**1. Introduction**

The production of titanium alloys by using the conventional process route is tremendously cost‐intensive. Therefore, there is a huge endeavor for an alternative process route. In an alu‐ minothermic reduction process, titanium oxide can be used to achieve a titanium alloy. The energy which is needed for the autothermic reduction is released by the reduction of titanium oxides as well as by metal oxides which are needed for the titanium alloy composition. As the energy released by these oxides is not sufficient, there are boosters like KClO<sup>4</sup> or CaO2 that

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

are necessary. To reduce the amount of these boosters, the process of mechanical activation of titanium oxide (rutile, anatase, and ilmenite) is helpful.

#### **1.1. Fundamentals of mechanical activation**

According to Butyagin, the mechanical activation of solids is defined as an increase in reac‐ tion ability due to stable changes in solids structure [1]. Mechanical activation represents a multi‐step process with changes in the energetic parameters and the amount of accumulated energy of solids in each step, and it is followed by the process of the defects accumulation, amorphization, formation of metastable polymorphous forms, and chemical reactions [2]. Depending on the number of solid phases involved, the solid‐state reactions by mechani‐ cal activation are classified into single (homogeneous or inhomogeneous reactions) and multi‐phase systems (heterogeneous reactions) (see **Table 1**). The homogeneous single‐phase solid‐state reactions are the defect reactions and inhomogeneous reactions are inter‐solid diffusions with the concentration gradients. During the heterogeneous multi‐phase solid‐ state reactions, the mass transport diffusion occurs across the phase boundaries, and one or more product phases are created [3–6].

#### **1.2. Type of milling devices**

The main problem for the technical application of the mechanical activation of minerals or ores is a suitable type of the mill. For initiation of mechanical activation, the impact load mechanism is required. This is performed in the vibratory mills that are manufactured in industrial scale. For mechanical activation examination only the lab‐scale mills are commonly used. They are based on the pressure load mechanism due to centrifugal force of motion. An industrial eccentric vibratory mill (type: ESM 656–0.5 ks, Siebtechnik GmbH, Germany) for the mechanical activation of TiO2 (rutile) and FeTiO3 (ilmenite) concentrates was used (see **Figure 1**).


α: rutile, β: anatase, and γ: amorphous TiO<sup>2</sup>

**Table 1.** Solid‐state reactions of the Ti systems carried out by mechanical activation.

Mechanically Activated Rutile and Ilmenite as the Starting Materials for Process of Titanium Alloys Production http://dx.doi.org/10.5772/intechopen.68747 85

**Figure 1.** Industrial eccentric vibratory mill (type: ESM 656–0.5 ks, Siebtechnik GmbH, Germany).

#### **2. TiO2 concentrate, rutile**

are necessary. To reduce the amount of these boosters, the process of mechanical activation of

According to Butyagin, the mechanical activation of solids is defined as an increase in reac‐ tion ability due to stable changes in solids structure [1]. Mechanical activation represents a multi‐step process with changes in the energetic parameters and the amount of accumulated energy of solids in each step, and it is followed by the process of the defects accumulation, amorphization, formation of metastable polymorphous forms, and chemical reactions [2]. Depending on the number of solid phases involved, the solid‐state reactions by mechani‐ cal activation are classified into single (homogeneous or inhomogeneous reactions) and multi‐phase systems (heterogeneous reactions) (see **Table 1**). The homogeneous single‐phase solid‐state reactions are the defect reactions and inhomogeneous reactions are inter‐solid diffusions with the concentration gradients. During the heterogeneous multi‐phase solid‐ state reactions, the mass transport diffusion occurs across the phase boundaries, and one or

The main problem for the technical application of the mechanical activation of minerals or ores is a suitable type of the mill. For initiation of mechanical activation, the impact load mechanism is required. This is performed in the vibratory mills that are manufactured in industrial scale. For mechanical activation examination only the lab‐scale mills are commonly used. They are based on the pressure load mechanism due to centrifugal force of motion. An industrial eccentric vibratory mill (type: ESM 656–0.5 ks, Siebtechnik GmbH, Germany)

(rutile) and FeTiO3

*<sup>γ</sup>Ti <sup>O</sup>*<sup>2</sup> *β* <sup>⟶</sup> *<sup>α</sup>Ti <sup>O</sup>*<sup>2</sup>

*<sup>α</sup>Ti <sup>O</sup>*<sup>2</sup> *β* <sup>⟶</sup> *<sup>α</sup>Ti <sup>O</sup>*2−*<sup>x</sup>*

*Ti <sup>O</sup>*<sup>2</sup>

*Ti* + *H*<sup>2</sup> <sup>↔</sup> *Ti <sup>H</sup>*<sup>2</sup>

+ 2.5 *<sup>O</sup>*<sup>2</sup> <sup>→</sup> <sup>2</sup>*Ti <sup>O</sup>*<sup>2</sup>

<sup>+</sup>*MgO* <sup>→</sup> *MgTi <sup>O</sup>*<sup>3</sup>

 + *F e* 2 *O*3

(ilmenite) concentrates was used

titanium oxide (rutile, anatase, and ilmenite) is helpful.

**1.1. Fundamentals of mechanical activation**

more product phases are created [3–6].

for the mechanical activation of TiO2

α: rutile, β: anatase, and γ: amorphous TiO<sup>2</sup>

**Type of reaction Example**

Heterogeneous 2*FeTi <sup>O</sup>*<sup>3</sup>

**Table 1.** Solid‐state reactions of the Ti systems carried out by mechanical activation.

(see **Figure 1**).

84 Titanium Dioxide

Homogeneous

Inhomogeneous

**1.2. Type of milling devices**

As input material, rutile concentrate of Australian origin (95% TiO2 ) is used with the following composition 57% Ti, 0.7% Zr, 0.7% Fe, 0.3% Nb, 0.2% Si, 0.1% Al, 0.1% Cr, <0.03% P, and <0.03% S.

### **2.1. Mechanical activation**

In order to identify the reaction ability of the mechanically activated rutile at the subsequent metallurgical reaction, the mechanical activation degrees, I/I0 are assigned. The ratios I/I0 represent the X‐ray diffraction intensities at the lattice plane (110) of rutile, whereas I<sup>0</sup> is the measured value for the untreated rutile (defined as 100% < 10 μm), and I is value for mechani‐ cally activated rutile. This ratio I/I0 is a parameter that gives information about grain size, lattice defects, and solid‐state reactions. The results in **Figure 2** showed the activation degree of the rutile concentrate milled for 1, 2, and 3 h was dependent on the specific energy consumption of milling. The degree of crystallinity, I/I0 of rutile crystal structure, decreased from 0.7 to 0.25, with an increase in milling time [6].

### **2.2. Aluminothermic reduction process for titanium alloys production**

The materials with a decreased crystallinity due to mechanical activation can be very useful for the aluminothermic reduction process to reduce the amount of boosters. An aluminothermic reaction presents the reduction of a metal oxide with aluminum as a reductant. The reduction is feasible when Al shows a greater chemical affinity for the non‐metal element of the com‐ pound than the desired metal which should be reduced. Regarding the redution of TiO2 with

**Figure 2.** The mechanical activaction degree dependence on the specific energy consumption for rutile concentrate.

Al, the intrinsic heat of the reaction is not sufficient to maintain the self‐sustained reaction [7]. Therefore, boosters (e.g., KClO<sup>4</sup> , CaO2 ) are added to reach the needed energy density. The modeling of the aluminothermic reaction mixture needs input parameters such as the required energy density, targeted adiabatic temperature, estimated heat losses, as well as aimed slag composition in order to improve the metal/slag separation. In order to reach the targeted tem‐ perature, changes in the mixture are not allowed to effect or vary the product alloy composi‐ tion [7]. Because of little difference in the energy density from 50 to 100 J.g−1 of aluminothermic reaction, the process window has to be exactly defined to supply slow propagation of reac‐ tion and early solidification. Rutile ore concentrate contains additional by‐components which make the determination of the process conditions more complex. **Table 2** gives an overview of the reduction reactions of the by‐components included in rutile concentrate [6].

The heats of these reactions differ significantly. Although the amount of these by‐components are not very high, the released heats of each reaction have to be taken into account due to the above explained narrow process window. The reduction of several by‐components is more favorable than the reduction of TiO2 thus remaining within the metal phase. Therefore, the com‐ position of the master alloy Ti‐6Al‐4V was carefully chosen, which corresponds to 60 wt.% of Ti, 24 wt.% of Al, and 16 wt.% of V. The investigations were focused on the definition of the required energy charging for the aluminothermic reaction with mechanically activated rutile to obtain a stable product. Important is the composition of the product, especially the contents of Ti, Al, and V and the by‐components as well as the oxygen content in order proceed in the upcoming refining steps to achieve a valuable titanium alloy that can be produced cost‐efficiently and can be used therefore in the car industry and other light‐weight applications. It has to be balanced Mechanically Activated Rutile and Ilmenite as the Starting Materials for Process of Titanium Alloys Production http://dx.doi.org/10.5772/intechopen.68747 87


**Table 2.** Heats of reduction per mole of oxides of by‐components in rutile ore.

Al, the intrinsic heat of the reaction is not sufficient to maintain the self‐sustained reaction [7].

**Figure 2.** The mechanical activaction degree dependence on the specific energy consumption for rutile concentrate.

modeling of the aluminothermic reaction mixture needs input parameters such as the required energy density, targeted adiabatic temperature, estimated heat losses, as well as aimed slag composition in order to improve the metal/slag separation. In order to reach the targeted tem‐ perature, changes in the mixture are not allowed to effect or vary the product alloy composi‐ tion [7]. Because of little difference in the energy density from 50 to 100 J.g−1 of aluminothermic reaction, the process window has to be exactly defined to supply slow propagation of reac‐ tion and early solidification. Rutile ore concentrate contains additional by‐components which make the determination of the process conditions more complex. **Table 2** gives an overview of

The heats of these reactions differ significantly. Although the amount of these by‐components are not very high, the released heats of each reaction have to be taken into account due to the above explained narrow process window. The reduction of several by‐components is more

position of the master alloy Ti‐6Al‐4V was carefully chosen, which corresponds to 60 wt.% of Ti, 24 wt.% of Al, and 16 wt.% of V. The investigations were focused on the definition of the required energy charging for the aluminothermic reaction with mechanically activated rutile to obtain a stable product. Important is the composition of the product, especially the contents of Ti, Al, and V and the by‐components as well as the oxygen content in order proceed in the upcoming refining steps to achieve a valuable titanium alloy that can be produced cost‐efficiently and can be used therefore in the car industry and other light‐weight applications. It has to be balanced

) are added to reach the needed energy density. The

thus remaining within the metal phase. Therefore, the com‐

, CaO2

the reduction reactions of the by‐components included in rutile concentrate [6].

Therefore, boosters (e.g., KClO<sup>4</sup>

86 Titanium Dioxide

favorable than the reduction of TiO2

out on how much booster can be saved by charging a reasonable mechanically activated rutile, minimizing the introduced energy for milling and maximizing the saved amount of booster [6]. Based on the promising results of the preliminary trials, further trials were conducted in small (8.4 kg of mixture) and mid‐scale (18.2 kg of mixture) levels, with a variation in the reaction parameters such as time of mechanical activation of rutile concentrate (0, 1, 2, and 3 h), grain size of Al (90–300, 500–800, and 700–1200 μm), and KClO<sup>4</sup> addition to achieve energy density of 2400 and 2500 J.g−1 for the aluminothermic reaction. The selected range for variation of each reaction parameter is shown in **Figure 3**.

**Figure 3.** Variation of the trial parameters for the aluminothermic experiments [6].

The non‐activated rutile (0 h) was used to compare the efficiency of the activation. The activa‐ tion duration varies between 1 and 3 h. There are three types of Al grain sizes. Due to pre‐trials, the two energy densities of 2400 and 2500 J.g−1 are used by KClO<sup>4</sup> addition [6]. This experimen‐ tal setup indicates clearly that the trials with 2 h activation time and fine Al particles showed the best results according to the reaction time of the aluminothermic reduction and a good metal‐slag separation. The metal composition was also the best in these trials. Small amounts of Fe and Si could be detected which would not interfere the final target alloy, Ti‐Al6‐V4 [6]. Because of avoiding the production of TiO2 via chlorination, the savings were up to 50%, and because of mechanical activation, the use of KClO<sup>4</sup> decreased by 30% remarkably [6]. Due to the fact that lime is used as slag component to decrease the liquid temperature of the final slag, there are investigations to avoid the KClO<sup>4</sup> completely by using CaO2 which will be reduced by Al to CaO and remains as slag component without producing any gas emissions. As the released heat by KClO<sup>4</sup> is nearly four times as high as the one by CaO2, there is much more CaO2 required to reach the needed energy density. Due to thermodynamic calculations, the amount of CaO should not exceed 50% because the liquid temperature of the slag will increase again and because of economic reasons, it should be used as sparsely as possible. As the energy density is decreased by mechanical activation, it is theoretical possible to reach a good amount of CaO in the slag and the needed energy density.

First trials were conducted with a 2 h mechanically activated rutile ore with CaO2 as booster, varying the energy density. Besides the four trials which were conducted with an energy density from 2250 up to 2350 J.g−1, the results were comparable to the experimental trials before. Due to the lower energy density in these trials, the metal‐slag separation was not sufficient which resulted in high oxygen content in the alloy. The results for the oxygen content for the various trials varying the energy density can be seen in **Figure 4**.

A closer look to the trials with an energy density of 2450 J.g−1 shows that low oxygen contents can be reached. But there is also a large deviation for the oxygen content. This leads to the

**Figure 4.** The various aluminothermic trials of the mechanically activated rutile for 2 h and CaO2 as a booster.

assumption that the oxygen may not be completely diluted. Instead, there could be small oxide particles in the metal fraction which is a result of the slag‐metal separation. Further investigations have to be performed. Therefore, a bigger‐scale experiment to improve the separation needs to be done as well. Remelting this material in a vacuum induction furnace with a special ceramic crucible will be investigated to homogenize the material.

Mechanically activated rutile ore can be used for aluminothermic reduction to produce a tita‐ nium master alloy. KClO<sup>4</sup> can be used, as well as CaO2 as booster. In this regard, a remarkable amount of KCl gas could be avoided. Using just CaO<sup>2</sup> as a booster could avoid the production of KCl completely.

#### **3. FeTiO3 concentrate, ilmenite**

The non‐activated rutile (0 h) was used to compare the efficiency of the activation. The activa‐ tion duration varies between 1 and 3 h. There are three types of Al grain sizes. Due to pre‐trials,

tal setup indicates clearly that the trials with 2 h activation time and fine Al particles showed the best results according to the reaction time of the aluminothermic reduction and a good metal‐slag separation. The metal composition was also the best in these trials. Small amounts of Fe and Si could be detected which would not interfere the final target alloy, Ti‐Al6‐V4 [6].

the fact that lime is used as slag component to decrease the liquid temperature of the final slag,

by Al to CaO and remains as slag component without producing any gas emissions. As the

varying the energy density. Besides the four trials which were conducted with an energy density from 2250 up to 2350 J.g−1, the results were comparable to the experimental trials before. Due to the lower energy density in these trials, the metal‐slag separation was not sufficient which resulted in high oxygen content in the alloy. The results for the oxygen content for the various

A closer look to the trials with an energy density of 2450 J.g−1 shows that low oxygen contents can be reached. But there is also a large deviation for the oxygen content. This leads to the

First trials were conducted with a 2 h mechanically activated rutile ore with CaO2

**Figure 4.** The various aluminothermic trials of the mechanically activated rutile for 2 h and CaO2

 required to reach the needed energy density. Due to thermodynamic calculations, the amount of CaO should not exceed 50% because the liquid temperature of the slag will increase again and because of economic reasons, it should be used as sparsely as possible. As the energy density is decreased by mechanical activation, it is theoretical possible to reach a good amount

completely by using CaO2

is nearly four times as high as the one by CaO2, there is much more

addition [6]. This experimen‐

which will be reduced

as a booster.

as booster,

via chlorination, the savings were up to 50%, and

decreased by 30% remarkably [6]. Due to

the two energy densities of 2400 and 2500 J.g−1 are used by KClO<sup>4</sup>

Because of avoiding the production of TiO2

there are investigations to avoid the KClO<sup>4</sup>

released heat by KClO<sup>4</sup>

CaO2

88 Titanium Dioxide

because of mechanical activation, the use of KClO<sup>4</sup>

of CaO in the slag and the needed energy density.

trials varying the energy density can be seen in **Figure 4**.

The beneficiation of ilmenites requires pyrometallurgical or chemical process steps to sepa‐ rate the iron content of approximately 30%. There are some methods of iron separation from FeTiO3 , which vary in their technical and energy demands. The chemical sulfate process, with H2 SO4 at < 220°C, yielding TiO2 in pigment quality, is difficult and complex because of the low solubility of ilmenite in H2 SO4 [3]. Nevertheless, for the production of synthetic TiO2 concen‐ trates except for the pyrometallurgical processes [8, 9], the connected pyro‐ and hydrometal‐ lurgical processes [10–13] were developed. One possibility of the direct hydrometallurgical processing of FeTiO3 is its pre‐treatment by mechanical activation [14]. The studies on the solubility of FeTiO3 after mechanical activation using different mills for ultrafine grinding such as vertical ball mills (attritors), planetary ball mills, and drum mills have been published, in which the structural changes of FeTiO3 without technical applicability was focused [15–17]. In general, due to mechanical activation, the solids are exposed to high mechanical stress, which is responsible for their specific surface area increase, the crystalline structure defects formation and leads to the enthalpy increase. Hence, mechanically activated solids and miner‐ als with low solubility are more leachable in subsequent hydrometallurgical process [18]. The application of mechanical activation of FeTiO3 by energy‐efficient milling as a pre‐treatment step in the hydrometallurgical process of synthetic TiO2 concentrates production might be a new realization to utilize such TiO2 materials (~95%) in aluminothermic Ti alloys generation.

#### **3.1. Mechanical activation and the kinetics of subsequent hydrometallurgical production of synthetic TiO2 by pressure leaching**

The investigations were carried out with FeTiO3 concentrates (>95% FeTiO3 , <5% SiO2 ) of Russian origin (GMD, Mineral Trade Company). The chemical composition was as follows: 34.43% Fe, 30.02% Ti, 0.76% Si, 0.47% Mg, 0.42% Al, 0.34% Mn, 0.11% Zn, 0.09% Ca, 0.07% Cr, 0.06% Co, 0.03% Ba, 31.63% O, and 1.57% insoluble rest.

For determination of the optimal milling conditions, a parameter study was done: mill feed quantities varied from 100 to 300 g/charge, activation times ranged from 15 to 60 min, the ampli‐ tude of inhomogeneous vibrations was 20 mm, and the revolutions of the motor of the mill, 960 min−1, were constant. The steel balls of 30 mm diameter were applied. Activation degrees and the ratios I/I0 at lattice plane (104) of FeTiO<sup>3</sup> after and before mechanical activation as a func‐ tion of mechanical activation time are shown in **Figure 5**. It is obvious that the ilmenite structure is strongly strained by the mechanical activation.

The leaching of mechanically activated FeTiO3 was performed in an autoclave, volume 2 l (Deutsch & Neumann, Germany). The following conditions were used: initial H2 SO4 con‐ centration of 10–30%, temperature of 100–150°C, leaching time of 15–90 min, Fe addition of 6–12%, the solid to liquid ratio of 50–200 g.l−1, and stirring rate of 250 min−1.

The influence of the activation time of FeTiO<sup>3</sup> on the TiO2 extraction to the precipitation prod‐ uct is shown in **Figure 6**. The curve for the total Fe extraction in the product reflects the disso‐ lution of FeTiO3 . The leaching tests confirm the dependence on the activation degree of FeTiO<sup>3</sup> . A critical point is that, after 15 min of mechanical activation, most of FeTiO3 is dissolved. This finding is extremely interesting from a technical point of view. The hydrolytic precipitation of TiO2 is influenced by an initial dissolution accelerated with increasing activation.

At temperatures >50°C and a pH value >1.5, the hydrolysis of titanyl sulfate solution, TiOSO4 to TiO2, is triggered. In the investigated temperature range of 100–150°C, the dissolution of FeTiO3 and the simultaneous precipitation of TiO2 take place in parallel.

The leaching time was varied in a range from 15 to 90 min. A general fact is that the dissolu‐ tion rate of FeTiO3 is fast. **Figure 7** shows the dissolution of ~64% FeTiO3 (corresponding to the dissolution of Fe) during 30 min of leaching at 120°C. By increasing the reaction temperature to 150°C, ~86% of FeTiO3 dissolves during 30 min of leaching. It results from **Figure 7** that the leaching time had a relatively low effect on the hydrolysis. After 60 min of leaching, the recovery

**Figure 5.** Activation degrees I/I0 of FeTiO3 versus mechanical activation time.

Mechanically Activated Rutile and Ilmenite as the Starting Materials for Process of Titanium Alloys Production http://dx.doi.org/10.5772/intechopen.68747 91

and the ratios I/I0

90 Titanium Dioxide

lution of FeTiO3

tion rate of FeTiO3

to 150°C, ~86% of FeTiO3

**Figure 5.** Activation degrees I/I0

of FeTiO3

TiO2

FeTiO3

at lattice plane (104) of FeTiO<sup>3</sup>

is strongly strained by the mechanical activation.

The leaching of mechanically activated FeTiO3

The influence of the activation time of FeTiO<sup>3</sup>

and the simultaneous precipitation of TiO2

tion of mechanical activation time are shown in **Figure 5**. It is obvious that the ilmenite structure

centration of 10–30%, temperature of 100–150°C, leaching time of 15–90 min, Fe addition of

uct is shown in **Figure 6**. The curve for the total Fe extraction in the product reflects the disso‐

finding is extremely interesting from a technical point of view. The hydrolytic precipitation of

At temperatures >50°C and a pH value >1.5, the hydrolysis of titanyl sulfate solution, TiOSO4 to TiO2, is triggered. In the investigated temperature range of 100–150°C, the dissolution of

The leaching time was varied in a range from 15 to 90 min. A general fact is that the dissolu‐

dissolution of Fe) during 30 min of leaching at 120°C. By increasing the reaction temperature

leaching time had a relatively low effect on the hydrolysis. After 60 min of leaching, the recovery

versus mechanical activation time.

is fast. **Figure 7** shows the dissolution of ~64% FeTiO3

is influenced by an initial dissolution accelerated with increasing activation.

on the TiO2

. The leaching tests confirm the dependence on the activation degree of FeTiO<sup>3</sup>

take place in parallel.

dissolves during 30 min of leaching. It results from **Figure 7** that the

(Deutsch & Neumann, Germany). The following conditions were used: initial H2

6–12%, the solid to liquid ratio of 50–200 g.l−1, and stirring rate of 250 min−1.

A critical point is that, after 15 min of mechanical activation, most of FeTiO3

after and before mechanical activation as a func‐

was performed in an autoclave, volume 2 l

extraction to the precipitation prod‐

SO4 con‐

is dissolved. This

(corresponding to the

.

**Figure 6.** Influence of the mechanical activation time of FeTiO<sup>3</sup> on the precipitation of TiO2 ; leaching temperature: 150°C, s/l ratio: 50 g.l−1, leaching time: 60 min, H2 SO4 : 30%, and Fe powder: 12%.

**Figure 7.** Influence of the leaching time and the temperature on the precipitation of TiO<sup>2</sup> ; s/l ratio: 50 g.l−1, mechanical activation time: 15 min, H2 SO4 : 30%, and Fe powder: 6%.

of precipitated TiO2 achieved ~93% and the content of Fe in TiO2 decreased to <6%. The synthetic TiO2 product assigned a relatively high purity. By decreasing the leaching temperature from 150 to 120°C, the obtaining of the high‐quality synthetic TiO2 concentrate is impossible [19].

It was detected that the addition of Fe powder, used as a reduction agent, influences the initial rate of FeTiO3 dissolution (86% with an addition of 6% Fe and 89–92% with an addition of 12% Fe) and after a leaching time of 60 min, the influence of the Fe additive is no longer identifiable [19].

Sulfate process requires ~2 tons of concentrated H2 SO4 per 1 ton of FeTiO3 for digestion. Subsequently, the generated digestion cake is leached with H2 O by pH < 1.5. Therefore, the direct leaching of mechanically activated FeTiO3 carried out by a described procedure requires a solid/acid ratio of 1:2 at least, which corresponds to 10% H2 SO4 and 77% dissolution of FeTiO3 (mechanically activated for 15 min) after 60 min of leaching, at 150°C, with addition of 10% Fe. By increasing the initial acid concentration to 20%, which corresponds to a ratio of 1:4, FeTiO3 dissolves to 89%. For technical dimensioning, the ratio of ilmenite to acid should be <1:4. An excessively high amount of acid would complicate the hydrolytic conditions.

The solid contents from 50 to 200 g.l−1 were investigated. In order to show the influence of mechanical activation on the leaching of FeTiO3 with different s/l ratios, two test series with activation times of 15 and 30 min were carried out. As expected, the residual Fe content in the product increases to 7% with increasing s/l ratio to 200 g.l−1 at a higher activation time. That means the activation time, 15 min, is sufficient to achieve 92% of dissolution of FeTiO<sup>3</sup> with s/l ratio of 200 g.l−1 and with 30% H2 SO4 at 150°C.

According to literature, the research on the leaching of the mechanically activated ilmenites demonstrated no technical applicability. For various types of the mills, the milling times of up to 200 h were used, and low s/l ratios (only 10 g.l−1) for the leaching process were employed [15–17, 20, 21]. The operating conditions determined in this investigation fulfill the require‐ ments for a technical implementation of the process for the production of a synthetic TiO2 product (95.23% TiO2 , 3.32% Fe2 O3 , 1.7% SiO2 , 1.2% CaO, 0.34% Al2 O3 , 0.007% P2 O5 , and 0.004% ZrO2 ), which is suitable for use in aluminothermic alloys production. **Figure 8** shows the process flowsheet on the coupling of hydrometallurgical processing of FeTiO<sup>3</sup> into syn‐ thetic TiO2 concentrate (anatase) with the aluminothermic production of TiAl alloys.

The energy required per ton of synthetic anatase is expected to be 506 kWh. Based on current costs for energy, this corresponds to approximately 212 €/t of synthetic anatase. This investigated pre‐treatment of ilmenite with mechanical activation and leaching enables new cost‐effective production methods for titanium‐based alloys. So far, only high‐purity rutile pigments have been used for the aluminothermic production of TiAl alloys [7, 22]. At 95% TiO2 , the synthetic TiO2 concentrate (anatase) that we produced meets the requirements for aluminothermy.

#### **3.2. Mechanical activation with metal addition and the kinetics of subsequent hydrometallurgical production of synthetic TiO2 by normal leaching**

Mechanical activation of FeTiO3 with Al powder in the stoichiometric ratio 1:2 caused its mechanochemical reduction already after 120 min. The product phases found on the thermo‐ dynamic calculations with 1100–1700°C (Al2 O3 , TiO, Fe2 Ti, and FeTi) have already appeared after 360 min of mechanochemical reduction. Such mechanochemical processing of FeTiO3

Mechanically Activated Rutile and Ilmenite as the Starting Materials for Process of Titanium Alloys Production http://dx.doi.org/10.5772/intechopen.68747 93

of precipitated TiO2

rate of FeTiO3

of FeTiO3

1:4, FeTiO3

TiO2

92 Titanium Dioxide

achieved ~93% and the content of Fe in TiO2

to 120°C, the obtaining of the high‐quality synthetic TiO2

Sulfate process requires ~2 tons of concentrated H2

the direct leaching of mechanically activated FeTiO3

mechanical activation on the leaching of FeTiO3

, 3.32% Fe2

**hydrometallurgical production of synthetic TiO2**

dynamic calculations with 1100–1700°C (Al2

Mechanical activation of FeTiO3

ratio of 200 g.l−1 and with 30% H2

product (95.23% TiO2

0.004% ZrO2

thetic TiO2

TiO2

Subsequently, the generated digestion cake is leached with H2

requires a solid/acid ratio of 1:2 at least, which corresponds to 10% H2

SO4

O3

product assigned a relatively high purity. By decreasing the leaching temperature from 150

dissolution (86% with an addition of 6% Fe and 89–92% with an addition of 12% Fe)

(mechanically activated for 15 min) after 60 min of leaching, at 150°C, with addition

dissolves to 89%. For technical dimensioning, the ratio of ilmenite to acid should

SO4

It was detected that the addition of Fe powder, used as a reduction agent, influences the initial

and after a leaching time of 60 min, the influence of the Fe additive is no longer identifiable [19].

of 10% Fe. By increasing the initial acid concentration to 20%, which corresponds to a ratio of

The solid contents from 50 to 200 g.l−1 were investigated. In order to show the influence of

activation times of 15 and 30 min were carried out. As expected, the residual Fe content in the product increases to 7% with increasing s/l ratio to 200 g.l−1 at a higher activation time. That

According to literature, the research on the leaching of the mechanically activated ilmenites demonstrated no technical applicability. For various types of the mills, the milling times of up to 200 h were used, and low s/l ratios (only 10 g.l−1) for the leaching process were employed [15–17, 20, 21]. The operating conditions determined in this investigation fulfill the require‐ ments for a technical implementation of the process for the production of a synthetic TiO2

concentrate (anatase) with the aluminothermic production of TiAl alloys.

The energy required per ton of synthetic anatase is expected to be 506 kWh. Based on current costs for energy, this corresponds to approximately 212 €/t of synthetic anatase. This investigated pre‐treatment of ilmenite with mechanical activation and leaching enables new cost‐effective production methods for titanium‐based alloys. So far, only high‐purity rutile pigments have

concentrate (anatase) that we produced meets the requirements for aluminothermy.

mechanochemical reduction already after 120 min. The product phases found on the thermo‐

after 360 min of mechanochemical reduction. Such mechanochemical processing of FeTiO3

, TiO, Fe2

O3

, 1.2% CaO, 0.34% Al2

 **by normal leaching**

with Al powder in the stoichiometric ratio 1:2 caused its

), which is suitable for use in aluminothermic alloys production. **Figure 8** shows

be <1:4. An excessively high amount of acid would complicate the hydrolytic conditions.

means the activation time, 15 min, is sufficient to achieve 92% of dissolution of FeTiO<sup>3</sup>

at 150°C.

, 1.7% SiO2

the process flowsheet on the coupling of hydrometallurgical processing of FeTiO<sup>3</sup>

been used for the aluminothermic production of TiAl alloys [7, 22]. At 95% TiO2

**3.2. Mechanical activation with metal addition and the kinetics of subsequent** 

decreased to <6%. The synthetic

O by pH < 1.5. Therefore,

and 77% dissolution

carried out by a described procedure

SO4

with different s/l ratios, two test series with

O3

Ti, and FeTi) have already appeared

, 0.007% P2

O5 , and

, the synthetic

into syn‐

for digestion.

with s/l

concentrate is impossible [19].

per 1 ton of FeTiO3

**Figure 8.** A process flowsheet of hydrometallurgical processing of FeTiO<sup>3</sup> connected with the aluminothermic production of titanium alloys.

concentrate decreases the temperature and subsequently the time of thermal reduction of FeTiO3 , which could be also used in the titanium alloys production [23]. For subsequent leach‐ ing in H2 SO4 (40%) at 50°C, mechanically activated FeTiO3 with Al in ratio 1:0.3 was tested. In this case, the necessary agglomerates of FeTiO3 /Al are created even after 15 min of mechanical activation. **Figure 9** shows the measured grain size distribution of the unmilled FeTiO3 and the activated FeTiO3 /Al mixtures.

The SEM image in **Figure 10** shows the formed agglomerates. The contact pressure caused by the impact stress on the agglomerates during the second stage of ultrafine milling (agglom‐ eration stage) leads to structures similar to briquettes with the highest bulk density [24, 25].

By leaching of agglomerated FeTiO3 /Al mixture with diluted H2 SO4 , the highly reactive atomic hydrogen (in nascent state) is created at the contact areas between FeTiO3 and Al, which imme‐ diately reacts and causes a partial reduction of the quadrivalent titanium to trivalent titanium. A Ti3+/Ti4+ dark violet to black solution is generated. The summation equation of the conversion of FeTiO3 with diluted H2 SO4 in the presence of hydrogen in nascent state is [24]:

$$2\text{Fe(II)Ti(IV)O}\_3 + 5\text{H}\_2\text{SO}\_4 + 2\text{H}^\circ \rightarrow 2\text{Fe}^{2+} + 2\text{SO}\_4^{2-} + 2\text{Ti}^{3+} + 3\text{SO}\_4^{2-} + 6\text{H}\_2\text{O} \tag{1}$$

**Figure 11** shows that the maximum Ti recovery of activated FeTiO3 reaches 23%. Activated FeTiO3 /Al mixture shows a 53% Ti dissolution after only 15 min of activation.

**Figure 9.** Grain size distributions of FeTiO3 /Al mixtures with various times of mechanical activation.

**Figure 10.** SEM image of formed FeTiO3 /Al agglomerates.

Mechanically Activated Rutile and Ilmenite as the Starting Materials for Process of Titanium Alloys Production http://dx.doi.org/10.5772/intechopen.68747 95

**Figure 11.** Influence of mechanical activation time of FeTiO<sup>3</sup> and FeTiO3 /Al mixtures on Ti extraction during 60 min of leaching.

Investigations on the influence of the initial H<sup>2</sup> SO4 concentration on the leaching of FeTiO3 /Al mixture (150 g.l−1) activated for 60 min, with the use of 30, 40, 50, or 60% H2 SO4 , show a maximum Ti recovery of 79% after a leaching time of 60 min and the use of 40% acid, cor‐ responding to a solid/acid ratio of 1:3.3. With the increase of the initial H2 SO4 to 50% (solids/ acid ratio 1:4.3), dissolved Ti3+ partially hydrolyses, which causes the decrease of Ti recovery to 42%. For technical scale, the solid/acid ratio should be <1:4 because an excess H2 SO4 com‐ plicates the conditions of subsequent TiO2 hydrolysis. Ti recovery after 60 min of leaching is ~78% when milling charge of 200 g was used. With a further increase to 300 g/charge, the Ti recovery decreases to 69%. For 600 g/charge, the Ti‐recovery reaches to 56%, which is still a high value. Ti recovery for the unmilled FeTiO3 was 0.3% only. A check of the s/l ratio per liter showed that the optimal ratio was 150 g.l−1 of FeTiO3 /Al mixture. For technical processes, at least 300 g.l−1 must be feasible. **Figure 12** evidences that the leaching rate of FeTiO3 /Al mixture at temperature 50°C is very fast. After 5 min of leaching, the Ti recovery was 69% and after 60 min of leaching, almost 80% of Ti was leached out.

In **Figure 13**, the flowsheet of the described process for production of synthetic TiO<sup>2</sup> was proposed [26]. In an open agitator vessel, FeTiO3 /Al mixture is dissolved at a temperature of 50°C since the strong bond in the briquetted mixture follows the shrinking core model [26]. Undesirable metals, Fe and Al, can be crystallized as a mixture of Fe, Al sulfates at tem‐ perature < 15°C. Ti(OH)3 precipitates during hydrolysis and by calcination oxidizes to TiO2 (anatase) with the following composition: 99% TiO2 , 0.59% Fe2 O3 , <0.1% Al2 O3 , <0.2% SiO2 , <0.03 ZrO2 , and 0.01% Cr2 O3 .

**Figure 10.** SEM image of formed FeTiO3

**Figure 9.** Grain size distributions of FeTiO3

94 Titanium Dioxide

/Al agglomerates.

/Al mixtures with various times of mechanical activation.

**Figure 12.** Influence of leaching time on Ti extraction of mechanically activated FeTiO<sup>3</sup> /Al mixtures for 60 min with 40% H2 SO4 and s/l ratio as 150 g.l−1.

**Figure 13.** The flowsheet of a proposed process for production of synthetic TiO<sup>2</sup> .
