Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
PROCESS FOR UPGRADING ASBESTOS TAILINGS
Document Type and Number:
WIPO Patent Application WO/2016/165003
Kind Code:
A1
Abstract:
A process for upgrading a serpentine-containing material is provided. The process includes feeding the serpentine-containing material into a first reactor. The serpentine-containing material is pre-treated in the first reactor to obtain a pre-treated material. The pre-treating includes drying the serpentine-containing material, and removing dust particles from the serpentine-containing material. The process also includes feeding the pre-treated material into a second reactor; and dehydrating and calcining the pre-treated material in the second reactor to obtain a calcined material.

Inventors:
GUERARD MARC-AURÈLE (CA)
GOSSELIN CLAUDE (CA)
Application Number:
PCT/CA2015/050304
Publication Date:
October 20, 2016
Filing Date:
April 13, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
LES SABLES OLIMAG INC (CA)
International Classes:
A62D3/40
Foreign References:
CA2130330A11993-09-02
CA1216403A1987-01-13
US4320022A1982-03-16
US4430157A1984-02-07
Attorney, Agent or Firm:
ROBIC LLP (1001 Square-Victoria Bloc E - 8th Floo, Montréal Québec H2Z 2B7, CA)
Download PDF:
Claims:
CLAIMS

1 . A process for upgrading a serpentine-containing material, the process comprising the steps of: a) feeding the serpentine-containing material into a first reactor; b) pre-treating the serpentine-containing material in the first reactor to obtain a pre-treated material, the pre-treating comprising: drying the serpentine-containing material; and removing dust particles from the serpentine-containing material; c) feeding the pre-treated material into a second reactor; and d) dehydrating and calcining the pre-treated material in the second reactor to obtain a calcined material.

2. The process of claim 1 , wherein drying of the serpentine-containing material is performed at a temperature between 300Ό and 500 Ό.

3. The process of claims 1 or 2, wherein the dust particles removed from the serpentine-containing material have a particle size of 150 microns or less.

4. The process of any one of claims 1 to 3, wherein the first reactor is a fluid bed reactor.

5. The process of claim 4, wherein the fluid bed reactor is one of a back mix fluid bed dryer and a plug flow fluid bed dryer.

6. The process of claim 4 or 5, wherein the fluid bed reactor is a vibrating fluid bed reactor.

7. The process of any one of claims 4 to 6, wherein the fluid bed reactor comprises a perforated plate comprising perforations having a size between 2.5 mm and 4 mm.

8. The process of any one of claims 4 to 7, wherein a residence time of the serpentine-containing material in the fluid bed reactor is between 5 minutes and 8 minutes.

9. The process of any one of claims 1 to 8, wherein the dehydrating of the pre- treated material is performed at a temperature between 700 and 900Ό.

10. The process of any one of claims 1 to 9, wherein the calcining of the dehydrated material is performed at a temperature between 900Ό and 1500 .

1 1 . The process of any one of claims 1 to 10, further comprising removing residues having a particle size larger than 2 cm from the serpentine- containing material.

12. The process of claim 1 1 , wherein the residues having a particle size larger than 2 cm are removed from the serpentine-containing material prior to step a). 13. The process of any one of claims 1 to 12, wherein the second reactor is a rotary kiln.

14. The process of claim 13, wherein the rotary kiln comprises a dehydrating zone where the pre-treated material is dehydrated and a calcining zone where the dehydrated material is calcined. 15. The process of claim 14, wherein the rotary kiln further comprises a cooling zone for cooling the calcined material.

16. The process of claim 14 or 15, wherein a residence time of the pre-treated material within the dehydrating zone is between 3 minutes and 5 minutes.

17. The process of any one of claims 14 to 16, wherein a residence time of the dehydrated material within the calcining zone is between 10 minutes and 25 minutes.

18. The process of any one of claims 1 to 17, wherein step d) comprises removing dust particles from the second reactor.

19. The process of claim 18, wherein the dust particles removed from the second reactor have a particle size of 150 microns or less

20. The process of any one of claims 1 to 19, wherein the serpentine-containing material includes asbestos tailings.

21 . The process of any one of claims 1 to 20, wherein the pre-treated material is stored at a storage temperature prior to step c).

22. The process of claim 21 , wherein the storage temperature is between 300Ό and 500<C.

23. The process of any one of claims 1 to 22, further comprising the step of: e) processing the calcined material to obtain a refractory material.

24. The process of claim 23, wherein step e) comprises crushing the calcined material.

25. The process of claim 23 or 24, wherein step e) comprises sieving the calcined material.

26. A refractory material, obtained by the process of any one of claims 23 to 25.

27. The refractory material of claim 26, comprising about 5 wt% or less of material having a particle size of less than 150 microns. 28. The refractory material of claim 27, comprising about 2 wt% or less of material having a particle size of less than 150 microns.

Description:
PROCESS FOR UPGRADING ASBESTOS TAILINGS

TECHNICAL FIELD

The technical field generally relates to upgrading asbestos tailings, and more specifically relates to a process for manufacturing refractory materials from asbestos tailings.

BACKGROUND

Asbestos has been widely used by manufacturers and builders because of its desirable physical properties such as sound insulation, tensile strength, resistance to fire, electrical and chemical damage, and affordability. Asbestos deposits normally occur in certain types of silicate rock which contain about 5 to 10% by volume of asbestos fibres. Consequently, separation of the fibres from asbestos ore leaves large quantities of by-products (also referred to herein as "asbestos tailings") which accumulate near extraction or processing sites. As asbestos deposits were widely harvested throughout the 20 th century, large quantities of asbestos tailings are now available and can serve as raw materials in novel commercial applications.

Canadian patent No. 1 ,216,403 describes a process for manufacturing a granular product from asbestos tailings, suitable for use as a refractory material and obtained from calcined asbestos tailings. The granular material obtained was found to have numerous advantages over silica sand, including having superior refractory properties as well as being devoid of noxious free silicate dusts.

Canadian patent No. 2, 130,330 describes a process for manufacturing a refractory material from asbestos tailings. The process includes mixing ground particles of the asbestos tailings with a magnesium oxide-based slurry to obtain a mixture, and calcining the mixture in a rotary kiln in order to obtain a refractory material. However, such refractory materials typically contain a relatively high amount of dust particles, which can cause a number of problems to the user.

Also, if introduced into the rotary kiln, the dust particles are dehydrated and calcined along with the rest of the material, which consumes additional energy. Furthermore, humid material or a water-based slurry is typically introduced into the rotary kiln, which also requires additional energy to be dried. Consequently, a portion of the rotary kiln is used for drying, and less surface area is available for dehydration and calcining of the asbestos tailings.

In light of the above, upgrading asbestos tailings still has a number of challenges. SUMMARY

In one general aspect, a process for upgrading a serpentine-containing material is provided. The process includes the steps of: a) feeding the serpentine-containing material into a first reactor; b) pre-treating the serpentine-containing material in the first reactor to obtain a pre-treated material, the pre-treating comprising: drying the serpentine-containing material; and removing dust particles from the serpentine-containing material; c) feeding the pre-treated material into a second reactor; and d) dehydrating and calcining the pre-treated material in the second reactor to obtain a calcined material.

In some embodiments, drying of the serpentine-containing material is performed at a temperature between 300 and 500 .

In some embodiments, the dust particles removed from the serpentine-containing material have a particle size of 150 microns or less. In some embodiments, the first reactor is a fluid bed reactor.

In some embodiments, the fluid bed reactor is one of a back mix fluid bed dryer and a plug flow fluid bed dryer.

In some embodiments, the fluid bed reactor is a vibrating fluid bed reactor. In some embodiments, the fluid bed reactor comprises a perforated plate comprising perforations having a size between 2.5 mm and 4 mm.

In some embodiments, a residence time of the serpentine-containing material in the fluid bed reactor is between 5 minutes and 8 minutes.

In some embodiments, the dehydrating of the pre-treated material is performed at a temperature between 700 and 900 .

In some embodiments, the calcining of the dehydrated material is performed at a temperature between 900 and 1500 .

In some embodiments, the process further comprises removing residues having a particle size larger than 2 cm from the serpentine-containing material. In some embodiments, the residues having a particle size larger than 2 cm are removed from the serpentine-containing material prior to step a).

In some embodiments, the second reactor is a rotary kiln.

In some embodiments, the rotary kiln comprises a dehydrating zone where the pre-treated material is dehydrated and a calcining zone where the dehydrated material is calcined.

In some embodiments, the rotary kiln further comprises a cooling zone for cooling the calcined material.

In some embodiments, a residence time of the pre-treated material within the dehydrating zone is between 3 minutes and 5 minutes. In some embodiments, a residence time of the dehydrated material within the calcining zone is between 10 minutes and 25 minutes.

In some embodiments, step d) comprises removing dust particles from the second reactor. In some embodiments, the dust particles removed from the second reactor have a particle size of 150 microns or less

In some embodiments, the serpentine-containing material includes asbestos tailings.

In some embodiments, the pre-treated material is stored at a storage temperature prior to step c).

In some embodiments, the storage temperature is between 300Ό and 500Ό.

In some embodiments, the process further comprises the step of: e) processing the calcined material to obtain a refractory material.

In some embodiments, step e) comprises crushing the calcined material. In some embodiments, step e) comprises sieving the calcined material.

In another general aspect, there is provided a refractory material, obtained by the process described herein.

In some embodiments, the refractory material comprises about 5 wt% or less of material having a particle size of less than 150 microns. In some embodiments, the refractory material comprises about 2 wt% or less of material having a particle size of less than 150 microns.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a process flow diagram of a prior process for manufacturing refractory materials from asbestos tailings; Figure 2 is a process flow diagram of a process for manufacturing refractory materials from asbestos tailings, according to an embodiment of the invention;

Figure 3 is a diagram representing a pre-treatment in a fluidized bed, according to an embodiment of the invention; Figure 4 is a scheme showing a system for manufacturing refractory materials from asbestos tailings, according to an embodiment of the invention;

Figure 5 is a graph showing granulometric compositions (US Mesh) of (i) a refractory material obtained using the process of Figure 2; and (ii) a comparative refractory material obtained using the process of Figure 1 ; and Figure 6 includes Figures 6A and 6B; Figure 6A shows zones of a rotary kiln used for dehydration and calcination of a material obtained from the process of Figure 1 ; and Figure 6B shows zones of a rotary kiln used for dehydration and calcination of a material obtained from the process of Figure 2.

DETAILED DESCRIPTION Various techniques that are described herein enable upgrading of serpentine- containing materials such as asbestos tailings. It is understood that by "upgrading" of a material, it is meant that the material is transformed by a series of process steps in order to obtain a product which may be sold, or be used for a certain purpose. For example, in some scenarios, upgrading of asbestos tailings allows obtaining a calcined material, which can be further processed to obtain a refractory material. It is therefore understood that some of the techniques described herein enable the manufacture of refractory material from asbestos tailings.

Asbestos tailings typically contain a substantial portion of hydrated magnesium silicates referred to as serpentine. Other components which occur with serpentine include brucite Mg(OH) 2 and hematite-magnetite Fe 2 O3-Fe 3 O 4 . Serpentine can be dehydrated and calcined in order to produce sintered angular shaped granules which can be useful as sandblasting or heat accumulating material, or to produce granular products useful as foundry mold sands. Typically, dehydration and calcining of serpentine involves heating the serpentine to a temperature of above 1200 , whereby the follo wing chemical reactions can take place:

1 ) dehydration reaction typically occurring between 600 and 900Ό to form an anhydrous magnesium silicate:

Mg 3 (Si 2 0 5 )(OH) 4 → 3 MgO-2Si0 2 + 2 H 2 0

2) conversion of the anhydrous magnesium silicate into forsterite Mg 2 Si0 4 and free silica Si0 2 , which typically occurs above 900Ό:

2 (3MgO · 2Si0 2 ) → 3 Mg 2 Si0 4 + Si0 2

3) reaction of forsterite with free silica, typically occuring above 1000 , thereby forming enstatite MgSi0 3 :

Mg 2 Si0 4 + Si0 2 → 2 MgSi0 3 The mixture of forsterite and enstatite thereby obtained typically has a high melting point above 1700Ό, which can make the mate rial suitable for the aforementioned applications.

It is understood that the term "asbestos tailings" as used herein refers to byproducts of the separation process of the asbestos fibres from asbestos ore. The asbestos tailings can be recovered from or near former asbestos production sites or facilities. The processes, systems and compositions described herein are exemplified using "asbestos tailings" as starting material, but it is understood that other serpentine-containing materials can be used. The serpentine-containing materials as referred to herein include materials wherein the primary component is serpentine and which include, for example, between 30 wt% and 100 wt% serpentine, between 50 wt% and 95 wt% serpentine, between 70 wt% and 95 wt% serpentine, or between 80 wt% and 95 wt% serpentine; with the balance to 100 wt% being at least one of a metal (such as iron, magnesium and/or nickel), a metal oxide (such as iron oxides (FeO, Fe 2 0 3 and/or Fe 3 0 4 ), magnesium oxides and/or nickel oxides) and a metal derivative (such as a magnesium hydroxide or an iron hydroxide). One non-limiting example of a serpentine-containing material includes between 90 wt% and 99 wt% serpentine, and between 1 wt% and 10 wt% iron oxides. Another non-limiting example of a serpentine-containing material includes between 90 wt% and 95 wt% serpentine, and between 5 wt% and 10 wt% iron oxides.

Referring to Figure 1 , a comparative prior process 100 for the manufacture of a refractory material from asbestos tailings 102 is provided. The process 100 includes directly introducing the asbestos tailings 102 into a rotary kiln 104. The asbestos tailings 102 is dried 106, dehydrated 1 10 and then calcined 1 14 in the rotary kiln 104 in order to obtain a calcined material 1 16 which can be recovered from the rotary kiln 104. The calcined material 1 16 is then typically crushed in a crushing step 1 18 and the crushed material 120 thereby obtained can be sieved in a sieving step 122 in order to obtain a refractory material 124. It is understood that by "directly introducing the asbestos tailings", it is meant that the asbestos tailings are introduced into the rotary kiln 104 without any pre-treatment or pre- drying step. Depending on the time of the year and the environmental conditions, the asbestos tailings 102 can therefore include a certain amount of moisture as well as a certain amount of unwanted material (also referred to as impurities).

It is understood that the term "moisture" can refer to water which can, for example, originate from rain or snow, and can be deposited onto the asbestos tailings 102. Such "moisture" is to be differentiated from water molecules which are embedded into certain molecular or ionic components of the asbestos tailings such as serpentine (such as in the form of hydrated magnesium silicates). Therefore, it is understood that a drying step can typically suffice for removing moisture, for example by vaporizing the moisture, whereas a dehydration step (or dehydration reaction) is typically needed (as step 1 above), to remove water molecules or hydroxide moieties embedded into some molecular or ionic components of the asbestos tailings 102. It is therefore understood that a drying step is typically performed at a lower temperature than a dehydration step. For example, a drying step for drying asbestos tailings can be performed between 100 and 500 , or between 300 and 500Ό, wherea s a dehydrating step can be performed between 600 and 900Ό, or betwee n 700 and 800Ό. It is understood that the "unwanted material" or the "impurities" which can be present in the asbestos tailings 102, can include residues which have a particle size larger than several cm, such as 2 cm, and/or materials which were initially not a by-product of the asbestos extraction process, such as wood-based or plastic- based residues. Such residues can for example be by-products of other unrelated processes, or waste material which was stored in conjunction with the asbestos tailings, or deposited at the same storage site than the asbestos tailings.

Now referring to Figure 2, a process 200 for manufacturing refractory materials from asbestos tailings 102, according to an embodiment of the invention, is provided. The asbestos tailings 102 can be recovered from or near former asbestos production sites or facilities. In some embodiments, the asbestos tailings 102 can initially be screened in a screening step 202, for example using a vibrating screen, in order to remove unwanted material and/or impurities (such as residues having a particle size larger than 2 cm), thereby obtaining screened asbestos tailings. The process 200 includes feeding (or introducing) the feed material 205 into a first reactor. The asbestos tailings 102 and/or the screened asbestos tailings are subjected to a pre-treatment 206 in the first reactor, and the pre-treated material obtained is then fed into a second reactor such as a rotary kiln 204 for further processing. It is understood that the asbestos tailings 102 and/or the screened asbestos tailings will be generally referred to herein as feed material 205. It is therefore understood that the feed material 205 can include screened asbestos tailings, asbestos tailings 102 (i.e., asbestos tailings which have not been screened) or a combination thereof. In some embodiments, the second reactor includes a rotary kiln, a shaft furnace, multiple hearth furnaces or a calcining oven. In some embodiments, the second reactor can further include a dust collector or a dust-collecting assembly.

In some embodiments, the pre-treatment 206 includes drying the feed material 205, and/or removing dust particles from the feed material 205 in order to obtain pre-treated asbestos tailings 208. In the embodiment shown in Figure 2, the pre- treatment 206 includes drying the feed material 205 and removing dust particles from the feed material 205. In some embodiments, the pre-treatment 206 including drying of the feed material 205 and removing of the dust particles from the feed material 205, can be performed in a single processing step. For example, the first reactor can include a dryer such as a spray dryer, a drum dryer, a pulse combustion dryer, a freeze dryer or a fluid bed dryer. In some embodiments, the first reactor can further include a dust collector or a dust- collecting assembly.

Still referring to Figure 2, in some embodiments, the pretreatment 206 which includes drying of the feed material 205 and removing of the dust particles from the feed material 205, can be performed in a fluidized bed. In other words, in some embodiments, the first reactor is a fluid bed reactor (also referred to as a fluid bed dryer). Hot gas or hot air 207A can be fed into the fluid bed reactor, and dust-containing gases 207B can be recovered therefrom. In some scenarios, the drying step can be performed at a temperature of between 300Ό and 500Ό. In some scenarios, the dust particles removed from the feed material 205 have a particle size of 150 microns or lower.

Still referring to Figure 2, the pre-treated asbestos tailings 208 is fed into a second reactor such as rotary kiln 204. The pre-treated asbestos tailings 208 can then be subjected to a dehydrating step 210 in the second reactor, in order to obtain dehydrated asbestos tailings 212, and the dehydrated asbestos tailings 212 can be subjected to a calcining step 214 in the second reactor, in order to obtain a calcined material 216. In some embodiments, the step of dehydrating 210 the pre-treated asbestos tailings 208 is performed at a temperature between 600 and 900Ό, or between 700 and 900 . In som e embodiments, the step of calcining the dehydrated asbestos tailings 214 is performed at a temperature between 900 and 1500Ό or between 1200 and 1500 . In some embodiments, the steps of dehydrating and calcining can be performed in the rotary kiln 204.

It is understood that the term "rotary kiln" as used herein refers to a pyroprocessing device used to raise the temperature of materials to a high temperature (such as a calcination temperature) in a continuous process. The rotary kiln is typically a cylindrical vessel, inclined slightly to the horizontal and rotatable about its longitudinal axis. When a rotary kiln is used, the feed material 205 is typically fed into the upper end of the cylindrical vessel and rotation of the vessel allows the material to gradually move down towards the lower end of the vessel. The material may undergo a certain amount of stirring and mixing. It is also understood that the rotary kiln can be used in a co-current configuration (wherein hot gases pass along the kiln in the same direction as the movement of the material) or in a counter-current configuration (wherein hot gases pass along the kiln in the opposite direction as the movement of the material). The hot gases may be generated by an external furnace, or may be generated by a flame inside the rotary kiln. Different types of fuel can be used, such as natural gas, oil, coke, coal, pulverized petroleum coke, pulverized coke, or a combination thereof. In some embodiments, the rotary kiln is rotating at between 0.75 and 1 .25 rpm. In some embodiments, the asbestos tailings are introduced into the rotary kiln at a rate of up to 10 tons per hour, for example between 8 and 10 tons per hour. In some embodiments, the temperature within the rotary kiln is a temperature gradient varying from between about 300Ό at the fe ed end to about 2500Ό proximate to the flame and/or at the discharge end.

Still referring to Figure 2, in some embodiments, the calcined material 216 can be further processed in order to obtain a refractory material 224. For example, the processing of the calcined material 216 can include crushing the calcined material 216 in a crushing step 218 to obtain a crushed material 220, and sieving the crushed material 220 in a sieving step 222 in order to obtain the refractory material 224. For example, the crushing step 218 can be performed in a crusher, such as a jaw crusher, a gyratory crusher, a cone crusher, an impact crusher, a mineral sizer or a combination thereof. In some scenarios, the crushing step 218 can allow breaking of the calcined material into smaller pieces, for example to obtain a desired average particle size for the pre-treated asbestos tailings 208, and/or to remove clumps of calcined material which may have formed during one of the dehydrating and the calcining steps 210, 214.

In some embodiments, the crushed material 220, or the calcined material 216 can be sieved, for example to remove the bigger and/or smaller particles of the material, and/or obtain a desired particle size distribution. For example, the sieving step 222 can include multiple sieving sub-steps to remove selected particle sizes with each sub-step.

In some embodiments, at least one of the dehydrating step and the calcining step includes removing dust particles. For example, dust can be removed from the rotary kiln during operation. A dust collector can allow collecting dust from one end of the rotary kiln in order to recover dust-containing gases 226, which can be further processed. In some implementations, the dust particles removed from the second reactor have a particle size of 150 microns or less (i.e., 100 Mesh US). Now referring to Figure 3, the pre-treatment 206 can be performed using a fluid bed dryer. In some embodiments, the feed material 205 is introduced into a fluid bed dryer 230. For example, the fluid bed dryer 230 can be a back mix fluid bed dryer, or a plug flow fluid bed dryer. Hot gas 232 required for drying can be generated in a hot gas generator 234, for example by using fuel such as oil, natural gas, coal or any other suitable fuel available. In some scenarios, the fuel can be burned in a combustion chamber 236 using a burner 238, and the hot gas 232 can be conveyed to and introduced into the fluid bed dryer 230 using a fan 240. The hot gas 232 can be introduced in the fluid bed dryer 230 at the bottom of the fluid bed dryer 230, through a perforated plate 242. In some embodiments, the perforated plate 242 includes perforations having a size between 1 mm and 5 mm, or between 2.5 mm and 4 mm, or between 2.7 mm and 4 mm. In some embodiments, the temperature of the hot gas can be between 100Ό and 500 , or between 300 and 500 . In some embodiments, th e hot gas can be introduced in the fluid bed dryer at a flow rate between 10000 CFM and 20000 CFM, between 13000 CFM and 17000 CFM, or at about 15000 CFM. Typically, the feed material 205 is conveyed from a feed end 230A of the fluid bed dryer 230 towards a discharge end 230B of the fluid bed dryer 230. In the fluid bed dryer 230, the feed material 205 comes in contact with the hot gas 232, which can dry the feed material 205. In some embodiments, the fluid bed dryer 230 is a vibrating fluid bed dryer, in which vibrations can cause the feed material 205 to be displaced from the feed end 230A to the discharge end 230B. In some implementations, the residence time of the feed material 205 in the fluid bed reactor is between 3 and 20 minutes, between 5 and 15 minutes, between 5 and 10 minutes, or between 5 and 8 minutes. In some scenarios, the combined action of vibrations and fluidization can ensure uniform drying and obtaining desired product moisture. In some embodiments, the fluid bed dryer 230 is configured such that an outlet gas 244 exiting from the fluid bed dryer 230 contains a certain amount of dust which was present in the feed material 205 (in such case, the outlet gas 244 can be referred to as a dust-containing gas). The dust-containing gas 244 can be passed through a dust collector 246. For example, the dust collector 246 can be a bag filter dust collector. The dust collector 246 can allow obtaining a dust-free gas 248.

In some embodiments, the pre-treatment includes measuring the humidity of the feed material 205, and selecting at least one of operational parameters of the fluid bed dryer (i.e., at least one of the temperature of the hot gas, the residence time of the material inside the fluid bed dryer, the flow rate of the hot gas, and the size of the perforations of the perforated plates) according to the humidity of the feed material. For example, in some scenarios wherein the humidity of the feed material is between 5% and 25%, the temperature of the hot gas can be set between 350 and 450 or of about 400 , the perf orations can be selected to have a diameter between 2.7 mm and 4 mm, the flow rate of the hot gas can be between 13000 CFM and 17000 CFM, and the residence time can be between 5 minutes and 8 minutes.

Now referring to Figure 4, a system for manufacturing refractory materials from asbestos tailings 102 is provided, according to an embodiment of the invention. In some embodiments, the asbestos tailings 102 can be recovered from or near former asbestos production sites or facilities and can be conveyed, for example using trucks 250, to a container 252. The asbestos tailings 102 can then be conveyed to a screening device 254, for example using a conveyor belt 255. In some embodiments, the screening device 254 can include a vibrating screener, such as a Tyrock™ screener. The screened asbestos tailings and/or the asbestos tailings 102 (generally referred to as feed material 205, as explained above), are fed into a fluid bed dryer 230. The feed material 205 is dried in the fluid bed dryer 230 and dust is removed from feed material 205 using a dust collector 246. The dried and dust-lean asbestos tailings (also referred to as pre- treated asbestos tailings 208) are then conveyed to be dehydrated and calcined in rotary kiln 204.

Still referring to Figure 4, it is understood that the pre-treated asbestos tailings 208 can either be directly fed into the rotary kiln 204, or be first conveyed to a feeding container 256 in order to be fed into the rotary kiln 204 at a later or desired time. The pre-treated asbestos tailings 208 can be conveyed to the feeding container 256 using, for example, a conveyor 257. In some embodiments, the temperature of the feeding container 256 is controlled such that the temperature of the pre-treated asbestos tailings 208 can remain substantially equal to the temperature inside the fluid bed dryer 230. In other words, the temperature of the pre-treated asbestos tailings 208 can be controlled and/or maintained before feeding the pre-treated asbestos tailings 208 into the rotary kiln 204. Still referring to Figure 4, in some embodiments, the second reactor such as the rotary kiln 204 can be provided with a dust collecting assembly 258. It is understood that the dust collecting assembly 258 can be provided at the feed end of the rotary kiln or at the discharge end of the rotary kiln. In the embodiment shown in Figure 4, the rotary kiln 204 is in a counter-current configuration, with the hot gases flowing from the discharge end of the rotary kiln 204 to the feed end of the rotary kiln 204. The dust collecting assembly 258 is therefore connected to the feed end of the rotary kiln 204. In some embodiments, dust- containing gas 259 is removed from the rotary kiln 204, and routed through the dust collecting assembly 258. In some embodiments, the dust-containing gas 259 is introduced into a cyclone 260 for separating larger solid residues present in the dust-containing gas 259. The larger solid residues 262 can be recycled back to the feeding container 256, while cycloned dust-containing gas 264 exists the cyclone 260 and can then be fed into a dust collector 266, or a series of dust collectors 266. The dust collectors 266 can separate the dust from the dust containing gas and a dust-lean or dust-free gas 268 can be recovered or released.

Now referring to Figure 6A, when the asbestos tailings 102 are directly fed into the rotary kiln 204 without being subjected to a pretreatment 206 as shown for example in Figure 1 , the configuration and temperature profile of the rotary kiln 104 includes a zone which is suitable for the drying of the asbestos tailings. As can be seen in Figure 6A, a portion of the rotary kiln 104 is therefore required in order to dry the asbestos tailings 102, which diminishes the available surface area for the dehydrating and calcining steps in the rotary kiln 104. Now referring to Figure 6B, the pre-treated asbestos tailings 208 are fed into the rotary kiln 204. As explained, the pre-treated asbestos tailings 208 are fed into the rotary kiln 204 at a high temperature. Therefore, the dehydrating step can start taking place immediately after the feeding into the rotary kiln 204, and both the dehydrating and the calcining steps can be performed using larger surface areas of the rotary kiln 204. This configuration can allow for the rotary kiln 204 to operate at higher rates, and therefore allow obtaining a higher amount of calcined material 216 in the same amount of time. In some embodiments, the rotary kiln 204 includes a dehydrating zone where the pre-treated material is dehydrated, and a calcining zone where the dehydrated material is calcined. A temperature gradient is typically provided inside the rotary kiln 204, as a flame provides heat to the rotary kiln 204 from one side of the rotaty kiln. In some implementations, the calcining zone extends from the source of the flame, proximate to the discharge end of the rotary kiln 204, to a point where the temperature is of about 900Ό. In some implementations, the dehydrating zon e extends from the feed end of the rotary kiln 204, to the point where the temperature is of about 900Ό. In some implementations, the rotary kiln 204 includes a cooling zone for cooling the calcined material. In some scenarios, the residence time of the pre-treated asbestos tailings in the dehydration zone is between 2 minutes and 10 minutes, or between 3 minutes and 5 minutes. In some scenarios, the residence time of the dehydrated material in the calcining zone is between 10 minutes and 40 minutes, between 10 minutes and 30 minutes, between 10 minutes and 25 minutes or between 15 minutes and 20 minutes.

In some scenarios, using a pre-treatment 206 which includes both drying and removing dust particles prior to the dehydrating and calcining steps can allow obtaining a refractory material which includes less material having a particle size of 150 m or lower, with the same crushing steps and sieving steps being performed on the calcined materials. Obtaining a refractory material including less material having a particle size of 150 m or lower can be advantageous for various reasons, as explained above. In some scenarios, the refractory material obtained according to the invention (i.e., using a process including a pre- treatment 206 as described herein), includes substantially less material having a particle size of 150 m or lower than a process which does not include a pre- treatment. In some scenarios, the refractory material obtained according to the invention includes 5 wt % or less of material having a particle size of 150 Mm or lower. In some scenarios, the refractory material obtained according to the invention includes 2 wt % or less of material having a particle size of 150 Mm or lower. In some scenarios, the refractory material obtained according to the invention includes 1 .5 wt % or less of material having a particle size of 150 m or lower.

EXAMPLES Example 1

Referring to Figure 5, experiments were conducted to compare the granulometry of refractory materials obtained without using a pretreatment (Refractory material A in Figure 5) and with a pretreatment (Refractory material B in Figure 5). In Figure 5, each one of the experimental data points shows the proportion (in wt%) of particles of material A or B which is retained by a mesh screen (positive mesh values) or which passes through a mesh screen (-140 mesh value).

To obtain Material A, humid asbestos tailings were screened using a Tyrock™ screener in order to remove materials having a size larger than 2 cm, and then directly introduced into a rotary kiln to be dried, dehydrated and calcined. The calcined material obtained was crushed and sieved to obtain refractory material A. A dust collector was operated to remove dust particles from the rotary kiln.

To obtain Material B, humid asbestos tailings were screened using a Tyrock™ screener in order to remove materials having a size larger than 2 cm. The screened material was introduced into a fluid bed dryer provided with a perforated plate having perforations between 2.7 mm and 4 mm, with hot air introduced at a temperature of about 400Ό and at a flow rate of about 15000 CFM. Dust particles smaller than about 150 microns were collected from the fluid bed dryer using a dust collector. The pre-treated material recovered from the fluid bed dryer was introduced at about 400Ό into a rota ry kiln to be dehydrated and calcined. The temperature of the pre-treated material was maintained at about 400Ό between exiting the fluid bed dryer and being introduced into the rotary kiln. The calcined material obtained was crushed and sieved to obtain refractory material B, using the same crushing and sieving conditions as for obtaining material A. A second dust collector was also operated to remove dust particles from the rotary kiln, using the same dust-collecting conditions as for material A.

It has been shown that Material B contains about 1 .5 wt% of material having a particle size smaller than 150 m, whereas Material A contains about 10 wt% of material having a size of 150 m or less. It has therefore been shown that pre- treating the asbestos tailings prior to introducing the material into the rotary kiln can allow for a reduction of the dust particles in the calcined material. It is believed that only operating a dust collector to remove dust particles directly from the rotary kiln does not allow removing as many dust particles, because the dust particles can agglomerate with the bulk of the material during the dehydration and/or calcination processes.