JP2000281398A - Treatment for converting waste into cement raw material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment process for converting waste such as municipal refuse incineration ash or sewage sludge incineration ash, into a treated material which contains substantially no sulfate ions and has a drastically reduced lead content and is suitable as a cement raw material by subjecting such waste to sulfuric acid leaching to elute and separate copper and zinc from the waste, further subjecting the sulfuric acid-leaching residue to alkali leaching to elute and separate lead from the residue and converting gypsum in the reside into calcium hydroxide. SOLUTION: This treatment process comprises: adding sulfuric acid to waste such as municipal refuse incineration ash or sewage sludge incineration ash or solid matter in a slurry of such waste thereby subjecting the waste to sulfuric acid leaching in a <=400 g/l solid/liquid ratio and at a pH of <=4, to decompose and elute copper and zinc, to solidify lead and calcium as lead sulfate and gypsum, respectively, so as to allow them to remain in the residue and to perform liquid-solid separation of the leachate and the residue from each other; and adding an alkali to the surface acid-leaching residue so as to form a slurry having a <=200 g/l solid/ liquid ratio and strong alkalinity of a pH of >=13.5, to leach most of lead, to convert gypsum into calcium hydroxide, to perform solid-liquid separation of the leachate and the alkali- leaching residue from each other and to remove sulfate ion. Thus, the recovered solid matter (alkali-leaching residue) containing substantially no lead and almost no sulfate ion is appropriately used as a cement raw material. Further preferably, the waste is subjected to water washing treatment in a 300 g/l solid/liquid ratio beforehand to remove water-soluble chlorine compounds.

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 harmful metals from various kinds of waste such as fly ash from incineration of municipal waste and converting the same into a raw material for cement.

[0002]

2. Description of the Related Art In recent years, the amount of waste such as fly ash from incineration of city garbage, fly ash from sewage sludge, or fly ash from molten slag has increased remarkably. Since these wastes contain a considerable amount of valuable metals such as copper, zinc, and lead, methods for recovering valuable metals from these wastes have been proposed as measures for waste disposal. Attempts have been made to use these as cement raw materials.

[0003] One example of the treatment method is a method in which the fly ash or incinerated ash is treated with sulfuric acid to elute copper, zinc, etc., and separate and collect them. However, in this method, the lead in the waste generates lead sulfate, and most of the lead remains as a solid content in the leaching residue. Further, calcium in the waste also reacts with sulfuric acid to form gypsum. A material containing a large amount of gypsum introduces an excessive amount of sulfate into cement, which is not preferable as a cement raw material. In addition, since lead is an unnecessary component in cement, such a material having a high lead content lacks suitability as a cement raw material.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional waste treatment, and an object of the present invention is to provide an optimal treatment method capable of utilizing the waste as a raw material for cement. ADVANTAGE OF THE INVENTION According to this invention, a sulfate content is hardly contained in the calcium content collect | recovered as a solid material, and lead content is significantly small, and therefore it is suitable as a cement raw material.

[0005]

Means for Solving the Problems: The present invention provides (1) a method of leaching out sulfuric acid leaching residue of waste by alkaline leaching at a pH of 13.5 or more to elute and separate lead in the residue, The present invention relates to a method for treating waste, characterized in that gypsum is converted into calcium hydroxide to be used as a cement raw material.

Further, the present invention provides (2) sulfuric acid leaching of waste and elution and separation of copper and zinc contained in the waste into a liquid, and alkali leaching of the sulfuric acid leaching residue at a pH of 13.5 or more. Thus, the present invention relates to a method for treating waste, characterized in that lead in a residue is eluted into a liquid and separated, and gypsum in the residue is converted into calcium hydroxide to be used as a cement raw material.

[0007]

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 drawing, the treatment method of the present invention comprises a step of solid-liquid separation by leaching waste with sulfuric acid (sulfuric acid leaching step) and a step of performing solid-liquid separation by leaching the residue of sulfuric acid leaching with alkali (alkali leaching step). And The waste to be treated in the present invention can be widely applied to municipal waste incineration ash, sewage sludge incineration ash, and incineration fly ash or molten slag fly ash. It is preferable to add water to these wastes to form a slurry, since water-soluble chlorine compounds contained in the wastes elute and the wastes are desalted.

(I) Sulfuric acid leaching step Sulfuric acid is added to the solid content of the waste or its slurry to form a sulfuric acid leaching slurry. The copper and zinc compounds contained in the waste are decomposed by the sulfuric acid and eluted into the liquid as copper sulfate or zinc sulfate. 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, copper and zinc can be separated from waste by solid-liquid separation of the sulfuric acid leached slurry. Although the sulfuric acid leaching depends on the waste, a good leaching effect can be obtained if the solid-liquid ratio is generally 400 g / l or less and the pH is 4 or less.

(II) Alkaline Leaching Step An alkali solution is added to the sulfuric acid leaching residue to elute lead sulfate contained in the residue, and the gypsum in the residue is changed to calcium hydroxide. This alkali leaching is performed under a strong alkali having a pH of 13.5 or more. In this alkaline leaching, the lead leaching rate is greatly affected by the pH of the leaching slurry liquid. Even when the slurry liquid is alkaline, the lead leaching rate is only about 20% around pH 12.5, and most of the lead does not elute. Remains. The lead elution rate increases with increasing pH, and p
With H13.4 or more, the lead elution rate reaches about 70% or more.

[0010] The form of calcium also depends on the pH of the leached slurry, and even if the slurry is alkaline, gypsum is hardly decomposed if the pH is lower than around 13.5. However, the pH is slightly higher than this,
If it is higher than around 3.5, most of the gypsum turns into calcium hydroxide. Thus, the form of calcium changes around pH 13.5. From the above, in the present alkaline leaching step, the pH of the leaching slurry liquid is made to be strongly alkaline of 13.5 or more, preferably pH 13.6 or more, and the gypsum is converted to calcium hydroxide to remove sulfate groups.

The alkaline solution used for the alkaline leaching is suitably caustic soda, caustic potash or the like. The alkali concentration may be within a range that can maintain the above-mentioned pH, and the solid-liquid ratio of the leaching slurry is suitably approximately 200 g / l or less, preferably 100 g / l or less. Since the lead in the residue is eluted into the liquid by the alkali leaching, the lead can be removed from the solid content by subjecting the liquid to solid-liquid separation. In addition, the gypsum in the solid content is converted into calcium hydroxide to remove sulfate groups. As described above, the solid content recovered through alkali leaching contains little lead or sulfate, and is suitable as a raw material for cement.

[0012]

EXAMPLES The processing method of the present invention will be specifically described below with reference to examples. The following examples do not limit the scope of the present invention.

Example Incineration fly ash containing heavy metals (Ca: 7.31 wt%, Pb: 2.09 wt%, C
u: 1.21 wt%, Zn: 0.11 wt%) was treated according to the method of the present invention as follows. First, in order to elute the water-soluble chlorine compound, the incinerated fly ash was washed with water under a condition of a solid-liquid ratio of 300 g / l. Next, a sulfuric acid acidic solution having a pH of 3 was added to the residue to form a slurry having a solid-liquid ratio of 250 g / l, and copper and zinc contained in the residue were eluted. After this slurry was subjected to solid-liquid separation with a filter press or the like, the residue was analyzed with an X-ray diffractometer, and it was confirmed that all the calcium content had changed to gypsum. The residue was alkali leached to elute lead. During this treatment, a 1 mol / l caustic soda solution was added to form a slurry having a solid-liquid ratio of 50 g / l, and the slurry was adjusted to pH 12.69 to pH 13.76 with caustic soda solution and sulfuric acid. After the reaction for 30 minutes, the residue obtained by solid-liquid separation was qualitatively analyzed by X-ray diffraction. The lead elution rate was determined from the total amount of lead contained in the liquid and the lead content in the alkaline leaching residue. The lead concentration in the solution was measured by ICP emission spectrometry, and the lead content in the residue was measured by flame atomic absorption method after aqua regia decomposition. The result is shown in FIG.

As shown in FIG. 2, the lead elution rate is highest around pH 13.5 of the slurry and reaches 70% or more.
It is about 20% at around pH 12.5. Further, as shown in FIG. 3, with respect to the solid content of the alkali leaching, according to the measurement results of the contained components by X-ray diffraction, the measurement peak of gypsum is observed in the alkali leaching at a pH of 13.5 or less, and calcium hydroxide is Has not occurred. On the other hand, in the alkaline leaching of pH 13.6 or more, the measurement peak of calcium hydroxide was detected instead of the measurement peak of gypsum, indicating that gypsum was converted to calcium hydroxide.

[0015]

According to the treatment method of the present invention, copper, lead, zinc, etc. can be effectively removed from municipal waste incineration ash, sewage sludge incineration ash, and waste such as incineration fly ash and molten slag fly ash. Since the calcium component which can be removed and which is recovered as a solid does not contain a sulfate group, it can be used as a cement raw material.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a change in lead elution rate with respect to pH.

FIG. 3 is a graph showing an X-ray diffraction result of a solid content after alkali leaching.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22B 15/14 C22B 13/04 19/00 19/24 // C22B 3/04 3/00 A (72) Inventor Keiichi Miura 2-4-2 Daisaku, Sakura City, Chiba Prefecture Pacific Term Cement Co., Ltd. Sakura Laboratory F-term (reference) 4D004 AA37 AB03 BA02 CA13 CA34 CA35 CA41 CA50 CC12 4K001 AA09 AA20 AA30 BA12 BA14 DB03 DB08 DB23

Claims (4)

[Claims] 1. Sulfuric acid leaching residue of waste is alkaline leached at pH 13.5 or more to elute and separate lead in the residue and convert gypsum in the residue to calcium hydroxide to produce cement raw material. A waste disposal method. 2. A waste product is leached with sulfuric acid to elute and separate copper and zinc contained in the waste product into a liquid, and the sulfuric acid leaching residue is alkali leached at a pH of 13.5 or more to remove lead from the residue. A waste treatment method characterized by dissolving and separating gypsum into a liquid and converting gypsum in the residue to calcium hydroxide to produce a cement raw material. 3. The waste treatment method according to claim 1, wherein the sulfuric acid leaching residue of the waste is alkali leached at a pH of 13.6 or more. 4. The waste treatment method according to claim 1, wherein the waste is incineration ash of municipal waste, incineration ash of sewage sludge, fly ash of these incineration or fly ash of molten slag.