JPS5995984A - Treatment of waste material containing harmful heavy metal - Google Patents

Abstract

PURPOSE:To convert harmful heavy metals to a stable form by adding a specific amt. of water to finely pulverized waste contg. the harmful heavy metals and the salt of alkali metals to adjust the pH thereof to a specific value then adding and mixing cement to and with the residue thereof and solidifying the same. CONSTITUTION:Water is added to finely pulverized waste or pulverized waste contg. harmful heavy metals (Cd, Pb, Zn, etc.) and the salt of alkali metals and or alkaline earth metals at >=2pts.wt., more preferably 2-10pts.wt. basing on 1pt.wt., the waste to prepare a slurry. The pH of such slurry is adjusted to >=9, more preferably 9-12 by using an acid or alkali and the slurry is filtered and is thus separated to filtrate and residue. Cement is added and mixed to and with the residue to solidify the residue into the form with which the harmful heavy metals can be discarded without any trouble. The filtrate is concd. by evaporation whereby harmless valuable materials are recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating hazardous wastes containing heavy metals, such as urban and industrial wastes, in a non-polluting manner.

Generally considered to be urban wastewater, it is the residue discharged when sludge etc. from wastewater treatment processes are incinerated.

Industrial waste contains various harmful heavy metals. However, there is no established treatment method for wastes such as tarst containing these harmful heavy metals. The current situation is that it is dumped in landfills, and even if it is treated with a cement hardening method and then dumped, there is a risk that it will leach out in rainwater and contaminate the environment around the landfill.

For example, when examining the chemical properties of waste such as dust generated during the incineration of municipal waste, it is found that: Dust, etc. contains a large amount of water-soluble salts in addition to water-insoluble oxides. , ■ The main form of the oxide contained in the dust etc. is S.
i02, AA20B r'CaO, and the salts are NaC/, .

KCl + Cact2 + Na2 SO, alkali such as 2So4; heavy metal or alkaline earth metal salt (
(hereinafter abbreviated as alkali]) (earth) metal salt); ■ Furthermore, harmful heavy metals (e.g. Cd, Pb +
Most of Zn + Cu, Hg) is also in the form of heavy metal salts in the form of chlorides or sulfates), and in order to immobilize heavy metals using conventional methods, dust containing large amounts of these salts Even if an attempt was made to harden the dust by directly adding cement to the dust, the large amount of salts contained in the dust inhibited the hardening reaction of the cement and the strength of the solidified product was low, and the dust could be easily washed away by rainwater etc. at the landfill site. Since it disintegrates when exposed to heavy metals, it is impossible to achieve the objective due to re-elution of heavy metals.

As described above, wastes such as dust containing large amounts of alkali (±) metal salts and heavy metals in the form of salts were extremely polluting and posed problems in treatment.

The present invention solves this problem, enables hazardous waste containing heavy metals to be dumped without any hindrance by the cement solidification method, and further provides an effective method for recovering harmless valuables that do not contain heavy metals from the waste. The purpose is to provide this in an inexpensive format.

The present invention produces a slurry by adding 2 or more parts of water to 1 part (by weight) of pulverized waste or pulverized waste containing hazardous heavy metals and salts of alkali metals and/or salts of alkaline earth metals. waste containing hazardous heavy metals, characterized in that the slurry is separated into a P solution and a residue by sweating in a state where the pH of the slurry is 9 or more, and cement is added to the obtained residue and mixed to solidify it. It is a method of processing things.

One embodiment of the present invention will be explained with reference to the drawings. First, waste A such as dust is put into a water tank B, immersed in water to form a slurry, and water-soluble alkali (±) metal salts and heavy metals are mixed together. Dissolve the salt in water. At this point, if the slurry has an alkaline pH of 9 or higher, most of the heavy metal salts contained in the waste will be in the form of hydroxides and will be cine-soluble. On the other hand, since the alkali (±) metal salts in the dust do not form hydroxides, they can be dissolved as they are, and since oxides are originally insoluble, PflNmL,
In this case, the slurry is suspended in a mixed state with the heavy metal hydroxide. Next, after settling the slurry,
Furthermore, if solid-liquid separation is performed by filtration using the filtration device E, the tear fluid F side contains NaCtr KCt+ and CaC/=21
Alkali (±) metal salts such as 2SO4 migrate to Na2SO41, and heavy metal hydroxides, iron hydroxide + S +02 + At203. Oxides such as CaO remain in a mixed state.

On the other hand, Nact, Kα-(:
The solution 1 containing alkali (±) metal salts such as aCt, 2, Na2SO4, K2SO4, etc. is recovered by evaporation and condensation in an evaporator H, for example, and then used as a non-hazardous substitute for potash or rock salt for industrial or fertilizer purposes. It can be used as raw material 2.

In this embodiment, f-overseparation is performed after precipitating a mixed state of a 0 compound with good sedimentation properties and a heavy metal hydroxide with poor sedimentation properties. , the sedimentation rate is faster than that of heavy metal rot hydroxide alone, and the P receptivity is also good.

Furthermore, the oxide also has an adsorption effect on heavy metal ions, and because the solubility of the hydroxide also adsorbs dissolved heavy metal ions and precipitates, it has the effect of preventing heavy metal ions from migrating to the liquid 1 side. It's a dog.

Cement K is added to the mixture 3 of heavy metals and oxides on the j4 disaster residue G side and mixed in a solidification device I to form a solidified product 4 with high mechanical strength. In other words, most of the alkali (±) metal salts that have an adverse effect on cement K migrate to the P liquid F side, and the salt content remaining in the mixture is extremely small, so that it cannot harden into cement. It is possible.

In the present invention, if the pH of the slurry is 9 or more, solid-liquid separation may be performed by direct filtration without adjusting the pH, but if the slurry has a pH of less than 9, it will shift to the f-liquid side. Ca(0H)2 increases the amount of heavy metal ions that occur, which interferes with the discharge of the P solution and the recovery of alkaline earth metals contained in the F solution.

Adjust the pH to 9 or higher using an alkali such as NaOH. Furthermore, if the waste contains heavy metals that dissolve in strong alkalinity, such as Pb + Zn + Cr, if the pH exceeds 12, they will migrate into the sap, so it is desirable to adjust the pH to 12 or less.

That is, the optimum pH range in this step is 9 or more and 12 or less, with Ca(OH)2, NaO
H etc. (r) Flukaline C or HCt, H2SO4
Adjust using acid such as.

In addition, in this series of steps, when dissolving waste such as dust in water, the ratio of water to waste [Water /waste (weight)] is 22 or more, preferably in the range of 2 to 1o. In order to mix and solidify the above-mentioned 1-pass residue and cement, the salt concentration in the residue must be reduced to 5.
If it is dissolved and removed to less than 0%, preferably less than 3u, it is possible to solidify cement, and the solidified material will not collapse after disposal, but if it is treated with the above waste and water ratio. This condition is satisfied.

Furthermore, when waste such as dust is discharged from an incineration facility, the P liquid may be evaporated using waste heat J, for example, waste gas, of the incineration facility.

In addition, since the f-liquid contains almost no harmful heavy metals, it can be discharged as is without recovering the alkali metal salts, and furthermore, waste such as the dust is discharged from the incineration facility. In some cases, it is also possible to dispose of the P liquid by absorbing it into the incineration ash, which does not contain any moisture discharged from the incinerator body and is likely to scatter during handling.

According to the method of the present invention, harmful and unstable heavy metal salts are converted into stable forms and then disposed of, while harmless alkaline (earth) metal salts are efficiently separated and recovered. This has the useful benefit of being able to accurately prevent heavy metal elution through proper treatment.

Next, examples of the present invention will be shown.

Example 1 Alkali (±) metal salt was 80% (Na(J23
．． 3%, KCl9.5%, Na2SO41
1.0%, K2S0433.0%, CaCt
2.3.2%), insoluble oxides are 10% (Si0
23.3%l At2031.5ji.

Electrostatic precipitated dust from a municipal waste incineration plant containing 3.0% CaO and 2.2% Mg was dissolved in 4 tons of water to form a slurry. As a result, the pH of this slurry was 6,
9, and Cd 45 ppm as harmful heavy metals,
Pb 1.7 ppm, Zn 1700 ppm l
1.0 ppm of Cr was detected. Next, Ca(OH
) 2 to adjust the pH of the slurry to 10.0 and stir it again to prepare a mixture consisting of heavy metal hydroxide and the oxide. Next, mix this mixture in a filter press for 1
passed. Ca + Pb + Zn in the sap at this time
+ Cr ions were analyzed and found to be 0.1 each.
ppm, 0. O5ppm +0.3 ppm, 0
．． 5 ppm, and the alkali in the sweet filter residue (±
) The concentration of metal salts had decreased by a factor of 30.

Next, 50% cement (per 1' dry residue) was added to the Δ'''i excess residue that had been filtered using a filter press, and the mixture was kneaded to form a solidified product. This solidified product was cured for one week. As a result, it becomes a strong assimilate with a crushing strength of 40 and 9/crA.
Moreover, it did not disintegrate even when immersed in water.

Furthermore, as a result of an elution test of this solidified material with water at pH 7 following the elution test method for hazardous waste announced by the Environment Agency, it was found that Cd
+ Pbt Both Zn and Cr were below 0.1 ppm, so there was no problem at all even if they were disposed of (regulatory value C
dO, 3 ppm, Pb 3 ppm, Zn has no regulation value, Cr 1.5 pI)m).

On the other hand, as a result of evaporating and concentrating the f liquid, NaCt, K (2.

A good white mixture was obtained.

Example 2゜Alkali (±) 60% metal salt (Nact24.8
%, K(!15.2Ll), Na2S045.5%
, K2SO43,256, Ca(J211.3%
), insoluble oxide is 30 parts (5i0215.1 part,
At2032.9 section.

Electrostatic precipitated dust from a municipal waste incineration plant containing CaO12.0] Ky was dissolved in 10 t of water to form a slurry. As a result, the pH of this slurry was 130, and Pb was 31. Oppm, Zn 20
0 ppm and 10 ppm of Cr were detected. Next, the pH of the slurry was adjusted to 11.5 using Hct and stirred again to prepare a mixture consisting of the heavy metal hydroxide and the above-mentioned oxide. This mixture was then filtered through a filter press. At this time, Pb+Zn in e-liquid,
Analysis of Cr ions revealed 0.02 ppr each.
n, 0.5 pprn, 0.3 PPm, and the concentration of alkaline earth metal salt in the filtration residue is 12
It had decreased dramatically.

Next, 30% cement (the dried filtration residue itself) was added to the filter residue that had been passed through the filter press once, and the mixture was kneaded to form a solidified product. After curing this solidified material for one week, the crushing strength was 50 Ky/cr! It was a solid solidified product and did not disintegrate even when immersed in water.

Furthermore, as a result of an elution test of this solidified material with water at pH 7 following the elution test method for hazardous wastes announced by the Environment Agency, it was found that Pb
, Zn, and Cr were all less than 0.1 ppm, so there was no problem at all even if they were disposed of (the regulatory value is Pb3).
ppm, Zn has no regulation value, Cr 1. spp
m).

- As a result of evaporating and concentrating the liquid, NaCl and Kct were obtained.

A very pure white mixture of Na2S04+K2SO4+CaCl2 was obtained.

[Brief explanation of drawings]

The drawings are system explanatory diagrams showing embodiments of the present invention. A...waste, B...aquarium, C...-alkali, D
...acid, E...1 filtration device, F...P liquid, G...
Residue, H... evaporator, ■... - solidification device, J.
...waste heat, K...cement, l...alkali (±
) Metal salt-containing solution, 2... Raw materials, 3... Mixture, 4
...Solidified material. Patent applicant: Patent attorney representing Ebara Infilco Co., Ltd.
Thousand 1) Minoru

Claims (1)

[Claims] 1. Adding 2 parts or more of water to 1 part (by weight) of pulverized waste or pulverized waste containing toxic heavy metals and salts of alkali metals and/or salts of alkaline earth metals. to form a slurry, and in a state where the pH of the slurry is 9 or more, it is passed through F' to separate it into a t-liquid and a residue, and cement is added and mixed to the obtained residue to solidify it. A method for treating waste containing hazardous heavy metals. 2 Adjust the pH of the slurry to 9 using acid or alkali.
12. The method according to claim 1, wherein the temperature is adjusted to .about.12. 3. The method according to claim 1 or 2, wherein 2 to 10 parts of water is added to 1 part (weight) of the waste.