CROSS-REFERENCE TO RELATED APPLICATIONS

None.

FIELD OF THE INVENTION

Embodiments of the invention relate to hydrometallurgical processing and more particularly, to novel iron control techniques and methods for selectively removing iron from hydromet solutions.

BACKGROUND OF THE INVENTION

Prior art iron control processes involve the synthesis of goethite to remove iron from solution via precipitation. Formation of goethite involves high temperatures (e.g., 80-100 °C) which cause metal value losses and increase overall operating expenditures (OPEX).

To date, all known hydrometallurgical processes used for iron control have difficulty in removing substantial amounts of iron, especially Fe(II),from hydrometallurgical process solutions, without incurring significant losses of other target metal values which may also be present in the solution. A downside of iron removal from a pregnant leach solution (PLS) is that a metal value must be kept in solution and not co-precipitate with the iron being precipitated. Additionally, the iron precipitate must be in particulate form and filterable as opposed to a ferric hydroxide gel. A downside of raffinate iron removal is that acid may be lost in pH adjustment and may need to be replenished which increases OPEX significantly due to added costs of pH adjustment reagents and acid which needs replacing.

In particular, to date, there is no known iron control/removal process that can achieve both greater than 90% selective separation of iron from a hydromet solution containing another metal value (e.g., copper and/or zinc), whilst still achieving greater than 90% recovery of the metal value after the iron has been selectively separated out of the hydromet solution with process residence times of less than one hour.

There exists a long felt need to provide an inexpensive process for removing most of the iron from a hydromet solution, without compromising metal value recovery.

OBJECTS OF THE INVENTION

It is an object of embodiments of the present invention, to affordably reduce iron buildup in hydrometallurgical solutions.

It is another object of embodiments of the present invention, to selectively remove iron from solution in the presence of dissolved copper (Cu ²⁺ ) and zinc (Zn ²⁺ ).

It is another object of embodiments of the present invention, to reduce the amount of metal value losses from solution which might be incurred during iron removal steps.

These and other objects of the present invention will be apparent from the drawings and description herein. Although every object of the invention is believed to be attained by at least one embodiment of the invention, there is not necessarily any one embodiment of the invention that achieves all of the objects of the invention. BRIEF SUMMARY OF THE INVENTION

A process for controlling iron within a hydromet solution and/or removing iron from a hydromet solution containing a dissolved metal value is disclosed. The process may comprise the step of seeding the hydromet solution with a seed precipitate material comprising iron. Seeding may be performed at a temperature less than 80 degrees Celsius, and preferably at a pH which is below 3. The process may further comprise the step of precipitating iron out of the hydromet solution to form an iron precipitate and a substantially iron-free solution. The process may further comprise the step of extracting a metal value from the substantially iron- free solution. In some embodiments, the metal value may be selected from copper, zinc, gold, silver, or a combination thereof, without limitation.

In some embodiments, at least 90% recovery of the metal value may be accomplished during the step of extracting a metal value from the substantially iron-free solution. In some embodiments, the seed precipitate material comprising iron may comprise a material selected from Fe ₂ 0 ₃ , basic iron sulfate, jarosite, goethite, and schwertmannite, without limitation. In some embodiments, the process may further comprise removing produced gypsum from the hydromet solution prior to the step of seeding the hydromet solution, without limitation. In some embodiments, at least 90% of the iron in the hydromet solution may be removed from the hydromet solution during the step of precipitating iron out of the hydromet solution, without limitation.

In some embodiments, the hydromet solution may have a residence time of less than

30 minutes during the combined steps of seeding the hydromet solution and precipitating iron out of the hydromet solution, without limitation. In some embodiments, the hydromet solution may comprise a copper and zinc pregnant leach solution; wherein and virtually no co-absorption of copper and zinc may occur during the process. In some embodiments, iron removed from the hydromet solution may comprise iron produced by leaching an iron- containing metal sulfide, such as FeS ₂ or CuFeS ₂ , without limitation.

Further details may be appreciated from the below detailed description, appended drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To complement the description which is being made, and for the purpose of aiding to better understand the features of the invention, a set of drawings illustrating various methods and systems according to certain embodiments has been added to the present specification as an integral part thereof, in which the following has been depicted with an illustrative and non limiting character. It should be understood that like reference numbers used in the drawings (if any are used) may identify like components. In the drawings:

FIG. 1 suggests an iron control/removal process according to some non-limiting embodiments.

FIG. 2 schematically illustrates preferred residence times of a hydromet solution during iron precipitation/removal steps discussed herein.

FIG. 3 schematically illustrates a non-limiting system or flowsheet which may be used to perform embodiments of the process disclosed herein.

FIGS. 4 and 5 schematically illustrate where embodiments may be employed within a leach circuit.

In the following, the invention will be described in more detail with reference to drawings in conjunction with exemplary embodiments. DETAILED DESCRIPTION OF THE INVENTION

The following description of the non-limiting embodiments shown in the drawings is merely exemplary in nature and is in no way intended to limit the inventions disclosed herein, their applications, or their uses.

Disclosed herein, are embodiments of a process for removing iron from hydromet solutions and/or for controlling iron buildup within a hydromet solution which can take place during the leaching of a metal sulfide. Some embodiments involve iron control and/or selective removal of iron from hydromet solutions which contain copper and/or zinc. It is envisaged that described embodiments may work equally well for pregnant leach solutions comprising other target metal values including, but not limited to, silver and/or gold.

Embodiments of the process may involve the step of controlling the pH level of the hydromet solution by adding a base or acid over time. Preferred pH values are below 3.0, for example, at or around 2.5, without limitation.

The process may further involve the step of controlling temperature by heating or cooling the hydromet solution as needed, for example, using a jacketed reactor or a reactor equipped with a thermocouple and a controllable heating element, heat exchanger, or the like, without limitation. In some embodiments, the process may involve the step of controlling temperature of the hydromet solution to be less than what is traditionally used to form goethite in conventional iron control processes (e.g., 80-100 degrees Celsius). More preferably, temperature of the hydromet solution may be controlled to be less than 80 degrees Celsius, but greater than 20 degrees Celsius. In some embodiments, the process may involve the step of controlling temperature of the hydromet solution to be within the range of between 30 °C and 70 °C, and more preferably, between approximately 40 °C and 60 °C, without limitation. For example, in some preferred embodiments, the hydromet solution may be maintained at approximately 45 degrees Celsius or 50 degrees Celsius, without limitation. Temperatures higher than 80 degrees Celsius which are used in prior art goethite and jarosite precipitation processes may lead to co-absorption of metal values in solution (e.g., copper, zinc, and Ag), and may lead to losses thereof during downstream recovery.

The inventors discovered that if the hydromet solution becomes too hot during the iron control/removal process, then copper and/or zinc losses are likely to occur, if such metal values are present within the hydromet solution. The inventors further discovered that optionally, a gypsum separation stage may be advantageously included prior to a final Cu precipitation step, prior to a final Zn precipitation step, or prior to the iron precipitation via seeding, without limitation.

The process may further comprise adding a particulate seed comprising iron as an Fe(III) oxide or an Fe(III) sulfate to the hydromet solution. In some embodiments, the particulate seed may comprise Fe Ch, without limitation. In some embodiments, the particulate seed may comprise basic iron sulfate (Fe(0H)S0 ₄ ), without limitation. In some embodiments, the particulate seed may comprise jarosite (MeFe ¹⁺ ₃ (0H) ₆ (S0 ₄ ) ₂ ), without limitation, wherein Me is known to be a +1 charged cation such as Na ⁺ or K ⁺ . In some embodiments, the particulate seed may comprise hematite (Fe ₃ 0 ₄ ), without limitation. If used, the hematite may be provided from iron ore, hematite concentrate, and/or autoclave leach residue comprising hematite, without limitation. In some embodiments, the particulate seed may comprise goethite (FeOOH), without limitation. In some embodiments, the particulate seed may comprise schwertmannite (FesOsiOFI SiT -nFbO; or, Fe ³⁺ ₁₆ 0 ₁₆ ( O H , S O _{4 ) 12- 13} · 10- 12 H ₂ O ) , without limitation. In some embodiments, the particulate seed may comprise a combination of two or more of the following, without limitation: Fe ₂ 0 ₃ , basic iron sulfate, jarosite, hematite, goethite, schwertmannite.

The inventors have discovered that the rate of Fe(III) precipitation may be a key determining factor in producing either goethite or schwertmannite as the precipitated iron product. Slow precipitation for Fe(III) seems to give goethite. Fast precipitation seems to yield schwertmannite.

According to some non-limitation embodiments, the process may facilitate

achievement of selective separation of 90% or more of the iron in solution from the hydromet solution, whilst still enabling greater than 90% recovery of a target metal (such as copper and/or zinc) from a pregnant leach solution (PLS).

According to some embodiments, it may be critical that the iron removal steps (e.g., seeding a hydromet solution, precipitating an iron product from the hydromet solution, and filtering the hydromet solution to remove iron solids therefrom) are performed within a residence time window which is less than 1/2 hour to avoid substantial losses of target metals from solution. According to some embodiments, a shorter window or slightly larger window may be expected. For example, according to some embodiments, it may be critical that the step of precipitating iron from a hydromet solution is performed within a residence time window that is less than about 15 minutes, or less than about 20 minutes, or less than about 25 minutes, or less than about 35 minutes, or less than about 40 minutes, without limitation.

In some embodiments, the iron control/removal process discussed herein may be able to handle ferric concentrations which are well-above established limitations of methods involving conventional iron removal via the formation of goethite. For example, embodiments of the iron control/removal process discussed herein may be used with hydromet solutions which contain soluble iron levels exceeding 1 gram per liter. The inventors unexpectedly were able to demonstrate that with embodiments of the present invention, seeding solutions having above 1 g/L iron therein still results in goethite precipitation - even though literature evidences the complete contrary - i.e., that ferric concentrations must be less than 1 g/L iron.

It should be made known that embodiments of the iron control/removal process discussed herein may be used in conjunction with many different types of hydromet solutions including those which contain metal values such as copper (Cu), zinc (Zn), silver (Ag), gold (Au), or a combination thereof, if present. It should also be understood that process condition changes may be made in order to form an iron precipitate that is easily filterable (e.g., for example, using an industrial filter such as a horizontal filter press or equivalent, without limitation). It will also be apparent that iron precipitate formed using embodiments of the invention may come in various forms and/or mineral phases, depending on process conditions used.

EXAMPLES

According to some non-limiting embodiments, a hydromet solution may comprise a pregnant leach solution (PLS) formed using acid, such as (preferably) sulfuric acid. Although a leach can be performed in other acids, such as hydrochloric acid, the inventors do not believe that a chloride series of iron precipitates may be present when practicing the herein-described steps. If hydrochloric acid is used to leach a metal sulfide, embodiments of the iron removal process might produce sulfate that would then allow the formation of iron sulfate phases, without limitation.

According to some embodiments, prior to precipitating iron out of a hydromet solution using the herein-described seeding techniques, a base (e.g., limestone, lime, calcium carbonate, calcium hydroxide, or the like) may be added to the hydromet solution to raise its pH to an intermediate pH capable of forming gypsum. After the formation of gypsum, the gypsum may be precipitated and filtered out of the hydromet solution, without limitation. Since gypsum is a solubility product between calcium and sulfate that is dependent on concentrations of calcium sulfate and temperature, actual pH values of the gypsum formation/precipitation steps may vary depending on solution composition and other process control variables.

After gypsum removal, the pH of the hydromet solution can be raised again to the point where iron hydrolyses and precipitates (e.g., at a pH between approximately 2 and 2.5). Slightly higher pH values are anticipated; however, they are not recommended since pH values greater than 2.5 substantially increase the risk of losing other transition metals which may be present in the hydromet solution (e.g., copper and/or zinc metal values). The aforementioned sequential process steps aim and generally serve to remove a bulk of the gypsum from the iron product; however, some gypsum may be present in the latter-precipitated iron product.

It was discovered by the inventors that for a Cu/Zn PLS hydromet solution, there is surprisingly (and unexpectedly) virtually no co-adsorption of copper and zinc during the first 30 minutes of residence time in a precipitation tank. However, adsorption becomes significant and prohibitive if the residence time of the Cu/Zn PLS hydromet solution within a precipitation tank exceeds 30 minutes during iron removal. Accordingly, preferred embodiments employ an iron precipitation step wherein a hydromet solution residence time is no greater than about a half hour during seeding and iron sulfate precipitation. It is anticipated that the limiting residence time will be a function of the process temperature, i.e., the higher the temperature the shorter the residence time needs to be in order to minimize co-precipitation of metal values. In some embodiments, process chemistry may involve maintaining pH within the range of 2.0 - 2.5, at a temperature of approximately 50°C, without limitation. In some embodiments, process chemistry involving neutralization of sulfuric acid (e.g., pH adjustment to a maximum of 2.5) may follow according to the equation H2SO4 + CaC0 ₃ + H ₂ 0

CaS0 ₄ -2H ₂ 0 + CO2, without limitation. In some embodiments, process chemistry involving ferrous iron oxidation may be done using H2O2 via the following chemistry: 2Fe ²⁺ + H2O2 + 40H 2FeOOH + 2¾0, without limitation. In some embodiments, process chemistry may involve Fe(II) Oxidation and FeOOH precipitation according to the following chemistry:

FeS0 ₄ + 0.25 0 ₂ + 1.5 H ₂ 0 FeOOH + H2SO4, or 2Fe(S0 ₄ ) + H2O2 + H2SO4 Fe ₂ (S0 ₄ )3 + 2¾0, without limitation.

In some embodiments, process chemistry may involve adjusting the hydromet solution pH to 0.9 with CaC0 ₃ , without limitation. In some embodiments, process chemistry may involve adding FeOOH seed at rate of 1 gram per g Fe to be removed from the hydromet solution, without limitation. In some embodiments, process chemistry may involve adding H2O2 to oxidize remaining Fe(II) to Fe(III), without limitation. In some embodiments, process chemistry may involve adding limestone slurry to the hydromet solution, as needed, to maintain the hydromet solution at a pH of approximately 2.0, without limitation. In some embodiments, process chemistry may involve increasing the pH of the hydromet solution to 2.5 using CaC0 ₃ , without limitation. In some embodiments, process chemistry may involve FeOOH precipitation for 1 hr. In some embodiments, Fe and Cu precipitation rates may be determined through periodic sampling of reactor liquor, without limitation.

In some embodiments, process chemistry may involve an operating temperature (50°C) and pH (1-2.5) during the precipitation process, wherein the iron product reports as goethite instead of Fe(OH) ₃ , without limitation. In some embodiments, process chemistry may involve copper and zinc remaining substantially un-hydrolyzed; wherein any incidental losses may be due to physical adsorption onto the goethite particles, without limitation. In some embodiments, where the hydromet solution is a copper PLS, process chemistry may involve relatively slow Cu adsorption kinetics. In such cases, controlling residence times within the iron precipitation and removal process may become a very important factor affecting downstream copper recoveries from the copper PLS. For example, in some embodiments, it may be necessary that residence times which are less than approximately 30 minutes be used during iron precipitation/removal.

In some embodiments, metal value losses in a hydromet solution (other than iron) may be minimal or negligible. For example, in some instances, zinc loss due to precipitation and/or physical adsorption onto goethite may be minimal (i.e., <0.5%) for a copper/zinc PLS, without limitation.

If the particular iron to be removed from the hydromet solution is primarily Fe(III), it may be more efficient and/or economical for embodiments to use hydrogen peroxide instead of oxygen to oxidize ferrous to ferric. At the temperature and pH of the precipitation process, the reaction between H2O2 and Fe ²⁺ may be essentially stoichiometric (e.g., 90+% efficient).

Removal of iron to the extent of 90+% may require that essentially all of the dissolved iron in the hydromet solution be in the +3 oxidation state. Where used herein, the term“hydromet solution” may comprise any solution within a hydrometallurgical process, including, but not limited to, a“pregnant leach solution (PLS)”, “raffinate”,“lixivian’,“electrolyte”,“catalyst ”,“additive”, or the like, without limitation.

It should be known that the particular features, processes, and benefits which are shown and described herein in detail are purely exemplary in nature and should not limit the scope of the invention. Moreover, although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention.

Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.