Drying composition to facilitate the drying of clay sludge

Abstract

The present invention relates to the technical aspects of clay sludge treatment, and more specifically to its conditioning / drying prior to disposal through appropriate channels. The drying composition of the invention allows for the easy transport and storage of clay sludge, namely any sludge containing significant amounts of clay minerals, such as kaolinite, illite, montmorillonite, and smectite, which are commonly found in clay sludge. This sludge is difficult to dry due to its high clay content. This drying composition comprises at least 75% and up to 99% by weight of a superabsorbent polymer coated with 1% to 25% by weight of a flocculating polymer. The invention also relates to the use of this composition for conditioning sludge, particularly clay sludge.

Description

Title of the invention: Drying composition to facilitate the drying of clay sludge

[0001] The present invention relates to the technical aspects of clay sludge treatment, and more particularly to its conditioning / drying prior to disposal through appropriate channels. The drying composition of the invention allows for the easy transport and storage of clay sludge, namely all sludge containing significant quantities of clay minerals, such as kaolinite, illite, montmorillonite, and smectite, which are commonly present in clay sludge. This sludge is difficult to dry due to its high clay content. This drying composition comprises at least 75% and up to 99% by weight of a superabsorbent polymer coated with 1% to 25% by weight of a flocculant polymer. The invention also relates to the use of the composition for conditioning sludge, particularly clay sludge. Technical field of the invention

[0002] The dewatering of clay sludge is essential to reduce transport and waste management costs, minimize environmental impact, and recover valuable resources in various industrial sectors. This type of sludge is generated by a large number of industrial activities. Among them are:

[0003] The mining and extractive industry: during the extraction and processing of ores, sludge containing clays and other fine particles is generated.

[0004] The oil and gas industry: drilling muds, rich in bentonite and other clays, must be dewatered to manage drilling waste and recover drilling fluids for reuse or treatment. Indeed, during excavation, the initially clean fluids become contaminated with materials from the excavated soil; they then become waste that must be disposed of and treated.

[0005] Dredging: This is a cleaning operation that consists of removing sediments accumulated at the bottom of bodies of water such as ponds, basins, reservoirs, and canals. Sediments resulting from the erosion of surrounding soils, transported by watercourses, often contain a large quantity of fine particles, including clays. The sedimentation of clay particles at the bottom of ponds and basins forms layers of clayey mud. This mud can accumulate over time, reducing the depth and capacity of the bodies of water.

[0006] Conditioning aimed at preparing the mud in order to dry it (i.e., remove its liquid form) is therefore generally necessary to facilitate its handling, its transport and storage. Among the various packaging methods used to prepare the sludge, the following are a non-exhaustive list:

[0007] - mechanical treatments: filtration, centrifugation...,

[0008] - chemical conditioning.

[0009] The invention relates to a new drying composition that, at very low dosages, absorbs the liquid portion of clay muds without damaging the clay structure. Indeed, clays are primarily composed of a type of silicate mineral characterized by a layered structure. Thanks to this layered structure, certain clays, such as smectites, can adsorb water molecules and swell by increasing their interlayer space. This structure thus explains the distinctive expansion and contraction capacities of clays, which are exploited in numerous industrial applications, such as drilling muds.

[0010] Those skilled in the art will understand that it is therefore very important to be able to preserve the structure of the clays during their conditioning in order to avoid releasing the water they have already absorbed and thus avoid additional drying costs. Technical background

[0011] Among the additives that have been recommended for attempting to dry sludge, we are familiar with patent FR3114980 of the applicant, which proposes to greatly improve the effectiveness of the chemical conditioning of saline sludge through the combined use of a superabsorbent polymer (SAP) and a flocculant. However, we have observed that this composition, when used to treat clay sludge, breaks down the layered structure of the clay, making its application unfavorable in this case, unless the additives in question are overused. Presentation of the invention

[0012] Mineral sludges with a high clay content are difficult to dry and therefore to transport because they contain a very high proportion of water. Furthermore, clay sludges can have very varied chemical properties depending on the minerals present. They can be acidic or basic, and some clays, such as bentonite, have high adsorption properties. Their conditioning / drying is thus made more complex.

[0013] The applicant has conducted numerous tests and demonstrated that when a composition based on a superabsorbent polymer (SAP) coated with a flocculant polymer is added to clay slurry, the slurry not only dries at very low concentrations but also extremely rapidly and without damaging the clay's layered structure. The composition of the invention is thus in solid, dry form, namely a powder, resulting from coating the SAP with a solution / dispersion incorporating a flocculant polymer and an agent liquid binder well known to the person skilled in the art (e.g., mineral and / or organic oil, polyethylene glycol...) to allow the flocculant to adhere homogeneously to the surface of the superabsorbent polymer.

[0014] According to the present invention, it has been found, unexpectedly, that a drying composition particularly effective for conditioning clay sludge can be used provided that it comprises at least 75% and up to 99% by weight of a superabsorbent polymer in powder form coated by 1% to 25% by weight of a flocculating polymer. Summary of the invention

[0015] The present invention relates to a powdered drying composition for optimal conditioning of clay sludge prior to its disposal through appropriate channels. The composition of the invention allows for the rapid and easy drying of clay sludge. This drying composition, namely, a superabsorbent polymer coated with a flocculant polymer, comprises: - at least 75% and up to 99% by weight of a superabsorbent polymer powder, preferably between 80% and 95% by weight, and advantageously between 85% and 95% by weight - and 1% to 25% by weight of a flocculant polymer powder, preferably between 5% and 20% by weight, and advantageously between 5% and 15% by weight.

[0016] The invention also relates to the use of the composition for conditioning clayey muds, possibly in combination with other commonly used additives such as carbonates, lime, cement...

[0017] The compositions according to the invention, when added to clay sludge, transform the latter into a transportable and storable sludge and eliminate all the drawbacks of the prior art. In particular, the drying of the clay sludge is no longer influenced by its chemical properties and the minerals present. Moreover, the presence of a flocculating polymer intimately associated with the superabsorbent polymer by a coating process within the composition makes it possible, quite surprisingly, to significantly reduce the quantity of superabsorbent polymer required to obtain a sludge that can be scooped and therefore transported. Detailed description of the invention

[0018] One object of the invention is to provide new drying compositions with optimized properties to facilitate the transport and storage of clay sludge, thereby simplifying its extraction. These compositions are in dry, powdered form, allowing for easy transport, storage, and application.

[0019] The present invention therefore relates to a new drying composition, namely, a superabsorbent polymer coated with a flocculant polymer for conditioning clay sludge comprising: - at least 75% and up to 99% by weight of a superabsorbent polymer powder, preferably between 80% and 95% by weight, and advantageously between 85% and 95% by weight - and 1% to 25% by weight of a flocculant polymer powder, preferably between 5% and 20% by weight, and advantageously between 5% and 15% by weight

[0020] The drying compositions made according to the invention, in the form of a powder, are used at a rate of 2 to 20 kg per tonne of clay sludge, preferably 3 to 15 kg per tonne of clay sludge.

[0021] The present invention relates to the technical field of clay sludge treatment. This sludge is difficult to dry due to its high clay content. The drying composition of the invention makes it possible to easily transport and store clay sludge, namely all sludge containing significant quantities of clay minerals, such as kaolinite, illite, montmorillonite, and smectite, which are commonly present in this type of sludge.

[0022] In practice, the superabsorbent polymer used is a water-retaining agent of natural or synthetic origin that has a water retention capacity greater than or equal to 30 times its weight in demineralized water, preferably greater than or equal to 50 times, advantageously greater than or equal to 100 times. This type of polymer is generally known by the abbreviation: SAP ("superabsorbent polymer"). It is generally in powder form, agglomerated or not. Its structure, based on a three-dimensional network resembling a multitude of small cavities, each capable of deforming and absorbing water, gives it the property of absorbing very large quantities of water and thus swelling.

[0023] Superabsorbent polymers of natural origin, usable within the scope of the present invention, are for example those described in patents US358364, US1693890, US3846404, US3935099 or US3661815... Examples include, but are not limited to: guar gum, alginates, carboxymethyl cellulose, dextran, xanthan gum...

[0024] Synthetic SAPs usable within the scope of the present invention are, for example, crosslinked or crosslinkable water-soluble polymers. Many types exist. Such polymers are described, for example, in French patent FR 2559158, which describes crosslinked polymers of acrylic or methacrylic acid, crosslinked grafted copolymers of the polysaccharide / acrylic or methacrylic acid type, and crosslinked terpolymers of the acrylic or methacrylic acid type. methacrylic / acrylamide / sulfonated acrylamide and their alkaline earth or alkali metal salts.

[0025] In a preferred embodiment, the monomers used for preparing the superabsorbent polymers are selected from acrylamide and / or partially or totally salified acrylic acid and / or partially or totally salified ATBS (acrylamido tert-butylsulfonate) and / or NVP (N-vinylpyrrolidone) and / or acryloylmorpholine and / or partially or totally salified itaconic acid. In a preferred embodiment, the superabsorbent polymers are anionic crosslinked homopolymers or copolymers based on partially or totally salified acrylic acid.

[0026] Other hydrophilic monomers, such as cationic monomers, but also hydrophobic monomers, can be used to produce superabsorbent polymers. Examples of cationic monomers include diallyldialkyl ammonium salts and dialkylaminoalkyl (meth)acrylate and dialkylaminoalkyl (meth)acrylamide monomers, as well as their quaternary ammonium or acid salts. In particular, quaternary or salified dimethylaminoethyl acrylate (ADAME) and / or dimethylaminoethyl methacrylate (MADAME), acrylamidopropyltrimethylammonium chloride (APTAC), and / or methacrylamidopropyltrimethylammonium chloride (MAPTAC) are examples.

[0027] Synthetic superabsorbent polymers are generally crosslinked with 100 to 6000 ppm of at least one crosslinking agent chosen from the group including acrylic compounds such as methylene bis acrylamide, allylic compounds such as tetra-allylammonium chloride, vinyl compounds such as divinyl benzene, diepoxy, metallic salts... Some may also have double crosslinking such as with an acrylic crosslinker.

[0028] For cost reasons, superabsorbent polymers of synthetic origin of the crosslinked sodium polyacrylate type will be preferred.

[0029] SAP can be obtained by all polymerization techniques well known to those skilled in the art: gel polymerization, precipitation polymerization, emulsion polymerization (aqueous or reverse) followed or not by a distillation step, suspension polymerization, solution polymerization, these polymerizations being followed or not by a step allowing isolation of a dry form of the (co)polymer by all types of means well known to those skilled in the art.

[0030] According to the invention, the superabsorbent polymer can be post-crosslinked on the surface, namely that they: - result from the polymerization with partial crosslinking of water-soluble ethylenically unsaturated monomers comprising at least one function carboxylic, in particular acrylic and methacrylic acids and their alkali salts, whether obtained by a polymerization process in solution, in bulk or in reverse suspension, as described for example in patent applications EP312952, EP441507 or EP742231... - and exhibit cross-linking on the exterior of the polymer grains. This surface cross-linking is called post-cross-linking because it occurs on the SAP powder after polymerization is complete and the SAP is partially dehydrated, during drying. Post-cross-linking allows the formation of a highly cross-linked shell around the SAP particles. The SAP particles then exhibit a "core-shell" structure.

[0031] The post-crosslinking steps of hydrophilic polymers possessing carboxylic and / or carboxylate groups with a polyfunctional agent are well known to those skilled in the art. The dry powder is typically post-crosslinked by reacting it with other crosslinking agents such as, for example, organic crosslinking agents and / or multivalent cations, to produce a surface layer that is more strongly crosslinked compared to the interior of the particles. Commonly used processes for surface post-crosslinking include a step of contacting the base polymer with a surface post-crosslinking agent followed by a subsequent heat treatment step. This latter step is intended to complete the surface post-crosslinking, the heat treatment generally being carried out hot, usually using continuous dryers. Examples include documents GB 2126591, EP789048, FR2923830...Many molecules described in the literature are capable of reacting quickly enough with the carboxyl groups of superabsorbent polymers (SAPs) to bridge the polymer chains. A well-known method involves post-treating the base superabsorbent polymer. This is done by subjecting the dried powder of the base superabsorbent polymer to additional cross-linking on a surface layer of its particles through a surface post-cross-linking step. This surface post-cross-linking increases the cross-linking density on the surface of the superabsorbent polymer particles, thereby reducing the absorption capacity of the superabsorbent polymer in the surface layer.

[0032] The invention will advantageously be implemented with superabsorbent polymer particles of spherical or non-spherical shape and whose average diameter is generally between 5 µm and 5000 µm and preferably between 100 and 250 µm. This water-retaining polymer (or the mixture of water-retaining polymers) represents at least 75% and up to 99% by weight, preferably between 80% and 95% by weight, and advantageously between 85% and 95% by weight of the drying composition according to the invention.

[0033] In practice, the flocculant polymer constituting one of the two essential elements of the composition according to the invention is a high molecular weight, water-soluble anionic or non-ionic (co)polymer in powder form, with a molecular weight greater than 10⁵ g / mol and preferably greater than 10⁶ g / mol. The high molecular weight, water-soluble polymer was obtained by polymerization of at least one monomer selected from:

[0034] - non-ionic monomers: water-soluble vinyl monomers. Preferred monomers belonging to this class include acrylamide and methacrylamide, acrylamide derivatives such as N-alkylacrylamide (e.g., N-isopropylacrylamide, N-tert-butylacrylamide, octylacrylamide), and N,N-dialkylacrylamides such as NN-dimethylacrylamide and N-methylolacrylamide. Vinylformamide, N-vinylpyridine, N-vinylpyrrolidone, hydroxyalkyl acrylates, and methacrylates can also be used. Acrylamide is a preferred nonionic vinyl monomer.

[0035] - and / or anionic monomers exhibiting acrylic functionalities, vinylic, maleic, fumaric, allylic and contain a carboxy, phosphonate, sulfonate, or other anionically charged group, or the ammonium or alkali earth metal or corresponding alkali metal salt of such a monomer. These include acrylic acid, methacrylic acid, acrylamidomethylpropanesulfonic acid, acrylamidomethylbutanoic acid, maleic acid, fumaric acid, itaconic acid, vinylsulfonic acid, styrene sulfonic acid, vinylphosphonic acid, allylsulfonic acid, allylphosphonic acid and their water-soluble salts of an alkali metal, an alkali earth metal, and ammonium.

[0036] The invention will advantageously be implemented with spherical or non-spherical flocculant polymer particles, ground and whose average diameter is much smaller than that of the superabsorbent polymer. The flocculant polymer (or the mixture of flocculant polymers) represents from 1% to 25% by weight of a flocculant polymer powder, preferably between 5% and 20% by weight, and advantageously between 5% and 15% by weight of the drying composition according to the invention.

[0037] The composition of the invention is in solid, dry form, namely a powder, resulting from coating the SAP powder with a solution / dispersion incorporating a flocculant polymer and a liquid binding agent well known to those skilled in the art (e.g., mineral and / or organic oil, polyethylene glycol, etc., preferably a mineral oil) to allow the flocculant to adhere to the surface of the superabsorbent polymer. Using any type of process well known to those skilled in the art, it is then sufficient to mix the flocculant solution / dispersion with the SAP. generally by spraying it under agitation to obtain a homogeneous coating of the SAP by the flocculant. The product thus obtained is a true “composition” comprising at least one superabsorbent polymer coated by at least one flocculant polymer, both as defined above.

[0038] During its use, the composition of the invention is added directly to the clay slurry by mechanical mixing (stirring screw, mechanical shovel, etc.) and provides an optimized drying and agglomerating effect. It has been observed that the composition produces combined effects far superior to the separate addition of the components, namely without the SAP and flocculant combination by a coating process. The drying composition of the invention has the property of dramatically increasing liquid retention capacity without affecting the clay's layered structure. This result was entirely unexpected since the presence of SAP leads to the destruction of the clay's layered structure, so those skilled in the art would not have been inclined to use this type of water-retaining polymer to solve the problem at hand.The presence of an anionic or non-ionic flocculant polymer coated around the SAP seems, for reasons that cannot be explained, to have a beneficial effect on the superabsorbent polymer by limiting the clay's sensitivity to it. There is therefore a real and unexpected synergy between the two ingredients in the composition when the flocculant is coated around the SAP.

[0039] The present invention also relates to any variant or adaptation which will become clear to a person skilled in the art, if necessary by resorting to some routine trials. Examples

[0040] Comparative tests were carried out using the following compounds: • Superabsorbent polymers (SAPs): as described in Table 1 below • Flocculant polymer (FP): “APROFLOC” PA03: high molecular weight (5.106 g / mol) anionic water-soluble polymer copolymer of sodium acrylate (30%) and acrylamide (70%)

[0041] [Tables 1] Product Reference Polymer Type Superabsorbent Polymer Trade Name Anionicity P150XL Crosslinked Sodium Polyacrylate “Apromud” P 150XL 100% Anionic G250 Crosslinked and Post-Crosslinked Sodium Polyacrylate “Apromud” G 300 100% Anionic

[0042] Drying tests (solidification / stabilization) were conducted on 2 types of clay mud from separate tunnel borings (B1 and B2).

[0043] For the realization of the examples presented in Table 2, - The superabsorbent polymers in Table 1 were coated using the flocculant polymer “APROFLOC” PA03 by spraying, under agitation, a dispersion incorporating the flocculant polymer and a mineral oil onto the surface of the superabsorbent polymer. The quantity of oil used varies depending on the proportion of flocculant polymer; it must be sufficient to obtain a sprayable, free-flowing dispersion. - The mixtures of the coated SAP with the clayey mud were carried out mechanically until homogenization and visual drying of the mud. - a turbidity test (synonymous with deterioration of the clay structure) is then carried out: 50g of treated (dried) sludge are then mixed under gentle stirring with 450 ml of water: the turbidity of the supernatant is assessed visually.

[0044] [Tables2] Nature of 1 a sludge Composition of the drying agent Dosage of Passé chant expressed in kg per tonne of sludge Turbidity of the sludge according to the turbidity test (YES or NO) Counter-example 1 B1 G250 (100%) 10 kg / tonne YES Counter-example 2 B1 P150XL (100%) 10 kg / tonne YES Counter-example 3 B2 G250 (100%) 10 kg / tonne YES Counter-example 4 B2 P150XL (100%) 10 kg / tonne YES Counter-example 5 B2 G250 (88%) simply mixed with PF (12%) 10 kg / tonne YES Counter-example 6 B2 P150XL (88%) simply mixed with PF (12%) 10 kg / tonne YES Example 1 B1 G250 (95%) coated with PF (5%) 10 kg / tonne NO Example 2 B2 G250 (88%) coated with PF (12%) 10 kg / tonne NO Example 3 B1 G250 (80%) coated with PF (20%) 10 kg / tonne NO Example 4 B2 P150XL (95%) coated with PF (5%) 10 kg / tonne NO Example 5 B1 P150XL (88%) coated with PF (12%) 10 kg / tonne NO Example 6 B2 P150XL (80%) coated with PF (20%) 10 kg / tonne NO

[0045] As can be seen in Table 2, compared to the addition of superabsorbent polymer alone, regardless of the specific superabsorbent polymer used, superabsorbent polymers coated with a flocculant polymer according to the invention allow the drying of clay sludge without disrupting its structure (negative turbidity test), while also reducing the amount of superabsorbent polymer required to achieve this result. The examples further clearly indicate that when the SAP according to the invention is not coated but simply mixed with SAP and PF, the sludge structure is also deteriorated. It appears that, unexpectedly, a synergistic effect occurs as soon as the flocculant polymer is coated (closely bonded) with the SAP. Moreover, we were able to visually observe that this drying process was also extremely rapid.The drying compositions of the invention, comprising at least 75% and up to 99% by weight of a superabsorbent polymer coated with 1% to 25% by weight of a flocculant polymer, are simultaneously simple (only one mixing point required), quick to implement, and effective. They thus perfectly meet the needs of industry for facilitating the transport and storage of clay sludge, namely all sludge containing significant quantities of clay minerals, such as kaolinite, illite, montmorillonite, and smectite, which are commonly present in clay sludge.

Claims

Demands

1. Composition for drying clayey sludge before disposal comprising a mixture consisting of - at least 75% and up to 99% by weight of a superabsorbent polymer powder, - and 1% to 25% by weight of a flocculant polymer powder, and characterized in that the superabsorbent polymer is coated by the flocculant polymer.

2. Composition for drying clayey sludge before disposal comprising a mixture consisting of - between 80% and 95% by weight, advantageously between 85% and 95% by weight of a superabsorbent polymer powder, - and between 5% and 20% by weight, advantageously between 5% and 15% by weight of a flocculant polymer powder, and characterized in that the superabsorbent polymer is coated by the flocculant polymer.

3. Composition according to claim 1 or 2 wherein said superabsorbent polymer has a water retention capacity greater than or equal to 30 times its weight in demineralized water, preferably greater than or equal to 50 times, advantageously greater than or equal to 100 times.

4. Composition according to any one of claims 1, 2 or 3 wherein said superabsorbent polymer is a homopolymer or a crosslinked synthetic copolymer comprising partially or totally salified acrylic acid, of the crosslinked sodium polyacrylate type.

5. Composition according to any one of the preceding claims wherein the flocculant polymer in powder form is a water-soluble anionic or non-ionic (co)polymer of high molecular weight soluble in water.

6. Composition according to claim 5 wherein said flocculant polymer has a molecular weight greater than 105 g / mol and preferably greater than 106 g / mol.

7. Composition according to claim 5 or 6 wherein said flocculant polymer has been obtained by polymerization of at least one monomer selected from - non-ionic monomers - and / or anionic monomers.

8. Composition according to any one of claims 5, 6 or 7 wherein the flocculant polymer is coated onto the superabsorbent polymer using a liquid binding agent preferably selected from mineral and / or organic oils or polyethylene glycol.

9. Use of the composition according to any one of claims 1 to 8 for the drying of sludge at a rate of 2 to 20 kg per tonne of sludge, preferably in the presence of clayey sludge.