FR2463100A1 - PROCESS FOR PRODUCING TITANIUM COMPOUNDS USING A REDUCER - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A PROCESS FOR OBTAINING TITANIUM COMPOUNDS BY MEANS OF A REDUCER. THE PROCESS CONSISTS OF REACTING A TITANIUM MATERIAL WITH DILUTED SULFURIC ACID IN THE PRESENCE OF A REDUCER. APPLICATION: MANUFACTURE OF TITANIUM DIOXIDE.

Description

i

  The present invention relates to the manufacture of

  posed with titanium and in particular with titanium dioxide

  silent. More particularly, the present invention relates to

  a new process of reacting a material

  tannin with dilute sulfuric acid in the presence of a reducing agent to prepare solutions of titanium salts which are

  can hydrolyze to obtain titanium dioxide pigment.

  Titanium dioxide is a well known compound having

  properties desirable as pigment and useful in

  paint and coating positions and in plastics. Several different processes are known for the manufacture of titanium dioxide, for example the process of

  sulfate and the chloride process. The present invention

  the manufacture of titanium compounds and in particular

  of titanium dioxide by the sulphate process.

  In the conventional sulphate process for the manufacture

  cation of titanium compounds, a titanium material is reacted

  such as ilmenite ores, including massive ilmenite and ilmenite sands or titaniferous

  furnace with concentrated sulfuric acid (for example -

  a concentration of 90 to 96%). The reaction is sometimes

  peeled digestion or digestion of ore. The reaction of diges-

  tion of the titaniferous material and the concentrated sulfuric acid

  tré is exothermic in nature and takes place very violently.

  Generally, the titaniferous material and sulfuric acid are

  than concentrated in a reactor called digestion tank. We have-

  usually pumps water into the digester to initiate and accelerate the reaction between acid and ore being

  given a large amount of heat which leads to

  vigorous boiling action of the aqueous acid solution between about 100 and 1900 ° C and the release of large amounts of water vapor and vapor resulting in particulate matter. As the violent reaction progresses, water is expelled and the reaction mass becomes solid; the reaction ends in solid phase at a temperature of about

  - 180 to 2150 C. The digestion process is a process

  continuous that is carried out in a single tank digestion. we

  uses as many digestion tanks as necessary,

  the desired capacity of the manufacturing facility

titanium sulphate solution.

  The solid mass resulting from the

  digestion, called cake. Then, dissolve the cake

  lide in water or diluted acid to obtain a solution of iron, titanium and other metal sulphates

  in the form of traces in the titaniferous material.

  The mixture is then treated to convert the ferric ion

  than in ferrous ion in a reduction step. If the iron of the

  lange is not completely reduced to the ferrous state, sulfa

  the ferric is entrained in the whole process and risk of

  cause impurities in the final product.

  To be certain that the iron content remains at

  iron and does not oxidize during the preparation of the

  reaction, it is best to allow the reduction to continue until the titanium solution contains

  small amount of trivalent titanium. In such a case, it is es-

  that the trivalent titanium content is within a gamma

  define me. Too much reduction gives a good return

  diocre in the hydrolysis step due to TiO2 losses.

  On the other hand, an insufficient reduction does not allow to have with certainty enough trivalent titanium to prevent

  the iron content to oxidize in the ferric state.

  As described in US Pat. No. 2,309,988, the conventional method of reducing trivalent iron is to immerse a basket containing scrap in a reactor containing the

  digestion cake not reduced in the dissolved state. Another pro-

  assigned is to discharge into the reactor a sufficient quantity

  iron and shake the mass of the solution or by hand.

  otherwise keep in contact with iron until the reduction

  occur. These methods tend to cause local overheating of the titanium solution and a local decrease in

  acidity, because of the reaction of iron and the solution. This-

  tends to give unstable solutions that vary by a lot

  from manufacturing to another. US Patent 1,014,793 discloses the

  ferrous state of the iron component of solutions of

  menite by introducing metallic zinc, sulfurous acid or sodium thiosulfate. In addition, tin reducing agents, crystalline titanium sulphate and sulfur dioxide have also been proposed as reducing agents. These prior techniques are effective

  when used with solutions of ilmenite previously

  digested but could not be used during the digestion reaction given the fluid loss of the solution and

  solidification. In addition, when the

  reaction, this technique could lead to a solution

  unstable, from which particles may separate

  spontaneously, therefore to a disordered hydrolysis reaction

  damaging the formation of titanium dioxide of pigmen-

silent.

  After the separate stages of digestion and reduction

  The resulting solution of iron and titanium sulphates thus obtained is treated by known means to eliminate the

  ferrous sulphate (green vitriol) and obtain a sulphate

  Titanyl fate which on hydrolysis gives hydrated titanium dioxide. Hydrated titanium dioxide is usually

  calcination treatment in a suitable oven to eliminate

  undermine the water of hydration and obtain the titanium dioxide pigment

  do not anhydrous. The above process is described in more detail by

  for example, US Pat. Nos. 1,504,672, 3,615,204 and 3,071,439.

  The present invention relates to a new sulphate process for the manufacture of titanium compounds which substantially avoids or eliminates the above disadvantages resulting from the conventional sulphate process. The term "titanium sulphate" is here collectively called titanium sulphates, such as sulphate

of titanyl and titanous sulphate.

  The invention relates to a method of

  react (a) a titaniferous material in a greater quantity of

  about 10 to 400% of the stoichiometric amount needed to react with sulfuric acid to form titanium sulphate

  and (b) a dilute solution of sulfuric acid having a concentration

  from about 25 to 60% by weight based on the total weight of the solution, at a temperature below about 1400 C,

  in the presence of a reducing agent which ensures the reduction of iron

  ferrous iron, to then cool the obtained mixture to a temperature below about 1100C, without precipitating the

  reaction products, to obtain a mixture containing sulphate

  titanium and to separate the undissolved solids to obtain

  add a solution of titanium sulphate.

  According to one embodiment, the method of initiating

  The invention comprises the following steps of (1) reacting (a) a titaniferous material in an amount of about 10 to 400% greater than the stoichiometric amount required to react with the sulfuric acid to form titanium sulfate, and b) a dilute solution of sulfuric acid having a concentration of about 25 to 60% by weight relative to the total weight of the solution, at a temperature below about 1400C, in the presence of a reducing agent which ensures the reduction of

  iron (III) iron (II), (2) to cool the mixture obtained until

  at a temperature below about 1100C without precipitation.

  the reaction products, (3) to remove from the mixture the

  -solids undissolved and iron sulphate to obtain a

  titanium sulfate solution, (4) hydrolyzing the titanium sulfate solution to obtain a hydrated titanium dioxide and a spent sulfuric acid solution, (5) calcining said hydrated titanium dioxide to obtain titanium dioxide and

  (6) recovering titanium dioxide.

  The attached figure represents an aspect of the invention in the form of a continuous process for the preparation of dioxide

of titanium.

  The salient features of the process of the invention

  reside in this discovery that can be made to react

  a titaniferous material with dilute sulfuric acid,

  in a liquid phase, in the presence of a reducing agent, to obtain a stable hydrolyzable solution of titanium sulphate, which can be used to prepare titanium compounds and

  titanium dioxide pigments. In particular, unexpectedly

  tense, it has been discovered that the presence of a reducer in the

  digestion step greatly accelerates the reaction between the

  titanium dioxide and diluted sulfuric acid to give a

  hydrolyzable solution of titanyl sulphate useful for the manufacture of

  titanium compounds. In addition, the use of a reduction

  in the digestion step eliminates the separate reduction step

  independent, necessary in the prior art,

after digestion.

  The digestion reaction is conducted with a material

  titaniferous. This is called titaniferous matter

  having a recoverable titanium content when treated according to the method of the invention. Examples are titaniferous socries, furnace slags, ilmenites, such as magnetic ilmenite, massive ilmenite, and ilmenite sands. The digestion reaction is conducted with a sufficient amount of titaniferous material to provide an excess of about 10-400% relative to the stoichiometric amount. It can also be said that this quantity represents from 1.1 to 5 times the stoichiometric quantity. The stoichiometry of the digestion reaction is represented by the equation: FeTiO 3 + 2H 2 SO 4> TiOSO 4 + FeSO 4 + 2H 2 O It is efficient and desirable to use an excess of titaniferous material in the digestion reaction to achieve a satisfactory and practicable process according to US Pat. invention without

  excessive grinding of the ore. Preferably, the titanium material

  It has a specific surface area of about 0.05 to 0.6 m 2 / cm 3. We

  could use an ore with a larger surface area

  However, this does not provide any advantage because of the increased cost of grinding. As indicated above, it is necessary to use in

  the digestion reaction an excess of material

  approximately 10 to 400% of the tannin relative to the stoichiometric

  metric needed to react with sulfuric acid. If smaller amounts of material are used, insufficient reaction rates and treatment times are obtained.

  long so that the process becomes unattractive economically

  cally. It is undesirable to use excess material

  higher than those recommended, given the fluidi-

  very small amount of the reaction mixture and the need for

  cycler large amounts of unreacted titaniferous material to the digestion reactors. For example, it has been unexpectedly observed that if the amount of titaniferous material, for example MacIntyre ilmenite, is doubled, then the stoichiometric amount required to react with 1 acfde / reaction rate is multiplied by a coefficient of

  the order of at least 10 in the last digestion reactor.

  It must also be recognized that reaction rates vary

  according to the source of titaniferous material used during the

management.

  The sulfuric acid used in the process of the in-

  The reaction should have a concentration of about 25 to 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 the titanium dioxide occurs during and in conjunction with the digestion reaction when such acids are used. Premature hydrolysis of titanium salt solutions prevents formation

  pigment-grade titanium dioxide at a later stage.

  the process. On the other hand, it is not desirable to

  use an acid with a concentration greater than 60% by weight because (1) the resulting solution is more viscous and difficult to handle, (2) the economy due to

  spent acid recycling, unless the acid is concentrated

  this increases unnecessarily the cost of operation and (3) the highest concentration of reaction products in

  the solution promotes the precipitation of mono-ferrous sulphate

  hydrated and recoverable titanyl sulfate dihydrate. The

  The presence of ferrous sulfate monohydrate renders ineffective the

  paration by gravity and is difficult to remove by filtration.

tion.

  The conditions of the reaction can be easily

  digestion rate according to the concentration of the diluted sulfuric acid and the specific amount of titaniferous material in excess that is used, to obtain optimal operation. AT

  For illustration purposes, if a sulfuric acid di-

  for example, having a concentration of less than 40%

  weight, it is necessary to operate initially at a temperature

  ant in the bottom of the preferred range, given the

  lower boiling of the diluted sulfuric acid. He is

  to increase the amount of titaniferous material used to digest as much material as possible in the first

  reactor, where the operating temperature and the

  reaction rates are usually higher. As

  As discussed below, the temperature in the following reactors is kept lower than in the first reactor and finally lowered to prevent or prevent premature hydrolysis of the titanium salt solution. The temperature at which the reaction of

  digestion is less than about 1400C and preferably

  between 550C and the boiling point of the solu-

  reaction, thus between about 55 and 1400C. It must be

  avoid choosing too low a temperature in the digestion reactor because the digestion reaction proceeds too slowly and thus requires an increased residence time of the reagents. It is also necessary to avoid increased residence times to prevent undesirable germ formation in the reaction solution by premature hydrolysis of the titanium salt. It is not recommended to choose a temperature higher than 1400C because the titanium salt hydrolyzes at speeds

  much higher, at higher temperatures. It must be

  avoid conducting the digestion reaction below 550C

  approximately, because the reaction products begin to pre-

  cipitate the solution and that the viscosity of the mixture increases

  te, so that the elimination of unreacted solids

  becomes very difficult. The preferred temperature of the reaction

  digestion rate is about 70 to 1100C.

  It should be noted that the digestion reaction of the procedure

  of the invention may be in batch form, for example in a reactor from which the mixture is removed, once the digestion has progressed to a desired extent, for the

  still deal in other reactors. According to a mode of

  In the preferred embodiment of the process of the invention, the digestion is carried out continuously in at least two reactors and the titaniferous material and the acid are flushed with direct current.

diluted sulfuric acid.

  When operating continuously, two or more digestion reactors are preferably used. The total number of reactors depends on the ease of adjustment of the reaction,

  the layout of the plant and manipulations.

  Preferably when performing the reaction of

  two reactors or stages, the first one

  reactor at a temperature below about 1400C, pre-

  less than about 1100C and the second

  temperature below 1000C, preferably below

about 750C.

  Preferably when carrying out the reaction of diges-

  in three reactors or stages, the first

  reactor at a temperature below about 1400C, pre-

  less than about 1100C. The second reactor has a

  temperature below 1100C, preferably below

  1000C and the third reactor at a lower temperature

  below about 800C, preferably below about 750C.

  Preferably, when the reaction of diges-

  in four reactors or stages, the first one is maintained

  reactor at a temperature of less than about 140 ° C, preferably

  less than about 1100C, the second reactor at a temperature below about 1100C, preferably below

  at around 900C, the third reactor at a temperature: below

  below about 1000C, preferably below 860C and the fourth reactor below about 90'C,

  preferably less than about 75 C.

  Preferably, when the reaction of diges-

  in five reactors or stages, the first one

  reactor at a temperature below about 1400C, pre-

  less than about 1100C, the second reactor at a temperature below about 1100C, preferably

  at about 900C, the third reactor at a lower temperature

  below about 1000C, preferably below about 850C, the fourth reactor at a temperature below about 90C, preferably below about 800C and the fifth

  reactor at a temperature below about 850C,

  less than about 750C.

  All reaction temperatures can be varied

  above according to the desired yield and the reaction times

  on each floor. One of the essential and salient features of the invention is that the temperature is lowered as the reaction progresses so as to prevent or

  avoid premature hydrolysis of the salt solutions of

  tane obtained. Uze premature hydrolysis prevents training

2 46 310 0

  of titanium dioxide of pigment quality.

  The duration of the digestion reaction in a reaction

  digestion is governed by the optimal degree of transfor-

  cation or digestion of the titaniferous material at this stage.

  In general, it is preferable to digest or react as much as possible of the titaniferous material in the first reactor or stage, where the temperature is maintained

  at the highest level, to prevent hydrolysis of sulphate

  titanium fate in the solution. For example, in a system

  multi-stage continuous process using a MacIntyre ore com-

  As a titaniferous material, it is sometimes possible to digest on the first stage up to about 90% by weight of the stoichiometric amount of ore introduced into the process, excluding excess. Preferably, about 30 to 80% and more preferably 60 to 80% by weight of the stoichiometric amount are digested in the first stage, excluding excess. Transformation is measured by the degree of reaction

  a stoichiometric quantity of titaniferous material.

  The temperature is used to control the digestion reaction preferably by acting on the ratio of active acid to titanium in the reaction solution. This ratio is an indication of the degree of transformation or digestion. The "active acid" is the total amount of free acid in the reaction solution plus the acid combined with titanium in the reaction solution. To calculate the ratio of active acid /

  titanium dioxide, the free acid is added to the solution.

  and the free acid combined with titanium in the solution and the sum divided by the amount of titanium in the solution (calculated as TiO2). For example, the active acid content of a solution can be determined by titrating a selected sample (pooled or pipetted) with 0.5N sodium hydroxide solution (NaOH) to pH 4.0 in a solution. buffered barium chloride / ammonium chloride. The titration gives the overall content of free acid and combined acid / TiO 2, which is called acid

  active. By way of illustration, in a beaker containing the

  sample, 60 ml of buffer solution con-

  holding 75 g / l of barium chloride and 250 g / l of ammonia chloride, diluted with water up to 250 ml and titrated by

  0.5N sodium hydroxide until the methylorange turns.

  In a batch process, the acid content

  It may vary widely and is not critical except that digestion and reduction must occur in the liquid phase. In a continuous process, the ratio of active acid can decrease, from infinity to the beginning of the reaction, to 1.50 to 7.0 at the completion of the reaction, depending on the digestion conditions. Generally> the ratio of active acid to

  TiO2 varies between 2.0 and 3.5. As the acid level increases

  tif decreases, the stability of the tita-

  in relation to hydrolysis decreases. Generally, the temperature of the reaction solution should be maintained below about 1400C and preferably below about 1100C, while the ratio of active acid to titanium (calculated as dioxide

  of titanium) decreases to about 2.0. As illustrations

  In a two-stage digestion process, the temperature of the reaction solution must be kept within

  first stage or reactor below about 1400C, by -

  example at 110 C until the active acid / dioxide ratio

  titanium in the solution decreases to about N, 0,

  whereby the temperature of the reaction solution is lowered below about 1000C, for example to 700C. In contrast, in a three-stage digestion process where the temperature of the first stage is maintained at about 1100C to obtain

  a mixture having an active acid / titanium dioxide ratio

  between 2.5 and 3.0, after which the reaction is

  in a second stage at a temperature of about 1000C to obtain a mixture having an active acid / titanium dioxide ratio between about 2.2 and 2.5 can be completed in a third stage, at a lower temperature

  at about 800C, to obtain a mixture having a ratio a-

  active acid / titanium dioxide of about 2.0.

  The reductant can be added at any stage of the digestion process. In a multiple digestion process, the reductant is preferably added to the first stage to initially maximize digestion of the ore and

  the reduction of iron (III) or ferric iron.

  Generally, iron reduction can be achieved

24 63 10 0

  (III) in the digestion mixture using standard reducers for the sulfate process. These can be gaseous reducers such as sulfur dioxide, which can be used alone or with activated charcoal. Other examples of reducing agents are sulfurous acid, sodium thiosulphate, titanous sulphate, reduced ilmenite and mixtures of

  these compounds, as well as metal compounds such as

  tin, iron, zinc, zirconium, titanium, aluminum, magnesium and mixtures thereof, including alloys containing them. These examples of reducing agents do not exclude other known agents. These agents can be used in the form of solutions or solids. A preferred solid reducer is under

the form of granules or powder.

* The amount of reducing agent used is an amount at least stoichiometric relative to the amount of iron (III) present. A small excess of reductant can be used, usually about 10% maximum of the amount needed to reduce all iron (III), in order to reduce

  also a quantity of titanium titan trivial trivial

  generally slow / l%. The following equation of the reaction of o-

  xydation-reduction demonstrates the stoichiometry of the system used

  including aluminum and iron as reducing agents: a) A1 + 3Fe + 3 = A1 + 3 + 3Fe + 2b) Fe + 2Fe + 3 = 3Fe + 2

  When using a reducer such as iron in

  the amount of reducer added to the solution in the reactions

  digestion depends on the amount of ferri-

  naked in the titaniferous feed material. In general, about 3 to 8% by weight of reducing agent is

  the total weight of the titaniferous material, in order to obtain

  satisfactory results in a process using a titaniferous material, such as ilmenite which contains 5 to 13% e Fe203. The addition of a reducing agent, such as iron powder / to another advantageous effect which is to accelerate the reaction of

digestion.

  It should be noted that the acceleration effect produced by iron on the digestion reaction increases as the

  Particle size of iron decreases.

  When the digestion reaction is complete, one

  can treat the mixture obtained, containing titanium sulphate

  iron sulphate and trace elements

  from the titaniferous material, to recover a solution of titanium sulphate and to prepare titanium compounds, or to treat it by conventional treatment techniques

  sulfates to prepare a titanium dioxide pigment.

  In the diagram of the attached figure, concerning the preparation of titanium dioxide in a reactor system with

  several stages, the reference 10 indicates a reactor of

  management. A titaniferous material such as ilmenite can be

  brought to the reactor 10, from an ore tank 11. From

  dilute sulfuric acid having a concentration of about 25

  60% by weight relative to the total weight of the acid solution.

  of and. formed of a mixture comprising acid-concentrate (96% by weight) coming from a source 12 of fresh acid, combined with either recycled acid (15 to 45% by weight) or 1 to water, can

  The ilmenite and the dilute sulfuric acid contained in the reactor 10 are agitated directly to the reactor 10.

  continuously at a temperature not exceeding the point

  ebullition of the solution contained in the reactor.

  The reagents contained in the digestion reactor are maintained at a temperature below about 1400C,

  preferably from about 55 to 140 C. More precisely, the reactions

  The contents of the reactor 10 are preferably maintained at 10 ° C. The digestion reactor 10 can be maintained at any suitable pressure; the atmospheric pressure is better

for reasons of economy. -

  When operating continuously in the digestive system,

  3-stage process which is shown in the accompanying single figure, the reaction mixture is transported from the reactor 10 to a conventional separator device 13, for example a cyclone filter or separator, in which a part is separated.

  or all unreacted ilmenite that is recy-

  Via the line 14 to the reactor 10, the reactor mixture can be continuously transported to the reactor without recycling the unreacted ilmenite to the reactor 10.

2463 100

  Preferably, the solution is maintained in the reaction

  at a slightly lower temperature than in the reaction

  For example, the mixture is maintained in the reactor at about 1000 ° C. The temperature of the reactor can be adjusted by adding recycled acid or water. Preferably, the digestion reactor 15 is at atmospheric pressure but

  higher pressures can be used if desired.

  The mixture can be transported continuously from the reactor

  to a conventional separator device 16, for example a filament

  or a cyclone separator, in which part or all of the unreacted ilmenite is separated and recycled

  by line 17 to the reactor 15. Alternatively, it is possible to transfer

  continuously carry the mixture of the digestion reactor 15 to the digestion reactor 18 without recycling the ilmenite not having

reacted towards the reactor 15.

  Preferably, the mixture is maintained in the reaction

  18 at about 700 ° C. and at atmospheric pressure.

  The mixture coming from reactor 18 is brought into con-

  an appropriate separation device 19, for example a

  or a gravity separator (or more than one of these devices, in series and / or in parallel), wherein unreacted ilmenite is separated from the liquid reaction product. Excess unreacted ilmenite is recycled through lines 21 and 21 'to the

  reactor 18 and / or the digestion reactor 10.

  reaction liquid from the separator 19 to the settling device 20, for example a conventional device or a "Lamella" device, where gangue or other undesirable solid material is removed from the product. The use of a device

  decantation "Lamella" does not form part of the invention.

  As mentioned above, the digestion reaction is conducted in the reactors 10, 15 and 18. It is not

  essential to conduct the reaction in three reactors of different

  management. In fact, one can drive the process in form

  discontinuous using a single digestion reactor. always

  However, it is better to use two or more

  digestion processors to carry out the process in a continuous manner. When only two reactors are used, the temperature of the second reactor such as the reactor can be adjusted

  at a lower level, for example at 70C.

  A suitable reducing agent from the reservoir 22 is added to the reactor 10 or reactor 15 or both to reduce the ferric iron contained in the digestion solution to ferrous iron. A reduced state prevents the passage of ferric salts as impurities in the titanium hydrate obtained subsequently. The amount of reducing agent added to the reagent solution in the digestion reactors depends on the amount of ferric iron contained in the feed ilmenite, such as

indicated above.

  It is possible by this measure to avoid a floor

  separate from the reduction of the solution, which would be necessary

  tration. The reducer can be added at any point

  of the digestion operation. We choose the quantity of reduction

  in such a way that not only all the ferric iron of the

  Menite is converted to the divalent state, but in addition a part of the titanium of the solution is reduced to the trivalent state, so as to obtain for the hydrolysis a solution of titanium sulphate containing enough titanium (III). The presence of trivalent titanium inhibits the formation of ferric iron which would adsorb on titanium dioxide particles in

the subsequent hydrolysis step.

  A certain amount of metal sulphates, that is,

  ie ferrous sulfate monohydrate, usually precipitates

  during the digestion reaction without any significant

  the fluidity of the mixture. We can easily dissolve

  ferrous sulfate monohydrate at the end of the reaction of

  management, adding water. We can replace at least one

  part of the water with titanium sulphate solution de-

  largely free of iron sulphate (by crystalli-

  and separation of the ferrous sulfate heptahydrate at a later stage of the process, described later). By this measure, we can minimize or avoid the addition of a supplement

  of water to the system. Ordinarily, the water must be removed

  at a later stage of the process, for example by spraying.

  The water or the aqueous solution of sulphate

  titanium fate to the reaction solution in the last reaction

  or at a convenient point between the last reactor and the separator 19 to provide cooling. The addition of water or aqueous titanium sulphate solution does not

part of the invention.

  The resulting solution containing titanium sulfate, iron sulfate and trace elements from ilmenite can be recovered and processed to prepare titanium compounds. Or, we can treat the solution

  to prepare a titanium dioxide pigment by sending the

  to the settling device 20 to remove

solids.

  When titanium dioxide is prepared, then the reaction solution of the decantation device 20 is conducted to a crystallizer 23 in which the ferrous sulfate heptahydrate (green vitriol) is crystallized and removed by known means. For example, we cool the solution between

  about 10 to 200C in a continuous vacuum crystallizer or

  continuous by applying a vacuum of 0.97 bar to form large crystals of FeSO4. 7H20 that can be easily filtered on a drum or table filter. We can wash the cake

  ferrous sulphate heptahydrate to recover the

  soluble tane. The solution from the filter can be concentrated by known means, for example by evaporation, before

  subject it to hydrolysis. We can also clarify the solution

  before or after crystallization and removal of sulphate

  ferrous filler heptahydrate. A clarification step before the

  crystallisation is advantageous if it is desired to obtain a sulphate

  ferrous iron heptahydrate of high purity which can be

  formed, for example for the preparation of reagents

  for the purification of water and the treatment of wastewater.

  Preferably, the solution is subjected to a step of

  fine filtration before hydrolysis. After removing the

  If necessary, a titanium sulphate solution having a favorable Fe: TiO 2 ratio, which can be directly hydrolysed or, optionally, evaporated with i, is obtained.

  known means in vacuum evaporator up to the concentration

  desired treatment of TiO 2, after which the hydrolysis is carried out.

  The solution from the crystallizer 23 is a solution

  Titanyl sulphate (TiOSO4), which is brought to the

  Hydrolysis system 24 where the titanyl sulphate is hydrolyzed

  by means known to obtain hydrated titanium dioxide

  you. Specifically, the titanyl sulfate solution is hydrolyzed to insoluble hydrated titanium dioxide by diluting the solution with water at elevated temperature. For example, a predetermined amount of titanyl sulfate solution, preferably having a higher titanium dioxide content, is preheated to a temperature above 90 ° C.

  at 200 g / l and added with stirring to the pure,

  at the same temperature and at - 4.5 parts of solution per 1 part of water. The solution is boiled and the titanium dioxide is precipitated as colloidal particles; the colloidal particles flocculate to give a hydrous filterable titanium dioxide. The manner of conducting the hydrolysis step is well known and described for example in

  U.S. Patents 1-851,487 and 3,071,439.

  After the hydrolysis, the hydrated titanium dioxide is filtered by means of the filter device 25 such as a filter

  Moore and the cake is brought to the calciner or

  calcination agent 26 is heated in a known manner to eliminate the water of hydration and the sulfuric acid adsorbed and

  obtain a titanium dioxide suitable as a pigment.

  A significant advantage of the process of the invention is that it makes it possible to reduce or even eliminate the major problem.

  posed by the rejection of the spent acid and which characterizes the

  conventional sulphate compound for the production of titanium dioxide pigment. More specifically, we retire or recycle

  the spent acid resulting from the digestion, crystal

  The process is used for the digestion reaction with ilmenite. Thus, the method of

  the invention makes it possible to eliminate totally or practically

  depleted acid as waste.

  By way of illustration, the spent acid from the

  25 is returned via line 27 to reactor 10. If desired, the spent acid from filter 25 can be concentrated.

  by evaporation in a known manner in the concentration device.

  28 before returning it to reactor 10.

  An additional and notable advantage of the process of the invention is that the recycled spent acid can be introduced directly into any or all of the digestion reactors to control the temperature in each

  reactor. This provides a convenient and efficient means of balancing

  brew and adjust the temperature from one reactor to another.

  The principle and the practice of the invention are

  glossed by the examples below which do not limit it because modifications will appear to any practitioner. All parts and percentages are by weight unless otherwise indicated. Transformations are measured by the degree of reaction experienced by a stoichiometric amount of

processed ore.

  The tests shown here and in the examples below are as follows:

  The specific surface area is measured by the method of

  Dimentation described in: Jacobsen, A.E. and Sullivan, W.F., "Method for Particle Size Distribution for the Entire Subaieve Range", Volume 19, page 855, Analytical Chemistry (november

1947).

Example 1

  800 g of ilmenite (MacIntyre ore) having a specific surface area of 0.39 m 2 / cm 3 were charged to a digestion reactor. 1.16 liter of 43% by weight sulfuric acid was added. The temperature of the reagents was raised to

  108 C heating with constant agitation using a-

  polytetrafluoroethylene (TEFLON) gitator. After 50 minutes

  In addition, a 15 ml sample of the material was

  Drain through a glass filter paper into a 100 ml polypropylene beaker. The active acid and titanium (expressed as TiO 2) were determined in the filtrate. The active acid content was 430 g / l, which is an active acid /

Titanium 7.1.

  Transformation is determined after about 1 1/4 hours by analyzing a sample of the solution. The filtrate analyzed had an active acid content of 396.9 g / l of

  H2S04 and a titanium content of 78.5 g / l (TiO2).

  After about 1 hour, 17 g of iron powder were added to the reactor to reduce the iron content.

ferric mixture.

  After about 1 3/4 hours, the temperature was lowered

  mixing temperature up to 70 C by placing the reactor in a cooling water tray. By analyzing a portion

  of the solution, after cooling and elimination of

  undissolved, an active acid content of 353.3 g / l H 2 SO 4 and a titanium content of 89.25 g / i (TiO 2) was found)

  an active acid / titanium ratio of 3.96.

  The mixture was maintained at 70 to 740C for about 15 hours. The mixture was cooled to about 50 ° C to quench the reaction, filtered to remove undissolved solids, and the active acid and titanium were assayed. The active acid content was 275.8 g / l and the titanium content was 1536.2 g / l (TiO2), an acid ratio

active / titanium of 2.025.

  The solution was stable and suitable for hydrolysis for the preparation of titanium dioxide pigment. We can

  to prepare a titanium dioxide pigment from the solution

  tion according to conventional transformation techniques.

Example 2

  A two-stage system was constructed comprising a heated, stirred, 5-liter first stage reactor which overflowed into a 25-liter, liquid, stirred second stage reactor. MacIntyre ilmenite having the following particle size distribution was continuously fed to the first stage at a rate of 3.78 g / min. Granulometry% by weight more than 149 pm 1.2 from 74 to 149 pm 35.8 from 44 to 74 pm 23.0 from 37 to 44 pm 6.0 less than 37 pim 34, where

  and containing 46.8% TiO2. We also brought to the first

  at a rate of 12.5 ml / min, dilute sulfuric acid solution having the following analysis: 29.9% of H 2 SO 4 1.4% of titanous sulphate (in TiO 2) 3.3% of soluble titanium ( TiO2) The titanium sulfate was added to the reactor to reduce the ferric iron in the mixture. Initially, sufficient ore was introduced into both stages to provide 100% excess relative to the stoichiometric requirement. The unreacted ore was recycled to the first stage.

  overflowing from the second floor in order to maintain this excess of

  will be in the system. The first stage reactor was set at 106 C and the second stage reactor at 710 C. The residence times at the first and second stages were respectively 6.8 hours and 34.2 hours. Once sufficient time had elapsed for the equilibrium to be established, 54.2% of the TiO2 contained in the feed ore was found to have reacted to the first stage and 28.2% to the second stage. . We got a

  overall transformation of 82.4% with both floors.

  The analysis of the final product was as follows: 9.4% soluble titanium (TiO2) 9.0% free H2SO4

0.3% titanous sulphate (TiO2).

Example 3

  The system described in Example 2 was operated with the following feed rates in the first stage reactor: 3.27 g / min ilmenite (46.8% TiO2) 12.28 g / min solution dilute acid containing 42% H2SO4

free, without titanous sulphate.

  Iron powder was also included in the first stage at a rate of 0.19 g / min. Iron powder was added

  to reduce the ferric iron content of the mixture.

  We kept in the system, as in example 2j

  an excess of ore of 100% relative to the stoichiometric requirement

  metric. The first stage reactor was set at 106 C and the second stage reactor at 72 C. The dwell times in the first and second stages were respectively about

  9.4 hours and 47.1 hours. Once the balance has been reached

  On the other hand, it was found that 73.9% of the feed ore 2 obtained had reacted at the first stage and 20.9% at the second stage. We have/

  an overall transformation of 94.9% with both floors. The-

  Analysis of the final product is as follows: 8.9% soluble titanium (TiO2) 8.8% free H2SO4 0.1% titanous sulphate (TiO2)

Example 4

  To prepare an acidic solution containing 41.4% by weight of sulfuric acid, 1385 g of sulfuric acid containing 96.5% by weight and 2087.5 g of spent acid containing 16.32% were combined.

  by weight of sulfuric acid and 515 g of water in a reactor.

  The acid was heated to 100 C with constant stirring. We have

  heated 2130 g of ilmenite (twice the amount stoichiometric

  metric) at 100 ° C. and introduced into the reactor. The temperature of the mixture was then raised to about 108 ° C.

  and held for 10.5 hours. We have collected

  samples of the mixture that were analyzed.

  After about 8.5 hours, there was no increase in

  tation of the soluble titanium content which indicated that the

  reaction had reached balance.

  After about 10.5 hours, the temperature was lowered

  of the mixture to 104 ° C. and 10 g of aluminum were added.

  granular nium. The mixture was allowed to react at 104 ° C.

  about 2 hours. Analysis of the mixture after addition of aluminum indicated an increase in soluble titanium content, indicating that an additional reaction was

  produced by the presence of aluminum as a reduction

tor.

  After about 2 hours, the temperature was lowered

  to 74.degree. C. The mixture was maintained at about 74.degree.

for about 6 hours.

  The mixture was then cooled to about 50 ° C

  to extinguish the reaction, it was filtered to remove the

  undissolved lides and the active acid and titanium were determined. The active acid content was 18.11% and the titanium content

  of 9.04% (TiO2), an active acid / titanium ratio of 2.00.

  It is obvious that the invention described above can be modified in many ways. These variants remain

  included in the scope of the invention.

Claims (7)

  1) A method for producing a titanium sulphate solution, characterized in that it consists in reacting (a) a titaniferous material in an amount greater by approximately 10 to 400% than the stoichiometric quantity necessary to react with the sulfuric acid to form titanium sulfate and   (b) a dilute solution of sulfuric acid having a   concentration of about 25 to 60% by weight relative to the total weight of the solution, at a temperature below about 1400C, in the presence of a reducing agent which ensures the reduction of ferric iron to ferrous iron, then cooling the mixture obtained up to a temperature below about 1100C,   without precipitating the reaction products, to obtain a   lange containing titanium sulphate and separating the solids   undissolved to obtain a solution of titanium sulfate.   2) Method of manufacturing titanium dioxide)   characterized in that it comprises: (1) reacting (a) a titaniferous material in an amount of about 10 to 400% greater than the stoichiometric amount required to react with the sulfuric acid to form titanium sulfate, and   (b) a dilute solution of sulfuric acid with a concentration   from about 25 to 60% by weight relative to the total weight of   solution of the solution, at a temperature below about 1400C, in the presence of a reducing agent which ensures the reduction of iron (III) iron (II), (2) to cool the mixture obtained   to a temperature below about 1100C without   cipitate the reaction products, (3) remove from the mixture the undissolved solids and iron sulfate to obtain a solution of titanium sulfate, (4) hydrolyze the titanium sulfate solution to obtain a titanium dioxide hydrate - And a spent sulfuric acid solution, (5) calcining said hydrated titanium dioxide to obtain   titanium and (6) to recover the titanium dioxide.   3) Method according to one of claims 1 or 2,   characterized in that the reaction between the titaniferous material and the dilute sulfuric acid is carried out at a temperature of from about 55 to 1400c.   4) Method according to one of claims 1 or 2 2463 100   characterized in that the resulting mixture is cooled to about 750C.   Method according to one of claims 1 or 2,   characterized in that the reducer is metallic tin, iron, zinc, zirconium, titanium, aluminum, magnesium,   sium, an alloy of these metals, sulfurous acid, thio-   sodium sulphate, sulfur dioxide, titanium sulphate,   Reduced ilmenite or a mixture of these compounds.   6) Method according to one of claims 1 or 2,   characterized in that the reducer is present in quantities   at least stoichiometric in relation to ferric iron   feels. 7) Process according to claim 2, characterized in that the step (1) is brought undissolved solids and the   reducing agent for reaction with sulfuric acid.   Process according to Claim 2, characterized in that the spent sulfuric acid solution from the hydrolysis step (4) is fed to the reaction step (1).   for the reaction with the titaniferous material.   9) Continuous process for producing titanium dioxide.   characterized by comprising: (1) reacting in response to   tinu (a) a titaniferous material in a greater quantity of   about 10 to 400o at the stoichiometric amount required for   react with sulfuric acid to give titanium sulphate   and (b) a dilute solution of sulfuric acid having a concentration of about 25 to 60% by weight based on the total weight of the solution, at a temperature below about 1 ° C, in the presence of a reducing agent which ensures the reduction of   ferric iron to ferrous iron, in at least stoichiometric amounts   metrically relative to the amount of ferric iron present, (2) cooling the resulting mixture to a temperature below about 1100C in a second reactor, without precipitating the mixture and while continuing the reaction, (3) separating the titaniferous material unreacted mixture to form a solution of iron sulfate and titanium sulfate, (4) removing iron sulfate from said solution to obtain   a solution of titanium sulphate, (5) to hydrolyze the solu-   titanium sulfate to obtain a hydrated titanium dioxide and a spent sulfuric acid solution;   ciner hydrated titanium dioxide to obtain the diboyde of -   titanium-and? <7) to recover titanium dioxide.   O10) Process according to claim 9, characterized in that the reducing agent is metallic tin, iron, zinc, zirconium, titanium aluminum, magnesium, an alloy of these metals, sulfurous acid, sodium thiosulfate, sulfur dioxide, titanium sulphate, reduced ilmenite or a mixture of these compounds.