JP7573482B2 - Method for recovering valuable metals from waste - Google Patents

Description

The present invention relates to a method for recovering valuable metals from waste.

Attempts are being made to effectively use waste materials such as municipal waste incineration ash, waste plastics, and shredder dust as raw materials for cement. These waste materials contain valuable metals, such as precious metals such as gold, silver, copper, palladium, and platinum. From the perspective of effective resource utilization, it is desirable to recover these valuable metals, but the cost of recovery is high.

Conventionally, various studies have been made to efficiently recover valuable metals from waste. For example, a method has been proposed in which valuable metal-containing waste is pulverized in a vertical roller mill into mill fine powder having a predetermined particle size distribution and mill waste containing coarse powder having a particle size distribution larger than the predetermined particle size distribution, the mill waste is pulverized so that the content of valuable metals in the mill waste is higher than the content of valuable metals in the waste, and the obtained mill waste is sorted to recover valuable metals (Patent Document 1). Also, a method has been proposed in which valuable metal-containing waste is pulverized in a vertical roller mill to obtain mill waste with a bulk density of 1.3 t/m3 or ^more , and the obtained mill waste is sorted to recover valuable metals (Patent Document 2).

JP 2016-89196 A JP 2021-1362 A

The methods described in Patent Documents 1 and 2 make it possible to recover mill waste containing concentrated valuable metals, but the raw material is incineration ash from municipal waste and the like, which is waste containing valuable metals, and the mill flour recovered by these methods is intended to be used as a raw material for ecocement.
On the other hand, when producing raw materials for ordinary cement, it is preferable to recover mill fine powder and mill waste rock with concentrated valuable metals while simultaneously grinding the raw materials for cement. In the raw material grinding process for ordinary cement, it is possible to simultaneously grind the clay raw material containing valuable metal-containing waste and the raw materials for cement such as limestone using a vertical roller mill, but it is difficult to set grinding conditions suitable for recovering valuable metals, and the grade of valuable metals is likely to decrease because the recovered mill waste rock is contaminated with limestone, etc.

The objective of the present invention is to provide a method for efficiently recovering high-quality valuable metals from valuable metal-containing waste.

The inventors have discovered that valuable metals can be efficiently recovered from non-magnetic materials by forming a mixture containing valuable metal-containing waste and a cement raw material selected from limestone and silica stone, pulverizing the mixture in a roller mill, further pulverizing the resulting mill waste, and magnetically separating the resulting waste.

That is, the present invention provides the following [1] to [4].
[1] A first crushing step of crushing a mixture containing valuable metal-containing waste and one or more cement raw materials selected from limestone and silica stone in a roller mill and recovering mill fine powder and mill waste stone;
A second crushing step of crushing the mill waste stone;
a magnetic separation step of separating the waste stones obtained in the second crushing step into magnetic particles and non-magnetic particles by magnetic separation;
A method for recovering valuable metals in waste, comprising a recovery step of recovering the non-magnetic material as valuable metals.
[2] The method for recovering valuable metals described in [1] above, wherein the valuable metal-containing waste includes incineration ash.
[3] The method for recovering valuable metals described in [1] or [2] above, wherein the particle size of the valuable metal-containing waste is 40 mm or less.
[4] The method according to any one of [1] to [3], wherein the crushing in the second crushing step is autogenous crushing.

According to the present invention, high-quality valuable metals can be efficiently recovered from valuable metal-containing waste. In addition, in the method of the present invention, valuable metal-containing waste and cement raw materials are simultaneously ground, so milled powder can be effectively used as a raw material for ordinary cement.

1 is a flow chart showing an example of a method for recovering valuable metals from waste according to the present invention. 1 is a flowchart showing a method for recovering valuable metals from waste carried out in Comparative Example 1.

The method for recovering valuable metals from waste of the present invention comprises a first crushing step, a second crushing step, a magnetic separation step, and a recovery step. Each step will be described in detail below. An example of the method for recovering valuable metals from waste of the present invention is shown in Figure 1.

(Preparation process)
Examples of valuable metal-containing waste (hereinafter, simply referred to as "waste") include incineration ash and construction waste soil. Examples of incineration ash include ash obtained by incinerating urban waste and industrial waste, and specifically, in addition to industrial waste such as sludge, waste plastics, scrap metal, scrap glass, scrap concrete, scrap ceramics, slag, and rubble, shredder dust generated by crushing scrapped automobiles and scrapped home appliances, and ash obtained by incinerating general waste can be used. Examples of construction waste soil include soil and sludge generated secondarily from construction and civil engineering works.

The waste used in this process may be adjusted in terms of moisture content and particle size according to its properties, thereby improving the ease of handling.
For example, the moisture content of the waste can be adjusted by drying the waste with a dryer to remove moisture. From the viewpoint of improving handleability, the moisture content of the dried waste is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

In addition, to adjust the particle size of waste, for example, the waste may be crushed using a crusher if necessary, followed by removing magnetic material using a magnetic separator, and then sieving using a classifier to collect waste of the desired particle size.
Examples of the crusher include a jaw crusher, an impact crusher, a hammer crusher, a roll crusher, and a rotary crusher. In order to adjust the particle size, the crusher may be equipped with a screen having a desired mesh size, or if no screen is installed, the fixed teeth, rotating teeth, inner wall, etc. may be adjusted to the desired clearance.

A magnetic separator can be used for magnetic separation. This makes it possible to remove coarse metal debris from the waste. The magnetic separator can be a commercially available device, and may be any of the drum, pulley, and hanging types, with no particular limitations. From the viewpoint of removing magnetic material, the surface magnetic flux density of the magnetic separator is preferably 700 to 10,000 gauss, more preferably 1,000 to 7,500 gauss, and even more preferably 1,500 to 5,000 gauss.

As a classifier, for example, a vibration type, an in-plane motion type, a rotary type, a fixed type, etc. can be used, and the desired sieve size can be installed.

After particle size adjustment, the waste preferably has a particle size of 40 mm or less, more preferably 30 mm or less, and even more preferably 20 mm or less.

[First step]
The first crushing step is a step of crushing a mixture containing waste and one or more cement raw materials selected from limestone and silica stone in a roller mill, and recovering mill fine powder and mill waste. Here, in this specification, "fine powder" refers to fine powder discharged by airflow during crushing, and "waste stone" refers to granular or lumpy solids that are not crushed into powder discharged by airflow.

In this process, first, a mixture containing waste material and one or more cement raw materials selected from limestone and silica stone is prepared.
The cement raw materials may contain cement raw materials other than limestone and silica (hereinafter referred to as "other cement raw materials"). Examples of other cement raw materials include iron raw materials such as steelmaking slag, coal ash, etc. For example, in this process, a mixture containing waste selected from incineration ash and construction generated soil, one or more cement raw materials selected from limestone and silica, and one or more other cement raw materials selected from coal ash and steelmaking slag can be used.
The mixture can be prepared by feeding the waste and the cement raw material into the roller mill in any order, provided that both are present together in the roller mill during crushing.

From the viewpoint of the efficiency of crushing the cement raw materials and the efficiency of recovering valuable metals, the content of waste in the mixture is preferably 0.5% by mass or more, more preferably 1% by mass or more, and is preferably 15% by mass or less, and more preferably 10% by mass or less.

There are no particular limitations on the roller mill, so long as it is a device that compresses and shears the mixture between multiple rollers and a rotating table while grinding it, and commercially available devices can be used. The ground mixture is classified by a separator at the top to obtain milled powder, while mixtures with large particle sizes are ground again by the rollers and table. A dam ring is provided around the table, and the powder that falls over the dam ring and is discharged is the mill waste. The milled powder obtained in this process can be sent to the firing process in the normal cement manufacturing process as a cement raw material.

The crushing time can be set appropriately depending on the type of waste and the production scale, but from the viewpoint of crushing efficiency as a cement raw material and valuable metal recovery efficiency, it is usually 100 to 400 t/h, and preferably 200 to 300 t/h.

[Second pulverization step]
This step is a step of pulverizing the mill waste obtained in the first pulverization step, thereby obtaining waste containing concentrated valuable metals.
The pulverizer used in the second crushing step can be any one that has a mechanism for selectively discharging the crushed fine powder with an airflow and a stone discharge mechanism. Examples include roller mills, vertical impact crushers, and autogenous crushers. Among them, the use of an autogenous crusher selectively crushes brittle materials such as limestone (nonmetallic materials), which are finely pulverized and easily transferred to the cement raw material, and can suppress the deterioration of cement quality due to the inclusion of crushed metal in the cement raw material. As the autogenous crusher, it is preferable to use an autogenous crushing mill that rolls a container with a scraping bar attached inside and crushes the material by collision between samples or between the sample and the casing, or a vertical autogenous crusher that rotates a rotor at high speed and crushes the material charged from the top by collision between the material filled in the device. The roller mill can be the same as that used in the first crushing step.
The grinding in this step may be semi-autogenous grinding. In this specification, the term "semi-autogenous grinding" refers to the case where a grinding medium is mixed with the raw material as an auxiliary in the autogenous grinding. As the grinding medium, a known medium such as a ball can be used, but the magnetic material recovered in the magnetic separation step described later may also be used as the medium.

The grinding time can be set appropriately depending on the type of waste and production scale, but from the viewpoint of valuable metal recovery efficiency, it is usually 1 to 10 t/h, and preferably 2 to 5 t/h.

[Magnetic sorting process]
This step is a step of separating the waste stones obtained in the second crushing step into non-magnetic materials and magnetic materials by magnetic separation.
For the magnetic separation, a known magnetic separator can be used, and for example, any of a drum type, a pulley type, and a hanging type may be used, without any particular limitation.
In magnetic separation, for example, heavy products are fed onto a drum with a permanent magnet inside, and magnetic materials contained in the heavy products are attracted to the drum surface, carried by the rotation of the drum, and discharged from a magnetic material discharge port. On the other hand, non-magnetic materials contained in the heavy products are separated from the drum surface and fall due to the rotation of the drum, and are discharged from a non-magnetic material discharge port.

From the viewpoint of promoting separation of non-magnetic materials from magnetic materials, the surface magnetic flux density of the magnetic separator is preferably 700 to 10,000 gauss, more preferably 1,000 to 7,500 gauss, and even more preferably 1,500 to 5,000 gauss.

[Recovery process]
This process is a process for recovering valuable metals from non-magnetic materials. This allows valuable metals to be recovered at a high quality and with a high yield. The magnetic materials can be used as raw materials for steel production.

By treating waste in this way, it is possible to efficiently recover high-quality valuable metals from the waste.

The following examples are provided to further explain the embodiments of the present invention. However, the present invention is not limited to the following examples.

The analysis of metal components was carried out by the method shown in Table 1 on the specimens to be analyzed which had been pretreated by matte fusion and then pulverized to a size of 100 μm or less.

Example 1
The incineration bottom ash was treated according to the flow chart shown in Figure 1. Specifically, the process is as follows.

(Preparation process)
The incineration bottom ash was crushed using an impact crusher, and then coarse metal debris was removed using a hanging magnetic separator and a drum magnetic separator. Samples with particle sizes of 20 mm or less were prepared using a vibrating sieve.
(First grinding step)
In terms of dry mass ratio, 70-80% by mass of limestone, 5-15% by mass of clay (including 0.5-2.3% by mass of incineration bottom ash), 1-2% by mass of iron raw material (steel slag, etc.), 4-5% by mass of silica stone, and 5-10% by mass of other cement raw materials (coal ash, etc.) were mixed and charged into a vertical roller mill and pulverized continuously for 10 days. The moisture content of the clay was adjusted in advance to 10% or less using a dryer.
In the vertical roller mill, the raw materials were crushed, and the milled fine powder collected by the air current was collected as a cement raw material. After crushing, the mill waste stone discharged from the bottom of the mill was collected as the crushed material.
(Second grinding step)
The collected mill waste stone was subjected to a crushing process using an autogenous crusher. As the autogenous crusher, an airflow discharge type autogenous crushing mill was used, which has a mechanism for crushing by collision and compression of raw materials caused by rolling of the device, and recovering crushed fine powder of 100 μm or less by airflow discharge.
After the crushing process, granular and lumpy solids that were not crushed into powder and discharged by the airflow were removed and collected as waste stones.
(Magnetic separation process)
The discharged stones were treated with a magnetic separator to separate them into magnetic and non-magnetic materials. The magnetic separator was a 1000G suspension type.
(Recovery process)
The non-magnetic materials were collected and analyzed for valuable metals, including gold, silver, copper, palladium, platinum, iron, aluminum, zinc, chromium, and lead. The results are shown in Table 2. The evaluation was performed by sampling once a day over 10 days of continuous processing, and the average, maximum, and minimum values of 10 evaluation results were shown.

Comparative Example 1
As shown in the flow chart of Figure 2, the same incineration bottom ash as in Example 1 was used for the treatment, except that the second crushing step was not performed. The non-magnetic materials were then collected and analyzed for valuable metals, including gold, silver, copper, palladium, platinum, iron, aluminum, zinc, chromium, and lead. The results are shown in Table 2.

From Table 2, it can be seen that by subjecting the mill waste obtained in the first crushing process to a second crushing process, more precious metals can be recovered.

Claims (3)

A first crushing step of crushing a mixture containing valuable metal-containing waste and one or more cement raw materials selected from limestone and silica stone in a roller mill and recovering mill fine powder and mill waste stone;
A second crushing step of crushing the mill waste stone by autogenous crushing;
a magnetic separation step of magnetically separating the waste stones obtained in the second crushing step and separating them into magnetic materials and non-magnetic materials;
A method for recovering valuable metals in waste, comprising a recovery step of recovering the non-magnetic material as valuable metals. The recovery method according to claim 1, wherein the valuable metal-containing waste material includes incineration ash. The recovery method according to claim 1 or 2, wherein the particle size of the valuable metal-containing waste is 40 mm or less.

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