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WO1991007512A1 - Acid digestion of caustic calcined magnesite - Google Patents

Acid digestion of caustic calcined magnesite Download PDF

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Publication number
WO1991007512A1
WO1991007512A1 PCT/AU1990/000549 AU9000549W WO9107512A1 WO 1991007512 A1 WO1991007512 A1 WO 1991007512A1 AU 9000549 W AU9000549 W AU 9000549W WO 9107512 A1 WO9107512 A1 WO 9107512A1
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WO
WIPO (PCT)
Prior art keywords
magnesite
ore
product
process according
caustic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/AU1990/000549
Other languages
French (fr)
Inventor
Dagwin Elsner
Malcolm Timothy Frost
Pamela Maree Hoobin
Michael Henry Llewellyn Jones
David Andrew Mccallum
Grant Maxwell Wigg
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commonwealth Scientific and Industrial Research Organization CSIRO
Original Assignee
Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
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Publication of WO1991007512A1 publication Critical patent/WO1991007512A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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
    • 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
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/02—Roasting processes
    • 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
    • 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

Definitions

  • the present invention relates to a process for the production of a purified magnesium product from magnesite ores. It is known in the prior art to calcine magnesite at temperatures in the range of 700 to 1000°C to produce caustic calcined magnesite (caustic magnesia) which is readily soluble in dilute acids. It is also known in the prior art to conduct leaching processes on said caustic magnesia. However difficulties are encountered in removing impurities from the leach product. In particular iron, nickel, manganese, lead and copper are difficult and also expensive to remove. Nickel impurities, which are especially difficult to remove, are of considerable importance as they contribute to corrosion in the final magnesium metal product.
  • a process for the production of a purified magnesium product which process includes providing a source of acid; and a magnesite-containing ore; subjecting the magnesite-containing ore to a calcining step at elevated temperature to form a caustic calcined magnesite (caustic magnesia) ; and subjecting the caustic calcined magnesite to at least a first acid digestion wherein the pH is maintained at a predetermined generally constant value.
  • the magnesite-containing ore may be of any suitable type.
  • a macrocrystalline magnesite ore or cryptocrystalline magnesite ore may be used.
  • a cryptocrystalline magnesite ore is preferred.
  • a cryptocrystalline magnesite ore from the Kunwarara region or Oldman region of Australia has been found to be suitable.
  • the magnesite-containing ore may be calcined in any known manner.
  • the magnesite-containing ore may be heated at temperatures of approximately 650°C to 900°C, preferably 700 to 750°C under calcining conditions. The heating may continue for approximately 2 to 8 hours, preferably approximately 3 to 5 hours.
  • the caustic magnesia may be subjected to a multiple-stage acid digestion.
  • the caustic magnesia is subjected to a multi-stage acid digestion at generally constant pH to form a substantially digested product.
  • the pH is maintained generally constant during the multiple stages by the simultaneous addition of caustic magnesia and acid.
  • a concentrated acid may be used.
  • a concentrated hydrochloric acid may be used.
  • the multi-stage acid digestion may be conducted at a pH in the range of approximately 2 to 5, preferably 4 or less.
  • the caustic magnesia may be subjected to preliminary crushing and/or grinding steps prior to leaching.
  • the multi-stage acid digestion may be conducted in any suitable container.
  • the containers may be provided with stirring means to suspend the magnesia in the slurry during acid digestion.
  • Preferably the first acid digestion and subsequent acid digestions are conducted in separate containers.
  • the multi-stage acid digestion may be conducted at elevated temperatures. Temperatures in the range of approximately 50 to 120°C have been found suitable. The heat of reaction is sufficient to maintain rapid dissolution without additional heating.
  • the process according to the present invention may include a number of process steps designed to substantially reduce the level of impurities in the magnesium chloride liquor.
  • the process may further include providing a neutralizing agent; and an oxidizing agent; contacting the final acid digestion product with a predetermined amount of neutralizing agent to raise the pH to neutral or near-neutral; and contacting the neutralized product with a predetermined amount of oxidizing agent to precipitate impurities therefrom to produce a purified product.
  • the oxidizing agent may be of any suitable type.
  • An oxidant such as chlorine (Cl 2 ), air, oxygen or hydrogen peroxide (H 2 0 2 ) may be used. Chlorine is preferred.
  • the neutralizing agent may be of any suitable type. However, due to the ready availability of caustic magnesia (MgO) this is the preferred neutralizing agent. A slurry of caustic magnesia may be used. The oxidation and neutralization steps may be conducted together or in any order. Simultaneous oxidation and neutralization is preferred. The amount of oxidizing agent necessary to reduce to a low level the iron and manganese impurities may vary from approximately 1 to 25 times the theoretical requirement.
  • MgO caustic magnesia
  • the amount of neutralizing agent added to reduce to a low level the iron and manganese impurities may vary from approximately 0.5 to 5% of each unit of magnesium extracted.
  • the agitation was by 2-blade pitched impeller.
  • the temperature was controlled by hotplate.
  • the pH and the redox potential were measured with standard equipment.
  • the product liquor contained 35% (w/w) MgCl 2 , 1 mg/L Fe, 0.2 mg/L Cu, 0.3 mg/L Ni, 0.2 mg/L Mn, 2.4 mg/L Pb.
  • a magnesite-containing ore was subjected to calcination.
  • the calcination operating conditions were as follows: source of magnesite ore KG2 magnesite calcination temperature 800°C time of calcination 3 hours size of calcine 100% minus 250 microns
  • the continuous-leaching plant consisted of a single 5 litre unbaffled beaker.
  • Caustic magnesia produced from Kunwarara magnesite as described above and hydrochloric acid (33% w/w) were simultaneously fed to the vessel.
  • the dry magnesia was added by gravity from an overhead hopper using a screen feeder.
  • the feeding of the acid was by metering pump.
  • the resulting leach slurry was transferred from the leach vessel to a storage container by metering pump.
  • the agitation was by six-blade turbine impeller.
  • the operating conditions were as follows: leaching temperature : 85 to 100°C residence time : 1.25 hours pH maintained at approximately 5 during acid digestion step.
  • the resulting leach liquor contained 35% (w/w) MgCl 2 , 5.6 mg/L Fe, 1.1 mg/L Cu, 2.9 mg/L Ni, 6.5 mg/L Mn, and 2.9 mg/L Pb.
  • the product liquor contained 35% (w/w) MgCl 2 , 1.4 mg/L Fe, 1.1 mg/L Cu, 2.9 mg/L Ni, 0.5 mg/L Mn, 2.8 mg/L Pb.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Environmental & Geological Engineering (AREA)
  • Materials Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Abstract

A purified magnesium product is produced by subjecting a magnesite-containing ore to a calcining step at 650 to 900 °C for approximately 2 to 8 hours to form a caustic calcined magnesite. This is subjected to a single or multi-stage acid digestion at 50 to 120 °C, with a generally constant pH of 2 to 5.

Description

Acid digestion of caustic calcined magnesite
The present invention relates to a process for the production of a purified magnesium product from magnesite ores. It is known in the prior art to calcine magnesite at temperatures in the range of 700 to 1000°C to produce caustic calcined magnesite (caustic magnesia) which is readily soluble in dilute acids. It is also known in the prior art to conduct leaching processes on said caustic magnesia. However difficulties are encountered in removing impurities from the leach product. In particular iron, nickel, manganese, lead and copper are difficult and also expensive to remove. Nickel impurities, which are especially difficult to remove, are of considerable importance as they contribute to corrosion in the final magnesium metal product.
Particularly severe difficulties have been encountered where attempts have been made to apply purification processes known in the prior art to leach solutions produced from caustic magnesia under neutral or near-neutral conditions (neutral leach) .
Accordingly, it is an object of the present invention to overcome or at . least alleviate one or more of the difficulties related to the prior art. Accordingly, in a first aspect of the present invention there is provided a process for the production of a purified magnesium product which process includes providing a source of acid; and a magnesite-containing ore; subjecting the magnesite-containing ore to a calcining step at elevated temperature to form a caustic calcined magnesite (caustic magnesia) ; and subjecting the caustic calcined magnesite to at least a first acid digestion wherein the pH is maintained at a predetermined generally constant value.
The magnesite-containing ore may be of any suitable type. A macrocrystalline magnesite ore or cryptocrystalline magnesite ore may be used. A cryptocrystalline magnesite ore is preferred. A cryptocrystalline magnesite ore from the Kunwarara region or Oldman region of Australia has been found to be suitable.
The magnesite-containing ore may be calcined in any known manner. The magnesite-containing ore may be heated at temperatures of approximately 650°C to 900°C, preferably 700 to 750°C under calcining conditions. The heating may continue for approximately 2 to 8 hours, preferably approximately 3 to 5 hours.
As discussed above, in the process according to the present invention, the caustic magnesia may be subjected to a multiple-stage acid digestion. Preferably the caustic magnesia is subjected to a multi-stage acid digestion at generally constant pH to form a substantially digested product. The pH is maintained generally constant during the multiple stages by the simultaneous addition of caustic magnesia and acid. A concentrated acid may be used. A concentrated hydrochloric acid may be used. The multi-stage acid digestion may be conducted at a pH in the range of approximately 2 to 5, preferably 4 or less. Depending on the calcination procedure chosen, the caustic magnesia may be subjected to preliminary crushing and/or grinding steps prior to leaching.
The multi-stage acid digestion may be conducted in any suitable container. The containers may be provided with stirring means to suspend the magnesia in the slurry during acid digestion. Preferably the first acid digestion and subsequent acid digestions are conducted in separate containers.
The multi-stage acid digestion may be conducted at elevated temperatures. Temperatures in the range of approximately 50 to 120°C have been found suitable. The heat of reaction is sufficient to maintain rapid dissolution without additional heating.
Once the digestion process has been completed, the process according to the present invention may include a number of process steps designed to substantially reduce the level of impurities in the magnesium chloride liquor.
Accordingly, in a preferred aspect of the present invention the process may further include providing a neutralizing agent; and an oxidizing agent; contacting the final acid digestion product with a predetermined amount of neutralizing agent to raise the pH to neutral or near-neutral; and contacting the neutralized product with a predetermined amount of oxidizing agent to precipitate impurities therefrom to produce a purified product.
The oxidizing agent may be of any suitable type. An oxidant such as chlorine (Cl2), air, oxygen or hydrogen peroxide (H202) may be used. Chlorine is preferred.
Similarly the neutralizing agent may be of any suitable type. However, due to the ready availability of caustic magnesia (MgO) this is the preferred neutralizing agent. A slurry of caustic magnesia may be used. The oxidation and neutralization steps may be conducted together or in any order. Simultaneous oxidation and neutralization is preferred. The amount of oxidizing agent necessary to reduce to a low level the iron and manganese impurities may vary from approximately 1 to 25 times the theoretical requirement.
The amount of neutralizing agent added to reduce to a low level the iron and manganese impurities may vary from approximately 0.5 to 5% of each unit of magnesium extracted.
It has been found that the combination of oxidation and neutralization substantially reduces the amount of iron and manganese impurities in the magnesium chloride leach liquors. During the precipitation of iron and manganese, a number of other impurities may be completely or partially removed either by coprecipitation or adsorption on the precipitate formed. Such minor impurities which are reduced include copper (Cu) , lead
(Pb), aluminium (Al) , silica (Si02) and, importantly, nickel (Ni) .
It has been found surprisingly that the combination of oxidation and neutralization does not substantially reduce the level of impurities in magnesium chloride liquors derived from neutral leaching of caustic magnesia as in the prior art. In particular, the levels of nickel, iron, copper and lead remained unacceptably high.
However, according to the present invention it has been found that the combination of oxidation and neutralization of liquors derived from acid leaching of caustic magnesia substantially lowers the level of impurities. In particular, the concentration of nickel can be reduced to well below 1 mg/L. In the following description the invention will be more fully described with reference to the accompanying drawing and examples. It should be understood, however, that the following description is illustrative only and should not be taken in any way as a restriction on the generality of the invention described above.
In Figure 1 there is provided a flowsheet of a process for the leaching of caustic calcined magnesite according to the present invention and the subsequent purification of the leach liquor. EXAMPLE 1
Caustic magnesia was leached with hydrochloric acid in the apparatus described in Example 2. The operating conditions were as follows: caustic magnesia : as in Example 1 leaching temperature : 90 to 120 °C; no heating applied residence time : 1.25 hours. pH maintained at approximately 4 during acid digestion step. After filtration the resulting leach liquor contained 35% (w/w) MgCl2, 31 mg/L Fe, 9 mg/L Cu, 9 mg/L
Ni, 250 mg/L Mn, 5 mg/L Pb.
A portion of the above leach liquor was purified batchwise in an unbaffled 1 L beaker. The same caustic magnesia was used to neutralize the solution. Chlorine gas was the oxidizing agent which was added to the solution together with nitrogen as the carrier gas.
The agitation was by 2-blade pitched impeller. The temperature was controlled by hotplate. The pH and the redox potential were measured with standard equipment.
The operating conditions were as follows: temperature 50°C
PH 5.4 redox potential + 1000 mV residence time 3 hours.
After filtering off the solids, the product liquor contained 35% (w/w) MgCl2, 1 mg/L Fe, 0.2 mg/L Cu, 0.3 mg/L Ni, 0.2 mg/L Mn, 2.4 mg/L Pb.
EXAMPLE 2
A magnesite-containing ore was subjected to calcination. The calcination operating conditions were as follows: source of magnesite ore KG2 magnesite calcination temperature 800°C time of calcination 3 hours size of calcine 100% minus 250 microns
The continuous-leaching plant consisted of a single 5 litre unbaffled beaker. Caustic magnesia produced from Kunwarara magnesite as described above and hydrochloric acid (33% w/w) were simultaneously fed to the vessel. The dry magnesia was added by gravity from an overhead hopper using a screen feeder. The feeding of the acid was by metering pump. The resulting leach slurry was transferred from the leach vessel to a storage container by metering pump.
The agitation was by six-blade turbine impeller.
No heating was applied. The pH during leaching was monitored with standard pH measuring equipment.
The operating conditions were as follows: leaching temperature : 85 to 100°C residence time : 1.25 hours pH maintained at approximately 5 during acid digestion step.
After filtration the resulting leach liquor contained 35% (w/w) MgCl2, 5.6 mg/L Fe, 1.1 mg/L Cu, 2.9 mg/L Ni, 6.5 mg/L Mn, and 2.9 mg/L Pb.
A portion of the above leach liquor was purified by oxidation/neutralization as described in Example 1.
After filtering off the solids, the product liquor contained 35% (w/w) MgCl2, 1.4 mg/L Fe, 1.1 mg/L Cu, 2.9 mg/L Ni, 0.5 mg/L Mn, 2.8 mg/L Pb.
Finally, it is to be understood that various other modifications and/or alterations may be made without departing from the spirit of the present invention as outlined herein.

Claims

1. A process for the production of a purified magnesium product, which process includes providing a source of acid; and a magnesite-containing ore; subjecting the magnesite-containing ore to a calcining step at elevated temperature to form a caustic calcined magnesite; and subjecting the caustic calcined magnesia to at least a first acid digestion wherein the pH is maintained at a predetermined generally constant value.
2. A process according to Claim 1 wherein the calcining step includes heating the magnesite-containing ore to a temperature of approximately 650°C to 900°C under calcining conditions for approximately 2 to 8 hours.
3. A process according to Claim 2 wherein the caustic calcined magnesite is subjected to a multi-stage acid digestion at a generally constant pH in the range of approximately 2 to 5, to form a substantially digested product.
4. A process according to Claim 3, which process further includes providing a neutralizing agent; and an oxidizing agent; contacting the final acid digestion product with a predetermined amount of neutralizing agent to raise the pH to near-neutral; and contacting the neutralized product with a predetermined amount of oxidizing agent to precipitate impurities therefrom to produce a purified product.
5. A process according to Claim 4, wherein the oxidizing agent is selected from chlorine, oxygen, hydrogen peroxide or air; and the neutralizing agent is a magnesium oxide in the form of a caustic slurry.
6. A process according to Claim 1 wherein the magnesite containing ore is a cryptocrystalline magnesite ore.
7. A process according to Claim 3, wherein the magnesite ore is provided in the form of a slurry with a magnesium salt-containing liquor, and is subjected to preliminary crushing and/or grinding steps prior to or after mixing with the liquor.
8. A process for the production of a magnesium product from an ore containing magnesite, substantially as hereinbefore described with particular reference to the accompanying examples.
PCT/AU1990/000549 1989-11-16 1990-11-16 Acid digestion of caustic calcined magnesite Ceased WO1991007512A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPJ742989 1989-11-16
AUPJ7429 1989-11-16

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WO1991007512A1 true WO1991007512A1 (en) 1991-05-30

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE36369E (en) * 1994-07-15 1999-11-02 Martin Marietta Magnesia Specialties, Inc. Stabilized pressure-hydrated magnesium hydroxide slurry from burnt magnesite and process for its production
CN116835617A (en) * 2023-06-28 2023-10-03 沈阳理工大学 A method for preparing micro-nano magnesium carbonate series products by one-step magnesite leaching method

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU3328389A (en) * 1988-04-22 1989-10-26 Australian Magnesium Operations Pty Ltd Production of Magnesite Product

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU3328389A (en) * 1988-04-22 1989-10-26 Australian Magnesium Operations Pty Ltd Production of Magnesite Product

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, Volume 93, No. 24, issued 1980, December 15 (Columbus, Ohio, USA), K.V. SIMONOV et al., "Technological Features of the Concentration of Natural and Caustic Magnesite by a Hydrochloric Acid Method", page 57, Abstract No. 224565W; & OGNEUPORY, 1980, (7), 14-18 (Russ.). *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE36369E (en) * 1994-07-15 1999-11-02 Martin Marietta Magnesia Specialties, Inc. Stabilized pressure-hydrated magnesium hydroxide slurry from burnt magnesite and process for its production
CN116835617A (en) * 2023-06-28 2023-10-03 沈阳理工大学 A method for preparing micro-nano magnesium carbonate series products by one-step magnesite leaching method

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