ore dressing method

Abstract

To provide a beneficiation method in which chalcopyrite and pyrite can be separated even for mineral slurries containing calcium.SOLUTION: A beneficiation method includes a mineral slurry production step of mixing a chalcopyrite and pyrite-containing mineral particle, calcium-containing water, and an iron source to yield a mineral slurry, a stirring step of stirring the mineral slurry, and an ore flotation step of performing ore floatation using the mineral slurry after the stirring step. The coexistence of calcium ion and iron ion suppresses the floating of pyrite. As a result, chalcopyrite and pyrite can be separated by ore flotation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a mineral dressing method, and more particularly to a mineral dressing method for separating chalcopyrite and pyrite. [Background technology]

[0002] The ore extracted from a mine contains useful minerals (minerals containing large amounts of the target metal) and gangue minerals (minerals containing almost no target metal). Therefore, a mineral dressing process is carried out to recover the useful minerals from the ore.

[0003] In general, ore dressing is carried out by crushing ore to obtain a mixed powder of useful minerals and gangue minerals, and then separating the powder into concentrate (a powder product with a higher proportion of useful minerals) and tailings (a powder product that is waste residue) by utilizing differences in physical properties such as specific gravity, magnetism, and hydrophilicity of each mineral species.

[0004] Flotation, which takes advantage of the differences in hydrophilicity of mineral species, is a well-known mineral beneficiation process. Flotation is performed by blowing air bubbles into a mineral slurry made by adding water to a mixed powder. Hydrophobic mineral particles adhere to the air bubbles and float, while hydrophilic mineral particles do not adhere to the bubbles and sink. To increase the efficiency of separating the floating and sinking ores, flotation agents such as collectors, depressants, and foaming agents are generally added to the mineral slurry.

[0005] Copper ore used in copper smelting contains not only the valuable mineral chalcopyrite but also the gangue mineral pyrite. Therefore, there is a need to separate chalcopyrite from pyrite by flotation. In flotation, which separates chalcopyrite from pyrite, the chalcopyrite is floated and collected as float. However, in the pH range below 10, the collector also adheres to the pyrite, making it easy for it to float, making it difficult to separate chalcopyrite from pyrite.

[0006] Therefore, it is known that the mineral slurry is made alkaline with a pH of 10 or more for flotation. In the pH range of 10 or more, a hydrophilic film of iron or calcium hydroxide is formed on the surface of pyrite, which suppresses the adhesion of collectors. In addition, xanthate ions and OH ions on the surface of pyrite - The pyrite is then exchanged with the slag, removing the xanthate, a type of collector. The surface of the pyrite is also oxidized, maintaining its hydrophilicity. This prevents the pyrite from floating.

[0007] However, to make the mineral slurry alkaline to a pH of 10 or higher, a large amount of a pH adjuster such as lime is required, which increases operating costs. Regarding this problem, Patent Document 1 discloses that adding a sulfoxy reagent to the mineral slurry suppresses the floating of sulfide-bearing gangue minerals such as pyrite without adjusting the pH. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-75575 Summary of the Invention [Problem to be solved by the invention]

[0009] According to the method of Patent Document 1, there is no need to adjust the pH, which reduces the cost of a pH adjuster. However, it requires the addition of a sulfoxy reagent. If the addition of a sulfoxy reagent becomes unnecessary, further cost reductions can be achieved.

[0010] In actual operations, seawater is sometimes used to produce the mineral slurry. Seawater contains calcium. If the mineral slurry is alkaline, CaCO3 precipitates on the surface of the mineral particles. This reduces the separation efficiency of chalcopyrite and pyrite during flotation.

[0011] In view of the above circumstances, an object of the present invention is to provide a mineral dressing method capable of separating chalcopyrite and pyrite even in a mineral slurry containing calcium. [Means for solving the problem]

[0012] The mineral dressing method of the first invention is characterized by comprising a mineral slurry production step of mixing mineral particles containing chalcopyrite and pyrite with water containing calcium and an iron source to obtain a mineral slurry, a stirring step of stirring the mineral slurry, and a flotation step of performing flotation using the mineral slurry after the stirring step. The ore dressing method of the second invention is characterized in that, in the first invention, the amount of the iron source added is an amount that gives a molar ratio of calcium ions to iron ions of 1 to 10 in the liquid phase of the mineral slurry. The ore dressing method of the third invention is characterized in that in the first or second invention, the stirring time in the stirring step exceeds the time at which the oxidation rate of pyrite changes from low to high. The ore dressing method of the fourth invention is characterized in that, in the first or second invention, the stirring time in the stirring step is more than 150 minutes. The ore dressing method of a fifth invention is characterized in that, in any one of the first to fourth inventions, the liquid phase of the mineral slurry is adjusted to a pH of 6 to 9 in the stirring step. [Effects of the Invention]

[0013] According to the present invention, the coexistence of calcium ions and iron ions suppresses the flotation of pyrite, and as a result, chalcopyrite and pyrite can be separated by flotation. [Brief explanation of the drawings]

[0014] [Figure 1] Figure (A) is a graph showing the change in total S concentration over time at pH 6. Figure (B) is a graph showing the change in total S concentration over time at pH 9. [Figure 2] FIG. 1 is an explanatory diagram of a flotation test. DETAILED DESCRIPTION OF THE INVENTION

[0015] Next, an embodiment of the present invention will be described. The ore dressing method according to one embodiment of the present invention includes (1) a pretreatment step, (2) a mineral slurry production step, (3) a stirring step, and (4) a flotation step. Note that the ore dressing method of this embodiment only needs to include at least (2) a mineral slurry production step, (3) a stirring step, and (4) a flotation step, and other steps may be omitted or added.

[0016] (1) Pretreatment process In the pre-treatment process, the ore is crushed and gangue is removed. Generally, copper ore contains useful minerals such as chalcopyrite (CuFeS2), bornite (Cu5FeS4), enargite (Cu3AsS4), chalcocite (Cu2S), and tennantite ((Cu, Fe, Zn) 12 Copper ore contains gangue minerals such as pyrite (FeS2), arsenopyrite (FeAsS), quartz, and feldspar.

[0017] Ore is crushed to obtain mineral particles. The particle size of the mineral particles is adjusted to match the size of the minerals contained in the ore so that a single mineral can be obtained. For example, in the case of chalcopyrite, it is common to adjust the particle size to about 100 μm under sieve. In practical operations using ore containing various minerals as raw material, it is common to crush the ore to about 100 μm under sieve, and then adjust the particle size of the ore to optimal conditions, taking into account factors such as flotation performance.

[0018] It is preferable to remove gangue from the ore as needed. Various ore-beneficiation methods, including flotation, can be used to remove gangue. For example, bulk flotation separates sulfide minerals from other gangue. Bulk flotation involves adding water to mineral particles (crushed ore) to obtain a mineral slurry, to which flotation agents such as collectors, depressants, and foaming agents are added. Air bubbles are then blown into the slurry to suspend the various sulfide minerals while allowing the gangue to settle and separate.

[0019] The sulfide minerals obtained by bulk flotation are called bulk concentrate. The concentrate to be supplied to the next step only needs to contain at least chalcopyrite and pyrite.

[0020] (2) Mineral slurry manufacturing process In the mineral slurry production process, mineral particles containing at least chalcopyrite and pyrite are mixed with water to obtain a mineral slurry. Water containing calcium, such as seawater, can be used as the water used to produce the mineral slurry. The calcium concentration of this water is, for example, 100 to 400 mg / L. Calcium chloride (CaCl2), calcium hydroxide (CaOH2), etc. can be used as a calcium source.

[0021] When calcium is contained in the liquid phase of the mineral slurry, CaCO3 precipitates on the surface of the mineral particles. This may result in a decrease in the efficiency of separation of chalcopyrite and pyrite in the subsequent flotation process. In this regard, the present inventors have found that the coexistence of iron ions can suppress the decrease in separation efficiency.

[0022] Therefore, an iron source is mixed in when producing the mineral slurry. Ferric chloride (FeCl3), ferric sulfate (Fe2(SO4)3), ferric nitrate (Fe(NO3)3), etc. can be used as the iron source. By mixing the iron source into the mineral slurry, calcium ions and iron ions coexist in the aqueous phase of the mineral slurry.

[0023] The timing of adding the iron source is not particularly limited. The iron source may be added to calcium-containing water, and then the mineral particles may be added to produce a mineral slurry. The mineral particles may be added to calcium-containing water, and then the iron source may be added. The mineral particles, calcium-containing water, and iron source may be mixed simultaneously.

[0024] Hereinafter, the molar ratio of calcium ions to iron ions in the liquid phase of the mineral slurry will be expressed as “Ca / Fe.” The amount of iron source added is preferably such that Ca / Fe is 1-10.

[0025] The reason why the coexistence of iron ions improves the separation efficiency of chalcopyrite and pyrite is that the oxidation of the pyrite surface is promoted by the mechanism shown in the following formulas A to C. In detail, in the first stage of oxidation, pyrite is oxidized and dissolved as shown in formula A, and then ferrous ions (Fe 2+ ) is oxidized to ferric ions (Fe 3+ ), which again acts as an oxidizing agent as shown in formula C, causing the second stage of oxidation of pyrite. 3+ ) promotes the reaction of formula C, i.e., promotes the oxidation of pyrite. Equation (A): Reaction of O2 adsorbed on the surface with FeS2 (first stage: oxidation dissolution) FeS2+7 / 2O2+H2O → Fe 2+ +SO4 2- +2H + Equation (B): Fe by dissolved oxygen 2+ Oxidation of Fe 2+ +1 / 4O2+4H + → Fe 3+ +1 / 2H2O Formula (C): Produced Fe 3+ and FeS2 (second stage oxidation dissolution) FeS2+14Fe 3+ +8H2O → 15Fe 2+ +2SO4 2- +16H +

[0026] The pH of the liquid phase of the mineral slurry is preferably 6 to 7. This will suppress calcium precipitation. Therefore, if necessary, a pH adjuster is added to the mineral slurry to adjust the pH. There are no particular limitations on the pH adjuster, but alkalis such as sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), and calcium carbonate (CaCO3) can be used. Acids such as hydrochloric acid (HCl) and sulfuric acid (H2SO4) can be used.

[0027] (3) Mixing process In the stirring step, the mineral slurry is stirred. For example, the mineral slurry is placed in an open-to-air tank and stirred with a stirrer. By stirring the mineral slurry, air is introduced into the liquid phase, increasing the dissolved oxygen concentration. The dissolved oxygen in the liquid phase oxidizes the surfaces of the chalcopyrite and pyrite mineral particles.

[0028] The inventors of the present invention analyzed the oxidation rates of chalcopyrite and pyrite and found the following: The oxidation rate of chalcopyrite is constant regardless of the stirring time. In contrast, the oxidation rate of pyrite is almost the same as that of chalcopyrite at the beginning of stirring, but becomes faster after a certain time has passed. That is, the oxidation rate of pyrite changes from a low rate to a high rate during stirring.

[0029] After the oxidation rate of pyrite has increased, the pyrite can be made more oxidized than the chalcopyrite. Furthermore, the longer the stirring time, the greater the difference in the degree of oxidation between pyrite and chalcopyrite. When pyrite is oxidized, hydrophilic ferric hydroxide is produced on the surface of the pyrite. This also suppresses the adhesion of the collector to the pyrite. Therefore, the hydrophilicity of pyrite is maintained, enabling the separation of chalcopyrite and pyrite in the subsequent flotation process.

[0030] Therefore, the stirring time of the mineral slurry is set to a time exceeding the point at which the oxidation rate of pyrite changes from low to high (hereinafter referred to as the "change point"). By stirring until the oxidation rate of pyrite becomes high, the pyrite can be made more oxidized than the chalcopyrite. This maintains the hydrophilicity of the pyrite. Therefore, in the subsequent flotation step, the chalcopyrite can be selectively floated, and the chalcopyrite and pyrite can be efficiently separated.

[0031] Furthermore, with this method, the liquid phase of the mineral slurry can remain at a low pH. Only a small amount of pH adjuster is required, reducing the cost of the pH adjuster. Furthermore, there is no need to add an oxidizing agent such as hydrogen peroxide to oxidize the pyrite. Therefore, the cost of the oxidizing agent can be reduced. In this way, the cost of the chemicals required to suppress the floating of pyrite can be reduced.

[0032] (4) Flotation process In the flotation process, flotation is performed using the stirred mineral slurry. By flotation, chalcopyrite is separated as float and pyrite as sink. More precisely, the raw minerals contained in the mineral slurry are separated into float, which has a higher proportion of chalcopyrite than the raw minerals, and sink, which has a higher proportion of pyrite than the raw minerals. The equipment and method used for flotation are not particularly limited, and a general multi-stage flotation equipment may be used.

[0033] Various gases can be used to inject into the mineral slurry during flotation. For example, atmospheric air is used when economic efficiency is a priority. To prevent changes in the degree of oxidation of the mineral particles, oxygen-free gases, such as nitrogen, are used. Conversely, oxygen is used to promote oxidation of the mineral particles. Sulfur dioxide gas is used to sulfide the mineral particles.

[0034] Flotation agents such as collectors, depressants, and foaming agents may be added to the mineral slurry. Collectors that can be used include sodium, xanthate, and ethyl xanthate. Depressants that can be used include gelatin, lactic acid, and starch. Foaming agents that can be used include MIBC (methyl isobutyl carbinol), pine oil, and cresylic acid. Flotation agents may be added to the mineral slurry during the flotation process, or they may be added to the mineral slurry during the stirring process. In addition, pH adjusters such as hydrochloric acid, hydrogen peroxide, caustic soda, and lime may be added to the mineral slurry to adjust the pH of the liquid phase of the mineral slurry.

[0035] As mentioned above, the presence of iron ions promotes oxidation of the pyrite surface and inhibits flotation of the pyrite, allowing chalcopyrite and pyrite to be separated by flotation.

[0036] Furthermore, by stirring the mineral slurry, it is possible to create a difference in the degree of oxidation between the chalcopyrite and the pyrite. Because chalcopyrite is less oxidized than pyrite, the inhibitor adheres to it more easily and it floats. On the other hand, because pyrite is more oxidized than chalcopyrite, it maintains its hydrophilicity and the inhibitor does not adhere to it as easily. Therefore, it is possible to selectively float the chalcopyrite while allowing the pyrite to settle, and chalcopyrite and pyrite can be separated efficiently.

[0037] The float containing a high proportion of chalcopyrite is further subjected to processes such as solid-liquid separation and washing, and the solids are recovered as a concentrate. The resulting concentrate may be fed to a stirring process. At this time, grinding may be performed to remove impurities adhering to the surfaces of the mineral particles. By repeating the stirring process and the flotation process, the purity of the chalcopyrite can be further increased. [Example]

[0038] Next, an example will be described. (mixing time) Chalcopyrite and pyrite samples were prepared. The composition of the chalcopyrite sample was 80% by mass chalcopyrite, 11% by mass pyrite, 5% by mass hematite (Fe2O3), and 4% by mass sphalerite (ZnS). The composition of the pyrite sample was 100% by mass pyrite. The grain sizes of both the chalcopyrite and pyrite samples were 106-150 μm. Each mineral sample was washed with concentrated hydrochloric acid and acetone to remove oxides and sulfur coatings from the mineral particle surfaces.

[0039] 300 mL of pure water was placed in a 500 mL beaker, and hydrochloric acid or sodium hydroxide was added as a pH adjuster to adjust the pH to 6 or 9. After adjusting the pH, 1.5 g of a chalcopyrite sample or pyrite sample was added to prepare mineral slurries. That is, four types of mineral slurries were prepared: a chalcopyrite slurry with a pH of 6, a pyrite slurry with a pH of 6, a chalcopyrite slurry with a pH of 9, and a pyrite slurry with a pH of 9. Sodium chloride was added to each mineral slurry to adjust the ionic strength of the aqueous phase to 0.05, equivalent to seawater.

[0040] Each mineral slurry was stirred using a magnetic stirrer (RS-6AN AS ONE, 1200 rpm; the same applies below). The dissolved oxygen concentration in the liquid phase of the mineral slurry during stirring was 7.0 mg / L. Five mL of the mineral slurry was sampled using a 5 mL polypropylene syringe at predetermined intervals after the start of stirring and filtered through a 0.1 μm syringe filter (manufactured by Nippon Pall). The filtrate was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the total S concentration.

[0041] Figure 1(A) shows the time change in total-S concentration at pH 6. Figure 1(B) shows the time change in total-S concentration at pH 9. When sulfide minerals are oxidized, sulfur dissolves into the liquid phase depending on the degree of oxidation. Therefore, the total-S concentration in the liquid phase indicates the degree of oxidation of the sulfide minerals. Furthermore, the rate of increase in total-S concentration, i.e., the slope of the graphs in Figures 1(A) and (B), indicates the oxidation rate of the sulfide minerals.

[0042] As can be seen from the graphs in Figure 1(A) and (B), oxidation of both pyrite and chalcopyrite progresses with the passage of stirring time. This is thought to be due to the oxidation of the mineral particle surfaces by the dissolved oxygen in the liquid phase.

[0043] In both pH 6 and pH 9, the oxidation rate of chalcopyrite (rate of increase in total-S concentration) is constant for at least 250 minutes of stirring. In contrast, the oxidation rate of pyrite is almost the same as that of chalcopyrite in the early stage of stirring, but becomes faster in the later stage of stirring. In other words, the oxidation rate of pyrite changes from low to high during stirring. The point at which the oxidation rate of pyrite changes from low to high (the change point) occurs at 150 minutes at pH 6 and 100 minutes at pH 9.

[0044] After the oxidation rate of pyrite has increased, the pyrite can be made more oxidized than the chalcopyrite. Furthermore, the longer the stirring time, the greater the difference in the degree of oxidation between pyrite and chalcopyrite. When pyrite is oxidized, hydrophilic ferric hydroxide is produced on the surface of the pyrite. This also inhibits the adhesion of the collector to the pyrite. Therefore, the hydrophilicity of pyrite is maintained, and chalcopyrite and pyrite can be separated by flotation.

[0045] From the viewpoint of creating a difference in the degree of oxidation between pyrite and chalcopyrite, the stirring time should be set to a time exceeding the time of change. To increase the difference in the degree of oxidation, it is preferable to continue stirring beyond the time of change. That is, the stirring time is preferably set to 10 minutes, more preferably 20 minutes, and even more preferably 30 minutes after the time of change.

[0046] If the stirring time is longer than 150 minutes at least in the pH range of 6 to 9, it is possible to differentiate the degree of oxidation between pyrite and chalcopyrite. From the viewpoint of increasing the difference in the degree of oxidation, the stirring time is preferably 160 minutes or more, more preferably 170 minutes or more, and even more preferably 180 minutes or more. It has been confirmed that a difference in the degree of oxidation occurs at least in the stirring time range up to 250 minutes.

[0047] (Single-unit flotation test) Chalcopyrite and pyrite samples were prepared. The compositions and particle sizes of the chalcopyrite and pyrite samples were as described above. Each mineral sample was washed with concentrated hydrochloric acid and acetone to remove oxides and sulfur coatings from the mineral particle surfaces.

[0048] Next, solutions for use in producing mineral slurry were prepared. Calcium chloride was added to pure water to prepare a solution with a calcium concentration of 100 mg / L. Next, ferric chloride was added to the solution as an iron source to adjust the iron concentration. Hereinafter, the solution without added iron source (iron concentration 0 mg / L) is referred to as Solution 1, the solution with an iron concentration of 10 mg / L as Solution 2, and the solution with an iron concentration of 100 mg / L as Solution 3. Solution 2 had a Ca / Fe ratio of 10, and Solution 3 had a Ca / Fe ratio of 1. Hydrochloric acid or sodium hydroxide was added as a pH adjuster to each solution to adjust the pH to 9 or 12. Sodium chloride was also added to each solution to adjust the ionic strength to 0.05, equivalent to that of seawater.

[0049] 100 mL of the solution was placed in a 200 mL beaker, and 0.5 g of chalcopyrite or pyrite sample was added to prepare a mineral slurry. The mineral slurry was stirred with a magnetic stirrer. The dissolved oxygen concentration in the liquid phase of the mineral slurry during stirring was 7.0 mg / L. The stirring time was 180 minutes.

[0050] Flotation tests were carried out by adding 10 μL of MIBC (methyl isobutyl carbinol) as a foaming agent and 50 g / t (50 g per 1 ton of mineral) of PAX (potassium amyl xanthate) as a collector to the mineral slurry.

[0051] The flotation test was performed using a Hallimond tube, as shown in Figure 2. The bottom of the Hallimond tube is equipped with a stirrer, allowing the liquid to be stirred. Gas can also be blown into the Hallimond tube from the bottom.

[0052] The flotation test was carried out as follows: First, the mineral slurry was placed in a Hallimond tube. Next, air was blown into the liquid in the Hallimond tube at a flow rate of 200 mL / min while stirring. The treatment time was 1 minute. The suspended mineral particles settled in the stagnation area in the middle of the Hallimond tube. The mineral particles that settled in the stagnation area were called float. Meanwhile, the mineral particles that settled at the bottom of the Hallimond tube were called sink.

[0053] The recovered float and sink ores were filtered, freeze-dried, and then weighed. A syringe filter with a pore size of 0.1 μm (manufactured by Nippon Pall) was used for filtration. The float rate was calculated from the weights of the float and sink ores using the following formula (1). Floating ore rate [mass%]={(floating ore weight) / (floating ore weight + sinking ore weight)}×100 ···(1)

[0054] The mineral slurry conditions and flotation rates when the pH was set to 9 are shown in Table 1. The mineral slurry conditions and flotation rates when the pH was set to 12 are shown in Table 2. In addition, using the results of flotation tests under the same conditions of pH, calcium concentration, and iron concentration, the flotation rate difference was calculated by subtracting the flotation rate of pyrite from the flotation rate of chalcopyrite. The results are shown in Tables 1 and 2. The flotation rate difference indicates the ease of separation of chalcopyrite and pyrite during flotation.

[0055] [Table 1]

[0056] [Table 2]

[0057] As can be seen from Table 1, at pH 9, when the iron concentration is 0 mg / L, the float difference is -8.8%. This means that pyrite floats more easily than chalcopyrite. Furthermore, because the absolute value of the float difference is small, separation of chalcopyrite and pyrite is difficult. In contrast, when the iron concentration is 10 mg / L, the float difference is 63.0%, and when the iron concentration is 100 mg / L, the float difference is 42.6%. This confirms that adding iron to the mineral slurry makes it easier to separate chalcopyrite and pyrite.

[0058] Table 2 shows a similar trend at pH 12. The float rate difference when the iron concentration is 0 mg / L is 26.1%. In contrast, the float rate difference when the iron concentration is 10 mg / L is 71.7%, and when the iron concentration is 100 mg / L, the float rate difference is 59.8%. Therefore, it was confirmed that even at pH 12, adding iron to the mineral slurry makes it easier to separate chalcopyrite and pyrite.

[0059] (Mixed system flotation test) A mixed sample was prepared by mixing a chalcopyrite sample and a pyrite sample in a weight ratio of 1:1. 100 mL of the solution was placed in a 200 mL beaker, and 0.5 g of the mixed sample was added to make a mineral slurry. The conditions and procedures were the same as those for the simple substance flotation test.

[0060] The float and sink recovered in the flotation test were filtered, freeze-dried, and then weighed. The float and sink were crushed in an agate mortar, dissolved in aqua regia, and analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to measure the copper content. The copper recovery rate was calculated from the weight and copper content of the float and sink using the following equation (2): Actual copper yield [%]={(floating ore copper grade x floating ore weight) / (floating ore copper grade x floating ore weight + settled ore copper grade x settled ore weight)}×100...(2)

[0061] The mineral slurry conditions and copper recovery rates are shown in Table 3. [Table 3]

[0062] As can be seen from Table 3, at pH 9, when the iron concentration is 0 mg / L, the copper recovery rate is 50.5%. In contrast, when the iron concentration is 100 mg / L, the copper recovery rate increases to 75.8%. Furthermore, at pH 12, when the iron concentration is 0 mg / L, the copper recovery rate is 51.5%. In contrast, when the iron concentration is 10 mg / L, the copper recovery rate increases to 61.4%. From the above, it was confirmed that adding iron makes it easier to separate chalcopyrite and pyrite, even in a mixed system.

Claims

[Claim 1] a mineral slurry production step of mixing mineral particles containing chalcopyrite and pyrite, water containing calcium, and ferric chloride as an iron source to obtain a mineral slurry; agitating the mineral slurry; a flotation step of performing flotation using the mineral slurry after the stirring step, an amount of the iron source added in the mineral slurry production step is an amount such that the liquid phase of the mineral slurry has an iron ion concentration of 10 to 100 mg / L relative to a calcium ion concentration of 100 mg / L; The stirring time in the stirring step is 180 minutes, The pH of the liquid phase of the mineral slurry in the stirring step is 9 to 12. A method for dressing characterized by:

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