JP2002126693A - Method for treatment waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment method which is capable of rapidly and efficiently filtering out zinc in liquid. SOLUTION: The method is to subject wastes to the separation of solid from liquid by acid leaching and recovering the zinc from the filtrate, in which a sulfuration source is introduced into the acid leaching filtrate to convert the zinc in the liquid to zinc sulfate and to settle the same and further this filtrate is regulated to alkalinity to convert the remaining zinc in the liquid to zinc hydroxide, and to settle the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for easily recovering zinc by forming a precipitate having good filterability when recovering zinc contained in waste. More specifically, fly ash generated in the cement manufacturing process, garbage incineration equipment, etc.
The present invention relates to a method for efficiently separating and recovering zinc when separating and recovering heavy metals such as copper, zinc, and lead from (dust) and the like.

[0002]

2. Description of the Related Art Dust and various industrial wastes discharged from garbage incineration facilities and sewage sludge incineration facilities, and various dusts such as dust discharged from a cement kiln and a high-temperature treatment process of soot are contained in copper in an amount of several percent. It contains heavy metals such as lead and zinc, and when these wastes are directly disposed of in landfills, there is a problem that heavy metals such as lead elute and cause environmental pollution.Therefore, it is necessary to separate and collect these as much as possible. I have.

[0003]

As a method for removing zinc contained in wastes, the wastes are subjected to acid leaching and solid-liquid separation, and then zinc is precipitated and removed from the filtrate as hydroxide or sulfide. There are known ways to do this. However, since zinc hydroxide is a colloidal precipitate, the filtration property is poor, and there is a problem that the filtration time is long or the filtration equipment is large. On the other hand, since zinc sulfide is an extremely fine precipitate, it easily passes through filter paper or filter cloth and is difficult to filter.

[0004] The present invention has solved such a problem in the conventional processing method, and provides a processing method for effectively separating zinc contained in a liquid. The treatment method of the present invention is suitable as a method for separating zinc when heavy metals such as copper, zinc, and lead are separated and collected from dust and the like generated in a cement production process, a garbage incineration facility, and the like.

[0005]

Means for Solving the Problems The present invention provides (1) a method for recovering zinc from acid-leached waste by solid-liquid separation and recovering zinc from the filtrate. The present invention relates to a method for treating waste, comprising converting zinc to zinc sulfide for precipitation, further adjusting the filtrate to alkalinity, and converting residual zinc in the liquid to zinc hydroxide for precipitation.

In the above treatment method of the present invention, (2) the waste is washed with water, desalted, and sodium sulfide is introduced into the acid leached filtrate of the desalted cake subjected to solid-liquid separation to precipitate zinc sulfide. A treatment method of adjusting the pH of the filtrate to 8 or more to precipitate zinc hydroxide, (3) a treatment method of adding sodium hydrosulfide having a zinc concentration of 0.6 equivalent or more contained in the acid leached filtrate,
(4) a step of washing and desalting the waste water to perform solid-liquid separation, a step of subjecting the desalted cake to acid-leaching to perform solid-liquid separation, a step of subjecting the acid-leached solid to solid-liquid separation by alkali leaching, A step of recovering lead from the filtrate, adding sodium bisulfide to the filtrate from which copper has been removed from the acid leached filtrate to precipitate zinc sulfide, and further removing the filtrate from the lead after the lead is recovered in the alkaline leaching step in the filtrate. The pH value is adjusted to 8 or more by adding to the solution, and a treatment method for precipitating zinc hydroxide is included.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 shows an example including the processing method of the present invention.
Shown in The treatment method shown in the figure is for washing waste such as dust with water.
(Water leaching) for solid-liquid separation, waste water treatment, acid-leaching of the desalted cake solid-liquid separated in the water washing step with sulfuric acid or the like, and solid-liquid separation, copper and zinc from the acid leached filtrate. The method includes a step of recovering by precipitation, a step of leaching the solid content of acid leaching with alkali, and a step of recovering lead from the filtrate of alkali leaching.

[0008] In the above processing method, chlorine and copper,
Wastes containing heavy metals such as lead and zinc are converted into an aqueous suspension (slurry) in the water washing treatment step, and chlorine is eluted into the washing water to desalinate. The desalted cake is crushed and led to an acid extraction step, and sulfuric acid and the like are added to form a slurry, and copper and zinc are eluted into the liquid. Copper and zinc are recovered from the acid leaching slurry. On the other hand, the solid content of the acid leaching slurry is led to an alkali leaching step, where caustic soda or the like is added to form a slurry, and lead is eluted into the liquid. This alkali leached slurry is subjected to solid-liquid separation, and the solid content (mainly calcium hydroxide) is used as a cement raw material. Further, lead is recovered from the filtrate. Hereinafter, each processing step will be described in order.

(I) Water Washing (Water Leaching) Step The waste treated according to the present invention is, for example, dust or various industrial waste discharged from a garbage incineration facility or a sewage sludge incineration facility, or a cement kiln or a dust. Includes various dusts discharged from the high-temperature treatment process. These wastes contain a large amount of chlorine compounds such as calcium chloride, and for example, many of them have a chlorine content of about 20%. The water washing step is a step of washing the waste with water and eluting a chlorine content into the washing water to desalinate. Specifically, waste is put into a slurry tank, and water or the like is added thereto to form a slurry, and chlorine is eluted in the water. Next, this slurry is guided to a solid-liquid separation means such as a filter press and filtered to obtain a desalted cake.

In this washing step, it is preferable to wash the aqueous slurry of the waste while maintaining the pH of the aqueous slurry (aqueous suspension) in the range of 8.5 to 13. The amount of copper, lead, and zinc contained in the waste material elutes into the liquid greatly depending on the pH of the slurry. By maintaining the pH of the aqueous slurry of the waste material in this range and performing a water-washing treatment, the copper, lead, and zinc are removed. Elution can be suppressed and these can be left in the solid content, while chlorine content can be selectively eluted and desalted. Caustic soda, slaked lime, sodium carbonate, alkaline treatment effluent, etc. may be added to increase the pH of the slurry to the alkaline side, and sulfuric acid or acidic treatment effluent may be added to adjust the pH to the acidic side.

By washing the desalted cake, the chlorine concentration in the cake can be further reduced. The amount of washing water is preferably 50% or more of the cake weight. Wash water volume is 50
%, The cleaning effect is poor and the residual chlorine concentration is high.
When washing is performed with a water amount of 0% or more, the residual chlorine concentration sharply decreases, and the residual chlorine can be reduced to 2% or less. This washing wastewater is recycled to the water leaching tank for reuse.

The desalted cake is crushed and sent to an acid leaching step. On the other hand, the liquid separated from the desalted cake is led to a wastewater treatment step, and a small amount of chromium or selenium contained in the liquid is reduced by adding ferrous sulfate or the like, and coprecipitated with the precipitation of iron hydroxide. Further, if necessary, a polymer flocculant was added to agglomerate the precipitate to enhance the filterability and perform solid-liquid separation. If the COD of the liquid was high, sodium hypochlorite was added to reduce the COD. Drain later.

(II) Acid Leaching Step An acid is added to the crushed desalted cake to elute copper and zinc. The acid used here is suitably an acid that insolubilizes lead remaining in the desalted cake while leaching copper or zinc into the slurry, and specifically sulfuric acid. The slurry preferably has a solid-liquid ratio of 500 g / liter or less, and is preferably an acidic slurry having a pH of 1 to 4. If the pH of the slurry is higher than 4, the copper leaching efficiency may decrease, which is not preferable. p
When H is lower than 1, the burden of the alkali treatment in the next step increases.
The leaching time is suitably 20 minutes or more, depending on the acid concentration, and may be about 30 minutes.

By the acid leaching treatment, copper and zinc in the desalted cake are leached into the liquid. The lead contained in the desalted cake leaches into the liquid at first, but immediately forms an insoluble lead compound such as lead sulfate and remains as a solid. Further, the calcium contained in the desalted cake also turns into gypsum (calcium sulfate) and remains as a solid. Therefore, by solid-liquid separation of the acid leached slurry, copper and zinc in the liquid and lead and calcium in the solid can be separated.
The solid content obtained by solid-liquid separation of the acid leaching slurry may be further washed, and the washing wastewater may be circulated to the acid leaching tank and reused.

On the other hand, the filtrate separated into solid and liquid in the acid leaching step is
Copper in the liquid is precipitated by adding a metal which is more base than copper, that is, powder such as zinc which has a higher ionization tendency than copper. It is preferable that the amount of addition be slightly larger than the amount of copper in the liquid. In addition, if this addition amount is too large, zinc powder or the like is mixed into the precipitated copper, and the quality of the recovered copper deteriorates. The amount of addition is suitably about 1.1 equivalents to the copper concentration in the solution. The precipitated copper precipitates and is collected by solid-liquid separation. Even when calcium is contained in the liquid, calcium has a higher ionization tendency than zinc and does not precipitate by the addition of zinc powder, so that high-grade copper can be recovered.

In the filtrate from which the copper precipitate has been separated, zinc eluted by acid leaching and zinc added during copper recovery are dissolved. Therefore, in the treatment method of the present invention, a sulfide source is introduced into the acidic filtrate to convert zinc in the liquid into zinc sulfide and precipitate it, and further adjust the filtrate to alkaline to remove residual zinc in the liquid with water. Turn into zinc oxide and precipitate. As a sulfur source, sodium hydrosulfide and the like are suitable. The amount of sodium hydrosulfide added is preferably 0.6 equivalent or more of the zinc concentration contained in the liquid. If the addition amount is smaller than this, the amount of zinc sulfide is too small relative to zinc hydroxide, and the effect of improving the filterability is not sufficient. Then, the pH of the filtrate is adjusted to 8 or more, preferably pH 9.5 to 12, by adding caustic soda or the drainage from the alkaline leaching step to the acidic filtrate, whereby zinc is converted into hydroxide and precipitated.

(III) Alkali Leaching Step An alkali is added to the solid content of the acid leaching slurry to form a slurry, and lead (mainly lead sulfate) is leached. Caustic soda is preferred as the alkali. The concentration of caustic soda is 1 moll
Or more, preferably 2 mol liter / liter or more. The solid-liquid ratio of the slurry is suitably 200 g / liter or less, and preferably 100 g / liter or less. The pH of the slurry is suitably 13.5 or more. By this alkali treatment, lead sulfate in the solid content is decomposed and eluted into the liquid. The lead elution rate increases with increasing slurry pH,
It is about 20% at around 2.5, but is about 70% at pH 13.5 or more. Further, when the pH of the slurry is 1
If it is less than 3.5, the gypsum is hardly decomposed, and turns into calcium hydroxide in a higher alkaline region. Therefore, in order to use calcium contained in the solid content as a cement raw material, the pH of the leached slurry is adjusted to a high alkali region of 13.5 or more to decompose gypsum and remove sulfate.

The solid content obtained by solid-liquid separation of the alkali leaching slurry is mainly composed of calcium hydroxide, and is preferably used as a cement raw material since sulfate is removed. Further, since lead is eluted and contained in the filtrate, this solid content contains almost no lead, copper and zinc, and there is no danger of bringing these heavy metals into the cement raw material. The collected solid is washed, and the washing wastewater is circulated and reused in an alkaline leaching tank.

Since lead is dissolved in the filtrate obtained by solid-liquid separation of the alkali leached slurry, a sulfurizing agent such as sodium hydrogen sulfide is added to the filtrate to convert the lead in the liquid into sulfide and precipitate it.
The amount of the sulfurizing agent to be added is suitably 1 to 2 equivalents to the lead content in the liquid. This is filtered to recover lead sulfide. If the recovered lead sulfide is used as a raw material for lead smelting, the sulfur content can be used as a heat source. Since the filtrate from which lead sulfide has been separated is a strong alkali solution (about pH 13), this is reused as an alkali source in the zinc recovery step and an alkali source in the water leaching step.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 Sulfuric acid solution containing 530 g of zinc powder 26.
After adding 456 g of sodium hydrosulfide to 5 liters (pH 3) to cause precipitation, the filtrate was further adjusted to pH 9.5 by adding a sodium hydroxide solution (concentration: 48%), and the precipitate was formed. The mixture was subjected to solid-liquid separation using a filter press. FIG. 2 shows the filterability of this solid-liquid separation. On the other hand, as Comparative Example 1, a precipitate was formed and solid-liquid separated under the same conditions as in the above Example, except that the sodium hydroxide solution was added alone to the filtrate without adding sodium hydrosulfide.

[Example 2] 20 kg of molten slag fly ash was added to water 6
Add 7 liters to make an aqueous slurry.
Water leaching was performed by adjusting to H12. This slurry was filtered with a filter press to obtain a desalted cake. 6.9 kg of the desalted cake was crushed, and 7 liters of water and 3 liters of sulfuric acid having a concentration of 4N were added thereto to obtain a sulfuric acid leaching slurry having a pH of 3, and the mixture was stirred and solid-liquid separated. The collected solid was washed with water, and 2 liters of the washing wastewater was circulated and added to a sulfuric acid leaching tank. On the other hand, zinc powder 280 was added to 14 liters of filtrate of sulfuric acid leaching slurry.
g, and the mixture was stirred.
Was recovered. After adding 240 g of sodium hydrosulfide to 14 liters of the filtrate after copper recovery, the filtrate (about pH 13) generated in the lead recovery in the subsequent step was further added to adjust the pH to 9.5 to 11,
The precipitate was subjected to solid-liquid separation, and 390 g of a solid content was recovered. This solid was confirmed by X-ray diffraction to be a mixture of zinc sulfide and zinc hydroxide. Next, 21 liters of water and caustic soda (48%
(Concentration) of 25 liters was added to obtain an alkaline leaching slurry having a pH of 13.7, and the mixture was stirred to be separated into a solid and a liquid to obtain 2.2 kg of a solid content mainly composed of calcium hydroxide. Wash this solid,
2.5 liters of the washing wastewater was circulated and reused in the alkaline leaching tank. Further, 62 g of sodium hydrogen sulfide was added to 27 liters of the filtrate from which the solid content was separated, and the precipitate was subjected to solid-liquid separation to obtain a lead sulfide solution.
80 g were recovered. A part (6 liters) of the filtrate generated by the solid-liquid separation of lead sulfide was circulated to the zinc recovery step and reused as an alkali source. Further, all the remaining filtrate (22 liters) was recycled to the water leaching step and reused.

[0022]

According to the treatment method of the present invention, zinc contained in an acidic solution is precipitated with good filterability, so that zinc in the solution can be efficiently separated into solid and liquid in a short time. Therefore, the efficiency of the zinc treatment step can be increased in the treatment step of separating and removing copper, zinc, lead, and the like contained in the waste.

[Brief description of the drawings]

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

FIG. 2 is a graph of filtration time and filtrate volume in Example 1.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22B 13/00 C22B 3/00 Q 15/00 13/04 19/00 15/08 19/22 19/24 (72) Inventor Masaya Ida 2-4-2, Daisaku, Sakura-shi, Chiba Pref., Central Research Institute of Cement Co., Ltd. (72) Inventor Keiichi Miura 2-4-2, Daisaku, Sakura-shi, Chiba Pref., Central Research Institute of Taiheiyo Cement Co., Ltd. F term (reference) 4D004 AA37 AB05 AB06 BA05 CA13 CA34 CA35 CA40 CC11 CC12 DA03 4K001 AA09 AA20 AA30 DB23 DB24

Claims (4)

[Claims] 1. A method for recovering zinc from solid filtrate by acid leaching the waste and recovering zinc from the filtrate, wherein a sulfide source is introduced into the acid leached filtrate to convert zinc in the liquid into zinc sulfide and precipitate it.
Further, a method of treating waste, comprising adjusting the filtrate to be alkaline and converting residual zinc in the solution to zinc hydroxide to precipitate. 2. The waste is washed with water and desalted, and sodium sulfide is introduced into the acid leached filtrate of the desalted cake subjected to solid-liquid separation to precipitate zinc sulfide, and the pH of the filtrate is adjusted to 8 or more. 2. The method according to claim 1, wherein zinc hydroxide is precipitated. 3. The zinc concentration in the acid leached filtrate of 0.6.
The treatment method according to claim 2, wherein an amount of sodium bisulfide equal to or more than the equivalent is added. 4. A step of washing and desalting the waste with water to carry out solid-liquid separation, a step of subjecting the desalted cake to solid-liquid separation by acid leaching, and a step of subjecting the acid-leached solid to solid-liquid separation by alkali leaching. Having a step of recovering lead from the alkali leached filtrate, adding sodium bisulfide to the filtrate from which copper has been removed from the acid leached filtrate to precipitate zinc sulfide, and further recovering lead in the alkali leached step in the filtrate. 3. The method according to claim 1, wherein the pH is adjusted to an alkalinity of 8 or more by adding a filtrate to precipitate zinc hydroxide.
Or the processing method of 3.