JP2000279971A - Treatment of heavy metal in waste material and treatment for forming cement raw material from the wastr mate rial. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment process for treating a waste material containing heavy metals, such as municipal refuse incineration ash, so as to be suitable as a cement raw material. SOLUTION: This treatment process for treating heavy metals in a waste material, comprises: a copper separation stage for adding iron to a liquid filtrate of a leachate slurry obtained by leaching the waste material with sulfuric acid, in an amount sufficient to provide a ratio of 0.9-1.2 equivalents of iron to the concentration of copper in the liquid filtrate, to separate copper in the liquid; next, an iron-zinc separation stage for adjusting the redox potential of the resulting liquid to convert iron ion in this liquid into trivalent iron ion and thereafter adjusting the pH of the liquid to convert the trivalent iron ion in the liquid into a ferric hydroxide precipitate and to separate iron from zinc. Thus, a waste material containing heavy metals is treated so that the treated product can be adapted as a cement raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing heavy metals such as copper from waste, and a method for converting the same into a raw material for cement. More specifically, the present invention relates to a method for efficiently removing copper, zinc, and the like from waste such as municipal waste incineration ash, sewage sludge incineration ash, or cement kiln dust, and treating the waste so that it can be used as a cement raw material.

[0002]

2. Description of the Related Art In recent years, the amount of waste such as municipal waste incineration ash, sewage sludge incineration ash or fly ash and molten slag has increased remarkably. Since these wastes contain a considerable amount of valuable metals such as copper, zinc and lead, a method of recovering valuable metals from these wastes has been proposed as a waste disposal method. I have.

[0003] One example of the treatment method is a method in which the incinerated ash or fly ash is treated with sulfuric acid to leach copper and zinc to separate and recover the same. In this method, the residue of the sulfuric acid leached slurry is removed. Since it contains a large amount of gypsum, it is difficult to use this as a cement raw material. On the other hand, since the filtrate obtained by solid-liquid separation contains copper, zinc, and the like, a method for efficiently separating and recovering these has been studied. As a method for recovering copper, the present inventors have proposed that the filtrate contains zinc. Proposed a method of precipitating copper in the liquid by adding iron or iron (Japanese Patent Application No. 10-2450)
05).

[0004]

The present invention provides the above processing method,
A treatment method that further improves the copper deposition process so that high-grade copper can be deposited, and efficiently separates iron and zinc contained in the filtrate from which copper has been separated, and makes the recovered residue suitable for cement raw materials. The purpose is to provide.

[0005]

That is, the present invention relates to a process for adding iron to a filtrate of a sulfuric acid leaching slurry of copper-containing waste to precipitate copper in the solution, and separating and recovering the deposited copper. The present invention relates to a method for treating heavy metals in waste, characterized in that iron is added in an amount of 0.9 equivalent to 1.2 equivalents or less with respect to the concentration of copper in a liquid to precipitate high-grade copper.

Further, the present invention provides a copper separation step of adding iron to a filtrate of a sulfuric acid leaching slurry of waste containing copper and zinc to precipitate copper in the liquid, and separating and recovering the deposited copper.
An iron-zinc separation step of precipitating and separating at least one of iron and zinc from a filtrate from which copper has been separated, wherein the oxidation-reduction potential of the liquid is 0.5 V or more in the iron-zinc separation step. And adjusting the pH of the solution to 2.9 to 5 to separate iron from zinc by precipitating iron after adjusting the pH of the solution to trivalent. The present invention relates to a method for treating heavy metals.

Further, according to the present invention, after the solid sulfuric acid leached slurry of solid waste is separated into solid and liquid, iron having a concentration of not less than 0.9 equivalent to not more than 1.2 equivalent relative to the concentration of copper in the liquid is added to the filtrate. After copper is separated by precipitation, the redox potential of the liquid from which copper has been separated is adjusted to 0.5 V or more to make the iron ions in the liquid trivalent, and then the pH of the liquid is adjusted to 2.9-5. The present invention relates to a method for converting waste into a cement raw material, characterized in that iron is precipitated by solidification, and solid matter obtained by solid-liquid separation is used as a cement raw material.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to embodiments. FIG. 1 shows an outline of the processing method of the present invention. As shown in the figure, the treatment method of the present invention has a step of leaching waste with sulfuric acid and solid-liquid separation (sulfuric acid leaching step) and a step of depositing copper from a filtrate of the sulfuric acid leaching slurry (copper precipitation step). More preferably, after the copper deposition step, a step of separating iron and zinc from the filtrate (iron / zinc separation step) is included.

The waste to be treated in the present invention includes:
It can be widely applied to incineration ash of city garbage, incineration ash of sewage sludge, and incineration fly ash or molten slag fly ash. These incinerated ash include incinerated fly ash and molten slag fly ash discharged from eco-cement produced from municipal waste incinerated ash, sewage sludge incinerated ash, and the like. These wastes mainly contain calcium compounds and the like in addition to valuable metals such as copper, zinc and lead.

(I) Sulfuric acid leaching step Sulfuric acid is added to the solid matter of the waste or the aqueous slurry thereof to form a sulfuric acid leached slurry. Prior to the sulfuric acid leaching, it is preferable to add water to the waste to form a slurry, since the water-soluble chlorine compound contained in the waste is leached and the waste is desalted. Copper and zinc or compounds of copper and zinc contained in the waste are leached into the liquid by the sulfuric acid. On the other hand, most of the lead contained in the waste becomes lead sulfate and solidifies, and remains in the leach residue. Calcium in the waste also reacts with sulfuric acid to form gypsum and remains in the leaching residue. Therefore, lead and calcium can be removed from the filtrate by solid-liquid separation of the sulfuric acid leached slurry. This sulfuric acid leaching depends on the type of waste,
If the solid-liquid ratio is about 300 g / l or less and the pH is about 4 or less, a good leaching effect can be obtained.

(II) Copper Separation Step Iron powder is added to the filtrate obtained by solid-liquid separation of the sulfuric acid leached slurry to precipitate copper (iron stripping). By adding iron powder to the filtrate, as the iron is ionized and eluted into the liquid, copper having a low ionization tendency is precipitated instead of iron and precipitates. This is collected by solid-liquid separation and removed from the filtrate.
In this iron stripping, calcium and zinc, which have a higher ionization tendency than iron, do not precipitate and copper is selectively precipitated, so that high-grade metallic copper can be recovered, and copper can be efficiently removed from the filtrate. Can be. Note that copper is precipitated even when zinc powder is used instead of iron powder. However, since zinc is considerably more expensive than iron, iron is significantly more advantageous in terms of cost. However, unlike the case of using zinc, when iron powder is used, delicate adjustment of iron addition amount and iron / zinc separation step as in the present invention are indispensable for precipitating high-grade copper. Even if zinc powder is replaced with iron powder, high-grade copper cannot be precipitated.

The amount of iron added is 0.9 with respect to the copper concentration in the solution.
An equivalent or more to 1.2 or less is appropriate. As shown in FIG. 2, the quality of the precipitated copper is affected by the amount of iron added. When the amount of iron added is around 0.8 equivalent to the copper concentration in the liquid, the copper quality is about 75%. 8 near 9 equivalents
Copper grade of about 0%. However, when the amount of iron added is in the range of 0.9 equivalent to 1.0 equivalent of the copper concentration, the quality of the precipitated copper is gradually improved, and near 1.0 equivalent, copper having a grade of about 95% can be obtained. Further, the amount of iron added is 1.0 equivalent to 1.
In the range of 2 equivalents, the copper quality is about 80 to 95%. Therefore, in order to recover copper of 80% or more, the amount of iron to be added should be 0.9 to 1.2 equivalents, preferably 1.0 to 1.10 equivalents of iron powder with respect to the copper concentration. I just need. If the addition amount of iron is small, precipitation of iron hydroxide [Fe (OH) ₃ ] occurs and mixes with the precipitated copper, lowering the copper quality. When the addition amount of iron is within the above range, the liquid becomes a reducing atmosphere, and iron hydroxide is not easily generated, so that iron is not mixed and copper quality is increased. On the other hand, if the amount of iron is more than the above range, unreacted iron remains and mixes with the precipitated copper, so that the copper quality deteriorates.

Usually, when a metal powder having a higher ionization tendency is added to a metal in a liquid to precipitate the metal in the liquid, the amount of the metal powder to be added is larger than the equivalent of the metal concentration in the liquid. Since the added metal powder remains in the liquid and mixes with the deposited metal to lower the quality, the quality of the deposited metal is generally increased by using slightly less added metal than the deposited metal. As shown in the stripping, when the added amount of zinc is 1 equivalent or more, the copper quality is reduced. However, as described above, in the iron stripping of the present invention, when the added amount of iron is smaller than the copper concentration in the liquid, ferric hydroxide is mixed into the precipitated copper, so that the copper concentration in the liquid is rather high. It is desirable to use a slightly larger addition amount, which is different from the conventional general method.

(III) Iron / Zinc Separation Step The filtrate after the above-mentioned iron stripping is sulfuric acid (pH around 4).
And the iron ions in the liquid are mainly divalent. Therefore, the oxidation-reduction potential of the filtrate was adjusted to be 0.5 V or more to convert the iron ions in the solution to trivalent, and subsequently, the pH of the solution was changed.
Is adjusted to 2.9 to 5 to precipitate ferric hydroxide [Fe (OH) ₃ ], which is separated from solid zinc by liquid-solid separation. In addition,
If iron ions contained in the filtrate from which copper has been separated are divalent, it is difficult to separate them from zinc. That is, ferrous hydroxide [Fe (O
H) ₂ ] and zinc hydroxide [Zn (OH) ₂ ] both precipitate in the pH range of 5.5 to 9, so that it is difficult to separate them. On the other hand, ferric hydroxide [Fe (OH) ₃ ] precipitates in a pH range of 2 to 5 where zinc hydroxide does not precipitate. Therefore, iron ions in the solution are changed from divalent to trivalent to precipitate ferric hydroxide.

The oxidation-reduction potential of the iron stripping solution is about 0.3 V, and iron ions in the solution are divalent. If the oxidation-reduction potential is increased to 0.5 V or more by adding hydrogen peroxide, sodium chlorate, or the like, iron ions are converted to trivalent. While maintaining this oxidation-reduction potential, caustic soda, sodium carbonate or the like is added to adjust the pH of the solution to 2.9 or more, preferably pH
Adjust to 3 or more to precipitate ferric hydroxide [Fe (OH) ₃ ]. When the pH is 6 or more, zinc hydroxide precipitates. Therefore, it is preferable to adjust the pH to 2.9 to pH5. Thereafter, by subjecting the solid to liquid-liquid separation and collecting the solid content, it can be separated from zinc remaining in the liquid component. The effect of separating zinc and iron by this method is high, and the residual zinc content of the recovered solid is about 100 ppm or less, and substantially no zinc is contained.

The solid content recovered by the above-mentioned processing steps is mainly ferric hydroxide, and contains substantially no zinc, and can be used as a cement raw material. In addition, since the filtrate excluding the solid content does not contain iron, high-quality zinc containing no iron can be recovered from the filtrate. Incidentally, in the method of forming hydroxide precipitate by alkali treatment without adjusting the oxidation-reduction potential of the filtrate from which copper has been separated, or by adding a sulfide agent to precipitate sulfide, iron and zinc in the liquid are mixed. As a result, it becomes a residue having a high zinc content, and is not suitable for a cement raw material as it is.

[0017]

EXAMPLES The processing method of the present invention will be specifically described below with reference to examples. In addition, these are illustrations and do not limit this invention.

(Example 1) Flying ash from incineration of municipal waste (Cu: 0.1%)
1000 ml of water was added to 250 g, the pH was adjusted to about 3 by adding sulfuric acid, and the mixture was stirred for 30 minutes and then separated into solid and liquid. 0.26 g of iron powder was added to 1000 ml of the separated filtrate, and mixed.
After a lapse of minutes, the resulting precipitate was subjected to solid-liquid separation to recover 0.24 g of copper. Although the surface of the recovered copper was partially oxidized, the copper quality was about 94%.

(Example 2) 1000 ml of water was added to 250 g of molten slag fly ash (Cu: 2.3%, Zn: 5.2%) of municipal waste incineration ash, and the pH was adjusted to about 3 by adding sulfuric acid. After stirring for minutes, solid-liquid separation was performed. To 1000 ml of the separated filtrate, 6 g of iron powder was added and mixed, and after 30 minutes, the resulting precipitate was separated by solid-liquid separation to recover 5.7 g of copper. Although the surface of the recovered copper was partially oxidized, the copper quality was about 93%. On the other hand, 6 ml of aqueous hydrogen peroxide was added to 1000 ml of the filtrate from which copper was recovered to adjust the oxidation-reduction potential to 0.8 V. The pH of the solution at this time was 2.7.
Met. Caustic soda was added to this solution to adjust the pH to 4, and the resulting precipitate was solid-liquid separated and 11.5 g of ferric hydroxide was added.
Was recovered. The recovered precipitate was confirmed to be ferric hydroxide by powder X-ray diffraction. The grade of iron is 51%,
Almost all was ferric hydroxide. The zinc concentration was 30 ppm, which was not a problem as a raw material for cement. Caustic soda was added to 1000 ml of the filtrate after collecting the ferric hydroxide to adjust the pH to 9, and the resulting precipitate was subjected to solid-liquid separation to recover 19.6 g of zinc hydroxide. The recovered precipitate was confirmed to be zinc hydroxide by powder X-ray diffraction.
The quality of zinc was 65%, and almost all the zinc was zinc hydroxide.

(Comparative Example 1) 1000 ml of water was added to 250 g of molten slag fly ash (Cu: 2.3%, Zn: 5.2%) of municipal waste incineration ash, and the pH was adjusted to about 3 by adding sulfuric acid. After stirring for minutes, the mixture was separated overnight. To 1000 ml of the separated filtrate, 6 g of iron powder was added and mixed, and after 30 minutes, the precipitate formed was separated by solid-liquid separation to recover 5.7 g of copper. Although the surface of the recovered copper was partially oxidized, the copper quality was about 93%. On the other hand, 21 g of sodium hydrogen sulfide was added to 1000 ml of the filtrate from which copper was recovered to precipitate sulfide, and 28 g of sulfide was recovered by solid-liquid separation. This recovered product was a mixture of iron sulfide and zinc sulfide. For this reason, it lacked suitability as a raw material for cement.

[0021]

According to the treatment method of the present invention, copper and zinc are efficiently removed from waste such as municipal waste incineration ash, sewage sludge incineration ash, or cement kiln dust, and the waste is treated so as to be suitable as a cement raw material. can do. Therefore, according to the present treatment method, it is possible to completely recycle waste. Further, according to the treatment method of the present invention, the quality of the recovered copper and zinc is high, and the recovery rate is good. Further, since iron powder is used for copper precipitation, the processing cost can be significantly reduced as compared with the case where zinc powder is used.

[Brief description of the drawings]

FIG. 1 is a process chart showing an outline of a processing method of the present invention.

FIG. 2 is a graph of the amount of iron and zinc added and the copper quality in the copper separation process.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 7/38 ZAB B09B 3/00 304H 304G (72) Inventor Keiichi Miura Daisaku 2-chome, 4-chome, Sakura City, Chiba Prefecture No. 2 Taiheiyo Cement Co., Ltd. Sakura Laboratory F-term (reference) 4D004 AA36 AA37 AA46 AB03 AC05 BA02 CA13 CA34 CA35 CA41 CC11 CC12 4D038 AA08 AA10 AB68 AB69 BB13 BB15 BB16 BB17 BB18

Claims (5)

[Claims] 1. A method for adding iron to a filtrate of a sulfuric acid leaching slurry of copper-containing waste to precipitate copper in the liquid, and separating and recovering the deposited copper. A method for treating heavy metals in wastes, comprising depositing high-grade copper at a concentration of 0.9 equivalent to 1.2 equivalents or less with respect to the copper concentration. 2. A copper separation step of adding iron to a filtrate of a sulfuric acid leaching slurry of waste containing copper and zinc to precipitate copper in the solution, separating and recovering the deposited copper, and a filtrate separating copper. A step of separating iron and zinc by precipitating and separating at least one of iron and zinc from the wastewater, wherein the oxidation-reduction potential of the liquid is adjusted to 0.5 V or more in the iron / zinc separation step. A method for treating heavy metals in wastes, comprising separating iron from the zinc by adjusting the pH of the solution to 2.9 to 5 after precipitating iron in the solution to precipitate iron. . 3. The processing method according to claim 2, wherein the amount of iron added in the copper separation step is 0.9 equivalent or more to 1.2 equivalents or less with respect to the copper concentration in the liquid to precipitate high-purity copper; Further, in the iron / zinc separation step, after adjusting the oxidation-reduction potential of the liquid to 0.5 V or more to make the iron ions in the liquid trivalent, the pH of the liquid is adjusted to 2.9 to 5 to adjust the iron ion. For treating heavy metals in wastes by separating zinc from the liquid by precipitating the same. 4. After separating the sulfuric acid leached slurry of the waste into solid and liquid, copper is added to the filtrate by adding 0.9 to 1.2 equivalents of iron with respect to the copper concentration in the liquid. And the redox potential of the liquid from which the copper was separated was 0.5 V
After making the iron ions in the solution trivalent by the above adjustment, the pH of the solution was adjusted to 2.9 to 5 to precipitate iron, and the solid obtained by solid-liquid separation was used as a cement raw material. A method for converting waste into a raw material for cement. 5. The treatment method according to claim 1, wherein the waste is incinerated municipal ash, incinerated sewage sludge, or fly ash or molten slag fly ash.