NL2010975A - METHOD FOR TREATING WASTE MATERIAL - Google Patents

Description

METHOD FOR TREATING WASTE MATERIAL

The invention relates to a method in which a waste material is treated which contains heavy metals, such as certain types of sludge from a purification device, which has the striking advantage that another waste material, which contains inertized heavy metals, is used . In a particular embodiment of the invention, the treatment comprises calcining the waste material.

The problems caused by the ever-increasing quantities of waste to be treated, treated and stored are generally known. These waste materials come from multiple sources. They originate, for example, from water treatment plants, from the dredging or purification of waterways or various industries and can contribute to soil contamination. Regarding sediment from waterway purification, this is particularly worrying given the quantities involved and their contamination with pollutants such as heavy metals and organic substances. An important part of the waterways of northern Europe is now blocked by sludge, which hinders shipping traffic. The economic and environmental consequences, directly or indirectly, are very large. On the other hand, it is well known that this worrying situation of the water network is mainly caused by the drawbacks of the current solutions for the treatment and storage of contaminated waste materials.

After all, a simple means of removing waste materials consists of discharging them by boat into the sea or transporting them to landfill sites. However, if the waste materials are contaminated with heavy metals or hazardous organic substances (which is generally the case with sediments from purifying waterways), this agent is of course unacceptable. After all, before they can be stored, the waste materials must be treated in order to meet the non-toxicity tests. It is also important that they can be dried effectively and economically, so that processing and storage thereof is facilitated.

The invention relates to the provision of a method for treating waste materials that is economically more favorable and / or technically more competitive than the methods according to the state of the art, in particular the methods described in the SOLVAY WO patents. 02/32817, WO 04/035490, WO 2005/100261 and WO 2007/080179, the entire contents of which are incorporated herein by reference, where applicable.

In view of this, the invention relates to a method for treating a first waste material containing non-inert heavy metals, and is characterized in that a mixture is formed comprising the first waste material and a second waste material which is a phosphating treatment comprises inertized heavy metals, whereby a third waste material, containing inert heavy metals, is produced.

The mixture can be homogeneous or heterogeneous. It is preferably substantially homogeneous.

The mixture formed may comprise components other than the first waste material and the second waste material, for example water and / or a surface active agent, or a gaseous fuel, such as oxygen or air.

The mixture can be obtained by any means. It can be obtained with the aid of a stirring device, for example in a mixing device which is provided for this purpose. The mixture does not necessarily require the use of mechanical dispersants; the mixture can therefore, for example, be formed in the space of a calcining oven or incinerator, to which the first waste material and the second waste material are added separately, but in which the turbulences caused by the gaseous fuel are exacerbated by the high temperature, that prevails in space, more than sufficiently ensure the mixing of the two types of waste material and.

If sufficient time is waited, simply bringing the first waste material into contact with the second waste material in the mixture can be sufficient to cause the heavy metals of the first waste material to become inert, and therefore also to produce the third waste material. . However, the waiting time for obtaining the desired effect can be very long when the mixture formed is kept under unfavorable conditions, in particular when it is kept both at a low temperature (e.g. below 80 ° C) and in a dry state. Thus, in order to render the heavy metals present in the first waste material inert, the mixture of the first waste material and the second waste material will advantageously be treated in a moist manner (preferably by forming an aqueous slurry of the two waste materials), or the mixture will also be kept at a high temperature (for example, higher than 200 ° C); in this case, when the first waste material and / or the second waste material contain organic material and are also mixed with a fuel, the inerting of the heavy materials will accompany the at least partial burning of the organic material, provided that the combustion temperature is sufficient high (higher than for example 400 ° C, even 550 ° C), the almost complete decomposition of the organic material into gaseous products (mainly carbon dioxide and water vapor) and the formation of slag and / or fly ash, solid residues containing inert heavy metals and advantageously form the third waste material according to the invention.

Eluable heavy metals.

Advantageously, more than 10% by weight, optionally more than 15% by weight or more than 20% by weight of the heavy metals present in the first waste material can be eluted in 0.5 M acetic acid.

Advantageously, more than 10% by weight of the heavy metals present in the second waste material can be eluted with 0.5 M acetic acid.

Advantageously, a maximum of 10% by weight of the heavy metals present in the third waste material can be eluted with 0.5 M acetic acid.

The eluable weight fraction of the heavy metals that are absent in the second waste material is advantageously at least 2 times lower, preferably at least 4 times lower, than the eluable weight fraction of the heavy metals that are present in the first waste material.

The eluable weight fraction of the heavy metals present in the third waste material is advantageously at most the eluable weight fraction of the heavy metals present in the second waste material and is preferably at most half.

Quantities of the first and second waste material.

The weight quantity of the first waste material is advantageously at least 10%, preferably at least 20% and particularly preferably at least 40% of the weight quantity of the second waste material.

The weight amount of the first waste material is at most 200%, preferably at most 100% and particularly preferably at most 60% of the weight amount of the second waste material.

Special embodiment of the invention, which relates to the phosphating treatment.

In a particular embodiment of the invention, an aqueous slurry is formed which comprises the first waste material and the second waste material, the slurry is converted into a foam, the slurry is matured for at least 12 hours after which it is dried to a dryness of at least 70 % is reached.

Preferred embodiment of the invention, which relates to the phosphating treatment.

In a preferred embodiment of the invention, the first waste material and the second waste material are calcined together in a calcining oven, whereby at least one product of co-calcining selected from the slag and fly ash, which form the third waste material and contains inert heavy metals, is obtained .

According to this preferred embodiment, it is advantageous for the first waste material and the second waste material together to form a self-combustible mixture in the calcining oven, which can be calcined in the absence of a third fuel with a much less increased calorific capacity, than that of the mixture, which is formed by the first waste material and the second waste material.

Still according to this preferred embodiment, co-calcining is carried out at a temperature or in a temperature range of 450 ° C to 1000 ° C.

The co-calcining is preferably carried out in an oxidizing atmosphere, using preferably ambient air as a fuel.

Possible after-treatment of the third waste material.

The third waste material is advantageously mixed with water, optionally a hydraulic binder is added, whereafter the whole comprising the third waste material, water and any hydraulic binder is thickened and hardened, so that a solid mass is formed.

Description of the first waste material.

The first waste material advantageously contains the organic material in usually a content of at least 5%, preferably at least 10%, particularly preferably at least 20%, very particularly preferably at least 40%, even more preferably at least 60% and most preferably at least 75%.

If desired, the first waste material contains the organic material in a content of usually a maximum of 95%, often a maximum of 90%.

The first waste material advantageously contains at least one calcium salt.

Advantageously, the first waste material is a sludge of natural origin, which must be dried to achieve a dryness of at least 70%. The first waste material can also be a waste material that comprises a non-natural waste material in the form of a solid.

The first waste material is preferably a sludge from a purification device that has been dried to a dryness of at least 80%, preferably at least 85%.

The first waste material advantageously has a dryness of at least 85%, preferably at least 90% and in certain special cases at least 99%.

Description of the second waste material.

The second waste material advantageously contains the organic material at a level of usually equal to at least 1%, preferably at least 2%, particularly preferably at least 5%, and sometimes at least 40%, at least 60% or at least 75%.

If desired, the second waste material contains the organic material in a content of usually equal to a maximum of 95%, preferably a maximum of 40%, and particularly preferably a maximum of 20%.

The second waste material usually contains at least one salt of at least one metal that is different from a heavy metal, which salt comprises at least one mono- or polyphosphate group, which corresponds to the general formula

wherein x is an integer positive number or zero (where x can be equal to 1, 2 or 3 - 9, for example) and wherein the (3 + x) oxygen atoms are characterized by an asterix (O *) independently of each other to a hydrogen atom or a metal atom other than a heavy metal.

The second waste material preferably contains at least one calcium phosphate, which comprises at least one mono- or polyphosphate group, which corresponds to the general formula

wherein x is an integer positive number or zero and wherein the (3 + x) oxygen atoms marked with an asterix (O *) are independently bound to a hydrogen atom or a metal atom other than a heavy metal, provided that at least one of them is bound to a calcium atom; sometimes more metal atoms are bound to oxygen atoms marked with an asterix (O *), and all are calcium atoms.

Preferably, the calcium phosphate is a salt selected from the calcium dihydrogen phosphate [Ca (H2PC> 4) 2], the "tricalcium phosphate TCP" [Ca ^ PO ^], the whitloc ticks [in particular the whitlockites corresponding to the formula Ca9 (Mg, Fe) (PO4) e (HP04)] and the apatites [in particular the apatites corresponding to the formula Caio (PC> 4) 6 (OH, F, Cl, Br) 2, such as hydroxyapatite], or includes the hydrated forms of said salts and mixtures thereof.

The calcium phosphate is particularly preferably anhydrous calcium mono-hydrogen phosphate (also called monetite) and / or a hydrated calcium mono-hydrogen phosphate (in particular brushite (CaHPC> 4.2 H 2 O). to the formula Ca9 (Mg, Fe) (PO4) 6 (HPC> 4) or still comprises it, still particularly preferably, the calcium phosphate is or comprises hydroxyapatite.

The weight of the at least one calcium phosphate present in the second waste material, expressed in phosphorus equivalent and relative to the weight of the dry matter of the first waste material, is advantageously at least 0.35%, preferably at least 0.5%, particularly preferably at least 0.7%. Furthermore, the weight of the at least one calcium phosphate, expressed in phosphorous equivalent and with respect to the weight of the dry matter of the first waste material, is advantageously at most 5%, preferably at most 3%, particularly preferably at most 2% and with very special preferably 0.7% -2%.

The phosphating treatment to which the second waste material is subjected is preferably a treatment with phosphoric acid; it is, moreover, preferably carried out in a moist environment.

Advantageously, the second waste material is a sludge of natural or non-natural origin, which must be dried to achieve a dryness of at least 70%. The second waste material also advantageously consists of sediments that come from purifying an aqueous environment, such as a watercourse or a region of stagnant water.

Preferably, the second waste material is a sludge with an initial dryness of less than 70% (i) which is converted to the state of a foam by adding phosphoric acid thereto, (ii) matured such that the phosphation is within the foam develops after which (iii) it is dried to achieve a dryness of at least 70%.

The sludge is particularly preferably matured for a sufficient time t 1 so that more than 50%, preferably more than 90% and particularly preferably substantially 100% of the phosphoric acid is converted into at least one metal phosphate. The at least one metal phosphate is advantageously or includes a calcium phosphate, in particular a calcium phosphate as described above. The duration t 1 is advantageously at least 5 minutes, preferably at least 15 minutes, particularly preferably at least 1 hour and very particularly preferably at least 3 hours.

The sludge is also aged with sufficient preference for a sufficient time 2 2 so that the weight percentage of the heavy metals that can be eluted in 0.5 M acetic acid containing the sludge is at least 2 times, preferably at least 4 times and with particular is preferably at least 6 times lower than the weight percentage of the heavy metals that can be eluted in 0.5 M acetic acid containing the sludge before adding the phosphoric acid.

Still with particular preference, the sludge is aged for a sufficient time so that a maximum of 10%, preferably a maximum of 7% and particularly preferably a maximum of 5% by weight of the heavy metals present in the second waste material can be eluted with 0 , 5 M acetic acid.

The second waste material advantageously has a dryness of at least 85%, preferably at least 90% and in certain special cases it is at least 99%.

Special embodiment of the invention.

In a particular embodiment of the invention, the method furthermore comprises the step of producing the second waste material by subjecting a waste material containing heavy non-inert metals to a phosphating treatment.

The present invention also relates to the use of a waste material (hereinafter referred to as the "second waste material") which is inertized by a phosphating treatment of another waste material containing non-inert heavy metals (previously referred to as the "first waste material") contains metals.

The present invention also relates to a method for forming a solid mass that can be used for the construction of a road, the manufacture of a stone or for the production of a concrete, according to which method the "third waste material" is mixed is added with water, optionally a hydraulic binder, after which the whole comprising the third waste material, water and any hydraulic binder, is thickened and hardened, so that the solid mass is formed.

Finally, the present invention relates to an end product, such as a road, a brick or a concrete, that the solid mass, which is described by the method as described in the preceding paragraph, or the method according to the invention according to the embodiment in which the third waste material has been subjected to an after-treatment as described above.

OTHER DETAILS OF THE PRESENT INVENTION.

Details of the nature of the first and second waste material.

The first waste material and the second waste material can be independently from each other: from decanting used water of industrial or urban origin, from cleaning soil, such as that from certain industrial sites; car grinding waste incineration sediments from rivers, fens, wells or sewers, and sediments from waterways (eg harbors, lakes, rivers, canals).

Dredging is a special form of purification. The dredging must be understood as a treatment of a certain size, which is carried out with heavy tools (suction pump, dredger, etc.), whereby the purification refers to any treatment in an aqueous environment that releases material, even of vegetable origin. , implies, for example, in a channel or in a low-water bed or the catchment area of a watercourse.

By fly ash is meant incineration ash, which is entrained by incineration smoke.

Further details of the heavy metals.

The heavy metal content of a waste material is obtained by summing the contents of each of the heavy metals present in the waste material.

A heavy metal is understood to be any metal selected from metals whose specific weight is at least 5 g / cm 3 (such as cadmium, chromium, copper, mercury, lead and zinc) as well as from beryllium, arsenic, selenium and antimony.

Asr content. The dry substances of the first waste material and the second waste material may independently contain at least 2 mg / kg, at least 10 mg / kg or at least 20 mg / kg As. It can contain a maximum of 500 mg / kg of As.

Cd content. The dry substances of the first waste material and the second waste material may independently contain at least 1 mg / kg, at least 5 mg / kg or at least 10 mg / kg Cd. It can contain a maximum of 250 mg / kg of Cd.

Cr content. The dry substances of the first waste material and the second waste material may independently contain at least 5 mg / kg, at least 25 mg / kg or at least 50 mg / kg Cr. It can contain a maximum of 1000 mg / kg of Cr.

Hg content. The dry matter of the first waste material and the second waste material may independently contain at least 0.1 mg / kg, at least 0.5 mg / kg or at least 1 mg / kg Hg. It can contain a maximum of 25 mg / kg of Hg.

Cu content, The dry matter of the first waste material and the second waste material may independently contain at least 5 mg / kg, at least 25 mg / kg, at least 100 mg / kg or at least 250 mg / kg Cu. It can contain a maximum of 1000 mg / kg Cu or a maximum of 10000 mg / kg Cu.

Pb-g.eh.alte. The dry matter of the first waste material and the second waste material may independently contain at least 5 mg / kg, at least 25 mg / kg, at least 100 mg / kg or at least 250 mg / kg Pb. It can contain a maximum of 1000 mg / kg Pb or a maximum of 10000 mg / kg Pb.

Zm content. The dry matter of the first waste material and the second waste material can independently be at least 5 mg / kg, at least 50 mg / kg, at least 200 mg / kg, at least 500 mg / kg or at least 1000 mg / kg Zn contain. It can contain a maximum of 10000 mg / kg of Zn or a maximum of 50000 mg / kg of Zn.

Ni content. The dry substances of the first waste material and the second waste material may independently contain at least 5 mg / kg, at least 15 mg / kg or at least 30 mg / kg Ni. It can contain a maximum of 500 mg / kg of Ni.

The levels are advantageously measured with optical emission spectrometry on plasma with inductive coupling (ICP - OES)

Further details of the dryness of waste are already mated.

The dryness of a sample of a waste material is determined by calculating the ratio of the weight of a sample before and after a residence time of 4 hours in an autoclave, which is kept at 100 ° C.

Details of the sludge.

By sludge is meant any aqueous substance that contains suspended solids. It may be of natural origin or due to the addition of water to a powdered solid obtained, for example, by grinding. When the sludge is of natural origin, it advantageously contains weak clay, mud and suspended mineral materials (sand even gravel). The sludge from the cleaning of waterways or polluting soil forms examples of natural sludge in which the invention can be applied. On the other hand, sludge resulting from the addition of water to incineration ash or to car grinding residues is exemplary of non-natural sludge to which the invention can be applied. The size of the grain distribution of the suspended particles in the sludge can be very wide, for example from less than 1 micron to a few hundred microns, even a few millimeters. The sludge often contains a high content of very fine particles. Often 10% by weight of the dry sludge is formed by particles with a diameter smaller than 5 micrometers, while the content of particles with a diameter larger than 500 micrometers can reach a few percent. On the other hand, the histograms of the grain distribution of certain types of sludge are multimodal, that is, they have multiple peaks.

Further details of the phosphating treatment with phosphoric acid

The amount of phosphoric acid to be used depends on the precise composition of the waste material to be treated and in particular on the content of heavy metals. In practice, a weight amount of at least 1% (preferably at least 2%) relative to the weight of the solid is used. It is preferred that the amount of phosphoric acid is less than 15%. Quantities of 2 - 6% are generally well suited.

It is interesting to use highly diluted phosphoric acid in which a source of inexpensive phosphate is dissolved, such as certain phosphorus-containing minerals containing P2O5, or calcining residues of animal meal, which is also rich in phosphates. For example, from an acid whose concentration corresponds to 20 ml of phosphoric acid diluted to 85% with 980 ml of water and the addition of phosphorus-containing minerals or calcined animal meal, an acid is obtained in a very economic manner which is suitable for the process according to the invention. invention. It has been observed that by phosphating the waste material, a waste material can be obtained in which the toxic compounds present in the waste material are rendered inert.

For treatment with the phosphoric acid in question, drynesses of less than 30% or in certain cases 40% are preferably avoided. When the dryness is higher than 70%, it is necessary in some cases to add water so that phosphating can be carried out optimally.

In a recommended variant of this treatment, the waste material is converted into a foam, after which it is present in the form of a foam (with foam, for a specific starting product, a condition of this product with a lower density than the starting product is meant). Converting into a foam facilitates the later processing of the waste material. After all, the inventors have observed that after a storage period, which typically ranges from 2-7 days, preferably 4-6 days, during which period the waste material, originally in the state of a foam, is left at normal outside temperatures ( but avoiding the gel), its consistency approximating a solid body that can easily be machined with construction tools such as excavators or bulldozers while still containing a lot of water (typically up to 40% by weight). low density appeared to give rise to better consistency. The density of the foam must usually be less than 95% of that of the waste material before treatment. Values lower than 90%, preferably lower than 85%, more preferably lower than 80%, are favorable. It is preferred that the density does not fall below 30%. Values of 60 - 75% are particularly suitable.

Foaming of the waste material can be carried out with any known foaming technique, which is tailored to the waste material to be treated. In general, phosphating the waste material with the aid of phosphoric acid causes a sufficient development of gas to obtain foaming. If it is insufficient, the foaming can be achieved in particular chemically by the addition of reagents which cause the development of gas in situ. In a preferred embodiment, the reaction of an acid, such as hydrochloric acid, sulfuric acid or phosphoric acid, with, for example, a carbonate, is used to cause the gas to be released. It has been observed that the release of H 2 S gas during phosphating improves the conversion of the sludge into a foam. The addition or presence of surfactants that stabilize the foam is also beneficial. In this regard, it has been observed that certain humic acids present in the sludge obtained by the cleaning of waterways have a favorable effect on foaming, probably caused by their surface-active character. As a function of the waste to be treated, it will, however, be appropriate to add certain surfactants, if desired, to obtain a foam with a density according to the invention. The selection of the most suitable surfactant and the amount thereof to be used will be made in a manner known per se from case to case. On the other hand, it is preferred that the waste material be mechanically stirred to facilitate foaming. The stirring intensity is selected as a function of the particular conditions of use of the method according to the invention. It is favorable that mechanical stirring is not too intense. The use of mixing screws should generally be avoided, since they usually impede the formation of the foam. The use of tubular reactors, which are segments of tubes, whether or not fitted with static mixers, is recommended. They advantageously have dimensions such that a residence time of 2-10 seconds is obtained. In any case, the mechanical stirring is controlled such that the foaming according to the invention is favored. In certain cases, it is preferred that the reagent causing foaming be added to the waste material after its passage through a pump that will cause the desired mechanical stirring. The use of static mixers can also be favorable to obtain the optimum intensity of the mechanical stirring.

Foaming advantageously comprises a ripening period. After all, the reaction of the waste material with phosphoric acid and / or any other reagent requires a certain time. It is recommended that the duration of the ripening period be sufficient so that 80%, preferably 90%, more preferably 95% of the reagents used. In general, a period of 2 days, preferably 3 days, is well suited.

According to a favorable variant, the method comprises a step of foaming and the resulting foam, which is advantageously matured, is dried. In the following description, "dried sludge" means the product obtained as a result of drying the foam. This product is no longer necessarily in the state of a foam because the foam tends to compact during drying. The foam is preferably subjected to an identical treatment as compost. Composting is a well-known technique for treating fermentable waste materials (which can be fermented), such as green waste. It consists essentially of storing the waste material in contact with air for an extended period of time at external ambient temperature, so that organic substances present in the waste material are degraded and removed by calculating the liquid it contains. The use, according to this embodiment of the invention, of techniques similar to composting for drying the foamed sludge containing organic substances - even non-fermentable - and heavy metals allows for surprisingly high drynesses to be obtained in a very economic manner. to become. The consumption of energy during any subsequent calcining of the foam is thereby reduced. Drying the foam with techniques that are similar to composting even make it possible to dispense with the calcination step, because the degradation of organic substances obtained is sufficient.

During drying, the waste material is advantageously stored for a sufficiently long period so that the water can be removed spontaneously, under the influence of gravity. A drying period of more than 24 hours is often necessary. The drying preferably lasts at least 48 hours. Drying for more than a month has not proved useful. Drying periods of one to two weeks have proven to be very suitable.

As explained above, when the waste material is present in the form of a foam, drying is easier and more effective. After all, the improved consistency of the dried foam makes it possible to process its mass with conventional building tools and, in particular, makes it possible to manipulate it during composting. This ensures that the desired drynesses are achieved faster.

According to a recommended variant of this embodiment, drying is carried out under conditions such that after 12 days of drying, the dried foam reaches a dryness of more than 65%, preferably 70%.

Drying can also be carried out directly on the earth. In a favorable embodiment of the method according to the invention, however, the foam is applied to a layer of sand.

In this embodiment, it is preferable for the layer of sand itself to be applied to a water-impermeable membrane to avoid contaminating the earth with heavy metals and thereby recovering the water from the phosphated sludge during composting , is possible. Membranes from plastic materials, for example from polyethylene or PVC, are very suitable.

Drying can take place outdoors, without protection against possible rain showers and large variations in temperature, on the understanding that it remains above 0 ° C. It is nevertheless preferred to use a closed drying system, such as a composting tunnel. Such composting tunnels are generally known in the field of the industrial treatment of organic waste materials that can be fermented. The composting tunnel is advantageously provided with air circulation systems and systems for collecting and treating emitted gases, such as hydrogen sulphide. The hydrogen sulfide is preferably recovered and, for example, treated on a biofilter or reinjected during a possible calcination. It is preferred that the composting tunnel comprises a layer of sand that is applied to a water-impermeable membrane.

Further details of calcination.

The calcination is intended to break down the organic material present in the first waste material and / or second waste material. The organic material may include, for example, non-polar hydrocarbons, aliphatic or aromatic (mono- or polycyclic) hydrocarbons and halogenated solvents. The calcining is generally carried out at a temperature higher than 450 ° C, so that the organic materials are sufficiently degraded. It is convenient to avoid an excessive temperature that would result in the evaporation of a portion of the heavy metals. In practice, the calcining temperature is lower than 1000 ° C. Preferably, the calcination temperature is higher than 500 ° C and lower than 800 ° C. In order to break down the organic materials particularly well and to evaporate as little heavy metals as possible, it is particularly favorable that the calcination temperature is 550 ° C - 750 ° C.

It has been observed that calcination is advantageously carried out under controlled atmosphere.

With this in mind, in a particular embodiment of the method according to the invention, this atmosphere is oxidizing. This variant facilitates the thickening of the possibly adjoining mortar, as described below. In this case, for example, ambient air can be used. It must therefore be ensured that the air is available in the oven in sufficient quantity.

In another particular embodiment, the atmosphere is reducing. This embodiment is particularly advantageous because it inhibits the formation of chromium VI.

The duration of the calcination depends on the composition of the waste material to be treated and the distribution of the material in the calcining oven. It must also be sufficient to break down the organic material.

Details of the after-treatment of the third waste material.

The product from the calcining step can be mixed with water and then thick and cured. In this embodiment, a reducing additive is preferably included in the mixing water. As an example, this additive can be selected from iron, manganese, compounds of iron (II), compounds of manganese (II) and reducing salts of alkali metals. Sodium sulfite is preferred. The reducing agent is advantageously added in a weight amount of 0.1-1% by weight of the dry substance present in the sludge.

During calcination, certain sludge, in particular that that is rich in calcite, causes the formation of puzzolan earth. In this case, it is not necessary to add a hydraulic binder to cause thickening and hardening.

When a hydraulic binder is necessary to ensure thickening and hardening, its precise composition is not critical. It usually consists of Portland cement. Puzzolane materials, such as carbon combustion ash, may also be suitable. A sufficient amount of mixed water must be added during mixing of the hydraulic binder with the calcining product, which is intended to form a mortar, to obtain a plastic slurry. The amount of the hydraulic binder to be used depends on various parameters, in particular on the chosen hydraulic binder, the composition of the sludge and the desired properties of the end product of the treatment method according to the invention, in particular its mechanical resistance. In practice it is often recommended to use a weight amount of binder in excess of 1% by weight of the calcining ash. According to the invention, it is desirable that the weight of the hydraulic binder is less than 50% and preferably does not exceed 30%.

In a favorable variant of the method according to the invention, a weight amount of hydraulic binder of more than 2% and less than 20% of the calcining product is used.

The shape of the solid mass obtained after curing, which can take several days, is that in which the mortar is produced. It may, for example, comprise stones or spherical or prismatic blocks. It is compact, almost without gaseous inclusions and therefore has good mechanical properties, in particular a sufficient hardness and shock resistance, so that processing and storage thereof is possible without problems.

The solid and compact mass obtained after curing advantageously respects the toxicity standards for extracted leaching products according to heavy procedures, such as those defined by the "TL" or "NEN" regulations.

The French triple leaching "TL" test is described in the French regulation XPX 31 - 210. The test protocol consists of grinding the substance so that it can pass through a 4 mm sieve. This ground substance is leached three times with demineralized water, in a liquid / solid ratio of 10, with constant stirring. At the end of each leaching, the content of heavy metals in the liquid is measured.

The Dutch test "NEN" consists, with regard to this test, of the fine grinding of the sample (smaller than 4 mm) and the addition to water in a water-washed substance ratio of 10. It is then held for three hours on a pH of 7, then also for three hours at pH of 4 (this is the minimum pH of rainwater). The pH adjustment is continuously carried out with the aid of an IN nitric acid solution (non-complexing acid). The content of heavy metals in the liquid phase is then determined by analysis.

According to the American test TCLP (Toxicity Characteristic Leaching Procedure), 100 g of solid is taken, passed through a 9.5 mm sieve, and the sample is contacted with 2000 ml of 5.7 g / l CTLCOOH solution for 18 hours.

Claims (41)

A method for treating a first waste material containing non-inert heavy metals, characterized in that a mixture is formed which comprises the first waste material and a second waste material which is made inert by a phosphating treatment of heavy metals, so that a third waste material is produced which contains inert heavy metals. A method according to claim 1, characterized in that: - more than 10% by weight of the heavy metals present in the first waste material can be eluted with 0.5 M acetic acid; - a maximum of 10% by weight of the heavy metals present in the second waste material can be eluted with 0.5 M acetic acid; and - a maximum of 10% by weight of the heavy metals present in the third waste material can be eluted with 0.5 M acetic acid. Method according to one of the preceding claims, characterized in that the weight fraction of the eluable heavy metals present in the second waste material is at least 4 times lower than the weight fraction of the eluable heavy metals contained in the first waste material are present. A method according to any one of the preceding claims, characterized in that the weight fraction of the eluable heavy metals present in the third waste material is at most half the weight fraction of the eluable heavy metals present in the second waste material , amounts. Method according to one of the preceding claims, characterized in that the weight fraction of the first waste material is at least 20% of the weight fraction of the second waste material. Method according to one of the preceding claims, characterized in that the weight fraction of the first waste material is at most 100% of the weight fraction of the second waste material. A method according to any one of the preceding claims, characterized in that an aqueous slurry is formed comprising the first waste material and the second waste material, the slurry is converted into a foam, the slurry is matured for at least 12 hours after which it is dried to achieve a dryness of at least 70%. Method according to one of the preceding claims, characterized in that the first waste material and the second waste material are calcined together in a calcining oven, at least one product of co-calcining selected from the slag and fly ash, which the third waste material, contains the inert heavy metals. A method according to claim 8, characterized in that the first waste material and the second waste material together form a self-combustible mixture in the calcining oven, which can be calcined in the absence of a third fuel with a much lower calorific capacity than the mixture , which is formed by the first waste material and the second waste material. Method according to claim 8 or 9, characterized in that the calcining together is carried out at a temperature or in a temperature range of 450 ° C - 1000 ° C. The method according to any of claims 8 to 10, characterized in that the co-calcining is carried out in an oxidizing atmosphere by using ambient air as a fuel. A method according to any one of claims 8-11, characterized in that the third waste material is mixed with water, optionally a hydraulic binder is added, whereafter the mixture comprising the third waste material, water and any hydraulic binder is thickened or hardening to form a solid mass. A method according to any one of the preceding claims, characterized in that the first waste material contains the organic substance in a content of usually equal to at least 5%. A method according to claim 13, characterized in that the first waste material contains the organic substance in a content equal to at least 75%. Method according to one of the preceding claims, characterized in that the first waste material contains at least one calcium salt. A method according to any one of the preceding claims, characterized in that the first waste material is a sludge of natural origin, which is dried if necessary to reach a dryness of at least 70%, or a waste material in solid form. A method according to claim 16, characterized in that the first waste material is a sludge from a purification device that has been dried to a dryness of at least 80%. Method according to one of the preceding claims, characterized in that the first waste material has a dryness of at least 85%. A method according to any one of the preceding claims, characterized in that the second waste material contains the organic material in a content of at least 2%. A method according to claim 19, characterized in that the second waste material contains the organic material in a content equal to a maximum of 20%. A method according to any one of the preceding claims, characterized in that the second waste material contains at least one calcium phosphate, which contains at least one mono- or polyphosphate group, which corresponds to the general formula

wherein x is an integer positive number or zero and wherein the (3 + x) oxygen atoms marked with an asterix (O *) are independently bonded to a hydrogen atom or to a metal atom other than a heavy metal, with provided that at least one of them is bound to a calcium atom. A method according to claim 21, characterized in that the calcium phosphate is a salt or comprises selected from the calcium dihydrogen phosphate [Ca (H2PC> 4) 2], the "tricalcium phosphate TCP" [Ca ^ PO ^ ö], the whitlockhites and apa -tites, the hydrated forms of said salts and mixtures thereof. A method according to claim 21 or 22, characterized in that the calcium phosphate is or comprises the anhydrous calcium monohydrogen sulfate and / or a hydrated calcium monohydrogen phosphate. A method according to any one of claims 21 to 23, characterized in that the calcium phosphate is or comprises a whitlockite corresponding to the formula Ca 9 (Mg, Fe) (PO 4) 6 (HPO 4). The method according to any of claims 21 to 24, characterized in that the calcium phosphate is or comprises hydroxyapatite. A method according to any one of claims 21 to 25, characterized in that the weight of the at least one calcium phosphate present in the second waste material, expressed in phosphorus equivalent and relative to the weight of the dry matter of the first waste material is at least 0.35%. A method according to any one of claims 21 to 26, characterized in that the weight of the at least one calcium phosphate, expressed in phosphorus equivalent and with respect to the weight of the dry matter of the first waste material, is a maximum of 5%. A method according to any one of the preceding claims, characterized in that the phosphating treatment to which the second waste material is subjected is a treatment with phosphoric acid which is carried out in a humid environment. A method according to any one of the preceding claims, characterized in that the second waste material is a sludge of natural or non-natural origin, which is dried if necessary to achieve a dryness of at least 70%. A method according to claim 29, characterized in that the second waste material consists of sediments that come from cleaning an aqueous environment, such as a watercourse or a region with stagnant water. A method according to claim 29 or 30, characterized in that the sludge is a sludge with an initial dryness of less than 70% (i) that is converted into the state of a foam to which the phosphoric acid is added, (ii) that maturing so that the phosphation develops inside the foam, after which (iii) it is dried so that a dryness of at least 70% is achieved. A method according to claim 31, characterized in that the maturation of the sludge is carried out for a sufficient time t1 so that more than 90% of the phosphoric acid is converted into at least one metal phosphate. The method according to claim 32, characterized in that the at least one metal phosphate is or comprises a calcium phosphate as described in any one of claims 21 to 25. The method according to claim 32 or 33, characterized in that the time t 1 is at least 1 hour. Method according to one of claims 31 to 34, characterized in that the sludge is matured for a time 2 sufficient for the weight percentage of the heavy metals that can be eluted with 0.5 M acetic acid, sludge that is 4 times lower than the percentage by weight of the heavy metals that is present in the sludge before adding the phosphoric acid, can be eluted with 0.5 M acetic acid. A method according to any one of claims 31 to 35, characterized in that the sludge is aged for a sufficient time t3 so that a maximum of 5% by weight of the heavy metals present in the second waste material is 0.5 M acetic acid can be eluted. A method according to any one of the preceding claims, characterized in that the second waste material has a dryness of at least 85%. A method according to any one of the preceding claims, characterized in that it furthermore comprises the step of producing the second waste material by subjecting a waste material containing non-inert heavy metals to the phosphating treatment. 39. Use of a waste material (called "second waste material") containing inertized heavy metals by a phosphating treatment, in particular as a phosphating agent of another waste material containing non-inert heavy metals (called "first waste material") . 40. A method for forming a solid mass, which can be used for the construction of a road, the manufacture of a stone or the preparation of a concrete, according to which method the waste material, which is used with the method according to one of claims 38 with the exception of 12 (the "third waste material") is produced, mixed with water, optionally a hydraulic binder is added and the mixture comprising the third waste material, water and any hydraulic binder is thickened or hardened so that the solid mass is formed. A finished product such as a road, a brick or a concrete, which comprises the solid mass formed by the method of claim 12 or by the method of claim 40.