NL1032604C2 - Method for fixing heavy metals in inorganic materials, in particular AVI bottom ash and soil. - Google Patents

Abstract

The fixation of heavy metals, present in inorganic materials having a macro-structure, mainly comprising oxides of silicon, calcium, and aluminium, in particular organic hydrophilic acids containing municipal solid waste incinerator (MSWI) bottom ash and polluted soil involves mixing the inorganic material, at a usual temperature and pressure, with a solid, in particular powdery activated carbon material.

Description

Title: Method for fixing heavy metals in inorganic materials, in particular AVI bottom ash and soil

The invention relates to a method for fixing heavy metals present in inorganic materials with a macrostructure, mainly consisting of oxides of silicon, calcium, aluminum and potassium, in particular organic hydrophilic acids containing AVI bottom ash and contaminated soil, by mixing the inorganic material, at normal temperature and pressure, with powdered, active carbon material.

It is known from literature (A. van Zomeren, RNJ Comans, 10 Environ. Sci. Technol., 2004, 38, 3927-3932) that the leaching of heavy metals from AVI bottom ash is promoted by the presence of natural organic material such as humic and fulvic acids. The metals complex with these organic substances into easily leachable complexes.

Active carbon materials are furthermore known to be able to bind or adsorb the above-mentioned organic acids.

It is known per se from DE 195.14.577 A1 that the adsorption of harmful substances, including heavy metals, to active carbon is better than to humus compounds ("Humine substances"), as well as the fact that heavy metals cannot be sufficiently immobilized with only active carbon. However, immobilisation of heavy metals through the use of a combination of humus compounds and active carbon is not mentioned or suggested.

It has now surprisingly been found that by adding solid, in particular powdered, active carbon to the bottom ash, the organic acids are bound and can no longer be leached out easily. As a result, the leaching of heavy metals (such as chromium, nickel, copper, zinc, arsenic, molybdenum, cadmium, tin, antimony, and lead, but in particular of copper and antimony) from AVl bottom ash.

It is noted that the content of organic acids, in particular the organic hydrophilic acids, such as humic and fulvic acid, measured as DOC ("dissolved organic carbon"), with bottom ash is generally between 20 and 600 mg / kg dry substance (measured by the column test). These concentrations of hydrophilic acids have not proved to be a problem using the method according to the invention. Said humic and fulvic acid have been detected in a manner known per se in the bottom ash and contaminated soil to be treated.

15 In order to further improve the environmental quality so that the product obtained can be classified in category 1 of the Building Materials Decree (now Soil Quality Decree), it is recommended that the leaching from the bottom ash of metals and salts such as chloride, bromide, fluoride and sulphate , to decrease. This can be achieved by washing the bottom ash, as pre-treatment; and / or stabilize the treated bottom ash with an inorganic hydraulic binder, for example a cement composition known as CEM 42.5.

25 I

The present invention therefore relates in a preferred embodiment to a process consisting of a washing process followed by an addition of solid, powdered active carbon material, whereby the above-mentioned organic substances, in particular the organic hydrophilic acids, such as humic and fulvic acids, remain bound in the bottom ash AVI, and in particular reducing the leaching of heavy metals (organic metal complexes). It has been found that the leaching of sulphate, halides (F, Cl, Br) and metals was also reduced. The particle size of the powdered carbon material is not critical, provided that it is small enough to allow intimate contact with the material to be treated.

Attractive preferred embodiments of the methods according to the invention are stated in the subclaims.

The invention furthermore relates to a method for immobilizing heavy metals and halides and sulphate present in inorganic materials with a macrostructure, mainly consisting of oxides of silicon, calcium, aluminum, and potassium, in particular AVI bottom ash or contaminated soil wherein an inorganic material treated according to the invention is mixed with a hydraulic binder to obtain a product in the presence of water to form a hard, stony, shaped or non-shaped product.

The amount of inorganic hydraulic binder to be added is preferably 1-15% by weight, in particular 1-20% by weight, based on the dry matter content of the treated inorganic material.

The invention will be explained below with reference to a bottom ash obtained from a waste incineration plant (in short: AVI) for the incineration of household waste.

Process Description

The process used to improve the environmental hygiene quality of WIP bottom ash can consist of the following components: 1. A washing process 2. Addition of solid, active carbon materials to the WIP bottom ash 35 3. Addition of an inorganic hydraulic binder 4

The washing process

The AVI bottom ash is preferably washed in 2 steps. In the first step, the AVI bottom ash is washed with an L / S-5 ratio ranging from 0.1 to 10 l / kg, but more particularly a L / S ratio ratio of 0.1 to 0.7. This washing step can, optionally, take place in the de-slagger of a waste incineration plant. When the bottom ash has undergone this first washing step, the bottom ash is then, preferably, backwashed with clean water with the aim of removing the adhering water (which often still contains salt anions, sulphate and (heavy) metals)) on the bottom ash .

Addition of solid active carbon materials to the AVI-15 bottom ash

A solid active carbon material is added to the bottom ash, preferably in powder form to ensure good contact, if desired after the AVI bottom ash has undergone the washing step described above. The added material can be active carbon, or carbon-containing fly ash that results from the gasification of waste wood. Concentrations at which the active carbon materials are added range from 0.1% to 10%, more particularly 0.1% - 3%. 1 2 3 4 5 6 7 8 9 10 11

In addition to the active carbon material, an inorganic hydraulic binder can be added ranging from 3 to 1 - 15%, more in particular 1-10%. Such a binder may consist of (a combination of) different types of cement, such as blast furnace cement, portland cement or 6 combinations with fly ash-containing cements, for example a 7 cement composition known as CEM 42.5 commercially available. The binder used preferably has a low gypsum content.

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Usually in an inorganic hydraulic binder 6-10% by weight of gypsum (calcium sulfate) is included to control the cure time 11 of the binder. However, it has been found that the amount of gypsum can be considerably reduced, and an amount of, for example, from 2-4% by weight, expediently about 2.5% by weight, nevertheless allows rapid curing of the mixture, without this being at the expense of starts from the hardness of the end product. It was found that with such a low-plaster cement, the leaching of, in particular, antimony, but also of other heavy metals such as zinc, could be considerably reduced.

The invention is further illustrated below with reference to the following examples.

i! ! Examples j

Example 1

The following recipe has been formulated on the basis of 100% AVI bottom ash containing copper contamination, which contained humic and fulvic acid (qualitatively proven):

Percentages

Recipes additives 1.0 Untreated No additives bottom ash (Zero sample) 1.1 / 1.2 Bottom ash and 1% activated carbon active carbon 1

The various recipes were then examined for leaching using the first stage of the cascade test (L / S = 20) in accordance with NEN 7349. The results (in mg / kg ds) are shown in the table below.

6

Copper

Recipe number (mg / kg) Ö7 2.40 j 1.1 0.29 1.2 0.14

The results show that addition of said active carbon material in powder form leads to a considerable reduction in copper leaching, despite the presence of organic hydrophilic acids.

Example 2

The following recipe has been compiled on the basis of 100% copper-contaminated soil, which also contains humus and | j

Fulvic acid contained: I

------ ----

Percentages j

Recipe number of additives 2.0 No additives 2.1 1% active carbon j 15 The recipe was then examined for leaching by means of! the first stage of the cascade test (L / S = 20) in accordance with NEN 7349.

The results (in mg / kg ds) are shown in the table below.

Copper

Recipe number (mg / kg) 2 ~ Ö 73 2.1 0.24 7

The results show that the addition of active carbon leads to a significant reduction in copper leaching.

5

Example 3

The following recipe was formulated on the basis of 100% AVI bottom ash, which contained humic and fulvic acid;

Percentages

Recipe number of additives 3.0 No additives 3.1 6% inorganic hydraulic binder * + 1% active carbon 10 * The inorganic hydraulic binder used had a plaster content of 2% by weight, based on the dry matter content of the binder.

The various recipes were then examined for leaching by means of the first stage of the cascade test (L / S = 20) in accordance with NEN 7349. The results (in mg / kg ds) are shown in the table below.

Antimony

Recipe number Copper (mg / kg) JTÖ 0.200 3.40 3.1 0.078 0.52

The results show that addition of active carbon, whether or not in combination with the inorganic hydraulic binder, leads to a considerable reduction in the leaching of both antimony and copper.

Similar results were obtained for molybdenum, and other heavy metals.

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It is noted that the invention has been illustrated in the above examples using an AVI bottom ash. However, similar results were obtained when using soil contaminated with heavy metals. The invention therefore generally relates to a method for treating materials with a macrostructure, which mainly consists of oxides of silicon, calcium, aluminum, and potassium, which structure is contaminated with heavy metals, such that the leaching of these heavy metals is considerably reduced.

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Claims (12)

1. A method for fixing heavy metals present in inorganic materials with a macrostructure, mainly consisting of oxides of silicon, calcium, aluminum and potassium, in particular organic hydrophilic acids containing AVI bottom ash and contaminated soil, by inorganic material, at normal temperature and pressure, to be mixed with solid, in particular powdered, active carbon material. Method according to claim 1, wherein the organic hydrophilic acids consist of fulvic acid and / or humic acid. 3. A method according to claims 1 or 2, wherein the inorganic material is mixed with 0.1% by weight - 10% by weight of solid active carbon material, in particular 0.1% by weight - 3% by weight, based on the dry matter content of the inorganic material. 4. Method according to one or more of claims 1-3, wherein the solid active carbon material consists of an active carbon, in particular in powder form; or a fly ash formed during the gasification of wood. 5. Method according to one or more of claims 1-4, wherein the inorganic material, prior to mixing with active carbon material, is subjected to a washing treatment with water to remove anionic salts, in particular chloride, bromide, fluoride, and sulphate . Method according to one or more of claims 1-5, wherein the washing treatment is carried out in 2 steps. 1032604 A method according to claim 6, wherein the washing treatment of the first step comprises contacting the bottom ash with water, with an L / S ratio of 0.1 - 10 1 / kg, in particular of about 0 , 1 - 0.7 l / kg. 5 A method according to claim 6, wherein the washing treatment of the 2nd step is carried out with an amount of water sufficient to remove the water hanging from the 1st step and hanging on the inorganic material. 9. Method according to one or more of claims 5-8, wherein the washing treatment, in the case of AVI bottom ash, is carried out in the slag remover of the! waste incineration plant. 15 10. Method for the immobilisation of heavy metals present in inorganic materials with a macrostructure, mainly consisting of oxides of silicon, calcium, potassium and aluminum, in particular organic hydrophilic AVI bottom ash or contaminated soil, wherein the inorganic material treated according to one or more of claims 1-9 is mixed with an inorganic hydraulic binder to obtain a product to be formed in the presence of water into a hard, stony material. 25 The method of claim 10, wherein a solid inorganic hydraulic binder is added in an amount; from 1-15% by weight, preferably 1-10% by weight, based on the dry matter content of the treated inorganic material. 30 | 12. Method according to claims 10-11, wherein a solid inorganic hydraulic binder is added with a plaster content of 1-4% by weight, preferably of 2-4% by weight, based on the dry matter content of the total amount of binder . 1032604