ES2536464A1 - Procedure for the inertization of fly ash from the incineration of urban solid waste (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Procedure for the inertization of fly ash from the incineration of urban solid waste containing heavy metals and chloride ions, in which the ash is mixed with a solution containing a stabilizing agent, obtaining treated ashes that keep the heavy metals in the form of solid more insoluble than the original ashes and which are dried. (Machine-translation by Google Translate, not legally binding)

Description

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Element

Bottom ash (mg / kg or ppm) Fly ash (mg / kg or ppm)

To the

22000-73000 49000-90000

AC

37000-120000 74000-130000

CD

0.3-71 50-450

Cu

190-8200 600-3200

Faith

4100-150000 12000-44000

Hg

0.02-7.8 0.7-30

Pb

98-14000 5300-26000

Yes

91000-310000 95000-210000

Zn

610-7800 9000-70000

Most metals are present as oxides, but quantities also appear

significant thereof in the form of chlorides and sulfates with a high degree of solubility in

5 water Because of this, fly ash has a high degree of leaching, which can

constitute an important environmental safety risk in the medium or long term, due to the

pollution of aquifers with the consequent negative action on plants, animals and

people. Therefore, special attention should be given to this point when considering management

of fly ash, and should be investigated in strategies that control and treat leachate 10 that may occur in the use and application of this waste in different fields, since

be agronomic, in construction, etc.

Due to their RTP character, fly ash must be managed in landfills

Special high-cost, which is currently the main destination of this waste. Thus

At present, avenues are sought that allow the recovery and reuse of this waste 15 for compliance with the European IPPC regulations (Royal Decree 653/2003 on

waste incineration). There are numerous possible uses in the literature for

reuse of fly ash, based primarily on its chemical composition. In

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liquid / solid ratio and high agitation speed, so that dangerous species, including Pb species, are transformed into soluble matter and pass into the wash water, thus inerting the ashes.

JP2011083687 consists in treating the fly ash rich in lead with an aqueous solution containing calcium ion, so that the lead passes into the liquid, giving rise to a solid component of low lead content.

Compared to the present invention, the procedures described in these last three documents involve the generation of a new waste, the wash water, which contains the extracted metals.

Document TW200906762 presents a process to regenerate the fly ash from MSW incinerators as cement, with an initial stage of extracting the ashes with water to remove the salts, second step of stabilization of heavy metals by wet grinding, and their subsequent use to make cement. Compared to the present invention, the described process involves at least two steps of ash treatment.

Document US5347073 stabilizes the lead of the fly ash by calcining a mixture of the ash together with certain calcium compounds in the presence of oxygen at a temperature between 475 and 600 ° C. Compared to the present invention, this process implies a high energy cost due to the high temperature.

JP01262978 describes a process for immobilizing lead and cadmium from fly ash, which consists of mixing the ashes with a phosphate source water soluble compound and an inorganic calcium compound. Compared to the present invention, this process involves a high cost of reagents.

Document CN102992464 describes the mixing of fly ash from the incineration of waste with high salinity wastewater, so that the content of soluble chlorides of fly ash is reduced, which allows it to be poured more safely. Compared with the present invention it does not describe the stabilization of heavy metals.

The present invention proposes a solution to the problem existing in the state of the art, which is to perform an inertization treatment that simultaneously allows the elimination of chlorides and other soluble salts from the ashes, and the immobilization of heavy metals therein, so that they are not leachable, which allows the declassification of fly ash as toxic and hazardous waste; this is achieved

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also with a minimum increase in weight of the ashes, which is very positive in the transport and subsequent use of the inertized ashes. The treatment is also carried out with a low cost reagent, with a very short residence time and at a low temperature.

Description of the invention

Inerting is a solution to the problem of waste management that consists of transforming hazardous waste, through physical and / or chemical treatments, into inert or non-hazardous waste according to current legislation. The effectiveness of the treatment is shown by subjecting the treated residue to a leaching test according to internationally accepted standards for this, as in the EN12457-4 standard.

According to the results of this leaching test, if the inertization treatment has been effective, the treated waste will be classified as non-hazardous or inert, and therefore suitable for being deposited in landfills that contain residues with a medium toxicity level. / low for the environment (Order AAA / 661/2013).

The present invention proposes a mixed separation solidification inertization process, according to the usually recognized technical terminology, which classifies the separation processes as those that consist in extracting the substances that confer their danger, such as heavy metals; and stabilization processes such as those that seek to reduce the hazardous nature of the residue and the toxicity of its components, limit the solubility of any contaminant present in the residue, and minimize the migration rate of the contaminants into the environment.

The proposed inertization procedure is a mixed stabilization separation process, since, on the one hand, you want to extract the chlorides (separation process) and, on the other, you want to immobilize heavy metals in the fly ash to prevent their leaching (process of stabilization).

The proposed procedure consists in treating the ashes with a stabilizing agent solution, with a very short contact time, followed by filtration and drying of the treated ashes. A soluble compound source of carbonate or bicarbonate ion, such as carbonates and alkali bicarbonates, is used as a stabilizing agent to achieve the extraction of chlorides and immobilization of metals. In this way a heterogeneous reaction occurs, where the alkaline cation favors the migration of the chloride ion to the solution, forming alkaline chloride in solution, and the metals present in the ashes remain therein, in the form of a more insoluble solid, the carbonates or

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-

-

-

-

-

-315 ± 31 -361 ± 25

Fly ash has been subjected to an X-ray Diffraction analysis to determine its composition. The diagram obtained is shown below:

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5 Figure 1. X-ray diffractogram of fly ash.

From the ICSD database (Inorganic Crystal Structure Database) it is established that the peaks recorded in the above diffractogram correspond to the following substances: Calcium hydroxychloride [CaCl (OH)], Portlandite [Ca (OH) 2], Silvita [ KCl], Halita [NaCl], Calcite [CaCO3] Anhydrite [CaSO4] and Quartz [SiO2], being the most abundant hydroxychloride of

10 calcium and portlandite.

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distilled water so that the electrode is submerged correctly and 5mL of 0.1M HNO3 is added to acidify the samples. With stirring, the sample is titrated by adding AgNO3 volumes, and the equivalence point of the potentiometric titration is determined. The concentration of chlorides in the eluate expressed in terms is calculated

5 total release, such as mg Chlorides / Kg fly ash on dry basis.

The concentrations of Zn (II), Cd (II), Pb (II) and Cu (II) in the eluate are determined by voltammetry. The measurement is carried out following DIN 38406 part 16. The concentration of each metal in the eluate expressed in terms of total release is calculated, that is, in mg metal / kg of fly ash on dry basis.

10 The values of the parameters measured in the leaching test eluate are shown in Table 2; Table 2 includes the limit values established by current national legislation for a waste to be admitted to the different types of landfill (Order AAA / 661/2013 of April 18, which amends Annexes I, II and III of Royal Decree 1481/2001, of December 27 by which waste disposal is regulated by

15 landfill deposit. Ministry of Environment, Official State Gazette, 97, 3108031111). All values correspond to the concentration in the eluate, expressed as milligrams per kilogram of fly ash on a dry basis.

Table 2. Admission limits for each landfill and classification of fly ash based on the measured concentrations of each parameter.

Concentration

Dump

Dump

Dump

(mg / kg)

R.

Do not

R.

R. Inert

dangerous Dangerous in the eluate of Classification

(mg / kg)

(mg / kg)

(mg / kg)

the ashes

treated

Cl-800 15000 25000 134000 R. Dangerous *

Zn R. No 4 50 200 28.3 dangerous

Cd R. No 0.041 5 5.6 dangerous

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Pb 0.5 10 50 24.0 R. Dangerous

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(mg / kg) (mg / kg) treated ashes

Cl-800 15000 25000 2000 R. Not dangerous

Zn 4 50 200 6.4 R. Not dangerous

CD

0.04 one 5 2.2 R. Inert

Pb

0.5 10 fifty 7.9 R. Do not

dangerous

Cu 2 50 100 0.3 R. Inert

From the results of Table 4 it follows that the treatment achieves the reduction of the levels of Cd and Cu in the leachate to very low values, so that the residue can be considered inert with respect to these parameters. The concentration of chlorides, Pb and Zn

5 decreases greatly with respect to untreated fly ash, and they are suitable for treated ashes to be admitted to a non-hazardous waste landfill.

This example shows that the proposed inertization procedure reduces the danger of fly ash, since, according to the leaching test performed on inertized ashes, the residue would be classified as non-waste

10 dangerous, and some of the parameters have lower values than the limits established by legislation for a waste to be considered as inert.

Example 4.- Procedure for inerting fly ash according to the invention. Composition of treated fly ash.

The inertization treatment is performed as described in example 2. The

15 ashes retained in the filter and dried at 110 ° C, called treated ashes, are analyzed by X-ray Diffraction, in order to know their composition and the obtained diffractogram is shown in Figure 3

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Figure 2. X-ray diffractogram of fly ash treated according to example 2.

By consulting the ICSD database, it is determined that the peaks recorded in the diffractogram of the treated ashes correspond to the following substances: Calcite [CaCO3], Portlandite [Ca (OH) 2] and Anhydrite [CaSO4], the majority component being the calcite

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Figure 4. Intensity and position of peaks for each substance according to ICSD.

According to these results, and the results of example 1, the chloride compounds that were present in the untreated fly ash are not found in the treated ones,

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To do this, 2 beakers are thermostatized at 30 ° C, one with 100 mL of solution 28.67 g / L of NaHCO3, and another with 100 mL of solution 18.08g / L of Na2CO3. 10 g of dry ash are poured onto each of the corresponding beakers, they are kept under stirring for 5 minutes and then the ashes are filtered under vacuum. Washing

5 the ashes retained in the filter with distilled water and all the filtrate obtained is made up to a volume of 500mL. The ashes retained in the filter are dried at 110 ° C and stored for further analysis. Each analysis is repeated in triplicate.

In order to know what amount of chlorides has been extracted from the ashes with this treatment, the determination of chlorides in the filtrate is carried out by

Voltammetry, as explained in example 1, using 5 ml of sample to be analyzed. The results are shown in Table 5.

Table 5. Analysis of the chloride content of the liquid resulting from the inertization of fly ash according to example 4. Comparison of the Na2CO3 and NaHCO3 samples.

Reagent Concentration Cl- (g / L) Standard deviation (g / L)

± 0.237 NaHCO3 2,801 ± 0.090

The range of values with respect to the average for sodium bicarbonate (2,711-2,891 g / L) is

15 included in the range of values with respect to the mean for sodium carbonate (2.4332.907) which means that there are no significant differences between both trials and that, therefore, statistically, it is considered that the extraction of Chlorides with both reagents is identical.

On the other hand, considering that fly ash contains 11 ± 2% of chlorides

20 soluble (Table 1), and taking into account the test conditions described above, the results in Table 5 indicate that the inertization test carried out under the conditions described, with any of the two stabilizing agents employed, has extracted all the soluble chlorides from fly ash

Claims (1)

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