The invention belongs to working operations, namely to methods of remediation of contaminated soil, by which the soil containing hazardous compounds is by means of chemical reactions transformed into less harmful substance.

The purpose of the invention is to enable economically efficient obtaining of construction material, which should be chemically neutral, inert and acceptable for the environment and human health, by using the soil, in which the concentration of water soluble compounds of heavy metals, in particular those on the basis of arsenic As, cadmium Cd and/or lead Pb and/or zinc Zn, essentially exceeds the values, which should be still acceptable for environment and/or not harmful for human health, so that the content of said contaminants in such obtained material should be below each pre-determined values.

Quite exactly, the purpose of the invention is transformation of such contaminated soil, in which the contents of chemical elements in water soluble compounds of heavy metals are the following:

As = 1 ,00 - 10,00 mg/kg of dry substance in said contaminated soil;

Cd = 0, 10 - 1 ,00 mg/kg of dry substance in said contaminated soil;

Pb = 1 ,00 - 10,00 mg/kg of dry substance in said contaminated soil; and

Zn = 5,00 - 50,00 mg/kg of dry substance in said contaminated soil; by means of transforming thereof into construction material, which should be acceptable for the environment and human health, in which the content of said chemical elements in a form of water soluble compounds of heavy metals should not exceed the following values:

As≤ 0,50 mg/kg of dry substance in such obtained construction material;

Cd≤ 0,04 mg/kg of dry substance in such obtained construction material;

Pb≤ 0,50 mg/kg of dry substance in such obtained construction material;

Zn≤ 4,00 mg/kg of dry substance in such obtained construction material;

wherein such obtained construction material should be inert and chemically neutral.

Remediation of the soil contaminated with compounds on the basis of arsenic As is disclosed in CN102974601 A. Such remediation is based on mixing of contaminated soil with montmorillonite, lime, magnesium carbonate and water. By means of such process, the content of As can be reduced below a pre-determined value, but the obtained products are at least slightly alkaline and not chemically neutral, and are as such therefore still harmful for the environment.

The present invention refers to a process for obtaining health- and environment acceptable, chemically neutral and inert construction material, wherein the concentration of water soluble compounds of heavy metals in such material does not exceed pre-determined limit values, namely

As < 0,50 mg/kg of dry substance in such obtained construction material;

Cd≤ 0,04 mg/kg of dry substance in such obtained construction material;

Pb≤ 0,50 mg/kg of dry substance in such obtained construction material;

Zn≤ 4,00 mg/kg of dry substance in such obtained construction material;

and wherein said material is obtained from a contaminated soil containing water soluble chemical compounds of heavy metals, which are harmful for the environment and human health, wherein the concentration thereof essentially exceeds the previously mentioned limit values, namely

As = 1 ,00 - 10,00 mg/kg of dry substance in said contaminated soil;

Cd = 0, 10 - 1,00 mg/kg of dry substance in said contaminated soil;

Pb = 1 ,00 - 10,00 mg/kg of dry substance in said contaminated soil; and

Zn - 5,00 - 50,00 mg/kg of dry substance in said contaminated soil.

The process according the invention comprises the following steps: 0 i) preparation of the contaminated soil, which includes excavation, separation of dry particles of contaminated soil by means of sieving in order to obtain fractions below 32 mm and above 32 mm, upon which the fraction of particles above 32 mm is crushed to granulation below 32 mm and temporarily deposited;

ii) mixing of such obtained and prepared contaminated soil according to step i) with a dispersion of Fe-nanoparticles;

iii) adding dry bentonite clay in powder form to said mixture of prepared contaminated soil and Fe-nanoparticles by taking into consideration content of the clay fraction within the contaminated soil itself, which is then followed by homogenization of such obtained mixture; iv) adding calcium electrofilter ash (EFP), which is followed by mixing and optionally adjusting of moisture to optimum value, which can deviate up to ± 2 %.;

v) in-situ or ex-situ application of such obtained material by spreading to layers having thickness up to 30 cm and compacting such established layer of construction material by means of suitable building machinery. The average density of such compacted layer is > 95 % of the density of the mixture, which is obtained by means of modified Proctor method (SIST EN 13286-2:2010/ AC:2013). The lower value of density can deviate up to 3 % in average.

Said dispersion of Fe-nanoparticles, which is added to the soil in step ii), contains up to 8 wt.% per weight of maghemite particles, or up to 3 wt.% of nZVI per weight of a dry contaminated soil.

Said bentonite clay is added in said step iii) in amount up to 10 % per weight of a dry contaminated soil.

Whenever the content of clay fraction or particles with granulation < 0,002 in the soil is high (according to classification (SIST EN ISO 14688-1 :2002/AC:2008), then the zeolitic tuff in powder form, is added to the mixture of contaminated soil and dispersion of Fe-nanoparticles instead of said bentonite clay. Such circumstances occur, if the content of clay, namely particles with granulation < 0,002 in the soil (SIST EN ISO 14688-1 :2002/AC:2008), exceeds 40 wt. % of the dry weight of the contaminated primary soil, and is pursuant to geotechnical classification (SIST EN ISO 14688-1 :2002/AC:2008) marked as CI, siCl, saCl, sasiCl, grCl or grsiCl.

Said zeolitic tuff is added in amount up to 10 wt.% per weight of a dry contaminated soil. The quantity of said calcareous fly ash (CFA) amounts up to 20 wt. % per weight of dry contaminated soil.

The object of the invention is therefore in-situ processing as well as in-situ or ex-situ processing as well as in-situ or ex-situ application of such processed contaminated soil by transforming it into a construction material for structural fills or embankments or a dam.

Previously mentioned excessive concentrations of water soluble zinc (Zri), cadmium (Cd), arsenic (As) and lead (Pb) are by means of such process reduced below the previously mentioned limit values.

Said process for transforming of each contaminated soil into a building construction material by means of combination of mechanical, chemical and geotechnical measures. Amendments used for remediation are represented by nanoparticles of zerovalent iron (nZVI) or maghemite nanoparticles, calcareous fly ash resulting from coal combustion, or zeolitic tuff.

Metals as pollutants are present in the environment merely due to human activities, in particular industrial activities. Their influence on environment is however not depending exclusively on concentration thereof, but in particular on their content in easily soluble mobile fraction. A degree of pollution of waste materials is pursuant to Slovenian legislation determined by means of a standardized test, which is based on extraction with water. Said test is performed for 24 hours by means of shaking, wherein the ratio between the material and water is 1 : 10, and the granulation of material is below 10 mm (SIST EN 12457-4:2004). Concentration of wastes in the water-extracted substance determines each degree of pollution and declares each waste material either as inert, acceptable or harmful. In order to protect the environment, the hazardous waste materials, which contain metals in high concentrations and are not suitable for deposition, must be remediated. Remediation leads to immobilization of content of metals in easily soluble fraction, upon which the standardized test for determining of each chemical properties of contents (SIST EN 1744-3:2002) is used in order to prove that concentration of each particular pollutant in each water-extracted substance does not exceed the value as prescribed for inert wastes. In this, the process of extraction is very similar, since the ratio between the weight of remediated material and the volume of water is 1 : 10, and the material is exposed to mixing by means of a standard impeller mixer. Concentration of the pollutant in the water-extracted substance determines a degree of immobilization of harmful metals in each remediated material, which shall not exceed the previously mentioned limit values.

The process according to the invention proposes a new and inventive approach for resolving of problems related to environment pollution. Such technology enables restoration of seriously degraded areas resulting from long-term industrial activities. These are mainly areas of iron and steel processing plants or metallurgical-chemical plants, where in particular inorganic pollutants were released to the air, water and soil, and where huge amounts of industrial waste were deposited. When industrial activities were terminated, these areas remain not only degraded and inoperative but also represent a permanent problem of pollution of the environment due to surface and underground water streams and also due to emission of powder dust particles.

Heavy metals like Zn, Cd, Pb and As, and also their compounds, are usually present in the environment as pollutants, which are in essential concentrations present in a water-soluble and mobile fraction. The environment may also be polluted with other elements, and moreover, the problems may also occur due to high values of water-soluble sulfate ions.

Arsenic As is the element, which belongs to semi-metals. Due to intensive application thereof in agriculture (manures, nutrition additives, spraying agents), in leather-processing and wood- processing industry, namely in protection of wood by CCA (abbreviation for chromated copper arsenate), due to emissions by ore-processing and metallurgical activities, or by coal combustion, arsenic is deemed to be a commonly present environment pollutant. In the soil, arsenic is commonly present in the form of oxyanions As(III) in As (VI), which are present in the form of inorganic complexes or organic compounds. Harmful influence of arsenic to the human body reflects in symptoms in view of vascular disorders, skin diseases and increasing the risk of cancer.

Cadmium Cd is a metallic element with a low melting point, and is one of the most mobile and harmful heavy metals. Where the soil has been polluted with cadmium as a consequence of metallurgical activities, cadmium is always present together with zinc Zn, wherein the concentration of cadmium Cd is usually approximately 200-times lower than the concentration of zinc Zn. Another source of pollution with cadmium is waste resulting from Ni/Cd batteries, waste resulting from steel-processing industry and manufacturing of pigments, as well as intensive application of manures containing cadmium. The commonly present form of cadmium in the soil is Cd(II). Regarding the organisms, cadmium is a non-essential element, which induces numerous harmful effects and symptoms, in particular chronical diseases of kidneys and bones, enzyme disorders and increasing the risk of cancer.

Lead Pb is due its malleable properties, specific density and low melting point one of the most useful heavy metals, but is also a harmful non-essential metallic element. Pollution of the soil with lead usually results from processing of lead ores, metallurgical industry, manufacturing of pigments, and also from inappropriate treatment of waste resulting from lead batteries, water piping system, weapons etc.. The most common form of lead in the soil is Pb(II), which, depending on conditions in each area, forms numerous inorganic or organic compounds. Harmful effects of lead Pb are seen in disorders of internal organs, kidneys and central nervous system, and the consequences are often deadly.

Zinc Zn is an essential metallic element, which is in small quantities required for regular functioning of organisms. It is also widely used for anti-corrosion protection (as sacrificed anode) in metal-processing industry. Pollution of the soil with zinc Zn merely results from metallurgical industry and mining activities, intensive application in agriculture, or also from sewage water and household waste. The most common form of zinc in the soil is Zn(II), which forms various inorganic compounds. For organisms, Zn is in higher concentrations toxic. Poisoning with zinc Zn results in enzyme functioning disorders and disorders in functioning of internal organs.

In the practice, the following activities are normally performed prior to starting the initial step of preparation of the contaminated soil:

- cutting down and removing plants, animals and eventual municipal wastes;

- arranging temporarily infrastructure, which is required for initiation of operations, which can be performed under a tent or in other covered area, by which the emission of dust particles is prevented including contamination of the surrounding therewith, wherein also the workers must be furnished with appropriate personal protective requisites.

Preparation of the contaminated soil in the sense of the process according to the invention furthermore includes:

- digging excavation of the contaminated soil;

- separation of the soil by means of sieving to fractions below 32 mm and above 32 mm, - crushing of fraction above 32 mm to a fraction below 32 mm;

- building a temporary deposition in the form of layers and in accordance with geotechnical procedures, by which the material is properly homogenized;

- performing a chemical analysis of such deposited material; and upon that

- making a decision about the way of remediation, depending on results of chemical analysis and concentration of elements in water-soluble mobile fraction (test in accordance with a standardized method for characterizing waste on the basis of extraction pursuant to SIST EN 12457-4:2004).

Temporarily intermediate deposition of the polluted soil is performed as follows:

- each fundamental ground must be clean and flat;

- deposition consists of layers, the thickness of each layer is up to 0,5 m, and the complete height of the deposit is 5 m at maximum;

- the material must be protected against meteorological influences.

A subsequent step in the process includes mixing of the contaminated soil with a dispersion of iron nanoparticles, in which the substrate is water, and which are either maghemite particles in some higher quantity up to 8 wt.%, or NZVI in smaller quantities up to 3 wt.%, both relative to the weight of a dry contaminated soil. Said mixing is performed in closed mixing systems, in which the moisture is maintained slightly above the optimal one, unless the nanoparticles are satisfactory dispersed within the contaminated soil.

During a still further stage of remediation, up to 10 wt.% of dry bentonite clay in powder form per dry weight is added to said wet mixture, depending on geo-mechanical properties of the soil, wherein the quantity of added clay is lower, if the content of clay fraction in a contaminated soil is higher, upon which such mixture is appropriately homogenized.

Whenever the content of clay fraction or particles with dimensions < 0,002 mm (pursuant to classification SIST EN ISO 14688-1 :2004/AC:2008) in the primary contaminated soil is relative high, 10 wt.% of dry zeolite tuff in powder form is added to the soil instead of said bentonite clay, upon which such obtained mixture is appropriately homogenized.

This happens when the primary contaminated soil comprises more than 40 wt.% of the clay fraction, namely particles with dimensions < 0,002 mm (pursuant to classification SIST EN ISO 14688- 1 :2004/AC:2008) per weight and is pursuant to geo-technical classification (SIST EN ISO 14688-2:2004) marked as CI, siCl, saCl, sasiCl, grCl or grsiCl.

Just prior to application, 20 wt.% of calcium electrofilter ash (EFP) is added to such obtained mixture, wherein the final mixing must assure an efficient distribution of added calcareous fly ash (CFA) within the complete media. Prior to termination of said mixing, the moisture is optionally adjusted to such optimal value, which enables achieving of each desired density of each layer.

The material is spread in layers having thickness up to 30 cm each. Then the layers are compacted by means of rollers with a required energy. The density of each layer must be in average at least > 95 % of the density of mixture achieved according to modified Procter method (SIST EN 13286-2:2010/AC:2013). The lower limit value of density can vary relative to the average value for 3 % at maximum.

After 28 days, a specimen is taken from such applied layer, upon which a chemical analysis of the water-extracted leaching from a remediated material is performed. Said material is prepared in accordance with standardized method of extraction as used in examination of chemical properties of aggregates (SIST EN 1744-3 :2002), by which the inertness of the construction composite is proven.

Having regard to particles with dimensions within the range of micro- and millimeters, nanoparticles excel much larger specific surface area and reactiveness, which enhances the efficiency of remediation. Nanoparticles of zerovalent iron (nZVI) are efficient reductants, since the elementary iron Fe° in contact with water oxidizes to Fe ²⁺ in Fe ³⁺ and electrons are released. Such obtained iron oxyhydroxides have high absorption properties. Remediation capability of nZVI is highly depending on pH and configuration of the remediated soil, nanoparticles of zerovalent iron (nZVI) are efficient in immobilization of two-valent and three-valent ions of heavy metals (As(III), Pb, Cd, Zn) and five-valent arsenic As(V). Mechanism of specific adsorption of heavy metals depends on standard redox potential (E ) of each metallic pollutant in comparison with standard redox potential Fe° of elementary iron. Metals having more negative or equal E° like Fe° of elementary iron in nZVI (like cadmium Cd, zinc Zn) can be removed exclusively by mechanism of specific adsorption on the surface of iron oxyhydroxides. Ions of metals and semi-metals (like e.g. arsenic As), the E of which is much more positive than Fe of the elementary iron, can be immobilized either by mechanisms of adsorption or reduction.

Maghemite iron nanoparticles are formed of mineral maghemite Fe ₂ Oi, In the presence of electromagnetic adhesion forces, they express supraparamagnetic properties. By maghemite nanoparticles, the mechanism of immobilization of heavy magnets is similar like by zerovalent iron nanoparticles nZVI. Surface adsorption processes are dominant, wherein the most efficient processes are specific adsorption or chemisorption and coprecipitation. In this, heavy metals are bond directly to oxide groups≡FeOX of maghemite nanoparticles, and stable surface complexes are formed and integrated into a crystalline lattice.

Iron nanoparticles due to adhesive electromagnetic forces on the surface thereof adhere to the surface of particles within the polluted soil. During the processes of oxidation and transformation to iron oxyhydroxides they form coverings, which physically immobilize contaminants. Such obtained iron hydroxides express amphoteric properties and the capacity of adsorption of heavy metals at various pH values. By slightly acid pH values, they adsorb anions and oxyanions due to process of protonation. By neutral or slightly alkaline pH values, they adsorb cations and cationic complexes due to process of deprotonation.

Calcareous fly ash consists merely of crystalized inorganic particles, predominantly the following minerals: anhydrite CaSO^ lime CaO, hematite Fe ₂ 0 ₃ , quarz S1O2, melilite Ca ₂ (Mg, Al)(Al, Si) ₂ 0 ₇ , mullite Al ₆ Si ₂ Oi3, merwinite Ca ₃ Mg(Si0 ₄ ) ₂ , periclase MgO, tricalcium aluminate Ca ₃ Al ₂ 06, gehlenite Ca ₂ Al(AlSi07), anorthite CaAl ₂ Si ₂ 0s, akermanite Ca ₂ Mg(Si ₂ 07) and some others. The majority of ash represent glassy-like silicate particles (up to 70 wt.%). The main chemical components of calcareous fly ashes are Si0 ₂ , Al ₂ 03, CaO, FeO and SO3. Due to high content of free CaO (not less than 5 wt.%, in average around 7 wt.%), such ashes express latent hydraulic and puzzolan properties, and in contact with water form hydration products, which are similar to those formed by hydration of Portland cement. Such processes lead to chemical and physical immobilization of heavy metals in each obtained mineral phases.

Processes of immobilization of heavy metals in the contaminated soil are enhanced by increasing pH value thereof thanks to neutralization of acids due to adding calcium electrofilter ash EFP. Metallic elements in alkaline conditions express pure mobility. By hydration of silicate phases, calcium silicate hydrates C-S-H are formed. By hydration of aluminate phases, minerals from the group of ettringite (4 -phase) and monosulphate hydrates (^ w-phase) are formed. Thanks to application of calcium electrofilter ash EFP, processes of hydration and solidifying lead to solidification of contaminated soil and physical immobilization of heavy metals. Contaminant Mechanism of immobilization in processes of hydration of Calcium electro filter ashes (EFP)

Integration into a crystal grid of Ca-Etringitte

As CaeAhiSO 4)i(OH) _\2 i2H ₂ O as well as coprecipitation and specific

adsorption on the surface of iron minerals.

Formation of poorly soluble double salts CdCa(OH)4 by substitution with Ca during formation of portlandite Ca(OH) ₂ and calcium

Cd silicate hydrates (C-S-H gel). Alternative mechanism is precipitation

of poorly soluble carbonate mineral otavite CdCOi or cadmium

orthosilicate Cd ₂ i0 ₄ .

Precipitation of minerals on the surface of calcium alumino-silicate

Pb hydrate minerals in the form of sulphate anglesite PbSO^ carbonate

cerusite PbCO and hydroxides Pb(OH) ₂ -

Precipitation of poorly soluble calcium zincate CaZri2(OH)ex2H ₂ 0

Zn on the surface of calcium alumino-silicate hydrates and mineral

smithsonite. Zinc hydroxides Zn(OH)2 and; other poorly soluble

compounds are formed.

Zeolites are alumino-silicate minerals with a porous cage-like crystalline structure, which enables cationic exchange and consequently adsorption of contaminants. In remediation of soil, artificial zeolites type A, X, Y or P are often used, which can be obtained by means of hydrothermal synthesis of natural or artificial materials. Major natural resources of zeolites worldwide are available in the form of zeolite tuffs, in which the content of zeolites is varying from 40 wt.% up to >90 wt.%. Usually are formed of the following zeolite minerals: analcime NaAlSi ₂ O ₆ -H ₂ 0, clinoptilolite (Na ₂ ,K ₂ , a) ₃ Ale iio0 ₇₂ x21H ₂ 0, heulandite

(Ca,Na2) ₃ AkSi ₃ o0 ₇₂ x21H ₂ 0, mordenite (Ca,Na2)Al ₈ Si ₄ Og6x28H ₂ 0, chabazite (Ca,K2,Na2) ₂ Al ₄ Sis0 ₂₄ xl2H ₂ 0, phillipsite K2(Ca,Na2,) ₂ AkSiio0 ₃ l2H ₂ 0 and some others. In addition to minerals, zeolitic tuff contain silica, minerals from the group of clay, amorphous phase and some other minerals, the content of which is less than 3 wt.%.

The crystalline lattiec of zeolites is formed by tetrahedrons S1O ₄ and AIO ₄ , which due to exchange of Si ⁴⁺ with Al ⁱ⁺ form negative charged surface sites, which can be filed with cations of heavy metals and alkalis. Adsorption capacity of zeolites depends on the ratio (Si + Al) : 0 = 1:2 and Si.Al, where the number of aluminium Al atoms determines the number of positive charges of adsorbed cations. The crystalline lattice forms a matrix of interconnected channels - a mesoporous structure with dimensions approximately 0,4 to 0,7 nm. During the process of remediation of the soil, water solutions of contaminants from the soil penetrate there-into. These are then in a non-specific manner adsorbed on free adsorption sites, or are exchanged with Na ⁺ , K^, Ca ²⁺ or Mg ²⁺ ions. In this, zeolites express the ability of selective adsorption, namely enhanced affinity in view of removing certain cations of heavy metals (e.g. a very common zeolite mineral clinoptilolite: Pb ²⁺ > Cc? ⁺ > Zn ⁺ ). The efficiency of adsorption essentially depends on pH value of the soil, since at low pH values protonation of free adsorption sites protonation occurs, by which the cations of heavy metals are replaced with ΐ? ^' .

Bentonite clay is a mixture of minerals, in which the minerals from the clay group, are predominant, usually montmorillonite ( yX nH ₂ 0)(Al ³⁺ 2- _y Mg ²⁺ _y )Si ⁴⁺ ₄ 0io(OH)2, wherein ^4" represents cations, which are bond to exchangeable sites. Said mineral belongs to the group of 2 : 1 phyllosilicates - smectites, which consists of aluminium oxide (O) octahedral layers, integrated between two silicium oxide (T) tetrahedral layers, or simplified, Γ-0-Γ layers. Negative surface charge is generated on the complete surface of the mineral. Due to isomorphic changes substitution Si ⁴ * with Al ³⁺ in said tetrahedral layer and Al ³⁺ with Mg ²⁺ in said tetrahedral layer. Negative electric charge and large specific surface of bentonite clay enable ionic exchange and adsorption of cations of heavy metals (Pb ²⁺ , Cd ²⁺ , Zn ²⁺ ). Here is included a mechanism of specific adsorption contributes by binding of cations directly to oxygen ligands and form tetrahedral or octahedral layers. Less efficient and more reversible is a process of non-specific adsorption, which occurs by adsorption of hydrated cationic complexes on the surface of tetrahedral layer, where increasing of pH value leads to precipitation of adsorbed contaminant. Major influence to adsorption processes of cations has the pH value of the soil. Processes are more efficient at alkaline pH values, namely in the absence of exchange between cations of heavy metals and H* ions, by which deprotonation of adsorption locations takes place.

Adsorption of anions to clays occurs at pH values <7 and on the borders of T-O-T layers of clay minerals, where the defects are most numerous and cations Al ³⁺ , Si ⁴⁺ are maximally exposed.

When pH values are low, by excessive ¥ a process of hydrolysis and formation of silanol ≡SiOH and aluminol≡AlOH groups is induced, due to which the bridging oxygen bonds Al-O-Si in tetrahedrons and octahedrons are split. In this, excessive positive charge is generated, which enables binding of anions or anionic complexes, for example five-valent arsenic As(V), which is at low pH values available as H2ASO4 or HAsO ^~ .

Said bentonite clay expands in contact with water, as soon as the molecules of water are introduced between the layers T-O-T. Pozzolanic reactive materials contain alkalis, mostly in the form of, as well as reactive glass-like phase and alumino-silicate minerals. Mixture of calcium calcareous fly ash and aluminosilicates in the form of clays or zeolites by adding water can result in formation of products of a pozzolanic reaction. Such products additionally contribute to stabilization and binding of remediated soil. Glass in zeolite tuffs, bentonite clays and calcareous fly ash CFA, alumino- silicate minerals (e.g. clays, zeolites, various aluminosilicates in said calcareous fly ash CFA) as well as sufficient content of free lime CaO in said calcareous fly ash CFA, are components, which by adding water lead to pozzolanic reaction.

In pozzolanic reactions, both with zeolites and clays, quite similar reaction products are obtained like in hydration of Portland cement. This means that immobilization mechanisms of pollutants in the soil are similar and include both a chemical immobilization (coprecipitation and integration into newly formed materials) and also physical immobilization within a cemented matrix.