Field of application

The present invention relates, broadly, to the treatment of ore materials.

In particular, the present invention relates to a method for treating a titano- magnetite ore, i.e. an iron-containing titanium ore.

Prior art

Titanium dioxide is a white pigment which is used to a large extent in industry and is normally obtained by the processing of titanium ores such as, for example, ilmenite. Iron is the principal impurity of titanium ores and consequently the primary objective of the methods known in the art is to achieve the greatest degree of separation of titanium and iron at the lowest costs.

A method for processing vanadium-containing titano-magnetite ores with direct alloying of steel is disclosed in RU patent No. 2423530. The method comprises the reduction of vanadium-containing titanomagnetite ore materials with coal or coal- containing materials in a direct liquid-phase reduction device with the simultaneous obtaining of cast iron and hot reducing gases, the metallization of oxidized vanadium- containing pellets in a metallization device at feeding hot reducing gases from the direct liquid-phase reduction device, feeding of the liquid cast iron, metallizated pellets and scrap to the electric arc furnace, and melting with obtaining of vanadium alloyed steel. However, a disadvantage of the method disclosed in RU 2423530 is loss of titanium to slug.

Another method for processing vanadium-containing titano-magnetite ores is disclosed in WO 201 1/143689. The method includes processing a titanomagnetite concentrate with hydrochloric acid, followed by extraction separation of vanadium and iron as vanadium oxide and ferrous oxide in the commodity form. The

disadvantage of the method is the presence of titanium both as unreacted residue and as product solution.

A further method for processing titanium-containing raw materials is disclosed in RU patent No 2365647. The method comprises the fluorination of the raw material (titano-magnetite ore material) by means of sintering with ammonium fluoride, ammonium bifluoride or the mixture thereof at 1 10-240°C followed by heat treatment of the fluorinated bulk at 300-600°C with formation of sublimation products. The sublimation products are trapped by water obtaining an ammonium fluorotitanate solution which is processed with an ammonia aqueous solution causing the precipitation of hydrated titanium dioxide and the formation of ammonium fluoride solution. The precipitate is filtered from the solution of the fluoride solution and heat treated obtaining anhydrous titanium dioxide. The ammonium fluoride solution is instead directed to regeneration of the fluorinating agent and then, after separating titanium by sublimation, the residue is subjected to oxidative pyrohydrolysis at 300- 650°C for 0.5-3 hours with formation of iron (III) oxide.

However, although the method disclosed in RU 2365647 may be satisfactory for application at an industrial level, it has the disadvantage that titanium dioxide may become contaminated by silicon compounds (mainly silicon dioxide) present in the starting raw ore materials.

As a result, the titanium oxide thus obtained may have a purity non adequate for some industrial applications. In this case, it would be necessary to remove silicon compounds which however would be complex and involve high operation and equipment costs. This problem takes on considerable importance especially when the ore material has a relatively high content of silicon which is the case of raw ore materials extracted from certain natural sites of origin and of some titanomagnetite concentrates.

In this context, it should also be noted that silicon dioxide has per se a certain economic value so that its recovery from raw ore materials may be of significant interest.

The main object of the present invention is therefore to provide a method for processing titanomagnetite ore materials which allows to obtain separately silicon dioxide, titanium dioxide and iron oxides (which may be then converted to metallic iron) from a complex raw material containing them in an efficient and cost-effective way so as to be applicable at an industrial level.

Summary of the invention

This problem is solved by a method for processing titanomagnetite ore materials (e.g. a titanomagnetite concentrate), the method comprising the steps of:

- reacting a titanomagnetite raw material with an ammonium fluoride reagent to obtain a fluorinated product, - heat treating the fluorinated product so obtained at a first temperature to obtain a first sublimate product containing ammonium fluorosilicate compound(s) and a first residue,

- heat treating the first residue so obtained at a second temperature higher than said first temperature to obtain a second sublimate product containing ammonium fluorotitanate compound(s) and a second residue,

- subjecting said second residue to pyrohydrolysis with water vapor to obtain a third residue containing iron oxides and a gaseous stream containing hydrogen fluoride.

According to a preferred embodiment of the invention, the first temperature in the first heating treatment of the fluorinated product is not higher than 350°C and preferably comprised between 320°C and 350°C while the second temperature in the second heating treatment of the fluorinated product (first residue) is above 350°C and preferably comprised between 500°C and 800°C.

The method according to the invention may further comprise appropriate steps for separating silicon as silicon dioxide from the first sublimate product containing ammonium fluorosilicate compound(s). Such steps include:

- de-sublimating (i.e. frosting) said first sublimate product containing ammonium fluorosilicate compound(s) to a solid state,

- dissolving said first sublimate product de-sublimated to a solid state and treating the resulting solution with an ammonia aqueous solution to obtain the precipitation of hydrated silicon dioxide and an ammonium fluoride solution,

- separating the hydrated silicon dioxide precipitate from the ammonium fluoride solution, and

- drying said hydrated silicon dioxide precipitate.

In the description, the term "de-sublimation" or "de-sublimated" has the meaning of an inverted sublimation, i.e. the process of transition of a substance directly from the gas state to a solid state without passing through an intermediate liquid phase.

Such process is also known as frosting.

The method according to the invention may further comprise appropriate steps for separating titanium as titanium oxide from the second sublimate product containing ammonium fluorotitanate compound(s). Such steps include: - de-sublimating (i.e. frosting) said second sublimate product containing ammonium fluorotitanate compound(s) to a solid state,

- dissolving said second sublimate product de-sublimated to a solid state and treating the resulting solution with an ammonia aqueous solution to obtain the precipitation of hydrated titanium dioxide and an ammonium fluoride solution,

- separating the hydrated titanium dioxide precipitate from the ammonium fluoride solution, and

- drying said hydrated titanium dioxide precipitate.

Advantageously, the ammonium fluoride solution separated from the hydrated silicon dioxide and/or the ammonium fluoride solution separated from the hydrated titanium dioxide may be subjected to appropriate treatments to obtain ammonium fluoride and an ammonium solution to be recycled in the fluorinating step and in the treatment of the dissolved fluorinated product respectively.

The method according to the invention may further comprise the step of reacting the third residue containing iron oxides with a reducing agent to obtain metallic iron.

It has been surprisingly found out that the execution of a heat treatment step on the product resulting from the fluorination of titanomagentite raw materials at a first lower temperature not higher than 350°C (preferably 320-350°C) followed by a separate second heat treatment and at a second higher temperature (instead of a single heat treatment step at high temperatures as in the prior art) allows a substantial and selective separation of Si and Ti compounds originally present in the raw material as ammonium fluorosilicates and ammonium fluorotitanates in separate gaseous

(sublimate) phases respectively.

As a result, titanium dioxide with higher purity can be obtained from the gaseous stream containing ammonium fluorotitanate and silicon dioxide from the separate gaseous stream containing ammonium fluorosilicate can also be obtained following the subsequent treatment steps of the method of the invention as specified above.

The above advantages are achieved without introducing significant complications to the existing plants for processing titanomagnetite raw materials so that the method of the invention is cost-effective and easily implementable at an industrial level.

Detailed description of the invention

The titanomagnetite raw material to be processed according to the method of the invention is normally an extract coming from appropriate ore extraction sites (e.g. ilmenite ores) and contains at least Ti, Si and Fe compounds. The extract may be subjected to appropriate pre-treatments before processing with the method of the invention. The starting material may also be a titanomagnetite concentrate obtained for example by dual wet magnetic separation methods.

According to the invention, the titanomagnetite concentrate is mixed with a fluorinating agent and the mixture is heated at a temperature preferably comprised between 1 10°C and 240°C and reacted under stirring to obtain a fluorinated product. The fluorinating agent is preferably chosen among ammonium fluoride, ammonium bifluoride and mixtures thereof. The fluorinating agent is used in a stoichiometric amount or in stoichiometric excess up to 50% with reference to the fluorination reactions of reactive titanomagnetite concentrate components. Typical amounts of fluorinating agent may be comprised between 240 % and 350 % by weight on the weight of the titanomagnetite concentrate.

By virtue of the fluorinating process, the output product is a mixture of fluorinated compounds including ammonium fluorinated compounds of at least Fe, Si and Ti obtained according to the following reactions:

FeTi0 ₃ + 10NH ₄ F→ (NH ₄ ) ₂ TiF ₆ + ( H ₄ ) ₂ FeF ₄ + 3H ₂ 0 + 6NH ₃

FeO + 4NH ₄ F→ (NH ₄ ) ₂ FeF ₄ + H ₂ 0 + 2NH ₃

Fe ₂ 0 ₃ + 12NH ₄ F→ 2(NH ₄ ) ₂ FeF ₅ + 3H ₂ 0 + 6NH ₃

Si0 ₂ + 6NH ₄ F→ (NH ₄ ) ₂ SiF ₆ + 2H ₂ 0 + 4NH ₃

The process gases also formed during the reaction and mainly containing ammonia and water are recovered and subjected to further treatments, as explained hereinafter, for appropriate recycle.

According to the invention, the fluorinated product obtained from the fluorinated process is subjected to two heat treatment steps in sequence. In the first step, the fluorinated product is heated to a lower temperature, preferably comprised between 320°C and 350°C to obtain a first sublimate product (first gaseous stream) containing mainly ammonium fluorosilicate compound(s) and a first residue. The temperature of the heat (sublimation) treatment is preferably maintained up to the termination of emanation of gaseous products. The first heat treatment allows the separation by sublimation of ammonium fluorosilicates (in particular ammonium hexafluorosilicate) and the decomposition of Fe fluorinated compounds (and possibly other non-Ti fluorinated compounds present in the fluorinated product) to respective iron fluorides according to the following reactions:

(NH ₄ ) ₂ FeF → FeF ₂ + 2NH ₃ + 2HF

(NH ₄ ) ₂ FeF ₅ → FeF ₃ + 2NH ₃ + 2HF

An excess ammonium fluoride is also formed in gaseous phase as part of the first sublimate product.

The gaseous (sublimate) products obtained from the first heat treatment is first de-sublimated to a solid phase and then dissolved with water. An ammonia aqueous solution is then added to the resulting solution allowing precipitation of hydrated silicon dioxide in an ammonium fluoride solution according to the following reaction:

(NH ₄ ) ₂ SiF ₆ + 4NH ₃ + 4H ₂ 0 = Si0 ₂ xnH ₂ OJ, + 6NH ₄ F

The ammonia aqueous solution has a concentration preferably comprised between 5 % and 25 % by weight on the weight of the ammonia solution. In particular, a preferred ammonia aqueous solution may have a concentration of 25%. Typical amounts of ammonia aqueous solution may be comprised between 160 % and 260 % by weight on the weight of ammonium fluorosilicates, such as (NH ₄ ) ₂ SiF6, contained in the de-sublimated product, in the case of use of a 25 % ammonia solution.

The hydrated silicon dioxide is separated from the ammonium fluoride solution by any conventional means, e.g. by filtration. The solid hydrated silicon dioxide may be dried in a conventional manner, e.g. by calcination at temperatures comprised between 500°C and 700°C, in particular 600°C, for a time sufficient to remove water. The remaining ammonium fluoride solution is also recovered and preferably subjected to further treatments, as explained hereinafter, for appropriate recycle.

According to the present invention, the first residue resulting from the fist heat treatment of the fluorinated products is subjected to a second heat treatment at a higher temperature above 350°C and preferably comprised between 500°C and 800°C to obtain a second sublimate product (second gaseous stream) and a second residue. The temperature of the heat (sublimation) treatment is preferably maintained up to the termination of emanation of gaseous products. The second heat treatment allows the separation by sublimation of ammonium fluorotitanates (in particular ammonium hexafluorotitanate) . The gaseous (sublimate) products obtained from the second heat treatment is first de-sublimated to a solid phase and then dissolved with water. An ammonia aqueous solution is added to the resulting solution allowing precipitation of hydrated titanium dioxide in an ammonium fluoride solution according to the following reaction:

(NH ₄ ) ₂ TiF ₆ + 4NH ₃ + 4H ₂ 0 = Ti0 ₂ *nH ₂ 0 j + 6NH F

The ammonia aqueous solution has a concentration preferably comprised between 5% and 25% by weight on the weight of the ammonia solution. In particular, a preferred ammonia aqueous solution may have a concentration of 25%. Typical amounts of ammonia aqueous solution may be comprised between 145 % and 245 % by weight on the weight of ammonium fluorotitanates, such as (NH ₄ ) ₂ TiF ₆ , contained in the de-sublimated product, in the case of use of a 25 % ammonia solution.

The hydrated titanium dioxide is separated from the ammonium fluoride solution by any conventional means, e.g. by filtration. The solid hydrated titanium dioxide may be dried in a conventional manner, e.g. by calcination at temperatures comprised between 500°C and 900°C, in particular 600°C, for a time sufficient to remove water. The remaining ammonium fluoride solution is also recovered and preferably subjected to further treatments, as explained hereinafter, for appropriate recycle.

The second (solid) residue obtained from the second heat treatment is then subjected to pyrohydrolysis with water vapor. This process allows conversion of iron fluorides (and possibly other metallic fluorides present in the second residue) to iron oxides according to the following reactions:

FeF ₂ + H ₂ 0→ FeO + 2HF

2FeF ₃ + 3H ₂ 0→ Fe ₂ 0 ₃ + 6HF

The pyrohydrolysis is carried out at a high temperature comprised preferably between 400°C and 700°C, in particular 650°C, preferably up to the termination of emanation of gaseous stream consisting essentially of hydrogen fluoride. Such a gaseous stream is advantageously washed with an ammonia aqueous solution so as to dissolve hydrogen fluoride and obtain an ammonium fluoride solution. The ammonium fluoride solution so obtained may be preferably subjected to further treatments, as explained hereinafter, for appropriate recycle. The solid residue obtained after pyrohydrolysis and mainly containing iron oxides may be advantageously subjected to a reduction step with an appropriate reducing agent to obtain metallic iron. Such a reduction step can be carried out by heating the mixture of the solid residue containing iron oxides and the reducing agent at a temperature comprised between 1600°C and 2000°C to produce a melt and maintaining such a temperature for a time comprise between 2 hours and 8 hours. Appropriate reducing agents may be coal or any coal-containing material. The reduction step may be performed by any conventional method known in the art, e.g. by electrosmelting.

Further features and advantages of the method for processing titanomagnetite raw materials according to the present invention shall become clearer from the following description of a preferred embodiment thereof, given for indicating and not limiting purposes with reference to the attached drawing.

Brief description of the drawing

Figure 1 is a block diagram showing a preferred implementation of the method for processing titanomagnetite raw materials according to the present invention.

Detailed description of a preferred embodiment

With reference to figure 1 , the process of the invention starts with the mixing of a titanomagnetite concentrate and a fluorinating agent (e.g. ammonium fluoride) in a mixing unit 1 such as for example a mixing screw. The resulting mixture in output from the mixing unit 1 is sent to a fluorination reactor 3 through the flow line 2. In the reactor 3, e.g. a rotary drum furnace, the fluorination reactions take place obtaining a fluorinated product as a mixture of fluorinated compounds including ammonium fluorinated compounds of at least Fe, Si and Ti and obtaining a gaseous stream mainly containing ammonia, water, hydrogen fluoride and dusts.

The gaseous stream in output from the fluorination reactor 3 is recovered and processed for appropriate recycle. In particular, it is sent through the flow line 4 to a dust collector 5 (e.g. a baffle for dusts) where dusts are separated for the remaining gas components of said gaseous stream. Dusts are recovered from the collector 5 through the flow line 6whereas the gaseous flow deprived from dusts is sent, through the flow line 7, to a heat exchanger 8 where it is cooled and then to an absorption unit 10 through the flow line 9. In the absorption unit 10, the gaseous stream is washed with liquid water entering the absorption unit 10 through the flow lines 1 1 and 1 1a obtaining an aqueous solution containing ammonia and ammonium fluoride which is recycled as explained below. Air is vented from the absorption unit through the flow line 12.

Turning now to the fluorination reactor 3, the fluorinated product exiting the reactor 3 is sent to a first sublimation unit 14, e.g. a furnace, through the flow line 13. In the first sublimation unit 14, the fluorinated product is subjected to a heat treatment at a lower temperature, preferably 320-350°C obtaining a first sublimate product in gaseous phase containing mainly ammonium fluorosilicate compounds (in particular (NH4)2SiF ₆ ), ammonia and hydrogen fluoride and a first residue containing ammonium fluorotitanates (in particular (NH ₄ ) ₂ TiF6), iron fluorides and possibly other metallic fluorides (e.g. A1F ₃ , MgF2). The gaseous phase (first sublimate product) exiting the first sublimation unit 14 is sent to a first de-sublimation unit 16 through the flow line 15 where it is cooled obtaining a solid product containing ammonium fluorosilicate compounds (in particular (NH4)2SiF ₆ ) and ammonium fluoride. The solid product exiting the first de-sublimation unit 16 is then sent to a first dissolution unit 18, through the flow line 17. In the first dissolution unit 18, said solid product is mixed with water which enters the unit 18 through the flow lines 1 1 and 1 lb obtaining an aqueous solution containing ammonium fluorosilicate compounds (in particular

(NH4)2SiF ₆ ) and ammonium fluoride.

Such a solution is then processed for separating Si as silicon dioxide and other valuable products to be recycled in the process. In particular, the solution exiting the first dissolution unit 18 is sent to a first precipitation unit 20, through the flow line 19. In the first precipitation unit 20, said solution is mixed with a portion of the aqueous solution containing ammonia and ammonium fluoride coming from the absorption unit 10 through the flow lines 21 and 21b which causes the precipitation of silicon dioxide. As a result, a dispersion of solid silicon dioxide in an ammonium fluoride solution is obtained which is sent to a first filtration unit 23 through the flow line 22. In the first filtration unit 23, solid silicon dioxide is separated from the solution and then sent to a first calcination unit 25 through the flow line 24. In the first calcination unit 25, silicon dioxide is calcinated to obtain a dry silicon dioxide finished product which exits the calcination unit 25 through the flow line 26. The solution separated in the first filtration unit 23 is mixed with gaseous water exiting the first calcination unit 25 through the flow line 27 and the mixture is sent to an evaporation unit 29 through a flow line 28 obtaining gaseous water and a liquid dispersion. The gaseous water is sent to a condenser 31 through the flow line 30 and the condensate (liquid water) is recovered through the flow line 32. The liquid dispersion exiting the evaporation unit 29 is instead sent to a filtration unit 34 through a flow line 33 obtaining solid ammonium fluoride (flow line 36) and liquid water (flow line 35).

Turning now to the first sublimation unit 14, the first residue containing ammonium fluorotitanates (in particular (NH4)2TiF ₆ ), iron fluorides and possibly other metallic fluorides (e.g. A1F ₃ , MgF ₂ ) is sent to a second sublimation unit 38, e.g. a furnace, through the flow line 37. In the second sublimation unit 38, the first residue is subjected to a heat treatment at a higher temperature (above 350°C) obtaining a second sublimate product in gaseous phase containing mainly ammonium fluorotitanate compounds (in particular (NH4) ₂ TiF ₆ ) and a second residue containing iron fluorides and possibly other metallic fluorides (e.g. AIF3, MgF ₂ ). The gaseous phase (second sublimate product) exiting the second sublimation unit 38 is sent to a second de- sublimation unit 40 through the flow line 39 where it is cooled obtaining a solid product containing ammonium fluorotitanate compounds (in particular (NH ₄ ) ₂ TiF ₆ ). The solid product exiting the second de-sublimation unit 40 is then sent to a second dissolution unit 42, through the flow line 41. In the second dissolution unit 42, said solid product is mixed with water which enters the unit 42 through the flow lines 1 1 and 11 c obtaining an aqueous solution containing ammonium fluorotitanate compounds (in particular (NH4) ₂ TiF ₆ ).

Such a solution is then processed for separating Ti as titanium dioxide and other valuable products to be recycled in the process. In particular, the solution exiting the second dissolution unit 42 is sent to a second precipitation unit 44, through the flow line 43. In the second precipitation unit 44, said solution is mixed with a portion of the aqueous solution containing ammonia and ammonium fluoride coming from the absorption unit 10 through the flow lines 21 and 21c which causes the precipitation of titanium dioxide. As a result, a dispersion of solid titanium dioxide in an ammonium fluoride aqueous solution is obtained which is sent to a second filtration unit 46 through the flow line 45. In the second filtration unit 46, solid titanium dioxide is separated from the solution and then sent to a second calcination unit 48 through the flow line 47. In the second calcination unit 48, titanium dioxide is calcinated to obtain a dry titanium dioxide finished product which exits the calcination unit 48 through the flow line 49.

Turning now to the second sublimation unit 38, the second residue containing iron fluorides and possibly other metallic fluorides (e.g. AIF3, MgF ₂ ) obtained in this unit 38 is sent to a pyrohydrolysis unit 53, e.g. a furnace, through the flow line 52. Water vapour is also introduced in the unit 53 through the flow line 54. In the unit 53, the second residue is subjected to pyrohydrolysis as known in the art obtaining a third residue containing mainly iron oxides and possibly aluminum oxide (AI2O3) and magnesium fluoride (MgF ₂ ) and a gaseous phase containing water and HF. The third residue is recovered by the pyrohydrolysis unit 53 through the flow line 55 and may be subjected to a reduction step for obtaining metallic iron. The gaseous phase exiting the pyrohydrolysis unit 53 is instead sent to an absorption unit 57, through the flow line 56, which also receive a portion of the ammonia and ammonium fluoride aqueous solution coming from the absorption unit 10 through the flow lines 21 and 21a. As a result, an ammonium fluoride aqueous solution is obtained which exits the absorption unit 57 through the flow line 58.

The ammonium fluoride aqueous solution coming from the flow line 58, the gaseous phases (essentially water) exiting from the second calcination unit 48 through the flow line 60 and the solution separated from the second filtration unit 46 are mixed together and the resulting mixture is recycled to the evaporation unit 29 through a flow line 51 for processing as explained above. The evaporation unit 29 also receives the mixture of the solution separated in the first filtration unit 23 and of the gaseous phase (essentially water) exiting the first calcination unit 25 through the flow line 28 for processing as explained above.

Examples

Example 1

50 g of a titanomagnetite concentrate obtained from the Zhambyl ore deposit of

Tymlay (Kazakhstan) and containing 21.9% FeO, 46.0% Fe ₂ 0 ₃ , 26.0% FeTi0 ₃ , 1.7% MgO, 1.6% AI2O3, 2.8% Si0 ₂ was mixed with 150g of ammonium fluoride and the resulting mixture was heated with constant stirring at 200°C, maintaining this temperature up to the termination of emanation of gaseous reaction products. A fluorinated product containing a mixture of fluorides was obtained. Such product was heated to 350°C, maintaining this temperature up to the termination of emanation of gaseous products, so obtaining a first sublimate (gaseous) product and a first residue.

The first sublimate product was trapped (i.e. de-sublimated) to produce a solid product which was dissolved in water. Then, 8 g of a 25% ammonia aqueous solution were added causing the formation of a silicon dioxide precipitate in the solution. Such solid precipitate - silicon dioxide, was separated by filtration and calcinated at 600°C for 2 hours. 1.37 g of silicon dioxide product were obtained after calcination which correspond to a theoretical yield of 98%.

The first residue was heated to 600°C maintaining this temperature up to the termination of emanation of gaseous products, so obtaining a second sublimate (gaseous) product and a second residue.

The second sublimate product was trapped (i.e. de-sublimated) to produce a solid product which was dissolved in water. Then, 28 g of a 25% ammonia aqueous solution were added causing the formation of a titanium dioxide precipitate in the solution. Such solid precipitate - titanium dioxide, was separated by filtration and calcinated at 600°C for 2 hours. 6.63 g of titanium dioxide product were obtained after calcination which correspond to a theoretical yield of 97%.

The remaining mixture of fluorides (second residue) was processed with water vapour at 650°C up to the termination of emanation of hydrogen fluoride. The resulting solid residue was allowed to cool, then mixed with the 1 1.75 g of coal and the mixture was melted to reduce iron oxides to metallic iron. At the end of the reduction step, 27.6 g of metallic iron (Fe) were obtained which correspond to a theoretical yield of 94%.

Example 2

The process of example 1 was repeated with the difference that 120 g of ammonium hydrodifluoride was used as a fluorinating agent in place of ammonium fluoride. The yield of silicon dioxide is of 1.34 g (96% of the theoretical value), the yield of titanium dioxide is of 6.5 g (95% of the theoretical value) and the yield of iron is of 27.9 g (95% of the theoretical value). Example 3

The process of example 1 was repeated with the difference that a slag from the smelting of iron from titanomagnetite concentrates containing 1.8% FeO, 66.7% Ti0 ₂ , 5.8% MgO, 1 1 % AI2O3, 14.7% Si0 ₂ was used as raw material for processing and that 250 g of ammonium fluoride were used. The yield of silicon dioxide is of 14.4 g (98% of theoretical value), the yield of titanium dioxide is of 64.5 g (96.7% of theoretical value) and the yield of iron is of 0.856 g (95% of theoretical value).