JP7747531B2 - Method for recovering precious metals from incineration ash using cement manufacturing facilities - Google Patents

Description

The present invention relates to a method for recovering precious metals from incineration ash using cement manufacturing equipment.

Conventionally, attempts have been made to recover precious metals from waste such as incineration ash by crushing it using a roller mill or by physical separation. For example, a method has been proposed in which valuable metal-containing waste is crushed in a vertical roller mill into mill waste containing fine mill powder having a predetermined particle size distribution and coarse mill powder having a particle size distribution larger than the predetermined particle size distribution, and the valuable metals are recovered by sorting the resulting mill waste (Patent Document 1), a method has been proposed in which valuable metals are crushed in a vertical roller mill to obtain mill waste having a bulk density of 1.3 t/m or ^more , and the valuable metals are recovered by sorting the resulting mill waste (Patent Document 2), and a method has been proposed in which waste is crushed in a vertical mill having a crushing section and a shape identification section, and metals are separated and removed by a metal separation section while producing a cement raw material (Patent Document 3).

JP 2016-89196 A Japanese Patent Application Laid-Open No. 2021-1362 JP 2013-28477 A

However, the conventional methods described above consume a large amount of heat to dry the incineration ash and require exhaust gas treatment equipment, which increases production costs and makes them unfeasible from a profitable perspective when only small amounts of incineration ash are involved. While the use of a modifier when drying the incineration ash is an option, this is also unfeasible from a profitable perspective when only small amounts of incineration ash are involved. Additionally, since incineration ash contains dioxins and metals and has a strong odor, it is desirable to use equipment that can prevent the dispersion of dioxins and odors associated with drying and grinding and that can suppress mill vibration and wear, but it is difficult to utilize existing cement manufacturing equipment as is.
An object of the present invention is to provide a method for efficiently recovering precious metals from incineration ash while using cement production equipment and suppressing the dispersion of dioxins and odors, as well as vibration and wear of the mill.

The inventors have discovered that by subjecting incineration ash to a specified pretreatment process, it is possible to not only efficiently recover precious metals but also produce cement clinker while suppressing the dispersion of dioxins and odors, as well as mill vibration and wear, even using existing cement manufacturing equipment.

That is, the present invention provides the following [1] to [8].
[1] A method for recovering precious metals from incineration ash using cement production equipment having a roller mill for pulverizing cement raw materials containing at least one selected from limestone and silica stone, a preheater for preheating the pulverized cement raw material introduced from the roller mill, and a cement kiln for firing the pulverized cement raw material introduced from the preheater,
an incineration ash pretreatment process in which incineration ash is crushed, the crushed material is subjected to magnetic separation to recover non-magnetic materials, and the non-magnetic materials are separated into first non-magnetic materials and second non-magnetic materials based on the physical or chemical properties of the non-magnetic materials;
a cement raw material grinding step of grinding the first non-magnetic material together with the cement raw material in a roller mill to separate the material into mill waste stone and mill fine powder;
Collect mill waste,
A method for recovering precious metals from incineration ash using cement manufacturing facilities.
[2] A method for treating incineration ash using cement production equipment having a roller mill for pulverizing cement raw materials containing at least one selected from limestone and silica stone, a preheater for preheating the pulverized cement raw material introduced from the roller mill, and a cement kiln for firing the pulverized cement raw material introduced from the preheater,
an incineration ash processing step of crushing the incineration ash, subjecting the crushed material to magnetic separation to recover non-magnetic materials, and separating the non-magnetic materials into first non-magnetic materials and second non-magnetic materials based on the physical or chemical properties of the non-magnetic materials;
a cement raw material grinding step of grinding the first non-magnetic material together with the cement raw material in a roller mill to separate the material into mill waste and mill fine powder;
A method for treating incineration ash using cement manufacturing equipment, comprising a cement firing step in which milled powder is charged into a preheater and a second non-magnetic material is charged into the bottom of a cement kiln.
[3] The precious metal recovery method or processing method according to [1] or [2], wherein in the incineration ash processing step, the non-magnetic materials are separated into first non-magnetic materials and second non-magnetic materials based on the particle size of the non-magnetic materials.
[4] A precious metal recovery method or treatment method according to [3], wherein the particle size of the first non-magnetized material is 0.1 mm or more, and the particle size of the second non-magnetized material is less than 0.1 mm.
[5] The precious metal recovery or processing method according to any one of [1] to [3], wherein in the incineration ash processing step, the non-magnetic materials are separated into first non-magnetic materials and second non-magnetic materials based on the odor index of the non-magnetic materials.
[6] A precious metal recovery method or treatment method according to [5], wherein the odor index of the first non-magnetized material is less than 30, and the odor index of the second non-magnetized material is 30 or more.
[7] A precious metal recovery method or treatment method according to any one of [1] to [3], wherein in the incineration ash treatment step, the non-magnetic materials are separated into first non-magnetic materials and second non-magnetic materials based on the dioxin toxicity equivalent of the non-magnetic materials.
[8] The precious metal recovery method or treatment method according to [7], wherein the dioxin toxicity equivalent of the first non-magnetized material is less than 0.01 ng-TEQ/g, and the dioxin toxicity equivalent of the second non-magnetized material is 0.01 ng-TEQ/g or more.

The present invention not only enables the efficient recovery of precious metals but also the production of cement clinker while suppressing the dispersion of dioxins and odors, as well as mill vibration and wear, while using existing cement production equipment. Therefore, the present invention is useful as a method for treating incineration ash.

1 is a schematic diagram showing an example of a cement manufacturing facility and an incineration ash pretreatment system applicable to the present invention.

A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Note that in the description of the drawings, identical elements will be given the same reference numerals, and duplicate explanations will be omitted. Also, for the sake of convenience, the dimensional proportions in the drawings do not necessarily match those in the description.

The precious metal recovery method and incineration ash treatment method of the present invention are characterized in that the incineration ash is subjected to a predetermined pretreatment step and then treated using a cement manufacturing facility.
An existing cement manufacturing facility can be used as the cement manufacturing facility. An example of a cement manufacturing facility and an incineration ash pretreatment system applicable to the present invention is shown in Figure 1.

The cement manufacturing facility shown in Figure 1 has a roller mill that grinds cement raw materials containing one or more selected from limestone and silica stone, a preheater that preheats the ground cement raw material introduced from the roller mill, and a cement kiln that fires the ground cement raw material introduced from the preheater.

The cement raw materials are usually fed into a roller mill, after passing through a dryer if necessary.
An example of a roller mill is a device that crushes a mixture by compressing and shearing it between multiple rollers and a rotating table. The crushed cement raw material is classified in a separator at the top to obtain mill-finished powder, and the mixture with larger particle sizes is crushed again between the rollers and table. A dam ring is provided around the table, and the material that falls over the dam ring is discharged as mill waste.

The cement raw materials are heated and crushed in a roller mill in the presence of exhaust gas supplied from the cement kiln, and then fed to a preheater via a raw material supply line. After being preheated in the preheater, they are fed into the cement kiln and burned to form cement clinker.

The preheater shown in Figure 1 is a multi-stage cyclone type with multiple cyclones connected in multiple stages from bottom to top, and preheats the pulverized cement raw materials to a predetermined temperature (800-900°C) using exhaust gas from the cement kiln.

A cement kiln, for example, has a horizontally oriented cylindrical kiln shell that slopes downward toward the downstream side. While rotating around its central axis, this kiln shell is heated with a burner that uses heavy oil or pulverized coal as fuel. The cement raw materials supplied from the preheater are heated to temperatures typically above 1000°C and burned to produce cement clinker. The cement clinker is then cooled by a cooler connected to the front of the kiln, located downstream of the cement kiln, and sent to the finishing process. The above is the same operation as in a typical cement manufacturing facility.

This cement manufacturing facility is equipped with an incineration ash pretreatment system for pretreating incineration ash and introducing it into the roller mill and the kiln end of the cement kiln.
This incineration ash pretreatment system magnetically separates crushed incineration ash, and separates the resulting non-magnetic materials into first non-magnetic materials and second non-magnetic materials based on their physical or chemical properties.The first non-magnetic materials are then supplied to a roller mill in a cement manufacturing facility, and the second non-magnetic materials are directly fed into the end of a cement kiln.

Next, we will explain one embodiment of a method for recovering precious metals from incineration ash and a method for treating incineration ash according to the present invention, using the cement manufacturing equipment and incineration ash pretreatment system configured as described above.

In the incineration ash pretreatment system, the incineration ash is first crushed as shown in Figure 1. This allows the aggregated ash particles to be broken down and the precious metals attached to the ash to be separated.
The incineration ash preferably used is bottom ash that accumulates at the bottom of an incinerator when municipal waste, industrial waste, sewage sludge, etc. are incinerated in the incinerator. More specifically, bottom ash obtained by incinerating industrial waste such as sludge, waste plastics, scrap metal, scrap glass, scrap concrete, scrap ceramics, slag, and rubble, as well as shredder dust generated by crushing used automobiles and used home appliances, general waste, etc., can be used. The incineration bottom ash may also contain incineration fly ash, which is soot and dust in the exhaust gas during incineration.
Among these, municipal waste incineration ash (including, for example, excavated incineration ash) is preferred as the incineration ash. Municipal waste incineration ash usually contains valuable metals such as copper, zinc, gold, silver, palladium, platinum, etc., in addition to chromium and lead, which are cement-repellent components.

Incineration ash contains moisture due to water cooling treatment and sprinkling to prevent dust generation, but can be used as is.
The moisture content of the incineration ash is usually 15 to 35% by mass, and the size is usually less than 40 mm.

Crushing machines can be used to crush the incineration ash, such as jaw crushers, impact crushers, hammer crushers, roll crushers, and rotary crushers.
The crushing treatment may be carried out two or more times. When the crushing treatment is carried out two or more times, the same or different crushers may be used.

Next, the crushed incineration ash is magnetically separated into magnetic and non-magnetic materials, and the non-magnetic materials are collected. This allows metal debris and other particles in the incineration material to be removed as magnetic materials.
For magnetic separation, a magnetic separator can be used, and any of a drum type, a pulley type, and a hanging type may be used, and there is no particular limitation.
From the viewpoint of removing magnetic substances, the surface magnetic flux density of the magnetic separator is preferably 700 to 10,000 gausses, more preferably 1,000 to 7,500 gausses, and even more preferably 1,500 to 5,000 gausses.
The magnetic separation may be performed two or more times. When the magnetic separation is performed two or more times, the same or different magnetic separators may be used, and the surface magnetic flux densities may be the same or different.

Next, the non-magnetic objects are separated into first non-magnetic objects and second non-magnetic objects based on the physical or chemical properties of the non-magnetic objects.
Examples of the physical properties of the non-magnetic material include particle size, shape, color, specific gravity, and electrical conductivity.
Examples of the chemical properties of non-magnetic materials include odor, the content of specific chemical substances, and loss on ignition.
In particular, in terms of being able to easily separate and separate the first non-magnetic material in which the precious metal is concentrated, it is preferable to use particle size as an indicator in the case of physical properties, and it is preferable to use odor or the content of specific chemical substances as an indicator in the case of chemical properties.

When non-magnetic materials are separated based on particle size, a sieve separator can be used, which may be, for example, a vibrating type, an in-plane motion type, a rotary type, or a fixed type.
Furthermore, two or more sieves with different mesh sizes may be used to classify the particles into a plurality of particle size groups, and for example, non-magnetic materials can be classified into three or more particle size groups.
The inventors have found that there is a correlation between the concentration of precious metals in non-magnetized materials and particle size, and that precious metals are unevenly distributed among the non-magnetized materials in particle groups with particle sizes of 0.1 mm or more, preferably particle sizes of 0.5 mm or more. Therefore, by using a sieve with 0.1 mm mesh, preferably a sieve with a particle size of 0.5 mm, to recover the under-sieve material as second non-magnetized materials and recovering the remainder as first non-magnetized materials, it is possible to efficiently recover the first non-magnetized materials in which precious metals are concentrated.

When the non-magnetized materials are subdivided into a plurality of particle size groups, it is preferable to separate them into the following combination of particle size groups from the viewpoint of precious metal recovery efficiency: The particle size group with the smallest particle size is recovered as the second non-magnetized materials, and the remaining particle size group is recovered as the first non-magnetized materials.
(1) A combination of non-magnetized objects with a particle size of less than 0.1 mm, non-magnetized objects with a particle size of 0.1 mm or more but less than 5 mm, and non-magnetized objects with a particle size of 5 mm or more. (2) A combination of non-magnetized objects with a particle size of less than 0.5 mm, non-magnetized objects with a particle size of 0.5 mm or more but less than 5 mm, and non-magnetized objects with a particle size of 5 mm or more. (3) A combination of non-magnetized objects with a particle size of less than 0.5 mm, non-magnetized objects with a particle size of 0.5 mm or more but less than 5 mm, non-magnetized objects with a particle size of 5 mm or more but less than 20 mm, and non-magnetized objects with a particle size of 20 mm or more.

Non-magnetic materials may also be separated based on their odor index. In this specification, "odor index" refers to the odor index stipulated in Article 1 of the Enforcement Regulations of the Offensive Odor Control Act, and is defined as follows: "The odor index is determined by diluting the sample gas or water to the point where the odor is no longer detectable by the human sense of smell, using a method prescribed by the Minister of the Environment, and then calculating the dilution factor (odor concentration) and multiplying the logarithm of that odor concentration by 10."

In the present invention, odor concentration is measured using the triangle odor bag method, and the odor index is calculated using the following formula (1).

Odor index = 10 x log (odor concentration) (1)

For example, an odor concentration of 2500 to 6000 converted to an odor index of 34 to 38, and an odor concentration of 200 to 450 converted to an odor index of 23 to 27. The smaller the odor index, the weaker the odor intensity, and it is generally said that an odor index of around 3 is the point at which even healthy people can no longer smell the odor.

The inventors discovered that there is a correlation between the concentration of precious metals in non-magnetized materials and the odor index, and that precious metals are concentrated in particle groups of non-magnetized materials with an odor index of less than 30. Therefore, by recovering particle groups with an odor index of 30 or more as second non-magnetized materials and recovering the remainder as first non-magnetized materials, it is possible to efficiently recover first non-magnetized materials in which precious metals are concentrated.

Furthermore, non-magnetic materials may be separated based on the dioxin toxicity equivalent amount. The dioxin toxicity equivalent amount can be measured, for example, in accordance with the "Simple Measurement Manual" for exhaust gases, soot, and cinders established by the Ministry of the Environment in March 2010.
Here, in this specification, "dioxin" refers to 2,3,7,8-tetrachlorodibenzo-p-dioxin and its analogous compounds, and is a concept that encompasses polychlorodibenzo-p-dioxins (PCDDs) in which 1 to 8 chlorine atoms are substituted on the dibenzo-p-dioxin nucleus, and polychlorodibenzofurans (PCDFs) in which 1 to 8 chlorine atoms are substituted on the dibenzofuran nucleus.

The inventors discovered that there is a correlation between the concentration of precious metals in non-magnetized matter and the dioxin toxicity equivalent, and that precious metals are concentrated in particle groups of non-magnetized matter with dioxin toxicity equivalents of less than 0.01 ng-TEQ/g. Therefore, by recovering particle groups with dioxin toxicity equivalents of 0.01 ng-TEQ/g or more as second non-magnetized matter and recovering the remainder as first non-magnetized matter, it is possible to efficiently recover the first non-magnetized matter in which precious metals are concentrated.

Furthermore, the inventors have discovered that the particle size, odor index, and dioxin toxicity equivalent described above are correlated with one another. That is, they have found that among non-magnetic materials, particle groups with particle sizes of 0.1 mm or more, preferably particle groups with particle sizes of 0.5 mm or more, have an odor index of less than 30 and a dioxin toxicity equivalent of less than 0.01 ng-TEQ/g. Therefore, by separating non-magnetic materials using one or more of these indicators, it is possible to efficiently recover the first non-magnetic material in which precious metals are concentrated.

In the present invention, the first non-magnetic material thus separated is pulverized together with cement raw materials in a roller mill in a cement manufacturing facility.
The cement raw material contains at least one or more selected from limestone and silica stone, but may also contain iron raw materials such as clay, coal ash, and steelmaking slag.
The first non-magnetic material and the cement raw material may be charged into the roller mill in any order, as long as both are present together in the roller mill during pulverization.

From the perspective of precious metal recovery efficiency and ensuring cement quality, the mass ratio of the cement raw material to the first non-magnetized material (first non-magnetized material/cement raw material) is preferably 1/300 or more, more preferably 1/200 or more, and is preferably 3/20 or less, even more preferably 1/10 or less.

The grinding time can be set appropriately depending on the production scale, etc., but from the perspective of grinding efficiency and precious metal recovery efficiency, it is usually 100 to 400 t/h, preferably 200 to 300 t/h.

The first non-magnetic material is pulverized together with the cement raw material in a roller mill and separated into mill waste and mill fine powder, and the mill waste, which is enriched in precious metals, is recovered.
In this way, valuable precious metals can be efficiently recovered and reused from incineration ash containing metals that are cement-repellent components.

Meanwhile, the milled flour is fed into the preheater of the cement manufacturing facility.
The milled powder fed into the first cyclone of the preheater is preheated by the high-temperature exhaust gas from the cement kiln rising from below as it falls successively into the lower cyclones, and is finally introduced into the bottom of the cement kiln from the lowest cyclone. The second non-magnetic material described above is also fed into the bottom of the cement kiln.
In the cement kiln, the second non-magnetic material is gradually transported from the kiln end to the kiln front, where it is heated by the combustion exhaust gas from the main burner and burned to form cement clinker. In this way, cement clinker can be produced using the second non-magnetic material as a raw material.

When producing cement clinker, it is heated for several tens of minutes in an atmosphere of 1000°C or higher, which decomposes dioxins and odorous substances into harmless substances. Incidentally, dioxins can be decomposed by leaving them in a high-temperature atmosphere of 800°C or higher for 2 seconds or more.
Therefore, by decomposing incineration ash containing dioxins and odorous substances into harmless substances, it can be effectively used as a cement raw material while improving the environment.

While the present invention has been described in detail above based on its embodiments, it is not limited to these embodiments. Various modifications to the present invention are possible without departing from the spirit of the invention. For example, in the incineration ash pretreatment system shown in Figure 1, non-magnetic materials separated by magnetic separation were separated based on their physical or chemical properties. However, the non-magnetic materials may also be washed with water for purposes such as chlorine removal, and then separated. The method for washing the non-magnetic materials is not particularly limited, as long as they are brought into contact with water. The amount and temperature of water used can be selected appropriately. The washed materials can be separated using a dehydrator. Similarly, the second non-magnetic materials may also be washed with water, and then the washed materials may be charged into the kiln chamber of a cement kiln. Furthermore, mill waste stone discharged from a roller mill may be physically separated to increase the purity of precious metals.

The following examples further illustrate embodiments of the present invention. However, the present invention is not limited to the examples below.

Example 1 As a raw material to be treated (subject sample), 100 kg of municipal waste incineration bottom ash was prepared.
As a pretreatment, the bottom ash from municipal waste incineration was crushed in an impact crusher, then subjected to removal of coarse magnetic metals in a hanging magnetic separator. Next, coarse metals above 20 mm in size were removed using a sieve, and the under-sieve residue was washed in a drum washer and dehydrated.
Next, the dehydrated product was treated using vibrating sieves with openings of 5 mm and 0.5 mm, and classified into three particle groups: over 5 mm, 0.5-5 mm, and under 0.5 mm. Of these, the under 0.5 mm particles that fell through the sieve were sent to a stirring tank, washed, and then dehydrated in a filter cloth dehydrator.

Samples of each particle group were evaluated for odor index, dioxin toxicity equivalent, and metal distribution ratio when dried.
The odor during drying was measured by placing 100 g of the sample in a 1 L airtight container and heating it to 105°C, and then inserting an odor sensor (NeoSigma, manufactured by Culmore) into the container at predetermined time intervals and measuring for 5 minutes. The odor sensor allows the odor index to be calculated as a converted value from the sensor reading by creating a calibration curve that correlates the sensor reading with odor index data previously evaluated using the three-point odor bag method.
The dioxin toxicity equivalent was determined by evaluating the dioxin toxicity equivalent in solid samples of each particle group in accordance with the "Simple Measurement Manual" established by the Ministry of the Environment in March 2010.
The metal distribution rate was evaluated from the weight ratio of each particle group and the metal concentration. The metal components were analyzed by the method shown in Table 1.
The evaluation results are shown in Table 2.

From Table 2, the following findings were obtained.
The analysis results of the metal distribution rate show that there are few precious metals in the particle group of less than 0.5 mm, and most of the precious metals are distributed in the particle group of 0.5 mm or more.
From the results of odor measurement, it was found that particle groups with high odor indices contained fewer precious metals, and most of the precious metals were distributed to particle groups with odor indices of less than 30.
The results of the dioxin toxicity equivalents show that the particle group with a high dioxin toxicity equivalent contains few precious metals, and most of the precious metals are distributed to the particle group with a dioxin toxicity equivalent of less than 0.01 ng-TEQ/g.
From the above results, it can be seen that the precious metal concentration is correlated with each of particle size, odor index, and dioxin toxicity equivalent, and that precious metals can be efficiently recovered from incineration ash by separating the first non-magnetic material using one or more of particle size, odor index, and dioxin toxicity equivalent as an indicator.

Next, for the fine particles of 0.5 mm or less (second non-magnetic material), assuming charging at the end of the kiln, the odor when heated to 800°C and the dioxin toxicity equivalent when heated to 1200°C were evaluated. The odor was measured by heating the tubular furnace to 800°C, and then drying at 105°C. The gas generated during this process was pumped into the tubular furnace and collected in a polyester bag, which was then analyzed using an odor sensor. The analysis resulted in an odor index of 25, which indicated a reduction in odor compared to drying at 105°C, confirming that the odorous substances had been decomposed by heating.
Furthermore, the dioxin toxicity equivalent in the sample after heat treatment at 1200°C was less than 0.01 ng-TEQ/g, and the reduction in dioxin toxicity equivalent confirmed that dioxin was decomposed by heating. It was also confirmed that dioxin was not dispersed by heating.
From the above results, it can be seen that when the second non-magnetic material is added to the kiln bottom, the dioxins and odorous substances are decomposed by high-temperature treatment and do not scatter, so even when using cement manufacturing equipment, the incineration ash containing dioxins and odors can be smoothly processed without causing any adverse effects caused by dioxins or odors, and can be effectively used as part of the cement manufacturing raw materials.

Claims (5)

A method for recovering precious metals from incineration ash using cement production equipment having a roller mill for pulverizing a cement raw material containing at least one selected from limestone and silica stone, a preheater for preheating the pulverized cement raw material introduced from the roller mill, and a cement kiln for firing the pulverized cement raw material introduced from the preheater,
an incineration ash pretreatment process in which incineration ash is crushed, the crushed material is subjected to magnetic separation to recover non-magnetic materials, and the non-magnetic materials are separated into first non-magnetic materials and second non-magnetic materials based on one or more physical or chemical properties of the non-magnetic materials selected from the following (1) to (3 );
(1) Particle size of non-magnetic particles
(2) Odor index of non-magnetic objects
(3) Dioxin toxicity equivalent of non-magnetic materials
a cement raw material grinding step of grinding the first non-magnetic material together with the cement raw material in a roller mill to separate the material into mill waste stone and mill fine powder;
Collect mill waste,
A method for recovering precious metals from incineration ash using cement manufacturing facilities. A method for treating incineration ash using cement production equipment having a roller mill for pulverizing a cement raw material containing at least one selected from limestone and silica stone, a preheater for preheating the pulverized cement raw material introduced from the roller mill, and a cement kiln for firing the pulverized cement raw material introduced from the preheater,
an incineration ash pretreatment process in which incineration ash is crushed, the crushed material is subjected to magnetic separation to recover non-magnetic materials, and the non-magnetic materials are separated into first non-magnetic materials and second non-magnetic materials based on one or more physical or chemical properties of the non-magnetic materials selected from the following (1) to (3 ) ;
(1) Particle size of non-magnetic particles
(2) Odor index of non-magnetic objects
(3) Dioxin toxicity equivalent of non-magnetic materials
a cement raw material grinding step of grinding the first non-magnetic material together with the cement raw material in a roller mill to separate the material into mill waste and mill fine powder;
A method for treating incineration ash using cement manufacturing equipment, comprising a cement firing step in which milled powder is charged into a preheater and a second non-magnetic material is charged into the bottom of a cement kiln. 3. The precious metal recovery or processing method according to claim 1 , wherein in (1), the particle size of the first non-magnetized matter is 0.1 mm or more, and the particle size of the second non-magnetized matter is less than 0.1 mm. 3. The precious metal recovery or treatment method according to claim 1 , wherein in (2), the odor index of the first non-magnetized material is less than 30, and the odor index of the second non-magnetized material is 30 or more. 3. A precious metal recovery or treatment method according to claim 1 or 2, wherein in (3), the dioxin toxicity equivalent of the first non-magnetized material is less than 0.01 ng-TEQ/g, and the dioxin toxicity equivalent of the second non-magnetized material is 0.01 ng-TEQ/g or more.