acid content was 430 g / l, giving a ratio of active acid to titanium of 7.1.

The conversion of the reaction was determined after about 1 1/4 hours by analyzing a sample of the reaction solution. The analyzed acid had an active acid content of 396.9 g / l and a titanium content of 78.5 g / l (TiCl 2).

After about 1 1/4 hours, 17 g of powdered iron was added to the reaction vessel to provide a reducing agent to the ferric iron content of the reaction mixture.

After about 1 3/4 hours, the temperature of the reaction mixture was lowered to 70 ° C by placing the reaction vessel in a cooling-water basin. Analysis of a portion of the reaction solution after cooling and removal of insoluble solids showed an active acid content of 353.3 g / l and a titanium content of 89.25 g / l (TiO 2), giving a ratio of active acid to titanium of 3.96.

The reaction mixture was maintained at 70-74 ° C for about 15 hours. The reaction mixture was cooled to about 50 ° C to quench the reaction, filtered to remove insoluble solids, and analyzed for active acid and titanium content. The active acid content was 275.8 g / l and the titanium content was 136.2 g / l (TiO 2), giving a ratio of active acid to titanium of 2.025.

20 7 0 5 6 2

The reaction solution was stable and suitable for hydrolysis to prepare a titanium dioxide pigment. The titanium dioxide pigment can be prepared from the reaction solution according to conventional manufacturing techniques.

5 Example 2

A two-stage system was constructed consisting of a heated, stirred five-liter first stage reactor with an overflow to a heated, stirred 25 liter second stage reactor. Maclntyre-10 ilmenite ore with the following particle size distribution (US-Standard sieves).

Mesh Weight% +100 1.2 + 200-100 35.8 15 + 325-200 23.0 + 400-325 6.0 -400 34.0 and containing 46.8% TiCl 2 were continuously fed to the first step at a rate of 3.78 g / min. A dilute solution of sulfur-20 acid as follows: 29.9% free t 2 SO 4 and 1.4% titanium (3) sulfate (as TiO 2) 3.3% soluble titanium 25 (as TiO 2) was also fed to the first step at a rate of 12.5 ml / min. Titanium (3) sulfate was added to the reaction vessel to provide a reducing agent for the ferric iron content of the reaction mixture. Both stages were initially charged with enough ore to achieve a 100% excess over the stoichiometric requirement. The unreacted ore flowing over the second stage was recycled to the first stage to maintain this excess ore in the system. The first stage reactor was set at 106 ° C, while the second stage reactor was set at 71 ° C. The residence times for the first and second stages were approximately 6.8 hours and 34.2 hours, respectively. After sufficient time had elapsed for the equilibrium to stabilize, it was found that 54.2% of the TiO 2 in the ore feed had reacted in the first stage and 28.2% had reacted in the second stage. In these two steps, an overall conversion of 82.4% was achieved.

Analysis of the final product was: 9.4% soluble titanium (as TiO 2) 9.0% free H 2 SO 3 0.3% titanium (3) sulfate (as TiO 2)

Example 3

The system described in Example 2 was operated at the following feed rates to the first stage reactor: 3.27 g / min ilmenite ore (46.8% TiO 2) 12.28 g / min dilute acid solution containing 42.9% free H 2 SO 4 and no titanium at all ( 3) sulfate.

Powdered iron was also fed to the first stage at a rate of 0.19 g / min. Powdered iron was added to the reaction vessel to provide a reducing agent for the ferric iron content of the reaction mixture.

A 100% excess of ore over the stoichiometric requirement was maintained in the system as in Example 2. The reactor of the first stage was adjusted to 106 ° C and the second stage to 72 ° C. The residence times for the first and second phases were approximately 9.4 hours and 47.1 hours, respectively. When equilibrium was reached, it was found that 73.9% of the TiO 2 in the ore feed had reacted in the first stage and 20.9% in the second stage. With these two steps, an overall conversion of 94.9% was achieved. Analysis of the final product was: 8.9% soluble titanium (as TiO 2) 8.8% free H 2 SO 4 0.1% titanium (3) sulfate (as TiO 2) 22 70562

Example 4

A reaction acid solution containing 41.6% by weight of sulfuric acid was prepared by combining 1,385 g of 96.5% sulfuric acid, 2,087.5 spent acid containing 16.32% by weight of sulfuric acid and 515 g of water in a reaction vessel. The reaction acid was heated to 100 ° C with constant stirring. 2,130 g of ilmenite ore, twice the stoichiometric amount, was heated to 100 ° C and charged to the reaction vessel. The temperature of the reaction mixture was then raised to about 108 ° C and maintained for 10.5 hours. Samples of the reaction mixture were taken periodically and analyzed. After about 8.5 hours, no further increase in soluble titanium levels was observed, indicating that the reaction had reached equilibrium.

After about 10.5 hours, the temperature of the reaction mixture was lowered to 104 ° C and 10 g of granular aluminum was added. The reaction mixture was allowed to react at 104 ° C for approximately two hours. Analysis of the reaction mixture after the addition of aluminum showed an increase in the content of soluble titanium, which indicated that an additional reaction had taken place due to the presence of an aluminum reducing agent.

After about two hours, the reaction temperature was lowered to 74 ° C. The reaction mixture was maintained at about 74 ° C for approximately six hours.

The reaction mixture was then cooled to about 50 ° C to quench the reaction, filtered to remove insoluble solids, and analyzed for active acid and titanium content. The active acid content was 18.11% and the titanium content was 9.04% (TiCl 2), giving a ratio of active acid to titanium of 2.00.

Claims (3)

23 70562 A process for preparing a titanium sulphate solution by treating a titanium-containing material with dilute sulfuric acid and reducing the ferric iron in the material to a ferrous iron with a reducing agent, characterized in that a) a titanium-containing material in an amount of about 10-400% greater than the stoichiometric amount with sulfuric acid to form titanium sulfate, and b) a dilute sulfuric acid solution having a concentration of about 25-60% by weight based on the total weight of the solution is reacted with each other at a temperature below about 140 ° C, preferably 55-140 ° C in the presence of a reducing agent - iron to ferrous iron, the resulting reaction mixture is cooled to a temperature below 110 ° C, preferably to 75 ° C, without precipitating reaction products to form a reaction mixture containing titanium sulfate, and insoluble solids are separated to form a titanium sulfate solution. Process according to Claim 1, characterized in that the reducing agent is metallic tin, iron, zinc, zirconium, titanium, aluminum, magnesium or an alloy thereof, sulfuric acid, sodium thiosulphate, sulfur dioxide, titanium (3) sulphate, reduced ilmenite or a mixture thereof. Process according to Claim 1, characterized in that the reducing agent is present in the reaction in an amount of at least a stoichiometric amount relative to the amount of ferric iron present.