WO1994011304A1 - Procede d'extraction des impuretes metalliques de la magnesite calcinee - Google Patents

Procede d'extraction des impuretes metalliques de la magnesite calcinee Download PDF

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Publication number
WO1994011304A1
WO1994011304A1 PCT/CA1992/000497 CA9200497W WO9411304A1 WO 1994011304 A1 WO1994011304 A1 WO 1994011304A1 CA 9200497 W CA9200497 W CA 9200497W WO 9411304 A1 WO9411304 A1 WO 9411304A1
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WIPO (PCT)
Prior art keywords
calcined magnesite
metal
temperature
magnesite
impurities
Prior art date
Application number
PCT/CA1992/000497
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English (en)
Inventor
Wendell E. Dunn, Jr.
Original Assignee
Deloro Magnesite Venture Fund
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
Application filed by Deloro Magnesite Venture Fund filed Critical Deloro Magnesite Venture Fund
Priority to AU29375/92A priority Critical patent/AU2937592A/en
Publication of WO1994011304A1 publication Critical patent/WO1994011304A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F5/00—Compounds of magnesium
    • C01F5/02—Magnesia

Definitions

  • Magnesite or magnesium carbonate (MgCO 3 ), is an important industrial source of magnesium. It is often referred to as “natural magnesium carbonate” or “crude magnesite” and can be readily decomposed upon heating, i.e., calcination, to magnesium oxide. Magnesite is a major industrial source of various grades of magnesium oxide (MgO), which is often also referred to as “magnesia” or “calcined magnesite.” The chemical activity of the various grades of magnesium oxide generally depend upon the temperature and duration of calcination.
  • Talc, silica, and other siliceous constituents are typically associated with magnesite in nature. These constituents can be present in amounts up to about 60% by weight. Iron is also present in magnesite, generally in the form of iron carbonates. It can be present in amounts up to about 10% by weight. Small amounts of other metals, such as nickel and manganese, generally in the form of carbonates, are also present. Significant amounts of talc, silica, and the siliceous constituents can generally be removed from the magnesite by a flotation process. The resulting magnesite concentrate typically still contains iron and other metal impurities, however.
  • the magnesite that has been subjected to a flotation process i.e., the flotation magnesite concentrate
  • a flotation process i.e., the flotation magnesite concentrate
  • the firing temperature used is generally below about 1450°C.
  • the resulting magnesium oxide can contain a small amount of CO 2 , e.g., about 2-10%.
  • This grade of magnesite is often referred to as "caustic-calcined magnesite,” “calcined magnesite,” or “calcined magnesia.” It typically displays absorptive capacity and moderate to high chemical
  • This grade of calcined magnesite is a refractory grade magnesium oxide and is often referred to as "dead- burnt magnesia.”
  • the metal carbonate impurities e.g., iron impurities
  • the iron oxides are generally in the form of ferrites, such as the magnesium ferrite MgO ⁇ Fe 2 O 3 .
  • the metal oxide impurities particularly the iron, detrimentally affects the refractory properties of the calcined magnesite.
  • the iron oxide impurities lowers the melting point of the refractory.
  • One method by which the metal impurities might be removed from calcined magnesite involves direct chlorination of the metal oxide impurities to form volatile metal chlorides.
  • treatment of calcined magnesite with chlorine gas at elevated temperatures requires reduction of the iron oxides along with
  • Chlorination processes such as these typically also result in the chlorination of MgO to MgCl 2 , thereby disadvantageously decreasing the amount of pure MgO formed.
  • the formation of even small amounts of liquid MgCl 2 can be detrimental to certain processing systems and cause interference with the reactor operation.
  • the presence of liquid MgCl 2 can destroy the fluidizability of the material. This is particularly true when the process is conducted within the temperature range in which the chlorination and volatilization of the metal impurities occurs at an economical and acceptable rate.
  • Fluidized beds are particularly sensitive to liquids, even tiny amounts, which can cause stickiness and destroy the fluidizability of the bed material.
  • Direct chlorination is not generally an
  • thermochemical calculations indicate that at very high temperatures it is possible to directly chlorinate a fully valent iron oxide, these temperatures are not economically efficient, and not suitable for an iron oxide impurity in an MgO system.
  • magnesium ferrite (MgO-Fe 2 O 3 ), which are very difficult to remove from calcined magnesite.
  • This single reduction step of the MgCO 3 starting material results in the formation of magnesium oxide and reduction of the iron carbonate
  • a method of purifying a titaniferous ore that uses carbon monoxide and chlorine (U.S. Patent No. 3,699,206, W.E. Dunn, Jr.).
  • the titaniferous ore which contains TiO 2 , however, typically contains much higher amounts of iron than does magnesite.
  • this method has not been considered practicable for materials containing very small amounts of metal impurities, such as iron, nickel, and manganese.
  • the formation of liquid MgCl 2 has also been considered an undesirable side effect of the process.
  • Yet another object of this invention is to provide the above conditions while removing a substantial amount of the iron, nickel, and manganese impurities.
  • Another object of the present invention is to achieve low levels of iron and other metal impurities in the final product in an economically efficient manner.
  • an object of the present invention is to conduct the process in a reactor of reasonable size, and under operating conditions that are economically efficient and minimize the use of reactants.
  • the present invention is directed to a process for the removal of metal oxide impurities, such as iron, nickel, and manganese, from calcined magnesite without producing significant amounts of magnesium chloride.
  • Calcined magnesite i.e., magnesium oxide (MgO)
  • MgO magnesium oxide
  • a process e.g., a flotation process, to remove silica, talc, and other siliceous components; and has been calcined under oxidizing conditions to remove volatile components and form calcined magnesite, i.e., magnesium oxide (MgO).
  • calcined natural magnesite the process is also envisioned to include the removal of metal impurities from magnesium oxide obtained from any other source and in any other manner.
  • the method of the present invention involves the use of a reducing gas capable of reducing oxides and ferrites of the metal impurities contained in the calcined magnesite to a lower valent state, in an alternating and cyclic manner with the use of a reducing gas followed by chlorine gas.
  • MgO is typically not placed in an environment or condition where the Cl 2 can preferentially attack it and make MgCl 2 .
  • the metal impurities e. g., iron, which are in a reduced metal oxide form after the reduction step, react preferentially with the Cl 2 to form metal chlorides, which are either volatile, such as FeCl 3 , or can be readily volatilized.
  • the process for removing metal impurities from contaminated, i.e., impure, magnesium oxide, preferably calcined magnesite includes the steps of: (1) contacting the impure magnesium oxide with a reducing gas capable of partially reducing oxides of the metal impurities to form magnesium oxide and partially reduced metal oxides, e.g., calcined magnesite containing partially reduced metal oxides; and (2) in the absence of a reducing gas,
  • volatilizable metal chlorides are formed. Although the reducing gas could totally reduce the impurity oxides if used in a great amount to zerovalent metals, it is
  • the process preferably involves using a calcined magnesite flotation concentrate, i.e., a still impure magnesium oxide obtained from the flotation and calcination of magnesium carbonate.
  • Calcined magnesite flotation concentrate typically contains about 65-80% material of less than 200 mesh, i.e., having a particle size of less than about 0.074 mm. With such a small particle size, the formation of more than trace amounts of liquid MgCl 2 can form a sticky mess that is very difficult to contend with in a fluidized bed reactor.
  • the process of the present invention involves cyclicly repeating the reducing and chlorinating steps until at least about 75% of the metal impurities are converted to volatilizable metal chlorides without the formation of MgCl 2 in more than trace amounts.
  • volatile metal chlorides e.g., iron chloride
  • volatilizable metal chlorides e.g., nickel and manganese chlorides
  • the reducing and chlorinating steps are repeated until at least about 90% of the metal impurities have been removed, and most preferably until at least about 95% have been removed.
  • the chlorination step of the process of the present invention is conducted at a temperature within a range of about 700-1100oC.
  • both the reducing step and the chlorinating step are conducted at a
  • both steps are conducted at a temperature within a range of about 750-1000°C.
  • both steps are advantageously and preferably conducted at a temperature within a range of about 750-850oC, and more preferably at a temperature within a range of about 750-800°C.
  • the present invention is directed toward further purification and improvement of contaminated, i.e., impure, magnesium oxide, preferably a calcined magnesite product, or a calcined magnesite concentrate produced from a
  • the calcined magnesite typically still contains iron impurities, as well as small amounts of nickel and manganese impurities. These metal impurities, particularly the iron impurities, can be effectively and efficiently removed by the method of the present invention.
  • the present invention involves chlorination at relatively high temperatures but in such a way that the chlorine does not react to a significant extent with the desired product of calcination, i.e., MgO, to produce
  • the method of the present invention it is possible to decrease the amount of metal impurities to a significantly low level in calcined magnesite.
  • at least about 75% of the metal impurities can be removed, more preferably at least about 90% can be removed, and most preferably at least about 95% can be removed.
  • the metal should be in a reduced oxide state, such as
  • Fe 3 O 4 rather than Fe 2 O 3 , but not in a completely reduced metallic iron state. This can be accomplished by first contacting the material with a reducing gas capable of partially reducing oxides of the metal impurities in calcined magnesite.
  • This reducing gas can be any that is capable of at least partially reducing the metal oxide impurities, i.e., the iron, nickel, and manganese impurities, within the calcined magnesite.
  • Producer gas is a low quality gas formed from hot carbon in a water- gas shift reaction.
  • the preferred reducing gas is CO.
  • the reduced metal oxides are only partially reduced oxides before the chlorine reaction step.
  • the metal oxides are generally never reduced to the zerovalent metal.
  • Fe 2 O 3 can be partially reduced to Fe 3 O 4 and then potentially further reduced to FeO, but FeO is not reduced further to zerovalent Fe, i.e., elemental iron, under the conditions of the present invention.
  • the reducing gas facilitates selective reduction of the metal oxide
  • the reducing gas reacts with Fe 2 O 3 to form Fe 3 O 4 but does not substantially react with the calcined
  • the reducing gas generally only reduces the iron oxide impurities and not the calcined magnesite. This is
  • the resultant reduced metal oxides are then contacted with chlorine gas to chlorinate the resultant reduced metal oxides to chlorides, which are volatilizable within the temperature range of the reaction.
  • Nickel and manganese chlorides are volatile at all temperatures within the temperature range of the process. Although nickel and manganese chlorides are not typically volatile at all temperatures within the temperature range of the process, under the conditions of the process of the invention they are capable of being volatilized, and thereby removed.
  • the chlorination step generally involves chlorination and volatilization of the metal impurities, e.g., iron oxides or ferrites, with the oxygen being left behind in the crystalline lattice.
  • the remaining metal impurities then combine with the oxygen and form the fully valent state.
  • volatile FeCl 3 and the fully valent Fe 2 O 3 are formed upon chlorination of the iron oxides Fe 3 O 4 and FeO.
  • invention generally involves the reduction of Fe 2 O 3 to Fe 3 O A and the chlorination of Fe 3 O 4 to FeCl 3 and Fe 2 O 3 ⁇
  • the contaminated magnesium oxide e.g., calcined magnesite.
  • the contaminated magnesium oxide is purged with an inert gas, such as N 2 or CO 2 , between the steps in which a reducing gas and Cl 2 are used.
  • the calcined magnesite is in a fine powdered form generally having a particle size of not greater than about 0.1 mm, and preferably not less than about 0.05 mm. More preferably the calcined magnesite has a particle size of not greater than about 0.074 mm, i.e., that which passes through a 200 mesh screen. Most preferably, the particle size of the calcined magnesite is about 0.05 mm to about 0.74 mm.
  • gas entrance concentrations of the reactants typically are about 100% to about 5%, more preferrably about 90% to 10%, and most preferrably about 75% to 15%. These percentages are based on volume.
  • Gas flow times for each portion of the cycle may vary for each gas, preferably with flow durations of about 1-10 minutes. More preferrably the gas flow times are about 2-8 minutes.
  • the inert gas purge time i.e., flow duration, is typically less than about 5 minutes, if an inert gas purge is used. More preferably, the inert gas purge time is about 1-3 minutes, and most preferrably about 1 minute. Gas concentrations, flow rates, and tiroes can be adjusted as the number of cycles increases to ensure total input to be above the stoichiometric demand for reduction and chlorination of the reduced metal oxides for that cycle.
  • a gaseous reductant accurately limits the time of the reduction step, and provides for a more precise separation of it from the chlorination step.
  • This type of process is designated herein as a "phased reaction,” i.e., one in which the reducing and chlorinating functions are separate steps.
  • the chlorination step of the cycling process is carried out at a temperature of about 700-1000°C.
  • both cycling steps i.e., the reduction and chlorination steps, are carried out at a temperature of about 700-1100°C, more preferably at a temperature of about 750-1000°C, and most preferably at a temperature of about 750-850oC, depending upon the calcination temperature and the heat balance requirements.
  • the cycling process steps are preferably carried out at a temperature of about 750-800°C. This temperature range is advantageous when highly active MgO is desired. Such active MgO is useful in coal-fired power plant scrubbers to remove sulfur from coal gases, and for acid neutralization in animal feed.
  • thermochemical reduction equilibria Although not limited to, thermochemical reduction equilibria.
  • Cyclical operation can be employed in any of a number of ways.
  • a batch reactor can be used, or the process can be carried out with a continuous solids feed to a set of reactors in series.
  • the process can also be carried out using a shaft furnace with pelletized calcined magnesite.
  • either batch or multiple reactor continuous flow can be employed, with the batch mode preferable.
  • a batch reaction mode two reactors in parallel are convenient and preferred, switching the Cl 2 and CO streams between the reactors, and recycling the excess gas as the iron content falls.
  • Example 1 A comparison of batch and continuous flow methods is presented in Example 1 and Table 2, which compares single reactor continuous flow and multiple reactor
  • velocities are usually limited by the feed particle size and the need for vigorous fluidization in order to fluidize a bed of MgO.
  • velocities, as well as concentrations of the gases, can vary during the process depending on the amount of metal impurities present, velocities can range from about 0.05 feet per second to about 0.5 feet per second, preferably from about 0.2 to 0.4 feet per second.
  • Cycle times can vary from two minutes to twenty minutes, preferably from three to ten minutes.
  • the number of cycles per batch is related to the "coefficient,” which is obtained by the equation:
  • %Fe represents the amount of Fe remaining after the process of the present invention
  • %Fe o represents the amount of Fe in the original sample
  • n is the number of cycles
  • x is the "coefficient,” which appears to remain substantially constant as the impurity, e.g., iron, content is reduced.
  • Gas concentrations are preferably varied as the metal impurity, particularly iron impurity, concentration varies.
  • the entering gas concentration can be lowered to avoid waste by the use of excess gas, particularly of Cl 2 .
  • gas velocities and flow times can vary as the concentration of metal impurities varies, so as to decrease the amount of waste gases.
  • the exiting gases from the fluidized reactor can be cooled in flues, preferably separate flues to effectuate gas recycling. Any CO 2 present could either be scrubbed from the CO stream or a portion by-passed to the CO
  • the method of the present invention is
  • the magnesite i.e., MgCO 3
  • MgCO 3 which has had the talc, silica, and other siliceous constituents removed
  • the calcined magnesite enters the reactor preferably at or near calcination temperatures, i.e., less than about 1450°C, preferably less than about 1100°C, and more preferably less than about 850oC.
  • the heat generated from the reduction/chlorination reactions is preferably used to maintain the temperature of the reactor.
  • the added surface area of MgO calcined at temperatures below about 800°C, and preferably at about 700°C to about 800°C, contributes significantly to reaction rates, such that lower temperatures of the reduction/chlorination process do not result in the expected lower rates of reaction and metal impurity removal .
  • thermochemistry as a guide, which is discussed in further detail below, the stages of the reduction of the metal impurities, e.g., iron reduction, can be characterized. Based on thermochemical values, one would expect cycle "coefficient" values to be 8/9ths;
  • thermodynamics of the process of the invention Although the scope of the invention is not to be bound by any particular theory, the following calculations and observations indicate the thermodynamics of the process of the invention. Also, the following discussion of the thermodynamics involved in the process of the present invention is discussed in terms of iron oxides, although this is not intended to be limiting in any manner.
  • thermodynamic tables results in an expected elimination of only about l/9th of the iron present per reduction/
  • Fe 2 O 3 to Fe 3 O 4 at 1000 K is 1.1 x 10 5 :1, which decreases with an increasing temperature to 2.7 x 10 4 :1 at 1300 K.
  • the second reduction step, Fe 3 O 4 to 3FeO has a CO 2 /CO ratio of only 1.43:1 at 1000 K, which increases to only 18.8:1 at 1300 K.
  • the ratio of the equilibria of the first reduction step to the second reduction step is 8539:1 at 1.000 K.
  • the ratio is still relatively high going from 8539:1 at 1000 K to 1451:1 at 1300 K. So, at all
  • thermochemical equilibria calculated from JANAF thermodynamic tables show the ease of reduction to Fe 3 O 4 from Fe 2 O 3 but the difficulty of going to FeO.
  • the "coefficients" are frequently below the 8/9ths value.
  • the amounts of the reducing gas and chlorine gas, the reaction temperature and velocity of the bed reactor can be varied with respect to each other as long as essentially no magnesium chloride is formed. These variables may be adjusted to improve the coefficient of iron removal and/or to improve economic efficiency.
  • Table 2 compares single reactor continuous flow with multiple reactor continuous flow, and with a batch method for removal of iron impurities using theoretical calculations.
  • the reactor used in this example consisted of a 4" diameter quartz reactor with a cone bottom, which was 48" tall with a 7" tall cone, and a side arm fitted with a ball joint to which was attached a glass condenser.
  • the reactor was heated with electrical windings so that the reactor zone and cone were held at the desired reaction
  • Magnesite flotation concentrate (2185 grams) was calcined at 1000oC to drive off volatile components, cooled, and removed from the reactor. The calcined
  • Gas flows were measured by capillary flow meters and the pressure was monitored by a water filled manometer.
  • the condition of the bed fluidization could be judged by the manometer fluctuations and confirmed by the state of the bed after cooling.
  • Table 3 shows the effect of widely varied conditions on the resulting coefficient.
  • An interesting effect of the calcination temperature is shown in comparing #3 and #4. Run #4, with a 1000oC calcination temperature and an 815°C reduction/chlorination temperature, was less effective at removing the iron, with a coefficient of

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Inorganic Chemistry (AREA)
  • Treating Waste Gases (AREA)

Abstract

Procédé d'extraction des impuretés métalliques, telles que, le fer, le manganèse et le nickel, d'un oxyde de magnésium impur, tel que la magnésite calcinée, sous des températures élevées. Le procédé consiste à exposer le matériau à un gaz réducteur capable de réduire partiellement les oxydes des impuretés métalliques puis à produire, avec du chlore, des chlorures métalliques volatilisables tout en limitant la formation de MgCl2. Les étapes de réduction et de chloration sont répétées cycliquement jusqu'à ce qu'environ 75 % des impuretés métalliques soient converties en chlorures métalliques volatilisables.
PCT/CA1992/000497 1992-11-12 1992-11-20 Procede d'extraction des impuretes metalliques de la magnesite calcinee WO1994011304A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU29375/92A AU2937592A (en) 1992-11-12 1992-11-20 Process for removing metal impurities from calcined magnesite

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US97508792A 1992-11-12 1992-11-12
US975,087 1992-11-12

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7070607B2 (en) 1998-01-27 2006-07-04 The Regents Of The University Of California Bioabsorbable polymeric implants and a method of using the same to create occlusions
CN104098280A (zh) * 2013-04-12 2014-10-15 沈阳铝镁设计研究院有限公司 一种低品位菱镁矿轻烧工艺
CN104098279A (zh) * 2013-04-12 2014-10-15 沈阳铝镁设计研究院有限公司 低品位菱镁矿轻烧工艺
CN111302672A (zh) * 2020-04-13 2020-06-19 鞍山盈丰新材料科技有限公司 一种电熔镁砂的加工原料及其制备方法
CN112094106A (zh) * 2020-08-19 2020-12-18 辽宁东和新材料股份有限公司 一种低二氧化硅含量的大结晶镁砂的制备方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2487497A (en) * 1948-05-08 1949-11-08 Permanente Metals Corp Process of purifying magnesia
US2571983A (en) * 1948-04-19 1951-10-16 Kaiser Aluminium Chem Corp Process of purifying magnesia containing impurities including iron, manganese, and boron
DE1592146B1 (de) * 1966-07-11 1972-04-27 Oesterr Amerikan Magnesit Verfahren zur herstellung von kaustischer magnesia oder sintermagnesia mit vermindertem eisengehalt
US3699206A (en) * 1970-03-23 1972-10-17 Dunn Inc Wendell E Process for beneficiation of titaniferous ores

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2571983A (en) * 1948-04-19 1951-10-16 Kaiser Aluminium Chem Corp Process of purifying magnesia containing impurities including iron, manganese, and boron
US2487497A (en) * 1948-05-08 1949-11-08 Permanente Metals Corp Process of purifying magnesia
DE1592146B1 (de) * 1966-07-11 1972-04-27 Oesterr Amerikan Magnesit Verfahren zur herstellung von kaustischer magnesia oder sintermagnesia mit vermindertem eisengehalt
US3699206A (en) * 1970-03-23 1972-10-17 Dunn Inc Wendell E Process for beneficiation of titaniferous ores

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7070607B2 (en) 1998-01-27 2006-07-04 The Regents Of The University Of California Bioabsorbable polymeric implants and a method of using the same to create occlusions
CN104098280A (zh) * 2013-04-12 2014-10-15 沈阳铝镁设计研究院有限公司 一种低品位菱镁矿轻烧工艺
CN104098279A (zh) * 2013-04-12 2014-10-15 沈阳铝镁设计研究院有限公司 低品位菱镁矿轻烧工艺
CN111302672A (zh) * 2020-04-13 2020-06-19 鞍山盈丰新材料科技有限公司 一种电熔镁砂的加工原料及其制备方法
CN111302672B (zh) * 2020-04-13 2021-11-19 鞍山盈丰新材料科技有限公司 一种电熔镁砂的加工原料及其制备方法
CN112094106A (zh) * 2020-08-19 2020-12-18 辽宁东和新材料股份有限公司 一种低二氧化硅含量的大结晶镁砂的制备方法

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