Title:
METHOD AND MEANS FOR USING MICROWAVE ENERGY TO OXIDIZE SULFIDIC COPPER ORE INTO A PRESCRIBED OXIDE-SULFATE PRODUCT
Kind Code:
A1


Abstract:
The present invention is directed to the microwave treatment of a class of selected metal ores and concentrates, particularly those known as chalcopyrite, in a fluidized bed reactor. The end product is commonly a mixture of copper oxide and copper sulfate, both of which are liquid soluble and directly recoverable by known techniques. The ratio of the oxide-sulfate mixture end product may be controlled by suitable control of microwave parameters.



Inventors:
Tranquilla, James (New Brunswick, CA)
Application Number:
11/858467
Publication Date:
05/22/2008
Filing Date:
09/20/2007
Assignee:
HW ADVANCED TECHNOLOGIES, INC. (Lakewood, CO, US)
Primary Class:
Other Classes:
204/157.43, 423/1, 423/23, 423/50, 423/52, 423/140, 423/146, 423/544, 423/592.1
International Classes:
C22B3/44
View Patent Images:



Primary Examiner:
COHEN, STEFANIE J
Attorney, Agent or Firm:
Sheridan Ross PC (Denver, CO, US)
Claims:
What is claimed is:

1. A process for recovering a selected metal from a sulfidic material, comprising: (a) passing microwave energy through a bed of the sulfidic material while the material is positioned in a fluidized bed reactor; (b) during step (a), passing a fluidizing gas through the reactor to fluidize the bed of sulfidic material to oxidize selected metal sulfides in the sulfidic material and form an oxidized selected metal-containing material; and (c) removing the oxidized selected metal-containing material from the fluidized bed reactor.

2. The process of claim 1, wherein the oxidized selected metal-containing material, after removal from the fluidized bed reactor, has a ratio of selected metal oxides to selected metal sulfates ranging from about 0.3:1 to about 8:1 and a sulfide sulfur content ranging from about 1 to about 0.5 wt. %.

3. The process of claim 1, wherein the sulfide sulfur content of the sulfidic material is at least about 7 wt. % and wherein a maximum temperature of the bed of sulfidic material and of the selected metal sulfides is no more than about 690° C.

4. The process of claim 1, wherein the selected metal is at least one of copper, nickel, cobalt, and manganese, wherein the fluidized bed is positioned above an inert bed of particulate material, the inert bed of particulate material being too heavy to be fluidized by the fluidizing gas in step (b), wherein the material has a P80 size ranging from about 35 microns to about 75 microns, and wherein the particulate material in the inert bed has a P80 size ranging from about 200 microns to about 300 microns.

5. The process of claim 1, wherein the oxidized material, when removed from the fluidized bed reactor, comprises no more than about 5 wt. % selected metal ferrites and wherein at least most of the selected metal in the oxidized material is in the form of a sulfate.

6. The process of claim 1, wherein the oxidized material, when removed from the fluidized bed reactor, has a maximum sulfide sulfur content of no more than about 1 wt. % and wherein at least most of the selected metal in the oxidized material is in the form of XO, where X is the selected metal.

7. The process of claim 1, wherein the selected metal-containing components of the selected metal-containing material are heated to a temperature ranging from about 580 to about 680° C., wherein a microwave energy source comprising one or more individual generating units generating the microwave energy has a power level in the range of about 1 kw to about 150 kw per generating unit, operates at a frequency ranging from about 300 MHz to about 3 GHz, wherein the reaction chamber has an unloaded Q value ranging from about 1,000 to about 25,000, wherein the microwave energy delivered to the sulfidic material ranges from about 250 to about 300,000 Joules/gm, and wherein at least most of the microwave energy has a frequency of about 915 MHz.

8. The process of claim 1, wherein the selected metal-containing sulfidic material has a sulfide sulfur concentration of no more than about 6 wt. % and wherein a residence time of the material in the reactor is no more than about 30 minutes.

9. The process of claim 1, wherein the fluidized bed reactor operates as a bubbling bed fluidized system, wherein a volumetric fluidizing gas-to-solids ratio is at least about 1:1, and wherein microwave interaction with the material occurs primarily within the selected metal-containing material.

10. A selected metal recovered by the process of claim 1.

11. A process for recovering a selected metal from a sulfide sulfur-containing material, comprising: (a) passing microwave energy through a bed of the sulfide sulfur-containing material while the material is positioned in a fluidized bed reactor; (b) during step (a), passing a fluidizing gas through the reactor to fluidize the bed of sulfide sulfur-containing material to oxidize selected metal sulfides in the sulfide sulfur-containing material and form an oxidized selected metal-containing material; and (c) removing the oxidized selected metal-containing material from the fluidized bed reactor, wherein the fluidized bed is positioned above an inert bed of particulate material, the inert bed of particulate material being too heavy to be fluidized by the fluidizing gas in step (b).

12. The process of claim 11, wherein the oxidized selected metal-containing material, after removal from the fluidized bed reactor, has a ratio of selected metal oxides to selected metal sulfates ranging from about 0.3:1 to about 8:1 and a sulfide sulfur content ranging from about 1 to about 0.5 wt. %.

13. The process of claim 11, wherein the sulfide sulfur content of the sulfide sulfur-containing material is at least about 7 wt. % and wherein a maximum temperature of the bed of sulfide sulfur-containing material and of the selected metal sulfides is no more than about 690° C.

14. The process of claim 11, wherein the selected metal is at least one of copper, nickel, cobalt, and manganese, wherein the sulfide sulfur-containing material has a P80 size ranging from about 35 microns to about 75 microns, and wherein the particulate material in the inert bed has a P80 size ranging from about 200 microns to about 300 microns.

15. The process of claim 11, wherein the oxidized material, when removed from the fluidized bed reactor, comprises no more than about 5 wt. % selected metal ferrites and wherein at least most of the selected metal in the oxidized material is in the form of a sulfate.

16. The process of claim 11, wherein the oxidized material, when removed from the fluidized bed reactor, has a maximum sulfide sulfur content of no more than about 1 wt. % and wherein at least most of the selected metal in the oxidized material is in the form of XO, where X is the selected metal.

17. The process of claim 11, wherein the selected metal-containing components of the selected metal-containing material are heated to a temperature ranging from about 580 to about 680° C., wherein a microwave energy source comprising one or more individual generating units generating the microwave energy has a power level in the range of about 1 kw to about 150 kw per generating unit, operates at a frequency ranging from about 300 MHz to about 3 GHz, wherein the reaction chamber has a Q value ranging from about 1,000 to about 25,000, wherein the microwave energy delivered to the sulfur-containing material ranges from about 250 to about 300,000 Joules/gm, and wherein at least most of the microwave energy has a frequency of about 915 MHz.

18. The process of claim 11, wherein the selected metal-containing and sulfide sulfur-containing material has a sulfide sulfur concentration of no more than about 6 wt.

19. The process of claim 11, wherein the fluidized bed reactor operates as a bubbling bed fluidized system and wherein microwave interaction with the selected metal-containing material occurs primarily within a lean phase medium.

20. A selected metal recovered by the process of claim 11.

Description:

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefits of U.S. Provisional Application Ser. No. 60/826,350, filed Sep. 20, 2006 entitled “Method and Means for Using Microwave Energy to Oxidize Sulfidic Copper Ore into a Prescribed Oxide-Sulfate Product”, which is incorporated herein by this reference.

FIELD OF THE INVENTION

The invention relates generally to the recovery of selected transition metals from sulfidic materials and particularly to the recovery of base metals, particularly copper, from sulfidic materials.

BACKGROUND OF THE INVENTION

Chalcopyrite is a commonly occurring sulfidic copper ore which must be oxidized to liberate the copper and make it amenable to conventional recovery techniques, which include smelting and solvent extraction (SX/EW). Due to the modest value of the finished copper metal, there is always a need for lower-cost methods of production. Coupled with this is the environmental concern over historical smelter operations, which has resulted in the recognition of SX/EW as the most environmentally attractive and economically viable method of treating sulfidic copper ores. However, for any of these processes to be economically successful, the ores must first be concentrated to increase the value per ton processed. Sulfide content may thus be increased many fold up to the order of 30% or greater to form a viable “smelter grade” concentrate.

A large portion of the cost of producing copper product is the cost associated with the production of the high-value concentrate. Of this, grinding is the most energy consumptive and costly, however this is an unavoidable step in conventional concentration which relies on increasingly finer grinding to liberate (and separate) the sulfide particles (containing the copper) within the ore. There is, therefore, a continuing need for more economical processing techniques, which will enable the usage of lower grade concentrates.

In sulfide roasters, chalcopyrite oxidizes according to the following reactions:


2CuFeS2+6.5O2→Fe2O3+2CuO+4SO2 (1)


2CuFeS2+7.5O2→Fe2O3+2CuSO4+2SO2 (2)


2CuFeS2+6O2→Cu2O.FeO3+4SO2 (3)

Reaction (3) is actually an intermediate reaction which, upon further oxidation, produces CuO.Fe2O3 which is an insoluble spinel product and is therefore undesirable. Since reaction (3) is only favored at temperatures greater than about 690° C., it is therefore necessary to restrict the operating temperature below this level to produce the desired oxide (CuO) and sulfate (CuSO4) products.

A process which operates on the basis of reactions (1) and (2) is essentially a roasting operation with a calcine product which is amenable to SX/EW recovery. If the roaster operation is carried to higher temperatures sufficient to liquefy the products, the result is a smelter which produces a metallic matte containing relatively impure copper as well as other products. Refining of the copper matte is carried out by dissolving the matte and performing an electrowinning operation.

An important part of the roasting and smelting operations is the necessity for high sulfur concentrations which provides the fuel to drive the process. Low sulfide concentrates must be augmented with auxiliary sulfide to act as fuel, without which the entire operation cools and extinguishes.

The use of radio frequency and microwave energy for heating many different types of minerals has been widely published in both the technical and patent literature. Many of these references relate to the relative absorption characteristics (microwave receptivity) of the materials rather than to any particular process. In nearly all cases, exposure of mineral materials to microwave energy was done by placing small samples into crucibles and heating in a domestic microwave oven.

Kruesi (U.S. Pat. No. 4,324,582) discloses the microwave heating of copper ores and the formation of oxide and sulfate products. More specifically, his disclosure relates to a situation in which these products are produced separately under different operating conditions (different temperature regimes). As well, Kruesi does not disclose an applicator or device in which the microwave process can be practiced such that the process variables (temperature, feed rate, gas composition, gas/solids intermixing) can be controlled as in an industrial process.

SUMMARY OF THE INVENTION

These and other needs are addressed by the various embodiments and configurations of the present invention. The present invention is directed generally to microwave-induced oxidation of selected metal sulfides to render the selected metal sulfides recoverable inexpensively by suitable selected metal recovery techniques.

In a first embodiment, a process for recovering a selected metal from a sulfidic material is provided that includes the steps:

(a) passing microwave energy through a bed of the sulfidic material while the material is positioned in a fluidized bed reactor;

(b) while the bed is irradiated, passing a fluidizing gas through the reactor to fluidize the bed of sulfidic material, oxidize selected metal sulfides in the sulfidic material, and form an oxidized selected metal-containing material; and

(c) removing the oxidized selected metal-containing material from the fluidized bed reactor.

The selected metal is preferably one or more of copper, nickel, cobalt, and manganese, with copper being more preferred.

The sulfide sulfur is oxidized to sulfates and/or sulfur dioxide, and the selected metal to selected metal sulfates or non-sulfur containing selected metal oxides, such as the compound XO, where X is the selected metal. The ratio of selected (sulfur-free) metal oxides to selected metal sulfates in the removed oxidized selected metal-containing material preferably ranges from about 0.3:1 to about 8:1, and the removed oxidized material preferably has a sulfide sulfur content of no more than about 0.5 wt. %. In one application, most of the selected metal in the removed oxidized material is in the form of a sulfate. In another application, most of the selected metal in the oxidized material is in the form of XO, where X is the selected metal.

In one configuration, the sulfide sulfur content of the sulfidic material, before oxidation, is at least about 7 wt. %.

In one configuration, the sulfide sulfur concentration of the sulfidic material, before oxidation, is no more than about 6 wt. %.

In both of the configurations, a maximum temperature of the bed of sulfidic material and of the selected metal sulfides, during microwave irradiation and fluidization, is no more than about 690° C. Below this temperature selected metal ferrite formation is discouraged. Preferably, the oxidized material, when removed from the fluidized bed reactor, includes no more than about 5 wt. % selected metal ferrites.

In an exemplary configuration, the selected metal-containing components of the selected metal-containing material are heated to a temperature ranging from about 580 to about 680° C. To accomplish this result, the microwave energy source comprising one or more individual generating units generating the microwave energy preferably has a power level ranging from about 1 kw to about 150 kw per generating unit and operates at a frequency ranging from about 300 MHz to about 3 GHz. The reaction chamber preferably has an unloaded Q value ranging from about 1,000 to about 25,000, and the microwave energy delivered to the carbon-containing and gold-containing material preferably ranges from about 250 to about 300,000 Joules/gm. Most, if not all, of the microwave energy has a preferred frequency of about 915 MHz.

In one reactor configuration, the fluidized bed of sulfidic material is positioned above an inert bed of particulate material. The inert bed of particulate material is too heavy to be fluidized by the fluidizing gas and is substantially inert chemically during microwave irradiation and bed fluidization. The particulate sulfidic material preferably has a P80 size ranging from about 35 microns to about 75 microns, and the particulate material in the inert bed a P80 size ranging from about 200 microns to about 300 microns.

The fluidized bed reactor can operate as a bubbling bed fluidized system, and the microwave interaction with the material can occur primarily within the lean phase medium (i.e., the bed of sulfidic material).

The present invention is particularly effective for the microwave treatment of a class of copper ores and concentrates known as chalcopyrite, whereby the end product is a mixture of copper oxide and copper sulfate, both of which are highly soluble in solvents, such as water and mineral acid, and directly amenable to solvent extraction electrowinning (SX/EW) copper recovery techniques. The problem of fine grains of copper-containing concentrates reporting to the slimes can be eliminated, thereby making it practical to recover the copper from copper concentrates.

Because sulfur-free copper oxides and copper sulfates are produced simultaneously under the same operating conditions, the ratio or relative proportions of (sulfur-free) copper oxides and copper sulfates in the removed oxidized material may be tailored for a selected downstream metal recovery process because of the precise process control afforded by the microwave process. For example, controlling the ratio can be a significant feature in the downstream metal recovery process because it provides a methodology for controlling excess acid generation during chemical pressure oxidation, such as in an autoclave. This can be particularly important in high and medium temperature pressure oxidation applications. An added advantage of the disclosed process is that it is most efficient in treating low concentration ores and concentrates known as “rough concentrates”. As will be appreciated, these materials are commonly more coarsely ground than copper ores and concentrates subjected to conventional pressure oxidation, thereby avoiding very significant grinding and concentrating costs and making it possible to economically process copper ores which would otherwise be subeconomic.

The present invention can provide a number of advantages depending on the particular configuration. By way of example, the use of microwave energy rather than radiant thermal energy can provide substantial energy savings. Microwaves heat and activate primarily the selected metal component of the sulfidic material and not the gangue (or other components). Microwave heating can extremely rapidly heat the selected metal components. The present invention can produce the selected metal oxide and sulfate end products more rapidly than by using either a simple batch process (as disclosed by Kruesi) or a conventional bubbling fluidized bed device. The microwave-controlled fluidized bed reactor of the present invention can beneficially operate as a “lean phase” (i.e. high gas to solids ratio) fluidized system similar to the elutriated (cyclone) product stream described herein.

These and other advantages will be apparent from the disclosure of the invention(s) contained herein.

As used herein, “at least one”, “one or more”, and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together.

It is to be noted that the term “a” or “an” entity refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. It is also to be noted that the terms “comprising”, “including”, and “having” can be used interchangeably.

“Sulfidic” refers to materials containing sulfide sulfur. The sulfide sulfur can be present as many types of compounds or minerals, including marcasite, pyrrhotite, chalcopyrite, arsenopyrite, bornite, chalcocite, covellite, galena, molybdenite, sphalerite, and tetrahedrite, to name but a few.

The preceding is a simplified summary of the invention to provide an understanding of some aspects of the invention. This summary is neither an extensive nor exhaustive overview of the invention and its various embodiments. It is intended neither to identify key or critical elements of the invention nor to delineate the scope of the invention but to present selected concepts of the invention in a simplified form as an introduction to the more detailed description presented below. As will be appreciated, other embodiments of the invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a fluidized bed reactor according to an embodiment of the invention;

FIGS. 2A and 2B are plots of percent copper recovery (vertical axis) against temperature (horizontal axis);

FIGS. 3A and 3B are plots of percent copper recovery (vertical axis) against temperature horizontal axis);

FIGS. 4A and 4B are plots of percent copper recovery (vertical axis) against lbs. sulfur/cubic foot of air (horizontal axis); and

FIGS. 5A and 5B are plots of percent copper recovery (vertical axis) against lbs. sulfur/cubic foot of air (horizontal axis).

DETAILED DESCRIPTION

The present invention discloses a means by which microwave energy is used to initiate and sustain the reactions described in (1) and (2) above. For sulfur concentrations above approximately 7 wt. %, these reactions, once initiated, will continue autogeneously using the heat generation from the burning sulfur; below 7 wt. % concentration, the process requires additional energy, which is herein disclosed as being microwave energy. Because the operation does not rely on the autogenous burning of sulfur as an energy source, the temperature may be controlled by a variety of means preferably to less than about 690° C. and more preferably within the range of about 580° C.-680° C. so as to prevent the formation of insoluble spinel and to control the oxide-sulfate ratio of the calcine product.

Microwave energy is particularly attractive because it heats selectively certain components of the material more than others. For most sulfidic materials, the gangue is weakly microwave absorptive, microwave reflective, or substantially transparent to microwave radiation while minerals containing certain metals, particularly copper, are highly absorbent of microwave energy. Other transition metals that form minerals absorptive of microwave energy include nickel, cobalt, and manganese from their oxide and silicate minerals and molybdenum and rhenium from their sulfide minerals. Examples of transition metals that are not too microwave absorptive include sphalerite and the oxide ores of zinc and iron.

FIG. 1 shows a first embodiment of the present invention. A fluidized bed reactor includes a metallic cavity (1) to which is connected a waveguide port (2) through which microwave energy is introduced into the cavity (1). The waveguide (3) is partitioned from the cavity by means of a window (4), which is transparent to the microwave energy but prevents gas and solids from entering the waveguide (3). A tuning device (5) is inserted into the waveguide (3) to maximize microwave energy transfer into the reactor vessel. Both the window (4) and tuner (5) devices are well known to those knowledgeable in the usage of microwave energy.

The microwave containment walls of the reactor 10 are preferably constructed of a microwave reflective material. The reaction vessel may optionally include an inner vessel which is constructed of essentially microwave-transparent material. Examples of suitable materials include alumina, aluminum silicate, quartz, and low-metal ceramics (which are substantially transparent to microwave energy) and stainless steel, carbon steel, nickel alloys and aluminum alloys (which are reflective of microwave energy).

The metal-containing material, which is commonly chalcopyrite ore or concentrate, is introduced into the reactor vessel by means of a screw fed duct (6). The rate at which material is fed into the reactor is determined by the speed of the screw feeder. Typically, the metal-containing material is fed into the vessel at a rate sufficient to provide a desired average residence time of the material in the reactor cavity.

The metal-containing material has a variety of components. Typically, the material comprises at least about 5 wt. % sulfide sulfur and more typically from about 7 to about 35 wt. % sulfide sulfur, at least about 5 wt. % and more typically from about 10 to about 30 wt. % selected base metal, and no more than about 5 wt. % selected base metal oxides, with the remainder being one or more of silicates, carbonates, and other oxides. In one configuration, the material contains no more than about 6 wt. % sulfide sulfur and is therefore not capable of autogenous oxidation. The material may be in the form of an ore, concentrate, tailings, or combinations thereof.

Because water is strongly absorptive of microwave energy, it is preferred that the material be dried before processing the reactor cavity (1). This is preferably done by heating the material at low temperature and/or exposing the material to sunlight or dry air for a prolonged period. Preferably, the water content of the material is no more than about 10 wt. % and even more preferably no more than about 1 wt. %. Excess water in the material can increase microwave energy requirements.

The metal-containing material to be processed is finely ground before introduction into the reactor vessel. Preferably, the material is comminuted to a P80 size preferably ranging from about 35 microns to about 75 microns and introduced through the screw fed duct (6) at a material flow rate ranging from about 4 lbs. sulfur/hr/square foot of fluidizing grate area to about 12 lbs. sulfur/hr/square foot of fluidizing grate area.

A molecular oxygen-containing fluidizing gas is introduced into the reactor vessel by means of an inlet duct (7), which is connected to a fluidizer distribution plate (8) located near the bottom of the reactor vessel. Gas velocity is controlled by means of a fan (9) installed in the gas inlet duct. Fluidizing gas preferably comprises at least about 15 mole % molecular oxygen and even more preferably is ambient air. Ambient air includes other components, primarily including water vapor, nitrogen, and carbon dioxide.

Solid materials within the reactor vessel include the material (10) to be treated and a resident sand bed (11). The sand bed (11) within the reactor vessel comprises heavier particles than the particulate material and is not fluidized by the gas stream. Thus, the sand in the sand bed (11) preferably remains in the reactor vessel and provides a thermal ballast (or heat retention media) for the reactor and a means for assisting in the cleanout of the reactor vessel. The sand typically has a P80 size preferably ranging from about 200 microns to about 300 microns. As will be appreciated, other inert materials may be employed in the bed (11) in lieu of or in addition to sand.

The material (10) to be treated is fluidized by the gas stream and carried by the fluidizing gas to the exhaust port (12) to which is attached a cyclonic filter or similar device (13). The device (13) separates the solids from the gas stream. Separated solids are removed as a calcine product (14). The exhaust gas stream (15) may then by further filtered as necessary and vented. A portion of the exhaust gas stream may be recirculated (16) and mixed with the inlet fluidizing gas as a means of controlling molecular oxygen content in the gas stream to the reactor vessel. Preferably, the molecular oxygen is present in an amount that is at least stoichiometric relative to the sulfide sulfur content of the material (10) and even more preferably in an amount that is at least about 110 to about 200% of the stoichiometric amount, and the molecular oxygen content of the fluidizing gas when introduced into the bottom of the vessel is at least about 10 mole % and even more preferably ranges from about 15 to about 20 mole %.

The fluidizing velocity of the gas is preferably sufficient to suspend the material (10), but not sufficient to suspend the sand in the bed (11), and provide a selected residence time of the material in the bed (10). Preferably, the velocity of the fluidizing gas ranges from about the minimum fluidization velocity of the largest ore material particle size to about the fluidization terminal velocity of the smallest ore particle size.

While the material is fluidized in the bed, it is irradiated with microwave energy. The microwave energy is absorbed by the selected metal sulfides, thereby rapidly heating the bed. The heating mechanism results from a combination of dielectric and ohmic heating, whereby both electrical displacement and conduction currents are used to convert the electromagnetic energy directly into heat within the material (10). The efficiency of this energy conversion is dependent upon the dielectric properties of the material to be treated. Microwave receptor elements, principally selected metal sulfides, are rapidly heated in a controlled manner.

Commonly, the fluidized bed operates as a lean phase fluidized system, and the microwave interaction with material occurs substantially within the lean phase medium. As will be appreciated, a lean phase system has a relatively high gas-to-solids ratio. Commonly, the volumetric fluidizing gas-to-solids ratio is at least about 1:1 and even more commonly ranges from about 2:1 to about 10:1.

The microwave energy heats the metal-containing materials to a temperature sufficiently high to oxidize the sulfide sulfur in the metal-containing material according to equations (1) and (2) above but insufficient to oxidize a significant amount of the sulfide sulfur according to equation (3) above. Preferably, no more than about 5 wt. % and even more preferably no more than about 1.0 wt. % of the sulfide sulfur is oxidized according to equation (3). At least most, and preferably at least about 90 wt. %, of the remaining sulfide sulfur is oxidized according to equations (1) and/or (2). Preferably, at least most, more preferably at least about 90%, and even more preferably at least about 95% of the selected metal is in the form of XO or XSO4 (where X is the selected metal) and no more than about 5%, more preferably no more than about 2.5%, and even more preferably no more than about 1.0% of the selected metal is in the form of a ferrite. To accomplish these results, the operating temperature of the bed is preferably no more than about 690° C., more preferably ranges from about 350 to about 680° C., even more preferably ranges from about 550 to about 680° C., and even more preferably ranges from about 580 to about 680° C.

The material outputted via output (12) from the reactor cavity has a preferred maximum sulfide sulfur content of no more than about 1 wt. % and even more preferably of no more than about 0.5 wt. %. Stated another way, preferably at least 80% and even more preferably at least about 95% of the sulfide sulfur is converted to a sulfate or other type of sulfur oxide.

Temperature, heating rate, and/or microwave coupling can be controlled in a number of ways. As will be appreciated, dielectric loss factors of the material constituents can be temperature dependent. Accordingly, it is desirable to optimize dynamically the coupling between the magnetron or other microwave generating source and the cavity (1) and the resonant tuning of the cavity (1). The degree of coupling or matching of the cavity with the magnetron determines the efficiency with which energy is delivered to the cavity (1). Preferred coupling is as close to unity as possible. In one approach, the power of the microwaves and the time of application of the microwaves are controlled. In another approach, the power of the microwaves is adjusted according to the heating temperature. In yet another approach, an aperture size of a variable iris and/or the tuner device (5) positioned in the waveguide is adjusted in response to the temperature of the bed and/or the power of the reflected microwaves (relative to the microwaves entering the reactor). Coupling is optimized as reflected energy is minimized.

Preferably, the microwave source comprising one or more individual generating units generates power levels in the range of about 1 kw to about 150 kw per generating unit. A preferred power level is from about 10 to about 120 kw per generating unit. The specific energy delivered to the bed in the cavity (1) ranges from about 250 to about 300,000 Joules/gm or from about 2 to about 20 kW-h/t. The unloaded Q factor in the cavity (1) preferably ranges from about 1,000 to about 25,000, but most preferably is at least about 200,000. The frequency of the microwave source preferably ranges from about 300 MHz to about 3 GHz, with preferred microwave frequencies being within the Industrial, Scientific, and Medical (ISM) bands of about 915 MHz and about 2,450 MHz, with the ISM band of about 915 MHz being particularly preferred.

Process control is normally effected using a variety of instrumentation positioned in the cavity (1). For example, temperature probes are installed at various positions within the fluidized bed and all feed and discharge lines, including the gas inlet and outlet lines. Gas pressure and product monitors are installed in all gas lines. Material flow through the reactor cavity is measured either through flow meters or by mass measurements. A microwave reflection detector is positioned in the waveguide.

In a batch operation, completion of sulfide sulfur oxidation can be indicated by a substantial drop in bed temperature even though microwave energy is still being passed through the bed. This is so because the microwave absorptivities of the gangue components of the material and of the selected metal oxides are substantially less than that of selected metal sulfides. Typically, the oxidized material is removed from the cavity when the bed temperature decreases, even more typically when the bed temperature decreases by at least about 50° C., even more typically by at least about 100° C., and even more typically by at least about 200° C.

Preferably, the residence time of the material in the reactor cavity is no more than about 30 minutes and even more preferably ranges from about 5 to about 10 minutes, though the precise residence time depends on the power of the microwave source and the nature of the gangue associated with the selected metal sulfide.

In operation, selected metal-containing material is quickly heated within the reactor vessel by the microwave energy such that the desired oxidation reactions occur essentially to completion within the time interval during which the ore material is transported (by the fluidizing gas stream) from the feed port (6) to the exhaust port (12). As will be appreciated, the fluidized bed reactor can be operated in any desirable manner, including as a bubbling bed fluidized system. Conditions within the reactor vessel may be controlled by the screw feed rate, gas velocity, microwave power intensity and fluidizing gas composition, the latter of which includes a provision to inject an inert gas (17) such as nitrogen to quickly starve the reactions. All of the control mechanisms may be actuated electronically and integrated into the overall reactor control system, which may be used to maintain a desired set of reactor operating conditions. By this means, for example, the reaction temperature may be maintained within a specified range to ensure the formation of desired products.

In one configuration, the molar or weight ratio of selected metal oxide to selected metal sulfates in the final oxidized material is controlled. This is done by controlling the power of the microwave generator and residence time. Controlling the ratio can be important to the downstream metal recovery process. Ratio control, for example, provides a methodology to control excess acid generation from sulfide sulfur. Preferably, the ratio of selected metal oxide to selected metal sulfates ranges from about 0.3:1 to about 8:1 and more preferably ranges from about 1:1 to about 8:1, and, when further sulfide sulfur oxidation is to be performed chemically, such as in an autoclave, the sulfide sulfur content of the oxidized material (after removal from the fluidized bed reactor) is preferably no more than about 1 wt. % and even more preferably ranges from about 1 to about 0.5 wt. %.

The selected metal may be recovered from the oxidized material using known hydrometallurgical methods. For example, the selected metal may be leached, such as using sulfuric acid or water, from the oxidized material to form a pregnant leach solution including the selected metal. The selected metal may be precipitated from the pregnant leach solution, electrochemically collected by cementation, or adsorbed onto an organic sorbent, solvent, or resin. The selected metal-loaded sorbent, solvent, or resin may be stripped using a mineral acid eluant, such as sulfuric acid, and the loaded eluant subjected to electrowinning. Alternatively, the selected metal may be directly electrowon from the pregnant leach solution without an intermediate sorbtion/desorbtion step.

EXPERIMENTAL

Chalcopyrite concentrate was used in a series of experiments to demonstrate the oxidation reactions. Feed material was analyzed and was found to consist of chalcopyrite (dominant), pyrite, minor isocubanite (CuFe2S3) and covellite (CuS). Chemical analysis is shown below.

Copper30%
Sulfur34%
Iron27%
Leachable copper6.7% 

Several lots of concentrate were prepared by blending with silica sand to 12 wt. %, 9 wt. % and 6 wt. % sulfur to simulate various rougher concentrate grades. All tests were conducted over periods of several hours in order to achieve steady state continuous feed operation. The following Table presents selected results.

Reactor Unit Flowrate
ConcentrateTemperatureOff-gaslbs/h/ft2Calcine Solubility (%)
Cu %S %Range (□ C.)SO2O2Total feedSWaterAcid
30.034600-6203.4-4.210.713.84.768.0100.0
10.612580-6004.5-5.18.542.85.175.099.5
7.99620-640 9.0-10.63.4129.911.766.097.0
5.36600-6207.5-9.44.1168.210.143.088.5

In these experiments, the fluidized bed microwave reactor was operated such that the product discharge comprised two separate streams. One stream consisted of material which was discharged from the reactor bed by means of an overflow weir through an air locked valve; this is designated as the calcine product. The other product stream consists of material which was directly elutriated by the fluidizing gas from the reactor and captured and separated from the gas in a cyclone filter; this stream is designated as the cyclone product. The significant difference between these streams is that the calcine product has an average residence time within the reactor vessel of several minutes (depending upon the weir height and feed rate) whereas the cyclone product has an average residence time of only a few seconds (depending upon the gas velocity and reactor height). These product streams relate to two different possible configurations for the reactor vessel.

FIGS. 2-5 present data relating the operation of the process over a range of operating conditions for a sulfur concentration of 6 wt. % which was determined to be at or slightly below the autogeneous sulfur concentration. Copper extractions averaged 96.7 wt. % and 89.3 wt. % across all tests for calcine and cyclone products respectively.

It may be noted that at high sulfur concentration, the feed capacity is limited and oxygen utilization is low. Material feed rate control is used to control operating temperature which must be limited to below 690° C. to prevent the formation of insoluble products.

As the sulfur concentration decreases (for rougher concentrates), the reactor capacity (expressed in lbs per hour per unit area of fluidizer) increases significantly due primarily to increased heat removal through the gangue material. Since sulfur capacity is directly related to copper production, this implies an increase in reactor copper productivity for low sulfur concentrates. Also, lower sulfur concentration results in increased oxygen utilization which provides added control of the product oxide-sulfate ratio and a further increase in SO2 concentration which leads to more efficient downstream acid generation.

A number of variations and modifications of the invention can be used. It would be possible to provide for some features of the invention without providing others.

For example in one alternative embodiment, the fluidized bed reactor is used to heat selected metals in non-sulfide form, such as oxides, hydroxyl carbonates, and silicates.

In another alternative embodiment, the selected metal sulfides are heated in the presence of molecular oxygen to convert them primarily to sulfates (a “sulfation roast”) or primarily to oxides and sulfur dioxide. Heating to convert the selected metal sulfides primarily to selected metal sulfates is preferred as the reaction requires less energy than complete conversion to selected metal oxides and sulfur dioxide. In addition, there will be a lesser amount of sulfur dioxide to scrub from the off-gas.

The present invention, in various embodiments, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various embodiments, subcombinations, and subsets thereof. Those of skill in the art will understand how to make and use the present invention after understanding the present disclosure. The present invention, in various embodiments, includes providing devices and processes in the absence of items not depicted and/or described herein or in various embodiments hereof, including in the absence of such items as may have been used in previous devices or processes, e.g., for improving performance, achieving ease and\or reducing cost of implementation.

The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments for the purpose of streamlining the disclosure. The features of the embodiments of the invention may be combined in alternate embodiments other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention.

Moreover, though the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations, combinations, and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.