Method for treating water to be treated and method for smelting copper

Abstract

To provide a method for obtaining a Cu-containing solid matter in which the intrusion of Br is prevented by improving a reduction process of water to be treated containing Cu ions and Br ions.SOLUTION: In the method for treating water to be treated, the water to be treated containing Cu ions and Br ions is mixed with a reducing agent, the oxidation reduction potential of the water to be treated is lowered to - 100mV or lower, and the precipitation of solid matter containing Cu is generated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating water to be treated, which recovers a solid material containing copper (Cu) from which bromine (Br) has been removed, from the water to be treated, which contains copper (Cu) ions and bromide ions, and a smelting method using the solid material. [Background technology]

[0002] Recently, urban mines have been attracting increasing attention, and efforts are being made to recover valuable metals from wastewater from production processes and discarded electronic devices that have reached the end of their lifespan or broken down. A specific example is a method that uses hydrometallurgy to recover valuable metals such as gold (Au), silver (Ag), and copper from wastewater generated during the manufacturing process of electronic components (plating, etching, etc.). Another proposed method involves using waste circuit boards containing valuable metals such as the aforementioned precious metals and platinum group elements as recycled raw materials, smelting them to remove impurities, and then carrying out a hydrometallurgy process such as acid leaching to recover the valuable metals.

[0003] Patent Document 1 proposes a method for recovering copper powder by adding atomized iron powder equivalent to 0.4 to 0.6 times the theoretical reaction amount of copper and hydrochloric acid to a target liquid such as iron chloride etching waste liquid used in etching printed circuit boards.

[0004] Furthermore, Patent Document 2 proposes a method for producing high-purity copper powder, in which iron powder is added to an iron chloride solution containing copper ions to precipitate metallic copper, and the ORP (oxidation-reduction potential) value of the solution when the iron powder is added is set to about 0 to -350 mV.

[0005] Furthermore, Patent Document 3 proposes a method for recovering valuables, which includes a step of leaching CIGS (Cu, indium (In), gallium (Ga), selenium (Se)) scrap generated in the manufacturing process of compound materials for solar cells with hydrochloric acid and adding iron to the leachate to precipitate copper and selenium, in which iron is added until the oxidation-reduction potential of the leachate reaches 100 to 600 mV. It also describes that if the oxidation-reduction potential of the leachate falls below 100 mV, In and Ga will also precipitate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-43797 [Patent Document 2] Japanese Patent Application Publication No. 4-131310 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-86436 Summary of the Invention [Problem to be solved by the invention]

[0007] The flue gas generated in the process of smelting the above-mentioned recycled materials contains valuable metals such as lead (Pb) and Cu, and these valuable metals are recovered from it.Specific procedures include, for example, leaching the flue gas with sulfuric acid to separate the metals that form sparingly soluble sulfates (precipitates) from the dissolved metals.

[0008] The sulfuric acid leachate produced by this sulfuric acid leaching contains mainly zinc (Zn) and Cu, but by adding a reducing agent to the leachate to reduce it, precipitating and recovering solids containing mainly Cu, and returning the Cu-containing solids to the smelting process to obtain Cu, it is possible to reduce the recovery loss of valuable materials (valuable metals other than Cu present in the leachate can be recovered separately). Note that the Cu-containing solids may also contain impurities other than Cu.

[0009] According to the inventors' research, when waste substrates and the like are used as recycled raw materials in the smelting process, the waste substrates and the like contain plastics, which contain flame retardants. Compounds containing bromine (Br) are widely used as flame retardants. As a result, the sulfuric acid leachate of the flue dust contains Br ions derived from the flame retardants, and it has been found that Br is trapped in the solid material containing Cu obtained by reduction of the leachate. This Br binds to Cu, degrading the quality of the recovered Cu. Furthermore, Br returning to the smelting process can cause problems, such as increased corrosion of the smelting equipment.

[0010] In this specification, when it is clear that various elements exist in an ionic state, for example in the water to be treated, the word "ion" will be added, but no strict distinction is intended between elements in an ionic state and those in a non-ionic state.

[0011] On the other hand, none of the prior art documents 1 to 3 described in the section [Background Art] mentions or suggests that Br ions may be contained in the sulfuric acid leachate or that Br may be mixed into the solid material containing Cu obtained by reduction from the leachate.

[0012] The present invention was made under the above circumstances, and the problem to be solved by the present invention is to prevent Br from being mixed into the resulting Cu-containing solid by improving the reduction process of the water to be treated, such as the sulfuric acid leachate, which contains Cu ions and Br ions. Another object of the present invention is to provide a method for obtaining a Cu-containing solid with reduced Br contamination, preferably in a short time and at low cost. [Means for solving the problem]

[0013] That is, the first invention to solve the above-mentioned problems is: This is a method for treating water to be treated, which involves mixing the water to be treated, which contains copper ions and bromide ions, with a reducing agent, lowering the oxidation-reduction potential of the water to -100 mV or less, and causing the precipitation of solids containing copper.

[0014] The second invention is: This is a method for treating water to be treated according to the first invention, in which the water to be treated is a sulfuric acid leachate obtained by melting a compound containing bromine and a raw material containing copper in a furnace, cooling the resulting exhaust gas, and leaching the resulting flue gas with sulfuric acid.

[0015] The third invention is In the method for treating water to be treated according to the first or second invention, the water to be treated, which has a pH of 1.5 or less, is mixed with the reducing agent and the oxidation-reduction potential is lowered.

[0016] The fourth invention is The method for treating water to be treated according to any one of the first to third aspects of the present invention, wherein the oxidation-reduction potential of the water to be treated is lowered to −200 mV or less to cause precipitation of the copper-containing solid matter.

[0017] The fifth invention is This is a method for treating water to be treated according to any one of the first to fourth inventions, in which a solid-liquid separation process is carried out on the water to be treated in which a precipitate of copper-containing solid matter has formed, thereby obtaining the copper-containing solid matter and a liquid component containing bromide ions.

[0018] The sixth invention is A fifth aspect of the present invention is a method for treating water to be treated according to the present invention, wherein the bromine content in the copper-containing solid is 1 mass % or less.

[0019] The seventh invention is This is the method for treating water to be treated according to any one of the first to sixth aspects of the present invention, wherein the reducing agent is at least one selected from the group consisting of iron powder, zinc powder, and solid iron particles having a size of 0.5 mm to 5 cm.

[0020] The eighth invention is This is a method for treating water to be treated according to any one of the first to seventh inventions, wherein the water to be treated further contains iron ions and zinc ions, and the copper ion content in the water to be treated is 6000 ppm or more and 35000 ppm or less, the bromide ion content is 600 ppm or more and 6000 ppm or less, the iron ion content is 500 ppm or more and 5000 ppm or less, and the zinc ion content is 2000 ppm or more and 18000 ppm or less.

[0021] The ninth invention is This is a method for treating water to be treated according to any one of the first to eighth aspects of the present invention, in which the water to be treated, which has an oxidation-reduction potential of +350 mV or higher, is mixed with the reducing agent and the oxidation-reduction potential is lowered.

[0022] The tenth invention is adding the iron solid to the water to be treated to lower its oxidation-reduction potential to a range of +150 mV to 0 mV; The seventh invention is a method for treating water to be treated, in which at least one metal powder selected from the group consisting of iron powder and zinc powder is added to the water to be treated to which the iron solids have been added, thereby lowering the oxidation-reduction potential of the water to -100 mV or less.

[0023] The eleventh invention is A tenth aspect of the present invention is a method for treating water to be treated, wherein the oxidation-reduction potential of the water to be treated is reduced to −200 mV or less by adding the metal powder.

[0024] The twelfth invention is the amount of the iron solids added is 80 to 110 parts by mass per 100 parts by mass of copper ions in the water to be treated, In the method for treating water to be treated according to the tenth or eleventh invention, the amount of the metal powder used is 10 to 30 parts by mass per 100 parts by mass of copper ions in the water to be treated.

[0025] The thirteenth invention is The iron solid is added to the water to be treated, and the mixture is stirred and mixed for 5 to 20 minutes to lower the oxidation-reduction potential of the water to be treated to a range of +150 mV to 0 mV; This is a method for treating water to be treated according to any one of the tenth to twelfth inventions, in which the metal powder is added to the water to be treated to which the iron solids have been added, and the mixture is stirred and mixed for 10 to 30 minutes to reduce the oxidation-reduction potential of the water to -200 mV or less.

[0026] The fourteenth invention is This is a method for treating water to be treated according to any one of the tenth to thirteenth inventions, wherein the iron powder and zinc powder have a volume-based cumulative 50% particle size of 20 to 120 μm as measured using a laser diffraction / scattering particle size distribution measuring device.

[0027] The fifteenth invention is A method for smelting copper, comprising carrying out a pyrometallurgical refining treatment on a copper-containing solid obtained by the method for treating water to be treated according to any one of the first to fourteenth aspects of the present invention. [Effects of the Invention]

[0028] According to the present invention, it is possible to suppress the incorporation of Br into solid matter containing Cu obtained from water to be treated that contains Cu ions and Br ions. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a process flow diagram showing a method for treating water to be treated according to the present invention. [Figure 2] 1 is a graph showing the correlation between the ORP value of water to be treated and the residual rate of Br ions in the filtrate. The "filtrate" and the "residual rate of Br ions" will be described later. DETAILED DESCRIPTION OF THE INVENTION

[0030] An embodiment of the present invention will be described with reference to FIG. 1, which is a process flow diagram showing the method for treating water to be treated according to the present invention.

[0031] (Smelting process) The water to be treated in the present invention is not particularly limited as long as it contains copper ions and bromide ions (hereinafter also referred to as Br ions). A typical example is a leachate obtained by subjecting waste substrates or the like to a dry smelting process and leaching the resulting flue gas with acid. In the dry smelting process, recycled materials such as waste substrates are fed into a furnace together with coke or the like (sometimes with a concentrate), heated and melted to produce a molten metal of precious metals such as copper, and the resulting slag is removed. When the exhaust gas generated in the smelting furnace is cooled during this process, flue gas is produced. In the waste substrates or the like, for example, Cu is present in the wiring portions, and Br (in the form of a Br-containing compound) is present in the plastic portions.

[0032] (Leaching process) The flue dust generated from the furnace is leached with a strong acid, typically sulfuric acid. The flue dust contains Cu and Br, and may also contain Fe and zinc (Zn). Leaching with a strong acid separates valuable metals that dissolve in the strong acid (Cu, Zn, etc.) from valuable metals that do not dissolve (Pb, Ag, etc.). Strong acids used for leaching include sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is preferred from the standpoint of chemical costs.

[0033] The acid leaching process produces an acid leachate, which is a representative example of the water to be treated according to the present invention. This water to be treated contains Cu ions and Br ions, and may further contain Fe ions and Zn ions. An example of the composition of the acid leachate is as follows: The content of Cu ions is 6000 ppm or more and 35000 ppm or less (it may be 6000 to 15000 ppm). The Br ion content is 600 ppm or more and 6000 ppm or less (it may be 600 to 2500 ppm). The content of Fe ions is 500 ppm or more and 5000 ppm or less (it may be 500 to 2000 ppm). The content of Zn ions is 2000 ppm or more and 18000 ppm or less (it may be 2000 to 8000 ppm). The content of Au ions is 50 ppm or less (may be 10 ppm or less). The content of Ag ions is 50 ppm or less (may be 10 ppm or less). The content of each of the platinum group elements (platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir)) is 50 ppm or less (or may be 10 ppm or less).

[0034] The initial ORP (oxidation-reduction potential) value of the obtained treated water is usually +350 mV or higher (usually +800 mV or lower).

[0035] (Reduction process) The water to be treated is mixed with a reducing agent, and the ORP value of the water to be treated is reduced to -100 mV or less, preferably -200 mV or less, to reduce Cu ions, thereby forming a precipitate of solid matter containing Cu in the water to be treated.

[0036] By performing solid-liquid separation on the treated water (slurry) containing solids containing Cu, the solid Cu can be recovered, and the filtrate is obtained as a liquid component. The liquid volume of the liquid component is substantially the same as the liquid volume of the treated water, and the concentration of Br ions in the treated water and the filtrate can be used to determine how many of the Br ions originally contained in the treated water did not transfer to the solids (Cu) but remained in the filtrate (residual rate (%)). In other words, the residual rate is "[Br ion concentration in the filtrate / Br ion concentration in the original treated water] (%)."

[0037] Figure 2 shows a graph showing the correlation between ORP and the residual rate (%) of Br in the filtrate. The ORP value (mV) was varied without changing the type of reducing agent used for a given sample of water to carry out a reduction reaction of copper ions in the water, and then solid-liquid separation was performed to determine the concentration of Br ions in the filtrate.

[0038] As is clear from the graph in Figure 2, when the ORP value of the water to be treated becomes -100 mV or less, more preferably -200 mV or less, most of the Br ions contained in the original water to be treated remain dissolved in the filtrate, and it can be seen that Br is not mixed into the solid matter containing Cu. According to the present invention, a Br residual rate of 95% or more, or even 98% or more, can be achieved.

[0039] Based on this result and the results of the Examples and Comparative Examples described below, the present inventors consider the process by which Br is separated from a solid material containing Cu according to the present invention as follows. In other words, in the water to be treated (which has a high ORP) before being mixed with the reducing agent, copper exists in the form of a divalent ion, which does not form a precipitate with Br ions. Then, when the water to be treated and the reducing agent are mixed and the initial ORP has not yet decreased significantly, Cu 2+ is reduced and precipitates as metallic copper, and Cu 1+ As the ORP decreases, the remaining Cu in the treated water 2+ and Cu, which forms copper bromide. + is reduced to metallic copper, and as a result, Br is ejected from the solid phase into the liquid phase.

[0040] The ORP of the water to be treated can be reduced by using a reducing agent with strong reducing power or by increasing the amount of reducing agent used. There are no particular restrictions on how much the ORP of the water to be treated should be reduced to, but in terms of the cost of the reducing agent, a reduction to -500 mV is sufficient. In other words, in this reduction step, it is preferable to reduce the ORP of the water to -200 mV to -500 mV.

[0041] As mentioned above, the water to be treated in the present invention is typically a strong acid leachate, and its pH is essentially strong acid. If the pH exceeds 1.5, it is preferable to adjust the pH to 1.5 or less, so that Cu, Fe, and Zn are dissolved as ions in the water to be treated, and then mix with the reducing agent and lower the ORP as described above. This allows Cu to be selectively precipitated as a solid by reduction, making it easier to separate from other metals. The pH can be adjusted, for example, by adding sulfuric acid to the water to be treated.

[0042] The reducing agent to be mixed with the water to be treated is preferably iron (Fe) or zinc (Zn). Specifically, at least one selected from the group consisting of iron powder, zinc powder, and solid iron can be used. From the viewpoint of chemical cost, Fe is preferred as the reducing agent.

[0043] The iron powder and zinc powder preferably have a volume-based cumulative 50% particle size (D50) of 20 to 120 μm as measured using a laser diffraction / scattering particle size distribution analyzer. Iron powder and zinc powder with a D50 in this range dissolve readily in a solution of about pH 1 and exhibit strong reducing power. From the viewpoints of reducing power and chemical costs, the D50 of the iron powder and zinc powder is more preferably 30 to 80 μm.

[0044] Furthermore, from the viewpoint of cost and reducing power, the dimensions of the iron solid are preferably 0.5 mm to 5 cm. The "dimensions" refer to the length of the long side of the smallest rectangle circumscribing the iron solid in a two-dimensional image, such as a photograph, obtained by photographing the iron solid. The rectangle may be a square. Photography is performed from two angles, and the angles are such that the two faces constituting the two two-dimensional images obtained as a result of photography are perpendicular to each other. The iron solid used in both two two-dimensional images has a long side of the smallest circumscribing rectangle that is 0.5 mm to 5 cm long. Furthermore, when photographing the two-dimensional images, no external deformation operations, such as stretching a rolled iron solid, are performed.

[0045] Furthermore, the iron solids having dimensions of 0.5 mm to 5 cm may include some whose dimensions are outside the range of 0.5 mm to 5 cm, and it is sufficient that 80% or more of the iron solids, by mass, pass through a sieve with 5 cm openings but do not pass through a sieve with 0.5 mm openings.

[0046] Examples of such iron solids include iron scrap generated during cutting and turning of steel or pig iron. These amorphous iron solids that do not have a specific shape are inexpensive and are preferred from the viewpoint of material cost.

[0047] The temperature of the water to be treated when carrying out this reduction step is not particularly limited, and it can be carried out at room temperature (about 20 to 40° C.), for example.

[0048] Regarding the iron powder and the zinc powder, either one of them may be mixed with the water to be treated, or both may be mixed with the water to be treated. When using these, specifically, for example, at least one of iron powder and zinc powder (hereinafter also referred to as "metal powder") is added to the water to be treated while stirring it. The amount of metal powder to be added should be such that the ORP value of the water to be treated is measured to be -100 mV or less, more preferably -200 mV or less.

[0049] According to the findings of the present inventors, the above-mentioned ORP value can be achieved by adding metal powder in an amount 0.85 times or more the mass of Cu ions contained in the water to be treated. When both iron powder and zinc powder are used, the above-mentioned amount is the total amount of these. From the viewpoint of cost, the upper limit of the amount of metal powder to be added is preferably no more than twice the mass of Cu ions contained in the water to be treated. From the viewpoints of reducing power and cost, the amount of metal powder to be used is more preferably 1.0 to 1.2 times the mass of Cu ions in the water to be treated.

[0050] Next, when mixing the water to be treated with iron solids to precipitate Cu in the water, the ORP value of the water to be treated is measured and iron solids are added in an amount that brings the ORP value to -100 mV or less, more preferably -200 mV or less. Iron solids are typically iron scrap, so the chemical cost is lower than that of iron powder or zinc powder.

[0051] However, iron solids are only a few millimeters to a few centimeters in size, and have a weak reducing power, so they do not dissolve well even in water to be treated with a pH of about 1. For this reason, a fairly large amount of iron solids must be used to reduce the ORP value to -100 mV or less, and more preferably -200 mV or less, by adding only iron solids (specifically, more than 200 parts by mass of iron solids must be used per 100 parts by mass of Cu ions in the water to be treated).

[0052] Furthermore, since the iron solids remain as solids in the water to be treated even after the reduction step is completed, they are separated from the water to be treated using a sieve, etc. The Cu solids produced in the reduction step are typically fine copper powder, which is smaller than the iron solids, and can be separated from the iron solids using the sieve.

[0053] <Combination of at least one of iron powder and zinc powder with iron solids> Hereinafter, a case where at least one of iron powder and zinc powder (metal powder) is used in combination with solid iron will be described. As mentioned above, iron powder and zinc powder are preferable as reducing agents to be mixed with the water to be treated from the viewpoint of reducing power, however, iron solids are less expensive as reducing agents.

[0054] As a result of research, the inventors have come up with the idea that the following two-stage reduction treatment can reduce the cost of the reducing agent and produce copper solids in a sufficient yield in a short time. Specifically, in the first stage, iron solids are added to the water to be treated to reduce the ORP value to a range of +150 to 0 mV, reducing and precipitating most of the Cu ions contained in the water. Then, in the second stage, metal powder is added to the water to reduce the ORP value of the water to -100 mV or less, preferably -200 mV or less, reducing substantially all of the remaining Cu ions contained in the water to precipitate as metallic copper, while also expelling Br from the solid phase, resulting in a solid containing Cu.

[0055] To reduce the ORP value to the above range, the amount of iron solids used is preferably 80 to 110 parts by mass, more preferably 90 to 110 parts by mass, per 100 parts by mass of Cu ions in the water to be treated, and the total amount of metal powder used is preferably 10 to 30 parts by mass, more preferably 12 to 25 parts by mass, per 100 parts by mass of Cu ions in the water to be treated. The iron solids and metal powder may be added all at once or continuously.

[0056] According to the findings of the inventors, in the first stage of treatment described above, the water to be treated is stirred and mixed with iron solids (the amount of iron solids used is within the above-mentioned range) for 5 to 20 minutes, and then in the second stage of treatment, the water to be treated is stirred and mixed with at least one of iron powder and zinc powder (the total amount of these used is within the above-mentioned range) for 10 to 30 minutes, so that substantially all of the Cu contained in the water to be treated can be precipitated (the ORP of the water to be treated will reach the range specified in this invention by the time the above-mentioned time has passed).

[0057] The combined use of the metal powder and solid iron described above is a preferable configuration from the viewpoints of reducing the cost of the reducing agent and shortening the time required for the reduction step.

[0058] On the other hand, if iron solids and metal powder are added simultaneously, or if the metal powder is added before the iron solids (with the amounts of each substance used being within the preferred ranges described above), the iron powder and zinc powder, which have strong reducing power, reduce Cu ions first, and these are consumed first. As a result, the iron solids, which have weak reducing power, are unable to sufficiently reduce the remaining Cu ions in the water to be treated, and the ORP is not sufficiently reduced. As a result, the benefits of using metal powder and iron solids in combination are lost (see Comparative Example 2, described below).

[0059] (Solid-liquid separation process) The slurry obtained by the reduction step is subjected to solid-liquid separation to recover a solid material containing Cu. The Br content in the solid material containing Cu is low. Specifically, for example, the recovered solid material has a Cu content of 70 to 85 mass%, an Fe content of 0.1 to 5 mass%, a Br content of 1 mass% or less (preferably 0.1 to 0.5 mass%), and the remainder being oxygen. As a result, the recovered solid material containing Cu can be used as a Cu raw material to be charged directly into a smelting furnace.

[0060] On the other hand, it was found that substantially all of the Br was present in the filtrate, which is the liquid component obtained by solid-liquid separation. The Fe in the Cu-containing solid is thought to originate from the iron solid. The iron solid also contains fine fragments, which cannot be adequately separated using the sieve described below and are thought to be mixed into the Cu-containing solid.

[0061] When iron solids are used in the reduction step, the solid component obtained in the solid-liquid separation step is a mixture of Cu-containing solids and the iron solids. Because they differ greatly in size (iron solids are larger), they can be easily separated using a sieve. Separation of the Cu-containing solids and the iron solids using a sieve may be performed before the solid-liquid separation step. That is, the slurry can be sieved to obtain a slurry from which almost all of the iron solids have been removed. Alternatively, the iron solids can be removed by magnetic separation.

[0062] Furthermore, as with the residual rate of Br ions in the filtrate, since the volume of the filtrate obtained by solid-liquid separation is substantially the same as the volume of the water to be treated, the degree to which the Cu ions initially contained in the water to be treated have been removed (Cu removal rate (%)) can be calculated from the copper ion concentrations in the water to be treated and the filtrate. That is, the Cu removal rate can be calculated using the formula "(1 - [Cu ion concentration in the filtrate / Cu ion concentration in the original water to be treated]) (%)." This Cu removal rate can be used as an indicator of the recovery rate of Cu as solids by the method for treating water to be treated of the present invention. According to the present invention, a Cu removal rate of 95% or more, preferably 98% or more, can be achieved. [Example]

[0063] Examples of the method for treating water to be treated according to the present invention will be described in detail below, but the present invention is not limited to the contents of these examples.

[0064] Various measurements carried out in the examples and comparative examples according to the present invention were carried out as follows. (Metal ion content measurement) Measurement was performed using an ICP emission spectrometer (Hitachi High-Tech Science, SPS-5100). (Br - (Measurement of content) Measurement was carried out using ion chromatography (Tosoh, IC-8100). (pH measurement) Measurements were taken at 25°C using a pH meter and electrode (HORIBA, D-73). (ORP value measurement) Measurements were taken at 25°C using a pH meter and electrode (HORIBA, D-73).

[0065] [Example 1] Waste substrates were used as recycled raw materials for smelting, and the flue gas-derived flue gas generated was leached with sulfuric acid. The resulting leachate was subjected to solid-liquid separation, and the resulting sulfuric acid leachate was used as the treated water in Example 1. The pH, ORP, and composition of the treated water in Example 1 are shown in Table 1.

[0066] [Table 1]

[0067] To 0.8 L of this water to be treated, 98% by mass of concentrated sulfuric acid was added to adjust the pH to 1. The ORP value of the pH-adjusted water to be treated was +500 mV. Next, while the water to be treated was being stirred at 300 rpm, iron solids (iron scraps with dimensions of approximately 1 to 20 mm) were added all at once to the water to be treated at room temperature in an amount equal to the mass of copper ions in the water to be treated, to form a mixed liquid (slurry).

[0068] The ORP value of this mixed solution was continuously measured, and when it dropped to +100 mV (approximately 10 minutes after adding the iron scrap), iron powder (manufactured by DOWA IP Creation Co., Ltd., cumulative 50% particle size on a volume basis measured by Microtrac particle size distribution measurement) was added little by little while continuing to stir the mixed solution. Then, when the ORP value of the mixed solution reached -200 mV, the addition of iron powder was stopped.

[0069] The amount of iron powder added up to the end of the iron powder addition was 0.18 times the mass of copper ions in the water being treated. The iron powder dissolved immediately after being added to the mixed solution. The ORP value of the mixed solution dropped to approximately -400 mV approximately 25 minutes after the addition of the iron scrap. Agitation of the mixed solution was stopped 30 minutes after the addition of the iron scrap (approximately 20 minutes after the start of the iron powder addition).

[0070] The mixed liquid (slurry containing copper powder) obtained by the above procedure was filtered, and a sample of the filtrate was collected and analyzed for Br ion and Cu ion concentrations, and the Br residual rate and Cu removal rate in the filtrate were calculated. The Cu removal rate was calculated by analyzing the Cu ion concentration in the filtrate and dividing it by the Cu ion concentration in the original water to be treated, which had been analyzed in advance, to obtain the "Cu removal rate (%)" in the filtrate: (1 - [Cu concentration in filtrate / Cu concentration in the original water to be treated]) (%).

[0071] Furthermore, the same treatment water as used above was subjected to the same operations up to the addition of iron powder (pH adjustment, addition of iron scrap, addition of iron powder) as described above. 15 minutes after the addition of the iron scrap, the mixed liquid was filtered, and samples of the resulting filtrate were collected and analyzed for the concentrations of Br ions and Cu ions, and the Br residual rate and Cu removal rate in the filtrate were calculated.

[0072] The above evaluation results are shown in Tables 2 and 3 below, together with the results of Example 2 and Comparative Examples 1 to 3, which will be described later.

[0073] [Table 2]

[0074] [Table 3]

[0075] From the results in Table 2, for Example 1, the Br residual rate in the filtrate 15 minutes after the addition of the Fe scrap was only 6.0%, suggesting that Br was mixed into the solid matter containing Cu. However, since the ORP value of the mixed liquid was -400 mV 25 minutes after the addition of the iron scrap, it is believed that Br redissolved from the solid matter containing Cu into the liquid phase, and the Br residual rate was 101.3% after 30 minutes. Note that the Br residual rate in the filtrate exceeding 100% is believed to be due to measurement error.

[0076] On the other hand, the results in Table 3 show that the Cu removal rate in the filtrate increased over time, reaching 99.9% after 30 minutes, indicating that almost all of the Cu had become solid.

[0077] After 30 minutes, the solid containing Cu was separated from the filtrate and the solid containing Cu was separated using a sieve with 0.5 mm openings, and the composition of the powder that remained under the sieve was measured. The results are shown in Table 4.

[0078] [Table 4]

[0079] The results in Table 4 also show that the powder that passed through the sieve is a solid material containing Cu with almost no Br, and can be used as a Cu raw material to be fed into a smelting furnace. The small amount of detected Fe is thought to be derived from particularly small fragments of the added iron solid. The amount of oxygen was calculated assuming that the solid was composed of Cu, Fe, Br, and the remainder oxygen.

[0080] [Comparative Example 1] The same water to be treated as in Example 1 was prepared and used as the water to be treated in Comparative Example 1. The same procedure as in Example 1 was carried out on the water to be treated, except that iron powder was not added. The ORP value of the mixed solution reached approximately 0 mV 37 minutes after the addition of the iron scrap and did not decrease any further. For the mixed solution (two samples) according to Comparative Example 1, which had undergone the above-described operations, samples of the filtrate were collected at 15 minutes and 30 minutes after the addition of the iron scrap, and the Br and Cu concentrations were analyzed, and the Br residual rate and Cu removal rate in the filtrate were calculated, as in Example 1. The results are shown in Tables 2 and 3 above.

[0081] From the results in Table 2, the Br residual rate in the filtrate was 1.2% after 15 minutes, suggesting that most of the Br was mixed into the solid matter containing Cu. It was also found that the Br residual rate was still very low at 1.74% after 30 minutes (when an additional sample was used and the Br residual rate was determined at 45 minutes, it was 20.7%). This suggests that most of the Br was still mixed into the solid matter containing Cu. This is likely due to the ORP value of the mixed solution being approximately 0 mV, which was not sufficiently reduced. It is also likely that the addition of solid iron or iron powder (or zinc powder) would reduce the ORP to the range specified in the present invention and increase the Br residual rate to a level similar to that of the Examples. The same is true for Comparative Examples 2 and 3 below.

[0082] On the other hand, the results in Table 3 show that the Cu removal rate in the filtrate increased over time, and after 30 minutes the Cu removal rate was 98.6%, suggesting that almost all of the Cu (along with Br, etc.) had turned into solid matter.

[0083] From the above results, it was considered that Br was present in the solid material containing Cu obtained in Comparative Example 1, and that when the solid material containing Cu was used as a Cu raw material in a smelting furnace, adverse effects such as a decrease in copper grade and corrosion of equipment would occur.

[0084] Comparative Example 2 The same water to be treated as in Example 1 was prepared and used as the water to be treated in Comparative Example 2. The water to be treated was adjusted to pH 1 in the same manner as in Example 1. Then, a mixture of iron solids (similar to Example 1) with an equal mass to the mass of copper in the water to be treated and iron powder (similar to Example 1) with a mass 0.18 times the mass was preliminarily added to the water to be treated at room temperature while stirring (300 rpm) to form a mixed liquid (slurry).

[0085] The decrease in the ORP value of the mixed liquid was more gradual than in Example 1, and the ORP value was around 0 mV approximately 30 minutes after the addition of the iron scrap.

[0086] The mixed solution (two samples) according to Comparative Example 2, which had undergone the above-described procedure, was filtered at 15 minutes and 30 minutes after the start of the procedure in the same manner as in Example 1. Samples of the filtrate were collected and analyzed for the concentrations of Br ions and Cu ions, and the Br residual rate and Cu removal rate in the filtrate were calculated. The results are shown in Tables 2 and 3.

[0087] From the results in Table 2, the Br remaining rate in the filtrate was 1.12% 15 minutes after the addition of the Fe scrap, and it was thought that most of the Br was mixed in the solid matter containing Cu. The Br remaining rate was 2.66% 30 minutes after the addition of the Fe scrap. This means that even at this point, most of the Br was mixed in the solid matter containing Cu.

[0088] Since iron powder has a stronger reducing power than solid iron and is more likely to act as a reducing agent, when they are added at the same time, it is thought that the iron powder is used in the reduction reaction first, and the solid iron is unable to sufficiently lower the ORP value, which is thought to have resulted in a low residual Br rate in the filtrate.

[0089] On the other hand, the results in Table 3 show that the Cu removal rate in the filtrate increased over time, reaching 99.6% after 30 minutes, suggesting that almost all of the Cu had become solid matter containing Cu.

[0090] Comparative Example 3 The same water to be treated as in Example 1 was prepared and used as the water to be treated in Comparative Example 3. The water to be treated was adjusted to pH 1 in the same manner as in Example 1. Then, iron solids (similar to those in Example 1) in an amount twice the mass of copper in the water to be treated were added all at once to the water to be treated at room temperature while stirring (300 rpm) to form a mixed liquid (slurry).

[0091] The decrease in the ORP value of the mixed liquid was more gradual than in Example 1, and the ORP value was approximately 0 mV approximately 30 minutes after the addition of the solid iron.

[0092] The mixed solution (two samples) according to Comparative Example 3, which had undergone the above procedure, was filtered at 15 minutes and 30 minutes in the same manner as in Example 1, and samples of the filtrate were collected and analyzed for the concentrations of Br ions and Cu ions, and the Br residual rate and Cu removal rate in the filtrate were calculated. The results are shown in Tables 2 and 3 above.

[0093] From the results in Table 2, the residual Br rate in the filtrate was 0.89% after 15 minutes and 1.42% after 30 minutes.

[0094] Furthermore, from the results in Table 3, it can be seen that the Cu removal rate in the filtrate increased over time, and after 30 minutes the Cu removal rate was 96.2%, suggesting that almost all of the Cu had become solid matter containing Cu.

[0095] [Example 2] The same water to be treated as in Example 1 was prepared and used as the water to be treated in Example 2. The same procedure as in Example 1 was carried out on the water to be treated, except that zinc powder (having a volume-based cumulative 50% particle diameter of approximately 60 μm as determined by a Microtrac particle size distribution analyzer) was used instead of iron powder.

[0096] The ORP value of the mixed solution was -385 mV approximately 30 minutes after the addition of the iron scrap.

[0097] The mixed solution of Example 2, which had undergone the above-described procedure, was filtered after 30 minutes had elapsed, and a sample of the filtrate was collected to analyze the concentrations of Br ions and Cu ions, and the Br residual rate and Cu removal rate in the filtrate were calculated. The results are shown in Tables 2 and 3.

[0098] From the results in Tables 2 and 3, when zinc powder was used, the Br residual rate was 101.39% and the Cu removal rate was 99.9% after 30 minutes, as in Example 1. Almost all of the Cu became solid matter containing Cu, and almost all of the Br was transferred to the filtrate. Note that the Br residual rate in the filtrate exceeding 100% is thought to be due to measurement error.

Claims

1. A method for treating water to be treated, which comprises mixing the water to be treated containing copper ions and bromide ions with a reducing agent, thereby lowering the oxidation-reduction potential of the water to -100 mV or less, and causing precipitation of copper-containing solids.

2. 2. A method for treating water to be treated as described in claim 1, wherein the water to be treated is a sulfuric acid leachate obtained by melting a compound containing bromine and a raw material containing copper in a furnace, cooling the resulting exhaust gas, and leaching the resulting ash with sulfuric acid.

3. 2. The method for treating water to be treated according to claim 1, wherein the water to be treated, which has a pH of 1.5 or less, is mixed with the reducing agent and the oxidation-reduction potential is lowered.

4. 2. The method for treating water to be treated according to claim 1, wherein the oxidation-reduction potential of the water to be treated is reduced to -200 mV or less to cause precipitation of the copper-containing solid matter.

5. 2. The method for treating water to be treated according to claim 1, wherein a solid-liquid separation process is performed on the water to be treated in which the copper-containing solid matter has precipitated, thereby obtaining the copper-containing solid matter and a liquid component containing bromide ions.

6. 6. The method for treating water to be treated according to claim 5, wherein the bromine content in the copper-containing solid matter is 1 mass % or less.

7. 2. The method for treating water to be treated according to claim 1, wherein the reducing agent is at least one selected from the group consisting of iron powder, zinc powder, and iron solids having a size of 0.5 mm to 5 cm.

8. The method for treating water to be treated according to claim 1, wherein the water to be treated further contains iron ions and zinc ions, and the copper ion content in the water to be treated is 6000 ppm or more and 35000 ppm or less, the bromide ion content is 600 ppm or more and 6000 ppm or less, the iron ion content is 500 ppm or more and 5000 ppm or less, and the zinc ion content is 2000 ppm or more and 18000 ppm or less.

9. 2. The method for treating water to be treated according to claim 1, wherein the water to be treated, which has an oxidation-reduction potential of +350 mV or higher, is mixed with the reducing agent and the oxidation-reduction potential is lowered.

10. adding the iron solid to the water to be treated to lower its oxidation-reduction potential to a range of +150 mV to 0 mV; The method for treating water to be treated according to claim 7, wherein at least one metal powder selected from the group consisting of iron powder and zinc powder is added to the water to be treated to which the iron solids have been added, thereby reducing the oxidation-reduction potential of the water to be treated to -100 mV or less.

11. The method for treating water to be treated according to claim 10, wherein the oxidation-reduction potential of the water to be treated is reduced to −200 mV or less by adding the metal powder.

12. the amount of the iron solids added is 80 to 110 parts by mass per 100 parts by mass of copper ions in the water to be treated, 12. The method for treating water to be treated according to claim 11, wherein the amount of the metal powder used is 10 to 30 parts by mass per 100 parts by mass of copper ions in the water to be treated.

13. The iron solid is added to the water to be treated, and the mixture is stirred and mixed for 5 to 20 minutes to lower the oxidation-reduction potential of the water to be treated to a range of +150 mV to 0 mV; The method for treating water to be treated according to claim 12, wherein the metal powder is added to the water to be treated to which the iron solids have been added, and the mixture is stirred and mixed for 10 to 30 minutes to reduce the oxidation-reduction potential of the water to be treated to -200 mV or less.

14. The method for treating water to be treated according to claim 10, wherein the iron powder and zinc powder have a volume-based cumulative 50% particle size of 20 to 120 μm as measured by a laser diffraction / scattering particle size distribution measuring device.

15. A copper smelting method, comprising carrying out a dry smelting process on a copper-containing solid obtained by the method for treating water to be treated according to any one of claims 1 to 14.

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