INTEGRATED PROCESS FOR DISPOSAL OF ORGANIC MATRICES

Abstract

 A process for decontaminating a contaminated organic material comprising or consisting of ion-exchange resins embedding toxic and/or radioactive pollutant ions, comprising the following steps:
a) subjecting said ion-exchange resin to a mineralization process in water by adding an oxidizer in the presence of catalysts based on iron sulphate, copper sulphate, or mixtures thereof;
b) recovering contaminated inorganic compounds;
c) preparing a stable matrix for the confinement and embedding of contaminated inorganic materials recovered in stage b)
characterized in that
stage b) comprises the following stages:
b1) adding the aqueous mixture from stage a) with an aqueous solution of an alkali metal hydroxide until a pH value of or above 9, preferably of between 9 and 11, still more preferably of 10 is reached for facilitating a precipitation and/or co-precipitation of said inorganic mineral compounds containing said toxic and/or radioactive metal ions;
b2) adding the suspension obtained in stage b1) with zeolites, in order to embed the residual ions of several toxic and/or radioactive metals, more preferably those of cesium, the compounds thereof being soluble at the alkaline pH of the solution; and said stage b2) being performed under vigorous and constant mixing subsequently to stage b1);
b3) separating the solid residue from the reaction mixture from stage b2) by filtration or subsequent decanting of the suspension and subsequent centrifugation of the decanted mixture.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an ameliorating process for treating ion-exchange resins containing toxic and/or radioactive ions by mineralizing said resins with a wet oxidation process and embedding the contaminated material in a stable confinement matrix.

BACKGROUND ART

[0002] A known process for decontaminating industrial wastewater or nuclear process water, which are loaded with toxic and/or radioactive contaminants, mainly consisting of metal cations, is to remove said pollutant species by ion-exchange resins capable of embedding the same.

[0003] To date, there is no universally recognized strategy for handling said spent resins. In the nuclear field, the most used one is to incorporate these contaminated resins directly in cementitious matrices, without prior treatment.

[0004] However, the predominantly organic nature of ion-exchange resins mainly accounts for the low loading factor in a cementitious matrix, resulting in the increase in the waste volume, in the long-term instability of said cementitious matrices and in the swelling thereof.

[0005] On the other hand, a wet oxidation process is known which allows said resins to be mineralized by an oxidation process otherwise referred to as "Fenton wet oxidation" [1].

[0006] The wet oxidation process consists in an oxidation reaction of the organic substances in the aqueous phase by means of an oxidizer, such as hydrogen peroxide, and in the presence of appropriate catalysts, such as iron and/or copper sulphates [1].

[0007] The process temperature ranging between 70 and 100°C boosts the oxidation kinetics, facilitating the conversion of the organic substance in carbon dioxide and water. The chemical energy of the aqueous compounds is converted into thermal energy which is recoverable intrinsically and/or extrinsically to the process itself. Further, the wet oxidation is conducted at ambient pressure and does not produce dust or ash emissions.

[0008] Upon completion of the wet oxidation process, three different physico-chemical types of products are obtained:

• a gaseous effluent: mainly consisting of carbon dioxide CO₂, water vapor H₂O, in addition to oxygen O₂. Further, the compounds NO_x and SO₂, mainly resulting from the decomposition of the functional groups -N(CH₃)₃OH and -SO₃H, respectively, are detected despite their very low concentrations. A very small part thereof usually consists of small-sized residual volatile organic compounds.
• a liquid effluent: a highly biodegradable effluent containing low-molecular organic acids, inorganic acids, ammonia and inorganic salts, intended for subsequent treatment;
• a solid residue: waste residual fraction, almost of inorganic nature, which can be disposed of.

[0009] Chemically, the wet oxidation reaction takes place in acidic environment and uses the hydrogen peroxide (about 35 wt.% based on the total weight) and catalysts, such as those iron- or copper-based, for example in sulphate form. It is thereby possible to obtain highly reactive radicals breaking down the organic matrix, resulting in a residual mineralization solution or composition [1].

[0010] According to such a process, once the residual mineralization solution or composition has been obtained, the latter must undergo an evaporation step. However, the evaporation step is particularly long-lasting and energy intensive. Further, especially when the waste organic matrix to be processed is a radioactive waste, being, for example, an ion-exchange resin employed in nuclear plants, the risk exists of mobility and dispersion of the most easily volatile radionuclides. Since it is not advisable to operate under negative pressure, it is necessary to conduct the evaporation at milder temperatures (70-80°C). In this case, in order to cause a complete and efficient evaporation of 1L of mineralization solution, at least 12 hours are needed.

[0011] Another issue to face is related to the residue obtained from the wet oxidation reaction, which cannot be employed or encapsulated directly in a slurry forming a cementitious matrix, as the residues obtained from the wet oxidation process are strongly acidic (acidic pH, such as near or below 1) and rich in sulphates. That is, the residues possess a low loading factor in a conventional cementitious matrix [1].

[0012] A first response to sulphate reduction for a possible conditioning in a cementitious matrix has been proposed in the past, for example by the Patent Document IT1206839. In this Patent Document, the authors suggest using a soda solution NaOH to decontaminate the mineralized solution from main contaminants. However, the abatement of several contaminants, such as strontium or cesium, requires the newly decontaminated solution to subsequently pass through adsorbing filters filled with special zeolites. All these secondary steps require significant amounts of water, therefore, in order to be able to proceed with the encapsulation of the contaminated material in the cement, the suspension should be previously concentrated, which accordingly involves a significant energy consumption in this case as well, and a potential production of secondary waste.

[0013] There exists a need to have a sustainable, simple and efficient integrated process allowing to embed such residue in a confinement material which is stable over time, thanks also to good mechanical properties thereof.

SUMMARY OF THE INVENTION

[0014] The Applicant has now found that it is possible to solve the problems above by the process constituting the subject matter of the present invention.

[0015] The inventive process also envisages a stage a) of mineralizing the ion-exchange resin in water by adding an oxidizer in the presence of catalysts selected from: iron sulphate, copper sulphate or respective mixtures of other metals (Al, Ce, Co, Mn, Ru) and compounds thereof, materials to be employed in heterogeneous oxidation mode, such as metal powders and oxides, fly ash, blast furnace slag, iron ore, clays such as kaolin and/or vermiculite, and other potential recycled materials containing catalyst metals[1];

a stage b) of recovering contaminated inorganic compounds,

and a stage c) of preparing the confinement matrix with inorganic materials.

[0016] However, stage b) is different as it comprises the following stages:

b1) adding the aqueous mixture from stage a) with an aqueous solution of an alkali metal hydroxide until a pH value of or above 9, preferably of between 9 and 11, still more preferably of 10, is reached. Thereby, the inorganic compounds of said toxic and/or radioactive metal ions precipitate and/or co-precipitate. A key role is played by the high iron content in solution which, being used as a catalyst, allows to obtain high decontamination yields even when the contaminants exist as trace radionuclides, and therefore the solubility products of the respective hydroxides are not sufficient to cause their precipitation to occur directly. In this case, the precipitation of iron in the form of hydroxide leads to co-precipitation of the other contaminants.

b2) adding the suspension obtained in stage b1) with zeolites, in order to embed by ion-exchange or adsorbtion the toxic and/or radioactive metal ions, more preferably those of cesium, the compounds thereof being soluble at the alkaline pH of the solution.

Step b2) occurs subsequently to stage b1) under vigorous and constant mixing.

[0017] Further, unlike the process described in the aforementioned Italian Patent, the addition of the zeolitic material is not performed on the filtered solution from which the pollutant metal ion compounds have been removed by addition of sodium hydroxide, but the zeolite is rather added directly to the aqueous suspension in which the pollutant metal ions have been or have simultaneously precipitated in alkaline environment; therefore, the concentration of the aqueous solution/suspension from stage a) is no longer necessarily performed.

[0018] Indeed, stage b3) of separating the solid contaminated material from the aqueous solution only consists in a filtration or decanting stage followed by centrifugation. The inventive process has the following advantages:

• as pointed out above, the evaporation step following the wet oxidation process is not necessarily performed; this step is replaced by that of decontamination by precipitation and/or co-precipitation and/or adsorption of contaminants. The potential mobility and volatilization of several nuclides possibly existing in the organic waste material is thereby limited;
• overall, a simplification of the process is achieved; energy consumption, process times and production costs are minimized;
• most contaminants, even when radionuclides such as cesium are present, are removed by precipitation and/or co-precipitation and/or adsorption in a single process stage or step by means of materials constituting the subsequent encapsulation matrix, thus without needing to provide secondary special measures for the removal thereof (such as, for example, filters with selective adsorbent materials, such as those mentioned in the patent cited above);
• the contaminated residue, i.e. the residue including all the contaminants, can be encapsulated directly in pastes forming a stable and sustainable, preferably geopolymeric, inorganic confinement matrix[2];
• it is an integrated and easily industrially scalable process.

DESCRIPTION OF THE FIGURES

[0019] Figure 1 depicts the leached mass fraction of the matrix constituents (Figure 1a) and of the contaminants (Figure 1b) as a function of time, assessed by immersion test according to the ANSI/ANS-16.1.2003 (R2017) protocol.

[0020] Figure 2 reports the leaching index of the matrix constituents (Figure 2a) and of the contaminants (Figure 2b) as a function of time, assessed by immersion test according to the same protocol used to perform the tests referred to in Figure 1.

DETAILED DESCRIPTION OF THE INVENTION

[0021] For the purposes of the present invention, the definition "comprising" includes the presence of further stages or components which are not expressly listed after this definition.

[0022] Instead, the definitions "consisting in", "consisting of" exclude the presence of further components/stages which are not expressly mentioned.

[0023] For the purposes of the present invention, pollutant material means a material comprising or consisting of spent ion-exchange resins containing toxic and/or radioactive material.

[0024] Such ion-exchange resins are preferably cation-exchange resins or mixtures of cation- and anion-exchange resins.

[0025] The spent cation- and anion-exchange resins used in stage a) are those usually employed to capture and fix contaminants, for example cationic resins such as: Amberlite IRN 77, Amberlite IR 120, Purolite NRW 100, Aldex C-800 H, Dowex HGR NG H; and anionic resins such as: Amberlite IRN 78, Amberlite IRA 410, Purolite NRW 400, Dowex SBR LC NG.

[0026] The cation-exchange resins are used for capturing pollutant cations Mⁿ⁺ (n = 1, 2, 3, etc.) of alkali metals, alkaline-earth metals, transition metals, lanthanides, actinides and mixtures thereof.

[0027] The anion-exchange resins are used for capturing pollutant anions of transition metals and halogens (TcO₄^-, MoO₄^2-, I^-, Cl^-, etc.).

[0028] The spent cation-exchange resin, for example, contains stable nuclides selected from those of cobalt, strontium, nickel, cesium and mixtures thereof; whereas the spent anion-exchange resin contains stable nuclides such as iodine.

[0029] The contaminated organic material in stage a) may in turn comprise other carbonaceous materials in liquid or solid state such as solvents and/or mixtures thereof, such as liquid scintillation radiometric measurement cocktails, or tributyl phosphate/kerosene for hydrometallurgical separation, and further nuclear grade graphite dust, contaminated with toxic and/or radioactive ions [1].

[0030] The contaminated organic material may comprise or consist of urban, industrial waste water, up to aqueous effluents with high dissolved organic content, such as surfactants and mixtures thereof, contaminated with toxic and/or radioactive ions [1].

[0031] The starting pollutant material employed in stage a) of the inventive process, in addition to containing stable nuclides of cobalt, strontium, nickel and cesium, could also contain iodine. And in this case, in the process of the present invention, most of it is released in the off-gas and can be collected after deposition in the condenser, whereas about 10% w/w remains in the mineralization solution.

[0032] To solve this problem, the part remaining in solution can be precipitated as silver iodide in stage b 1) by adding silver nitrate or in stage b2) by adding zeolites, preferably activated with silver ions.

[0033] The temperature in stage a) is preferably ranging between 70 and 100°C, instead the pH is preferably ranging between 0.5 and 3, more preferably between 1 and 2.

[0034] The alkali hydroxide added in stage b1) is preferably selected from sodium and potassium hydroxide.

[0035] For the purposes of the present invention, the zeolites used in stage b2) of the process constituting the subject matter of the present invention are contained in a tuff having a high surface area, which is added in weight ratios ranging between 100 and 400 with respect to the amount of toxic and/or radioactive alkali metal ion.

[0036] The zeolite is preferably selected from: chabazite, mordenite, clinoptilolite, erionite, stilbite, heulandite, but more preferably chabazite and clinoptilolite [3].

[0037] By the inventive process it is possible to decontaminate nickel, cobalt, strontium >97%, preferably >98% by weight, and cesium in amounts >92%, preferably >95% by weight, based on the total weight of the corresponding elements contained in the starting ionic resin (see Tables 1 and 2).

[0038] The tuffaceous material, used for construction purposes in the Opus Caementicium of ancient Rome, is preferably selected as a precursor in the inorganic matrix since it is naturally rich in zeolites, thanks to its great durability over time, and to its wide availability and low-cost obtainability with limited environmental impact. Indeed, as sole pre-treatment, it only requires grinding instead of energy-intensive calcinations as in the case of metakaolin or clinker. The main technical reason for selecting this material is the proven retention of radionuclides through ion exchange, which makes cesium sequestration efficient during the decontamination of the mineralization solution [3].

[0039] In the inventive process, adding zeolite and particularly tuff in step b2) involves that stage b3) does not require energy-intensive stages such as concentrating the aqueous suspension.

[0040] Further, adding zeolite and particularly tuff does not involve adopting special expedients to carry out the preparation of the confinement matrix.

[0041] The inorganic matrix obtained in stage c) is preferably a geopolymeric matrix selected due to its improved sustainability, stability and compatibility with sulphates compared to conventional cementitious matrices [2].

[0042] For the purposes of the present invention, geopolymer means a compound of inorganic polymers derived from the chemical reaction, at room temperature, between aluminosilicates constituting the precursor materials, alkaline solution and any additives. The prefix "geo" refers to the chemical composition and mineralogical structure of the material similar to that of natural rocks.

[0043] Indeed, in the process according to the present invention, stage c) of preparing the geopolymeric matrix comprises in particular the following sub-stages [2]:

c1) adding the precipitate from stage b3) with waste precursors containing aluminosilicates, an activator consisting of an alkali metal hydroxide and water, and any further additives capable of facilitating the workability of the slurry and the filling of the material in a mold or formwork;

c2) curing the material from preceding stage c1) for a time comprised between 14 and 90 days, preferably of 28 days.

[0044] As waste materials, blast furnace slag, fly ashes or mixtures thereof, black electric arc furnace slag, bauxite residue, mining waste, urban or food industry waste ashes (palm oil, grain husks, and mixtures thereof) are preferably added; as activator, sodium hydroxide, preferably in pellet or chip form, and finally alumina as additive capable of boosting the reactivity.

[0045] Once hardened, the geopolymeric material obtained by the inventive process has leaching indices, both for the constituents of the matrix and the contaminated materials embedded therein, higher than the minimum reference value generally imposed by the national regulatory authority on this category of waste (i.e. lower limit leaching index equal to 6), thus exceeding the acceptability threshold before accessing a future repository.

[0046] Further, mechanical compression tests were conducted on the group of reference specimens and on the one from the water immersion test to simulate in a simple and conservative way a potential accidental scenario of the future repository (post-immersion). As reported in the Table 2 below, the specimens containing the residue after the leaching test showed a higher resistance to compressive strength. Probably, this difference has to be attributed to the heterogeneous presence of defects (voids and microfractures) in the samples rather than to a real ameliorating effect resulting from the immersion in water [2]. In any case, the result can be considered very promising for future application.

[0047] The following examples are reported for illustrative purposes of the process according to the present invention.

EXAMPLES

Example 1 applied only on cationic resin.

Wet oxidation step

[0048] In particular, a surrogate waste was prepared loading (> 80% by weight on the total weight) the cationic resin (in this case, 100 g of DuPont cationic resin Amberlite IRN77, exchange capacity ≥ 1.8 meq/mL) with solutions containing several stable nuclides (Cs, Co, Sr, Ni) selected as representatives of important contaminants and radioactive activation and fission products. The total amount of said nuclides loaded into the resin is as follows: 5.3 meq of Co and Ni, 5.1 meq of Sr, 2.2 meq of Cs. The surrogate waste is then loaded in a laboratory flask (3000 mL) along with the catalyst solution (500 mL, 0.2 M FeSO₄·7H₂O), concentrated (96% w/w) sulphuric acid is added until reaching a pH value of about 1, and the whole is maintained under stirring for about 15-20 minutes. The mixture is heated to a temperature preferably ranging between 60°C and 70°C by heating jacket or thermal bath under atmospheric pressure conditions. Once the optimal temperature has been reached, the external heat source is turned off and the oxidizer is added in a controlled manner through a peristaltic pump at a maximum rate of 2 mL/min until complete mineralization within about 5 hours. The reaction temperature reaches the maximum value of about 90°C within 1 hour and remains constant for about 3 hours; thereafter, the temperature begins to decrease until it stabilizes at around 60-70°C. The evolution of the oxidation process is monitored qualitatively from the different shades of colour that the mixture takes on. This becomes black-coloured near the reaction peak, then increasingly lightens moving from brown to yellow. The temperature and colour trends of the mixture are practical methods for simply monitoring the evolution of the process and the occurred mineralization of the loaded resin, as they are consistent with the total organic carbon (TOC) analyses conducted on aliquots of solution taken in different steps of the digestive process.

Decontamination step

[0049] According to the present invention, the decontamination step was appropriately optimized on a small scale by adding different amounts of NaOH, and/or chabazitic zeolite tuff to the mineralization solution. Tests were conducted to check whether other compounds such as BaSO₄ and Al₂(SO₄)₃ in addition to sodium hydroxide and chabazitic zeolite tuff also acted as precipitating agents of pollutant ions. As can be seen from Table 1 below, only an alkali metal hydroxide allowed an almost complete removal of pollutant metal ions such as cobalt, nickel and strontium.

[0050] Instead, the addition of chabazitic zeolite tuff allowed the removal of cesium in an amount ranging between 92% and 95%.

Table 1 - Qualitative trend of the decontamination step tested on a small scale with different potential co-precipitators.

Sample	Co-precipitator	Contaminants remaining in the supernatant [%]
		Co	Ni	Sr	Cs
1	NaOH pH 9	< 2	< 2	< 2	100
2	0.1 M BaSO4	100	100	58	100
3	0.2 M BaSO4	100	100	35	100
4	0.3 M Al2(SO4)3	100	100	86	43
5	0.2 M Al2(SO4)3	100	100	100	50
6	0.5 g TUFF	100	100	100	51
7	1 g TUFF	100	100	100	20
8	NaOH pH 10 + 1 g TUFF	< 2	< 2	< 2	5
9	NaOH pH 10 + 0.3 g TUFF	< 2	< 2	< 2	8

[0051] The same reactants were further tested in different basic environments (pH 10-12) for promoting a good decontamination yield and obtaining a residue suitable for being embedded directly in a geopolymeric matrix by alkali activation.

[0052] The studies conducted using NaOH and chabazitic zeolite tuff in different ratios showed a remarkable formation of precipitate and a clear, pale yellow end effluent.

[0053] The test was conducted under optimal conditions on a large scale (100 g of treated cationic resin), adding about 75 mL of NaOH to the mineralized solution (1100 mL, pH less than 1) until the pH was about 10, in order to precipitate contaminants such as cobalt, nickel and strontium (in addition to lanthanides, actinides and other transition metals, if present). Thereafter, chabazitic zeolite tuff (120 g) was added to allow the quantitative abatement of cesium in the solution.

[0054] Then, the sample remains under stirring for 1 hour, before being centrifuged at a maximum of 3500 rpm for about 15 minutes. The supernatant is then decanted, recovered and weighed before a representative aliquot is taken to assess the decontamination yield. The wet residue obtained is collected and weighed before adding the rest of the components necessary to obtain a geopolymeric encapsulation matrix.

[0055] To assess the decontamination yield of the effluent produced, two representative aliquots are taken before and after the process, and, once appropriately diluted, they are injected into a single quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS). The analyses conducted highlighted a single-stage decontamination yield of cobalt, nickel and strontium greater than 97%, and greater than 95% for cesium (Table 2).

Table 2: Decontamination yields (%) on a bigger scale (100 g).

	BEFORE		AFTER		TOTAL YIELD (%)
	ppm	mg	ppm	mg
Co	142.2	171.1	3.5	3.890	98 ± 0.5
Ni	141.5	165.5	3.6	3.981	97 ± 0.5
Sr	61.3	71.7	5.0	5.537	97 ± 1
Cs	282.9	331.1	13.9	15.284	95 ± 0.6

[0056] Thus, even on a larger scale (Table 2) the decontamination yields are consistent with those obtained on a small scale (Table 1).

Conditioning of encapsulation step

[0057] The goal of the conditioning step is to encapsulate the previously exposed residue obtained from the decontamination stage directly in a stable and durable matrix, obtaining an end product suited for final disposal. In order to characterize some important properties of the end product, equilateral cylindrical specimens having a side of 5 cm were prepared.

[0058] A portion of the residual sludge (33.5% w/w) was weighed into a beaker and blast furnace slag (24.5% w/w), fly ash (24.4% w/w), alumina (2% w/w), NaOH in pellet form (5.8% w/w) and demineralized water (12.5% w/w) were added thereto. The whole was vigorously mixed until obtaining a slurry which was workable and suitable for being filled in a formwork. The specimen was then subjected to a curing process lasting 28 days until complete hardening to allow it to be extruded from the formwork and experimental tests to be carried out in order to demonstrate its durability in view of the final disposal. Overall, the integrated disposal process allows to obtain an end specimen with a loading factor of 12.5 % w/w, calculated as the ratio of untreated resin equivalent mass to total specimen mass.

[0059] In particular, two equal-sized groups of specimens were thus prepared from the same decontamination residue and using the same precursor and activator materials. One group was taken as a reference, whereas the other one was immersed for its entire volume in ultra-pure water to test the durability thereof. The test, conducted in semi-dynamic mode according to the ANSI/ANS-16.1.2003 (R2017) experimental protocol, lasted 1 month. The conductivity and pH measurements reported in the Table 3 below were conducted on aliquots of the leachate recovered at well-defined time intervals (2, 5, 24, 72, 168, 240 h).

Table 3 - Conductivity and pH measurements carried out on leachates of specimens from the cation resin-only treatment.

Leachate	Conductivity [mS]	pH
White (ultra-pure water)	0.00046	5.5
1 (2 h)	0.67	9
2 (5 h)	0.46	8.5
3 (24 h)	0.77	9.5
4 (24 h)	0.48	9
5 (72 h)	1.03	9.5
6 (168 h)	1.10	9.5
7 (168 h)	0.87	9.5
8 (240 h)	0.92	9.5

[0060] The characterization of the leachate was completed with mass spectrometry measurements to quantify the concentrations of contaminants and main constituents released over time. The cumulative concentrations reported in Figure 1 allowed to determine the diffusion coefficients (cm²/s), and thus the leaching indices reported in Figure 2.

[0061] As can be seen from Figure 2, the indices calculated for the elements constituting the matrix and for the contaminants are much higher than the limit generally imposed by the national regulatory authority on this category of waste (i.e., lower limit leaching index of 6), thus exceeding the acceptability threshold required for accessing a radioactive waste repository. Mechanical compression tests were further conducted on the group of reference specimens and on the one from the immersion test (post-immersion). As reported in Table 4, the specimens containing the residue after the leaching test showed a higher resistance to compressive strength. Probably, this difference must be attributed to the heterogeneous presence of defects (voids and microfractures) in the samples rather than to a real ameliorating effect due to the immersion in water.

Table 4 - Compression test of specimens

Specimens	Compression strength (MPa)
Reference	7.2 ± 0.7
Post-immersion	12.9 ± 1.3

Example 2 - The inventive process applied to a mixed bed (cationic resin mixed with anionic resin).

[0062] To complement what has been previously demonstrated, the process was further tested for treating a mixed bed of cationic and anionic resins using a co-catalyst system (FeSO₄ + CuSO₄). In the same way as with the sole cationic resin, a representative surrogate waste was prepared by loading the mixed bed of resins with a feed of stable nuclides representative of the main fission and activation products, in this case adding also iodine with a loading factor >90% w/w, corresponding to about 28 meq.

[0063] Also in this case, different batches of resins (from 20 g to 200 g) were effectively treated as demonstrated by Chemical Oxygen Demand (COD) analyses conducted on aliquots of solution taken during the process.

[0064] The solution from the oxidative process was subjected to the same decontamination step with NaOH solution and chabazitic zeolite tuff. The analyses conducted showed the same effective abatement of cobalt, nickel, strontium and cesium. As for iodine, only about 10% w/w of that initially loaded apparently remains in solution after the oxidative process, whereas most of it can be easily collected by deposition in the condenser downstream of the reactor.

[0065] The present invention highlights the poor decontamination of iodine in the mineralized solution, and in the solution collected downstream of the system. However, this can be effectively solved by using natural or artificial zeolites activated with silver, or directly the silver nitrate compound (AgNO₃).

[0066] The residue obtained in these preliminary steps was encapsulated in geopolymeric matrix in the same way as with the sole cationic resin residue.

[0067] A group of specimens was then subjected to a curing process lasting 28 days until complete hardening to allow it to be extruded and subjected to leaching and mechanical compression tests.

[0068] Further, one group of specimens was taken as a reference, whereas the other one was completely immersed in ultra-pure water to test the stability thereof. The test, conducted in static mode, lasted 15 days. The analysis of the leachate conducted by mass spectrometry showed similar leached mass values for cobalt, nickel, strontium and cesium, while a greater mobility of iodine has apparently been observed in these preliminary tests, although the limited content of iodine in solution makes the quantification of its decontamination less accurate and reliable.

[0069] The leachate was further subjected to COD analysis, obtaining a value of about 72 mg/L, thus below the limits generally imposed on effluent release into the environment (< 100 mg/L).

[0070] Mechanical compression tests were then conducted on the group of reference specimens and on the one from the immersion tests (post-immersion). As can be seen from Table 5, the results obtained are promising.

Table 5 - Compression tests of mixed-bed specimens.

Specimens	Compression stress (MPa)
Reference	20.8 ± 2.1
Post-immersion	18.9 ± 1.9

Literature

[0071] 

1. S.A. Walling, et al. "Fenton and Fenton-like wet oxidation for degradation and destruction of organic radioactive wastes", in: npj Materials Degradation 5 (2021).

2. A. Santi, et al. "Design of sustainable geopolymeric matrices for encapsulation of treated radioactive solid organic waste", in: Frontiers in Materials. DOI: 10.3389/fmats.2022.1005864.

3. W. Baek, et al. "Cation exchange of cesium and cation selectivity of natural zeolites: Chabazite, stilbite, and heulandite". ln: Microporous and Mesoporous Materials 264 (2018), pp. 159-166

Claims

1. A process of decontamination of a contaminated organic material comprising or consisting of ion-exchange resins embedding toxic and/or radioactive pollutant ions, comprising the following steps:

a) subjecting said ion-exchange resin to a mineralization process in water by adding an oxidizer in the presence of catalysts selected from iron and/or copper sulphate, and mixtures thereof, or mixtures of other metals selected from Al, Ce, Co, Mn, Ru, and compounds thereof; metal dusts and oxides, fly ash, blast furnace slag, iron ores, clays selected from kaolin and/or vermiculite;

b) recovering contaminated inorganic compounds;

c) preparing a confinement matrix with contaminated inorganic materials recovered in stage b)

wherein
stage b) comprises the following stages:

b1) adding the aqueous mixture from stage a) with an aqueous solution of an alkali metal hydroxide until a pH value of or above 9, preferably of between 9 and 11, still more preferably of 10, is reached and precipitating and/or co-precipitating said inorganic mineral compounds containing said toxic and/or radioactive metal ions;

b2) adding the suspension obtained in stage b1) with zeolites, in order to embed the residual ions of several toxic and/or radioactive metals, mainly cesium, the compounds thereof being soluble at the alkaline pH of the solution, said stage b2) being performed subsequently to stage b1);

b3) separating the solid residue from the reaction solution from stage b2) by filtration or decanting followed by centrifugation of the decanted solid.

2. The process according to claim 1, wherein the ionic resins containing contaminated material used in stage a) are selected from cation-exchange resins or a mixture of cationic and anionic resins.

3. The process according to claim 1 or 2, wherein the contaminated organic material comprises cation-exchange resins containing pollutant cations of alkali metals, alkaline earth metals, transition metals, lanthanides, actinides, and mixtures thereof, such as cobalt, strontium, nickel, cesium, and mixtures thereof.

4. The process according to any one of claims 1-3, wherein the contaminated organic material comprises anion-exchange resins containing pollutant anions, such as iodine and/or other halogens, transition metal ions; and the non-precipitated iodine remaining in solution after stage a) is precipitated as silver iodide by adding an aqueous solution of silver nitrate in stage b1), or by adding a zeolite, possibly loaded with silver ions, in stage b2).

5. The process according to any one of claims from 1 to 4, wherein the contaminated organic material used in step a) may in turn comprise other carbonaceous materials in liquid or solid state, such as solvents and/or mixtures thereof, as liquid scintillation radiometric measurement cocktails, or tributyl phosphate/kerosene for hydrometallurgical separation, and further nuclear grade graphite dust, contaminated with toxic and/or radioactive ions.

6. The process according to any one of claims from 1 to 4, wherein the contaminated material comprises or consists of urban, industrial wastewater, up to aqueous effluents with high dissolved organic content, such as surfactants and mixtures thereof, contaminated with toxic and/or radioactive ions.

7. The process according to any one of claims from 1 to 6, wherein the zeolite is selected from: chabazite, mordenite, clinoptilolite, erionite, stilbite, heulandite e/o mixtures thereof, more preferably chabazite and/or clinoptilolite, added as pure mineral or contained in naturally rich zeolite tuff.

8. The process according to any one of claims 1-7, wherein, when said material contains cesium, in stage b2) a zeolite conglobated in chabazite tuff is added.

9. The process according to any one of claims from 1 to 8, wherein, in stage b2), the zeolite tuff is added in weight ratios relative to the amount of toxic and/or radioactive alkali metal ion, in weight ratios comprised between 100 and 400.

10. The process according to any one of claims from 1 to 9, wherein stage a) is carried out at a temperature comprised between 70 and 100 °C, at a pH value comprised between 0.5 and 3, preferably of between 1 and 2.

11. The process according to any one of claims from 1 to 10, wherein the alkali hydroxide aqueous solution used in stage b1 is selected from sodium and potassium hydroxide.

12. The process according to any one of claims from 1 to 11, wherein the confinement matrix comprises or better consists of a geopolymeric binder.

13. The process according to claim 12, wherein stage c) envisages the following operational steps:

c1) adding the precipitate from stage b3) with precursors selected from waste aluminosilicates, an activator consisting of an alkali metal hydroxide and any further additives capable of facilitating the workability of the paste and the filling of the material in a mold or formwork;

c2) curing the material from preceding stage c1) for a time comprised between 14 and 90 days, preferably of 28 days.

14. The process according to claim 13, wherein the waste aluminosilicate precursors are selected from fly ash, blast furnace slag, black electric arc furnace slag, bauxite residue, mining waste, urban or food industry waste ashes, as: palm oil, grain husks, and mixtures thereof, the activator is sodium hydroxide, preferably in pellet or chip form, and the additive capable of improving the composition and the compression strength is alumina.

Drawing