JPH10265861A - Method for recovering valuable material from secondary fly ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely recover valuable metals from secondary fly ash of incineration at a low cost by adjusting the pH of the soln., which is obtd. by mixing the secondary fly ash and water, dissolving the valuable materials into the soln. and subjecting the soln. to a sepn. of solid from the liquid at need, then bringing metal zinc into contact with this soln., separating the soln. to cement and tailing and obtaining zinc hydroxide and aq. chloride soln. by adjusting the pH of this tailing. SOLUTION: The most of the valuable metals in the secondary fly ash are chlorides and nearly the entire amt. thereof relatively easily dissolves in the water. The greater part of the valuable metals and alkaline metals are, therefore, included in the aq. soln. The pH of the soln. is adjusted to 4 to 6.5 after the sepn. of the solid from the liquid and the metal zinc is brought into contact therewith to form the components electrochemically nobler than the zinc into an insoluble metal form. Consequently, lead, chromium, mercury, thallium, etc., deposit as the cement. The pH of the tailing from which the cement is separated is adjusted to 9 to 11 and while the remaining valuable metals are codeposited, the zinc is precipitated in the form of the zinc hydroxide. The soln. of the alkaline metal chlorides which do not contain harmful materials is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the recovery of valuable materials from secondary fly ash generated during melting treatment of incineration ash and fly ash in an incinerator.

[0002]

2. Description of the Related Art Conventionally, landfill processing has been performed as final disposal of incinerated ash and fly ash generated by incineration of general waste. 2. Description of the Related Art In recent years, the amount of incineration of general waste has increased, and landfilling of generated incineration ash and fly ash has begun to hinder. In addition, the landfill itself has become a controlled landfill with stricter management standards, and the number of municipalities that dispose of these incinerated ash and fly ash by melting, rendering them harmless, reducing their volume, and then landfilling them has increased. I have.

[0003] However, at the time of this melting treatment, dust (secondary fly ash) in which heavy metals are concentrated at a higher concentration is generated. In such secondary fly ash, a polymer liquid complexing agent which forms a stable complex compound with a heavy metal generally contained is added as a fixing material, and the heavy metal is insolubilized and landfilled. However, the main component of the secondary fly ash is a water-soluble sodium salt or potassium salt, and the danger of heavy metal elution due to acid rain cannot be denied.

[0004] Attempts have been made to consider and recover heavy metals in secondary fly ash as resources. However, when sintering to smelt the valuables in the secondary fly ash, almost all of the chlorine content is distributed to the sintering gas as volatile chlorides such as lead chloride and zinc chloride, which imposes a burden on exhaust gas cleaning. Or
It has not been put into practical use due to problems such as corrosion of equipment materials.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of recovering valuable metals more reliably and cheaply than incinerated secondary fly ash containing valuable metals. .

[0006]

According to the method of the present invention for solving the above-mentioned problems, a secondary fly ash and water are mixed, valuables are dissolved in the solution, and if necessary, the pH of the solution is adjusted to 9 or less. To 11
After the solid-liquid separation, the pH of the resulting solution was adjusted to 4 to 6.5, metal zinc was brought into contact with the solution to separate it into cement and tail liquid, and then the pH of the tail liquid was adjusted to 9 to 11. To obtain zinc hydroxide and an aqueous solution of chloride.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Most of the valuable metals in the secondary fly ash are in the form of chloride, and almost all of them can be dissolved in water relatively easily except for lead chloride which is a hardly soluble chloride. Therefore, the solution obtained by mixing the secondary fly ash and water contains a trace amount of lead, most valuable metals and alkali metals. Usually, this solution often shows slight acidity.

The pH of this solution is adjusted to 9 to 11 in order to separate components other than alkali metals from hydroxides and alkali metals. If the pH is less than 9, the heavy metal component in the solution will not sufficiently turn into hydroxide. pH
If it exceeds 11, lead, zinc, copper and the like form soluble complex salts. Basically, there is no problem as long as the pH can be adjusted to a predetermined value as an alkali for adjusting the pH. However, if the finally obtained waste liquid is evaporated and concentrated to recover the salt, water is used. A caustic such as sodium oxide is desirable, and calcium hydroxide may be used if discharged. This step can be omitted if it does not hinder the cementation reaction in the next step.

The pH of a solution having a pH of 9 to 11 after solid-liquid separation
The reason why the metal zinc is brought into contact with the solution in the range of 4 to 6.5 or as it is is to fix components electrochemically more noble than zinc in an insoluble metal form. In addition, this is because hexavalent chromium is converted into trivalent chromium which easily becomes a hydroxide. As a result, a part of lead, chromium, mercury, thallium and the like remaining in the solution is precipitated as cement. The reason for setting the pH to 4 to 6.5 is that when the pH is lower than 4, consumption by chemical dissolution of zinc metal takes precedence, and removal of lead, copper, cadmium, arsenic, mercury, selenium, thallium and the like becomes insufficient. . In particular, when a large amount of arsenic is present, hydrogen arsenide gas is easily generated, which is not preferable in terms of working environment. If the pH exceeds 6.5, some of the coexisting components will precipitate as hydroxides, causing a reaction hindrance.

As the pH adjuster, a mineral acid is preferred. However, in the case of a large amount of lead, when sulfuric acid is used, lead precipitates as lead sulfate, and the time until the completion of the reaction is prolonged.

The shape of the metallic zinc to be used may be flaky or plate-like metallic zinc, but powdered zinc is preferred from the viewpoint of increasing the reaction surface area and shortening the reaction time. In addition, the addition amount is required to be at least 1 chemical equivalent to the coexisting reactant, but it is empirical, but the addition amount of 5 chemical equivalents to lead or copper is preferable.

The tail liquor obtained by solid-liquid separation of the generated cement contains zinc. The pH is adjusted to 9 to 11 in order to remove the zinc. At this time, the zinc precipitates as zinc hydroxide while co-precipitating valuable metals remaining in the tail liquid. If the pH is less than 9, the production of zinc hydroxide becomes insufficient,
Above pH 11, zinc forms soluble complexes.

The alkali used at this time is preferably caustic if recovery is necessary, and if discharged after re-adjustment of pH, it is preferable to use calcium hydroxide from the viewpoint of removing soluble fluorine.

As described above, the method of the present invention separates and recovers valuable materials in secondary fly ash into a form suitable for a lead and zinc smelting raw material, and removes alkali metal chloride as a main component to remove harmful substances. It is obtained as a salt solution that does not contain, and as a treatment of this salt solution, the salt may be recovered by an evaporative concentration method.
May be readjusted and discharged.

[0015]

Next, the present invention will be further described with reference to examples.

(Example 1) The main component is chlorine 5 based on the dry amount.
2.7% by weight, sodium 22.7% by weight, potassium 1
2.7% by weight, 6.15% by weight of zinc and 1.68% of lead
% By weight, 0.63% by weight of copper, 0.07% by weight of cadmium, 0.17% by weight of chromium, 0.07% by weight of arsenic, 0.0017% by weight of mercury, 0.0035% of selenium
Wt%, thallium 0.007 wt%, fluorine 0.3
1.0 kg of secondary fly ash consisting of 10% by weight was suspended in 10 liters of industrial water, stirred at room temperature for 10 minutes, and then 171 g of calcium hydroxide was added to adjust the pH to 10.7. Solid-liquid separation was performed to obtain a neutralized precipitate having a moisture content of 58.6% and a wet mud amount of 585 g, and 9.6 liter of an alkaline solution.

The obtained neutralized residue is chlorine 4.
5 wt%, sodium 8.0 wt%, potassium 0.7 wt%, zinc 25.2 wt%, lead 6.57 wt%, copper 2.
59% by weight, cadmium 0.26% by weight, chromium 0.6
4% by weight, arsenic 0.29% by weight, mercury 0.0036% by weight, selenium 0.012% by weight, thallium 0.01% by weight
Hereinafter, 0.9% by weight of fluorine and 16.0% by weight of calcium
It was.

The alkaline solution contains 54 g of chlorine /
l, zinc 4.89 mg / l, lead 24.8 mg / l,
0.62 mg / l copper, 0.05 mg / cadmium /
1, chromium 3.96 mg / l, arsenic 0.30 mg / l
1, mercury 0.26 mg / l, selenium 3.6 mg / l
l, thallium 0.13mg / l, fluorine 5.0mg
/ L.

The results show that most of the heavy metals could be compressed to a quarter of the volume, and the chlorine extraction rate was about 98%, indicating that sufficient removal was achieved.

In an alkaline solution, the surface area is 460 cm at room temperature.
2. 200mm x 100mm x with weight of 1430g
A 10 mm thick metal zinc plate was added and stirred for 180 minutes. Thereafter, the metal zinc plate was pulled up and suction-filtered to obtain a cement and a tail liquid.

The cement has a moisture content of 25.6%, including those adhering to a metal zinc plate, and a wet mud amount of 0.3 g, and 7.8% by weight of zinc and 61.9% by weight of lead on a dry basis. 0.5% by weight. The heavy metal in the tail liquor contained 1 zinc.
13 mg / l, lead 0.98 mg / l, chromium 0.0
4 mg / l, arsenic 0.09 mg / l, thallium 0.
06mg / l, copper, cadmium, selenium 0.05mg
/ L or less and mercury was 0.0005 mg / l or less, and valuable metals other than zinc eluted by the reaction could be obtained as solids.

Next, 1.4 g of calcium hydroxide powder was added to the tail liquid with stirring to adjust the pH to 10.0, and then the mixture was separated into solid and liquid by a suction filter. An amount of 10.8 g of zinc hydroxide and 9.5 l of aqueous chloride solution were obtained. Zinc hydroxide is zinc 41.2 on a dry basis.
% Of zinc in the aqueous chloride solution was 0.14 mg /
l, lead, copper, cadmium, chromium, arsenic, selenium, and thallium are all 0.05 mg / l or less, and mercury is 0.00
It was less than 05 mg / l, indicating that valuable resources were completely removed. It can be seen that this chloride aqueous solution can be easily discharged if it is neutralized again with sulfuric acid.

Example 2 1.0 kg of the secondary fly ash used in Example 1 was suspended in 10 liters of industrial water and stirred at room temperature for 10 minutes to obtain an extract. This extract has a pH
Was 4.3, and the cementation was possible as it was.

To this extract, 59 g of zinc metal powder was added and stirred for 180 minutes. Thereafter, suction filtration was performed to obtain a cement and a tail liquid.

The cement has a moisture content of 22.1% and a wet mud amount of 98.
g, 56.7% by weight of zinc and 22.22% of lead on a dry basis.
0% by weight and 14.5% by weight of copper. The heavy metals in the tail liquor were 7720 mg / l zinc and 0.18 lead.
mg / l, chromium 0.06 mg / l, thallium 0.
0.05 mg / l, copper, cadmium, arsenic, selenium 0.0
The content was 5 mg / l or less and the amount of mercury was 0.0005 mg / l or less, and valuable metals other than zinc eluted by the reaction could be obtained as solids.

Next, 14 g of calcium hydroxide powder was added to the tail liquid with stirring to adjust the pH to 10.0, followed by solid-liquid separation with a suction filter, and a water content of 76.4% and a wet mud amount of 762 g. Of zinc hydroxide and 9.5 liters of an aqueous chloride solution. Zinc hydroxide is 42.5% by weight of zinc on a dry basis, zinc in an aqueous chloride solution is 0.18 mg / l,
Lead, copper, cadmium, chromium, arsenic, selenium, and thallium are all 0.05 mg / l or less, and mercury is 0.0005 or less.
mg / l or less, indicating that valuable resources were completely removed. It can be seen that this chloride aqueous solution can be easily discharged if it is neutralized again with sulfuric acid. In addition, cement and zinc hydroxide concentrated and separated
It becomes suitable as a zinc smelting raw material.

Comparative Example 1 An inorganic flocculant was added to 9.6 liters of an alkaline solution obtained in the same manner as in Example 1. As an aggregating agent, ferrous sulfate, which is also effective as a reducing agent, is used, and 20 ml of a ferrous sulfate solution having a concentration of 100 g / l is used because an alkaline solution is yellow and coexistence of hexavalent chromium is a concern. Iron hydroxide generated after the addition and stirring for 30 minutes was subjected to solid-liquid separation with a suction filtration device. The resulting precipitate had a moisture content of 76.4% and a wet sludge amount of 7.6 g. The amount of the obtained aqueous chloride solution was 9.6 liters, and the amount of zinc was 0.1 liter.
07mg / l, lead 0.05mg / l, copper 0.25m
g / l, mercury 0.16 mg / l, thallium 0.14
mg / l, cadmium, chromium, arsenic, selenium 0.0
It was less than 5 mg / l.

In this embodiment, the effect of removing valuable metals is poor as compared with the embodiment, and in particular, mercury is about 30 times as high as the wastewater standard.

[0029]

According to the method of the present invention, valuable metals in secondary fly ash can be easily converted into zinc / lead smelting raw materials.

Claims (2)

[Claims] 1. The secondary fly ash and water are mixed, valuables are dissolved in the solution, and if necessary, solid-liquid separation is performed.
4 to 6.5, contacting metal zinc, separating into cement and tail liquid, and then adjusting the pH of the tail liquid to 9 to 11 to obtain zinc hydroxide and chloride aqueous solution. Of valuables from secondary fly ash. 2. Mixing secondary fly ash and water, dissolving valuable materials in the solution, adjusting the pH of the solution to 9 to 11, separating the solution into solid and liquid, and adjusting the pH of the obtained solution to 4 To 6.5, contacted with metallic zinc, separated into cement and tail liquid,
Then, the pH of the tail liquor is adjusted to 9 to 11 to obtain zinc hydroxide and an aqueous solution of chloride.