CA2235424A1 - Process for the preparation of a magnesium chloride solution by quick lixiviation of asbestos tailings - Google Patents
Process for the preparation of a magnesium chloride solution by quick lixiviation of asbestos tailings Download PDFInfo
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- CA2235424A1 CA2235424A1 CA 2235424 CA2235424A CA2235424A1 CA 2235424 A1 CA2235424 A1 CA 2235424A1 CA 2235424 CA2235424 CA 2235424 CA 2235424 A CA2235424 A CA 2235424A CA 2235424 A1 CA2235424 A1 CA 2235424A1
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- lixiviation
- tailings
- improved process
- hydrochloric acid
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
- C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
- C22B3/10—Hydrochloric acid, other halogenated acids or salts thereof
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B26/00—Obtaining alkali, alkaline earth metals or magnesium
- C22B26/20—Obtaining alkaline earth metals or magnesium
- C22B26/22—Obtaining magnesium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
- C22B7/006—Wet processes
- C22B7/007—Wet processes by acid leaching
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
A process for the preparation of a magnesium chloride solution by lixiviation of asbestos tailings with an aqueous solution of hydrochloric acid having a concentration of about 20% by weight. In this process, the asbestos tailings used as starting material have a granulometry equal to or lower than 62 mesh; the lixiviation is carried out at a temperature close to the temperature of ebullition of the mixture, this temperature of ebullition ranging between 115 and 120°C; and the lixiviation is carried out with asbestos tailings and hydrochloric acid in such amounts that the stoichiometric ratio tailings/HCl ranges between 1.2 and 2.25. Under the above conditions of operation, the time required to obtain almost entire transformation of the hydrochloric acid into magnesium chloride and other metal chlorides is of about 5 to 15 min. and there is no filtration problem because of the presence of silica gel.
Description
PROCESS FOR THE PREPARATION OF A MAGNESIUM
CHLORIDE SOLUTION BY QUICK LIXIVIATION OF
ASBESTOS TAILINGS
FIELD OF THE INVENTION
The present invention is concerned with a process for the quick preparation of a magnesium chloride (MgCl2) solution from asbestos tailings.
More particularly, the invention is concerned with a process wherein the requested magnesium chloride solution is obtained by the lixiviation of asbestos tailings with an aqueous hydrochloric acid solution.
By "quick lixiviation", there is meant a lixiviation carried out for a period of time ranging from 5 to 15 minutes.
BACKGROUND OF THE INVENTION
As is known, there is presently a very high demand for magnesium in metal form.
As is also known, magnesium can be produced by electrolysis of MgCl2 solutions.
As is further known, MgClz solutions can be obtained by subjecting magnesium silicate-containing mineral such as serpentine to a lixiviation with hydrochloric acid.
Such minerals are found, by way of example, as tailings in asbestos mines.
There is an excellent bibliographical review on the chemical transformation of asbestos tailings. This review entitled "The activation of magnesium in serpentine by calcination and chemical utilisation of asbestos tailings - a review" was published by N. NAGAMORI, A.J. PLUMTON and R. LE HOUILLER in CIM Bulletin, December 1980, pp. 144 to 156.
In this article, it is mentioned on page 149 that:
"Both natural and calcined serpentine can be leached with hydrochloric acid...
A leaching with an excess of HCI is suggested to recover silica gel, which can be obtained by the ftltration of the upper layer only of the leached slurry after a settling. Leaching with an excess of serpentine is proposed to minimize the dissolution of silica in the leached slurry so as to facilitate the subsequent filtration".
It is therefore clearly suggested that the lixiviation must be carried out with an excess of tailings in order to reduce the risk of dissolution of silica and, accordingly, the formation of silica gel.
U.S. patent No. 2,398,493 (BUTT et al) assigned to INTERNATIONAL
MINERALS AND CHEMICAL CORP. discloses a process for the production of magnesium using serpentine or any other asbestos tailings as starting material. The tailings used as starting material is subjected to a screening and to a preliminary treatment to remove the magnetic elements contained therein. The material is then subj ected to a lixiviation with an aqueous solution of a hydrochloric acid solution having a concentration of 20% by weight, obtained by recycling the chloride obtained in the electrolysis cell used for the production of pure magnesium. The salt solution that is produced is then subjected to a supplemental purification treatment by precipitation, which is achieved by addition of magnesia (Mg0), followed by a filtration.
T'he purified salt solution that is obtained, is then concentrated and dried before introduction into the electrolysis cell.
In the BUTT patent, there is disclosed that the asbestos tailings must preferably have a granulometry of about 60 mesh. It is also suggested that the lixiviation be carried out at a temperature of 95 to 100°C or higher. Example 2 which is the most relevant one, makes reference to a reaction temperature of 110°C. In the same example 2, reference is also made to a reaction time of about 15 min. and the stoichiometric ratio tailings/HCL, as it can be calculated, is of about 1.09.
U.S. patent No. 2,549,798 (GEE et al) assigned to the UNITED STATES OF
AMERICA, discloses a process for preparing magnesium chloride from asbestos tailings, comprising a lixiviation carried out in two steps with an hydrochloric acid solution having a concentration of 20% by weight, followed by a reaction of the obtained salt solution with a magnesia, and a final separation of the impurities.
In this patent, there is mentioned in column 3, lines 4 to 11 that the tailings used as starting materials must have a granulometry lower than 20 mesh in order to obtain good results. It is also indicated that a major portion of the ground tailings should have a granulometry lower than 200 mesh. In the only example given in this patent, reference made to a lixiviation temperature of 109°C and the stoichiometric ratio tailings/HC1 is of about 1.15. This ratio is actually an average ratio, since the lixiviation is carried out in two successive steps, the first being one carned for about 10 min. with the stoichiometric ratio tailings/HCl of about 0.27, the other one for about 30 min. with a stoichiometric ratio tailings/HCl of about 6.15.
U.S. patent No. 5,091,161 and its Canadian counterpart No. 1,303,327 (HARRIS
et al) both granted to METALLURGY NORANDA INC. disclose and claim a process for preparing an aqueous solution of magnesium chloride (hereinafter called "salt solution") from siliceous magnesium minerals, such as serpentine which is one of the main components of asbestos tailings.
This process is devised to be carned out in a continuous manner. It comprises a first step wherein the material to be treated is introduced into a reactor containing a hydrochloric acid solution. The starting products are reacted at a temperature higher than SO°C but lower than the ebullition temperature of the solution.
More particularly, the reaction is carried out at a temperature preferably ranging between 80 and 90°C, in such a manner that the pH remains under 1.5. Such permits to extract magnesium from the tailings while avoiding the formation of silica gel. In the examples given in this patent, the lixiviation reaction is carned out in the reactor with a stoichiometric ratio tailings/HCl ranging between 1.03 and 1.18 for a period of time of about 130 min.
The process disclosed and claimed in these patents to HARRIS et al also comprises a second step wherein the salt solution that is obtained is transferred into a second reactor in which reactive magnesia, which can be calcinated magnesia or magnesium oxide obtained by spray roasting, is introduced to react with the salt solution and to keep the pH of the same between 4 and 7. This particular treatment carried out in the second separate reactor at a pH different from the first one causes a precipitation of almost all the other impurities containing the salt solution while avoiding again the formation of silica gel.
Last of all, in a third step, the purified salt solution is transferred into a concentration system in order to recover the requested magnesium chloride solution.
Upon reading of the most relevant documents known to the inventors, including those quoted hereinabove, it seems to be known for numerous years that the main difficulty of the existing process of preparation of magnesium chloride solutions by lixiviation of asbestos tailings with hydrochloric acid lies in the filtration, or rather in the impossibility of filtration of the solution in the presence of silica gel.
The formation of silica gel is, depending of the authors, attributed to the ratio tailings/HCI, the reaction temperature, the pH at the end of the reaction and the reaction time. It is also suggested that the granulometry of the tailings play a role.
Upon reading of the very same documents, it seems also that, to solve this problem, it has already been suggested:
1- to use a stoichiometric ratio tailings/HCL higher than 1 (see in particular the article of N. NAGAMORI et al mentioned hereinabove; see also U.S. patent No.
4,289,736 (LALANCETTE) assigned to the UNIVERSITE DE SHERBROOKE or U.S.
patentNo. 4,944,928 (GRILL et al) assigned to VEITSCHER MAGNESTIWERKE AG;
furthermore, see the examples given in the various patents listed hereinabove;
2- to carry out the lixiviation at a high temperature, that is at a temperature higher than 80°C (see almost all the documents listed hereinabove);
3- to carry out the lixiviation at a pH lower than 1.5 and, at the end of the reaction, to quickly increase the pH (see in particular the patents of HARRIS
et al); and 4- preferably, to proceed to the pH increase into successive steps instead of one (see the patent of BUTT).
In practice, it seems obvious that there is an interaction between these different parameters regarding the formation of silicic acid during the lixiviation reaction and the resulting formation of silica gel.
SUMMARY OF THE INVENTION
The present invention is based on the discovery made by the inventors that, in a process for the preparation of a magnesium chloride solution by lixiviation of asbestos tailings, one may convert almost entirely the hydrochloric acid used as starting material into magnesium chloride or other metal chlorides provided that:
- the asbestos tailings used as starting material have a granulometry equal to a lower of -62 mesh;
- the lixiviation is carried out at a temperature close to the temperature of ebullition of the mixture, this temperature of ebullition ranging between 115 and 120°C;
and - the lixiviation is carned out with asbestos tailings and hydrochloric acid in such amounts that the stoichiometric ratio tailings/HCl ranges between 1.2 and 2.25.
Thus, it has been found in a very surprising manner that, in the above condition of operation (1) the time required to obtain almost entire transformation of the 5 hydrochloric acid into magnesium chloride and other chlorides is of about 5 to 15 min.
and (2) there is no filtration problem because of the presence of silica gel.
This time of reaction is very short as compared to the time of reaction exemplified in the document discussed herein above, which are about one to several hours. It is obvious that a short time of reaction favorizes continuous conditions.
Thus, the invention lies in the selection of a plurality of very specific parameters which, when combined together, gives a result which is extremely interesting from an industrial standpoint and unexpected in view of what was already known in this field.
The process according to the invention as claimed hereinafter is thus essentially a process for the preparation of a magnesium chloride solution wherein asbestos tailings previously demagnetized if such is needed, are subjected to lixiviation with an aqueous hydrochloric acid solution having a concentration ranging between 18 and 25%
by weight, preferably about 20% by weight. This process is characterized in that:
before the lixiviation, the asbestos tailings are treated in such a manner as to have a granulometry equal to or lower than -62 mesh;
use is made of asbestos tailings and hydrochloric acid (HCl) in such amounts that a suspension is obtained which, at the beginning of the lixiviation, has a stoichiometric ratio tailings/HCl ranging between 1.2 and 2.25, preferably 1.6 and 2, the most preferred range between about 1.8; and the lixiviation is carried out at a temperature ranging between 100°C
and a temperature of ebullition of the suspension, the lixiviation temperature being preferably of about 110°C.
By producing as disclosed herein above, one may complete the lixiviation in a period of time ranging from 5 to 15 min., the preferred period of time being between 5 and 7.5 min.
Preferably, the lixiviation is carned out under stirring and comprises a preheating of the hydrochloric acid solution to a temperature of about 60°C
followed by an addition of the asbestos tailings, this addition causing a fast increase of a temperature which is then kept at the requested value.
Once the lixiviation is completed, the pH of the suspension can be quickly increased to a value ranging between 4 and 5 and the suspension can be subjected to a separation in order to recover the requested magnesium chloride solution in the form of a first salt solution. The pH of the first salt solution that is recovered, can then be increased into a value ranging between 6 and 7 and the first salt solution can then be subjected to another separation in order to recover a second salt solution.
Alternatively, once the lixiviation is completed, the pH of the suspension can be quickly increased directly to a value ranging from 6 and 7 and the suspension can be subjected to a separation.
In all cases, the requested increase in pH is preferably obtained by addition of magnesium oxide (Mg0) in the suspension and/or the first salt solution.
The invention will be better understood upon reading the following detailed description and non-restrictive examples, made with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a curve giving the reaction kinetics expressed as the total amount of hydrochloric acid consumed as a function of the time during a lixiviation reaction carried out with stoichiometric ratios tailings/HCl equal to 1,20; 1,50; 1,80 and 2,25, respectively, using, as a stating material, asbestos tailings having a granulometry lower than 62 mesh; and Fig. 2 is curve similar to the one shown in Fig. 1, except that the reactions were carried out with stoichiometric ratios tailings/HCl equal to 1.20 and 1.80, respectively, using, as a starting material, asbestos tailings having a granulometry lower than 20 mesh only.
DETAILED DESCRIPTION OF THE INVENTION
As previously explained, the process according to the invention is intended to be used for the preparation of a magnesium chloride solution like those used for the production of magnesium in the metal form by electrolysis.
This process which is essentially a lixiviation process, uses, as starting materials, of:
- an aqueous solution of hydrochloric acid; and - asbestos tailings.
The hydrochloric acid solution has a concentration ranging between 18 and 25%
by weight. Preferably, this concentration is of about 20% by weight, since this percentage is the one which corresponds to an azeotropic mixture. The acidic solution may advantageously be obtained by recycling the hydrochloric acid generated during the production of magnesium by electrolysis.
The asbestos tailings used as starting material can be of any known type. In the tests that were carried out by the inventor, the asbestos tailings were from a mine of JM
ASBESTOS INC. (Quebec). These tailings also called "raw residues" are obtained from a grinding system used for the extraction of chrysotile asbestos fibers. Table I
hereinafter gives the granulometric distribution of these tailings.
TABLE I
Distribution of the granulometric fractions of the raw residues Granulometric fraction I Distribution In order to eliminate an important part of the magnetic fraction which may consume hydrochloric acid, it is very useful to demagnetize the tailings before using them. This demagnetization can be carried out with an apparatus of the type Eriez. By way of example, Table II hereinafter gives the percentage of magnetic and non-magnetic fractions obtained for different granulometric fractions.
TABLE II
Distribution of the magnetic and non-magnetic fractions in the tailings Distribution (%) Granulometric fraction raw residues (mesh) _4+l0 ~ -10+24 ~ -24+62 ~ -62 magnetic ~ 20 ~ 38 I 40 I 30 non-magnetic ~ 80 I 62 I 60 I 70 Table III hereinafter gives a full chemical analysis of the residues.
CHLORIDE SOLUTION BY QUICK LIXIVIATION OF
ASBESTOS TAILINGS
FIELD OF THE INVENTION
The present invention is concerned with a process for the quick preparation of a magnesium chloride (MgCl2) solution from asbestos tailings.
More particularly, the invention is concerned with a process wherein the requested magnesium chloride solution is obtained by the lixiviation of asbestos tailings with an aqueous hydrochloric acid solution.
By "quick lixiviation", there is meant a lixiviation carried out for a period of time ranging from 5 to 15 minutes.
BACKGROUND OF THE INVENTION
As is known, there is presently a very high demand for magnesium in metal form.
As is also known, magnesium can be produced by electrolysis of MgCl2 solutions.
As is further known, MgClz solutions can be obtained by subjecting magnesium silicate-containing mineral such as serpentine to a lixiviation with hydrochloric acid.
Such minerals are found, by way of example, as tailings in asbestos mines.
There is an excellent bibliographical review on the chemical transformation of asbestos tailings. This review entitled "The activation of magnesium in serpentine by calcination and chemical utilisation of asbestos tailings - a review" was published by N. NAGAMORI, A.J. PLUMTON and R. LE HOUILLER in CIM Bulletin, December 1980, pp. 144 to 156.
In this article, it is mentioned on page 149 that:
"Both natural and calcined serpentine can be leached with hydrochloric acid...
A leaching with an excess of HCI is suggested to recover silica gel, which can be obtained by the ftltration of the upper layer only of the leached slurry after a settling. Leaching with an excess of serpentine is proposed to minimize the dissolution of silica in the leached slurry so as to facilitate the subsequent filtration".
It is therefore clearly suggested that the lixiviation must be carried out with an excess of tailings in order to reduce the risk of dissolution of silica and, accordingly, the formation of silica gel.
U.S. patent No. 2,398,493 (BUTT et al) assigned to INTERNATIONAL
MINERALS AND CHEMICAL CORP. discloses a process for the production of magnesium using serpentine or any other asbestos tailings as starting material. The tailings used as starting material is subjected to a screening and to a preliminary treatment to remove the magnetic elements contained therein. The material is then subj ected to a lixiviation with an aqueous solution of a hydrochloric acid solution having a concentration of 20% by weight, obtained by recycling the chloride obtained in the electrolysis cell used for the production of pure magnesium. The salt solution that is produced is then subjected to a supplemental purification treatment by precipitation, which is achieved by addition of magnesia (Mg0), followed by a filtration.
T'he purified salt solution that is obtained, is then concentrated and dried before introduction into the electrolysis cell.
In the BUTT patent, there is disclosed that the asbestos tailings must preferably have a granulometry of about 60 mesh. It is also suggested that the lixiviation be carried out at a temperature of 95 to 100°C or higher. Example 2 which is the most relevant one, makes reference to a reaction temperature of 110°C. In the same example 2, reference is also made to a reaction time of about 15 min. and the stoichiometric ratio tailings/HCL, as it can be calculated, is of about 1.09.
U.S. patent No. 2,549,798 (GEE et al) assigned to the UNITED STATES OF
AMERICA, discloses a process for preparing magnesium chloride from asbestos tailings, comprising a lixiviation carried out in two steps with an hydrochloric acid solution having a concentration of 20% by weight, followed by a reaction of the obtained salt solution with a magnesia, and a final separation of the impurities.
In this patent, there is mentioned in column 3, lines 4 to 11 that the tailings used as starting materials must have a granulometry lower than 20 mesh in order to obtain good results. It is also indicated that a major portion of the ground tailings should have a granulometry lower than 200 mesh. In the only example given in this patent, reference made to a lixiviation temperature of 109°C and the stoichiometric ratio tailings/HC1 is of about 1.15. This ratio is actually an average ratio, since the lixiviation is carried out in two successive steps, the first being one carned for about 10 min. with the stoichiometric ratio tailings/HCl of about 0.27, the other one for about 30 min. with a stoichiometric ratio tailings/HCl of about 6.15.
U.S. patent No. 5,091,161 and its Canadian counterpart No. 1,303,327 (HARRIS
et al) both granted to METALLURGY NORANDA INC. disclose and claim a process for preparing an aqueous solution of magnesium chloride (hereinafter called "salt solution") from siliceous magnesium minerals, such as serpentine which is one of the main components of asbestos tailings.
This process is devised to be carned out in a continuous manner. It comprises a first step wherein the material to be treated is introduced into a reactor containing a hydrochloric acid solution. The starting products are reacted at a temperature higher than SO°C but lower than the ebullition temperature of the solution.
More particularly, the reaction is carried out at a temperature preferably ranging between 80 and 90°C, in such a manner that the pH remains under 1.5. Such permits to extract magnesium from the tailings while avoiding the formation of silica gel. In the examples given in this patent, the lixiviation reaction is carned out in the reactor with a stoichiometric ratio tailings/HCl ranging between 1.03 and 1.18 for a period of time of about 130 min.
The process disclosed and claimed in these patents to HARRIS et al also comprises a second step wherein the salt solution that is obtained is transferred into a second reactor in which reactive magnesia, which can be calcinated magnesia or magnesium oxide obtained by spray roasting, is introduced to react with the salt solution and to keep the pH of the same between 4 and 7. This particular treatment carried out in the second separate reactor at a pH different from the first one causes a precipitation of almost all the other impurities containing the salt solution while avoiding again the formation of silica gel.
Last of all, in a third step, the purified salt solution is transferred into a concentration system in order to recover the requested magnesium chloride solution.
Upon reading of the most relevant documents known to the inventors, including those quoted hereinabove, it seems to be known for numerous years that the main difficulty of the existing process of preparation of magnesium chloride solutions by lixiviation of asbestos tailings with hydrochloric acid lies in the filtration, or rather in the impossibility of filtration of the solution in the presence of silica gel.
The formation of silica gel is, depending of the authors, attributed to the ratio tailings/HCI, the reaction temperature, the pH at the end of the reaction and the reaction time. It is also suggested that the granulometry of the tailings play a role.
Upon reading of the very same documents, it seems also that, to solve this problem, it has already been suggested:
1- to use a stoichiometric ratio tailings/HCL higher than 1 (see in particular the article of N. NAGAMORI et al mentioned hereinabove; see also U.S. patent No.
4,289,736 (LALANCETTE) assigned to the UNIVERSITE DE SHERBROOKE or U.S.
patentNo. 4,944,928 (GRILL et al) assigned to VEITSCHER MAGNESTIWERKE AG;
furthermore, see the examples given in the various patents listed hereinabove;
2- to carry out the lixiviation at a high temperature, that is at a temperature higher than 80°C (see almost all the documents listed hereinabove);
3- to carry out the lixiviation at a pH lower than 1.5 and, at the end of the reaction, to quickly increase the pH (see in particular the patents of HARRIS
et al); and 4- preferably, to proceed to the pH increase into successive steps instead of one (see the patent of BUTT).
In practice, it seems obvious that there is an interaction between these different parameters regarding the formation of silicic acid during the lixiviation reaction and the resulting formation of silica gel.
SUMMARY OF THE INVENTION
The present invention is based on the discovery made by the inventors that, in a process for the preparation of a magnesium chloride solution by lixiviation of asbestos tailings, one may convert almost entirely the hydrochloric acid used as starting material into magnesium chloride or other metal chlorides provided that:
- the asbestos tailings used as starting material have a granulometry equal to a lower of -62 mesh;
- the lixiviation is carried out at a temperature close to the temperature of ebullition of the mixture, this temperature of ebullition ranging between 115 and 120°C;
and - the lixiviation is carned out with asbestos tailings and hydrochloric acid in such amounts that the stoichiometric ratio tailings/HCl ranges between 1.2 and 2.25.
Thus, it has been found in a very surprising manner that, in the above condition of operation (1) the time required to obtain almost entire transformation of the 5 hydrochloric acid into magnesium chloride and other chlorides is of about 5 to 15 min.
and (2) there is no filtration problem because of the presence of silica gel.
This time of reaction is very short as compared to the time of reaction exemplified in the document discussed herein above, which are about one to several hours. It is obvious that a short time of reaction favorizes continuous conditions.
Thus, the invention lies in the selection of a plurality of very specific parameters which, when combined together, gives a result which is extremely interesting from an industrial standpoint and unexpected in view of what was already known in this field.
The process according to the invention as claimed hereinafter is thus essentially a process for the preparation of a magnesium chloride solution wherein asbestos tailings previously demagnetized if such is needed, are subjected to lixiviation with an aqueous hydrochloric acid solution having a concentration ranging between 18 and 25%
by weight, preferably about 20% by weight. This process is characterized in that:
before the lixiviation, the asbestos tailings are treated in such a manner as to have a granulometry equal to or lower than -62 mesh;
use is made of asbestos tailings and hydrochloric acid (HCl) in such amounts that a suspension is obtained which, at the beginning of the lixiviation, has a stoichiometric ratio tailings/HCl ranging between 1.2 and 2.25, preferably 1.6 and 2, the most preferred range between about 1.8; and the lixiviation is carried out at a temperature ranging between 100°C
and a temperature of ebullition of the suspension, the lixiviation temperature being preferably of about 110°C.
By producing as disclosed herein above, one may complete the lixiviation in a period of time ranging from 5 to 15 min., the preferred period of time being between 5 and 7.5 min.
Preferably, the lixiviation is carned out under stirring and comprises a preheating of the hydrochloric acid solution to a temperature of about 60°C
followed by an addition of the asbestos tailings, this addition causing a fast increase of a temperature which is then kept at the requested value.
Once the lixiviation is completed, the pH of the suspension can be quickly increased to a value ranging between 4 and 5 and the suspension can be subjected to a separation in order to recover the requested magnesium chloride solution in the form of a first salt solution. The pH of the first salt solution that is recovered, can then be increased into a value ranging between 6 and 7 and the first salt solution can then be subjected to another separation in order to recover a second salt solution.
Alternatively, once the lixiviation is completed, the pH of the suspension can be quickly increased directly to a value ranging from 6 and 7 and the suspension can be subjected to a separation.
In all cases, the requested increase in pH is preferably obtained by addition of magnesium oxide (Mg0) in the suspension and/or the first salt solution.
The invention will be better understood upon reading the following detailed description and non-restrictive examples, made with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a curve giving the reaction kinetics expressed as the total amount of hydrochloric acid consumed as a function of the time during a lixiviation reaction carried out with stoichiometric ratios tailings/HCl equal to 1,20; 1,50; 1,80 and 2,25, respectively, using, as a stating material, asbestos tailings having a granulometry lower than 62 mesh; and Fig. 2 is curve similar to the one shown in Fig. 1, except that the reactions were carried out with stoichiometric ratios tailings/HCl equal to 1.20 and 1.80, respectively, using, as a starting material, asbestos tailings having a granulometry lower than 20 mesh only.
DETAILED DESCRIPTION OF THE INVENTION
As previously explained, the process according to the invention is intended to be used for the preparation of a magnesium chloride solution like those used for the production of magnesium in the metal form by electrolysis.
This process which is essentially a lixiviation process, uses, as starting materials, of:
- an aqueous solution of hydrochloric acid; and - asbestos tailings.
The hydrochloric acid solution has a concentration ranging between 18 and 25%
by weight. Preferably, this concentration is of about 20% by weight, since this percentage is the one which corresponds to an azeotropic mixture. The acidic solution may advantageously be obtained by recycling the hydrochloric acid generated during the production of magnesium by electrolysis.
The asbestos tailings used as starting material can be of any known type. In the tests that were carried out by the inventor, the asbestos tailings were from a mine of JM
ASBESTOS INC. (Quebec). These tailings also called "raw residues" are obtained from a grinding system used for the extraction of chrysotile asbestos fibers. Table I
hereinafter gives the granulometric distribution of these tailings.
TABLE I
Distribution of the granulometric fractions of the raw residues Granulometric fraction I Distribution In order to eliminate an important part of the magnetic fraction which may consume hydrochloric acid, it is very useful to demagnetize the tailings before using them. This demagnetization can be carried out with an apparatus of the type Eriez. By way of example, Table II hereinafter gives the percentage of magnetic and non-magnetic fractions obtained for different granulometric fractions.
TABLE II
Distribution of the magnetic and non-magnetic fractions in the tailings Distribution (%) Granulometric fraction raw residues (mesh) _4+l0 ~ -10+24 ~ -24+62 ~ -62 magnetic ~ 20 ~ 38 I 40 I 30 non-magnetic ~ 80 I 62 I 60 I 70 Table III hereinafter gives a full chemical analysis of the residues.
TABLE III
Chemical analysis of the raw residues Chemical compounds Percentage (%) (oxides) Raw residues Demagnetised residues Mg0 37.6 38.0 Si02 38.9 ~ 41.3 Fe203 4.87 2.05 Fe0 2.35 1.76 A1203 1.37 1.66 Ca0 0.27 0.64 Ni0 0.33 0.33 Cr203 0.34 0.32 Na20 0.18 0.26 K2p 0.22 0.17 Mn0 0.09 0.10 Ti02 0.04 0.04 Once the residues are screened and demagnetised, the lixiviation reaction can be carried out by using the process disclosed hereinabove, which is the one that was used for carrying out in labs the following lixiviation tests with hydrochloric acid on asbestos tailings.
2.16 kg of an aqueous solution of hydrochloric acid having a concentration of 20% by weight of acid was poured in a plate container of 4 liters. The acidic solution was heated to a temperature of 60°C by keeping it under stirnng with a stirrer of 10 trademark Lightin model serial No. 30, provided with an acid-resistant blade. When the acidic solution reached the temperature of 60°C, the requested amount of asbestos tailings previously demagnetized was then added. The temperature of the suspension under stirnng increases to about 110°C within less than 5 minutes and was kept at this value for the duration of the experiment by means of a heating plate of trademark Corning PC 351.
During the tests that were carried out, samples of about 50 g of solution were picked up every 2.5 minutes and filtered on a Buckner funnel. Samples of l Og of the filtered solution were then poured into 100 ml of cold water. The samples were then analysed with a spectrophotometer of trademark Varian 400. The magnesium dissolution kinetics was then established.
Table IV gives the results obtained with different multiplication factors of the tailings/HCl stoichiometric ratio, using, as a starting material, screened and/or ground tailings having a granulometry lower than 62 mesh.
Chemical analysis of the raw residues Chemical compounds Percentage (%) (oxides) Raw residues Demagnetised residues Mg0 37.6 38.0 Si02 38.9 ~ 41.3 Fe203 4.87 2.05 Fe0 2.35 1.76 A1203 1.37 1.66 Ca0 0.27 0.64 Ni0 0.33 0.33 Cr203 0.34 0.32 Na20 0.18 0.26 K2p 0.22 0.17 Mn0 0.09 0.10 Ti02 0.04 0.04 Once the residues are screened and demagnetised, the lixiviation reaction can be carried out by using the process disclosed hereinabove, which is the one that was used for carrying out in labs the following lixiviation tests with hydrochloric acid on asbestos tailings.
2.16 kg of an aqueous solution of hydrochloric acid having a concentration of 20% by weight of acid was poured in a plate container of 4 liters. The acidic solution was heated to a temperature of 60°C by keeping it under stirnng with a stirrer of 10 trademark Lightin model serial No. 30, provided with an acid-resistant blade. When the acidic solution reached the temperature of 60°C, the requested amount of asbestos tailings previously demagnetized was then added. The temperature of the suspension under stirnng increases to about 110°C within less than 5 minutes and was kept at this value for the duration of the experiment by means of a heating plate of trademark Corning PC 351.
During the tests that were carried out, samples of about 50 g of solution were picked up every 2.5 minutes and filtered on a Buckner funnel. Samples of l Og of the filtered solution were then poured into 100 ml of cold water. The samples were then analysed with a spectrophotometer of trademark Varian 400. The magnesium dissolution kinetics was then established.
Table IV gives the results obtained with different multiplication factors of the tailings/HCl stoichiometric ratio, using, as a starting material, screened and/or ground tailings having a granulometry lower than 62 mesh.
TABLE IV
Reaction kinetics with tailings of less of 62 mesh Reac- Multiplication factor of the stoichiometric ratio (tailingsIHCI) tion time 1.20 1.50 1.80 2.25 (min) 0.0 0 0 0 0 0 0 0 0 0 0 0 0 2.5 29.030.3 32.736.8 48.051.6 40.363.1 67.340.7 79.785.2 5.0 46.648.3 51.460.3 78.783.4 60.194.2 99.448.6 95.199.4 7.5 56.358.1 61.569.7 91.096.0 60.895.2 99.949.6 97.199.9 10.0 69.471.5 75.571.9 93.898.6 60.394.2 98.848.2 94.398.7 12.5 75.877.9 82.172.5 94.799.4 58.691.7 99.148.7 95.399.8 15.0 78.882.3 86.671.8 93.798.3 60.494.5 98.949.2 96.398.6 The results that are reported hereinabove are illustrated in Fig. 1.
From a practical standpoint, the stoichiometric ratio tailings/HCl is defined as the ratio between the amount of tailings and the amount of HCl (100%) required to transform all the metal oxides of Table III, except Si02, in their corresponding metal chlorides. Under these conditions, the multiplication factor of the stoichiometric tailings/HC ratio represents the multiplication factor of the amount of tailings used in the test as compared to the amount that is required for the stoichiometric ratio.
In Table IV hereinabove, column 1 of each test carried out with a same factor gives the percentage of Mg2+ lixiviated in the solution, expressed as a function of the amount of Mg2+ initially present in the tailings. Column 2 gives the percentage of HCl used for dissolving Mg2+ with respect to the initial amount of HC1. Last of all, column 3 gives the percentage of HCl used for dissolving Mg2+ and the other metal impurities with respect to the initial amounts of HCI. This last percentage is the one that is given in Fig. 1.
As is clearly shown in Table IV and Fig. 1, the time required for 98 to 100%
of HCl to be used for dissolving Mg2+ and the other metallic impurities are respectively of minutes, 5 minutes and 5 minutes for multiplication factors of the stoichiometric ratio equal to 1.50, 1.80 and 2.25. When the multiplication factor of the stoichiometric ratio is 1.20, only 87% of HCl is used after a reaction time of 15 min.
10 By of comparison, Table V and Fig. 2 give the results obtained under the same experimental conditions on asbestos tailings having an higher granulometry fraction of about 20 mesh, with multiplication factors of the stoichiometric ratio of 1.20 and 1.80.
Reaction kinetics with tailings of less of 62 mesh Reac- Multiplication factor of the stoichiometric ratio (tailingsIHCI) tion time 1.20 1.50 1.80 2.25 (min) 0.0 0 0 0 0 0 0 0 0 0 0 0 0 2.5 29.030.3 32.736.8 48.051.6 40.363.1 67.340.7 79.785.2 5.0 46.648.3 51.460.3 78.783.4 60.194.2 99.448.6 95.199.4 7.5 56.358.1 61.569.7 91.096.0 60.895.2 99.949.6 97.199.9 10.0 69.471.5 75.571.9 93.898.6 60.394.2 98.848.2 94.398.7 12.5 75.877.9 82.172.5 94.799.4 58.691.7 99.148.7 95.399.8 15.0 78.882.3 86.671.8 93.798.3 60.494.5 98.949.2 96.398.6 The results that are reported hereinabove are illustrated in Fig. 1.
From a practical standpoint, the stoichiometric ratio tailings/HCl is defined as the ratio between the amount of tailings and the amount of HCl (100%) required to transform all the metal oxides of Table III, except Si02, in their corresponding metal chlorides. Under these conditions, the multiplication factor of the stoichiometric tailings/HC ratio represents the multiplication factor of the amount of tailings used in the test as compared to the amount that is required for the stoichiometric ratio.
In Table IV hereinabove, column 1 of each test carried out with a same factor gives the percentage of Mg2+ lixiviated in the solution, expressed as a function of the amount of Mg2+ initially present in the tailings. Column 2 gives the percentage of HCl used for dissolving Mg2+ with respect to the initial amount of HC1. Last of all, column 3 gives the percentage of HCl used for dissolving Mg2+ and the other metal impurities with respect to the initial amounts of HCI. This last percentage is the one that is given in Fig. 1.
As is clearly shown in Table IV and Fig. 1, the time required for 98 to 100%
of HCl to be used for dissolving Mg2+ and the other metallic impurities are respectively of minutes, 5 minutes and 5 minutes for multiplication factors of the stoichiometric ratio equal to 1.50, 1.80 and 2.25. When the multiplication factor of the stoichiometric ratio is 1.20, only 87% of HCl is used after a reaction time of 15 min.
10 By of comparison, Table V and Fig. 2 give the results obtained under the same experimental conditions on asbestos tailings having an higher granulometry fraction of about 20 mesh, with multiplication factors of the stoichiometric ratio of 1.20 and 1.80.
TABLE V
Reaction kinetic with tailings of -20 mesh Reaction Multiplication factor of the stoichiometric ratio time (Tailings/HCl) (minutes) 1.20 1.80 0.0 0 0 0 0 0 0 2.5 17.2 17.0 19.7 31.8 49.7 53.7 S.0 27.2 28.4 30.9 46.2 72.3 77.4 7.5 38.1 39.7 42.7 52.7 82.6 88.1 10.0 53.2 55.6 59.3 58.1 91.0 96.7 12.5 64.5 67.3 71.8 57.5 90.1 95.5 15.0 69:1 72.2 76.9 58.1 91.0 96.5 As can be seen, with this granulometry and for a multiplication factor of the stroechiometric ratio equal to 1.20, the percentage of HCl used to dissolve Mg2+ and the other metal impurities was equal to 77% after a reaction time of 1 S minutes.
For a multiplication factor of the stoichiometric of 1.80, this percentage was equal to 97%
after a reaction time of 10 minutes.
In all the tests reported in Table IV and Table V and illustrated in figures 1 and 2, separation of the liquid phase from the residual solid phase has never been a problem.
Reaction kinetic with tailings of -20 mesh Reaction Multiplication factor of the stoichiometric ratio time (Tailings/HCl) (minutes) 1.20 1.80 0.0 0 0 0 0 0 0 2.5 17.2 17.0 19.7 31.8 49.7 53.7 S.0 27.2 28.4 30.9 46.2 72.3 77.4 7.5 38.1 39.7 42.7 52.7 82.6 88.1 10.0 53.2 55.6 59.3 58.1 91.0 96.7 12.5 64.5 67.3 71.8 57.5 90.1 95.5 15.0 69:1 72.2 76.9 58.1 91.0 96.5 As can be seen, with this granulometry and for a multiplication factor of the stroechiometric ratio equal to 1.20, the percentage of HCl used to dissolve Mg2+ and the other metal impurities was equal to 77% after a reaction time of 1 S minutes.
For a multiplication factor of the stoichiometric of 1.80, this percentage was equal to 97%
after a reaction time of 10 minutes.
In all the tests reported in Table IV and Table V and illustrated in figures 1 and 2, separation of the liquid phase from the residual solid phase has never been a problem.
Decantation occurred and the liquid phase was separated by conventional techniques of filtration by gravity or under vacuum. No silica gel was produced or no other gelatinization of the reaction products was detected.
Thus, the process according to the invention which uses an excess of asbestos tailings over the basic stoichiometric amount required for the reaction permits a quick and almost complete use of the hydrochloric acid. As a matter of fact, hydrochloric acid is the only starting material which is expensive in the lixiviation process.
Indeed, the asbestos tailings are of very low cost.
The process according to the invention is therefore particularly interesting if it is used on the premises of mines where the supply of asbestos tailings of the requested granulometry is easily available. Moreover, the disposal of the solid residues after reaction, even in excess, does not present any major problem in this particular case.
An amount of 2.16 kg of HCl 20% was introduced into a Becher of 4 liters. This solution was stirred and heated to 60°C. An amount of 0.96 kg of asbestos tailing having a granulometric fraction equal to or lower than 62 mesh was demagnetized and added thereto. Under these conditions, the multiplication factor of the stoichiometric ratio tailings/HCl was equal to 1.80. After 3 to 4 minutes, the reaction temperature reached 105 to 110°C. After a reaction time of 7.5 minutes, the pH of the suspension was equal to about 0.9 to 1Ø In this test, HCl was almost entirely used.
At the end of the reaction, the pH of the suspension was adjusted to 4.2-4.3 by addition of 15 g of MgO. The pH adjustment was almost instantaneous and the suspension was centrifugated in order to separate the liquid from the solids.
The centrifugal machine that was used was a laboratory centrifugal machine of trademark Soiltest model AP-174, having a capacity of 2 liters. The centrifugation speed was progressively raised up to 5000 rpm. The centrifugation time was about 10 minutes. The amount of salt solution that was recovered was equal to about 88% of the original amount of salt solution. The amount of salt solution retains in the solid after centrifugation was equal to 466 g per kg (384 cm3/kg).
For comparison purpose, the reaction residues were washed with water. This washing was repeated three times within the same centrifugation machine. The amount of water held in the solids after centrifugation was equal to 391 g per kg (391 cm3/kg), that is an amount slidely higher than the amount of salt solution retained during the centrifugation after lixiviation. These data indicate that the liquid retention is essentially due to the granulometry of the residues and not to the generation of a gelification system 5 during the lixiviation of the asbestos tailings with hydrochloric acid.
The pH of the salt solution recovered after the first centrifugation of the suspension obtained during the lixiviation was then adjusted a second time to 6.2-6.3 by addition of 52 g of Mg0 in order to transform the impurities present in the form of soluble metal chlorides into insoluble metal hydroxides. The suspension was again 10 filtered and Table VI hereinafter gives the composition of the salt solution that was so obtained.
TABLEAU VI
Composition of the salt solution The process of purification of the salt solution by successive adjustment of the pH to 4.2-4.3 and 6.2-6.3 is called "two-stage purification process" and this process is the one used in the industrial MgClz process called Riithner-HCl-Route. This is also a purification process disclosed in U.S. patent No. 5,091,161 (HARRIS et al).
The quick lixiviation process according to the invention can thus be used in combination with this conventional two-stage purification process.
A lixiviation process as disclosed in example 2 was carned out. After the time of reaction of 7.5 minutes, the pH of the suspension was adjusted to 6.2-6.3 by addition of 67 g of MgO. The adjustment of the pH was practically instantaneous and the suspension was centrifugated in order to separate the liquid from the solids.
The centrifugation conditions were identical to those described in example 2. The amount of salt solution that was recovered was equal to about 83% of the total amount of salt solution originally present. The amount of salt solution retained in the solids after centrifugation was equal 663 g per kg (551 cm3/kg). This amount is higher than the one reported in example 2, probably because of the presence of metal hydroxide of high specific surface area.
The composition of the salt solution that was so obtained is given in Table VII.
TABLE VII
Composition of the salt solution As can be seen, the quick lixiviation process according to the invention can also be used with a purification process carried out in a single stage.
Thus, the process according to the invention which uses an excess of asbestos tailings over the basic stoichiometric amount required for the reaction permits a quick and almost complete use of the hydrochloric acid. As a matter of fact, hydrochloric acid is the only starting material which is expensive in the lixiviation process.
Indeed, the asbestos tailings are of very low cost.
The process according to the invention is therefore particularly interesting if it is used on the premises of mines where the supply of asbestos tailings of the requested granulometry is easily available. Moreover, the disposal of the solid residues after reaction, even in excess, does not present any major problem in this particular case.
An amount of 2.16 kg of HCl 20% was introduced into a Becher of 4 liters. This solution was stirred and heated to 60°C. An amount of 0.96 kg of asbestos tailing having a granulometric fraction equal to or lower than 62 mesh was demagnetized and added thereto. Under these conditions, the multiplication factor of the stoichiometric ratio tailings/HCl was equal to 1.80. After 3 to 4 minutes, the reaction temperature reached 105 to 110°C. After a reaction time of 7.5 minutes, the pH of the suspension was equal to about 0.9 to 1Ø In this test, HCl was almost entirely used.
At the end of the reaction, the pH of the suspension was adjusted to 4.2-4.3 by addition of 15 g of MgO. The pH adjustment was almost instantaneous and the suspension was centrifugated in order to separate the liquid from the solids.
The centrifugal machine that was used was a laboratory centrifugal machine of trademark Soiltest model AP-174, having a capacity of 2 liters. The centrifugation speed was progressively raised up to 5000 rpm. The centrifugation time was about 10 minutes. The amount of salt solution that was recovered was equal to about 88% of the original amount of salt solution. The amount of salt solution retains in the solid after centrifugation was equal to 466 g per kg (384 cm3/kg).
For comparison purpose, the reaction residues were washed with water. This washing was repeated three times within the same centrifugation machine. The amount of water held in the solids after centrifugation was equal to 391 g per kg (391 cm3/kg), that is an amount slidely higher than the amount of salt solution retained during the centrifugation after lixiviation. These data indicate that the liquid retention is essentially due to the granulometry of the residues and not to the generation of a gelification system 5 during the lixiviation of the asbestos tailings with hydrochloric acid.
The pH of the salt solution recovered after the first centrifugation of the suspension obtained during the lixiviation was then adjusted a second time to 6.2-6.3 by addition of 52 g of Mg0 in order to transform the impurities present in the form of soluble metal chlorides into insoluble metal hydroxides. The suspension was again 10 filtered and Table VI hereinafter gives the composition of the salt solution that was so obtained.
TABLEAU VI
Composition of the salt solution The process of purification of the salt solution by successive adjustment of the pH to 4.2-4.3 and 6.2-6.3 is called "two-stage purification process" and this process is the one used in the industrial MgClz process called Riithner-HCl-Route. This is also a purification process disclosed in U.S. patent No. 5,091,161 (HARRIS et al).
The quick lixiviation process according to the invention can thus be used in combination with this conventional two-stage purification process.
A lixiviation process as disclosed in example 2 was carned out. After the time of reaction of 7.5 minutes, the pH of the suspension was adjusted to 6.2-6.3 by addition of 67 g of MgO. The adjustment of the pH was practically instantaneous and the suspension was centrifugated in order to separate the liquid from the solids.
The centrifugation conditions were identical to those described in example 2. The amount of salt solution that was recovered was equal to about 83% of the total amount of salt solution originally present. The amount of salt solution retained in the solids after centrifugation was equal 663 g per kg (551 cm3/kg). This amount is higher than the one reported in example 2, probably because of the presence of metal hydroxide of high specific surface area.
The composition of the salt solution that was so obtained is given in Table VII.
TABLE VII
Composition of the salt solution As can be seen, the quick lixiviation process according to the invention can also be used with a purification process carried out in a single stage.
Claims (20)
1. In a process for the preparation of a magnesium chloride solution wherein asbestos tailings are subjected to lixiviation with an aqueous hydrochloric acid solution having a concentration ranging between 18 and 25% by weight, the improvement wherein:
before the lixiviation, the asbestos tailings are treated in such a manner as to have a granulometry equal to or lower than 62 mesh;
use is made of asbestos tailings and hydrochloric acid (HCl) in such amounts that a suspension is obtained which, at the beginning of the lixiviation, has a stoichiometric ratio tailings/HCl ranging between 1.2 and 2.25; and the lixiviation is carried out at temperature ranging between 100°C and the temperature of ebullition of the suspension.
before the lixiviation, the asbestos tailings are treated in such a manner as to have a granulometry equal to or lower than 62 mesh;
use is made of asbestos tailings and hydrochloric acid (HCl) in such amounts that a suspension is obtained which, at the beginning of the lixiviation, has a stoichiometric ratio tailings/HCl ranging between 1.2 and 2.25; and the lixiviation is carried out at temperature ranging between 100°C and the temperature of ebullition of the suspension.
2. The improved process of claim 1, wherein the asbestos tailings used as starting material are previously demagnetized.
3. The improved process of claim 2, wherein the lixiviation is carried out for a period of time ranging from 5 and 15 minutes.
4. The improved process of claim 3, wherein the lixiviation is carried out for a period of time ranging from 5 to 7.5 minutes.
5. The improved process of claim 3, wherein the amounts of asbestos tailings and hydrochloric acid are such that the stoichiometric ratio tailings/HCl ranges between 1.6 and 2.
6. The improved process of claim 4, wherein the amounts of asbestos tailings and hydrochloric acid are such that the stoichiometric ratio tailings/HCl be equal to about 1.8.
7. The improved process of claim 3, wherein the lixiviation is carried out at temperature of about 110°C.
8. The improved process of claim 3, wherein the aqueous hydrochloric acid solution has a concentration equal to about 20% by weight.
9. The improved process of claim 3, wherein the lixiviation is carried out under stirring and comprises a preheating of the hydrochloric acid solution to a temperature of about 60°C followed by an addition of the asbestos tailings, said addition causing a fast increase of the temperature which is then kept at the requested value.
10. The improved process of claim 3, wherein, once the lixiviation is completed, the pH of the suspension is quickly increased to a value ranging between 4 and 5 and said suspension is then subjected to a separation in order to recover the requested magnesium chloride solution in the form of a first salt solution.
11. The improved process of claim 10, wherein the pH of the first salt solution that is recovered is increased to a value ranging from 6 and 7 and said first salt solution is then subjected to another separation in order to recover a second salt solution.
12. The improved process of claim 10, wherein the requested increases of the pH is achieved by addition of magnesium oxide into the suspension and first salt solution, respectively.
13. The improved process of claim 3, wherein, once the lixiviation is completed, the pH of the suspension is quickly increased to a value ranging from 6 and 7 and said suspension is subjected to a separation.
14. The improved process of claim 13, wherein the requested increase of the pH is achieved by addition of magnesium oxide into the suspension.
15. The improved process of claim 3, wherein:
the amounts of asbestos tailings and hydrochloric acid are such that the stoichiometric ratio tailings/HCl ranges between 1.6 and 2;
the aqueous hydrochloric acid solution has a concentration equal to about 20%
by weight;
the lixiviation is carried out under stirring and comprises a preheating of hydrochloric acid solution to a temperature of about 60°C followed by an addition of the asbestos tailings, said addition causing a fast increase of the temperature which is then kept at the requested value.
the amounts of asbestos tailings and hydrochloric acid are such that the stoichiometric ratio tailings/HCl ranges between 1.6 and 2;
the aqueous hydrochloric acid solution has a concentration equal to about 20%
by weight;
the lixiviation is carried out under stirring and comprises a preheating of hydrochloric acid solution to a temperature of about 60°C followed by an addition of the asbestos tailings, said addition causing a fast increase of the temperature which is then kept at the requested value.
16. The improved process of claim 15, wherein the lixiviation is carried out for a period of time ranging from 5 to 7.5 minutes at a temperature of about 110°C.
17. The improved process of claim 16, wherein the amounts of asbestos tailings and hydrochloric acid are such that the stoichiometric ratio tailings/HCl be equal to about 1.8.
18. The improved process of claim 17, wherein, once the lixiviation is completed, the pH of the suspension is quickly increased to a value ranging between 4 and 5 and said suspension is then subjected to a separation in order to recover the requested magnesium chloride solution in the form of a first salt solution.
19. The improved process of claim 18, wherein the pH of the first salt solution that is recovered, is increased to a value ranging from 6 and 7 and said first salt solution is then subjected to another separation in order to recover a second salt solution.
20. The improved process of claim 17, wherein, once lixiviation is completed, the pH of the suspension is quickly increased to a value ranging from 6 and 7 and said suspension is subjected to a separation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2235424 CA2235424A1 (en) | 1998-05-15 | 1998-05-15 | Process for the preparation of a magnesium chloride solution by quick lixiviation of asbestos tailings |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2235424 CA2235424A1 (en) | 1998-05-15 | 1998-05-15 | Process for the preparation of a magnesium chloride solution by quick lixiviation of asbestos tailings |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2235424A1 true CA2235424A1 (en) | 1999-11-15 |
Family
ID=29275580
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2235424 Abandoned CA2235424A1 (en) | 1998-05-15 | 1998-05-15 | Process for the preparation of a magnesium chloride solution by quick lixiviation of asbestos tailings |
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| CA (1) | CA2235424A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2930892A1 (en) * | 2008-05-07 | 2009-11-13 | Toulouse Inst Nat Polytech | PROCESS FOR TREATING AN INDUTRIAL WASTE COMPRISING ASBESTOS AND A HYDRAULIC BINDER |
| FR2930893A1 (en) * | 2008-05-07 | 2009-11-13 | Toulouse Inst Nat Polytech | PROCESS FOR TREATING ASBESTOSOLIDATE SOLID |
| FR3026032A1 (en) * | 2014-09-22 | 2016-03-25 | Paul Poggi | MOBILE UNIT OF ASBESTOS NEUTRALIZATION |
| CN111393127A (en) * | 2020-03-16 | 2020-07-10 | 华南理工大学 | Method for preparing silicon-magnesium gel from asbestos tailings magnetic separation iron fine powder and residues |
| US11331526B2 (en) | 2015-09-22 | 2022-05-17 | Paul Poggi | Method and stationary or movable device for neutralizing and recycling asbestos waste |
-
1998
- 1998-05-15 CA CA 2235424 patent/CA2235424A1/en not_active Abandoned
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2930892A1 (en) * | 2008-05-07 | 2009-11-13 | Toulouse Inst Nat Polytech | PROCESS FOR TREATING AN INDUTRIAL WASTE COMPRISING ASBESTOS AND A HYDRAULIC BINDER |
| FR2930893A1 (en) * | 2008-05-07 | 2009-11-13 | Toulouse Inst Nat Polytech | PROCESS FOR TREATING ASBESTOSOLIDATE SOLID |
| WO2009141566A2 (en) * | 2008-05-07 | 2009-11-26 | Institut National Polytechnique De Toulouse (Inpt) | Method for treating industrial waste containing asbestos and a hydraulic binding agent |
| WO2009141565A2 (en) * | 2008-05-07 | 2009-11-26 | Institut National Polytechnique De Toulouse (Inpt) | Method for treating an asbestos solid |
| WO2009141566A3 (en) * | 2008-05-07 | 2010-03-25 | Institut National Polytechnique De Toulouse (Inpt) | Method for treating industrial waste containing asbestos and a hydraulic binding agent |
| WO2009141565A3 (en) * | 2008-05-07 | 2010-05-27 | Institut National Polytechnique De Toulouse (Inpt) | Method for treating an asbestos solid |
| FR3026032A1 (en) * | 2014-09-22 | 2016-03-25 | Paul Poggi | MOBILE UNIT OF ASBESTOS NEUTRALIZATION |
| WO2016046493A1 (en) * | 2014-09-22 | 2016-03-31 | Paul Poggi | Method and system for neutralizing asbestos |
| US11331526B2 (en) | 2015-09-22 | 2022-05-17 | Paul Poggi | Method and stationary or movable device for neutralizing and recycling asbestos waste |
| CN111393127A (en) * | 2020-03-16 | 2020-07-10 | 华南理工大学 | Method for preparing silicon-magnesium gel from asbestos tailings magnetic separation iron fine powder and residues |
| CN111393127B (en) * | 2020-03-16 | 2021-07-20 | 华南理工大学 | Method for preparing silicon-magnesium gel from asbestos tailings magnetic separation iron fine powder and residues |
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