Method for recovering precious metals from chlorine bypass dust

Abstract

To provide a method for efficiently recovering precious metal from chlorine bypass dust.SOLUTION: Provided is a method for recovering precious metal from chlorine bypass dust that includes: a first step of mixing chlorine bypass dust with one or more solvents selected from water at 5 to 70°C and hydrophilic organic solvent to prepare a slurry; a second step of centrifuging the slurry to separate it into a supernatant and precipitates having particle sizes D99 of 28 to 37 μm; and a third step of recovering the precipitates.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for recovering precious metals from chlorine bypass dust.

Background Art

[0002] In the cement manufacturing process, volatile components such as chlorine, sulfur, and alkali are the causes of problems such as blockage of the preheater when cement raw materials are fired in a cement kiln. Paying particular attention to the fact that chlorine becomes a problem, a chlorine bypass system is adopted in which a part of the combustion gas is extracted from the kiln exhaust gas flow path from the kiln end of the cement kiln to the lowermost cyclone to remove chlorine. Among them, since it has been found that chlorine is unevenly distributed on the fine powder side in the chlorine bypass dust, the dust is separated into coarse powder and fine powder by a classifier, the coarse powder is returned to the cement kiln system, and the fine powder (chlorine bypass dust) containing separated potassium chloride, etc. is recovered and added within a range not exceeding the specified value of the chlorine concentration during the cement grinding process and reused as a cement raw material has been proposed (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, the recycling of waste through cement raw materialization and fuelization has been promoted, and the waste processed in cement plants includes various types such as municipal solid waste incineration main ash, automobile shredder dust (ASR), and sewage sludge incineration ash. Therefore, as the amount of waste treated increases, the amount of volatile components such as chlorine, sulfur, and alkali brought into the cement kiln also increases, and the amount of chlorine bypass dust generated also increases. Therefore, it is difficult to utilize all the generated chlorine bypass dust in the cement manufacturing process, and it is predicted that the amount of chlorine bypass dust generated will further increase in the future. Thus, the development of a new effective utilization method is required. An object of the present invention is to provide a method for efficiently recovering precious metals from chlorine bypass dust.

Means for Solving the Problems

[0005] The present inventors have conducted a detailed study to develop a new effective utilization method for chlorine bypass dust. As a result, it has been found that chlorine bypass dust contains abundant precious metals, and the precious metals are unevenly distributed together with chlorine in fine powder with a particle size below a specific size. Then, by mixing chlorine bypass dust with one or more solvents selected from water and hydrophilic organic solvents at a specific temperature to prepare a slurry, centrifuging the slurry to separate it into a supernatant and a precipitate having a specific particle size distribution, and recovering the precipitate, it has been found that precious metals can be efficiently recovered from chlorine bypass dust.

[0006] That is, the present invention provides the following [1] to [4]. 〔1〕A first step of mixing chlorine bypass dust with one or more solvents selected from water at 5 to 70 °C and hydrophilic organic solvents to prepare a slurry, centrifuging the slurry to separate it into a supernatant and a precipitate with a particle diameter D 99 of 28 to 37 μm in a second step, and a third step of recovering the precipitate A method for recovering precious metals from chlorine bypass dust, including the above steps. 〔2〕The precious metal recovery method according to the above [1], wherein a solvent that is 2 mass times or more of the chlorine bypass dust is mixed. 〔3〕The precious metal recovery method according to the above 〔1〕 or 〔2〕, wherein the solvent is water. 〔4〕The precious metal recovery method according to any one of the above 〔1〕 to 〔3〕, wherein the precious metal contains gold.

Advantages of the Invention

[0007] According to the present invention, precious metals can be efficiently recovered from chlorine bypass dust. Therefore, the present invention is useful as a new effective utilization method for chlorine bypass dust.

Embodiments for Carrying Out the Invention

[0008] The precious metal recovery method from chlorine bypass dust of the present invention includes a first step, a second step, and a third step. Hereinafter, each step will be described in detail.

[0009] 〔First Step〕 The first step is a step of mixing chlorine bypass dust and a solvent at 5 to 70 °C to prepare a slurry. Here, in this specification, "chlorine bypass dust" refers to fine powder separated by extracting a part of combustion gas from the kiln exhaust gas flow path from the kiln end of a cement kiln in a cement manufacturing facility to the lowermost cyclone, cooling the extracted gas, and classifying it into coarse powder and fine powder. In addition, the chlorine bypass dust used in the present invention is not particularly limited as long as it is generated in the cement manufacturing process. Also, the cement raw materials used in the cement manufacturing process include ash obtained by incinerating municipal waste and industrial waste, such as sludge, waste plastics, metal scraps, glass scraps, concrete scraps, ceramic scraps, mine tailings, rubble, etc. industrial waste, as well as shredder dust generated by crushing waste automobiles and waste household appliances, and ash obtained by incinerating general waste may also be included.

[0010] The solvent to be mixed with the chlorine bypass dust is water, a hydrophilic organic solvent, or a mixture thereof. Thereby, the soluble components in the chlorine bypass dust can be eluted. Examples of the water include tap water defined in Appendix C of JIS A 5303 and water other than the tap water (for example, river water, lake water, well water, groundwater, industrial water). The hydrophilic organic solvent is not particularly limited as long as it shows affinity with water. Examples thereof include alcohols such as ethanol and methanol, ketones such as acetone, ethers such as tetrahydrofuran and dioxane, and esters such as ethyl acetate. Among them, alcohol is preferable. The proportion of the hydrophilic organic solvent in the aqueous solution is preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less.

[0011] The temperature of the solvent is 5 to 70°C. If the temperature of the solvent is too low, the solubility of the soluble components in the chlorine bypass dust decreases, and if it is too high, the recovery rate of the noble metal decreases. From such a viewpoint, the temperature of the solvent is preferably 10°C or higher, more preferably 15°C or higher, still more preferably 18°C or higher, and preferably 65°C or lower, more preferably 60°C or lower, still more preferably 55°C or lower. Therefore, the temperature of the solvent is preferably 10 to 70°C, more preferably 10 to 65°C, still more preferably 15 to 60°C, and even more preferably 18 to 55°C.

[0012] From the viewpoints of elution of the soluble components in the chlorine bypass dust and recovery of the noble metal, the amount of the solvent used is preferably 2 times by mass or more, more preferably 3 times by mass or more, still more preferably 4 times by mass or more, even more preferably 5 times by mass or more with respect to the chlorine bypass dust. From the viewpoint of production efficiency, it is preferably 15 times by mass or less, more preferably 12 times by mass or less, still more preferably 10 times by mass or less, and even more preferably 8 times by mass or less. Therefore, the amount of the solvent used is preferably 2 to 15 times by mass, more preferably 3 to 12 times by mass, still more preferably 4 to 10 times by mass, and even more preferably 5 to 8 times by mass with respect to the chlorine bypass dust.

[0013] The method of mixing chlorine bypass dust and a solvent is not particularly limited. For example, the chlorine bypass dust and the solvent may be charged and mixed in any order, or both may be charged and mixed simultaneously.

[0014] 〔Second step〕 The second step is a step of centrifuging the slurry to separate it into a supernatant and a precipitate having a particle diameter D 99 of 28 to 37 μm. The inventors of the present invention have found that when the particle diameter D 99 of the precipitate formed after centrifugation is within the above range, the noble metal concentration in the precipitate is increased. Here, in this specification, "particle diameter D 99 " means the particle diameter corresponding to 99% of the cumulative distribution curve created on a volume basis by measuring the particle size distribution of a sample obtained by ultrasonically dispersing a mixture of 0.03 g of the precipitate and 30 mL of isopropanol at room temperature for 3 minutes using an ultrasonic device (ultrasonic homogenizer US-150E manufactured by Nippon Seiki Co., Ltd.). As a particle size distribution measuring device by the laser diffraction / scattering method, for example, Microtrac MT3300EX II (manufactured by Microtrac Bell) can be used. can be used.

[0015] The centrifugation may be, for example, any of a separation plate type, a cylindrical type, a decanter type, etc., and general equipment can be used. The conditions for centrifugation are not particularly limited as long as two layers of a supernatant and a precipitate are formed after centrifugation and the particle diameter D 99 of the precipitate is within the above range. For example, the following conditions can be mentioned. The centrifugal force is preferably 300 G or more, more preferably 400 G or more, still more preferably 500 G or more, even more preferably 600 G or more, and preferably 2500 G or less, more preferably 2000 G or less, still more preferably 1600 G or less, and even more preferably 1200 G or less. Therefore, the centrifugal force is preferably 300 to 2500 G, more preferably 400 to 2000 G, still more preferably 500 to 1600 G, and even more preferably 600 to 1200 G. Also, the time can be appropriately set according to the centrifugal force, but it is preferably 30 seconds or more, more preferably 50 seconds or more, still more preferably 70 seconds or more, even more preferably 90 seconds or more, and preferably 270 seconds or less, more preferably 250 seconds or less, still more preferably 230 seconds or less, even more preferably 200 seconds or less. Therefore, the time is preferably 30 to 270 seconds, more preferably 50 to 250 seconds, still more preferably 70 to 230 seconds, and even more preferably 90 to 200 seconds.

[0016] The particle diameter D of the precipitate formed after centrifugation 99 is 28 to 37 μm. From the viewpoint of improving the noble metal concentration, 29 μm or more is preferable, 29.5 μm or more is preferable, 30 μm or more is still more preferable, and 36 μm or less is preferable, 35 μm or less is more preferable, 34 μm or less is still more preferable. Therefore, such particle diameter D 99 is preferably 29 to 36 μm, more preferably 29.5 to 35 μm, and still more preferably 30 to 34 μm.

[0017] 〔The third step〕 The third step is a step of recovering the precipitate. Thereby, the precipitate in which the noble metal is concentrated is recovered. The noble metal recovered by this step contains at least gold, and preferably contains gold and one or more selected from silver, copper, platinum, and palladium. For example, decantation or filtration may be performed for the recovery of the precipitate. The recovered precipitate may be dried. The drying method is not particularly limited, and known heat drying means can be adopted. The drying temperature is, for example, 80 to 300 °C. Also, the recovered precipitate may be subjected to one or more selected from, for example, a classification step, a pneumatic separation step, a specific gravity separation step, and a magnetic separation step to further improve the grade of the noble metal. In each step, equipment generally used in the technical field can be used.

Examples

[0018] Hereinafter, embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[0019] 1. Analysis of noble metals Nitric acid-hydrochloric acid mixture was added to the sample, and the decomposed sample using a microwave sample pretreatment device ETHOS EASY manufactured by Milestone was used as an analysis sample. For the analysis, quantitative analysis was performed using an ICP-MS 7700X manufactured by Agilent.

[0020] 2. Measurement of particle size distribution of precipitate 0.03 g of the precipitate and 30 mL of isopropanol were ultrasonically dispersed at room temperature for 3 minutes using an ultrasonic device (ultrasonic homogenizer US-150E manufactured by Nippon Seiki Co., Ltd.). Then, the particle diameter was measured using a Microtrac particle size analyzer (Microtrac MT3300EX II manufactured by Microtrac Bell) by the laser diffraction / scattering method, and a volume-based particle size distribution was created.

[0021] Example 1 Chlorine bypass dust and water at 20 °C were put into a centrifuge tube (volume 50 mL) at a mass ratio of 1:6 and manually stirred for 1 minute to prepare a slurry. Next, the slurry was centrifuged using a centrifuge (CN-2060 manufactured by AS ONE) under the conditions shown in Table 1. After centrifugation, the precipitate and the supernatant were quickly separated, and the precipitate was collected. Then, the particle size distribution of the precipitate was measured. Also, after drying the precipitate at 105 °C for 24 hours, the noble metal concentration of the precipitate was analyzed. The results are shown in Table 1.

[0022] Comparative Examples 1 to 3 The precipitate was collected by the same operation as in Example 1 except that the centrifugation conditions were changed to those shown in Table 1. Then, the particle size distribution of the precipitate was measured and the noble metal concentration of the precipitate was analyzed in the same manner as in Example 1. The results are shown in Table 1.

[0023] Example 2 Precipitates were collected by the same operations as in Example 1, except that they were mixed with water at the temperatures shown in Table 1. Then, the particle size distribution of the precipitates was measured and the noble metal concentration of the precipitates was analyzed in the same manner as in Example 1. The results are shown in Table 1.

[0024] Comparative Examples 4 to 6 Precipitates were collected by the same operations as in Example 2, except that the centrifugation was changed to the conditions shown in Table 1. Then, the particle size distribution of the precipitates was measured and the noble metal concentration of the precipitates was analyzed in the same manner as in Example 1. The results are shown in Table 1.

[0025] Comparative Example 7 Precipitates were collected by the same operations as in Comparative Example 2, except that they were mixed with water at the temperatures shown in Table 1. Then, the particle size distribution of the precipitates was measured and the noble metal concentration of the precipitates was analyzed in the same manner as in Example 1. The results are shown in Table 1.

[0026] Comparative Example 8 Precipitates were collected by the same operations as in Example 1, except that they were mixed with water at the temperatures shown in Table 1. Then, the particle size distribution of the precipitates was measured and the noble metal concentration of the precipitates was analyzed in the same manner as in Example 1. The results are shown in Table 1.

[0027] Example 3 Precipitates were collected by the same operations as in Example 2, except that an aqueous solution with ethanol added at the ratio shown in Table 1 was used as the solvent. Then, the particle size distribution of the precipitates was measured and the noble metal concentration of the precipitates was analyzed in the same manner as in Example 1. The results are shown in Table 1.

[0028]

Table 1

[0029] From Table 1, for the slurry obtained by mixing chlorine bypass dust and a solvent at a predetermined temperature, the particle diameter D of the precipitate 99By performing centrifugation so that it is within a predetermined range, it can be seen that a precipitate in which the noble metal concentration is concentrated to 5 times or more compared to before the treatment can be recovered. Further, from the comparison between Example 2 and Example 3, it can be seen that even if the solvent contains a hydrophilic organic solvent, the same effect as that of water is achieved.

Claims

1. A first step of preparing a slurry by mixing chlorine bypass dust containing gold and a solvent that is a solvent at 5 to 70°C and is selected from an aqueous solution containing water and 20% by mass or less of ethanol. Centrifuging the slurry to separate it into a supernatant and a precipitate with a particle size D 99 of 28 to 37 μm in a second step. A third step of recovering the precipitate in which gold is concentrated A method for recovering precious metals from chlorine bypass dust, comprising the above steps.

2. The method for recovering precious metals according to Claim 1, wherein a solvent that is 2 mass times or more that of the chlorine bypass dust is mixed.

3. The method for recovering precious metals according to Claim 1 or 2, wherein the solvent is water.

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