CA2263497A1 - Method for microwave induced oxidation of sulphidic ore material in fluidized bed without sulphur dioxide emissions - Google Patents
Method for microwave induced oxidation of sulphidic ore material in fluidized bed without sulphur dioxide emissions Download PDFInfo
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- CA2263497A1 CA2263497A1 CA002263497A CA2263497A CA2263497A1 CA 2263497 A1 CA2263497 A1 CA 2263497A1 CA 002263497 A CA002263497 A CA 002263497A CA 2263497 A CA2263497 A CA 2263497A CA 2263497 A1 CA2263497 A1 CA 2263497A1
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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
- 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
- C22B1/00—Preliminary treatment of ores or scrap
- C22B1/02—Roasting processes
- C22B1/10—Roasting processes in fluidised form
-
- 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
- C22B11/00—Obtaining noble metals
- C22B11/02—Obtaining noble metals by dry 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
- C22B15/00—Obtaining copper
- C22B15/0002—Preliminary treatment
- C22B15/001—Preliminary treatment with modification of the copper constituent
- C22B15/0013—Preliminary treatment with modification of the copper constituent by roasting
- C22B15/0015—Oxidizing roasting
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2208/00—Processes carried out in the presence of solid particles; Reactors therefor
- B01J2208/00008—Controlling the process
- B01J2208/00017—Controlling the temperature
- B01J2208/00026—Controlling or regulating the heat exchange system
- B01J2208/00035—Controlling or regulating the heat exchange system involving measured parameters
- B01J2208/00044—Temperature measurement
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- Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
Abstract
The present invention relates to a method for processing pyrite minerals, using a microwave energized fluidizing reactor, under temperature conditions that provide reaction products that are relatively free of SO2 emissions. The controlled temperature conditions at which the reaction products are hematite and elemental sulphur may be achieved by recirculating and cooling a portion of the outgoing fluidizing gas and by adjusting the microwave energy supplied to the fluidized bed.
Description
W O 98/08g8g PCT/CA97/00561 TITLE OF THE INVENTION
MEI~HOD FOR MICROWAVE INDUCED OXIDATION OF SULPH~DIC ORE MATERIAL lN
Fl,UII)l~ED BED WlTHOUT SULPHUR DIOXIDE F~ SJONS
REFERENCE TO RELATED CASES
This application is a colllihluation-in-part of U.S. Patent Application Serial No. 08/703,703 filed August 27, 1996, entitled "Method and Apparatus for Oxidation of Sulphidic Ores and Ore Concentrates Without the Production of Sulphur Dioxide Gas" by the same inventors herein ~IELD OF INVENTION
This invention relates to a microwave fluidized bed reactor which is used to oxidize pyritic ores by controlling microwave power density, oxygen conçentration and fl~ i7ing gas flow in such a way as to prevent oxidation of the sulphur into gaseous sulphur dioxide.
BACKGROUND OF THE lNVENTION
Many commercially important metals occur naturally in chP.mi~l composition with sulphur and iron, including gold and copper. These sulphidic compounds are difficult to process to a state where the important metals can be recovered.
Methods for separating metals from their sulphidic host minerals fall into two categories: Pyromet~llurgical recovery and hydrometallurgical recovery.Pyrometallurgical recovery involves heating the ore mass and in the process decomposing the sulphide through oxidation resulting in the formation of sulphurdioxide gas. Hydrometallurgical recovery on the other hand involves the dissolution , .... .. . . . . . .. . .
WO 98/08g89 PC~/CA97/0~561 of the ore con~ti~lent~ in a liquid medium in which one or more chemical reactions can be initiated which will cause the important metals to form a new, recoverable compound. Pyrometallurgical recovery is unsatisfactory today because of the for~nation of sulphur dioxide gas in the so-called roaster oxidation reaction.
Accordingly, this technique has largely been abandoned due to legi.cl~ti-~n restricting sulphur dioxide emissions. Hydrometallurgical recovery is also an unsatisfactoryprocess because metal recovery is hindered and, in many cases, rendered practically useless in the presence of sulphidic compounds.
Recent developments in this area include bio-oxidation where bacterial enzymes are used to oxidize sulphidic ores. However, this process is highly sensitive to variables such as Le~ eldture~ sulphur concentration, and the presence of other minerals that may be toxic to the bacteria. Furthermore, the process is extremely expensive and relatively slow, rçn-l~ring it commercially unviable in many situations.
Conventional pyrite roaster reactions are described by:
(I) FeS2 ~ FeS + S
al) 4FeS + 7~2 ~ 2Fe203 + 4SO2 (m) S+O2~S02 In reaction (I), pyrite (FeS2) is decomposed into pyrrhotite (FeS) and elementalsulphur (S). In the presence of oxygen and at sufficiently high temperature the associated reactions (II) and (m) include the oxidation of pyrrhotite to form hematite and sulphur dioxide, and of sulphur to form sulphur dioxide. These reactions arehighly exothermic, hence it is not possible in conventional roasting reactors to prevent the temperature from increasing to the point where SO2 is produced. In fact, in conventional roaster operation, this exothermic energy is necessary to provide the reaction energy needed to cause (I) to occur. This reaction, when augmented by steam and oxygen, may be used as a means of producing high quality SO2 as a desired product, as disclosed by Jukkola in United States Patent No. 3,632,312.
An alternative reaction to (I) - (m) is:
(IV) 2FeS2 ~ 1.502 ~ Fe203 ~ 4S
by which pyrite is oxidized directly into h~m~ite and elemental sulphur. Table 1 and Figure 4 present a thermodynamic analysis of this reaction at various temperatures.
Tryer, for example, teaches this reaction (IV) in Australian Patent No. 9674.
However, Tryer states in his disclosure that it is necçs.s~ry to m~in1~in the operating temperature within the range 800~C - 1000~C to promote the combination of a highconcentration of SO2 with ferrous sulphide to produce sulphur, a process which often requires the introduction of additional SO2 to make up the neces.s~ry concentration.
An associated reaction, the combination of sulphur with hPm~tite to form m~gn~tite (Fe3O4) and SO2 is described by:
(V) 3Fe,03 + S ~ 2Fe304 + O.SSO2 which is described in Table 2 and Figure 3 and which is favored only for temperatures above approximately 800~K (527~C).
Thus, in order for reaction (IV) to be favored and to avoid the entire roaster reaction a-m), the operating temperature must be m~int~ined below approxil,lately 1000~K (727~C). Further, in order to avoid the reaction (V) the te"lpe~ re must be m~int~in~d below approximately 800~K (527~C) The most strongly favored pyrite reaction is the one which produces hematite (Fe2O3) and SO2 shown as the lowermost curve in Figure 4 from data in Table 3. In order to avoidthis reaction, oxygen must be restricted to allow the production of elemental sulphur (central curve in Figure 4). Accordingly, to limit SO2 production, the preferredoperating temperature is below 527~C where the reaction products of pyrite and oxygen are restricted to hematite and sulphur as described in reaction (IV).
The ability to m~int~in the otherwise highly exothermic oxidation reaction temperature below 527~C requires separate control of: (1) the oxygen supplied to the reaction; (2) the power (energy) introduced into the material; and (3) the gas flow through the reaction environment (coolant). Control of the aforesaid factors can be achieved, in association with the present invention, using a fluidi_ed bed reactor with power supplied by microwave energy, for treating pyritic mineral ore.
Fl~-irli7.ed bed reactors are presently widely used in many ore processing applications where strong interaction between a solid product and gasmedium is required and the use of microwave energy to provide some or all of therequired reaction energy has been disclosed in, for example, U.S. Patents Nos.
.. ....
CA 02263497 l999-02-l6 3,528,179; 4,126,945; 4,967,486; 4,511,362; 4,476,098; 5,382,412 and 5,051,456.
The use of a fluidi7ed bed reactor with a microwave source of power provides the ability to control the oxygen supply to the material undergoing treatment (which governs the rate of reaction and hence reaction temperature) independently of the microwzve power (which supplies the energy to initiate the chemical reaction and compensates for other energy losses). The use of microwave energy also provided the unique ability to selectively heat certain materials in the presence of lessabsorptive gangue m~teli~l~ as is the case with pyritic ores.
The exhaust stream from the reactor is depleted of oxygen as a con~P~uenre of the oxidation reaction with the fluidi_ed bed and consists principally of rutrogen. It has been found that by diverting and preferably cooling the exhaust stream and reintroducing it into the reactor with the fluidizing stream that it is effective as a coolant and thus provides the final factor required to achieve the preferred chemical reaction to process pyrite minerals under telllpe~dLIn~ conditions that provide reaction products that are free of SO2 emissions.
SU~IMARY OF THE IlWENTION
Thus the invention comprises a method of oxidizing pyritic ores using a reaction vessel. The method comprises the steps of: (a) fluidi_ing a bed of pyritic ore in said reactor using a fluidi_ing gas; (b) heating said bed of ore with microwave energy to initiate an exothermic oxidation reaction in the bed; and (c) cooling the lenll)eldlul~ of the reaction in said bed to a temperature at which the p~ere~led reaction products are hP.m~tite and elemental sulphur.
The invention also comprises a method of oxidizing pyritic ores using a fl~ li7ing bed reactor. The method comprises the steps of: (a) heating a bed of pyritic ore with microwave energy to initiate an exothermic oxidation reaction within the bed; (b) controlling the in~low of oxygen to the reaction in the reaction chamber;
and (c) cooling the tel"pe-dlul~ of the reaction in said bed to a tt;lllpeld~ule at which the reaction products are hem~tite and elemental sulphur, while Contin~ing to supply said bed with microwave energy to selectively heat the pyrite in the presence of m~gn~tite and hP.~ e.
The invention still further comprises a method for the oxitli7~tion of pyritic ores, without the production of SO2 as a by product, using a fluidized bed reactor powered by microwave energy. The method comprises the steps of: (a) isolating the vent gases from the reactor when in operation; (b) cooling the said vent gases; and (c) re-introducing the vent gases into the fluidization gases in the reactor to cool the internal reaction temperature.
BRIEF DESCRIPTION OF THE DR~WlNGS
The following is a description by way of example of a preferred embodiment of the present invention, reference being made to the accompanying drawings in which:
FIGURE I is a cross sectional view of a flui~li7ed bed reactor of the present invention;
FIGURE 2 is a graph showing thermodynamic stability data of Table l;
FIGURE 3 is a graph showing thermodynamic stability data of Table 2; and FIGURE 4 is a graph showing the Gibbs Free Energy for various pyrite reactions from data of Table 3.
While the invention will be described in conjunction with the i1hlstrate~1 embodiment, it will be understood that it is not intended to limit the invention to such embodiment. On the contrary, it is inte.ndec~ to cover all alternatives, modifîcations and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the drawings, similar features have been given similar reference numerals. As illustrated in Figure 1 a reactor vessel, such as a fluidized bed reactor .. , . ... . . . .. _ .
W O 98/08989 PCTICA97/00~61 10, comprises a tubular waveguide resonator reaction chamber or cavity 12, bed fluidizer screen 14, and a pressure chamber 16. The reaction chamber 12 is connecteA
to a microwave energy source via waveguide fittings 18 and 20 which may include a coupling iris (not shown) as well as a pressurized gas seal 22. T~e reaction chamber 12 has a material inlet valve 24, material exit valve 26, gas inlet valve 28 and a gas exhaust port 30. Exhaust port 30 is connected to pipe 40 which is in turn connected to particulate separator 42 (which may be a cyclonic s~al~lol), and a first control valve 44. Control valve 44 is connected by pipe 41 to heat exchanger 46 and second control valve 48, which is connected by pipe 43 to the gas inlet valve 28.
Pipe 40 has a gas exit port temperature monitor 50 and an SO2 sensor 52.
Solid material to be processed, usually pyritic ore, is introduced through the inlet valve and is to be flni(li7e~1 by gas 32 which is supplied from an external source through pipe 43 to control valve 48 and the gas inlet valve 28. The introduction of gas will cause the material which has been introduced through the inlet valve to form a fluidized bed 34 which is suspended through the adjustment of the gas pressure in the pl'~SSUIt; chamber 16 and the bed fluidizer screen 14. The fluidized bed is then ready for treatment with microwave energy which is introduced into the reaction chamber from the top via the waveguide fittings. When the bed is in a fluidized state, the solid material is heated by the dielectric and resistive effects caused by interaction between the electrom~gnlotic field and the solid material constit"ent~ .
The flni~ ing gas will be continuously pumped through valve 28 and exh~ ted through port 30 during the treatment process. The exhaust stream will be passed through particulate separator 42 to clean the gas of particulate matter (either fines blown free from the fluidized bed or sulphur powder produced from the reaction). The stream will then pass through control valve 44 by which some or all of the exhaust stream, which will be depleted of ~2 and consist primarily of N2, can be recirculated back to the chamber after being passed through heat exchanger 46 and second control valve 48. Second control valve 48 allows the exhaust gas to be mixed with fresh air, or gases (if required), to provide the fluidizing stream and act as a coolant for the reaction chamber to achieve the l~r~fc. .cd chemical reaction to process CA 02263497 l999-02-l6 pyrite minerals under tel~peldlu,~ conditions that provide reaction products that are free of SO2 emissions The region 36 above the suspended fluidized bed 34 is generally esse.nti~lly free of solid material and consists primarily of fluidized gas and gaseous reaction products. The gas seal 22 permits the tr~n~mi.~ion of microwave energy into the reaction chamber 12 while isolating the atmosphere and contents of the chamber from the connPcting waveguide attached via fittings 18 and 20.
Tre~tment of a pyritic ore, according to the present invention, will now be described in greater detail.
The pyritic ore is loaded into the reaction chamber 12 through valve 24. The ore is then fluidized into the bed 34 by pumping a fluidizing gas, which is generally just air, through valve 28. Next microwave energy is applied, via the waveguide fitting. The microwave energy raises the fluidized bed to the ,~ r~d operating temperature in the range of about 300~C - 550~C, where as can be seen from the data of Table 1 and shown in Figure 2, pyrite is prerel~d over pyrrhotite.
Additionally, as can be seen in Table 2 and Figure 3, recombination of hematite and sulphur (reaction (IV)) is not favoured at temperatures below 550~C. Once the lellll)eldlllre of the bed has been raised to aboul 300~C the sulphur-hematite reaction commences If the tempeldlur~ rises too quickly (i.e. the N2 in the vent gasses is not yet sufficient to restrict the amount of ~2 and thus cool the reaction), N2 can be introduced into the fluidizing strea~n via valve 48. The reaction can be monitored by checking the particulate separator 42, which will reveal the presence of sulphur, an in~ tor of the reaction, or by a tell-peldlllre spike from temperature probe 50 since the initial pyrite reaction is exothermic.
In view of the fact that pyrite reaction is extremely exothPrrnic, the - temperature of the reaction chamber will continue to rise (in conventional reactors the running lempelature is usually between 600~C and 750~C), causing the release of SO2; unless the reaction is cooled to favour reaction (IV).
First of all, the reaction can be cooled by re l~cing the input of microwave energy; although, as will be ~ cu.~sec7 below, it is preferable to m~int~in at least some input of microwave energy, in the range of 0.5kw. The second control , ~ CA 02263497 1999-02-16 C.
of the reaction temperature is through the manipulation of the recirculating gases which, due to the reaction in the chamber, has been reduced to primarily N~. If the r,~ction has not sufficiently reduced the ~2 from the circulating gases, additional inert gasses can be introduced into the stream to control the amount of O~ in the reactor.
Additionally, the recirc~ ting gases themselves can be cooled prior to reintroduction into the reaction chamber.
Pyrite can be selectively heated while in the presence of m~gn~titç and hem~tite since it absorbs microwave energy more efficiently. Accordingly, it may be treated by the continued application of microwave energy during the exothermic reaction which is ongoing in the reaction chamber while at the same time the mass of the bed is being cooled by the recirc~ ting gas stream.
Once the trç~tmPnt process has been completed and the fluidized material appropliately heated or processed, it is ejected from the reactor through port 30 by increasing the flui~i7ing gas pressure. Any material which has fallen through screen 14 during loading and processing of the chamber is removed through valve 26.
Although described as preferably being tubular, the reaction chamber 12 can be of any appropriate dimension or geometry as dictated by the microwave field distribution. Additionally, while being described as an iris coupled resonator, the reaction chamber may operate as a termin~t~ waveguide (iris fully open) in which case the absorptive action of the load material gives the reactor the characteristics of a travelling-wave applicator.
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MEI~HOD FOR MICROWAVE INDUCED OXIDATION OF SULPH~DIC ORE MATERIAL lN
Fl,UII)l~ED BED WlTHOUT SULPHUR DIOXIDE F~ SJONS
REFERENCE TO RELATED CASES
This application is a colllihluation-in-part of U.S. Patent Application Serial No. 08/703,703 filed August 27, 1996, entitled "Method and Apparatus for Oxidation of Sulphidic Ores and Ore Concentrates Without the Production of Sulphur Dioxide Gas" by the same inventors herein ~IELD OF INVENTION
This invention relates to a microwave fluidized bed reactor which is used to oxidize pyritic ores by controlling microwave power density, oxygen conçentration and fl~ i7ing gas flow in such a way as to prevent oxidation of the sulphur into gaseous sulphur dioxide.
BACKGROUND OF THE lNVENTION
Many commercially important metals occur naturally in chP.mi~l composition with sulphur and iron, including gold and copper. These sulphidic compounds are difficult to process to a state where the important metals can be recovered.
Methods for separating metals from their sulphidic host minerals fall into two categories: Pyromet~llurgical recovery and hydrometallurgical recovery.Pyrometallurgical recovery involves heating the ore mass and in the process decomposing the sulphide through oxidation resulting in the formation of sulphurdioxide gas. Hydrometallurgical recovery on the other hand involves the dissolution , .... .. . . . . . .. . .
WO 98/08g89 PC~/CA97/0~561 of the ore con~ti~lent~ in a liquid medium in which one or more chemical reactions can be initiated which will cause the important metals to form a new, recoverable compound. Pyrometallurgical recovery is unsatisfactory today because of the for~nation of sulphur dioxide gas in the so-called roaster oxidation reaction.
Accordingly, this technique has largely been abandoned due to legi.cl~ti-~n restricting sulphur dioxide emissions. Hydrometallurgical recovery is also an unsatisfactoryprocess because metal recovery is hindered and, in many cases, rendered practically useless in the presence of sulphidic compounds.
Recent developments in this area include bio-oxidation where bacterial enzymes are used to oxidize sulphidic ores. However, this process is highly sensitive to variables such as Le~ eldture~ sulphur concentration, and the presence of other minerals that may be toxic to the bacteria. Furthermore, the process is extremely expensive and relatively slow, rçn-l~ring it commercially unviable in many situations.
Conventional pyrite roaster reactions are described by:
(I) FeS2 ~ FeS + S
al) 4FeS + 7~2 ~ 2Fe203 + 4SO2 (m) S+O2~S02 In reaction (I), pyrite (FeS2) is decomposed into pyrrhotite (FeS) and elementalsulphur (S). In the presence of oxygen and at sufficiently high temperature the associated reactions (II) and (m) include the oxidation of pyrrhotite to form hematite and sulphur dioxide, and of sulphur to form sulphur dioxide. These reactions arehighly exothermic, hence it is not possible in conventional roasting reactors to prevent the temperature from increasing to the point where SO2 is produced. In fact, in conventional roaster operation, this exothermic energy is necessary to provide the reaction energy needed to cause (I) to occur. This reaction, when augmented by steam and oxygen, may be used as a means of producing high quality SO2 as a desired product, as disclosed by Jukkola in United States Patent No. 3,632,312.
An alternative reaction to (I) - (m) is:
(IV) 2FeS2 ~ 1.502 ~ Fe203 ~ 4S
by which pyrite is oxidized directly into h~m~ite and elemental sulphur. Table 1 and Figure 4 present a thermodynamic analysis of this reaction at various temperatures.
Tryer, for example, teaches this reaction (IV) in Australian Patent No. 9674.
However, Tryer states in his disclosure that it is necçs.s~ry to m~in1~in the operating temperature within the range 800~C - 1000~C to promote the combination of a highconcentration of SO2 with ferrous sulphide to produce sulphur, a process which often requires the introduction of additional SO2 to make up the neces.s~ry concentration.
An associated reaction, the combination of sulphur with hPm~tite to form m~gn~tite (Fe3O4) and SO2 is described by:
(V) 3Fe,03 + S ~ 2Fe304 + O.SSO2 which is described in Table 2 and Figure 3 and which is favored only for temperatures above approximately 800~K (527~C).
Thus, in order for reaction (IV) to be favored and to avoid the entire roaster reaction a-m), the operating temperature must be m~int~ined below approxil,lately 1000~K (727~C). Further, in order to avoid the reaction (V) the te"lpe~ re must be m~int~in~d below approximately 800~K (527~C) The most strongly favored pyrite reaction is the one which produces hematite (Fe2O3) and SO2 shown as the lowermost curve in Figure 4 from data in Table 3. In order to avoidthis reaction, oxygen must be restricted to allow the production of elemental sulphur (central curve in Figure 4). Accordingly, to limit SO2 production, the preferredoperating temperature is below 527~C where the reaction products of pyrite and oxygen are restricted to hematite and sulphur as described in reaction (IV).
The ability to m~int~in the otherwise highly exothermic oxidation reaction temperature below 527~C requires separate control of: (1) the oxygen supplied to the reaction; (2) the power (energy) introduced into the material; and (3) the gas flow through the reaction environment (coolant). Control of the aforesaid factors can be achieved, in association with the present invention, using a fluidi_ed bed reactor with power supplied by microwave energy, for treating pyritic mineral ore.
Fl~-irli7.ed bed reactors are presently widely used in many ore processing applications where strong interaction between a solid product and gasmedium is required and the use of microwave energy to provide some or all of therequired reaction energy has been disclosed in, for example, U.S. Patents Nos.
.. ....
CA 02263497 l999-02-l6 3,528,179; 4,126,945; 4,967,486; 4,511,362; 4,476,098; 5,382,412 and 5,051,456.
The use of a fluidi7ed bed reactor with a microwave source of power provides the ability to control the oxygen supply to the material undergoing treatment (which governs the rate of reaction and hence reaction temperature) independently of the microwzve power (which supplies the energy to initiate the chemical reaction and compensates for other energy losses). The use of microwave energy also provided the unique ability to selectively heat certain materials in the presence of lessabsorptive gangue m~teli~l~ as is the case with pyritic ores.
The exhaust stream from the reactor is depleted of oxygen as a con~P~uenre of the oxidation reaction with the fluidi_ed bed and consists principally of rutrogen. It has been found that by diverting and preferably cooling the exhaust stream and reintroducing it into the reactor with the fluidizing stream that it is effective as a coolant and thus provides the final factor required to achieve the preferred chemical reaction to process pyrite minerals under telllpe~dLIn~ conditions that provide reaction products that are free of SO2 emissions.
SU~IMARY OF THE IlWENTION
Thus the invention comprises a method of oxidizing pyritic ores using a reaction vessel. The method comprises the steps of: (a) fluidi_ing a bed of pyritic ore in said reactor using a fluidi_ing gas; (b) heating said bed of ore with microwave energy to initiate an exothermic oxidation reaction in the bed; and (c) cooling the lenll)eldlul~ of the reaction in said bed to a temperature at which the p~ere~led reaction products are hP.m~tite and elemental sulphur.
The invention also comprises a method of oxidizing pyritic ores using a fl~ li7ing bed reactor. The method comprises the steps of: (a) heating a bed of pyritic ore with microwave energy to initiate an exothermic oxidation reaction within the bed; (b) controlling the in~low of oxygen to the reaction in the reaction chamber;
and (c) cooling the tel"pe-dlul~ of the reaction in said bed to a tt;lllpeld~ule at which the reaction products are hem~tite and elemental sulphur, while Contin~ing to supply said bed with microwave energy to selectively heat the pyrite in the presence of m~gn~tite and hP.~ e.
The invention still further comprises a method for the oxitli7~tion of pyritic ores, without the production of SO2 as a by product, using a fluidized bed reactor powered by microwave energy. The method comprises the steps of: (a) isolating the vent gases from the reactor when in operation; (b) cooling the said vent gases; and (c) re-introducing the vent gases into the fluidization gases in the reactor to cool the internal reaction temperature.
BRIEF DESCRIPTION OF THE DR~WlNGS
The following is a description by way of example of a preferred embodiment of the present invention, reference being made to the accompanying drawings in which:
FIGURE I is a cross sectional view of a flui~li7ed bed reactor of the present invention;
FIGURE 2 is a graph showing thermodynamic stability data of Table l;
FIGURE 3 is a graph showing thermodynamic stability data of Table 2; and FIGURE 4 is a graph showing the Gibbs Free Energy for various pyrite reactions from data of Table 3.
While the invention will be described in conjunction with the i1hlstrate~1 embodiment, it will be understood that it is not intended to limit the invention to such embodiment. On the contrary, it is inte.ndec~ to cover all alternatives, modifîcations and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the drawings, similar features have been given similar reference numerals. As illustrated in Figure 1 a reactor vessel, such as a fluidized bed reactor .. , . ... . . . .. _ .
W O 98/08989 PCTICA97/00~61 10, comprises a tubular waveguide resonator reaction chamber or cavity 12, bed fluidizer screen 14, and a pressure chamber 16. The reaction chamber 12 is connecteA
to a microwave energy source via waveguide fittings 18 and 20 which may include a coupling iris (not shown) as well as a pressurized gas seal 22. T~e reaction chamber 12 has a material inlet valve 24, material exit valve 26, gas inlet valve 28 and a gas exhaust port 30. Exhaust port 30 is connected to pipe 40 which is in turn connected to particulate separator 42 (which may be a cyclonic s~al~lol), and a first control valve 44. Control valve 44 is connected by pipe 41 to heat exchanger 46 and second control valve 48, which is connected by pipe 43 to the gas inlet valve 28.
Pipe 40 has a gas exit port temperature monitor 50 and an SO2 sensor 52.
Solid material to be processed, usually pyritic ore, is introduced through the inlet valve and is to be flni(li7e~1 by gas 32 which is supplied from an external source through pipe 43 to control valve 48 and the gas inlet valve 28. The introduction of gas will cause the material which has been introduced through the inlet valve to form a fluidized bed 34 which is suspended through the adjustment of the gas pressure in the pl'~SSUIt; chamber 16 and the bed fluidizer screen 14. The fluidized bed is then ready for treatment with microwave energy which is introduced into the reaction chamber from the top via the waveguide fittings. When the bed is in a fluidized state, the solid material is heated by the dielectric and resistive effects caused by interaction between the electrom~gnlotic field and the solid material constit"ent~ .
The flni~ ing gas will be continuously pumped through valve 28 and exh~ ted through port 30 during the treatment process. The exhaust stream will be passed through particulate separator 42 to clean the gas of particulate matter (either fines blown free from the fluidized bed or sulphur powder produced from the reaction). The stream will then pass through control valve 44 by which some or all of the exhaust stream, which will be depleted of ~2 and consist primarily of N2, can be recirculated back to the chamber after being passed through heat exchanger 46 and second control valve 48. Second control valve 48 allows the exhaust gas to be mixed with fresh air, or gases (if required), to provide the fluidizing stream and act as a coolant for the reaction chamber to achieve the l~r~fc. .cd chemical reaction to process CA 02263497 l999-02-l6 pyrite minerals under tel~peldlu,~ conditions that provide reaction products that are free of SO2 emissions The region 36 above the suspended fluidized bed 34 is generally esse.nti~lly free of solid material and consists primarily of fluidized gas and gaseous reaction products. The gas seal 22 permits the tr~n~mi.~ion of microwave energy into the reaction chamber 12 while isolating the atmosphere and contents of the chamber from the connPcting waveguide attached via fittings 18 and 20.
Tre~tment of a pyritic ore, according to the present invention, will now be described in greater detail.
The pyritic ore is loaded into the reaction chamber 12 through valve 24. The ore is then fluidized into the bed 34 by pumping a fluidizing gas, which is generally just air, through valve 28. Next microwave energy is applied, via the waveguide fitting. The microwave energy raises the fluidized bed to the ,~ r~d operating temperature in the range of about 300~C - 550~C, where as can be seen from the data of Table 1 and shown in Figure 2, pyrite is prerel~d over pyrrhotite.
Additionally, as can be seen in Table 2 and Figure 3, recombination of hematite and sulphur (reaction (IV)) is not favoured at temperatures below 550~C. Once the lellll)eldlllre of the bed has been raised to aboul 300~C the sulphur-hematite reaction commences If the tempeldlur~ rises too quickly (i.e. the N2 in the vent gasses is not yet sufficient to restrict the amount of ~2 and thus cool the reaction), N2 can be introduced into the fluidizing strea~n via valve 48. The reaction can be monitored by checking the particulate separator 42, which will reveal the presence of sulphur, an in~ tor of the reaction, or by a tell-peldlllre spike from temperature probe 50 since the initial pyrite reaction is exothermic.
In view of the fact that pyrite reaction is extremely exothPrrnic, the - temperature of the reaction chamber will continue to rise (in conventional reactors the running lempelature is usually between 600~C and 750~C), causing the release of SO2; unless the reaction is cooled to favour reaction (IV).
First of all, the reaction can be cooled by re l~cing the input of microwave energy; although, as will be ~ cu.~sec7 below, it is preferable to m~int~in at least some input of microwave energy, in the range of 0.5kw. The second control , ~ CA 02263497 1999-02-16 C.
of the reaction temperature is through the manipulation of the recirculating gases which, due to the reaction in the chamber, has been reduced to primarily N~. If the r,~ction has not sufficiently reduced the ~2 from the circulating gases, additional inert gasses can be introduced into the stream to control the amount of O~ in the reactor.
Additionally, the recirc~ ting gases themselves can be cooled prior to reintroduction into the reaction chamber.
Pyrite can be selectively heated while in the presence of m~gn~titç and hem~tite since it absorbs microwave energy more efficiently. Accordingly, it may be treated by the continued application of microwave energy during the exothermic reaction which is ongoing in the reaction chamber while at the same time the mass of the bed is being cooled by the recirc~ ting gas stream.
Once the trç~tmPnt process has been completed and the fluidized material appropliately heated or processed, it is ejected from the reactor through port 30 by increasing the flui~i7ing gas pressure. Any material which has fallen through screen 14 during loading and processing of the chamber is removed through valve 26.
Although described as preferably being tubular, the reaction chamber 12 can be of any appropriate dimension or geometry as dictated by the microwave field distribution. Additionally, while being described as an iris coupled resonator, the reaction chamber may operate as a termin~t~ waveguide (iris fully open) in which case the absorptive action of the load material gives the reactor the characteristics of a travelling-wave applicator.
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Claims (9)
1. A method of oxidizing pyritic ores using a reaction in a reactor vessel, said method comprising the steps of:
(a) heating a bed of pyritic ore in the reaction chamber of said reactor vessel using microwave energy to initiate a controlled, sub-autogenous exothermic oxidation reaction within the bed;
(b) controlling the inflow of oxygen to the reaction in the reaction chamber so as to avoid the reaction of oxygen with pyrite in order to limit production of SO2; and (c) cooling the temperature of the reaction in said vessel to a temperature within the range of about 300°C to 550°C at which the reaction products are hematite and elemental sulphur.
(a) heating a bed of pyritic ore in the reaction chamber of said reactor vessel using microwave energy to initiate a controlled, sub-autogenous exothermic oxidation reaction within the bed;
(b) controlling the inflow of oxygen to the reaction in the reaction chamber so as to avoid the reaction of oxygen with pyrite in order to limit production of SO2; and (c) cooling the temperature of the reaction in said vessel to a temperature within the range of about 300°C to 550°C at which the reaction products are hematite and elemental sulphur.
2. A method according to claim 1 wherein the reactor vessel is a fluidizing bed reactor which uses a fluidizing gas to fluidize the bed of pyritic ore.
3. A method according to claim 2 wherein the cooling step comprises recirculating a portion of the outgoing fluidizing gases from the reaction chamber back into the chamber.
4. A method according to claim 3 wherein N2 or another inert gas is introduced into the recirculated fluidizing gas.
5. A method according to claim 3 wherein said recirculated gas is cooled by a heat exchanger.
6. A method according to claim 1 wherein the cooling step comprises reducing the microwave energy that is supplied to the bed.
7. A method of oxidizing pyritic ores using a fluidizing bed reactor according to claim 1 wherein during the cooling step microwave energy supply to the bed is continued to selectively heat the pyrite in the presence of magnetite and hematite.
8. A method according to claim 3 further comprising the step of monitoring the temperature of the outgoing fluidizing gases.
9. A method according to claim 3 further comprising the step of monitoring the sulphur content of the outgoing fluidizing gases.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US70370396A | 1996-08-27 | 1996-08-27 | |
| US08/703,703 | 1996-08-27 | ||
| US89710397A | 1997-07-18 | 1997-07-18 | |
| US08/897,103 | 1997-07-18 | ||
| PCT/CA1997/000561 WO1998008989A1 (en) | 1996-08-27 | 1997-08-08 | Method for microwave induced oxidation of sulphidic ore material in fluidized bed without sulphur dioxide emissions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2263497A1 true CA2263497A1 (en) | 1998-03-05 |
Family
ID=27107190
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002263497A Abandoned CA2263497A1 (en) | 1996-08-27 | 1997-08-08 | Method for microwave induced oxidation of sulphidic ore material in fluidized bed without sulphur dioxide emissions |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0950122A1 (en) |
| AU (1) | AU721221B2 (en) |
| CA (1) | CA2263497A1 (en) |
| WO (1) | WO1998008989A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5972302A (en) * | 1996-08-27 | 1999-10-26 | Emr Microwave Technology Corporation | Method for the microwave induced oxidation of pyritic ores without the production of sulphur dioxide |
| AT408992B (en) * | 2000-06-28 | 2002-04-25 | Voest Alpine Ind Anlagen | Process for the direct reduction of fine ore, and installation for carrying out the process |
| DE10260744A1 (en) * | 2002-12-23 | 2004-07-01 | Outokumpu Oyj | Process and plant for the thermal treatment of granular solids |
| DE10260733B4 (en) | 2002-12-23 | 2010-08-12 | Outokumpu Oyj | Process and plant for the heat treatment of iron oxide-containing solids |
| DE10260742A1 (en) * | 2002-12-23 | 2004-07-08 | Outokumpu Oyj | Process and plant for the thermal treatment of granular solids in a fluidized bed |
| DE102010022400B4 (en) * | 2010-06-01 | 2013-04-25 | Outotec Oyj | Process and plant for lowering the residual carbon content of ash |
| FR3136541B1 (en) * | 2022-06-14 | 2024-06-21 | Innovation & Dev Company | microwave and fluidized bed calcination furnace |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2209331A (en) * | 1936-11-12 | 1940-07-30 | Haglund Ture Robert | Roasting process |
| US4324582A (en) * | 1980-06-11 | 1982-04-13 | Kruesi Paul R | Process for the recovery of copper from its ores |
| US4678478A (en) * | 1986-04-14 | 1987-07-07 | Massachusetts Institute Of Technology | Method for desulfurization of coal |
| JPH0711594B2 (en) * | 1987-05-21 | 1995-02-08 | 動力炉・核燃料開発事業団 | Fluidized bed system |
| US5123956A (en) * | 1991-04-12 | 1992-06-23 | Newmont Mining Corporation | Process for treating ore having recoverable gold values and including arsenic-, carbon- and sulfur-containing components by roasting in an oxygen-enriched gaseous atmosphere |
| JP2766586B2 (en) * | 1992-06-23 | 1998-06-18 | 大阪ガスエンジニアリング株式会社 | Method and apparatus for roasting granular processed products |
| DE4329417C1 (en) * | 1993-09-01 | 1994-08-18 | Metallgesellschaft Ag | Process for roasting refractory gold ores |
-
1997
- 1997-08-08 CA CA002263497A patent/CA2263497A1/en not_active Abandoned
- 1997-08-08 EP EP97935397A patent/EP0950122A1/en not_active Withdrawn
- 1997-08-08 WO PCT/CA1997/000561 patent/WO1998008989A1/en not_active Application Discontinuation
- 1997-08-08 AU AU38439/97A patent/AU721221B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| WO1998008989A1 (en) | 1998-03-05 |
| AU3843997A (en) | 1998-03-19 |
| AU721221B2 (en) | 2000-06-29 |
| EP0950122A1 (en) | 1999-10-20 |
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| EEER | Examination request | ||
| FZDE | Discontinued |