CA2060878C - Process of roasting refractory gold ores - Google Patents
Process of roasting refractory gold ores Download PDFInfo
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- CA2060878C CA2060878C CA002060878A CA2060878A CA2060878C CA 2060878 C CA2060878 C CA 2060878C CA 002060878 A CA002060878 A CA 002060878A CA 2060878 A CA2060878 A CA 2060878A CA 2060878 C CA2060878 C CA 2060878C
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- fluidized bed
- reactor
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- sulfur
- solids
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- 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
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
- B01J8/1845—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles with particles moving upwards while fluidised
- B01J8/1863—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles with particles moving upwards while fluidised followed by a downward movement outside the reactor and subsequently re-entering it
-
- 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
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C10/00—Fluidised bed combustion apparatus
- F23C10/02—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed
- F23C10/04—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone
- F23C10/08—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone characterised by the arrangement of separation apparatus, e.g. cyclones, for separating particles from the flue gases
- F23C10/10—Fluidised bed combustion apparatus with means specially adapted for achieving or promoting a circulating movement of particles within the bed or for a recirculation of particles entrained from the bed the particles being circulated to a section, e.g. a heat-exchange section or a return duct, at least partially shielded from the combustion zone, before being reintroduced into the combustion zone characterised by the arrangement of separation apparatus, e.g. cyclones, for separating particles from the flue gases the separation apparatus being located outside the combustion chamber
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C2206/00—Fluidised bed combustion
- F23C2206/10—Circulating fluidised bed
- F23C2206/101—Entrained or fast fluidised bed
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- Environmental & Geological Engineering (AREA)
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- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- General Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
Abstract
Refractory gold ores are roasted by means of oxygen-containing gases in a circulating fluidized bed at temperatures of 500 to 750°C. The temperature in the lower portion of the fluidized bed contained in the reactor is adjusted to be 4 to 30°C higher than the temperature in the upper portion of the fluidized bed. The fluidizing gas is caused to floor into the reactor at a velocity of 30 to 200 m/sec.
Description
2a~'~~3'~~
The present invention reiates to a process of roasting refractory gold ayes by means of oxygen-containing gases in a fluidized bed.
Refractory gold ores are ores which cannot direct-ly be leached with ~iaCl'~ and which as ogld-bearing substan-ces contain pyrites, arsenonyrites or pyrites associated with more or less oroanic carbon.'In the processing of such materials the leaching roith cyanide moat be preceded by an oxidation of the contents of sulfur and carbon to the highest possible degree. that oxidation has been efFec-tern in the past r~ainlv by roasting, put sulfuric acid must be produced to remove of the 50~, which is Formed by the roastinn, From the roaster exhaust gas. In many cases, how-ever, the site of the mine is so unfavorable that the sul-(uric acid which is produced is rather a ballast. Pesides, the roastinn resulted in a clogninq of part of the pores of the particles by recrystallized ironoxidea so that the yield of gold Haas decreased.
For this reason the oxidation has increasingly been effected more recently by other processes, such as pressure oxidation in an autoclave, bacterial leaching or - ?. -oxidation by nitric acid or chlorine. The diciaive dif-ference from roasting resides in that in said processes the sulfur is directly produced as sulfuric acid and/or iron sulfate and must be neutralized with CaC03 and CaD before the leaching with cyanide. Part of safd processes are much more expensive than roasting.
"Journal of the South African Institute of Mining and Metallurgy", Uol. 86, No. 5, May 1986, discloses on pages 157 to 160 that flotation concentratpa of gold-con-tainino pyrites can be roasted or pyrolyzed in a fluidized bed. Ttie oyrolysis is effected in a fluidized bed,which is operated with nitrogon a~ a fluidizing gas and which is heated to 70D to 800°C by electric resistance heating. The reactor comprises two concentric tubes. The material is charged in-to the annular space and subsides therein and is then raised in the inner tube and in part falls back into the outer an-.
nular space. The sulfur which has been distilled off is con-densed. flut the final product aF the ~pyrolyeis corlsista only of FeS. pesidea, expensive electric power is required to produce the heat requtied for the reaction.
German Patent Specification 26 24 302 di,scloaes that sulfide ores or ore concentrates can be roasted at temperatures between 450 and 1200°C in a circulating fluidi-zed be~i system, n~hich is fed with oxygen-containing fluidizing gases. Solids are removed Prom the reactor of the circulating fluidized bed system and are cooled in a separate fluidized bed Goole rPart of the cooled solids are recycled to the reactor. The heated fluidizing air from the fluidized bed cooler is fed as secondary air to the reactor. Information on the roasting of refractory gold ores has not been fur-nished in connection with that process.
I,t is an object of the invention to provide for the roasting of refractory gold ores a process which will result in an optimum product for the leaching with cyanides and in which the production of sulfuric acid can be omitted if this is necessary.
In accordance with the present invention, that object is achieved with a process of roasting refractory gold ores by means of oxygen-containing gases in fluidized bed having an upper portion and a lower portion, the process comprising the steps of;
- roasting the gold ores in a circulating fluidized bed system at temperatures from 500 to 750°C, the fluidized bed system comprising a fluidized bed reactor containing the fluidized bed;
- adjusting the temperature in the lower portion of the fluidized bed to be 4 to 30°C higher than the temperature in the upper portion of the fluidized bed, and causing the fluidizing gas to flow into the reactor at a velocity of 30 to 200 m/sec.
According to a preferable aspect of the invention a method is proposed for roasting refractory gold ore in a fluidized bed which is located in a fluidized bed reactor above a perforated bottom which has numerous gas passage 3a openings, the fluidized bed having a lower part and an upper part, wherein air or air enriched with oxygen is passed upwards through the perforated bottom into the fluidized bed as fluidizing gas, the gold ore is roasted in the fluidized bed at temperatures of 500 750°C and solids-containing exhaust gas withdrawn from the reactor is passed through a cyclone to separate off solids, the method is characterized in that the roasting of the gold ore is effected in a circulating fluidized bed, with the solids concentration within the reactor constantly decreasing from bottom to top, that the solids-containing exhaust gas is passed from the reactor into the cyclone and the solids separated off in the cyclone are returned to the fluidized bed reactor in a quantity per hour which corresponds to at least 5 times the weight of the solids contained in the reactor, that the gold ore to be roasted is introduced into the fluidized bed at least 1 m above the perforated bottom, that the temperature in the lower part of the fluidized bed is set to 4 to 30°C higher than in the upper part of the fluidized bed and that the fluidizing gas emerges from the openings of the perforated bottom into the fluidized bed at velocities of 30 to 200 m/sec.
The refractory gold ores which may be used may consist of ores or of concentrate. The oxygen-containing gases which may be used may consist of air or of oxygen enriched air. The circulating fluidized bed system preferably consists of the fluidized bed reactor, the recycle cyclone, and the recycle line for recycling the solids collected in the recycle cyclone. The term "recycle cyclone" is applicable to one 2~6~~~'~~
recycle cyclone or to a plurality of recycling cyclones having,gas paths connected in parallel. From an "orthodox"
fluidized bed, in which a dense pbe~se is separated by a distinct density step from the overlying gas space, the fluidized bed used in accordance with the invention differs in that the fluidized bed reactor contains states'of dis-tribution having no defined boundary layer. There,is no density step betmeen..a dense phase and an overlying dust space, and the solids concentration decreases gradually in the reactor from bottom to top. The following regions will be obt~i~ned if the operatiriq conditions are defined by the Froude and Archimedes .numbers f' ~ ~_~ <10, 0.1 < 'J/4 -. Frz . -.-.. ......
' ;.,/~ k ,/a g and 0,01 < Ar <_ 100 , wherein ~k~ , g ~ Jo k - ~O ~ ) Ax ~ _........~~_......_..__...._ ~ g , y,a end u2 Fr2 a ' _..___.. _....
q . dk 2~~~~'~8 - 4a -and a - the relative gas velocity in m/sec Rr - the Nrchimedes number Fr - the Froude number ~g ~ the density of the gas in kg/m~
~k - the density of the solid particles in kg/m~
dk - the diameter of the spherical particles in m '= the,k~nematic viacoaity in mx/sec a ~- the constant of oravitation in m/secZ
The suspension discharged from the Fluidized bed reactor is fed to the recycle cyclone of the circulating fluidized bed systzm and substantially all solids are col-lected From said suspension in the recycle cyclone and are recycled to the fluidized bed reactor in such a manner that the weight of solids circulated per hour in the circulating fluidized bed system is at least five times the weight of the solids contained in the fluidized bed reactor. The temperature in the fluidized bed reactor is adjusted to a constant~value within the stated range but the temperature in the lower portion of the fluidized bed is higher by the stated amount than the temperature in the upper portion of the fluidized bed. The higher temperature in the lower re-gion of the fluidized bed is achieved in that the ore is fed on a level which is spaced a predetermined distance of at least 1 meter above the bottom so that an atmosphere which is richer in oxygen is maintained below the Feeding level and Fe3D4 is oxidized to Fe203 in said atmosphere. The FeZ03 enters the upper portion of the fluidized bed, where the atmosphere is poorer in oxygen, and is o~rtly reduced there to Fe~04 and is then'returned to the lower portion, where it is reoxidized. The oxidation of Fe304 to Fe203 supplies part of the heat which is required in the process.
The oxygen content of the fed gas is ad~asted to a value nahich is close to the stoichiometric value related to the sulfur and carbon contents of the material. The tempera-tuts difference between the lower and upper portions of the fluidized bed is a reliable measure of the ratio of Fe203 to Fe304 in the calcine which is discharged. The optimum ratio of magnetite to hematite for the leaching with cyanide will be achieved by a selection of the proper temperature difference in the reactor for the feed material used. The temperature difference will be controlled by the oxygen content of the fed gases. The velocity of 30 to 200 m/sec of the fluidlzing gas is the velocity at which the fluidizing gas exits from the openings of the perforate bottom into the reactor. If the ore has a low caha~ific value, the fluidizing gas or a partial stream of the flui-dazing gas can be preheated by an indirect heat exchange.
That preheating may be effected by the exhaust gas from the circulating fluidized bed system or by the discharged solids. If the ore has a low calorific value, a directly preheated secondary gas may be fed to the reactor above the perforate bottom and the preheating may be effected in a separate fluidized bed cooler, which contains an orthodox fluidized bed. The hot calcine is discharged into that fluidized bed cooler and is cooled therein with oxygen-con-taining fluidizino gas. The oxygen-containing fLuidizing gas which has thus been heated is fed as secondary ass to the reactor of the circulating fluidized bed system. The fluidized bed cooler may also contain cooling surfaces, through which the FLWidizing gas for the circulating fluii dazed bed is passed and is thus preheated. If the circu-lating fluidized bed system is fed with a concentrate which has relatively high contents of sulfur and/or carbon, it will be necessary to dissipate heat from the fluidized bed. That dissipation of heat may be effected by cooling surfaces in the fluidized bed reactor or by a cooler for a circulated stream. That cooler for a circulated stream is a separate fluidized bed cooler, which contains a stationary fluidized bed and is fed with the solids collected in the recycle cyclone or part of said solids and is also fed with oxygen-containing gases as a Fluidizing gas. The flui-dized bed contains cooling registers, which are flown through'; e.g., by water. The cooled solids or part of the cooled so7.ids are recycled to the reactor of the circulat-ing fluidized bed system. The heated fluidizing gas may be Ped as a secondary gas to the fluidized bed reactor of the circulating fluidized bed system. The dissipation of heat or a dissipation of part of the heat to be dissipated may also be effected in that the concentrate is fed as an aque-our suspension to the fluidized bed reactor. The exit of the fluidizing gas at the stated velocity will mainly re-cult in the lower portion of the flui'dizing reactor in a certain grinding action on the recirculated coarse solids.
That grinding action will tear open the partly dense cover-ins layers of iron oxide on the surface of the oarticles and in the outer portion of the pores of the particles and will result in an excellent leachability. At the same time the particle size is reduced fzrom, e.g. , 5096 t 35 ~Sm to 6596 < 35 um.
Recording to a preferred feature the temperature in the lower portion of the fluidized bed in the reactor is adjaeted to be 4 to 12°C higher than the temperature in the upper portion of the fluidized bed. R particularly good ratio of Fe304 to Fe~03 in the discharged calcine will be achievad~by the adjustment of a temperature in that range.
Recording to a preferred feature the fluidizing gas is caused to flow into the reactor at a velocity of 50 to 100 m/sec. R good orinding action will be achieved at a relatively low expenditure by the use of a velocity in that range.
Recording to a preferred Pasture a sulfur-binding material is fed to the reactor at such a rate that a pre-dominant part of the sulfur content of the gold are will be bound. The sulfur-binding material which may be used may consist of Ca-containing materials, such as limestone, CaO, and dolomite. Part of the deaulfurizing agent may alterna-tively be contained in the gangue of the ore. The S0? which has been formed is bound by the sulfur-binding material main-ly as a sulFate and/or sulfite of calcium; the proportion ofw.
sulfite will be low. If it is desireri to bind most of the S0~ by the Ca-containing material and to achieve a good leachability, the temperature W~11 be preferably be main-tained in the range from 65D to 750°C and particularly in the range from 650 to 7D0°C. Those temperature ranges are the optimum ranges for achieving a binding of the S0~ and as well as a good leachability of the calcine. Part of the heat required for the reaction is also produced by the pro-duction of sulfate.
According to a preferred feature the sulfur-bind-inq material is fed at a rate which is in excess of the rate that is required far binding the sulfur and most of the sur-plus is reacted to form CaO. In this manner the Ca0 required for adjusting the off value for the leaching with cyanide can be produced in a desirable manner so that substantially less CaD or no Ca0 needs to be added for adjusting the pH
value for the subsequent leaching with cyanide.
according to a preferred feature, additional fuel is fed to the fluidized bed. Solid, gaseous o.r liquid Fuels may be fed to the fluidized bed. This will permit an economi-cal roasting also of gold ores which do not contain sulfur and/or coarbon in the amount required far the production of the heat rohich is required.
According to a preferred feature, sulfur-binding material before being fed to the reactor of the circulat-ing fluidized bed is calcined in a separate fluidized bed and the resulting calcine is fed in a hot state to the reactor.
The separate fluidized bed may be constituted also by a circulating fluidized bed or by an orthodox fluidized bed.
That feature will be particularly desirable if low-cost na-tural gas is available, wh~h owing to its high ignition temperature of at least 670°C and its low degree of com-bustion at the relatively low roasting temperatures cannot be used in the circulating fluidized bed. In such case part or all of the Ca0 which is required for binding the S0~ and/
or for adjusting the pH value is produced in the separate fluidized bed by calcination at, e.g., 950°C with the aid of natural gas and is fed at an elevated temperature to the reactor of the circulating fluidized bed system. As a result, the entire heat of sulfatization of the Ca0 will additionally be available for the roasting; that heat will usually be sufficient for an autothermic roasting process.
In the oombination which is optimum as regards thermal ener-gy, a decomposition of CaC03 is effected in such a manner in the separate fluidized bed and in the circulating fluidized bed for roasting that the rate at which CaC03 is decomposed in the separate fluidized bed is just sufficient to maintain an autothermic roasting in the circulatinn fluidized bed used far roasting.
The invention will be described more in detail with reference to an example and a draining.
According to Figure 1 a metering pump 1 feeds the material to be processed into the distributor pot 2. The concentrate suspension is uniformly fed through downcomers 3 into the lower portion of the reactor 4 of the circulat-ing fluidized bed system. Atmospheric air as an oxidizing and fluidizing gas is fed by the fan 5 into the windbox 6 associated with the reactor 4 and flows from there through the perforate bottom 7. The suspension of oxidized solids (calcine) and roaster exhaust gas is discharged from the reactor 4 and is fed to the recycle cyclone 8 of the cir-culating fluidized bed system. Substantially all solids are removed from said suspension in said cyclone and are re-cycled to the reactor 4 through the recycle line 9 and the fluidized seal pot 10. Calcine is continuously ~ withdrawn from tha iluidized seal pot 10 through the discharge line 11. The dust-laden roaster exhaust gas which leaves the recycle cyclone 8 is fed in the gas line 12 to means for cooling, dedusting and further processing. The flow control valve 13 is used for a supply of water at a metered rate to the con-centrate slurry to be fed. The reactor 4 has a height of 25 m above the perforate bottom 7 and the downcomers 3 effect a feeding on a level which is 4 meters above said bottom.
EXAMPLE
A refractory pyrite ore concentrate is used, which contains 40 g gold per 1000 kg and 33.3' sulfide sulfur, which is present as pyrite. The particl= size amounts to d50 = 30 um and 100°6 X00 Nm. In an aqueous slurry contain-ing 70~ solids, concentrate at a rate of Z4,OOD kg/h is fed into the reactor 4 through the downcomers 3. Rir at a tem-perature of 60°C is fed under a.pressure of 1.2 bars at a rate of 37,D00 sm~/h (sm~ = standard cubic meter) into the windbox 6. The air flows at a velocity of 60 m/sec through the openings of the perforate bottom 7. The temperature amounts to 650°C in the lower portion of the reactor and to 642°C in its upper portion. The rate at which air is fed is controlled to effect a near-stoichiometric combustion. The oxygen content in the upper portion of the reactor is 0.596.
In the calcine discharged through the discharge line 11 the ration of Fe~03 to Fe304 equals 4:1. The content of sulfide sulfur is 0.2%. R gold yield of 9596 is achieved in the fur-ther processing. The roaster exhaust gas in line 12 cpntais 14.6% S02 and ; 0.59'0 oxygen.
The advantages afforded by the invention reside in that a formation of covering layers of iron oxide on the particles will substantially be avoided owing to the grinding action. Besides, an optimum ratio of Fe~04 to Fe203 in the calcine can exactly be achieved and sulfur and carbon are substantially completely combusted so that the resulting aalcine has very good leaching properties. Fluctuations in the chemical cpmpositpn of the ores can be detected immediate-ly and the pregiven temperature difference in the reactor can be re-established by a correction of the rate at which oxygen is infected. 8y an addition of sulfur-binding agents the SDI content of the =xhaust gas can be decreased to such low values that a succeeding plant for producing sulfuric acid will not be required.
The present invention reiates to a process of roasting refractory gold ayes by means of oxygen-containing gases in a fluidized bed.
Refractory gold ores are ores which cannot direct-ly be leached with ~iaCl'~ and which as ogld-bearing substan-ces contain pyrites, arsenonyrites or pyrites associated with more or less oroanic carbon.'In the processing of such materials the leaching roith cyanide moat be preceded by an oxidation of the contents of sulfur and carbon to the highest possible degree. that oxidation has been efFec-tern in the past r~ainlv by roasting, put sulfuric acid must be produced to remove of the 50~, which is Formed by the roastinn, From the roaster exhaust gas. In many cases, how-ever, the site of the mine is so unfavorable that the sul-(uric acid which is produced is rather a ballast. Pesides, the roastinn resulted in a clogninq of part of the pores of the particles by recrystallized ironoxidea so that the yield of gold Haas decreased.
For this reason the oxidation has increasingly been effected more recently by other processes, such as pressure oxidation in an autoclave, bacterial leaching or - ?. -oxidation by nitric acid or chlorine. The diciaive dif-ference from roasting resides in that in said processes the sulfur is directly produced as sulfuric acid and/or iron sulfate and must be neutralized with CaC03 and CaD before the leaching with cyanide. Part of safd processes are much more expensive than roasting.
"Journal of the South African Institute of Mining and Metallurgy", Uol. 86, No. 5, May 1986, discloses on pages 157 to 160 that flotation concentratpa of gold-con-tainino pyrites can be roasted or pyrolyzed in a fluidized bed. Ttie oyrolysis is effected in a fluidized bed,which is operated with nitrogon a~ a fluidizing gas and which is heated to 70D to 800°C by electric resistance heating. The reactor comprises two concentric tubes. The material is charged in-to the annular space and subsides therein and is then raised in the inner tube and in part falls back into the outer an-.
nular space. The sulfur which has been distilled off is con-densed. flut the final product aF the ~pyrolyeis corlsista only of FeS. pesidea, expensive electric power is required to produce the heat requtied for the reaction.
German Patent Specification 26 24 302 di,scloaes that sulfide ores or ore concentrates can be roasted at temperatures between 450 and 1200°C in a circulating fluidi-zed be~i system, n~hich is fed with oxygen-containing fluidizing gases. Solids are removed Prom the reactor of the circulating fluidized bed system and are cooled in a separate fluidized bed Goole rPart of the cooled solids are recycled to the reactor. The heated fluidizing air from the fluidized bed cooler is fed as secondary air to the reactor. Information on the roasting of refractory gold ores has not been fur-nished in connection with that process.
I,t is an object of the invention to provide for the roasting of refractory gold ores a process which will result in an optimum product for the leaching with cyanides and in which the production of sulfuric acid can be omitted if this is necessary.
In accordance with the present invention, that object is achieved with a process of roasting refractory gold ores by means of oxygen-containing gases in fluidized bed having an upper portion and a lower portion, the process comprising the steps of;
- roasting the gold ores in a circulating fluidized bed system at temperatures from 500 to 750°C, the fluidized bed system comprising a fluidized bed reactor containing the fluidized bed;
- adjusting the temperature in the lower portion of the fluidized bed to be 4 to 30°C higher than the temperature in the upper portion of the fluidized bed, and causing the fluidizing gas to flow into the reactor at a velocity of 30 to 200 m/sec.
According to a preferable aspect of the invention a method is proposed for roasting refractory gold ore in a fluidized bed which is located in a fluidized bed reactor above a perforated bottom which has numerous gas passage 3a openings, the fluidized bed having a lower part and an upper part, wherein air or air enriched with oxygen is passed upwards through the perforated bottom into the fluidized bed as fluidizing gas, the gold ore is roasted in the fluidized bed at temperatures of 500 750°C and solids-containing exhaust gas withdrawn from the reactor is passed through a cyclone to separate off solids, the method is characterized in that the roasting of the gold ore is effected in a circulating fluidized bed, with the solids concentration within the reactor constantly decreasing from bottom to top, that the solids-containing exhaust gas is passed from the reactor into the cyclone and the solids separated off in the cyclone are returned to the fluidized bed reactor in a quantity per hour which corresponds to at least 5 times the weight of the solids contained in the reactor, that the gold ore to be roasted is introduced into the fluidized bed at least 1 m above the perforated bottom, that the temperature in the lower part of the fluidized bed is set to 4 to 30°C higher than in the upper part of the fluidized bed and that the fluidizing gas emerges from the openings of the perforated bottom into the fluidized bed at velocities of 30 to 200 m/sec.
The refractory gold ores which may be used may consist of ores or of concentrate. The oxygen-containing gases which may be used may consist of air or of oxygen enriched air. The circulating fluidized bed system preferably consists of the fluidized bed reactor, the recycle cyclone, and the recycle line for recycling the solids collected in the recycle cyclone. The term "recycle cyclone" is applicable to one 2~6~~~'~~
recycle cyclone or to a plurality of recycling cyclones having,gas paths connected in parallel. From an "orthodox"
fluidized bed, in which a dense pbe~se is separated by a distinct density step from the overlying gas space, the fluidized bed used in accordance with the invention differs in that the fluidized bed reactor contains states'of dis-tribution having no defined boundary layer. There,is no density step betmeen..a dense phase and an overlying dust space, and the solids concentration decreases gradually in the reactor from bottom to top. The following regions will be obt~i~ned if the operatiriq conditions are defined by the Froude and Archimedes .numbers f' ~ ~_~ <10, 0.1 < 'J/4 -. Frz . -.-.. ......
' ;.,/~ k ,/a g and 0,01 < Ar <_ 100 , wherein ~k~ , g ~ Jo k - ~O ~ ) Ax ~ _........~~_......_..__...._ ~ g , y,a end u2 Fr2 a ' _..___.. _....
q . dk 2~~~~'~8 - 4a -and a - the relative gas velocity in m/sec Rr - the Nrchimedes number Fr - the Froude number ~g ~ the density of the gas in kg/m~
~k - the density of the solid particles in kg/m~
dk - the diameter of the spherical particles in m '= the,k~nematic viacoaity in mx/sec a ~- the constant of oravitation in m/secZ
The suspension discharged from the Fluidized bed reactor is fed to the recycle cyclone of the circulating fluidized bed systzm and substantially all solids are col-lected From said suspension in the recycle cyclone and are recycled to the fluidized bed reactor in such a manner that the weight of solids circulated per hour in the circulating fluidized bed system is at least five times the weight of the solids contained in the fluidized bed reactor. The temperature in the fluidized bed reactor is adjusted to a constant~value within the stated range but the temperature in the lower portion of the fluidized bed is higher by the stated amount than the temperature in the upper portion of the fluidized bed. The higher temperature in the lower re-gion of the fluidized bed is achieved in that the ore is fed on a level which is spaced a predetermined distance of at least 1 meter above the bottom so that an atmosphere which is richer in oxygen is maintained below the Feeding level and Fe3D4 is oxidized to Fe203 in said atmosphere. The FeZ03 enters the upper portion of the fluidized bed, where the atmosphere is poorer in oxygen, and is o~rtly reduced there to Fe~04 and is then'returned to the lower portion, where it is reoxidized. The oxidation of Fe304 to Fe203 supplies part of the heat which is required in the process.
The oxygen content of the fed gas is ad~asted to a value nahich is close to the stoichiometric value related to the sulfur and carbon contents of the material. The tempera-tuts difference between the lower and upper portions of the fluidized bed is a reliable measure of the ratio of Fe203 to Fe304 in the calcine which is discharged. The optimum ratio of magnetite to hematite for the leaching with cyanide will be achieved by a selection of the proper temperature difference in the reactor for the feed material used. The temperature difference will be controlled by the oxygen content of the fed gases. The velocity of 30 to 200 m/sec of the fluidlzing gas is the velocity at which the fluidizing gas exits from the openings of the perforate bottom into the reactor. If the ore has a low caha~ific value, the fluidizing gas or a partial stream of the flui-dazing gas can be preheated by an indirect heat exchange.
That preheating may be effected by the exhaust gas from the circulating fluidized bed system or by the discharged solids. If the ore has a low calorific value, a directly preheated secondary gas may be fed to the reactor above the perforate bottom and the preheating may be effected in a separate fluidized bed cooler, which contains an orthodox fluidized bed. The hot calcine is discharged into that fluidized bed cooler and is cooled therein with oxygen-con-taining fluidizino gas. The oxygen-containing fLuidizing gas which has thus been heated is fed as secondary ass to the reactor of the circulating fluidized bed system. The fluidized bed cooler may also contain cooling surfaces, through which the FLWidizing gas for the circulating fluii dazed bed is passed and is thus preheated. If the circu-lating fluidized bed system is fed with a concentrate which has relatively high contents of sulfur and/or carbon, it will be necessary to dissipate heat from the fluidized bed. That dissipation of heat may be effected by cooling surfaces in the fluidized bed reactor or by a cooler for a circulated stream. That cooler for a circulated stream is a separate fluidized bed cooler, which contains a stationary fluidized bed and is fed with the solids collected in the recycle cyclone or part of said solids and is also fed with oxygen-containing gases as a Fluidizing gas. The flui-dized bed contains cooling registers, which are flown through'; e.g., by water. The cooled solids or part of the cooled so7.ids are recycled to the reactor of the circulat-ing fluidized bed system. The heated fluidizing gas may be Ped as a secondary gas to the fluidized bed reactor of the circulating fluidized bed system. The dissipation of heat or a dissipation of part of the heat to be dissipated may also be effected in that the concentrate is fed as an aque-our suspension to the fluidized bed reactor. The exit of the fluidizing gas at the stated velocity will mainly re-cult in the lower portion of the flui'dizing reactor in a certain grinding action on the recirculated coarse solids.
That grinding action will tear open the partly dense cover-ins layers of iron oxide on the surface of the oarticles and in the outer portion of the pores of the particles and will result in an excellent leachability. At the same time the particle size is reduced fzrom, e.g. , 5096 t 35 ~Sm to 6596 < 35 um.
Recording to a preferred feature the temperature in the lower portion of the fluidized bed in the reactor is adjaeted to be 4 to 12°C higher than the temperature in the upper portion of the fluidized bed. R particularly good ratio of Fe304 to Fe~03 in the discharged calcine will be achievad~by the adjustment of a temperature in that range.
Recording to a preferred feature the fluidizing gas is caused to flow into the reactor at a velocity of 50 to 100 m/sec. R good orinding action will be achieved at a relatively low expenditure by the use of a velocity in that range.
Recording to a preferred Pasture a sulfur-binding material is fed to the reactor at such a rate that a pre-dominant part of the sulfur content of the gold are will be bound. The sulfur-binding material which may be used may consist of Ca-containing materials, such as limestone, CaO, and dolomite. Part of the deaulfurizing agent may alterna-tively be contained in the gangue of the ore. The S0? which has been formed is bound by the sulfur-binding material main-ly as a sulFate and/or sulfite of calcium; the proportion ofw.
sulfite will be low. If it is desireri to bind most of the S0~ by the Ca-containing material and to achieve a good leachability, the temperature W~11 be preferably be main-tained in the range from 65D to 750°C and particularly in the range from 650 to 7D0°C. Those temperature ranges are the optimum ranges for achieving a binding of the S0~ and as well as a good leachability of the calcine. Part of the heat required for the reaction is also produced by the pro-duction of sulfate.
According to a preferred feature the sulfur-bind-inq material is fed at a rate which is in excess of the rate that is required far binding the sulfur and most of the sur-plus is reacted to form CaO. In this manner the Ca0 required for adjusting the off value for the leaching with cyanide can be produced in a desirable manner so that substantially less CaD or no Ca0 needs to be added for adjusting the pH
value for the subsequent leaching with cyanide.
according to a preferred feature, additional fuel is fed to the fluidized bed. Solid, gaseous o.r liquid Fuels may be fed to the fluidized bed. This will permit an economi-cal roasting also of gold ores which do not contain sulfur and/or coarbon in the amount required far the production of the heat rohich is required.
According to a preferred feature, sulfur-binding material before being fed to the reactor of the circulat-ing fluidized bed is calcined in a separate fluidized bed and the resulting calcine is fed in a hot state to the reactor.
The separate fluidized bed may be constituted also by a circulating fluidized bed or by an orthodox fluidized bed.
That feature will be particularly desirable if low-cost na-tural gas is available, wh~h owing to its high ignition temperature of at least 670°C and its low degree of com-bustion at the relatively low roasting temperatures cannot be used in the circulating fluidized bed. In such case part or all of the Ca0 which is required for binding the S0~ and/
or for adjusting the pH value is produced in the separate fluidized bed by calcination at, e.g., 950°C with the aid of natural gas and is fed at an elevated temperature to the reactor of the circulating fluidized bed system. As a result, the entire heat of sulfatization of the Ca0 will additionally be available for the roasting; that heat will usually be sufficient for an autothermic roasting process.
In the oombination which is optimum as regards thermal ener-gy, a decomposition of CaC03 is effected in such a manner in the separate fluidized bed and in the circulating fluidized bed for roasting that the rate at which CaC03 is decomposed in the separate fluidized bed is just sufficient to maintain an autothermic roasting in the circulatinn fluidized bed used far roasting.
The invention will be described more in detail with reference to an example and a draining.
According to Figure 1 a metering pump 1 feeds the material to be processed into the distributor pot 2. The concentrate suspension is uniformly fed through downcomers 3 into the lower portion of the reactor 4 of the circulat-ing fluidized bed system. Atmospheric air as an oxidizing and fluidizing gas is fed by the fan 5 into the windbox 6 associated with the reactor 4 and flows from there through the perforate bottom 7. The suspension of oxidized solids (calcine) and roaster exhaust gas is discharged from the reactor 4 and is fed to the recycle cyclone 8 of the cir-culating fluidized bed system. Substantially all solids are removed from said suspension in said cyclone and are re-cycled to the reactor 4 through the recycle line 9 and the fluidized seal pot 10. Calcine is continuously ~ withdrawn from tha iluidized seal pot 10 through the discharge line 11. The dust-laden roaster exhaust gas which leaves the recycle cyclone 8 is fed in the gas line 12 to means for cooling, dedusting and further processing. The flow control valve 13 is used for a supply of water at a metered rate to the con-centrate slurry to be fed. The reactor 4 has a height of 25 m above the perforate bottom 7 and the downcomers 3 effect a feeding on a level which is 4 meters above said bottom.
EXAMPLE
A refractory pyrite ore concentrate is used, which contains 40 g gold per 1000 kg and 33.3' sulfide sulfur, which is present as pyrite. The particl= size amounts to d50 = 30 um and 100°6 X00 Nm. In an aqueous slurry contain-ing 70~ solids, concentrate at a rate of Z4,OOD kg/h is fed into the reactor 4 through the downcomers 3. Rir at a tem-perature of 60°C is fed under a.pressure of 1.2 bars at a rate of 37,D00 sm~/h (sm~ = standard cubic meter) into the windbox 6. The air flows at a velocity of 60 m/sec through the openings of the perforate bottom 7. The temperature amounts to 650°C in the lower portion of the reactor and to 642°C in its upper portion. The rate at which air is fed is controlled to effect a near-stoichiometric combustion. The oxygen content in the upper portion of the reactor is 0.596.
In the calcine discharged through the discharge line 11 the ration of Fe~03 to Fe304 equals 4:1. The content of sulfide sulfur is 0.2%. R gold yield of 9596 is achieved in the fur-ther processing. The roaster exhaust gas in line 12 cpntais 14.6% S02 and ; 0.59'0 oxygen.
The advantages afforded by the invention reside in that a formation of covering layers of iron oxide on the particles will substantially be avoided owing to the grinding action. Besides, an optimum ratio of Fe~04 to Fe203 in the calcine can exactly be achieved and sulfur and carbon are substantially completely combusted so that the resulting aalcine has very good leaching properties. Fluctuations in the chemical cpmpositpn of the ores can be detected immediate-ly and the pregiven temperature difference in the reactor can be re-established by a correction of the rate at which oxygen is infected. 8y an addition of sulfur-binding agents the SDI content of the =xhaust gas can be decreased to such low values that a succeeding plant for producing sulfuric acid will not be required.
Claims (11)
1. A process of roasting refractory gold ores by means of oxygen-containing gases in fluidized bed having an upper portion and a lower portion, the process comprising the steps of:
- roasting the gold ores in a circulating fluidized bed system at temperatures from 500 to 750°C, the fluidized bed system comprising a fluidized bed reactor containing the fluidized beds - adjusting the temperature in the lower portion of the fluidized bed to be 4 to 30°C higher than the temperature in the upper portion of the fluidized bed, and - causing the fluidizing gas to flow into the reactor at a velocity of 30 to 200 m/sec.
- roasting the gold ores in a circulating fluidized bed system at temperatures from 500 to 750°C, the fluidized bed system comprising a fluidized bed reactor containing the fluidized beds - adjusting the temperature in the lower portion of the fluidized bed to be 4 to 30°C higher than the temperature in the upper portion of the fluidized bed, and - causing the fluidizing gas to flow into the reactor at a velocity of 30 to 200 m/sec.
2. A process according to claim 1, characte-rized in that the temperature in the lower portion of the fluidized bed is adjusted to be 4 to 12°C higher than the temperature in the upper portion of the fluidized bed.
3. A process according to claim 1 or 2, charac-terized in that the fluidizing gas is caused to flow into the reactor at a velocity of 50 to 100 m/sec.
4. A process according to claim 1, 2 or 3, characterized in that a sulfur-binding material is fed to the reactor at such a rata that a predominant part of the sulfur content of the gold ore is bound.
5. A process according to claim 4, characte-rized in that the sulfur-binding material is fed at a rate which is in excess of the rate that is required for binding the sulfur, thereby providing an excess of sulfur-binding material which reacts to form CaO.
6. A process according to any one of claims 1 to 5, charactetized in that additional fuel is fed to the fluidized bed.
7. A process according to any one of claims 4 to 6, characterized in that sulfur-binding material before being fed to the reactor of the circulating fluidized bed is calcined in a separate fluidized bed and the resulting calcine is fed in a hot state to the reactor.
8. A method for roasting refractory gold ore in a fluidized bed which is located in a fluidized bed reactor above a perforated bottom which has numerous gas passage openings, the fluidized bed having a lower part and an upper part, wherein air or air enriched with oxygen is passed upwards through the perforated bottom into the fluidized bed as fluidizing gas, the gold ore is roasted in the fluidized bed at temperatures of 500 750°C and solids-containing exhaust gas withdrawn from the reactor is passed through a cyclone to separate off solids, characterized in that the roasting of the gold ore is effected in a circulating fluidized bed, with the solids concentration within the reactor constantly decreasing from bottom to top, that the solid-containing exhaust gas is passed from the reactor into the cyclone and solids separated off in the cyclone are returned to the fluidized bed reactor in a quantity per hour which corresponds to at least 5 times the weight of the solids contained in the reactor, that the gold ore to be roasted is introduced into the fluidized bed at least 1 m above the perforated bottom, that the temperature in the lower part of the fluidized bed is set to 4 to 30°C higher than in the upper part of the fluidized bed and that the fluidizing gas emerges from the openings of the perforated bottom into the fluidized bed at velocities of 30 to 200 m/sec.
9. A method according to claim 8, characterized in that a sulphur-binding material is added to the reactor and the quantity is set such that the sulphur content of the gold ore is predominantly bound.
10. A method according to one of claims 8 or 9, characterized in that additional fuel is introduced into the fluidized bed.
11. A method according to claim 9, characterized in that the sulphur-binding material is calcined in a separate fluidized bed before being used in the reactor and the calcined product is passed into the reactor in the hot state.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4103965.3 | 1991-02-09 | ||
| DE4103965A DE4103965C1 (en) | 1991-02-09 | 1991-02-09 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2060878A1 CA2060878A1 (en) | 1992-08-10 |
| CA2060878C true CA2060878C (en) | 2003-01-28 |
Family
ID=6424724
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002060878A Expired - Lifetime CA2060878C (en) | 1991-02-09 | 1992-02-07 | Process of roasting refractory gold ores |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0501542B1 (en) |
| AU (1) | AU643870B2 (en) |
| BR (1) | BR9200431A (en) |
| CA (1) | CA2060878C (en) |
| DE (2) | DE4103965C1 (en) |
| ES (1) | ES2087427T3 (en) |
| OA (1) | OA09588A (en) |
| ZA (1) | ZA92946B (en) |
Families Citing this family (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ZA926237B (en) * | 1991-09-25 | 1993-03-03 | Bhp Utah Int Inc | Sulfide roasting with lime. |
| US5380504A (en) * | 1993-04-23 | 1995-01-10 | Fuller Company | Treatment of gold bearing ore |
| DE4329417C1 (en) * | 1993-09-01 | 1994-08-18 | Metallgesellschaft Ag | Process for roasting refractory gold ores |
| 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 |
| DE19719481C2 (en) * | 1997-05-07 | 2000-09-07 | Metallgesellschaft Ag | Process for setting a circulating fluidized bed |
| AUPP208498A0 (en) * | 1998-03-02 | 1998-03-26 | Arton (No 001) Pty Ltd | Gold recovery process |
| DE10260739B3 (en) | 2002-12-23 | 2004-09-16 | Outokumpu Oy | Process and plant for producing metal oxide from metal compounds |
| DE10260741A1 (en) | 2002-12-23 | 2004-07-08 | Outokumpu Oyj | Process and plant for the heat treatment of fine-grained solids |
| DE10260738A1 (en) | 2002-12-23 | 2004-07-15 | Outokumpu Oyj | Process and plant for conveying fine-grained solids |
| DE10260733B4 (en) | 2002-12-23 | 2010-08-12 | Outokumpu Oyj | Process and plant for the heat treatment of iron oxide-containing solids |
| DE10260737B4 (en) | 2002-12-23 | 2005-06-30 | Outokumpu Oyj | Process and plant for the heat treatment of titanium-containing solids |
| DE10260731B4 (en) | 2002-12-23 | 2005-04-14 | Outokumpu Oyj | Process and plant for the heat treatment of iron oxide-containing solids |
| DE10260734B4 (en) | 2002-12-23 | 2005-05-04 | Outokumpu Oyj | Process and plant for the production of carbon coke |
| DE102015107435A1 (en) * | 2015-05-12 | 2016-11-17 | Outotec (Finland) Oy | Process for the partial roasting of copper- and / or gold-containing concentrates |
| DE102019209044A1 (en) * | 2019-06-21 | 2020-12-24 | Litherm Technologies GmbH | PROCESS AND DEVICE FOR MANUFACTURING FIRED END PRODUCTS FROM NATURAL GRAINY MATERIALS CONTAINING CARBONATE AS EDUCT |
| EP3799592B1 (en) | 2019-06-21 | 2022-04-13 | Litherm Technologies Gmbh | Method and device for producing fired end products from natural, carbonaceous, granular materials as starting material |
| DE102019209043A1 (en) * | 2019-06-21 | 2020-12-24 | Litherm Technologies GmbH | PROCESS FOR MANUFACTURING FIRED END PRODUCTS FROM NATURAL, CARBONATE-CONTAINING GRAINY SUBSTANCES AS EDUCT AND DEVICE FOR CARRYING OUT THIS PROCESS |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2650159A (en) * | 1949-11-23 | 1953-08-25 | Dorr Co | Treating arsenical gold ores |
| US2596580A (en) * | 1950-01-05 | 1952-05-13 | Dorr Co | Treating arsenical gold ores |
| DE2624302A1 (en) * | 1976-05-31 | 1977-12-22 | Metallgesellschaft Ag | PROCEDURE FOR CARRYING OUT EXOTHERMAL PROCESSES |
| US4919715A (en) * | 1988-06-03 | 1990-04-24 | Freeport Mcmoran Inc. | Treating refractory gold ores via oxygen-enriched roasting |
-
1991
- 1991-02-09 DE DE4103965A patent/DE4103965C1/de not_active Expired - Lifetime
-
1992
- 1992-02-03 ES ES92200288T patent/ES2087427T3/en not_active Expired - Lifetime
- 1992-02-03 DE DE59206264T patent/DE59206264D1/en not_active Expired - Fee Related
- 1992-02-03 EP EP92200288A patent/EP0501542B1/en not_active Expired - Lifetime
- 1992-02-07 OA OA60144A patent/OA09588A/en unknown
- 1992-02-07 BR BR929200431A patent/BR9200431A/en not_active IP Right Cessation
- 1992-02-07 CA CA002060878A patent/CA2060878C/en not_active Expired - Lifetime
- 1992-02-07 AU AU10769/92A patent/AU643870B2/en not_active Expired
- 1992-02-10 ZA ZA92946A patent/ZA92946B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| EP0501542B1 (en) | 1996-05-15 |
| EP0501542A1 (en) | 1992-09-02 |
| BR9200431A (en) | 1992-10-13 |
| DE59206264D1 (en) | 1996-06-20 |
| ZA92946B (en) | 1993-08-10 |
| ES2087427T3 (en) | 1996-07-16 |
| CA2060878A1 (en) | 1992-08-10 |
| AU643870B2 (en) | 1993-11-25 |
| OA09588A (en) | 1993-04-30 |
| AU1076992A (en) | 1992-08-13 |
| DE4103965C1 (en) | 1992-04-09 |
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