OTHER APPLICATIONS

[0001] The present application claims priority from Canadian Patent Application No. 3,133,266 filed October 1 ^st , 2021.

TECHNICAL FIELD

[0002] The present disclosure relates to processes for increasing yield in mineral extraction. Specifically, the present disclosure relates to an improved froth floatation process which produces froth having a lower proportion of gangue.

BACKGROUND

[0003] Froth flotation is a method used to, amongst other applications, separate valuable minerals from gangue. Generally, an ore comprising both valuable minerals and gangue is ground and added to a liquid to create a mineral pulp or slurry in a floatation apparatus. Frothing agents are added to the mixture, which is then aerated with air bubbles.

[0004] Particles with greater hydrophobicity (i.e. , the propensity of a particle to be repelled by water) attach themselves to the air bubbles and cause them to rise to the surface, forming a froth. Particles with lower hydrophobicity do not attach themselves to the air bubbles and stay in the slurry. The hydrophobic particles may then be separated from the hydrophilic (or less hydrophobic) particles by skimming the froth from the floating apparatus. [0005] Froth flotation is useful in separating particles having similar density, where other methods such as gravity-based separation methods are ineffective. In particular, froth flotation is used to process copper, zinc, silver, lead, and nickel, amongst many other minerals.

SUMMARY

[0006] It is an object of the present disclosure to provide an improved method for separating minerals from gangue using froth floatation.

[0007] In a first aspect, there is provided a process for separating mineral from gangue by froth floatation, comprising: adding, to a mineral pulp within a floatation cell, citric acid (C6H6O7) until a target pH is achieved; aerating the mineral pulp; stirring the mineral pulp until a froth is obtained; and collecting the froth.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present disclosure will be better understood with reference to the drawings in which:

[0009] Figure 1 is a cross-sectional diagram of a flotation apparatus according to at least one embodiment of the present disclosure.

[0010] Figure 2 is a cross-sectional diagram of a flotation apparatus according to at least one embodiment of the present disclosure.

[0011] Figure 3 is a cross-section diagram of a flotation apparatus according to at least one embodiment of the present disclosure. [0012] Figure 4 is a flow diagram illustrating a method according to the present disclosure.

[0013] Figure 5 is a graph comparing performance of a method according to the present disclosure with known methods.

[0014] Figure 6 is a graph comparing performance of a method according to the present disclosure with known methods.

[0015] Figure 7 is a graph comparing performance of a method according to the present disclosure with known methods.

[0016] Figure 8 is a graph comparing performance of a method according to the present disclosure with known methods.

DETAILED DESCRIPTION

[0017] The proportion of valuable minerals found in ore is in constant decline, as deposits with high concentrations of valuable minerals become rarer and rarer. Such ores having low concentration of valuable minerals are generally characterized with greater mineral complexity, thereby reducing the efficiency of existing processes for separating minerals from gangue.

[0018] This problem affects operations targeting base minerals such as copper and nickel, which face additional challenges for controlling the amount of silicate and magnesium gangues found in the concentrate. Magnesium oxide gangues are of particular concern to the industry, with a requirement for nickel concentrates of having a Fe/MgO ratio of at least 5 in many applications. [0019] The mining industry therefore is in need of improved processes for improving yield and more efficiently extracting minerals from ores having a low concentration of valuable minerals.

[0020] Reference is made to Figure 1 , which illustrates an exemplary floatation apparatus which may be used to practice the present disclosure. However, the flotation apparatus illustrated in Figure 1, known in the art as a mechanical cell, is merely provided as an example, and the present disclosure may be practiced with other types of flotation apparatuses.

[0021] The flotation apparatus 100 comprises a cell 102 for holding a mineral pulp 108. The mineral pulp 108 may enter the cell 102 via inlet 104. The mineral pulp 108 is generally comprised of liquid and mineral particles. The liquid is typically water which may be combined with various agents. The mineral particles are obtained from ore containing valuable minerals which is reduced to particles through grinding or other known methods.

[0022] Generally, froth floatation is more effective with particle sizes around 100 microns, however the present disclosure is not limited to any specific particle size.

[0023] It has been found that the process of the present disclosure is more efficient with ore that is ground to a particle size allowing for a high degree of mineral release. The optimal particle size varies according to different minerals. Testing has revealed that in the case of pentlandite, a particle size distribution for P80 of approximately 20 microns to be optimal with the process of the present disclosure. P80 is an indication of the particle size distribution, such that 80% of particles have a size which is smaller. [0024] Mineral pulp 108 may be mixed by agitator 105 which is rotated by shaft 103. Shaft 103 is driven by a motor (not shown).

[0025] Flotation apparatus 100 further comprises an outlet tube 106 for emptying the cell 102 of its content.

[0026] Flotation apparatus 100 further comprises a mechanism for adding air bubbles to mineral pulp 108. According to at least one embodiment, shaft 103 is connected to an air source (not shown) and a valve 107 at the bottom of agitator 105 is used to selectively provide air into the mineral pulp 108.

[0027] During operation, mineral pulp 108 is added to the cell 102 via inlet 104. Frothing agents are added to the mineral pulp 108 and the mineral pulp 108 is aerated through valve 107, creating air bubbles 109 within mineral pulp 108.

[0028] Mineral particles having greater hydrophobicity naturally attach themselves to the air bubbles 109, thereby creating a froth 120 which floats to the surface of cell 102, as illustrated in Figure 2. The remaining portion of the mineral pulp are the tailings 110.

[0029] Accordingly, particles with greater hydrophobicity are separated from particles with lower hydrophobicity. The particles with greater hydrophobicity are in the froth 120 whereas the particles with lower hydrophobicity are found in the tailings 110.

[0030] The froth 120 may be removed from the cell 102 using known means, whereas the tailings 110 may be evacuated through outlet 106. [0031] In some cases, the desirable particles may be particles with greater hydrophobicity and form part of the froth 120. In other cases, the desirable particles may be particles with lower hydrophobicity and form part of the tailings 110. The portion of the mineral pulp comprising valuable minerals after froth floatation is called the concentrate.

[0032] The greater the difference in hydrophobicity between desirable particles and undesirable particles, the greater the separation is achieved.

[0033] Reference is now made to Figure 3, in which a simplified version of an apparatus for performing froth floatation is illustrated. The apparatus illustrated in Figure 3 is known in the art as a floatation column, and is provided as a nonlimiting example of an apparatus that can be used to perform a method according to the present disclosure.

[0034] As seen in Figure 3, a floatation column 300 comprises a tank 301, which is generally cylindrical and elongated vertically. Tank 301 is filled with a liquid, which is generally water.

[0035] Above the tank is upper portion 304, which may comprise various devices for retrieving and cleaning the froth from tank 301.

[0036] Near the upper portion of tank 301 is located mineral pulp feed 302. Mineral pulp feed 302 releases mineral ore 305 into tank 301 at a controlled rate.

[0037] At the bottom of tank 301 is located air injection device 303 which injects air bubbles 308 within tank 301 at high velocities. This creates upward currents of air bubbles 308 which mix with descending mineral ore 305. As the bubbles 308 enter in contact with hydrophobic particles of mineral ore 305, they become loaded with the hydrophobic particles. Loaded bubbles 309 rise in the column and form part of the froth 307.

[0038] Hydrophilic particles 306, which do not attach themselves to bubbles 308, fall to the bottom of tank 301 where they may be retrieved by various known means.

[0039] According to at least one embodiment of the present disclosure, a process for froth floatation which decreases the hydrophobicity of gangue particles is provided. By decreasing the hydrophobicity of gangue particles, gangue particles are more likely to find themselves in the tailings and less likely to find themselves in the froth. The process of the present disclosure is particularly suited for improving the effectiveness of froth floatation for mineral pulps containing sulfides, such as for example pentlandite and chalcopyrite.

[0040] The process of the present disclosure reduces the hydrophobicity of gangue particles by adding conditioning reagents to the mineral pulp in sequence.

[0041] During conventional froth floatation processes, magnesium gangue particles may naturally float to the surface. Accordingly, strategies have been developed to decrease the hydrophobicity of these particles. Agents such as polysaccharides, and synthetic or natural polymers such as guar gum or carboxymethyl cellulose (CMC) are commonly used to reduce the propensity of gangue particles to float. However, these techniques have limited effectiveness as such agents also reduce the propensity of desirable particles to float, thereby reducing yield.

[0042] According to the present disclosure, treating the mineral pulp with citric acid (CeHeO?) prior to the use of an agent such as CMC significantly reduces the amount of non-sulfide gangue found in the concentrate, without any apparent reduction in the floatation of valuable minerals. This allows to maintain a commercially viable yield while improving the quality of the concentrate in terms of its Fe/MgO ratio.

[0043] Reference is now made to Figure 4, which illustrates a process according to at least one embodiment of the present disclosure.

[0044] The process of Figure 4 starts at block 400, with a mineral slurry contained in a floatation cell. The floatation cell may be a cell as described with respect to Figures 1 and 2.

[0045] At block 410, citric acid, either in solution or in solid form is added to the mineral slurry and the resulting mixture is agitated until a desired pH for the solution is obtained. It has been observed that efficiency of the froth floatation process increases as the pH decreases.

[0046] Specifically, no improvements to the efficiency of separation are found for a pH of 7 or above. Generally, a pH in the range between 5 and 7 has been found to produce improved results. According to at least one embodiment of the present disclosure, the desired pH is 6.

[0047] At block 420, floatation depression agents are added in order to reduce the hydrophobicity of gangue particles. According to at least one embodiment, carboxymethyl cellulose (CMC) is used as a floatation depression agent.

Furthermore, according to at least some embodiments of the present disclosure the amount of CMC used is between 100 grams and 1000 grams per ton of mineral. In yet another embodiment, the amount of CMC used is 500 grams per ton of mineral. [0048] The desired pH and the amount of CMC used may vary according to the specific minerals in the mineral slurry. For example, in a nickel cleaning circuit with feed ore containing 10% Magnesium 30% pyrrhotite and 1% nickel, 250 grams of CMC per ton of mineral has been shown to provide maximum nickel recovery. For ores containing more magnesium and higher proportion of active magnesium (mainly talc and serpentine) higher CMC amounts are needed.

[0049] Returning now to the process of Figure 4, at block 430, other agents such as collectors and frothers are added to the floatation cell. At block 440, the mineral slurry along with the citric acid, CMC, collectors, and frothers is stirred to ensure thorough mixing of the mineral slurry, and air bubbles are introduced, for example through a valve 107 as shown in Figure 1 , and the frothing process is initiated.

[0050] Once a froth is formed in the floatation cell, the froth may be collected from the floatation cell, through known means, at block 450. The process then ends at block 460.

[0051] It has been observed that using the process described above, that compared to known methods, statistically similar amounts of valuable minerals are extracted, but statistically lower amounts of gangue is found in the extracted minerals. In other words, the ratio of valuable mineral to gangue in the concentrate is significantly improved with respect to prior art methods.

[0052] Reference is now made to Figure 5, which illustrates results of the process described with respect to Figure 4, in which citric acid is added to the mineral slurry until a pH of 6 is obtained, in comparison with results of a standard process in which no citric acid is added to the mineral slurry. [0053] The results illustrated in Figure 5 show the amount of nickel sulfide, specifically pentlandite, recovered from a mineral slurry using froth floatation over time. Curve 501 shows the results using a prior art process, without the addition of citric acid. Curve 502 shows the results using a process according to the present disclosure, with the addition of citric acid. In both cases, 200 grams of CMC per ton of mineral were added to the mineral slurry.

[0054] As can be seen from Figure 5, curves 501 and 502 are very similar, with a yield of approximately 20% after 1 minute, and a yield above 60% after 10 minutes. Accordingly, the amount of pentlandite recovered from froth floatation is not significantly affected by the addition of citric acid.

[0055] Reference is now made to Figure 6, which illustrates further results of the process described with respect to Figure 4. Figure 6 illustrates the amount of magnesium gangue which is recovered with the pentlandite. Curve 601 shows the results using a prior art process, without the addition of citric acid. Curve 602 shows the results using a process according to the present disclosure, with the addition of citric acid until a pH of 6 is obtained. In both cases, 200 grams of CMC per ton of mineral were added to the mineral slurry.

[0056] As can be seen from Figure 6, curve 601 is consistently higher than curve 602. Specifically, the process without citric acid recuperates about 5% of the magnesium after 1 minute, and almost 35% of the magnesium after 10 minutes. In contrast, the process with citric acid recuperates less than 5% of the magnesium after 1 minute, and less than 20% of the magnesium after 10 minutes.

[0057] Therefore, the addition of citric acid in froth floatation as described herein allows to produce a concentrate with a similar amount of valuable minerals but with less undesirable gangue. [0058] These results are further illustrated with respect to Figure 7. Figure 7 illustrates the amount of pentlandite recovered as a function of the amount of magnesium gangue recovered. Curve 701 shows the results using a prior art process, without the addition of citric acid. Curve 702 shows the results using a process according to the present disclosure, with the addition of citric acid until a pH of 6 is obtained.

[0059] As can be seen from Figure 7, prior art processes range from about 5% of recovered magnesium gangue for 20% of recovered pentlandite, to almost 35% of recovered magnesium gangue for 65% of recovered pentlandite. In contrast, a process according to the present disclosure produces slightly less than 5% of recovered magnesium gangue for 20% of recovered pentlandite, and less than 20% of recovered magnesium gangue for 65% of recovered pentlandite.

[0060] Reference is now made to Figure 8, which shows how a process according to the present disclosure performs in a factory setting. The x-axis represents the percentage of magnesium gangue that is recovered, and the y- axis represents the percentage of pentlandite that is recovered.

[0061] In Figure 8, data 801 relates to a prior art process in a factory setting, where froth floatation was performed with a mineral slurry having a pH of 8.5. Data 802 relates to a process according to the present disclosure in a factory setting, where froth floatation was performed with a mineral slurry having a pH of 6.5, and the mineral slurry was conditioned with citric acid. Data 803 relates to a process in a laboratory setting, where froth floatation was performed with a mineral slurry having a pH of 6.5, and the mineral slurry was conditioned with citric acid. Data 804 relates to a prior art process in a laboratory setting, where froth floatation was performed with a mineral slurry having a pH of 8.5. [0062] As can be seen from Figure 8, adding citric acid to the mineral slurry is beneficial for reducing the ratio of gangue in the concentrate produced by froth floatation, whether in a laboratory setting or a factory setting.

[0063] Therefore, the process according to the present disclosure produces a concentrate with a smaller proportion of undesirable gangue. More specifically, when the mineral pulp is conditioned with citric acid, the proportion of recovered pentlandite remains substantially the same as with standard conditions without citric acid. However, when the mineral pulp is conditioned with citric acid, the proportion of recovered gangue is substantially lower than with standard conditions without citric acid.

[0064] Therefore, the selectivity of the process for pentlandite over magnesium gangue is significantly improved. In other words, magnesium gangue is more efficiently separated from the desirable minerals during froth floatation. The increase in selectivity without any diminution of yield of valuable minerals makes processes according to the present disclosure particularly beneficial.

[0065] The embodiments described herein are examples of structures, systems or methods having elements corresponding to elements of the techniques of this application. This written description may enable those skilled in the art to make and use embodiments having alternative elements that likewise correspond to the elements of the techniques of this application. The intended scope of the techniques of this application thus includes other structures, systems or methods that do not differ from the techniques of this application as described herein, and further includes other structures, systems or methods with insubstantial differences from the techniques of this application as described herein. [0066] Moreover, the previous detailed description is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention described herein. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article "a" or "an" is not intended to mean "one and only one" unless specifically so stated, but rather "one or more". All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

[0067] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.

[0068] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification or claims refer to at least one of something selected from the group consisting of A, B, C .... and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.