WO2018158492A1

WO2018158492A1 - Method of treating titanium-containing slag

Info

Publication number: WO2018158492A1
Application number: PCT/FI2017/050137
Authority: WO
Inventors: Mikko Ruonala; Eero KOLEHMAINEN
Original assignee: Outotec (Finland) Oy
Priority date: 2017-03-02
Filing date: 2017-03-02
Publication date: 2018-09-07
Also published as: EA201991781A1; PH12019501948A1; EA037945B1; CN110418852A; CA3054603A1; NZ757065A

Abstract

A method and an apparatus for treating titanium-containing slag is disclosed. The method comprises contacting a titanium-containing slag (2) with a first sulphuric acid leach solution (4) for dissolving impurities contained in the slag to obtain a first slurry. In the method, the first slurry (8) is subjected to a solid-liquid separation (10) to obtain a first sulphuric acid leach solution containing the dissolved impurities from a first titanium-containing leach residue (12).

Description

METHOD OF TREATING TITANIUM-CONTAINING SLAG

FIELD OF THE INVENTION

The present invention relates to a method and apparatus of treating titanium-containing slag. BACKGROUND

Typically titanium-containing slag, such as titania slag is obtained as a by-product from a process wherein titanium-bearing concentrate, e.g. magnetite, is smelted. In addition to titanium, the slag contains often impurities, such as aluminium, magnesium, calcium and silica. Prior to the use of titanium-contain- ing slag in a pigment process, some of the impurities contained in the slag have to be removed and thereby the titanium content increased.

Conventionally, alkali treatment has been suggested to increase titanium oxide content of a titanium-containing slag. Alkali treatment is used especially in order to remove silica from the slag. According to Liu et al. Kinetics on the desiliconization during alkaline leaching of titanium slag, Advanced Materials Research, vols. 233 - 235, 201 1 , 1322-1327, alkali treatment is typically carried out with concentrated sodium hydroxide solution in a temperature of above 100 °C in hydrometallurgical operations. Highly concentrated alkali is needed in order to solubilize silica from the slag. Alkali treatment can also be carried out by a pyrometallurgical roasting process which may require operation temperature of up to 1000 °C. According to Dong et al, Upgrading of a Ti-slag by roast-leach process, Hydrometallurgy, 1 13 - 1 14, 2012, 1 19 - 121 and Lasheen, T.A., Soda ash roasting of titania slag product from Rosetta ilmenite, Hydrometallurgy, 93, 2008, 124 - 128, the roasting process is followed a hydrometallurgical leaching process.

A drawback associated with the use of sodium hydroxide is that sodium hydroxide is able to react with aluminium and silica and thereby forming sodium aluminium silicate precipitates which are difficult to remove from titania solids. BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is thus to provide a method and an apparatus for implementing the method so as to alleviate disadvantages associated with presence of impurities in slags. The objects of the invention are achieved by a method and an arrangement which are characterized by what is stated in the independent claims. Preferred embodiments are disclosed in the dependent claims.

The method comprises leaching slag under such conditions that only impurities are leached, and titanium, e.g. in the form of titania, remains in the solid form. Furthermore, the conditions of the method prohibit silica from gelling and thus the separation of solid matter form the leaching solution is made easier. In the method, titanium-containing slag, typically titania slag, is leached in a rather dilute sulphuric acid solution thereby dissolving the impurities of the slag and retaining the titanium, typically titania, in the solids. The solids containing titanium may be readily separated from the impurities leached into the sulphuric acid solution. The method may be performed under atmospheric conditions, i.e. atmospheric pressure and below the boiling point of the solution.

An advantage of the method and arrangement is that by leaching with dilute sulphuric acid solution only the undesired impurities of the titanium-con- taining slag are dissolved and the titanium, typically titania, remains in the solid form. A further advantage is that slurry density in the leaching step is such that impurities contained in the slag, such as aluminium, magnesium, calcium and silica, are able to enter the leaching solution. In other words, the solubility product of the leaching solution does not prohibit the leaching of the impurities. In addition to dissolving titanium compounds, the higher sulphuric acid concentration has also the disadvantage of gelling the silica dissolved from the slag. It was also surprisingly found out that by using the right parameters of the method, this can be prohibited. A further advantage is that the method is performed under atmospheric conditions, which results in economical savings. BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which

Figure 1 is an example embodiment of the invention including a fur- ther optional example embodiment of the invention shown with dashed line,

Figure 2 shows titanium and titania mass fractions in the solids after leaching in Example A.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment relates to a method for treating titanium-containing slag by removing impurities from the slag and thereby increasing the titanium concentration in the slag. Typically the titanium is in the form of titania (T1O2). The method of treating titanium-containing slag comprises

a) contacting a titanium-containing slag with a first sulphuric acid leach solution for dissolving impurities contained in the slag to obtain a first slurry,

b) subjecting the first slurry to a solid-liquid separation to obtain a first sulphuric acid leach solution containing the dissolved impurities from a first titanium-containing leach residue.

The content of the titanium-containing slag varies depending on the source and process from which the slag is obtained. Titania content in the titanium-containing slag is typically in the range of 45 to 55 weight-%. The content of main impurities, such as S1O2 and AI2O3, is typically in the range of 5 to 15 weight-% and 10 to 20 weight -%, respectively. The slag is typically ground to a suitable particle size before subjecting to the leaching step(s).

The first sulphuric acid leaching in step a) typically increases titania content in the slag (solid matter) approximately to 70 weight-%, even to 73 weight-%. The titania content of the end product is chosen by using suitable process parameters and depends on the requirements of the subsequent process steps.

In the first step a) titanium-containing slag is contacted, typically under mixing, with sulphuric acid. The concentration of the sulphuric acid in the solution is typically in the range of 2 to 20 weight-%, more typically 3 to 15 weight-%, even more typically in the range of 5 to 15 weight-%, even more typically in the range of 8 to 12 weight-%. The leaching is carried out in a tempera- ture below the boiling point of the solution, typically in a temperature below 100 °C. Typically the temperature of the leaching solution is kept between 40 °C and the boiling point of the solution. The elevated temperature enhances the leaching of the impurities from the slag. The pressure is kept atmospheric during the leaching step. The retention time of step a) is typically in the range of 6 - 30 h, typically 10 - 20 h. The gelling of the silica leached from the slag can be avoided by using a suitable retention time. When the gelling of the silica can be avoided, the solid-liquid separation is easier to perform.

During the leaching most of the aluminium, magnesium, calcium and silica contained in the slag are dissolved from the slag into the sulphuric acid leach solution. However, titanium is not dissolved and it remains in the slag. After a suitable retention time in the leaching a solid-liquid separation step b) is performed. Typically the solid-liquid separation is performed by any suitable method known in the art, such as filtration.

If it is desired to increase the titania content in the slag above 70 weight-%, the method may contain a further sulphuric acid leaching step.

In addition to steps a) and b), the method may further comprise c) contacting the titanium-containing leach residue with a second sulphuric acid leach solution for dissolving impurities contained in the titanium-containing leach residue to obtain a second slurry,

d) subjecting the second slurry to a solid-liquid separation to obtain a second sulphuric acid leach solution containing dissolved impurities from a second titanium-containing leach residue.

The concentrations of sulphuric acid in the first and second sulphuric acid leach solution may be selected independently and are typically in the range of 2 to 20 weight-%, more typically 3 to 15 weight-%, even more typically in the range of 5 to 15 weight-%, even more typically in the range of 8 to 12 weight-%. The leaching in the presented sulphuric acid concentration has an effect of dissolving metal impurities, especially S1O2. In other words, the sulphuric acid concentration is in a suitable level so that the solubilizing of S1O2 is not hindered, but on the other hand it is high enough for dissolving Al, Mg, Ca, Fe, etc.

According to an embodiment, the concentrations of sulphuric acid in first and second leach solutions are approximately in the same level. According to another embodiment, the sulphuric acid concentration is in the second leaching solution lower than in the first leaching solution. In this manner the removal of impurities is enhanced in the second leaching, but the dissolving of titanium from the slag is avoided. The possibly remaining S1O2 is removed in the second leaching step. Also the remaining metal impurities are leached further. If the sulphuric acid concentration in the second leach solution is too high, titanium losses occur due to the dissolving of the titanium from the slag. Typically the first leaching step a) comprises a leaching solution, wherein the sulphuric acid concentra- tion is higher than in the second leaching step, such as 2 to 20 weight-%, more typically 3 to 15 weight-%, even more typically in the range of 5 to 15 weight-%, even more typically in the range of 8 to 12 weight-%. The sulphuric acid concentration in the first leaching step may also be in the range of 5 to 10 weight-%. Typically in the second leaching step c) the sulphuric acid concentration of the second leach solution is chosen to be lower than in the first step, such as 2 to 10 weight-%, typically 2 to 7 weight-%, more typically 2 - 5 weight-%. From the presented ranges the sulphuric acid concentrations are typically selected in such a manner that either they are approximately at a same level, or the sulphuric acid concentration of the second leach solution is lower than the sulphuric acid concentration of the first leach solution. According to an embodiment, the first leaching step a) comprises a leaching solution, wherein the sulphuric acid concentration is 10 weight-% and the second leaching step c) comprises a leaching solution, wherein the sulphuric acid concentration is 5 weight-%.

Typically the temperatures of the first and second sulphuric acid leach solution are selected independently to be below boiling point of the solution, typically in a temperature below 100 °C. Typically the temperature of the leaching solution is kept between 40 °C and the boiling point of the solution.

Typically, the retention times of steps a) and c) are selected independently to be in the range of 6 - 30 h, typically 10 - 20 h.

Typically also the solid-liquid separation in steps b) and d) are se- lected independently from any suitable method known in the art, such as filtration.

After the second sulphuric acid leaching step the titania content in the solids of the slag has been increased to approximately 73 - 76 weight-%.

An embodiment discloses an apparatus of treating titanium-contain- ing slag, wherein the apparatus comprises

a) a first leach unit wherein a titanium-containing slag is contacted with a first sulphuric acid leach solution for dissolving impurities contained in the slag to obtain a first slurry,

b) a first solid-liquid separation unit wherein the first slurry is sub- jected to a solid-liquid separation to obtain a first sulphuric acid leach solution containing the dissolved impurities from a first titanium-containing leach residue.

The apparatus may also further comprise

c) a second leach unit, wherein the titanium-containing leach residue is contacted with a second sulphuric acid leach solution for dissolving impurities contained in the titanium-containing leach residue to obtain a second slurry, d) a second solid-liquid separation unit, wherein the second slurry is subjected to a solid-liquid separation to obtain a second sulphuric acid leach solution containing dissolved impurities from a second titanium-containing leach residue.

Typically in the apparatus, the concentrations of sulphuric acid in the first and second sulphuric acid leach solution are selected independently and are typically in the range of 2 to 20 weight-%, more typically 3 to 15 weight-%, even more typically in the range of 5 to 15 weight-%, even more typically in the range of 8 to 12 weight-%.Typically the first leaching unit a) comprises a leaching solution, wherein the sulphuric acid concentration is higher than in the sec- ond leaching unit, such as 5 to 15 weight-%, typically 5 to 10 weight-%. Typically in the second leaching unit the sulphuric acid concentration of the second leach solution is lower than in the first unit, such as 2 to 10 weight-%, typically 2 to 7 weight-%, more typically 2 to 5 weight-%. According to an embodiment, the concentration of sulphuric acid in first and second leach units are approximately in the same level. According to another embodiment, the sulphuric acid concentration is in the second leaching solution lower than in the first leaching solution. In this manner the removal of impurities is enhanced in the second leaching, but the dissolving of titanium from the slag is avoided. If the sulphuric acid concentration in the second leach solution is too high, titanium losses occur due to the dissolving of the titanium from the slag. From the presented ranges the sulphuric acid concentrations are typically selected in such a manner that either they are at a same level, or the sulphuric acid concentration of the second leach solution is lower than the sulphuric acid concentration of the first leach solution. According to an embodiment, the first leaching step a) comprises a leaching solution, wherein the sulphuric acid concentration is 10 weight-% and the second leaching step c) comprises a leaching solution, wherein the sulphuric acid concentration is 5 weight-%.

Typically the temperatures of the first and second sulphuric acid leach solution are selected independently to be below the boiling point of the solution, typically in a temperature below 100 °C. Typically the temperature of the leaching solution is kept between 40 °C and the boiling point of the solution.

LIST OF REFERENCE NUMBERS

2 titanium-containing slag

4 first sulphuric acid solution

6 first leaching step

8 first slurry

10 first solid-liquid separation step

12 leach residue which has an increased titanium content 14 second leaching step

16 second sulphuric acid solution 18 second slurry

20 second solid-liquid separation step

22 end product which has an increased titanium content Figure 1 illustrates an exemplary embodiment. In figure 1 , titanium- containing slag 2 is subjected to a first leaching step 6 in the presence of a first sulphuric acid solution. The titanium-containing slag may be ground to a suitable particle size before subjecting to the first leaching step 6. The temperature is kept below the boiling point of the leaching solution in the first leaching step and the pressure is kept atmospheric. The retention time in the first leaching step 6 is between 6 to 30 h. The sulphuric acid concentration is kept at approximately 10 weight-%. In the first leaching step 6 the impurities are leached from the titanium-containing slag thereby forming a first slurry 8 containing impurities in the leached form in the first leach solution and slag in solid form. The first slurry 8 is subjected to a first solid-liquid separation step 10 which is typically filtration. From the first solid-liquid separation step leach residue which has increased titanium-content 12 is obtained. Optionally the leach residue 12 may be subjected to a second leaching step 14. The second leaching step is performed in the presence of a second sulphuric acid solution 16. The temperature is kept below the boiling point of the leaching solution in the second leaching step and the pressure is kept atmospheric. The retention time in the second leaching step 14 is between 6 to 30 h. The sulphuric acid concentration is kept at approximately 5 weight-%. In the second leaching step 14 the impurities are leached from the titanium-containing slag thereby forming a second slurry 18 containing impurities in the leached from in the first leach solution and slag in solid form. The second slurry 18 is subjected to a second solid-liquid separation step 20 which is typically filtration. From the second solid-liquid separation step 20 end product 22 which has increased titanium content, is obtained. EXAMPLES

Titania slag and sulphuric acid with different concentrations were mixed for the leaching of impurities. The leaching temperature was 90-95 °C. The end products with following metal concentrations were obtained. Table 1 . The composition of the end product from the leaching of ti- tania slag with sulphuric acid. The leaching was carried out at one leaching step

Table 2. The composition of the end product from the leaching of ti- tania slag with sulphuric acid. The leaching was carried out at one leaching step with a leaching time of 24 h and at temperature of 90 °C.

Table 3. The composition of the end product from the leaching of ti- tania slag with sulphuric acid. The leaching was carried out at two leaching steps with a leaching time of 12 h in each leaching step and at temperature of 90 °C.

Example A: the titanium and titania mass fractions in the solids after leaching are shown in figure 2 as follows:

a) titania slag, feed material,

b) 1 step (5% acid) and 2 step (5% acid),

c) 1 step (5% acid) and 2 step (10% acid),

d) 1 step (10% acid) and 2 step (10% acid),

e) 1 step (5% acid, 24 h leaching time),

f) 1 step (5% acid). It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1 . A method of treating titanium-containing slag, wherein the method comprises

2. The method according to claim 1 , wherein the method further comprises

c) contacting the titanium-containing leach residue with a second sulphuric acid leach solution for dissolving impurities contained in the titanium-containing leach residue to obtain a second slurry,

3. The method according to claim 1 or 2, wherein the concentrations of sulphuric acid in the first and second sulphuric acid leach solution are selected independently and are in the range of 2 to 20 weight-%, more typically 3 to 15 weight-%, even more typically in the range of 5 to 15 weight-%, even more typically in the range of 8 to 12 weight-%.

4. The method according to any one of the preceding claims, wherein the concentration of sulphuric acid in the first sulphuric acid leach solution is typically in the range of 2 to 20 weight-%, more typically 3 to 15 weight-%, even more typically in the range of 5 to 15 weight-%, even more typically in the range of 8 to 12 weight-%, and the concentration of the sulphuric acid in the second sulphuric acid leach solution is lower than the first sulphuric acid leach solution and selected to be 2 to 10 weight-%, typically 2 to 7 weight-%, more typically 2 to 5 weight-%.

5. The method according to any one of the preceding claims, wherein the temperatures of the first and second sulphuric acid leach solution are selected independently to be below the boiling point of the respective solution, typically the temperatures of the first and second sulphuric acid leach solution are selected independently to be between 40 °C and the boiling point of the respective solution.

6. The method according to any one of the preceding claims, wherein retention times of steps a) and c) are selected independently to be in the range of 6 - 30 h, typically 10 - 20 h.

7. The method according to any one of the preceding claims, wherein the solid-liquid separation in steps b) and d) is selected independently from any suitable methods known in the art, such as filtering.

8. An apparatus of treating titanium-containing slag, wherein the apparatus comprises

b) a first solid-liquid separation unit wherein the first slurry is subjected to a solid-liquid separation to obtain a first sulphuric acid leach solution containing the dissolved impurities from a first titanium-containing leach residue.

9. The apparatus according to claim 8, wherein the apparatus further comprises

c) a second leach unit, wherein the titanium-containing leach residue is contacted with a second sulphuric acid leach solution under atmospheric pressure and in a temperature below 100 °C for dissolving impurities contained in the titanium-containing leach residue to obtain a second slurry,

d) a second solid-liquid separation unit, wherein the second slurry is subjected to a solid-liquid separation to obtain a second sulphuric acid leach solution containing dissolved impurities from a second titanium-containing leach residue.

10. The apparatus according to claim 8 or 9, wherein the concentrations of sulphuric acid in the first and second sulphuric acid leach solution are selected independently and are in the range of 3 to 15 weight-%, typically in the range of 5 to 10 weight-%.

1 1 . The apparatus according to any one of the preceding claims 8 to 10, wherein the concentration of sulphuric acid in the first sulphuric acid leach solution is typically in the range of 2 to 20 weight-%, more typically 3 to 15 weight-%, even more typically in the range of 5 to 15 weight-%, even more typically in the range of 8 to 12 weight-% and the concentration of the sulphuric acid in the second sulphuric acid leach solution is 2 to 10 weight-%, typically 2 to 7 weight-%, more typically 2 - 5 weight -%.

12. The apparatus according to any one of the preceding claims 8 -

1 1 , wherein the temperatures of the first and second sulphuric acid leach solution are selected independently to be below the boiling point of the respective solution, typically the temperatures of the first and second sulphuric acid leach solution are selected independently to be between 40 °C and the boiling point of the respective solution.

13. The apparatus according to any one of the preceding claims 8 -

12, wherein retention times in units a) and c) are selected independently to be in the range of 6 - 30 h, typically 10 - 20 h.

14. The apparatus according to any one of the preceding claims 8 -

13, wherein the solid-liquid separation in units b) and d) is selected independently from any suitable solid-liquid separation units known in the art, such as filtering.